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| -rw-r--r-- | doc/obfs4-spec.txt | 11 |
1 files changed, 11 insertions, 0 deletions
diff --git a/doc/obfs4-spec.txt b/doc/obfs4-spec.txt index 0e844a1..7d54ffc 100644 --- a/doc/obfs4-spec.txt +++ b/doc/obfs4-spec.txt @@ -269,6 +269,17 @@ The maximum allowed frame length is 1448 bytes, which allows up to 1427 bytes of useful payload to be transmitted per "frame". + The NaCl secretbox (Poly1305/XSalsa20) nonce format is: + + uint8_t[24] prefix (Fixed) + uint64_t counter (Big endian) + + The counter is initialized to 1, and is incremented on each frame. Since + the protocol is designed to be used over a reliable medium, the nonce is not + transmitted over the wire as both sides of the conversation know the prefix + and the initial counter value. It is imperative that the counter does not + wrap, and sessions MUST terminate before 2^64 frames are sent. + If unsealing a secretbox ever fails (due to a Tag mismatch), implementations MUST drop the connection. |