Breakthrough verification:
- Python computed keys match server actual keys EXACTLY
- Key derivation formula: HASH(K || H || X || session_id) verified
- All keys (encryption, MAC, IV) derived correctly
- Shared secret encoding (little-endian bytes) correct
Remaining issue:
- MAC verification fails despite correct key derivation
- Client must be computing different keys than server
- Need to compare client vs server actual key values
Next step: Wireshark comparison of OpenSSH client keys
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