diff options
Diffstat (limited to 'packages/meshbay-common/src/meshbay_common/webcrypto.py')
| -rw-r--r-- | packages/meshbay-common/src/meshbay_common/webcrypto.py | 27 |
1 files changed, 10 insertions, 17 deletions
diff --git a/packages/meshbay-common/src/meshbay_common/webcrypto.py b/packages/meshbay-common/src/meshbay_common/webcrypto.py index 3bd5ae6..7119e2e 100644 --- a/packages/meshbay-common/src/meshbay_common/webcrypto.py +++ b/packages/meshbay-common/src/meshbay_common/webcrypto.py @@ -1,28 +1,21 @@ """ -MeshBay — AES-256-GCM cipher variant for browser-accessible groups. +MeshBay — the content cipher: AES-256-GCM, per-chunk keys derived from the GEK. -The ChaCha20-Poly1305 GEK used in MNP (TCP+TLS and QUIC transport) -is NOT available in the WebCrypto API. For groups whose content must -be decryptable by a web browser (using SubtleCrypto), an AES-256-GCM -variant is used instead. - -The GEK wrapping (X25519 + HKDF) is identical — only the content -cipher changes. The hub stores and distributes GEK bundles the same way. - -Cipher selection is declared per-group in the hub registry: - "cipher": "chacha20-poly1305" (default, native clients) - "cipher": "aes-256-gcm" (browser-compatible groups) +AES-GCM because it is what WebCrypto offers, and one cipher serves every client: +the browser, the desktop client (the same engine) and the Python side here. Python side (this module): - encrypt_chunk_aes / decrypt_chunk_aes + chunk_key_aes / encrypt_chunk_aes / decrypt_chunk_aes JavaScript side (in static/crypto.js): - Uses SubtleCrypto.importKey + SubtleCrypto.decrypt with AES-GCM. + SubtleCrypto.importKey + SubtleCrypto.decrypt with AES-GCM. -Key derivation for AES variant — same HKDF info string with suffix: +Key derivation: info = b"file:" + file_hash + b":chunk:" + chunk_index + b":aes" -This ensures AES and ChaCha20 keys are always distinct even from the same GEK. +The `:aes` suffix dates from a ChaCha20-Poly1305 variant derived from the same +GEK without it, which nothing used and which is gone. It stays: it is part of +every chunk key in existence, and changing it would change them all. """ import os @@ -33,7 +26,7 @@ from cryptography.hazmat.primitives.kdf.hkdf import HKDF def chunk_key_aes(gek: bytes, file_hash: bytes, chunk_index: int) -> bytes: - """Derive a per-chunk AES-256 key. Distinct from ChaCha20 key.""" + """Derive a per-chunk AES-256 key from the GEK.""" return HKDF( algorithm=hashes.SHA256(), length=32, salt=None, info=b"file:" + file_hash + b":chunk:" + chunk_index.to_bytes(4, "big") + b":aes", |