refactor(hub): the transport holds an identity, never a private key

Two public keys, sign() and shared(); the apps take transport.signFn. What
holds the keys (this page, or the desktop main process) is the identity's
business alone.

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

1 files changed, 7 insertions, 7 deletions

diff --git a/packages/meshbay-hub/src/meshbay_hub/static/crypto.js b/packages/meshbay-hub/src/meshbay_hub/static/crypto.js
index 0ca8ee5..27e97d3 100644
--- a/packages/meshbay-hub/src/meshbay_hub/static/crypto.js
+++ b/packages/meshbay-hub/src/meshbay_hub/static/crypto.js
@@ -278,17 +278,17 @@ async function verifyChatSignature(deviceRaw, groupId, epoch, nonce, ct, sig) {
 
 // ── GEK unwrapping (ECIES) ─────────────────────────────────────────────────────
 
-async function unwrapGEK(bundle, skXPkcs8, pkXRaw) {
+/**
+ * Unwrap a group key wrapped for our X25519 key. `shared(pkEphRaw)` is the
+ * agreement with the ephemeral key — done by whatever holds the private key
+ * (the identity object, transport.js), so this never sees one.
+ */
+async function unwrapGEK(bundle, shared, pkXRaw) {
   const pkEphRaw = b64decode(bundle.pk_eph_b64);
   const nonce = b64decode(bundle.nonce_b64);
   const wrapped = b64decode(bundle.wrapped_b64);
 
-  const skX = await crypto.subtle.importKey(
-    'pkcs8', skXPkcs8, { name: 'X25519' }, false, ['deriveBits']);
-  const pkEph = await crypto.subtle.importKey(
-    'raw', pkEphRaw, { name: 'X25519' }, false, []);
-  const sharedBits = await crypto.subtle.deriveBits(
-    { name: 'X25519', public: pkEph }, skX, 256);
+  const sharedBits = await shared(pkEphRaw);
 
   const sharedKey = await crypto.subtle.importKey(
     'raw', sharedBits, 'HKDF', false, ['deriveKey']);