fix: bound pending admin challenges and sign every value an op acts on

Any member could make a node hold unbounded challenge requests; a
connection now keeps at most 8, 64 KiB each. root_add, group_attach,
invite_create and tmdb_config signed less than they did; their subjects
are now canonical JSON of every value (the TMDB token by SHA-256).
MNP 5.0, floor kept at 4.0.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

1 files changed, 39 insertions, 1 deletions

diff --git a/packages/meshbay-hub/src/meshbay_hub/static/crypto.js b/packages/meshbay-hub/src/meshbay_hub/static/crypto.js
index b74732c..0ca8ee5 100644
--- a/packages/meshbay-hub/src/meshbay_hub/static/crypto.js
+++ b/packages/meshbay-hub/src/meshbay_hub/static/crypto.js
@@ -307,6 +307,43 @@ function b64encode(bytes) {
   return btoa(String.fromCharCode(...bytes));
 }
 
+// ── Admin operation subjects ────────────────────────────────────────────────
+// Mirrors meshbay_common/adminop.py. The subject is what the signature covers of
+// a request, so an operation whose effect is several values names them all.
+// Canonical JSON — sorted keys, no whitespace — so both sides build the same
+// bytes, and `null`, `""` and a value stay distinct.
+
+function adminSubject(fields) {
+  const sorted = {};
+  for (const k of Object.keys(fields).sort()) sorted[k] = fields[k];
+  return JSON.stringify(sorted);
+}
+
+// A secret named without being written: null (unchanged) and '' (clear) as
+// themselves, anything else as its SHA-256.
+async function secretDigest(value) {
+  if (!value) return value;
+  const d = await crypto.subtle.digest('SHA-256', new TextEncoder().encode(value));
+  return 'sha256:' + Array.from(new Uint8Array(d))
+    .map((b) => b.toString(16).padStart(2, '0')).join('');
+}
+
+function rootAddSubject(path, name, kind, writable, removable) {
+  return adminSubject({ path, name, kind, writable, removable });
+}
+
+function groupAttachSubject(name, sharedDir, writable) {
+  return adminSubject({ name, shared_dir: sharedDir, writable });
+}
+
+function inviteCreateSubject(userId, username) {
+  return adminSubject({ user_id: userId, username });
+}
+
+async function tmdbConfigSubject(token, language) {
+  return adminSubject({ token: await secretDigest(token), language });
+}
+
 // ── Admin operation transcript ───────────────────────────────────────────────
 // Mirrors meshbay_common/adminop.py::admin_transcript(). Both sides build these
 // bytes independently; they are never taken off the wire.
@@ -535,7 +572,8 @@ window.MeshBayCrypto = {
   importGEK, deriveChunkKey, decryptChunkBin,
   openGroup, sealGroup,
   unwrapGEK, b64encode, b64decode,
-  adminTranscript, handshakeTranscript, handshakeProof, webrtcBinding,
+  adminTranscript, adminSubject, rootAddSubject, groupAttachSubject,
+  inviteCreateSubject, tmdbConfigSubject, handshakeTranscript, handshakeProof, webrtcBinding,
   challengeTranscript, joinTranscript, verifyNodeSignature, constantTimeEqual,
   deviceRequestTranscript, deviceAddTranscript, deviceHelloTranscript,
   deviceCodeHash,