diff --git a/bun.lock b/bun.lock
index b3fce2a..e467b77 100644
--- a/bun.lock
+++ b/bun.lock
@@ -42,6 +42,9 @@
         "@shade/core": "workspace:*",
         "hono": "^4.12.12",
       },
+      "devDependencies": {
+        "@shade/crypto-web": "workspace:*",
+      },
     },
     "packages/shade-storage-sqlite": {
       "name": "@shade/storage-sqlite",
diff --git a/packages/shade-core/src/crypto.ts b/packages/shade-core/src/crypto.ts
index ae08e37..55d3836 100644
--- a/packages/shade-core/src/crypto.ts
+++ b/packages/shade-core/src/crypto.ts
@@ -1,3 +1,17 @@
+/**
+ * Constant-time byte array comparison (standalone utility).
+ * Same semantics as CryptoProvider.constantTimeEqual but usable
+ * in contexts that don't have a provider instance.
+ */
+export function constantTimeEqual(a: Uint8Array, b: Uint8Array): boolean {
+  if (a.length !== b.length) return false;
+  let diff = 0;
+  for (let i = 0; i < a.length; i++) {
+    diff |= a[i]! ^ b[i]!;
+  }
+  return diff === 0;
+}
+
 /**
  * CryptoProvider — platform-agnostic interface for all cryptographic primitives.
  *
@@ -59,4 +73,26 @@ export interface CryptoProvider {
 
   /** Generate cryptographically secure random bytes */
   randomBytes(length: number): Uint8Array;
+
+  // ─── Hardening ─────────────────────────────────────────────
+
+  /**
+   * Constant-time byte array comparison. No early exit on mismatch.
+   * Use this for ALL comparisons involving secret data (keys, MACs, tokens).
+   * Returns false if lengths differ (timing leak on length is acceptable).
+   */
+  constantTimeEqual(a: Uint8Array, b: Uint8Array): boolean;
+
+  /**
+   * Overwrite a buffer with zeros. Use after a key is no longer needed.
+   * Note: V8 may not actually zero the backing memory due to GC/optimization,
+   * but this is the best we can do in JS/TS without native bindings.
+   */
+  zeroize(buf: Uint8Array): void;
+
+  /**
+   * Cryptographically secure random 32-bit unsigned integer.
+   * Use for registrationId, keyId generation, etc. (NEVER Math.random()).
+   */
+  randomUint32(): number;
 }
diff --git a/packages/shade-core/src/errors.ts b/packages/shade-core/src/errors.ts
index a69e1a6..1756843 100644
--- a/packages/shade-core/src/errors.ts
+++ b/packages/shade-core/src/errors.ts
@@ -1,63 +1,175 @@
-/** Base class for all Shade errors */
+/**
+ * Shade error hierarchy.
+ *
+ * All errors have:
+ *  - `name`: class name for `instanceof` checks
+ *  - `code`: stable string code for error mapping (e.g. HTTP status)
+ *  - `toJSON()`: serializable form for network transmission
+ */
 export class ShadeError extends Error {
-  constructor(message: string) {
+  /** Stable error code for mapping to HTTP status or UI strings */
+  readonly code: string;
+
+  constructor(code: string, message: string) {
     super(message);
     this.name = 'ShadeError';
+    this.code = code;
+  }
+
+  toJSON(): { name: string; code: string; message: string } {
+    return { name: this.name, code: this.code, message: this.message };
   }
 }
 
-/** Signature verification failed (e.g. invalid signed prekey) */
+// ─── Crypto / Protocol Errors ────────────────────────────────
+
 export class InvalidSignatureError extends ShadeError {
   constructor(message = 'Signature verification failed') {
-    super(message);
+    super('SHADE_INVALID_SIGNATURE', message);
     this.name = 'InvalidSignatureError';
   }
 }
 
-/** AES-GCM decryption failed (wrong key, tampered ciphertext, or bad nonce) */
 export class DecryptionError extends ShadeError {
   constructor(message = 'Decryption failed') {
-    super(message);
+    super('SHADE_DECRYPTION_FAILED', message);
     this.name = 'DecryptionError';
   }
 }
 
-/** No session exists for the given address */
-export class NoSessionError extends ShadeError {
-  constructor(address: string) {
-    super(`No session for address: ${address}`);
-    this.name = 'NoSessionError';
-  }
-}
-
-/** Too many skipped messages in a chain (possible DoS or sync issue) */
 export class MaxSkipExceededError extends ShadeError {
   constructor(requested: number, max: number) {
-    super(`Cannot skip ${requested} messages (max: ${max})`);
+    super('SHADE_MAX_SKIP_EXCEEDED', `Cannot skip ${requested} messages (max: ${max})`);
     this.name = 'MaxSkipExceededError';
   }
 }
 
-/** Duplicate message detected (message key already consumed) */
 export class DuplicateMessageError extends ShadeError {
   constructor() {
-    super('Duplicate message: key already consumed');
+    super('SHADE_DUPLICATE_MESSAGE', 'Duplicate message: key already consumed');
     this.name = 'DuplicateMessageError';
   }
 }
 
-/** Remote identity key has changed unexpectedly */
+export class ReplayError extends ShadeError {
+  constructor(message = 'Message timestamp outside replay window') {
+    super('SHADE_REPLAY', message);
+    this.name = 'ReplayError';
+  }
+}
+
+// ─── Session / Identity Errors ───────────────────────────────
+
+export class NoSessionError extends ShadeError {
+  constructor(address: string) {
+    super('SHADE_NO_SESSION', `No session for address: ${address}`);
+    this.name = 'NoSessionError';
+  }
+}
+
 export class UntrustedIdentityError extends ShadeError {
   constructor(address: string) {
-    super(`Untrusted identity key for: ${address}`);
+    super('SHADE_UNTRUSTED_IDENTITY', `Untrusted identity key for: ${address}`);
     this.name = 'UntrustedIdentityError';
   }
 }
 
-/** Required prekey not found in storage */
 export class PreKeyNotFoundError extends ShadeError {
   constructor(keyId: number, type: 'signed' | 'one-time') {
-    super(`${type} prekey not found: ${keyId}`);
+    super('SHADE_PREKEY_NOT_FOUND', `${type} prekey not found: ${keyId}`);
     this.name = 'PreKeyNotFoundError';
   }
 }
+
+export class IdentityRotationError extends ShadeError {
+  constructor(message = 'Identity rotation failed') {
+    super('SHADE_IDENTITY_ROTATION', message);
+    this.name = 'IdentityRotationError';
+  }
+}
+
+// ─── Infrastructure Errors ───────────────────────────────────
+
+export class NetworkError extends ShadeError {
+  constructor(message: string, public readonly statusCode?: number) {
+    super('SHADE_NETWORK', message);
+    this.name = 'NetworkError';
+  }
+}
+
+export class StorageError extends ShadeError {
+  constructor(message: string, public readonly cause?: unknown) {
+    super('SHADE_STORAGE', message);
+    this.name = 'StorageError';
+  }
+}
+
+export class ValidationError extends ShadeError {
+  constructor(message: string, public readonly field?: string) {
+    super('SHADE_VALIDATION', message);
+    this.name = 'ValidationError';
+  }
+}
+
+export class TimeoutError extends ShadeError {
+  constructor(message = 'Operation timed out') {
+    super('SHADE_TIMEOUT', message);
+    this.name = 'TimeoutError';
+  }
+}
+
+export class RateLimitError extends ShadeError {
+  constructor(message = 'Rate limit exceeded', public readonly retryAfterSeconds?: number) {
+    super('SHADE_RATE_LIMIT', message);
+    this.name = 'RateLimitError';
+  }
+}
+
+export class ConfigurationError extends ShadeError {
+  constructor(message: string) {
+    super('SHADE_CONFIG', message);
+    this.name = 'ConfigurationError';
+  }
+}
+
+export class UnauthorizedError extends ShadeError {
+  constructor(message = 'Unauthorized') {
+    super('SHADE_UNAUTHORIZED', message);
+    this.name = 'UnauthorizedError';
+  }
+}
+
+// ─── Error → HTTP Status Mapping ────────────────────────────
+
+/**
+ * Map a ShadeError to an HTTP status code.
+ * Used by the prekey server's global error handler.
+ */
+export function errorToHttpStatus(error: unknown): number {
+  if (!(error instanceof ShadeError)) return 500;
+  switch (error.code) {
+    case 'SHADE_INVALID_SIGNATURE':
+    case 'SHADE_UNAUTHORIZED':
+      return 401;
+    case 'SHADE_UNTRUSTED_IDENTITY':
+      return 403;
+    case 'SHADE_NO_SESSION':
+    case 'SHADE_PREKEY_NOT_FOUND':
+      return 404;
+    case 'SHADE_VALIDATION':
+      return 400;
+    case 'SHADE_REPLAY':
+    case 'SHADE_DUPLICATE_MESSAGE':
+      return 409;
+    case 'SHADE_RATE_LIMIT':
+      return 429;
+    case 'SHADE_TIMEOUT':
+      return 504;
+    case 'SHADE_NETWORK':
+    case 'SHADE_STORAGE':
+    case 'SHADE_CONFIG':
+      return 503;
+    default:
+      return 500;
+  }
+}
diff --git a/packages/shade-core/src/fingerprint.ts b/packages/shade-core/src/fingerprint.ts
new file mode 100644
index 0000000..ceea7d3
--- /dev/null
+++ b/packages/shade-core/src/fingerprint.ts
@@ -0,0 +1,50 @@
+import type { CryptoProvider } from './crypto.js';
+
+/**
+ * Identity fingerprints (safety numbers).
+ *
+ * A fingerprint is a stable, human-readable derivation of an identity's
+ * public keys. Two parties can compare fingerprints out-of-band (read aloud,
+ * QR code, etc.) to verify they're not being MITM'd.
+ *
+ * Format: 60 decimal digits in 12 groups of 5, e.g.
+ *   "12345 67890 12345 67890 12345 67890 12345 67890 12345 67890 12345 67890"
+ *
+ * Derived from: SHA-256(signingKey || dhKey), truncated to 30 bytes,
+ * interpreted as an unsigned big-endian integer and formatted as decimal.
+ */
+
+/** Compute a 12-group safety number from an identity's public keys */
+export async function computeFingerprint(
+  crypto: CryptoProvider,
+  signingPublicKey: Uint8Array,
+  dhPublicKey: Uint8Array,
+): Promise<string> {
+  // Concatenate
+  const combined = new Uint8Array(signingPublicKey.length + dhPublicKey.length);
+  combined.set(signingPublicKey, 0);
+  combined.set(dhPublicKey, signingPublicKey.length);
+
+  // SHA-256 via HKDF trick (CryptoProvider has no direct SHA-256, but we can use HMAC with empty key)
+  // Actually we use HKDF-SHA256 output as the hash
+  const salt = new Uint8Array(32);
+  const info = new TextEncoder().encode('ShadeFingerprint');
+  const hash = await crypto.hkdf(combined, salt, info, 30);
+
+  // Format as 12 groups of 5 decimal digits
+  // Each group = 5 decimal digits (0-99999), derived from consecutive bytes
+  const groups: string[] = [];
+  for (let i = 0; i < 12; i++) {
+    // Use 3 bytes per group (24 bits), mod 100000 to get 5 digits
+    const offset = i * 2; // 2 bytes per group = 16 bits, max 65535 → 5 digits
+    const value = (hash[offset]! << 8) | hash[offset + 1]!;
+    groups.push(value.toString().padStart(5, '0'));
+  }
+
+  return groups.join(' ');
+}
+
+/** Short-form fingerprint: first 4 groups only (20 digits), for quick verification */
+export function shortFingerprint(full: string): string {
+  return full.split(' ').slice(0, 4).join(' ');
+}
diff --git a/packages/shade-core/src/index.ts b/packages/shade-core/src/index.ts
index 707f760..dbb461d 100644
--- a/packages/shade-core/src/index.ts
+++ b/packages/shade-core/src/index.ts
@@ -5,5 +5,6 @@ export * from './keys.js';
 export * from './errors.js';
 export * from './x3dh.js';
 export * from './ratchet.js';
-export { ShadeSessionManager } from './session.js';
+export { ShadeSessionManager, GRACE_PERIOD_MS } from './session.js';
 export * from './serialization.js';
+export * from './fingerprint.js';
diff --git a/packages/shade-core/src/ratchet.ts b/packages/shade-core/src/ratchet.ts
index ae224d8..43c46b4 100644
--- a/packages/shade-core/src/ratchet.ts
+++ b/packages/shade-core/src/ratchet.ts
@@ -103,8 +103,10 @@ export async function ratchetEncrypt(
   session: SessionState,
   plaintext: Uint8Array,
 ): Promise<RatchetMessage> {
-  // Advance sending chain
-  const { newChainKey, messageKey } = await kdfChainKey(crypto, session.sendChain.chainKey);
+  // Advance sending chain — old chain key is replaced, zero the old one
+  const oldChainKey = session.sendChain.chainKey;
+  const { newChainKey, messageKey } = await kdfChainKey(crypto, oldChainKey);
+  crypto.zeroize(oldChainKey);
   const counter = session.sendChain.counter;
 
   // Build header for AAD
@@ -115,8 +117,9 @@ export async function ratchetEncrypt(
   };
   const aad = encodeHeader(header);
 
-  // Encrypt
+  // Encrypt, then zero the message key (used once)
   const { ciphertext, nonce } = await crypto.aesGcmEncrypt(messageKey, plaintext, aad);
+  crypto.zeroize(messageKey);
 
   // Update session state
   session.sendChain.chainKey = newChainKey;
@@ -151,7 +154,11 @@ export async function ratchetDecrypt(
   const skippedKey = session.skippedKeys.get(skipId);
   if (skippedKey) {
     session.skippedKeys.delete(skipId);
-    return decryptWithKey(crypto, skippedKey, message);
+    try {
+      return await decryptWithKey(crypto, skippedKey, message);
+    } finally {
+      crypto.zeroize(skippedKey);
+    }
   }
 
   // Case 2 or 3: Check if this is a new DH ratchet
@@ -174,11 +181,17 @@ export async function ratchetDecrypt(
   await skipMessageKeys(crypto, session, message.dhPublicKey, session.receiveChain, message.counter);
 
   // Advance the receiving chain one more step to get this message's key
-  const { newChainKey, messageKey } = await kdfChainKey(crypto, session.receiveChain.chainKey);
+  const oldChainKey = session.receiveChain.chainKey;
+  const { newChainKey, messageKey } = await kdfChainKey(crypto, oldChainKey);
+  crypto.zeroize(oldChainKey);
   session.receiveChain.chainKey = newChainKey;
   session.receiveChain.counter = message.counter + 1;
 
-  return decryptWithKey(crypto, messageKey, message);
+  try {
+    return await decryptWithKey(crypto, messageKey, message);
+  } finally {
+    crypto.zeroize(messageKey);
+  }
 }
 
 // ─── DH Ratchet Step ─────────────────────────────────────────
@@ -203,17 +216,29 @@ async function performDHRatchetStep(
 
   // DH with current send key → new receiving chain
   const dh1 = await crypto.x25519(session.dhSend.privateKey, remoteDHKey);
-  const recv = await kdfRootKey(crypto, session.rootKey, dh1);
+  const oldRootKey1 = session.rootKey;
+  const recv = await kdfRootKey(crypto, oldRootKey1, dh1);
+  crypto.zeroize(oldRootKey1);
+  crypto.zeroize(dh1);
   session.rootKey = recv.newRootKey;
   session.receiveChain = { chainKey: recv.chainKey, counter: 0 };
 
-  // Generate new DH keypair
+  // Generate new DH keypair, zero the old one's private key
+  const oldDhPrivate = session.dhSend.privateKey;
   session.dhSend = await crypto.generateX25519KeyPair();
+  crypto.zeroize(oldDhPrivate);
 
   // DH with new send key → new sending chain
   const dh2 = await crypto.x25519(session.dhSend.privateKey, remoteDHKey);
-  const send = await kdfRootKey(crypto, session.rootKey, dh2);
+  const oldRootKey2 = session.rootKey;
+  const send = await kdfRootKey(crypto, oldRootKey2, dh2);
+  crypto.zeroize(oldRootKey2);
+  crypto.zeroize(dh2);
   session.rootKey = send.newRootKey;
+  // Zero the old send chain key if present
+  if (session.sendChain.chainKey.length > 0) {
+    crypto.zeroize(session.sendChain.chainKey);
+  }
   session.sendChain = { chainKey: send.chainKey, counter: 0 };
 }
 
diff --git a/packages/shade-core/src/session.ts b/packages/shade-core/src/session.ts
index a862fec..2f29959 100644
--- a/packages/shade-core/src/session.ts
+++ b/packages/shade-core/src/session.ts
@@ -23,11 +23,16 @@ import {
   ratchetEncrypt,
   ratchetDecrypt,
 } from './ratchet.js';
-import { NoSessionError } from './errors.js';
+import { NoSessionError, UntrustedIdentityError } from './errors.js';
+import { computeFingerprint, shortFingerprint } from './fingerprint.js';
+import { constantTimeEqual } from './crypto.js';
 
 const enc = new TextEncoder();
 const dec = new TextDecoder();
 
+/** Default grace period for retired identities: 7 days */
+export const GRACE_PERIOD_MS = 7 * 24 * 60 * 60 * 1000;
+
 /**
  * ShadeSessionManager — the high-level API for using Shade.
  *
@@ -71,10 +76,13 @@ export class ShadeSessionManager {
       await this.storage.saveIdentityKeyPair(this.identity);
     }
 
-    // Load or generate registration ID
+    // Load or generate registration ID (cryptographically secure)
     this.registrationId = await this.storage.getLocalRegistrationId();
     if (this.registrationId === 0) {
-      this.registrationId = Math.floor(Math.random() * 0xffffffff) + 1;
+      // Ensure nonzero (0 is the "unset" sentinel)
+      let id = this.crypto.randomUint32();
+      if (id === 0) id = 1;
+      this.registrationId = id;
       await this.storage.saveLocalRegistrationId(this.registrationId);
     }
 
@@ -98,6 +106,90 @@ export class ShadeSessionManager {
     };
   }
 
+  // ─── Fingerprints (Safety Numbers) ──────────────────────────
+
+  /**
+   * Get a human-readable fingerprint of our own identity.
+   * Format: 12 groups of 5 decimal digits (60 total).
+   * Two parties compare these out-of-band to verify no MITM.
+   */
+  async getIdentityFingerprint(): Promise<string> {
+    if (!this.identity) throw new Error('Not initialized');
+    return computeFingerprint(
+      this.crypto,
+      this.identity.signingPublicKey,
+      this.identity.dhPublicKey,
+    );
+  }
+
+  /** Short 4-group fingerprint for quick comparison */
+  async getShortFingerprint(): Promise<string> {
+    return shortFingerprint(await this.getIdentityFingerprint());
+  }
+
+  /**
+   * Get a fingerprint for a remote peer's identity.
+   * Throws NoSessionError if we haven't established a session with them.
+   */
+  async getRemoteFingerprint(address: string): Promise<string> {
+    const session = await this.storage.getSession(address);
+    if (!session) throw new NoSessionError(address);
+    // The session stores remoteIdentityKey (DH key). We need the signing key too,
+    // which we don't store per-session. For now, fingerprint using just the DH key
+    // (still unique per identity, just shorter).
+    // In the future, store remoteIdentitySigningKey alongside.
+    return computeFingerprint(
+      this.crypto,
+      session.remoteIdentityKey,
+      session.remoteIdentityKey,
+    );
+  }
+
+  // ─── Prekey Stock Management ────────────────────────────────
+
+  /**
+   * Ensure the one-time prekey stock is above a minimum threshold.
+   * If below `min`, generates enough to bring it up to `target`.
+   * Returns the number of new keys generated (0 if no action needed).
+   */
+  async ensurePreKeyStock(min = 5, target = 20): Promise<number> {
+    const current = await this.storage.getOneTimePreKeyCount();
+    if (current >= min) return 0;
+    const needed = target - current;
+    await this.generateOneTimePreKeys(needed);
+    return needed;
+  }
+
+  // ─── Session Reset / Identity Change ────────────────────────
+
+  /**
+   * Delete the session for a peer. The next message will trigger a fresh X3DH.
+   * Use this when a peer has reinstalled or when recovering from out-of-sync state.
+   */
+  async resetSession(address: string): Promise<void> {
+    await this.storage.removeSession(address);
+    // Note: we keep the trusted identity; new session will verify against it.
+  }
+
+  /**
+   * Accept a changed remote identity. This should only be called after
+   * verifying the new identity out-of-band (e.g., comparing fingerprints).
+   * After this, any pinned trust for this address is replaced.
+   */
+  async acceptIdentityChange(address: string, newIdentityKey: Uint8Array): Promise<void> {
+    await this.storage.saveTrustedIdentity(address, newIdentityKey);
+    // Also reset the session so the next message triggers a fresh X3DH
+    await this.storage.removeSession(address);
+  }
+
+  /**
+   * Check whether a remote identity key matches what we have pinned for an address.
+   * Returns true on TOFU (no pinned key yet) or exact match.
+   */
+  async verifyRemoteIdentity(address: string, identityKey: Uint8Array): Promise<boolean> {
+    return this.storage.isTrustedIdentity(address, identityKey);
+  }
+
   // ─── Prekey Management ─────────────────────────────────────
 
   /** Create a prekey bundle to publish to the prekey server */
@@ -133,6 +225,65 @@ export class ShadeSessionManager {
     return spk;
   }
 
+  // ─── Identity Rotation (with grace period) ─────────────────
+
+  /**
+   * Rotate the identity keypair.
+   *
+   * Archives the current identity (kept for grace period decryption of
+   * old sessions), generates a fresh identity + signed prekey, and returns
+   * a new prekey bundle ready to publish to the prekey server.
+   *
+   * Callers should:
+   *   1. Call this method
+   *   2. Re-publish the new bundle via ShadeFetchTransport.register()
+   *   3. Optionally broadcast the rotation to known peers out-of-band
+   *
+   * The old identity is retained for GRACE_PERIOD_MS so existing sessions
+   * continue decrypting. Call `pruneExpiredIdentities()` periodically.
+   */
+  async rotateIdentity(): Promise<PreKeyBundle> {
+    if (!this.identity) throw new Error('Not initialized');
+
+    // Archive current identity
+    await this.storage.addRetiredIdentity({
+      keyPair: this.identity,
+      retiredAt: Date.now(),
+    });
+
+    // Generate new identity + save
+    this.identity = await generateIdentityKeyPair(this.crypto);
+    await this.storage.saveIdentityKeyPair(this.identity);
+
+    // Generate new signed prekey (under the new identity)
+    const newSpkId = this.currentSignedPreKeyId + 1;
+    const spk = await generateSignedPreKey(this.crypto, this.identity, newSpkId);
+    await this.storage.saveSignedPreKey(spk);
+    this.currentSignedPreKeyId = newSpkId;
+
+    // Return a fresh bundle for re-publication
+    return createPreKeyBundle(this.registrationId, this.identity, spk);
+  }
+
+  /**
+   * Get all retired identities that are still within the grace period.
+   * Used internally for trying previous identities when X3DH fails.
+   */
+  async getActiveRetiredIdentities(gracePeriodMs = GRACE_PERIOD_MS): Promise<IdentityKeyPair[]> {
+    const all = await this.storage.getRetiredIdentities();
+    const cutoff = Date.now() - gracePeriodMs;
+    return all.filter((r) => r.retiredAt >= cutoff).map((r) => r.keyPair);
+  }
+
+  /**
+   * Delete retired identities older than the grace period.
+   * Call this periodically (e.g., daily cleanup task).
+   */
+  async pruneExpiredIdentities(gracePeriodMs = GRACE_PERIOD_MS): Promise<void> {
+    const cutoff = Date.now() - gracePeriodMs;
+    await this.storage.pruneRetiredIdentities(cutoff);
+  }
+
   // ─── Session Establishment ─────────────────────────────────
 
   /**
diff --git a/packages/shade-core/src/storage.ts b/packages/shade-core/src/storage.ts
index 5252936..64c3c35 100644
--- a/packages/shade-core/src/storage.ts
+++ b/packages/shade-core/src/storage.ts
@@ -1,5 +1,11 @@
 import type { IdentityKeyPair, SignedPreKey, OneTimePreKey, SessionState } from './types.js';
 
+/** A retired identity kept in history during the rotation grace period */
+export interface RetiredIdentity {
+  keyPair: IdentityKeyPair;
+  retiredAt: number;
+}
+
 /**
  * StorageProvider — abstract interface for persisting cryptographic state.
  *
@@ -65,4 +71,15 @@ export interface StorageProvider {
 
   /** Save a trusted remote identity key */
   saveTrustedIdentity(address: string, identityKey: Uint8Array): Promise<void>;
+
+  // ─── Identity History (rotation with grace period) ──────
+
+  /** Add an identity to the retired history */
+  addRetiredIdentity(identity: RetiredIdentity): Promise<void>;
+
+  /** Get all retired identities (for grace-period decryption) */
+  getRetiredIdentities(): Promise<RetiredIdentity[]>;
+
+  /** Remove retired identities older than the given timestamp */
+  pruneRetiredIdentities(olderThan: number): Promise<void>;
 }
diff --git a/packages/shade-core/tests/errors.test.ts b/packages/shade-core/tests/errors.test.ts
new file mode 100644
index 0000000..c5abe1e
--- /dev/null
+++ b/packages/shade-core/tests/errors.test.ts
@@ -0,0 +1,119 @@
+import { describe, test, expect } from 'bun:test';
+import {
+  ShadeError,
+  InvalidSignatureError,
+  DecryptionError,
+  NoSessionError,
+  MaxSkipExceededError,
+  DuplicateMessageError,
+  UntrustedIdentityError,
+  PreKeyNotFoundError,
+  ReplayError,
+  IdentityRotationError,
+  NetworkError,
+  StorageError,
+  ValidationError,
+  TimeoutError,
+  RateLimitError,
+  ConfigurationError,
+  UnauthorizedError,
+  errorToHttpStatus,
+} from '../src/errors.js';
+
+describe('Error hierarchy', () => {
+  test('all errors extend ShadeError', () => {
+    const errors = [
+      new InvalidSignatureError(),
+      new DecryptionError(),
+      new NoSessionError('addr'),
+      new MaxSkipExceededError(1001, 1000),
+      new DuplicateMessageError(),
+      new UntrustedIdentityError('addr'),
+      new PreKeyNotFoundError(1, 'signed'),
+      new ReplayError(),
+      new IdentityRotationError(),
+      new NetworkError('net'),
+      new StorageError('storage'),
+      new ValidationError('val'),
+      new TimeoutError(),
+      new RateLimitError(),
+      new ConfigurationError('cfg'),
+      new UnauthorizedError(),
+    ];
+    for (const e of errors) {
+      expect(e).toBeInstanceOf(ShadeError);
+      expect(e).toBeInstanceOf(Error);
+      expect(e.code).toMatch(/^SHADE_/);
+      expect(e.name).not.toBe('ShadeError');
+    }
+  });
+
+  test('toJSON produces serializable form', () => {
+    const e = new InvalidSignatureError('bad sig');
+    const json = e.toJSON();
+    expect(json.name).toBe('InvalidSignatureError');
+    expect(json.code).toBe('SHADE_INVALID_SIGNATURE');
+    expect(json.message).toBe('bad sig');
+
+    const str = JSON.stringify(e);
+    const parsed = JSON.parse(str);
+    expect(parsed.code).toBe('SHADE_INVALID_SIGNATURE');
+  });
+
+  test('NetworkError carries status code', () => {
+    const e = new NetworkError('server error', 503);
+    expect(e.statusCode).toBe(503);
+  });
+
+  test('RateLimitError carries retry-after', () => {
+    const e = new RateLimitError('too many', 60);
+    expect(e.retryAfterSeconds).toBe(60);
+  });
+
+  test('ValidationError carries field name', () => {
+    const e = new ValidationError('must be positive', 'count');
+    expect(e.field).toBe('count');
+  });
+});
+
+describe('errorToHttpStatus', () => {
+  test('unknown error → 500', () => {
+    expect(errorToHttpStatus(new Error('plain'))).toBe(500);
+    expect(errorToHttpStatus('string error')).toBe(500);
+    expect(errorToHttpStatus(null)).toBe(500);
+  });
+
+  test('auth errors → 401/403', () => {
+    expect(errorToHttpStatus(new InvalidSignatureError())).toBe(401);
+    expect(errorToHttpStatus(new UnauthorizedError())).toBe(401);
+    expect(errorToHttpStatus(new UntrustedIdentityError('x'))).toBe(403);
+  });
+
+  test('not-found errors → 404', () => {
+    expect(errorToHttpStatus(new NoSessionError('x'))).toBe(404);
+    expect(errorToHttpStatus(new PreKeyNotFoundError(1, 'signed'))).toBe(404);
+  });
+
+  test('validation → 400', () => {
+    expect(errorToHttpStatus(new ValidationError('bad'))).toBe(400);
+  });
+
+  test('replay/duplicate → 409', () => {
+    expect(errorToHttpStatus(new ReplayError())).toBe(409);
+    expect(errorToHttpStatus(new DuplicateMessageError())).toBe(409);
+  });
+
+  test('rate limit → 429', () => {
+    expect(errorToHttpStatus(new RateLimitError())).toBe(429);
+  });
+
+  test('infra errors → 503', () => {
+    expect(errorToHttpStatus(new NetworkError('x'))).toBe(503);
+    expect(errorToHttpStatus(new StorageError('x'))).toBe(503);
+    expect(errorToHttpStatus(new ConfigurationError('x'))).toBe(503);
+  });
+
+  test('timeout → 504', () => {
+    expect(errorToHttpStatus(new TimeoutError())).toBe(504);
+  });
+});
diff --git a/packages/shade-core/tests/fingerprint-session.test.ts b/packages/shade-core/tests/fingerprint-session.test.ts
new file mode 100644
index 0000000..e3ffb26
--- /dev/null
+++ b/packages/shade-core/tests/fingerprint-session.test.ts
@@ -0,0 +1,164 @@
+import { describe, test, expect } from 'bun:test';
+import { SubtleCryptoProvider, MemoryStorage } from '@shade/crypto-web';
+import { ShadeSessionManager, computeFingerprint, shortFingerprint } from '../src/index.js';
+
+const crypto = new SubtleCryptoProvider();
+
+describe('Fingerprints (safety numbers)', () => {
+  test('computeFingerprint produces 12 groups of 5 digits', async () => {
+    const sig = crypto.randomBytes(32);
+    const dh = crypto.randomBytes(32);
+    const fp = await computeFingerprint(crypto, sig, dh);
+
+    const groups = fp.split(' ');
+    expect(groups.length).toBe(12);
+    for (const g of groups) {
+      expect(g).toMatch(/^\d{5}$/);
+    }
+  });
+
+  test('same input produces same fingerprint (deterministic)', async () => {
+    const sig = new Uint8Array(32).fill(0xab);
+    const dh = new Uint8Array(32).fill(0xcd);
+    const fp1 = await computeFingerprint(crypto, sig, dh);
+    const fp2 = await computeFingerprint(crypto, sig, dh);
+    expect(fp1).toBe(fp2);
+  });
+
+  test('different identities produce different fingerprints', async () => {
+    const sig1 = crypto.randomBytes(32);
+    const dh1 = crypto.randomBytes(32);
+    const sig2 = crypto.randomBytes(32);
+    const dh2 = crypto.randomBytes(32);
+
+    const fp1 = await computeFingerprint(crypto, sig1, dh1);
+    const fp2 = await computeFingerprint(crypto, sig2, dh2);
+    expect(fp1).not.toBe(fp2);
+  });
+
+  test('shortFingerprint is 4 groups', () => {
+    const full = '11111 22222 33333 44444 55555 66666 77777 88888 99999 11111 22222 33333';
+    expect(shortFingerprint(full)).toBe('11111 22222 33333 44444');
+  });
+});
+
+describe('ShadeSessionManager fingerprints', () => {
+  test('getIdentityFingerprint returns stable value', async () => {
+    const storage = new MemoryStorage();
+    const mgr = new ShadeSessionManager(crypto, storage);
+    await mgr.initialize();
+
+    const fp1 = await mgr.getIdentityFingerprint();
+    const fp2 = await mgr.getIdentityFingerprint();
+    expect(fp1).toBe(fp2);
+    expect(fp1.split(' ').length).toBe(12);
+  });
+
+  test('fingerprint persists across SessionManager instances', async () => {
+    const storage = new MemoryStorage();
+    const mgr1 = new ShadeSessionManager(crypto, storage);
+    await mgr1.initialize();
+    const fp1 = await mgr1.getIdentityFingerprint();
+
+    const mgr2 = new ShadeSessionManager(crypto, storage);
+    await mgr2.initialize();
+    const fp2 = await mgr2.getIdentityFingerprint();
+
+    expect(fp1).toBe(fp2);
+  });
+
+  test('different identities have different fingerprints', async () => {
+    const alice = new ShadeSessionManager(crypto, new MemoryStorage());
+    const bob = new ShadeSessionManager(crypto, new MemoryStorage());
+    await alice.initialize();
+    await bob.initialize();
+
+    const fpA = await alice.getIdentityFingerprint();
+    const fpB = await bob.getIdentityFingerprint();
+    expect(fpA).not.toBe(fpB);
+  });
+
+  test('getShortFingerprint returns 4 groups', async () => {
+    const mgr = new ShadeSessionManager(crypto, new MemoryStorage());
+    await mgr.initialize();
+    const short = await mgr.getShortFingerprint();
+    expect(short.split(' ').length).toBe(4);
+  });
+});
+
+describe('Prekey stock management', () => {
+  test('ensurePreKeyStock generates keys when below min', async () => {
+    const mgr = new ShadeSessionManager(crypto, new MemoryStorage());
+    await mgr.initialize();
+
+    // Start with 0 OTPKs
+    const generated = await mgr.ensurePreKeyStock(5, 10);
+    expect(generated).toBe(10);
+  });
+
+  test('ensurePreKeyStock does nothing when above min', async () => {
+    const mgr = new ShadeSessionManager(crypto, new MemoryStorage());
+    await mgr.initialize();
+
+    await mgr.generateOneTimePreKeys(10);
+    const generated = await mgr.ensurePreKeyStock(5, 10);
+    expect(generated).toBe(0);
+  });
+
+  test('ensurePreKeyStock tops up to target', async () => {
+    const mgr = new ShadeSessionManager(crypto, new MemoryStorage());
+    await mgr.initialize();
+
+    await mgr.generateOneTimePreKeys(3);
+    // Below min of 5, should generate enough to reach target of 20
+    const generated = await mgr.ensurePreKeyStock(5, 20);
+    expect(generated).toBe(17);
+  });
+});
+
+describe('Session reset + identity change', () => {
+  async function setupPair() {
+    const alice = new ShadeSessionManager(crypto, new MemoryStorage());
+    const bob = new ShadeSessionManager(crypto, new MemoryStorage());
+    await alice.initialize();
+    await bob.initialize();
+
+    const otpks = await bob.generateOneTimePreKeys(5);
+    const bundle = await bob.createPreKeyBundle();
+    bundle.oneTimePreKey = { keyId: otpks[0].keyId, publicKey: otpks[0].keyPair.publicKey };
+    await alice.initSessionFromBundle('bob', bundle);
+    return { alice, bob };
+  }
+
+  test('resetSession removes the session', async () => {
+    const { alice } = await setupPair();
+
+    // Encrypt once to confirm session exists
+    await alice.encrypt('bob', 'hello');
+
+    await alice.resetSession('bob');
+    expect(alice.encrypt('bob', 'next')).rejects.toThrow('No session');
+  });
+
+  test('acceptIdentityChange updates pinned trust', async () => {
+    const { alice, bob } = await setupPair();
+
+    // Alice verifies Bob's current identity
+    const bobId = bob.getPublicIdentity();
+    expect(await alice.verifyRemoteIdentity('bob', bobId.dhKey)).toBe(true);
+
+    // Different key is rejected
+    const fakeKey = crypto.randomBytes(32);
+    expect(await alice.verifyRemoteIdentity('bob', fakeKey)).toBe(false);
+
+    // Accept the fake key as the new Bob
+    await alice.acceptIdentityChange('bob', fakeKey);
+
+    // Now the fake key is trusted, old one isn't
+    expect(await alice.verifyRemoteIdentity('bob', fakeKey)).toBe(true);
+    expect(await alice.verifyRemoteIdentity('bob', bobId.dhKey)).toBe(false);
+
+    // Session was also removed
+    expect(alice.encrypt('bob', 'test')).rejects.toThrow('No session');
+  });
+});
diff --git a/packages/shade-core/tests/identity-rotation.test.ts b/packages/shade-core/tests/identity-rotation.test.ts
new file mode 100644
index 0000000..156f91b
--- /dev/null
+++ b/packages/shade-core/tests/identity-rotation.test.ts
@@ -0,0 +1,131 @@
+import { describe, test, expect } from 'bun:test';
+import { SubtleCryptoProvider, MemoryStorage } from '@shade/crypto-web';
+import { ShadeSessionManager, GRACE_PERIOD_MS } from '../src/index.js';
+
+const crypto = new SubtleCryptoProvider();
+
+describe('Identity rotation', () => {
+  test('rotateIdentity generates new identity and archives old', async () => {
+    const storage = new MemoryStorage();
+    const mgr = new ShadeSessionManager(crypto, storage);
+    await mgr.initialize();
+
+    const oldFp = await mgr.getIdentityFingerprint();
+    const oldPub = mgr.getPublicIdentity();
+
+    await mgr.rotateIdentity();
+
+    const newFp = await mgr.getIdentityFingerprint();
+    const newPub = mgr.getPublicIdentity();
+
+    // New identity should differ
+    expect(newFp).not.toBe(oldFp);
+    expect(newPub.signingKey).not.toEqual(oldPub.signingKey);
+    expect(newPub.dhKey).not.toEqual(oldPub.dhKey);
+
+    // Old identity is archived
+    const retired = await storage.getRetiredIdentities();
+    expect(retired.length).toBe(1);
+    expect(retired[0].keyPair.signingPublicKey).toEqual(oldPub.signingKey);
+  });
+
+  test('rotation returns a new prekey bundle', async () => {
+    const mgr = new ShadeSessionManager(crypto, new MemoryStorage());
+    await mgr.initialize();
+
+    const bundle = await mgr.rotateIdentity();
+    expect(bundle.identitySigningKey.length).toBe(32);
+    expect(bundle.identityDHKey.length).toBe(32);
+    expect(bundle.signedPreKey.keyId).toBe(2); // advanced
+    expect(bundle.signedPreKey.signature.length).toBe(64);
+  });
+
+  test('getActiveRetiredIdentities returns entries within grace period', async () => {
+    const mgr = new ShadeSessionManager(crypto, new MemoryStorage());
+    await mgr.initialize();
+
+    await mgr.rotateIdentity();
+    await mgr.rotateIdentity();
+
+    const active = await mgr.getActiveRetiredIdentities();
+    expect(active.length).toBe(2);
+  });
+
+  test('getActiveRetiredIdentities filters out expired entries', async () => {
+    const storage = new MemoryStorage();
+    const mgr = new ShadeSessionManager(crypto, storage);
+    await mgr.initialize();
+
+    // Manually add a very old retired identity
+    await storage.addRetiredIdentity({
+      keyPair: (await mgr.getPublicIdentity()) as any, // placeholder
+      retiredAt: Date.now() - (GRACE_PERIOD_MS + 1000),
+    });
+
+    // And a fresh one
+    await mgr.rotateIdentity();
+
+    const active = await mgr.getActiveRetiredIdentities();
+    expect(active.length).toBe(1);
+  });
+
+  test('pruneExpiredIdentities removes old entries', async () => {
+    const storage = new MemoryStorage();
+    const mgr = new ShadeSessionManager(crypto, storage);
+    await mgr.initialize();
+
+    // Rotate twice
+    await mgr.rotateIdentity();
+    await mgr.rotateIdentity();
+
+    expect((await storage.getRetiredIdentities()).length).toBe(2);
+
+    // Default grace period: nothing is expired yet
+    await mgr.pruneExpiredIdentities();
+    expect((await storage.getRetiredIdentities()).length).toBe(2);
+
+    // Force prune with 0 grace → everything goes
+    await mgr.pruneExpiredIdentities(0);
+    expect((await storage.getRetiredIdentities()).length).toBe(0);
+  });
+
+  test('rotation persists across manager restart', async () => {
+    const storage = new MemoryStorage();
+    const mgr1 = new ShadeSessionManager(crypto, storage);
+    await mgr1.initialize();
+    await mgr1.rotateIdentity();
+    const fp1 = await mgr1.getIdentityFingerprint();
+
+    const mgr2 = new ShadeSessionManager(crypto, storage);
+    await mgr2.initialize();
+    const fp2 = await mgr2.getIdentityFingerprint();
+
+    expect(fp1).toBe(fp2);
+  });
+
+  test('existing sessions survive identity rotation', async () => {
+    // Set up Alice-Bob conversation
+    const alice = new ShadeSessionManager(crypto, new MemoryStorage());
+    const bob = new ShadeSessionManager(crypto, new MemoryStorage());
+    await alice.initialize();
+    await bob.initialize();
+
+    const otpks = await bob.generateOneTimePreKeys(5);
+    const bundle = await bob.createPreKeyBundle();
+    bundle.oneTimePreKey = { keyId: otpks[0].keyId, publicKey: otpks[0].keyPair.publicKey };
+    await alice.initSessionFromBundle('bob', bundle);
+
+    // Exchange messages to establish bidirectional session
+    const env1 = await alice.encrypt('bob', 'hello');
+    expect(await bob.decrypt('alice', env1)).toBe('hello');
+    const env2 = await bob.encrypt('alice', 'hi');
+    expect(await alice.decrypt('bob', env2)).toBe('hi');
+
+    // Alice rotates her identity — but her session with Bob should still work
+    // because the Double Ratchet uses ephemeral DH keys, not identity keys
+    await alice.rotateIdentity();
+
+    const env3 = await alice.encrypt('bob', 'after rotation');
+    expect(await bob.decrypt('alice', env3)).toBe('after rotation');
+  });
+});
diff --git a/packages/shade-crypto-web/src/memory-storage.ts b/packages/shade-crypto-web/src/memory-storage.ts
index e2483d5..37462bb 100644
--- a/packages/shade-crypto-web/src/memory-storage.ts
+++ b/packages/shade-crypto-web/src/memory-storage.ts
@@ -1,4 +1,5 @@
-import type { StorageProvider, IdentityKeyPair, SignedPreKey, OneTimePreKey, SessionState } from '@shade/core';
+import type { StorageProvider, IdentityKeyPair, SignedPreKey, OneTimePreKey, SessionState, RetiredIdentity } from '@shade/core';
+import { constantTimeEqual } from '@shade/core';
 
 /**
  * In-memory StorageProvider for testing and embedded use.
@@ -11,6 +12,7 @@ export class MemoryStorage implements StorageProvider {
   private oneTimePreKeys = new Map<number, OneTimePreKey>();
   private sessions = new Map<string, SessionState>();
   private trustedIdentities = new Map<string, Uint8Array>();
+  private retiredIdentities: RetiredIdentity[] = [];
 
   // ─── Identity ──────────────────────────────────────────────
 
@@ -81,18 +83,24 @@ export class MemoryStorage implements StorageProvider {
   async isTrustedIdentity(address: string, identityKey: Uint8Array): Promise<boolean> {
     const stored = this.trustedIdentities.get(address);
     if (!stored) return true; // TOFU: trust on first use
-    return arraysEqual(stored, identityKey);
+    return constantTimeEqual(stored, identityKey);
   }
 
   async saveTrustedIdentity(address: string, identityKey: Uint8Array): Promise<void> {
     this.trustedIdentities.set(address, identityKey);
   }
-}
 
-function arraysEqual(a: Uint8Array, b: Uint8Array): boolean {
-  if (a.length !== b.length) return false;
-  for (let i = 0; i < a.length; i++) {
-    if (a[i] !== b[i]) return false;
+  // ─── Identity History ─────────────────────────────────────
+
+  async addRetiredIdentity(identity: RetiredIdentity): Promise<void> {
+    this.retiredIdentities.push(identity);
+  }
+
+  async getRetiredIdentities(): Promise<RetiredIdentity[]> {
+    return [...this.retiredIdentities];
+  }
+
+  async pruneRetiredIdentities(olderThan: number): Promise<void> {
+    this.retiredIdentities = this.retiredIdentities.filter((r) => r.retiredAt >= olderThan);
   }
-  return true;
 }
diff --git a/packages/shade-crypto-web/src/provider.ts b/packages/shade-crypto-web/src/provider.ts
index 61b092c..b964e9f 100644
--- a/packages/shade-crypto-web/src/provider.ts
+++ b/packages/shade-crypto-web/src/provider.ts
@@ -115,4 +115,24 @@ export class SubtleCryptoProvider implements CryptoProvider {
     globalThis.crypto.getRandomValues(buf);
     return buf;
   }
+
+  // ─── Hardening ─────────────────────────────────────────────
+
+  constantTimeEqual(a: Uint8Array, b: Uint8Array): boolean {
+    if (a.length !== b.length) return false;
+    let diff = 0;
+    for (let i = 0; i < a.length; i++) {
+      diff |= a[i]! ^ b[i]!;
+    }
+    return diff === 0;
+  }
+
+  zeroize(buf: Uint8Array): void {
+    buf.fill(0);
+  }
+
+  randomUint32(): number {
+    const buf = this.randomBytes(4);
+    return new DataView(buf.buffer, buf.byteOffset, 4).getUint32(0, false);
+  }
 }
diff --git a/packages/shade-crypto-web/tests/hardening.test.ts b/packages/shade-crypto-web/tests/hardening.test.ts
new file mode 100644
index 0000000..584f342
--- /dev/null
+++ b/packages/shade-crypto-web/tests/hardening.test.ts
@@ -0,0 +1,143 @@
+import { describe, test, expect } from 'bun:test';
+import { SubtleCryptoProvider } from '../src/provider.js';
+import { constantTimeEqual } from '@shade/core';
+
+const crypto = new SubtleCryptoProvider();
+
+describe('Cryptographic Hardening', () => {
+  // ─── constantTimeEqual ───────────────────────────────────
+
+  describe('constantTimeEqual', () => {
+    test('equal arrays return true', () => {
+      const a = new Uint8Array([1, 2, 3, 4, 5]);
+      const b = new Uint8Array([1, 2, 3, 4, 5]);
+      expect(crypto.constantTimeEqual(a, b)).toBe(true);
+    });
+
+    test('unequal arrays return false', () => {
+      const a = new Uint8Array([1, 2, 3, 4, 5]);
+      const b = new Uint8Array([1, 2, 3, 4, 6]);
+      expect(crypto.constantTimeEqual(a, b)).toBe(false);
+    });
+
+    test('different lengths return false', () => {
+      const a = new Uint8Array([1, 2, 3]);
+      const b = new Uint8Array([1, 2, 3, 4]);
+      expect(crypto.constantTimeEqual(a, b)).toBe(false);
+    });
+
+    test('empty arrays are equal', () => {
+      expect(crypto.constantTimeEqual(new Uint8Array(0), new Uint8Array(0))).toBe(true);
+    });
+
+    test('works on full 32-byte keys', () => {
+      const k1 = crypto.randomBytes(32);
+      const k2 = new Uint8Array(k1);
+      expect(crypto.constantTimeEqual(k1, k2)).toBe(true);
+
+      k2[31] ^= 0x01;
+      expect(crypto.constantTimeEqual(k1, k2)).toBe(false);
+    });
+
+    test('standalone function gives same result', () => {
+      const a = crypto.randomBytes(32);
+      const b = new Uint8Array(a);
+      expect(constantTimeEqual(a, b)).toBe(true);
+      b[0] ^= 0x01;
+      expect(constantTimeEqual(a, b)).toBe(false);
+    });
+
+    // Statistical timing test — measure variance between mismatch-at-start vs mismatch-at-end
+    // This is noisy on CI but catches obvious early-exit regressions.
+    test('timing variance stays bounded across mismatch positions', () => {
+      const len = 256;
+      const target = crypto.randomBytes(len);
+
+      const mismatchAtStart = new Uint8Array(target);
+      mismatchAtStart[0] ^= 0xff;
+
+      const mismatchAtEnd = new Uint8Array(target);
+      mismatchAtEnd[len - 1] ^= 0xff;
+
+      // Measure many iterations to get a stable signal
+      const iterations = 50000;
+
+      const start1 = performance.now();
+      for (let i = 0; i < iterations; i++) {
+        crypto.constantTimeEqual(target, mismatchAtStart);
+      }
+      const timeStart = performance.now() - start1;
+
+      const start2 = performance.now();
+      for (let i = 0; i < iterations; i++) {
+        crypto.constantTimeEqual(target, mismatchAtEnd);
+      }
+      const timeEnd = performance.now() - start2;
+
+      // With constant-time comparison, these should be very close.
+      // Non-constant-time would show timeEnd >> timeStart (early exit vs full scan).
+      // Allow 2x variance for JIT/noise, but it should never be 10x.
+      const ratio = Math.max(timeStart, timeEnd) / Math.min(timeStart, timeEnd);
+      expect(ratio).toBeLessThan(3);
+    });
+  });
+
+  // ─── zeroize ──────────────────────────────────────────────
+
+  describe('zeroize', () => {
+    test('fills buffer with zeros', () => {
+      const buf = crypto.randomBytes(32);
+      // Make sure it's not already zero
+      const anyNonZero = buf.some((b) => b !== 0);
+      expect(anyNonZero).toBe(true);
+
+      crypto.zeroize(buf);
+      expect(buf.every((b) => b === 0)).toBe(true);
+    });
+
+    test('handles empty buffer', () => {
+      crypto.zeroize(new Uint8Array(0));
+      // Should not throw
+    });
+
+    test('handles large buffer', () => {
+      const buf = crypto.randomBytes(4096);
+      crypto.zeroize(buf);
+      expect(buf.every((b) => b === 0)).toBe(true);
+    });
+  });
+
+  // ─── randomUint32 ─────────────────────────────────────────
+
+  describe('randomUint32', () => {
+    test('returns number in 32-bit unsigned range', () => {
+      for (let i = 0; i < 100; i++) {
+        const n = crypto.randomUint32();
+        expect(n).toBeGreaterThanOrEqual(0);
+        expect(n).toBeLessThanOrEqual(0xffffffff);
+        expect(Number.isInteger(n)).toBe(true);
+      }
+    });
+
+    test('produces different values each call', () => {
+      const values = new Set<number>();
+      for (let i = 0; i < 100; i++) {
+        values.add(crypto.randomUint32());
+      }
+      // With 32 bits, 100 samples should all be unique
+      expect(values.size).toBe(100);
+    });
+
+    test('distribution is not biased toward low values', () => {
+      // Generate many and check that at least some are above 2^31
+      // (would fail if using Math.random() with weird multiplier bugs)
+      let highCount = 0;
+      for (let i = 0; i < 1000; i++) {
+        if (crypto.randomUint32() >= 0x80000000) highCount++;
+      }
+      // Should be around 500, accept 400-600 as "not obviously broken"
+      expect(highCount).toBeGreaterThan(400);
+      expect(highCount).toBeLessThan(600);
+    });
+  });
+});
diff --git a/packages/shade-server/package.json b/packages/shade-server/package.json
index aa41aa8..2afdd96 100644
--- a/packages/shade-server/package.json
+++ b/packages/shade-server/package.json
@@ -7,5 +7,8 @@
   "dependencies": {
     "@shade/core": "workspace:*",
     "hono": "^4.12.12"
+  },
+  "devDependencies": {
+    "@shade/crypto-web": "workspace:*"
   }
 }
diff --git a/packages/shade-server/src/auth.ts b/packages/shade-server/src/auth.ts
new file mode 100644
index 0000000..cc48ab8
--- /dev/null
+++ b/packages/shade-server/src/auth.ts
@@ -0,0 +1,133 @@
+import type { CryptoProvider } from '@shade/core';
+import { fromBase64, UnauthorizedError, ValidationError, ReplayError } from '@shade/core';
+
+/**
+ * Self-authenticated prekey server.
+ *
+ * Each write request must include a signature over a canonical
+ * representation of the body (excluding the signature field itself)
+ * using the identity's Ed25519 signing key.
+ *
+ * On register: the signing key is extracted from the body itself
+ * (TOFU — first registration establishes the identity).
+ *
+ * On replenish/delete: the signing key is looked up from the stored
+ * identity record for the address.
+ */
+
+/** Maximum age of a signed request, in milliseconds */
+const MAX_SIGNATURE_AGE_MS = 5 * 60 * 1000; // 5 minutes
+
+/** Maximum clock skew tolerated (future timestamps) */
+const MAX_FUTURE_SKEW_MS = 1 * 60 * 1000; // 1 minute
+
+interface SignedPayload {
+  signedAt: number;
+  signature: string; // base64
+  [key: string]: unknown;
+}
+
+/**
+ * Canonicalize a payload for signing by omitting the `signature` field
+ * and using deterministic JSON key ordering.
+ *
+ * Both signer and verifier must produce identical bytes.
+ */
+export function canonicalizePayload(payload: SignedPayload): Uint8Array {
+  const { signature, ...rest } = payload;
+  // Sort keys to be deterministic
+  const sorted = Object.keys(rest)
+    .sort()
+    .reduce<Record<string, unknown>>((acc, key) => {
+      acc[key] = (rest as Record<string, unknown>)[key];
+      return acc;
+    }, {});
+  return new TextEncoder().encode(JSON.stringify(sorted));
+}
+
+/**
+ * Sign a payload with an Ed25519 signing private key.
+ * Returns the payload with `signature` and `signedAt` set.
+ */
+export async function signPayload<T extends Record<string, unknown>>(
+  crypto: CryptoProvider,
+  signingPrivateKey: Uint8Array,
+  payload: T,
+): Promise<T & { signedAt: number; signature: string }> {
+  const signedAt = Date.now();
+  const bytes = canonicalizePayload({ ...payload, signedAt, signature: '' });
+  const sig = await crypto.sign(signingPrivateKey, bytes);
+  return {
+    ...payload,
+    signedAt,
+    signature: Buffer.from(sig).toString('base64'),
+  };
+}
+
+/**
+ * Verify a signed payload against a given signing public key.
+ *
+ * Throws:
+ *  - ValidationError if signedAt or signature fields are missing/malformed
+ *  - ReplayError if signedAt is outside the allowed window
+ *  - UnauthorizedError if the signature does not verify
+ */
+export async function verifyPayload(
+  crypto: CryptoProvider,
+  signingPublicKey: Uint8Array,
+  payload: unknown,
+): Promise<void> {
+  if (!payload || typeof payload !== 'object') {
+    throw new ValidationError('Payload must be an object');
+  }
+  const p = payload as SignedPayload;
+
+  if (typeof p.signedAt !== 'number') {
+    throw new ValidationError('Missing or invalid signedAt', 'signedAt');
+  }
+  if (typeof p.signature !== 'string') {
+    throw new ValidationError('Missing or invalid signature', 'signature');
+  }
+
+  const now = Date.now();
+  const age = now - p.signedAt;
+  if (age > MAX_SIGNATURE_AGE_MS) {
+    throw new ReplayError(`Signature too old: ${age}ms`);
+  }
+  if (age < -MAX_FUTURE_SKEW_MS) {
+    throw new ReplayError(`Signature in the future: ${-age}ms ahead`);
+  }
+
+  let sigBytes: Uint8Array;
+  try {
+    sigBytes = fromBase64(p.signature);
+  } catch {
+    throw new ValidationError('Signature is not valid base64', 'signature');
+  }
+
+  const canonical = canonicalizePayload(p);
+  const valid = await crypto.verify(signingPublicKey, canonical, sigBytes);
+  if (!valid) {
+    throw new UnauthorizedError('Invalid signature');
+  }
+}
+
+// ─── Address validation ─────────────────────────────────────
+
+const ADDRESS_REGEX = /^[a-zA-Z0-9][a-zA-Z0-9:_\-.]{0,255}$/;
+
+/**
+ * Validate a peer address string.
+ * Allows alphanumeric, :, _, -, . with max 256 chars and must start with alphanumeric.
+ * Rejects path traversal, unicode tricks, and empty strings.
+ */
+export function validateAddress(address: unknown): string {
+  if (typeof address !== 'string') {
+    throw new ValidationError('Address must be a string', 'address');
+  }
+  const normalized = address.normalize('NFKC');
+  if (!ADDRESS_REGEX.test(normalized)) {
+    throw new ValidationError('Invalid address format', 'address');
+  }
+  return normalized;
+}
diff --git a/packages/shade-server/src/index.ts b/packages/shade-server/src/index.ts
index 9b6bd6b..50c7548 100644
--- a/packages/shade-server/src/index.ts
+++ b/packages/shade-server/src/index.ts
@@ -1,4 +1,5 @@
-import { Hono } from 'hono';
+import type { Hono } from 'hono';
+import type { CryptoProvider } from '@shade/core';
 import { createPrekeyRoutes } from './routes.js';
 import { MemoryPrekeyStore } from './memory-store.js';
 import type { PrekeyStore } from './store.js';
@@ -6,23 +7,30 @@ import type { PrekeyStore } from './store.js';
 export { createPrekeyRoutes } from './routes.js';
 export { MemoryPrekeyStore } from './memory-store.js';
 export type { PrekeyStore } from './store.js';
+export { verifyPayload, signPayload, canonicalizePayload, validateAddress } from './auth.js';
 
 /**
  * Create a standalone Shade Prekey Server.
  *
- * Can be used standalone (Docker) or embedded in another Hono app.
+ * Requires a CryptoProvider for signature verification on write routes.
  *
  * Standalone:
- *   const server = createPrekeyServer();
+ *   const crypto = new SubtleCryptoProvider();
+ *   const server = createPrekeyServer({ crypto });
  *   export default { port: 3900, fetch: server.fetch };
  *
- * Embedded:
+ * Embedded in another Hono app:
  *   const app = new Hono();
- *   app.route('/shade', createPrekeyServer());
+ *   app.route('/shade', createPrekeyServer({ crypto }));
  */
-export function createPrekeyServer(options?: {
+export function createPrekeyServer(options: {
+  crypto: CryptoProvider;
   store?: PrekeyStore;
+  disableRateLimit?: boolean;
 }): Hono {
-  const store = options?.store ?? new MemoryPrekeyStore();
-  return createPrekeyRoutes(store);
+  const store = options.store ?? new MemoryPrekeyStore();
+  return createPrekeyRoutes(store, options.crypto, { disableRateLimit: options.disableRateLimit });
 }
+
+export { RateLimiter, MemoryRateLimitStore } from './rate-limit.js';
+export type { RateLimitStore, RateLimitConfig } from './rate-limit.js';
diff --git a/packages/shade-server/src/rate-limit.ts b/packages/shade-server/src/rate-limit.ts
new file mode 100644
index 0000000..d8a369a
--- /dev/null
+++ b/packages/shade-server/src/rate-limit.ts
@@ -0,0 +1,103 @@
+import { RateLimitError } from '@shade/core';
+
+/**
+ * Simple token-bucket rate limiter with pluggable storage.
+ *
+ * Default storage is in-memory (Map). For distributed deployments,
+ * swap in a Redis-backed RateLimitStore implementation.
+ */
+
+export interface RateLimitStore {
+  /** Get the current token count and last refill time for a key */
+  get(key: string): Promise<{ tokens: number; lastRefill: number } | null>;
+  /** Store the current token count and last refill time */
+  set(key: string, tokens: number, lastRefill: number): Promise<void>;
+}
+
+export class MemoryRateLimitStore implements RateLimitStore {
+  private entries = new Map<string, { tokens: number; lastRefill: number }>();
+
+  async get(key: string) {
+    return this.entries.get(key) ?? null;
+  }
+
+  async set(key: string, tokens: number, lastRefill: number) {
+    this.entries.set(key, { tokens, lastRefill });
+  }
+
+  /** Periodic cleanup: drop entries older than `maxAge` ms */
+  cleanup(maxAge: number) {
+    const now = Date.now();
+    for (const [key, entry] of this.entries) {
+      if (now - entry.lastRefill > maxAge) {
+        this.entries.delete(key);
+      }
+    }
+  }
+}
+
+export interface RateLimitConfig {
+  /** Maximum tokens in the bucket (burst capacity) */
+  capacity: number;
+  /** Tokens added per second */
+  refillPerSecond: number;
+}
+
+export class RateLimiter {
+  constructor(
+    private readonly store: RateLimitStore,
+    private readonly config: RateLimitConfig,
+  ) {}
+
+  /**
+   * Attempt to consume one token for the given key.
+   * Throws RateLimitError if no tokens available.
+   */
+  async consume(key: string, tokens = 1): Promise<void> {
+    const now = Date.now();
+    const entry = await this.store.get(key);
+
+    let currentTokens: number;
+    if (!entry) {
+      currentTokens = this.config.capacity;
+    } else {
+      const elapsed = (now - entry.lastRefill) / 1000;
+      const refilled = elapsed * this.config.refillPerSecond;
+      currentTokens = Math.min(this.config.capacity, entry.tokens + refilled);
+    }
+
+    if (currentTokens < tokens) {
+      const needed = tokens - currentTokens;
+      const retryAfter = Math.ceil(needed / this.config.refillPerSecond);
+      throw new RateLimitError(`Rate limit exceeded for ${key}`, retryAfter);
+    }
+
+    await this.store.set(key, currentTokens - tokens, now);
+  }
+}
+
+// ─── Preset configurations ──────────────────────────────────
+
+/** Register: 5 per hour (prevent identity flooding) */
+export const REGISTER_LIMIT: RateLimitConfig = {
+  capacity: 5,
+  refillPerSecond: 5 / 3600, // 5 per hour
+};
+
+/** Fetch bundle: 60 per minute (anonymous, high limit) */
+export const FETCH_LIMIT: RateLimitConfig = {
+  capacity: 60,
+  refillPerSecond: 1,
+};
+
+/** Replenish: 10 per minute per identity */
+export const REPLENISH_LIMIT: RateLimitConfig = {
+  capacity: 10,
+  refillPerSecond: 10 / 60,
+};
+
+/** Delete: 5 per hour per identity */
+export const DELETE_LIMIT: RateLimitConfig = {
+  capacity: 5,
+  refillPerSecond: 5 / 3600,
+};
diff --git a/packages/shade-server/src/routes.ts b/packages/shade-server/src/routes.ts
index 7b46815..1fa8b58 100644
--- a/packages/shade-server/src/routes.ts
+++ b/packages/shade-server/src/routes.ts
@@ -1,35 +1,93 @@
 import { Hono } from 'hono';
+import type { CryptoProvider } from '@shade/core';
+import { fromBase64, errorToHttpStatus, ShadeError, ValidationError } from '@shade/core';
 import type { PrekeyStore } from './store.js';
+import { verifyPayload, validateAddress } from './auth.js';
+import { RateLimiter, MemoryRateLimitStore, REGISTER_LIMIT, FETCH_LIMIT, REPLENISH_LIMIT, DELETE_LIMIT } from './rate-limit.js';
+
+/** Max POST body size in bytes (64KB) */
+const MAX_BODY_SIZE = 64 * 1024;
 
 /**
  * Create the Shade Prekey Server Hono app.
  *
  * Routes:
- *   POST   /v1/keys/register        — Register identity + upload prekey bundle
- *   GET    /v1/keys/bundle/:address  — Fetch a prekey bundle (consumes one OTP key)
- *   POST   /v1/keys/replenish       — Upload additional one-time prekeys
- *   GET    /v1/keys/count/:address   — Get remaining one-time prekey count
- *   DELETE /v1/keys/:address         — Unregister (delete all keys)
+ *   POST   /v1/keys/register        — Register identity + upload prekey bundle (SIGNED)
+ *   GET    /v1/keys/bundle/:address  — Fetch a prekey bundle (anonymous)
+ *   POST   /v1/keys/replenish       — Upload additional one-time prekeys (SIGNED)
+ *   GET    /v1/keys/count/:address   — Get remaining one-time prekey count (anonymous)
+ *   DELETE /v1/keys/:address         — Unregister (SIGNED)
+ *
+ * Write routes require a valid Ed25519 signature. See auth.ts.
  */
-export function createPrekeyRoutes(store: PrekeyStore): Hono {
+export interface PrekeyRoutesOptions {
+  /** Disable rate limiting (for tests). Default: enabled. */
+  disableRateLimit?: boolean;
+}
+
+export function createPrekeyRoutes(
+  store: PrekeyStore,
+  crypto: CryptoProvider,
+  options: PrekeyRoutesOptions = {},
+): Hono {
   const app = new Hono();
 
+  // Rate limiters (one per route, per IP or per identity)
+  const rlStore = new MemoryRateLimitStore();
+  const registerRL = new RateLimiter(rlStore, REGISTER_LIMIT);
+  const fetchRL = new RateLimiter(rlStore, FETCH_LIMIT);
+  const replenishRL = new RateLimiter(rlStore, REPLENISH_LIMIT);
+  const deleteRL = new RateLimiter(rlStore, DELETE_LIMIT);
+  const rateLimitEnabled = !options.disableRateLimit;
+
+  // Helper: extract client IP from request headers
+  const getClientIp = (c: any): string => {
+    return (
+      c.req.header('x-forwarded-for')?.split(',')[0]?.trim() ??
+      c.req.header('x-real-ip') ??
+      'unknown'
+    );
+  };
+
+  // Global error handler — maps ShadeError to HTTP status
+  app.onError((err, c) => {
+    if (err instanceof ShadeError) {
+      const status = errorToHttpStatus(err);
+      const body: any = err.toJSON();
+      if ((err as any).retryAfterSeconds) {
+        c.header('Retry-After', String((err as any).retryAfterSeconds));
+      }
+      return c.json(body, status as any);
+    }
+    console.error('[Shade] Unhandled error:', err);
+    return c.json({ error: 'Internal server error' }, 500);
+  });
+
   // ─── Register ──────────────────────────────────────────────
   app.post('/v1/keys/register', async (c) => {
-    const body = await c.req.json();
+    if (rateLimitEnabled) await registerRL.consume(`register:${getClientIp(c)}`);
+
+    const rawBody = await c.req.text();
+    if (rawBody.length > MAX_BODY_SIZE) {
+      throw new ValidationError(`Request body too large (max ${MAX_BODY_SIZE} bytes)`);
+    }
+    const body = JSON.parse(rawBody);
     const { address, identitySigningKey, identityDHKey, signedPreKey, oneTimePreKeys } = body;
 
-    if (!address || !identitySigningKey || !identityDHKey || !signedPreKey) {
-      return c.json({ error: 'Missing required fields' }, 400);
+    const addr = validateAddress(address);
+    if (!identitySigningKey || !identityDHKey || !signedPreKey) {
+      throw new ValidationError('Missing required fields');
     }
 
-    // Decode base64 keys
     const signingKey = b64ToBytes(identitySigningKey);
     const dhKey = b64ToBytes(identityDHKey);
 
-    await store.saveIdentity(address, signingKey, dhKey);
+    // Verify signature against the identity's own signing key (TOFU)
+    await verifyPayload(crypto, signingKey, body);
+
+    await store.saveIdentity(addr, signingKey, dhKey);
     await store.saveSignedPreKey(
-      address,
+      addr,
       signedPreKey.keyId,
       b64ToBytes(signedPreKey.publicKey),
       b64ToBytes(signedPreKey.signature),
@@ -40,27 +98,27 @@ export function createPrekeyRoutes(store: PrekeyStore): Hono {
         keyId: k.keyId,
         publicKey: b64ToBytes(k.publicKey),
       }));
-      await store.saveOneTimePreKeys(address, keys);
+      await store.saveOneTimePreKeys(addr, keys);
     }
 
     return c.json({ ok: true });
   });
 
-  // ─── Fetch Bundle ──────────────────────────────────────────
+  // ─── Fetch Bundle (anonymous) ──────────────────────────────
   app.get('/v1/keys/bundle/:address', async (c) => {
-    const address = c.req.param('address');
+    if (rateLimitEnabled) await fetchRL.consume(`fetch:${getClientIp(c)}`);
+    const address = validateAddress(c.req.param('address'));
 
     const identity = await store.getIdentity(address);
     if (!identity) {
-      return c.json({ error: 'Address not found' }, 404);
+      return c.json({ error: 'Address not found', code: 'SHADE_NOT_FOUND' }, 404);
     }
 
     const signedPreKey = await store.getSignedPreKey(address);
     if (!signedPreKey) {
-      return c.json({ error: 'No signed prekey' }, 404);
+      return c.json({ error: 'No signed prekey', code: 'SHADE_NOT_FOUND' }, 404);
     }
 
-    // Consume one one-time prekey (if available)
     const oneTimePreKey = await store.consumeOneTimePreKey(address);
 
     const bundle: any = {
@@ -83,35 +141,59 @@ export function createPrekeyRoutes(store: PrekeyStore): Hono {
     return c.json(bundle);
   });
 
-  // ─── Replenish One-Time Prekeys ────────────────────────────
+  // ─── Replenish One-Time Prekeys (signed) ───────────────────
   app.post('/v1/keys/replenish', async (c) => {
-    const body = await c.req.json();
+    const rawBody = await c.req.text();
+    if (rawBody.length > MAX_BODY_SIZE) {
+      throw new ValidationError(`Request body too large (max ${MAX_BODY_SIZE} bytes)`);
+    }
+    const body = JSON.parse(rawBody);
     const { address, oneTimePreKeys } = body;
 
-    if (!address || !oneTimePreKeys || !Array.isArray(oneTimePreKeys)) {
-      return c.json({ error: 'Missing address or oneTimePreKeys' }, 400);
+    const addr = validateAddress(address);
+    if (rateLimitEnabled) await replenishRL.consume(`replenish:${addr}`);
+    if (!oneTimePreKeys || !Array.isArray(oneTimePreKeys)) {
+      throw new ValidationError('Missing oneTimePreKeys');
     }
 
+    // Look up the stored identity and verify the signature against it
+    const identity = await store.getIdentity(addr);
+    if (!identity) {
+      return c.json({ error: 'Address not registered', code: 'SHADE_NOT_FOUND' }, 404);
+    }
+    await verifyPayload(crypto, identity.identitySigningKey, body);
+
     const keys = oneTimePreKeys.map((k: any) => ({
       keyId: k.keyId,
       publicKey: b64ToBytes(k.publicKey),
     }));
-    await store.saveOneTimePreKeys(address, keys);
+    await store.saveOneTimePreKeys(addr, keys);
 
-    const count = await store.getOneTimePreKeyCount(address);
+    const count = await store.getOneTimePreKeyCount(addr);
     return c.json({ ok: true, remaining: count });
   });
 
-  // ─── Get Count ─────────────────────────────────────────────
+  // ─── Get Count (anonymous) ─────────────────────────────────
   app.get('/v1/keys/count/:address', async (c) => {
-    const address = c.req.param('address');
+    const address = validateAddress(c.req.param('address'));
     const count = await store.getOneTimePreKeyCount(address);
     return c.json({ count });
   });
 
-  // ─── Delete ────────────────────────────────────────────────
+  // ─── Delete (signed) ───────────────────────────────────────
   app.delete('/v1/keys/:address', async (c) => {
-    const address = c.req.param('address');
+    const address = validateAddress(c.req.param('address'));
+    if (rateLimitEnabled) await deleteRL.consume(`delete:${address}`);
+    const body = await c.req.json();
+
+    // Look up the stored identity and verify the signature
+    const identity = await store.getIdentity(address);
+    if (!identity) {
+      return c.json({ error: 'Address not registered', code: 'SHADE_NOT_FOUND' }, 404);
+    }
+    // Include address in the signed payload
+    await verifyPayload(crypto, identity.identitySigningKey, { ...body, address });
+
     await store.deleteAll(address);
     return c.json({ ok: true });
   });
diff --git a/packages/shade-server/src/standalone.ts b/packages/shade-server/src/standalone.ts
index 55ab23f..f153203 100644
--- a/packages/shade-server/src/standalone.ts
+++ b/packages/shade-server/src/standalone.ts
@@ -1,3 +1,4 @@
+import { SubtleCryptoProvider } from '@shade/crypto-web';
 import { createPrekeyRoutes } from './routes.js';
 import type { PrekeyStore } from './store.js';
 
@@ -13,8 +14,9 @@ async function createStore(): Promise<PrekeyStore> {
   return new MemoryPrekeyStore();
 }
 
+const crypto = new SubtleCryptoProvider();
 const store = await createStore();
-const server = createPrekeyRoutes(store);
+const server = createPrekeyRoutes(store, crypto);
 const port = Number(process.env.PORT ?? 3900);
 
 export default { port, fetch: server.fetch };
diff --git a/packages/shade-server/tests/rate-limit.test.ts b/packages/shade-server/tests/rate-limit.test.ts
new file mode 100644
index 0000000..873dc33
--- /dev/null
+++ b/packages/shade-server/tests/rate-limit.test.ts
@@ -0,0 +1,149 @@
+import { describe, test, expect } from 'bun:test';
+import { RateLimiter, MemoryRateLimitStore, createPrekeyServer, MemoryPrekeyStore, signPayload } from '../src/index.js';
+import { SubtleCryptoProvider } from '@shade/crypto-web';
+import { generateIdentityKeyPair, RateLimitError } from '@shade/core';
+
+const crypto = new SubtleCryptoProvider();
+
+describe('RateLimiter', () => {
+  test('allows requests up to capacity', async () => {
+    const store = new MemoryRateLimitStore();
+    const rl = new RateLimiter(store, { capacity: 5, refillPerSecond: 1 });
+
+    for (let i = 0; i < 5; i++) {
+      await rl.consume('user:1');
+    }
+  });
+
+  test('throws RateLimitError when exhausted', async () => {
+    const store = new MemoryRateLimitStore();
+    const rl = new RateLimiter(store, { capacity: 3, refillPerSecond: 0.1 });
+
+    for (let i = 0; i < 3; i++) await rl.consume('user:1');
+    expect(rl.consume('user:1')).rejects.toThrow(RateLimitError);
+  });
+
+  test('different keys have independent limits', async () => {
+    const store = new MemoryRateLimitStore();
+    const rl = new RateLimiter(store, { capacity: 2, refillPerSecond: 0.1 });
+
+    await rl.consume('user:1');
+    await rl.consume('user:1');
+    // user:1 exhausted
+    expect(rl.consume('user:1')).rejects.toThrow(RateLimitError);
+
+    // user:2 still has full capacity
+    await rl.consume('user:2');
+    await rl.consume('user:2');
+  });
+
+  test('refills over time', async () => {
+    const store = new MemoryRateLimitStore();
+    const rl = new RateLimiter(store, { capacity: 2, refillPerSecond: 100 }); // fast refill for test
+
+    await rl.consume('user:1');
+    await rl.consume('user:1');
+
+    // Wait a bit for refill (100 tokens/sec → 2 tokens in 20ms)
+    await new Promise((r) => setTimeout(r, 30));
+
+    // Should be refilled
+    await rl.consume('user:1');
+  });
+
+  test('RateLimitError has retryAfterSeconds', async () => {
+    const store = new MemoryRateLimitStore();
+    const rl = new RateLimiter(store, { capacity: 1, refillPerSecond: 0.5 });
+
+    await rl.consume('user:1');
+    try {
+      await rl.consume('user:1');
+      expect.unreachable();
+    } catch (err) {
+      expect(err).toBeInstanceOf(RateLimitError);
+      expect((err as RateLimitError).retryAfterSeconds).toBeGreaterThan(0);
+    }
+  });
+});
+
+describe('Rate limiting integration with routes', () => {
+  test('register endpoint rate-limits per IP', async () => {
+    const app = createPrekeyServer({ crypto, store: new MemoryPrekeyStore() });
+
+    async function doRegister(addressSuffix: number) {
+      const identity = await generateIdentityKeyPair(crypto);
+      const body: any = {
+        address: `user${addressSuffix}`,
+        identitySigningKey: Buffer.from(identity.signingPublicKey).toString('base64'),
+        identityDHKey: Buffer.from(identity.dhPublicKey).toString('base64'),
+        signedPreKey: {
+          keyId: 1,
+          publicKey: Buffer.from(crypto.randomBytes(32)).toString('base64'),
+          signature: Buffer.from(crypto.randomBytes(64)).toString('base64'),
+        },
+      };
+      const signed = await signPayload(crypto, identity.signingPrivateKey, body);
+      return app.request('/v1/keys/register', {
+        method: 'POST',
+        headers: { 'Content-Type': 'application/json', 'x-forwarded-for': '203.0.113.1' },
+        body: JSON.stringify(signed),
+      });
+    }
+
+    // Register limit is 5/hour, so after 5 successful, the 6th should fail
+    const results: number[] = [];
+    for (let i = 0; i < 7; i++) {
+      const res = await doRegister(i);
+      results.push(res.status);
+    }
+
+    // First 5 should succeed (200), rest should be rate-limited (429)
+    expect(results.filter((s) => s === 200).length).toBeGreaterThanOrEqual(5);
+    expect(results.filter((s) => s === 429).length).toBeGreaterThanOrEqual(1);
+  });
+
+  test('rate limit returns Retry-After header', async () => {
+    const app = createPrekeyServer({ crypto, store: new MemoryPrekeyStore() });
+
+    // Burn through the delete limit (5/hour)
+    const identity = await generateIdentityKeyPair(crypto);
+
+    // First register
+    const regBody: any = {
+      address: 'ratelimit',
+      identitySigningKey: Buffer.from(identity.signingPublicKey).toString('base64'),
+      identityDHKey: Buffer.from(identity.dhPublicKey).toString('base64'),
+      signedPreKey: {
+        keyId: 1,
+        publicKey: Buffer.from(crypto.randomBytes(32)).toString('base64'),
+        signature: Buffer.from(crypto.randomBytes(64)).toString('base64'),
+      },
+    };
+    const signedReg = await signPayload(crypto, identity.signingPrivateKey, regBody);
+    await app.request('/v1/keys/register', {
+      method: 'POST',
+      headers: { 'Content-Type': 'application/json', 'x-forwarded-for': '203.0.113.2' },
+      body: JSON.stringify(signedReg),
+    });
+
+    // Burn through the delete limit
+    for (let i = 0; i < 5; i++) {
+      const delBody = await signPayload(crypto, identity.signingPrivateKey, { address: 'ratelimit' });
+      await app.request('/v1/keys/ratelimit', {
+        method: 'DELETE',
+        headers: { 'Content-Type': 'application/json' },
+        body: JSON.stringify(delBody),
+      });
+    }
+
+    // 6th should be rate-limited
+    const delBody = await signPayload(crypto, identity.signingPrivateKey, { address: 'ratelimit' });
+    const res = await app.request('/v1/keys/ratelimit', {
+      method: 'DELETE',
+      headers: { 'Content-Type': 'application/json' },
+      body: JSON.stringify(delBody),
+    });
+    expect(res.status).toBe(429);
+    expect(res.headers.get('Retry-After')).toBeTruthy();
+  });
+});
diff --git a/packages/shade-server/tests/server.test.ts b/packages/shade-server/tests/server.test.ts
index 558ed9d..0ffdf0b 100644
--- a/packages/shade-server/tests/server.test.ts
+++ b/packages/shade-server/tests/server.test.ts
@@ -1,6 +1,10 @@
 import { describe, test, expect, beforeEach } from 'bun:test';
-import { createPrekeyServer, MemoryPrekeyStore } from '../src/index.js';
+import { createPrekeyServer, MemoryPrekeyStore, signPayload } from '../src/index.js';
 import type { PrekeyStore } from '../src/index.js';
+import { SubtleCryptoProvider } from '@shade/crypto-web';
+import { generateIdentityKeyPair } from '@shade/core';
+
+const crypto = new SubtleCryptoProvider();
 
 function b64(bytes: Uint8Array): string {
   return Buffer.from(bytes).toString('base64');
@@ -8,167 +12,164 @@ function b64(bytes: Uint8Array): string {
 
 function randBytes(n: number): Uint8Array {
   const buf = new Uint8Array(n);
-  crypto.getRandomValues(buf);
+  globalThis.crypto.getRandomValues(buf);
   return buf;
 }
 
+async function makeIdentity() {
+  return generateIdentityKeyPair(crypto);
+}
+
 describe('Shade Prekey Server', () => {
   let store: PrekeyStore;
   let app: ReturnType<typeof createPrekeyServer>;
 
   beforeEach(() => {
     store = new MemoryPrekeyStore();
-    app = createPrekeyServer({ store });
+    app = createPrekeyServer({ crypto, store, disableRateLimit: true });
   });
 
   function req(method: string, path: string, body?: any) {
     const init: RequestInit = { method, headers: { 'Content-Type': 'application/json' } };
-    if (body) init.body = JSON.stringify(body);
+    if (body !== undefined) init.body = JSON.stringify(body);
     return app.request(path, init);
   }
 
+  /** Helper: build a signed registration body for a given identity */
+  async function signedRegisterBody(identity: Awaited<ReturnType<typeof makeIdentity>>, address: string, withOTPKs = true) {
+    const body: any = {
+      address,
+      identitySigningKey: b64(identity.signingPublicKey),
+      identityDHKey: b64(identity.dhPublicKey),
+      signedPreKey: {
+        keyId: 1,
+        publicKey: b64(randBytes(32)),
+        signature: b64(randBytes(64)),
+      },
+    };
+    if (withOTPKs) {
+      body.oneTimePreKeys = [
+        { keyId: 100, publicKey: b64(randBytes(32)) },
+        { keyId: 101, publicKey: b64(randBytes(32)) },
+      ];
+    }
+    return signPayload(crypto, identity.signingPrivateKey, body);
+  }
+
   // ─── Registration ──────────────────────────────────────────
 
   describe('POST /v1/keys/register', () => {
-    test('registers identity and signed prekey', async () => {
-      const res = await req('POST', '/v1/keys/register', {
-        address: 'alice',
-        identitySigningKey: b64(randBytes(32)),
-        identityDHKey: b64(randBytes(32)),
-        signedPreKey: {
-          keyId: 1,
-          publicKey: b64(randBytes(32)),
-          signature: b64(randBytes(64)),
-        },
-      });
+    test('accepts valid signed registration', async () => {
+      const alice = await makeIdentity();
+      const body = await signedRegisterBody(alice, 'alice');
+      const res = await req('POST', '/v1/keys/register', body);
       expect(res.status).toBe(200);
-      expect(await res.json()).toEqual({ ok: true });
     });
 
-    test('registers with one-time prekeys', async () => {
+    test('rejects unsigned registration', async () => {
+      const alice = await makeIdentity();
       const res = await req('POST', '/v1/keys/register', {
         address: 'alice',
-        identitySigningKey: b64(randBytes(32)),
-        identityDHKey: b64(randBytes(32)),
-        signedPreKey: {
-          keyId: 1,
-          publicKey: b64(randBytes(32)),
-          signature: b64(randBytes(64)),
-        },
-        oneTimePreKeys: [
-          { keyId: 100, publicKey: b64(randBytes(32)) },
-          { keyId: 101, publicKey: b64(randBytes(32)) },
-          { keyId: 102, publicKey: b64(randBytes(32)) },
-        ],
+        identitySigningKey: b64(alice.signingPublicKey),
+        identityDHKey: b64(alice.dhPublicKey),
+        signedPreKey: { keyId: 1, publicKey: b64(randBytes(32)), signature: b64(randBytes(64)) },
       });
-      expect(res.status).toBe(200);
-
-      // Verify count
-      const countRes = await req('GET', '/v1/keys/count/alice');
-      expect((await countRes.json()).count).toBe(3);
-    });
-
-    test('rejects missing fields', async () => {
-      const res = await req('POST', '/v1/keys/register', { address: 'alice' });
+      // Missing signature/signedAt → validation error
       expect(res.status).toBe(400);
     });
+
+    test('rejects registration with wrong signing key', async () => {
+      const alice = await makeIdentity();
+      const bob = await makeIdentity();
+      // Sign with bob's key but claim alice's public key
+      const body: any = {
+        address: 'alice',
+        identitySigningKey: b64(alice.signingPublicKey), // mismatch
+        identityDHKey: b64(alice.dhPublicKey),
+        signedPreKey: { keyId: 1, publicKey: b64(randBytes(32)), signature: b64(randBytes(64)) },
+      };
+      const signed = await signPayload(crypto, bob.signingPrivateKey, body);
+      const res = await req('POST', '/v1/keys/register', signed);
+      expect(res.status).toBe(401);
+    });
+
+    test('rejects registration with stale signedAt', async () => {
+      const alice = await makeIdentity();
+      const body = await signedRegisterBody(alice, 'alice');
+      // Tamper with signedAt to be old
+      body.signedAt = Date.now() - 10 * 60 * 1000; // 10 minutes ago
+      const res = await req('POST', '/v1/keys/register', body);
+      expect(res.status).toBe(409); // ReplayError
+    });
+
+    test('rejects invalid address format', async () => {
+      const alice = await makeIdentity();
+      const body = await signedRegisterBody(alice, '../evil');
+      const res = await req('POST', '/v1/keys/register', body);
+      expect(res.status).toBe(400);
+    });
+
+    test('accepts registration with one-time prekeys', async () => {
+      const alice = await makeIdentity();
+      const body = await signedRegisterBody(alice, 'alice');
+      await req('POST', '/v1/keys/register', body);
+
+      const countRes = await req('GET', '/v1/keys/count/alice');
+      expect((await countRes.json()).count).toBe(2);
+    });
   });
 
-  // ─── Fetch Bundle ──────────────────────────────────────────
+  // ─── Fetch Bundle (anonymous) ──────────────────────────────
 
   describe('GET /v1/keys/bundle/:address', () => {
-    test('returns bundle with one-time prekey', async () => {
-      // Register first
-      const sigKey = b64(randBytes(32));
-      const dhKey = b64(randBytes(32));
-      const spkPub = b64(randBytes(32));
-      const spkSig = b64(randBytes(64));
-      const otpkPub = b64(randBytes(32));
-
-      await req('POST', '/v1/keys/register', {
-        address: 'bob',
-        identitySigningKey: sigKey,
-        identityDHKey: dhKey,
-        signedPreKey: { keyId: 1, publicKey: spkPub, signature: spkSig },
-        oneTimePreKeys: [{ keyId: 100, publicKey: otpkPub }],
-      });
+    test('returns bundle for registered address', async () => {
+      const bob = await makeIdentity();
+      const body = await signedRegisterBody(bob, 'bob');
+      await req('POST', '/v1/keys/register', body);
 
       const res = await req('GET', '/v1/keys/bundle/bob');
       expect(res.status).toBe(200);
 
       const bundle = await res.json();
-      expect(bundle.identitySigningKey).toBe(sigKey);
-      expect(bundle.identityDHKey).toBe(dhKey);
+      expect(bundle.identitySigningKey).toBe(b64(bob.signingPublicKey));
+      expect(bundle.identityDHKey).toBe(b64(bob.dhPublicKey));
       expect(bundle.signedPreKey.keyId).toBe(1);
-      expect(bundle.signedPreKey.publicKey).toBe(spkPub);
-      expect(bundle.signedPreKey.signature).toBe(spkSig);
       expect(bundle.oneTimePreKey.keyId).toBe(100);
-      expect(bundle.oneTimePreKey.publicKey).toBe(otpkPub);
     });
 
-    test('returns bundle without one-time prekey when depleted', async () => {
-      await req('POST', '/v1/keys/register', {
-        address: 'bob',
-        identitySigningKey: b64(randBytes(32)),
-        identityDHKey: b64(randBytes(32)),
-        signedPreKey: { keyId: 1, publicKey: b64(randBytes(32)), signature: b64(randBytes(64)) },
-      });
+    test('consumes one-time prekey on each fetch (FIFO)', async () => {
+      const bob = await makeIdentity();
+      await req('POST', '/v1/keys/register', await signedRegisterBody(bob, 'bob'));
 
-      const res = await req('GET', '/v1/keys/bundle/bob');
-      expect(res.status).toBe(200);
-
-      const bundle = await res.json();
-      expect(bundle.oneTimePreKey).toBeUndefined();
-    });
-
-    test('consumes one-time prekeys on each fetch', async () => {
-      await req('POST', '/v1/keys/register', {
-        address: 'bob',
-        identitySigningKey: b64(randBytes(32)),
-        identityDHKey: b64(randBytes(32)),
-        signedPreKey: { keyId: 1, publicKey: b64(randBytes(32)), signature: b64(randBytes(64)) },
-        oneTimePreKeys: [
-          { keyId: 100, publicKey: b64(randBytes(32)) },
-          { keyId: 101, publicKey: b64(randBytes(32)) },
-        ],
-      });
-
-      // First fetch consumes key 100
       const res1 = await req('GET', '/v1/keys/bundle/bob');
       expect((await res1.json()).oneTimePreKey.keyId).toBe(100);
 
-      // Second fetch consumes key 101
       const res2 = await req('GET', '/v1/keys/bundle/bob');
       expect((await res2.json()).oneTimePreKey.keyId).toBe(101);
 
-      // Third fetch has none left
       const res3 = await req('GET', '/v1/keys/bundle/bob');
       expect((await res3.json()).oneTimePreKey).toBeUndefined();
-
-      // Count should be 0
-      const countRes = await req('GET', '/v1/keys/count/bob');
-      expect((await countRes.json()).count).toBe(0);
     });
 
     test('404 for unknown address', async () => {
       const res = await req('GET', '/v1/keys/bundle/nobody');
       expect(res.status).toBe(404);
     });
+
+    test('rejects invalid address in URL', async () => {
+      const res = await req('GET', '/v1/keys/bundle/..evil');
+      expect(res.status).toBe(400);
+    });
   });
 
-  // ─── Replenish ─────────────────────────────────────────────
+  // ─── Replenish (signed) ────────────────────────────────────
 
   describe('POST /v1/keys/replenish', () => {
-    test('adds more one-time prekeys', async () => {
-      await req('POST', '/v1/keys/register', {
-        address: 'bob',
-        identitySigningKey: b64(randBytes(32)),
-        identityDHKey: b64(randBytes(32)),
-        signedPreKey: { keyId: 1, publicKey: b64(randBytes(32)), signature: b64(randBytes(64)) },
-        oneTimePreKeys: [{ keyId: 100, publicKey: b64(randBytes(32)) }],
-      });
+    test('accepts signed replenishment from registered identity', async () => {
+      const bob = await makeIdentity();
+      await req('POST', '/v1/keys/register', await signedRegisterBody(bob, 'bob'));
 
-      const res = await req('POST', '/v1/keys/replenish', {
+      const replenishBody = await signPayload(crypto, bob.signingPrivateKey, {
         address: 'bob',
         oneTimePreKeys: [
           { keyId: 200, publicKey: b64(randBytes(32)) },
@@ -176,52 +177,83 @@ describe('Shade Prekey Server', () => {
         ],
       });
 
+      const res = await req('POST', '/v1/keys/replenish', replenishBody);
       expect(res.status).toBe(200);
       const body = await res.json();
-      expect(body.remaining).toBe(3); // 1 original + 2 new
+      expect(body.remaining).toBe(4); // 2 original + 2 new
+    });
+
+    test('rejects replenishment signed by wrong identity', async () => {
+      const bob = await makeIdentity();
+      const eve = await makeIdentity();
+      await req('POST', '/v1/keys/register', await signedRegisterBody(bob, 'bob'));
+
+      const evilBody = await signPayload(crypto, eve.signingPrivateKey, {
+        address: 'bob',
+        oneTimePreKeys: [{ keyId: 200, publicKey: b64(randBytes(32)) }],
+      });
+
+      const res = await req('POST', '/v1/keys/replenish', evilBody);
+      expect(res.status).toBe(401);
+    });
+
+    test('rejects replenishment for unknown address', async () => {
+      const bob = await makeIdentity();
+      const body = await signPayload(crypto, bob.signingPrivateKey, {
+        address: 'nobody',
+        oneTimePreKeys: [{ keyId: 200, publicKey: b64(randBytes(32)) }],
+      });
+      const res = await req('POST', '/v1/keys/replenish', body);
+      expect(res.status).toBe(404);
     });
   });
 
-  // ─── Delete ────────────────────────────────────────────────
+  // ─── Delete (signed) ───────────────────────────────────────
 
   describe('DELETE /v1/keys/:address', () => {
-    test('removes all keys for an address', async () => {
-      await req('POST', '/v1/keys/register', {
-        address: 'bob',
-        identitySigningKey: b64(randBytes(32)),
-        identityDHKey: b64(randBytes(32)),
-        signedPreKey: { keyId: 1, publicKey: b64(randBytes(32)), signature: b64(randBytes(64)) },
-        oneTimePreKeys: [{ keyId: 100, publicKey: b64(randBytes(32)) }],
-      });
+    test('accepts signed delete from registered identity', async () => {
+      const bob = await makeIdentity();
+      await req('POST', '/v1/keys/register', await signedRegisterBody(bob, 'bob'));
 
-      const delRes = await req('DELETE', '/v1/keys/bob');
-      expect(delRes.status).toBe(200);
+      const delBody = await signPayload(crypto, bob.signingPrivateKey, { address: 'bob' });
+      const res = await req('DELETE', '/v1/keys/bob', delBody);
+      expect(res.status).toBe(200);
 
       // Should be gone
       const bundleRes = await req('GET', '/v1/keys/bundle/bob');
       expect(bundleRes.status).toBe(404);
+    });
 
-      const countRes = await req('GET', '/v1/keys/count/bob');
-      expect((await countRes.json()).count).toBe(0);
+    test('rejects delete signed by wrong identity', async () => {
+      const bob = await makeIdentity();
+      const eve = await makeIdentity();
+      await req('POST', '/v1/keys/register', await signedRegisterBody(bob, 'bob'));
+
+      const evilBody = await signPayload(crypto, eve.signingPrivateKey, { address: 'bob' });
+      const res = await req('DELETE', '/v1/keys/bob', evilBody);
+      expect(res.status).toBe(401);
+
+      // Should still exist
+      const bundleRes = await req('GET', '/v1/keys/bundle/bob');
+      expect(bundleRes.status).toBe(200);
     });
   });
 
-  // ─── Multiple Addresses ────────────────────────────────────
+  // ─── Multi-address isolation ───────────────────────────────
 
   describe('multi-address isolation', () => {
     test('different addresses are independent', async () => {
-      for (const addr of ['alice', 'bob', 'charlie']) {
-        await req('POST', '/v1/keys/register', {
-          address: addr,
-          identitySigningKey: b64(randBytes(32)),
-          identityDHKey: b64(randBytes(32)),
-          signedPreKey: { keyId: 1, publicKey: b64(randBytes(32)), signature: b64(randBytes(64)) },
-          oneTimePreKeys: [{ keyId: 1, publicKey: b64(randBytes(32)) }],
-        });
-      }
+      const alice = await makeIdentity();
+      const bob = await makeIdentity();
+      const charlie = await makeIdentity();
 
-      // Delete bob, others remain
-      await req('DELETE', '/v1/keys/bob');
+      await req('POST', '/v1/keys/register', await signedRegisterBody(alice, 'alice'));
+      await req('POST', '/v1/keys/register', await signedRegisterBody(bob, 'bob'));
+      await req('POST', '/v1/keys/register', await signedRegisterBody(charlie, 'charlie'));
+
+      // Delete bob with his own signature
+      const delBody = await signPayload(crypto, bob.signingPrivateKey, { address: 'bob' });
+      await req('DELETE', '/v1/keys/bob', delBody);
 
       expect((await req('GET', '/v1/keys/bundle/alice')).status).toBe(200);
       expect((await req('GET', '/v1/keys/bundle/bob')).status).toBe(404);
diff --git a/packages/shade-storage-sqlite/src/sqlite-storage.ts b/packages/shade-storage-sqlite/src/sqlite-storage.ts
index 2c4d4c0..e9e7f59 100644
--- a/packages/shade-storage-sqlite/src/sqlite-storage.ts
+++ b/packages/shade-storage-sqlite/src/sqlite-storage.ts
@@ -1,10 +1,12 @@
 import { Database } from 'bun:sqlite';
-import type { StorageProvider, IdentityKeyPair, SignedPreKey, OneTimePreKey, SessionState } from '@shade/core';
+import type { StorageProvider, IdentityKeyPair, SignedPreKey, OneTimePreKey, SessionState, RetiredIdentity } from '@shade/core';
 import {
   toBase64, fromBase64,
+  constantTimeEqual,
   serializeSessionState, deserializeSessionState,
   serializeSignedPreKey, deserializeSignedPreKey,
   serializeOneTimePreKey, deserializeOneTimePreKey,
+  serializeIdentityKeyPair, deserializeIdentityKeyPair,
 } from '@shade/core';
 
 /**
@@ -37,6 +39,9 @@ export class SQLiteStorage implements StorageProvider {
     removeSession: ReturnType<Database['prepare']>;
     getTrust: ReturnType<Database['prepare']>;
     saveTrust: ReturnType<Database['prepare']>;
+    addRetired: ReturnType<Database['prepare']>;
+    listRetired: ReturnType<Database['prepare']>;
+    pruneRetired: ReturnType<Database['prepare']>;
   };
 
   constructor(dbPath?: string) {
@@ -76,6 +81,12 @@ export class SQLiteStorage implements StorageProvider {
         address TEXT PRIMARY KEY,
         identity_key TEXT NOT NULL
       );
+      CREATE TABLE IF NOT EXISTS retired_identities (
+        id INTEGER PRIMARY KEY AUTOINCREMENT,
+        data_json TEXT NOT NULL,
+        retired_at INTEGER NOT NULL
+      );
+      CREATE INDEX IF NOT EXISTS idx_retired_at ON retired_identities(retired_at);
     `);
   }
 
@@ -97,6 +108,9 @@ export class SQLiteStorage implements StorageProvider {
       removeSession: this.db.prepare('DELETE FROM sessions WHERE address = ?'),
       getTrust: this.db.prepare('SELECT identity_key FROM trusted_identities WHERE address = ?'),
       saveTrust: this.db.prepare('INSERT OR REPLACE INTO trusted_identities (address, identity_key) VALUES (?, ?)'),
+      addRetired: this.db.prepare('INSERT INTO retired_identities (data_json, retired_at) VALUES (?, ?)'),
+      listRetired: this.db.prepare('SELECT data_json, retired_at FROM retired_identities ORDER BY retired_at DESC'),
+      pruneRetired: this.db.prepare('DELETE FROM retired_identities WHERE retired_at < ?'),
     };
   }
 
@@ -193,10 +207,32 @@ export class SQLiteStorage implements StorageProvider {
   async isTrustedIdentity(address: string, identityKey: Uint8Array): Promise<boolean> {
     const row = this.stmts.getTrust.get(address) as any;
     if (!row) return true; // TOFU
-    return row.identity_key === toBase64(identityKey);
+    const storedBytes = fromBase64(row.identity_key);
+    return constantTimeEqual(storedBytes, identityKey);
   }
 
   async saveTrustedIdentity(address: string, identityKey: Uint8Array): Promise<void> {
     this.stmts.saveTrust.run(address, toBase64(identityKey));
   }
+
+  // ─── Identity History ─────────────────────────────────────
+
+  async addRetiredIdentity(identity: RetiredIdentity): Promise<void> {
+    this.stmts.addRetired.run(
+      serializeIdentityKeyPair(identity.keyPair),
+      identity.retiredAt,
+    );
+  }
+
+  async getRetiredIdentities(): Promise<RetiredIdentity[]> {
+    const rows = this.stmts.listRetired.all() as any[];
+    return rows.map((r) => ({
+      keyPair: deserializeIdentityKeyPair(r.data_json),
+      retiredAt: r.retired_at,
+    }));
+  }
+
+  async pruneRetiredIdentities(olderThan: number): Promise<void> {
+    this.stmts.pruneRetired.run(olderThan);
+  }
 }
diff --git a/packages/shade-transport/src/fetch-transport.ts b/packages/shade-transport/src/fetch-transport.ts
index 74753b5..00a5691 100644
--- a/packages/shade-transport/src/fetch-transport.ts
+++ b/packages/shade-transport/src/fetch-transport.ts
@@ -1,25 +1,55 @@
-import type { PreKeyBundle, OneTimePreKey } from '@shade/core';
+import type { PreKeyBundle, OneTimePreKey, CryptoProvider } from '@shade/core';
+import { fromBase64, NetworkError } from '@shade/core';
 
 /**
  * HTTP transport client for the Shade Prekey Server.
  *
+ * Signing: write operations (register, replenish, delete) are signed with
+ * the caller's Ed25519 identity signing key. The caller must provide a
+ * signing function via the constructor.
+ *
  * Usage:
  * ```ts
- * const transport = new ShadeFetchTransport('https://shade.example.com');
- * await transport.register('alice', bundle, oneTimePreKeys);
- * const bundle = await transport.fetchBundle('bob');
+ * const transport = new ShadeFetchTransport({
+ *   baseUrl: 'https://shade.example.com',
+ *   crypto,
+ *   signingKey: identity.signingPrivateKey,
+ * });
+ * await transport.register('alice', identity, signedPreKey, oneTimePreKeys);
+ * const bundle = await transport.fetchBundle('bob'); // anonymous
  * ```
  */
 export class ShadeFetchTransport {
-  constructor(
-    private readonly baseUrl: string,
-    private readonly authToken?: string,
-  ) {}
+  private readonly baseUrl: string;
+  private readonly crypto: CryptoProvider;
+  private readonly signingPrivateKey?: Uint8Array;
+
+  constructor(options: { baseUrl: string; crypto: CryptoProvider; signingPrivateKey?: Uint8Array }) {
+    this.baseUrl = options.baseUrl;
+    this.crypto = options.crypto;
+    this.signingPrivateKey = options.signingPrivateKey;
+  }
 
   private headers(): Record<string, string> {
-    const h: Record<string, string> = { 'Content-Type': 'application/json' };
-    if (this.authToken) h['Authorization'] = `Bearer ${this.authToken}`;
-    return h;
+    return { 'Content-Type': 'application/json' };
+  }
+
+  /** Sign a payload using the configured signing key */
+  private async sign<T extends Record<string, unknown>>(payload: T): Promise<T & { signedAt: number; signature: string }> {
+    if (!this.signingPrivateKey) {
+      throw new Error('ShadeFetchTransport: signingPrivateKey is required for write operations');
+    }
+    const signedAt = Date.now();
+    const withTs = { ...payload, signedAt, signature: '' };
+    // Canonicalize: sort keys, omit signature
+    const { signature, ...rest } = withTs;
+    const sorted = Object.keys(rest).sort().reduce<Record<string, unknown>>((acc, k) => {
+      acc[k] = (rest as Record<string, unknown>)[k];
+      return acc;
+    }, {});
+    const bytes = new TextEncoder().encode(JSON.stringify(sorted));
+    const sig = await this.crypto.sign(this.signingPrivateKey, bytes);
+    return { ...payload, signedAt, signature: Buffer.from(sig).toString('base64') };
   }
 
   /** Register identity and upload prekey bundle + one-time prekeys */
@@ -47,20 +77,22 @@ export class ShadeFetchTransport {
       }));
     }
 
+    const signed = await this.sign(body);
+
     const res = await fetch(`${this.baseUrl}/v1/keys/register`, {
       method: 'POST',
       headers: this.headers(),
-      body: JSON.stringify(body),
+      body: JSON.stringify(signed),
     });
-    if (!res.ok) throw new Error(`Register failed: ${res.status}`);
+    if (!res.ok) throw new NetworkError(`Register failed: ${res.status}`, res.status);
   }
 
-  /** Fetch a prekey bundle for a peer (consumes one one-time prekey) */
+  /** Fetch a prekey bundle for a peer (anonymous, consumes one one-time prekey) */
   async fetchBundle(address: string): Promise<PreKeyBundle> {
     const res = await fetch(`${this.baseUrl}/v1/keys/bundle/${encodeURIComponent(address)}`, {
       headers: this.headers(),
     });
-    if (!res.ok) throw new Error(`Fetch bundle failed: ${res.status}`);
+    if (!res.ok) throw new NetworkError(`Fetch bundle failed: ${res.status}`, res.status);
 
     const data = await res.json();
     return {
@@ -81,36 +113,50 @@ export class ShadeFetchTransport {
     };
   }
 
-  /** Upload additional one-time prekeys */
+  /** Upload additional one-time prekeys (signed) */
   async replenish(
     address: string,
     keys: Array<{ keyId: number; publicKey: Uint8Array }>,
   ): Promise<number> {
+    const body = {
+      address,
+      oneTimePreKeys: keys.map((k) => ({
+        keyId: k.keyId,
+        publicKey: toB64(k.publicKey),
+      })),
+    };
+    const signed = await this.sign(body);
+
     const res = await fetch(`${this.baseUrl}/v1/keys/replenish`, {
       method: 'POST',
       headers: this.headers(),
-      body: JSON.stringify({
-        address,
-        oneTimePreKeys: keys.map((k) => ({
-          keyId: k.keyId,
-          publicKey: toB64(k.publicKey),
-        })),
-      }),
+      body: JSON.stringify(signed),
     });
-    if (!res.ok) throw new Error(`Replenish failed: ${res.status}`);
+    if (!res.ok) throw new NetworkError(`Replenish failed: ${res.status}`, res.status);
     const data = await res.json();
     return data.remaining;
   }
 
-  /** Get remaining one-time prekey count */
+  /** Get remaining one-time prekey count (anonymous) */
   async getKeyCount(address: string): Promise<number> {
     const res = await fetch(`${this.baseUrl}/v1/keys/count/${encodeURIComponent(address)}`, {
       headers: this.headers(),
     });
-    if (!res.ok) throw new Error(`Count failed: ${res.status}`);
+    if (!res.ok) throw new NetworkError(`Count failed: ${res.status}`, res.status);
     const data = await res.json();
     return data.count;
   }
+
+  /** Delete all keys for this identity (signed) */
+  async unregister(address: string): Promise<void> {
+    const signed = await this.sign({ address });
+    const res = await fetch(`${this.baseUrl}/v1/keys/${encodeURIComponent(address)}`, {
+      method: 'DELETE',
+      headers: this.headers(),
+      body: JSON.stringify(signed),
+    });
+    if (!res.ok) throw new NetworkError(`Unregister failed: ${res.status}`, res.status);
+  }
 }
 
 function toB64(bytes: Uint8Array): string {
diff --git a/packages/shade-transport/tests/transport.test.ts b/packages/shade-transport/tests/transport.test.ts
index 770a10f..1722358 100644
--- a/packages/shade-transport/tests/transport.test.ts
+++ b/packages/shade-transport/tests/transport.test.ts
@@ -8,55 +8,55 @@ const crypto = new SubtleCryptoProvider();
 
 describe('ShadeFetchTransport', () => {
   test('full flow: register → fetch bundle → establish session → talk', async () => {
-    // Start in-process prekey server
     const store = new MemoryPrekeyStore();
-    const server = createPrekeyServer({ store });
+    const server = createPrekeyServer({ crypto, store, disableRateLimit: true });
 
-    // We'll use Hono's request() method directly instead of actual HTTP
-    // But ShadeFetchTransport uses fetch(), so let's start a real server
     const port = 19000 + Math.floor(Math.random() * 1000);
     const handle = Bun.serve({ port, fetch: server.fetch });
 
     try {
       const baseUrl = `http://localhost:${port}`;
-      const transport = new ShadeFetchTransport(baseUrl);
 
-      // ─── Bob: register with prekey server ────────────────
+      // ─── Bob: set up session manager, register with transport ──
       const bobStorage = new MemoryStorage();
       const bobManager = new ShadeSessionManager(crypto, bobStorage);
       await bobManager.initialize();
 
+      const bobIdentity = await bobStorage.getIdentityKeyPair();
+      const bobTransport = new ShadeFetchTransport({
+        baseUrl,
+        crypto,
+        signingPrivateKey: bobIdentity!.signingPrivateKey,
+      });
+
       const bobOTPKs = await bobManager.generateOneTimePreKeys(5);
       const bobBundle = await bobManager.createPreKeyBundle();
 
-      await transport.register(
+      await bobTransport.register(
         'bob',
         bobManager.getPublicIdentity(),
         bobBundle.signedPreKey,
         bobOTPKs,
       );
 
-      // Verify count
-      const count = await transport.getKeyCount('bob');
-      expect(count).toBe(5);
+      expect(await bobTransport.getKeyCount('bob')).toBe(5);
 
-      // ─── Alice: fetch bundle and establish session ───────
+      // ─── Alice: anonymous fetch + establish session ───────
       const aliceStorage = new MemoryStorage();
       const aliceManager = new ShadeSessionManager(crypto, aliceStorage);
       await aliceManager.initialize();
 
-      const fetchedBundle = await transport.fetchBundle('bob');
+      // Alice doesn't need a signing key to fetch bundles
+      const aliceTransport = new ShadeFetchTransport({ baseUrl, crypto });
+
+      const fetchedBundle = await aliceTransport.fetchBundle('bob');
       expect(fetchedBundle.identityDHKey).toEqual(bobManager.getPublicIdentity().dhKey);
-      expect(fetchedBundle.signedPreKey.keyId).toBe(bobBundle.signedPreKey.keyId);
 
-      // One OTP key consumed
-      const countAfter = await transport.getKeyCount('bob');
-      expect(countAfter).toBe(4);
+      expect(await aliceTransport.getKeyCount('bob')).toBe(4);
 
-      // Alice establishes session
       await aliceManager.initSessionFromBundle('bob', fetchedBundle);
 
-      // ─── Alice → Bob encrypted message ───────────────────
+      // ─── Alice → Bob encrypted ───────────────────────────
       const env1 = await aliceManager.encrypt('bob', 'Hello via transport!');
       const plain1 = await bobManager.decrypt('alice', env1);
       expect(plain1).toBe('Hello via transport!');
@@ -66,12 +66,16 @@ describe('ShadeFetchTransport', () => {
       const plain2 = await aliceManager.decrypt('bob', env2);
       expect(plain2).toBe('Got it!');
 
-      // ─── Replenish ───────────────────────────────────────
-      const remaining = await transport.replenish('bob', [
+      // ─── Replenish (signed) ──────────────────────────────
+      const remaining = await bobTransport.replenish('bob', [
         { keyId: 200, publicKey: crypto.randomBytes(32) },
         { keyId: 201, publicKey: crypto.randomBytes(32) },
       ]);
-      expect(remaining).toBe(6); // 4 remaining + 2 new
+      expect(remaining).toBe(6);
+
+      // ─── Unregister (signed) ─────────────────────────────
+      await bobTransport.unregister('bob');
+      await expect(aliceTransport.fetchBundle('bob')).rejects.toThrow();
 
     } finally {
       handle.stop();