Warren
1650708ac7
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Implement Phase 1 AES-GCM packet processing: AEAD encryption/decryption
Phase 1 complete implementation:
- AES-GCM AEAD encryption (EncryptedPacket::new)
- AES-GCM AEAD decryption (EncryptedPacket::read)
- AES-GCM packet structure: packet_length plaintext + ciphertext + 16-byte tag
- AES-GCM nonce: sequence_number (4 bytes -> 12 bytes)
- AES-CTR fallback preserved (MtE mode)
Key differences AES-GCM vs AES-CTR:
- AES-GCM: packet_length is plaintext (as AAD)
- AES-CTR: packet_length is encrypted
- AES-GCM: 16-byte GCM tag (no separate MAC)
- AES-CTR: 32-byte HMAC-SHA256 MAC
Performance improvement:
- AES-GCM: encrypt+authenticate in one step (AEAD)
- AES-CTR: MAC-then-Encrypt (2 steps)
Testing:
- OpenSSH client negotiated aes256-gcm@openssh.com
- cipher_mode set to AesGcm successfully
- Next: full SSH connection test