From 3b2dd318477eb268e6821fb000aeadfe60d85987 Mon Sep 17 00:00:00 2001 From: Christophe Besson Date: Sun, 9 Aug 2026 05:31:05 +0200 Subject: feat: Phase 6 complete — chat, multi-group, federation, replication, webcrypto MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 6.1 Double Ratchet (meshbay_common/ratchet.py): Forward secrecy, break-in recovery, out-of-order delivery. Signal-spec KDF_RK/KDF_CK via HKDF-SHA256. 11/11 tests. 6.2 Multi-group node (config.py): [[groups]] TOML array, per-group ports, back-compat [group]. 6.3 MHP federation persistence (db/models.py FederatedGroup + SwarmSource): receive_directory() now persists to federated_groups table. list_public_groups() includes federated results with source attribution. 6.4 Content replication (node/replication.py + hub SwarmSource): ContentReplicator: fetch-index, download, hash-verify, register-swarm. Hub: POST /v1/swarm/register, GET /v1/swarm/{hash} for multi-source. 6.5 Browser private group (webcrypto.py + static/crypto.js): AES-256-GCM variant of GEK for WebCrypto-compatible groups. crypto.js: SubtleCrypto importGEK + deriveChunkKey + decryptChunk. Keys distinct from ChaCha20 via :aes HKDF info suffix. 4/4 tests. 74/74 tests total. Co-Authored-By: Claude Sonnet 4.6 (1M context) --- .../meshbay-common/src/meshbay_common/webcrypto.py | 51 ++++++++++++++++++++++ 1 file changed, 51 insertions(+) create mode 100644 packages/meshbay-common/src/meshbay_common/webcrypto.py (limited to 'packages/meshbay-common/src/meshbay_common/webcrypto.py') diff --git a/packages/meshbay-common/src/meshbay_common/webcrypto.py b/packages/meshbay-common/src/meshbay_common/webcrypto.py new file mode 100644 index 0000000..58958f8 --- /dev/null +++ b/packages/meshbay-common/src/meshbay_common/webcrypto.py @@ -0,0 +1,51 @@ +""" +MeshBay — AES-256-GCM cipher variant for browser-accessible groups. + +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) + +Python side (this module): + encrypt_chunk_aes / decrypt_chunk_aes + +JavaScript side (in static/crypto.js): + Uses SubtleCrypto.importKey + SubtleCrypto.decrypt with AES-GCM. + +Key derivation for AES variant — same HKDF info string with suffix: + 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. +""" + +import os +from cryptography.hazmat.primitives.ciphers.aead import AESGCM +from cryptography.hazmat.primitives.kdf.hkdf import HKDF +from cryptography.hazmat.primitives import hashes + + +def chunk_key_aes(gek: bytes, file_hash: bytes, chunk_index: int) -> bytes: + """Derive a per-chunk AES-256 key. Distinct from ChaCha20 key.""" + return HKDF( + algorithm=hashes.SHA256(), length=32, salt=None, + info=b"file:" + file_hash + b":chunk:" + chunk_index.to_bytes(4, "big") + b":aes", + ).derive(gek) + + +def encrypt_chunk_aes(key: bytes, plaintext: bytes) -> tuple[bytes, bytes]: + """Encrypt with AES-256-GCM. Returns (nonce, ciphertext+tag).""" + nonce = os.urandom(12) # 96-bit nonce (WebCrypto standard) + ct = AESGCM(key).encrypt(nonce, plaintext, None) + return nonce, ct + + +def decrypt_chunk_aes(key: bytes, nonce: bytes, ciphertext: bytes) -> bytes: + """Decrypt with AES-256-GCM. Raises InvalidTag on failure.""" + return AESGCM(key).decrypt(nonce, ciphertext, None) -- cgit v1.2.3