Move utils to root

frontend/src/utils/crypto/backup.ts

@@ -0,0 +1,68 @@
+import { aesGcmDecrypt, aesGcmEncrypt } from "./symmetric";
+import { importPassword, deriveKEK, randomBytes } from "./kdf";
+
+export interface PrivateKeyBundle {
+	version: 1;
+	privateKey: Uint8Array; // X25519 private key
+}
+
+export interface EncryptedBackupBlob {
+	salt: Uint8Array; // for PBKDF2 derivation of KEK
+	iv: Uint8Array; // AES-GCM IV
+	ciphertext: Uint8Array; // encrypted serialized PrivateKeyBundle
+}
+
+export function serializeBundle(bundle: PrivateKeyBundle): Uint8Array {
+	const header = new Uint8Array([bundle.version]);
+	const len = new Uint8Array(new Uint32Array([bundle.privateKey.length]).buffer);
+	const out = new Uint8Array(1 + 4 + bundle.privateKey.length);
+	out.set(header, 0);
+	out.set(len, 1);
+	out.set(bundle.privateKey, 5);
+	return out;
+}
+
+export function deserializeBundle(data: Uint8Array): PrivateKeyBundle {
+	const version = data[0] as 1;
+	const len = new Uint32Array(data.slice(1, 5).buffer)[0];
+	const pk = data.slice(5, 5 + len);
+	return { version, privateKey: pk };
+}
+
+export async function encryptBackupWithPassword(password: string, bundle: PrivateKeyBundle): Promise<EncryptedBackupBlob> {
+	const salt = randomBytes(16);
+	const pw = await importPassword(password);
+	const kek = await deriveKEK(pw, salt);
+	const serialized = serializeBundle(bundle);
+	const { iv, ciphertext } = await aesGcmEncrypt(kek, serialized);
+	return { salt, iv, ciphertext };
+}
+
+export async function decryptBackupWithPassword(password: string, blob: EncryptedBackupBlob): Promise<PrivateKeyBundle> {
+	const pw = await importPassword(password);
+	const kek = await deriveKEK(pw, blob.salt);
+	const plaintext = await aesGcmDecrypt(kek, blob.iv, blob.ciphertext);
+	return deserializeBundle(plaintext);
+}
+
+export function encodeBlob(blob: EncryptedBackupBlob): string {
+	function b64(a: Uint8Array) { return btoa(String.fromCharCode(...a)); }
+	return JSON.stringify({
+		salt: b64(blob.salt),
+		iv: b64(blob.iv),
+		ciphertext: b64(blob.ciphertext)
+	});
+}
+
+export function decodeBlob(json: string): EncryptedBackupBlob {
+	function ub64(s: string) {
+		const bin = atob(s);
+		const arr = new Uint8Array(bin.length);
+		for (let i = 0; i < bin.length; i++) arr[i] = bin.charCodeAt(i);
+		return arr;
+	}
+	const obj = JSON.parse(json);
+	return { salt: ub64(obj.salt), iv: ub64(obj.iv), ciphertext: ub64(obj.ciphertext) };
+}
+
+