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Add full chacha20-poly1305@openssh.com support to the crypto backend: encrypt, decrypt_length, and decrypt_body methods using the SSH AEAD construction (two-key split, Poly1305 tag over enc_length + enc_body). Register the cipher in CipherSuite as the preferred encryption algorithm, add AEAD_CIPHERS sentinel set, and fix the strict-KEX signal token from the incorrect v01 suffix to the correct v00.
Wire chacha20-poly1305 into the sync transport: add key fields (_chacha20_key_out/in), encrypt and decrypt through the backend methods, and switch _cipher_block_sizes to treat chacha20 as block size 8. Switch _packet_buffer from bytes to bytearray to eliminate O(n) copies on buffer advance. Add PacketProfiler (SPINDLEX_PROFILE=1) for per-stage build/encrypt/write timing. Fix validate_packet_structure minimum size check to be AEAD-compatible (minimum body 8 bytes instead of the previous MIN_PACKET_SIZE constant).
Implement the chacha20-poly1305 inbound packet path in AsyncTransport: read enc_length (4B) → decrypt length → read enc_body + tag (16B) → verify Poly1305 and decrypt body via the crypto backend. Reset the outbound sequence number to 0 after sending NEWKEYS when strict-KEX is active (Terrapin defense). Move the writer presence check before packet build/encrypt so no work is done on an uninitialised transport.
Add _query_limits() to SFTPClient: after version negotiation, if the server advertises limits@openssh.com, send SSH_FXP_EXTENDED and parse the 4×uint64 reply to extract max_write_len. Store in _max_write_len (defaults to 64 KB if the extension is absent or the call fails). Update SFTPFile.write() and SFTPClient.put() to use _max_write_len instead of the hardcoded SFTP_MAX_PACKET_SIZE constant. On OpenSSH this raises the write chunk from 64 KB to 255 KB, reducing round trips for a 1 MB upload from ~16 to ~4 and matching asyncssh throughput. Track send_offset as a dedicated field on SFTPFile instead of recomputing it from the queue on every write iteration.
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Add chacha20-poly1305@openssh.com to benchmark_ciphers.py cipher profiles and raise SFTP_CHUNK from 16 KB to 32 KB to match the new default. Extend benchmark_production.py: add chacha20 to CIPHER_ALGORITHMS, add MAC_ALGORITHMS list (hmac-sha2-256, hmac-sha2-512), add per-MAC correctness checks and silent-fallback detection for nonexistent MACs, and add mac parameter to _force_algos(). Remove diffie-hellman-group16-sha512 from KEX list as it is not implemented.
![github-advanced-security[bot]](https://avatars.githubusercontent.com/in/57789?s=60&v=4){kind=small}
Add docs/algorithms.md: full reference for all supported KEX, host key, cipher, and MAC algorithms with preference order, notes, and an explicit list of unsupported/excluded algorithms. Replace the inline algorithm lists in security.md with a cross-reference to the new page to avoid duplication. Add algorithms.md to the mkdocs nav. Add .ruff_cache/ to .gitignore.
Reflect the 0.7.x release line: ChaCha20-Poly1305 as the preferred cipher, limits@openssh.com SFTP write chunk negotiation (up to 255 KB), and Terrapin strict-KEX. Update the beta warning, key features, benchmark table, and security section accordingly.
Bump version to 0.7.0 in pyproject.toml, _version.py, and CITATION.cff. Update CITATION date to 2026-05-16. Update supported-version tables in SECURITY.md and docs/security.md to mark 0.7.x as supported and 0.6.x as end-of-life. Add 0.7.0 entry to docs/changelog.md covering ChaCha20-Poly1305, limits@openssh.com SFTP negotiation, PacketProfiler, strict-KEX fix, bytearray buffer, and all related fixes. Update docs/index.md and docs/performance.md: replace stale AES-256-CTR references with ChaCha20-Poly1305 as preferred cipher, document the limits@openssh.com write-chunk negotiation, and add a PacketProfiler section with usage example and sample output.
Ruff: fix import order in sftp_client.py, remove unused MIN_PACKET_SIZE import from protocol/utils.py, sort imports and remove unused os import in test_chacha20.py and test_chacha20_local.py, replace bare except with except Exception. Mypy: add assert narrowing for Optional[bytes] chacha20 key fields at all call sites in transport.py and async_transport.py. Bandit: suppress B110 (try/except/pass) on the non-fatal limits query fallback in sftp_client.py._query_limits(). Ruff format: reformat five files to satisfy black-compatible style.
Replace all explicit references to competitor library names (asyncssh, paramiko, AsyncSSH, Paramiko) in docs, changelog, meta, and issue templates with generic alternatives such as "other SSH libraries" and "other leading SSH libraries". Benchmark scripts are unaffected per project policy.
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Description
Implements the
chacha20-poly1305@openssh.comcipher in the crypto backend and integratesit into both the sync and async packet paths in the transport layer. Also adds strict-KEX
state reset on the async receive path, and negotiates the
limits@openssh.comSFTPextension to enable larger write chunks for better throughput.
Fixes # (issue)
Type of Change
Select exactly one option. These stable tokens are parsed by CI and release automation.
How Has This Been Tested?
pytest tests/test_...pytest -m integrationChecklist