Warren 81ae052f48 Revert X25519 byte reversal: OpenSSH doesn't reverse bytes ...

Key findings:
1. RFC 8731 says 'reinterpret as big-endian' = logical interpretation
2. OpenSSH sshbuf_put_bignum2_bytes() uses little-endian bytes directly
3. With reversal: signature verification fails
4. Without reversal: signature accepted, MAC still fails

Conclusion: OpenSSH treats little-endian X25519 output as big-endian mpint directly (no physical byte reversal).

Remaining issue: MAC verification fails despite signature success.
Next: need to compare client vs server key derivation details.

2026-06-14 20:16:46 +08:00

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