Three encoding bugs found by IETF interop test vectors:
1. ExpandWithLabel: label and context length prefixes must use
QUIC-style variable-length integer encoding (VarInt), not fixed-size
opaque prefixes. Values < 64 use 1 byte, 64-16383 use 2 bytes with
0x40 prefix. This is critical when GroupContext (112+ bytes) is
passed as context.
2. RefHash: label and value also use VarInt-prefixed opaque fields,
matching the MLS TLS codec convention.
3. SecretTree: DeriveTreeSecret must pass the generation counter as a
uint32 big-endian context parameter, not empty context. This affects
key/nonce derivation and ratchet advancement.
Also fixes:
- SignContent and EncryptWithLabel/DecryptWithLabel info encoding
updated to use VarInt
- KeySchedule test updated to use initial_init_secret from test vector
(not hardcoded zeros)
- Added putOpaqueVarInt() to TlsWriter for QUIC-style VarInt encoding
https://claude.ai/code/session_01NocQDWj2Y92FugjfgazzL3
Claude
d1409c84bc