fix(sync): secure encrypted snapshot lifecycle

cloudflare/src/sync_vault_bootstrap_proof.ts

@@ -0,0 +1,75 @@
+import type { Env } from "./bindings.js";
+import { verifyEd25519Signature } from "./device_crypto.js";
+import type { WrappedAccountKeyDocument } from "./sync_vault.js";
+
+const BOOTSTRAP_DOMAIN = "elydora-sync-vault-bootstrap-v2";
+const PUBLIC_KEY_PATTERN = /^[a-f0-9]{64}$/;
+
+const APPROVED_V2_SIGNING_KEY_QUERY = `
+  SELECT keys.signing_public_key
+  FROM user_devices AS device
+  INNER JOIN user_device_keys AS keys
+    ON keys.user_id = device.user_id AND keys.device_id = device.device_id
+  WHERE device.user_id = ? AND device.device_id = ?
+    AND device.approval_status = 'approved' AND device.revoked_at IS NULL
+    AND keys.key_protocol_version = 2 AND keys.signing_public_key IS NOT NULL
+`;
+
+export interface SyncVaultBootstrapProofInput {
+  keyId: string;
+  generation: number;
+  envelope: WrappedAccountKeyDocument;
+  idempotencyKey: string;
+}
+
+interface SigningKeyRow {
+  signing_public_key: unknown;
+}
+
+export async function syncVaultBootstrapProofValid(
+  env: Env,
+  userId: string,
+  deviceId: string,
+  bootstrap: SyncVaultBootstrapProofInput,
+  proof: string,
+): Promise<boolean> {
+  const row = await env.ELY_DB.prepare(APPROVED_V2_SIGNING_KEY_QUERY)
+    .bind(userId, deviceId)
+    .first<SigningKeyRow>();
+  if (
+    row === null ||
+    typeof row.signing_public_key !== "string" ||
+    !PUBLIC_KEY_PATTERN.test(row.signing_public_key)
+  ) {
+    return false;
+  }
+  return verifyEd25519Signature(
+    row.signing_public_key,
+    proof,
+    syncVaultBootstrapProofBytes(userId, deviceId, bootstrap),
+  );
+}
+
+export function syncVaultBootstrapProofBytes(
+  userId: string,
+  deviceId: string,
+  bootstrap: SyncVaultBootstrapProofInput,
+): Uint8Array {
+  const values: (number | string)[] = [
+    BOOTSTRAP_DOMAIN,
+    userId,
+    deviceId,
+    bootstrap.keyId,
+    bootstrap.generation,
+    bootstrap.envelope.version,
+    bootstrap.envelope.suite,
+    bootstrap.envelope.encapped_key,
+    bootstrap.envelope.ciphertext,
+    bootstrap.idempotencyKey,
+  ];
+  const encoder = new TextEncoder();
+  return encoder.encode(values.map((value) => {
+    const text = value.toString();
+    return `${encoder.encode(text).byteLength}:${text}`;
+  }).join(""));
+}