From 5c5d41e46297e47dfae9dece8b33158b0283ce4e Mon Sep 17 00:00:00 2001
From: Jannis Braun <151788261+TheZwiss@users.noreply.github.com>
Date: Tue, 31 Mar 2026 18:12:16 +0200
Subject: [PATCH] feat(federation): wire nonce verification into relay and sync
 handlers (FED-008)

Pass nonce through to verifySignature and enforce replay protection in
both /api/federation/relay and /api/federation/sync: reject duplicate
nonces (409), reject nonce-less requests from peers that previously sent
nonces (401), warn for legacy peers, and auto-ratchet nonceSupported flag.
---
 packages/server/src/routes/federation.ts | 36 ++++++++++++++++++++++--
 1 file changed, 34 insertions(+), 2 deletions(-)

diff --git a/packages/server/src/routes/federation.ts b/packages/server/src/routes/federation.ts
index a0a1c549..b9b47ef8 100644
--- a/packages/server/src/routes/federation.ts
+++ b/packages/server/src/routes/federation.ts
@@ -461,10 +461,22 @@ export async function federationRoutes(app: FastifyInstance): Promise<void> {
 
       // Serialize body back to JSON for HMAC verification (we control both sides)
       const bodyString = JSON.stringify(request.body);
-      if (!verifySignature(bodyString, fedHeaders.signature, peer.hmacSecret, fedHeaders.timestamp)) {
+      if (!verifySignature(bodyString, fedHeaders.signature, peer.hmacSecret, fedHeaders.timestamp, fedHeaders.nonce)) {
         return reply.code(401).send({ error: 'Invalid signature', statusCode: 401 });
       }
 
+      // 1c. Nonce-based replay protection
+      if (fedHeaders.nonce) {
+        if (isNonceDuplicate(peer.origin, fedHeaders.nonce)) {
+          return reply.code(409).send({ error: 'Duplicate nonce — possible replay', statusCode: 409 });
+        }
+      } else if (peer.nonceSupported) {
+        // Peer previously sent nonces but this request doesn't have one — reject
+        return reply.code(401).send({ error: 'Nonce required — peer previously supported nonces', statusCode: 401 });
+      } else {
+        console.warn(`[federation] Peer ${peer.origin} does not support replay protection (no nonce)`);
+      }
+
       // 2. Validate request body shape
       const body = request.body;
       if (!body || body.version !== 1 || !Array.isArray(body.events)) {
@@ -488,6 +500,7 @@ export async function federationRoutes(app: FastifyInstance): Promise<void> {
         .set({
           lastSeenAt: Date.now(),
           consecutiveFailures: 0,
+          ...(fedHeaders.nonce && !peer.nonceSupported ? { nonceSupported: 1 } : {}),
         })
         .where(eq(schema.federationPeers.id, peer.id))
         .run();
@@ -537,10 +550,29 @@ export async function federationRoutes(app: FastifyInstance): Promise<void> {
       }
 
       const bodyString = JSON.stringify(request.body);
-      if (!verifySignature(bodyString, fedHeaders.signature, peer.hmacSecret, fedHeaders.timestamp)) {
+      if (!verifySignature(bodyString, fedHeaders.signature, peer.hmacSecret, fedHeaders.timestamp, fedHeaders.nonce)) {
         return reply.code(401).send({ error: 'Invalid signature', statusCode: 401 });
       }
 
+      // 1b. Nonce-based replay protection
+      if (fedHeaders.nonce) {
+        if (isNonceDuplicate(peer.origin, fedHeaders.nonce)) {
+          return reply.code(409).send({ error: 'Duplicate nonce — possible replay', statusCode: 409 });
+        }
+      } else if (peer.nonceSupported) {
+        return reply.code(401).send({ error: 'Nonce required — peer previously supported nonces', statusCode: 401 });
+      } else {
+        console.warn(`[federation] Peer ${peer.origin} does not support replay protection (no nonce) [sync]`);
+      }
+
+      // Ratchet: mark peer as nonce-supporting if this is the first nonce we've seen
+      if (fedHeaders.nonce && !peer.nonceSupported) {
+        db.update(schema.federationPeers)
+          .set({ nonceSupported: 1 })
+          .where(eq(schema.federationPeers.id, peer.id))
+          .run();
+      }
+
       // 2. Validate & normalize request body
       const body = request.body;
       if (!body || typeof body.sinceTimestamp !== 'number' || body.sinceTimestamp < 0) {