fix(cert): exempt roots from the responder-cert checks (symmetric with the init-side gates)#97
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…h the init-side gates) (#96) Follow-up from the #36/#41 hardening (PR #95). That branch added is_root exemption to all five init-side cert gates. The three pre-existing responder-cert checks — an initiator verifying the responder's msg2 cert in handle_handshake_resp, relayed_handshake_resp, and rekey_resp_core — lacked it, so a root whose cert lapsed while still in the signed root set, acting as a responder, would be rejected by an initiator. Roots are trusted via the signed root set, not a member cert, so gate all three on !is_root(responder pubkey) too. New test initiator_admits_root_responder_despite_missing_cert (root establishes despite no cert); initiator_rejects_responder_with_bad_cert stays green (non-root still rejected). 237 unit green, clippy clean.
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Closes #96. Follow-up from the #36/#41 session-lifecycle hardening (PR #95).
Problem
PR #95 introduced a shared
is_roothelper and exempts always-admit roots from all five init-side cert gates it added (rekey re-verify + re-admission gate on both direct/relay paths, and the liveness sweep). The three pre-existing responder-cert checks — an initiator verifying the responder's msg2 cert inhandle_handshake_resp,relayed_handshake_resp, andrekey_resp_core— were left without the exemption.So a root whose cert lapsed while still in the signed root set, acting as a responder, would be rejected by an initiator completing a handshake with it. Roots are trusted via the signed root set, not a member cert (you revoke a root by removing it from the root set), so this is an inconsistency with the exemption model the rest of the code follows.
Fix
Gate all three responder-cert checks on
!self.is_root(self.peers[idx].pubkey)too — a root responder is admitted even with a missing/lapsed cert; a non-root responder still requires a valid cert. These are notdrop_sessionteardown sites; they only refuse to complete.Testing
initiator_admits_root_responder_despite_missing_cert: an initiator completing a handshake with a root responder that presents no cert establishes (confirmed failing before the fix, passing after).initiator_rejects_responder_with_bad_cert(non-root) stays green — proving the exemption is root-only.-D warnings, fmt — all clean.