feat(crypto): sender-key per-conversation multi-device E2EE

2026-04-19 19:27:24 +02:00
parent e57f81c9c3
commit 75618637e2
11 changed files with 703 additions and 142 deletions
@@ -0,0 +1,277 @@
+import {
+  decryptWithConvKey,
+  encryptWithConvKey,
+  generateConvKey,
+  unwrapConvKey,
+  wrapConvKeyForRecipient,
+} from '../crypto/sessionKeys.js';
+import { bytesToPgHex, pgHexToBytes } from '../supabase/bytea.js';
+import type { AppSupabaseClient } from '../supabase/client.js';
+
+// db-types in this monorepo is a static snapshot generated against the older
+// schema. The new `conversation_keys` table + `active_key_version` column on
+// `conversations` aren't in there yet. Until the codegen catches up we bypass
+// the typed builder for those calls.
+function rawFrom(client: AppSupabaseClient, table: string) {
+  // eslint-disable-next-line @typescript-eslint/no-explicit-any
+  return (client as unknown as { from: (t: string) => any }).from(table);
+}
+
+// Per-conversation symmetric key management. Replaces per-device envelopes
+// with a single conv-key (32-byte XSalsa20-Poly1305) wrapped to each device's
+// X25519 pubkey via crypto_box.
+
+interface DeviceKey {
+  deviceId: string;
+  userId: string;
+  publicKey: Uint8Array;
+}
+
+export interface OwnDeviceCtx {
+  userId: string;
+  deviceId: string;
+  privateKey: Uint8Array;
+}
+
+export interface ConvKeyHandle {
+  conversationId: string;
+  keyVersion: number;
+  key: Uint8Array;
+}
+
+// In-process cache to avoid re-fetching + re-unwrapping every send/decrypt.
+const cache = new Map<string, ConvKeyHandle>();
+const cacheKey = (convId: string, version: number) => convId + '@' + version;
+
+export function clearConvKeyCache(): void {
+  cache.clear();
+}
+
+async function listDeviceKeys(
+  client: AppSupabaseClient,
+  conversationId: string,
+): Promise<DeviceKey[]> {
+  const { data: members, error: mErr } = await client
+    .from('conversation_members')
+    .select('user_id, accepted')
+    .eq('conversation_id', conversationId);
+  if (mErr) throw mErr;
+  const memberIds = (members ?? []).filter((m) => m.accepted).map((m) => m.user_id);
+  if (memberIds.length === 0) return [];
+
+  const { data: devices, error: dErr } = await client
+    .from('devices')
+    .select('id, user_id, public_key')
+    .in('user_id', memberIds);
+  if (dErr) throw dErr;
+
+  return (devices ?? []).map((d) => ({
+    deviceId: d.id,
+    userId: d.user_id,
+    publicKey: pgHexToBytes(d.public_key),
+  }));
+}
+
+async function fetchActiveKeyVersion(
+  client: AppSupabaseClient,
+  conversationId: string,
+): Promise<number> {
+  const { data, error } = await rawFrom(client, 'conversations')
+    .select('active_key_version')
+    .eq('id', conversationId)
+    .single();
+  if (error) throw error;
+  return (data as { active_key_version: number }).active_key_version;
+}
+
+interface SenderInfo {
+  senderDeviceId: string;
+  senderPublicKey: Uint8Array;
+}
+
+async function fetchKeyBundle(
+  client: AppSupabaseClient,
+  conversationId: string,
+  ownDeviceId: string,
+  keyVersion: number,
+): Promise<{ encryptedKey: Uint8Array; nonce: Uint8Array; sender: SenderInfo } | null> {
+  const { data, error } = await rawFrom(client, 'conversation_keys')
+    .select('encrypted_key, nonce, sender_device_id')
+    .eq('conversation_id', conversationId)
+    .eq('recipient_device_id', ownDeviceId)
+    .eq('key_version', keyVersion)
+    .maybeSingle();
+  if (error) throw error;
+  if (!data) return null;
+
+  const row = data as {
+    encrypted_key: string;
+    nonce: string;
+    sender_device_id: string;
+  };
+  const { data: dev, error: dErr } = await client
+    .from('devices')
+    .select('id, public_key')
+    .eq('id', row.sender_device_id)
+    .single();
+  if (dErr) throw dErr;
+
+  return {
+    encryptedKey: pgHexToBytes(row.encrypted_key),
+    nonce: pgHexToBytes(row.nonce),
+    sender: {
+      senderDeviceId: dev.id,
+      senderPublicKey: pgHexToBytes(dev.public_key),
+    },
+  };
+}
+
+// Bootstraps a brand-new conv-key, wrapping it for every member device that
+// currently exists (including the caller's own devices). Used the first time
+// a conversation needs a key, or when rotation is requested.
+export async function bootstrapConvKey(
+  client: AppSupabaseClient,
+  conversationId: string,
+  own: OwnDeviceCtx,
+  keyVersion: number,
+): Promise<ConvKeyHandle> {
+  const convKey = generateConvKey();
+  const recipients = await listDeviceKeys(client, conversationId);
+  if (recipients.length === 0) {
+    throw new Error('cannot bootstrap conv key — no recipient devices');
+  }
+
+  const rows: Array<{
+    conversation_id: string;
+    recipient_device_id: string;
+    key_version: number;
+    sender_device_id: string;
+    encrypted_key: string;
+    nonce: string;
+  }> = [];
+  for (const r of recipients) {
+    const wrapped = await wrapConvKeyForRecipient(convKey, r.publicKey, own.privateKey);
+    rows.push({
+      conversation_id: conversationId,
+      recipient_device_id: r.deviceId,
+      key_version: keyVersion,
+      sender_device_id: own.deviceId,
+      encrypted_key: bytesToPgHex(wrapped.ciphertext),
+      nonce: bytesToPgHex(wrapped.nonce),
+    });
+  }
+
+  const { error } = await rawFrom(client, 'conversation_keys').insert(rows);
+  if (error) throw error;
+
+  const handle = { conversationId, keyVersion, key: convKey };
+  cache.set(cacheKey(conversationId, keyVersion), handle);
+  return handle;
+}
+
+// Resolves the current conv-key for `conversationId`. Order:
+//   1) cache hit
+//   2) DB row for own device → unwrap
+//   3) bootstrap a brand-new key (only valid path if NO existing keys exist
+//      for any device — i.e. this is the conversation's very first message)
+export async function getOrCreateConvKey(
+  client: AppSupabaseClient,
+  conversationId: string,
+  own: OwnDeviceCtx,
+): Promise<ConvKeyHandle> {
+  const version = await fetchActiveKeyVersion(client, conversationId);
+  const cached = cache.get(cacheKey(conversationId, version));
+  if (cached) return cached;
+
+  const bundle = await fetchKeyBundle(client, conversationId, own.deviceId, version);
+  if (bundle) {
+    const key = await unwrapConvKey(
+      bundle.encryptedKey,
+      bundle.nonce,
+      bundle.sender.senderPublicKey,
+      own.privateKey,
+    );
+    const handle = { conversationId, keyVersion: version, key };
+    cache.set(cacheKey(conversationId, version), handle);
+    return handle;
+  }
+
+  // No bundle yet for THIS device. Two cases:
+  //   - I'm the first ever sender → bootstrap.
+  //   - Conversation already has keys but my device wasn't included yet → I
+  //     have to wait until an existing device wraps the key for me.
+  const { count, error: cntErr } = await rawFrom(client, 'conversation_keys')
+    .select('recipient_device_id', { count: 'exact', head: true })
+    .eq('conversation_id', conversationId)
+    .eq('key_version', version);
+  if (cntErr) throw cntErr;
+
+  if ((count ?? 0) > 0) {
+    throw new Error(
+      'Awaiting conversation key — another device must share it with this device.',
+    );
+  }
+  return bootstrapConvKey(client, conversationId, own, version);
+}
+
+// Read-only variant: never bootstraps. Returns null if no key bundle exists
+// for this device yet.
+export async function tryGetConvKey(
+  client: AppSupabaseClient,
+  conversationId: string,
+  ownDeviceId: string,
+  ownPrivateKey: Uint8Array,
+  keyVersion: number,
+): Promise<ConvKeyHandle | null> {
+  const cached = cache.get(cacheKey(conversationId, keyVersion));
+  if (cached) return cached;
+
+  const bundle = await fetchKeyBundle(client, conversationId, ownDeviceId, keyVersion);
+  if (!bundle) return null;
+  const key = await unwrapConvKey(
+    bundle.encryptedKey,
+    bundle.nonce,
+    bundle.sender.senderPublicKey,
+    ownPrivateKey,
+  );
+  const handle = { conversationId, keyVersion, key };
+  cache.set(cacheKey(conversationId, keyVersion), handle);
+  return handle;
+}
+
+// Wraps the active conv-key for a single new device (e.g. when a peer
+// registers a new device). The caller's device must have an unwrapped copy
+// of the conv-key in cache (or be able to fetch it).
+export async function shareConvKeyToDevice(
+  client: AppSupabaseClient,
+  conversationId: string,
+  recipientDeviceId: string,
+  recipientPublicKey: Uint8Array,
+  own: OwnDeviceCtx,
+): Promise<void> {
+  const version = await fetchActiveKeyVersion(client, conversationId);
+  const handle =
+    cache.get(cacheKey(conversationId, version)) ??
+    (await tryGetConvKey(client, conversationId, own.deviceId, own.privateKey, version));
+  if (!handle) {
+    throw new Error('cannot share conv key — own device does not have it yet');
+  }
+
+  const wrapped = await wrapConvKeyForRecipient(
+    handle.key,
+    recipientPublicKey,
+    own.privateKey,
+  );
+  const { error } = await rawFrom(client, 'conversation_keys').insert({
+    conversation_id: conversationId,
+    recipient_device_id: recipientDeviceId,
+    key_version: version,
+    sender_device_id: own.deviceId,
+    encrypted_key: bytesToPgHex(wrapped.ciphertext),
+    nonce: bytesToPgHex(wrapped.nonce),
+  });
+  if (error && !String(error.message ?? '').includes('duplicate')) throw error;
+}
+
+// Re-exports for convenience.
+export { decryptWithConvKey, encryptWithConvKey };