feat: Phase 12 — P2P crypto material, password split, node Ed25519 auth

Baseline commit capturing in-progress Phase 12 work that was already present
in the working tree (uncommitted) before the Phase 11.5 security remediation
begins. Committed as-is, without review or modification, so that remediation
changes arrive as a separable diff.

Contents: BundleStore (P2P GEK + keypair bundles), password split
(auth_key / bundle_key), node Ed25519 auth (POST /v1/nodes/auth, node-scoped
JWT), GEK-HMAC handshake proof with DTLS channel binding, Ed25519 admin
challenge-response, node local admin UI rewrite, browser key persistence.

Not authored in this session — captured to establish a baseline.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

1 files changed, 16 insertions, 0 deletions

diff --git a/packages/meshbay-hub/src/meshbay_hub/static/crypto.js b/packages/meshbay-hub/src/meshbay_hub/static/crypto.js
index eb96eef..5ebf624 100644
--- a/packages/meshbay-hub/src/meshbay_hub/static/crypto.js
+++ b/packages/meshbay-hub/src/meshbay_hub/static/crypto.js
@@ -230,8 +230,24 @@ function b64encode(bytes) {
   return btoa(String.fromCharCode(...bytes));
 }
 
+// ── GEK proof (HMAC-SHA256 for handshake challenge) ─────────────────────────
+
+async function hmacGEK(gekRaw, nonceB64, offerFp, answerFp) {
+  const nonce = b64decode(nonceB64);
+  const data = concatBuffers([
+    nonce,
+    offerFp || new Uint8Array(0),
+    answerFp || new Uint8Array(0),
+  ]);
+  const key = await crypto.subtle.importKey(
+    'raw', gekRaw, { name: 'HMAC', hash: 'SHA-256' }, false, ['sign']);
+  const sig = await crypto.subtle.sign('HMAC', key, data);
+  return b64encode(new Uint8Array(sig));
+}
+
 // Export for use in app.js
 window.MeshBayCrypto = {
   importGEK, deriveChunkKey, decryptChunk, decryptChunkBin, decryptFile,
   generateGEK, wrapGEK, unwrapGEK, encryptChunk, b64encode, b64decode,
+  hmacGEK,
 };