Addresses critical security gaps identified in the RFC 9420 audit:
1. Epoch and group ID verification in decrypt (RFC 9420 Section 6.1):
- PrivateMessage.epoch must match current group epoch
- PrivateMessage.groupId must match current group ID
- Rejects messages from wrong epoch/group immediately
2. Remove proposal sender authorization (RFC 9420 Section 12.1.2):
- Cannot remove yourself via Remove (use SelfRemove)
- Target leaf index must be in range and non-blank
- Committer is implicitly authorized for inline proposals
3. KeyPackage lifetime validation (RFC 9420 Section 10.1):
- Checks notBefore/notAfter against current time on Add proposals
- Rejects expired or not-yet-valid KeyPackages
4. Unified proposal application in commit():
- commit() now uses applyProposal() for all validation
- Same authorization checks apply to both commit() and processCommit()
- addedMembers tracked before apply for Welcome generation
All 120 MLS tests pass (41 interop + 79 unit), 0 failures.
https://claude.ai/code/session_01NocQDWj2Y92FugjfgazzL3
Claude
9be7cfd27a