# OpenSSH Interoperability Test Results
**Project**: fynx-proto SSH Implementation
**Version**: 0.1.0
**Test Date**: 2025-10-18
**Status**: ✅ Phase 1 Complete - Ready for External Testing
## Summary
The fynx SSH implementation (Phase 1 - v0.1.0) has completed all internal integration tests. The codebase is ready for external OpenSSH interoperability testing.
### Implementation Status
| SSH Packet Layer | ✅ Complete | RFC 4253 Section 6 |
| Transport Layer | ✅ Complete | Version exchange, KEX |
| Authentication | ✅ Complete | Password auth (RFC 4252) |
| Connection Protocol | ✅ Complete | Channel management (RFC 4254) |
| Client Implementation | ✅ Complete | 1215 lines, full TCP I/O |
| Server Implementation | ✅ Complete | 905 lines, full TCP I/O |
| Encryption | ✅ Complete | ChaCha20-Poly1305, AES-GCM |
| Integration Tests | ✅ 6/6 Passing | Client-server communication |
## Supported Algorithms
### Key Exchange (KEX)
- ✅ `curve25519-sha256` - Primary KEX algorithm
- ✅ `curve25519-sha256@libssh.org` - Alternative name
- ✅ `diffie-hellman-group14-sha256` - 2048-bit MODP group (implemented but not primary)
### Host Key Algorithms
- ✅ `ssh-ed25519` - Primary host key algorithm
- ✅ `rsa-sha2-256` - RSA with SHA-256
- ✅ `rsa-sha2-512` - RSA with SHA-512
- ✅ `ecdsa-sha2-nistp256` - ECDSA P-256
- ✅ `ecdsa-sha2-nistp384` - ECDSA P-384
- ✅ `ecdsa-sha2-nistp521` - ECDSA P-521
### Encryption Ciphers
- ✅ `chacha20-poly1305@openssh.com` - Primary cipher (AEAD)
- ✅ `aes128-gcm@openssh.com` - AES-128-GCM (AEAD)
- ✅ `aes256-gcm@openssh.com` - AES-256-GCM (AEAD)
- ⏸️ `aes128-ctr` - Defined but not implemented (Stage 6)
- ⏸️ `aes256-ctr` - Defined but not implemented (Stage 6)
### MAC Algorithms
- ✅ Integrated with AEAD ciphers (ChaCha20-Poly1305, AES-GCM)
- ✅ `hmac-sha2-256` - For CTR mode (when implemented)
- ✅ `hmac-sha2-512` - For CTR mode (when implemented)
### Compression
- ✅ `none` - No compression (security best practice)
## Expected Compatibility
### Modern OpenSSH (v8.0+)
**Expected Result**: ✅ **Full Compatibility**
Modern OpenSSH versions support all algorithms implemented in fynx:
- Curve25519 KEX (supported since OpenSSH 6.5)
- ChaCha20-Poly1305 cipher (supported since OpenSSH 6.5)
- Ed25519 host keys (supported since OpenSSH 6.5)
**Test Commands**:
```bash
# Should work out of the box
ssh -p 2222 user@localhost
# Explicit algorithm selection
ssh -o KexAlgorithms=curve25519-sha256 \
-o Ciphers=chacha20-poly1305@openssh.com \
-o HostKeyAlgorithms=ssh-ed25519 \
-p 2222 user@localhost
```
### OpenSSH 7.x
**Expected Result**: ✅ **Full Compatibility**
OpenSSH 7.x has strong support for modern algorithms.
### OpenSSH 6.5-6.9
**Expected Result**: ✅ **Likely Compatible**
These versions introduced Curve25519 and ChaCha20-Poly1305, should work.
### OpenSSH < 6.5
**Expected Result**: ⚠️ **May Need AES-CTR** (Stage 6)
Older versions may not support ChaCha20-Poly1305 and require AES-CTR fallback.
## Testing Instructions
### Automated Tests
```bash
cd fynx/crates/proto
# Build tests
cargo test --test openssh_interop
# Run with OpenSSH server (requires setup)
export SSH_TEST_USER="testuser"
export SSH_TEST_PASS="testpass"
cargo test --test openssh_interop -- --ignored --nocapture
```
### Manual Testing
See [OPENSSH_TESTING.md](./OPENSSH_TESTING.md) for detailed instructions.
**Quick Start**:
1. Start OpenSSH server on port 22
2. Run: `cargo test --test openssh_interop test_connect_to_openssh_localhost -- --ignored --nocapture`
## Test Results (Pending External Validation)
### Test 1: fynx Client → OpenSSH Server
| TCP Connection | ⏳ Pending | Requires OpenSSH server |
| Version Exchange | ⏳ Pending | Should succeed |
| Curve25519 KEX | ⏳ Pending | Should succeed |
| Ed25519 Host Key | ⏳ Pending | Should succeed |
| ChaCha20-Poly1305 Encryption | ⏳ Pending | Should succeed |
| Password Authentication | ⏳ Pending | Should succeed |
| Command Execution | ⏳ Pending | Should succeed |
### Test 2: OpenSSH Client → fynx Server
| TCP Connection | ⏳ Pending | Run simple_server example |
| Version Exchange | ⏳ Pending | Should succeed |
| KEX Negotiation | ⏳ Pending | Should succeed |
| Host Key Verification | ⏳ Pending | May need known_hosts entry |
| Encryption | ⏳ Pending | Should succeed |
| Authentication | ⏳ Pending | Should succeed |
| Shell/Command | ⏳ Pending | Should succeed |
### Internal Integration Tests
| test_version_exchange | ✅ Pass | Version negotiation works |
| test_kex_with_signature_verification | ✅ Pass | KEX with host key verification |
| test_exchange_hash_consistency | ✅ Pass | Hash computation correct |
| test_authentication_failure | ✅ Pass | Failed auth handled correctly |
| test_authentication_flow | ✅ Pass | Password auth works |
| test_full_ssh_flow | ✅ Pass | End-to-end works |
## Known Limitations
### Currently Not Supported (Future Phases)
- ❌ Public key authentication (Phase 2)
- ❌ Port forwarding (Phase 3)
- ❌ X11 forwarding (Phase 3)
- ❌ Agent forwarding (Phase 3)
- ❌ Compression (zlib) - Intentional for security
- ❌ SFTP subsystem (Phase 3/4)
- ❌ SCP protocol (Phase 3/4)
### Stage 6 Enhancements (Optional)
- ⏸️ AES-CTR ciphers (for older SSH server compatibility)
- ⏸️ Encrypt-then-MAC (ETM) variants
- ⏸️ Keepalive support
- ⏸️ window-change request
- ⏸️ signal request
## Security Considerations
### Strengths
- ✅ Modern cryptographic algorithms only
- ✅ AEAD ciphers (authenticated encryption)
- ✅ Constant-time MAC verification
- ✅ Memory zeroization for sensitive data
- ✅ No unsafe code
- ✅ No compression (prevents CRIME-style attacks)
### Limitations
- ⚠️ Host key verification accepts any key (INSECURE - needs known_hosts)
- ⚠️ No rate limiting on authentication attempts (future enhancement)
- ⚠️ No connection limits (future enhancement)
## Next Steps
### Before v0.1.0 Release
1. ✅ Complete Phase 1 implementation
2. ⏳ Run OpenSSH interoperability tests
3. ⏳ Document any compatibility issues
4. ⏳ Add CI/CD automation
5. ⏳ Security audit
### Phase 1.1 (Optional)
- Implement AES-CTR if interop tests show need
- Add keepalive support
- Enhance timeout handling
### Phase 2+ (Future)
- Public key authentication
- Multi-factor authentication
- Port forwarding
- SFTP/SCP support
## Contributing
To help with interoperability testing:
1. Test against your SSH servers
2. Report results in GitHub issues
3. Include OpenSSH version
4. Include debug logs (`ssh -vvv`)
## References
- [OPENSSH_TESTING.md](./OPENSSH_TESTING.md) - Detailed testing guide
- [IMPLEMENTATION_PLAN.md](../../IMPLEMENTATION_PLAN.md) - Full roadmap
- [RFC 4251](https://www.rfc-editor.org/rfc/rfc4251) - SSH Architecture
- [RFC 4253](https://www.rfc-editor.org/rfc/rfc4253) - SSH Transport Layer
- [RFC 4252](https://www.rfc-editor.org/rfc/rfc4252) - SSH Authentication
- [RFC 4254](https://www.rfc-editor.org/rfc/rfc4254) - SSH Connection Protocol
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**Last Updated**: 2025-10-18
**Next Review**: After external OpenSSH testing
**Maintained By**: Fynx Core Team