46 lines
1.9 KiB
TypeScript
46 lines
1.9 KiB
TypeScript
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/**
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* Encoding helpers shared by the setup, request, and guardian modules.
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* Kept as a tiny standalone module so individual flows don't carry
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* private base64 helpers; consistent encoding across send/receive
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* sides.
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*/
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/** Base64url (no padding) — used for both `recoveryKey → passphrase` and arbitrary share bytes. */
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export function bytesToBase64Url(bytes: Uint8Array): string {
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let bin = '';
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for (let i = 0; i < bytes.length; i++) bin += String.fromCharCode(bytes[i]!);
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return btoa(bin).replace(/\+/g, '-').replace(/\//g, '_').replace(/=+$/, '');
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}
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export function base64UrlToBytes(s: string): Uint8Array {
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const padded = s.replace(/-/g, '+').replace(/_/g, '/');
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const padding = padded.length % 4 === 0 ? 0 : 4 - (padded.length % 4);
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const bin = atob(padded + '='.repeat(padding));
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const out = new Uint8Array(bin.length);
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for (let i = 0; i < bin.length; i++) out[i] = bin.charCodeAt(i);
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return out;
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}
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/**
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* Convert a `recoveryKey` (32 random bytes) to the passphrase that
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* `Shade.exportBackup` / `Shade.importBackup` expect. We use base64url
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* because:
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* - it's a string, satisfying the export/import API,
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* - 32 bytes encodes to 43 characters, comfortably above the 12-char
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* minimum the exportBackup helper enforces,
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* - the encoding is deterministic so split + reconstruct + decode
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* yields the identical passphrase the original device used.
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*
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* The HKDF inside `exportBackup` is a deterministic KDF that's
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* cryptographically appropriate for a 32-byte uniformly-random IKM
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* (this is exactly the standard HKDF use case). The fact that the
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* passphrase API was designed for human-typed passwords does not
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* weaken the construction here.
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*/
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export function recoveryKeyToBackupPassphrase(key: Uint8Array): string {
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if (key.length !== 32) {
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throw new Error(`recoveryKey must be 32 bytes (got ${key.length})`);
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}
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return `shade-rk:${bytesToBase64Url(key)}`;
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}
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