X-Git-Url: http://www.git.cypherpunks.ru/?p=govpn.git;a=blobdiff_plain;f=doc%2Ftransport.texi;h=e5f5abba9eba15dec245489f2aa53c807d007b5f;hp=97fdce8ba04e397dca7542d38a3d9214196166cb;hb=0bf04621961589bc735dc8bd8a075d7db24c4178;hpb=87f01e08c6135b3e2b092903d56d7c49b3f126a5

diff --git a/doc/transport.texi b/doc/transport.texi
index 97fdce8..e5f5abb 100644
--- a/doc/transport.texi
+++ b/doc/transport.texi
@@ -2,60 +2,50 @@
 @section Transport protocol
 
 @verbatim
-TAG || ENCRYPTED || NONCE <-- PACKET
- ^         ^          ^
- |         |          |
- |         |          +------------+
- |         |                       |
- |         +------------+          |
- |                      |          |
- +-->AUTH(AUTH_KEY, ENCRYPTED || NONCE)
-                        ^          ^
-                        |          |
-+-----------------------+          |
-|                                  |
-|                   +--------------+
-|                   |
-+--> ENCRYPT(KEY, NONCE, PAYLOAD)
-                    ^       ^
-                    |       |
-                    |       +--> SIZE || DATA [|| NOISE]
-                    |
-                    +--> PRP(PRP_KEY, SERIAL)
+     NONCE = 64bit(ZEROS) || 64bit(MAC(MAC_KEY, SERIAL))
+   PAYLOAD = DATA || PAD [|| ZEROS]
+CIPHERTEXT = ENCRYPT(KEY, NONCE, PAYLOAD)
+       TAG = AUTH(AUTH_KEY, CIPHERTEXT || NONCE)
+   MESSAGE = TAG || CIPHERTEXT || NONCE
 @end verbatim
 
 @code{SERIAL} is message's serial number. Odds are reserved for
-client(->server) messages, evens for server(->client) messages.
+client (to server) messages, evens for server (to client) messages.
 
-@code{PRP} is XTEA block cipher algorithm used here as PRP (pseudo
-random permutation function) to obfuscate @code{SERIAL}. Plaintext
-@code{SERIAL} state is kept in peers internal state, but encrypted
-before transmission.
-
-XTEA's encryption key is the first 128-bit of Salsa20's output with
-established common key and zero nonce (message nonces start from 1).
+@code{MAC} is BLAKE2b-MAC used to obfuscate @code{SERIAL}. MAC's key
+@code{MAC_KEY} is the first 256-bit of ChaCha20's output with established
+common key and zero nonce (message nonces start from 1).
 
 @verbatim
-PRP_KEY = ENCRYPT(KEY, 0, 128-bit)
+MAC_KEY = 256bit(ENCRYPT(KEY, 0))
 @end verbatim
 
-@code{ENCRYPT} is Salsa20 stream cipher, with established session
+@code{ENCRYPT} is ChaCha20 stream cipher, with established session
 @code{KEY} and obfuscated @code{SERIAL} used as a nonce. 512 bit of
-Salsa20's output is ignored and only remaining is XORed with ther data,
+ChaCha20's output is ignored and only remaining is XORed with ther data,
 encrypting it.
 
-@code{SIZE} is big-endian @emph{uint16} storing length of the
-@code{DATA}.
-
-@code{NOISE} is optional. It is just some junk data, intended to fill up
-packet to MTU size. This is useful for concealing payload packets length.
+@code{DATA} is padded using ISO/IEC 7816-4 format (@code{PAD} (0x80
+byte) with optional @code{ZEROS} following), to fill up packet to
+conceal payload packet length.
 
 @code{AUTH} is Poly1305 authentication function. First 256 bits of
-Salsa20's output are used as a one-time key for @code{AUTH}.
+ChaCha20's output are used as a one-time key for @code{AUTH}.
 
 @verbatim
-AUTH_KEY = ENCRYPT(KEY, NONCE, 256 bit)
+AUTH_KEY = 256bit(ENCRYPT(KEY, NONCE))
 @end verbatim
 
 To prevent replay attacks we must remember received @code{SERIAL}s and
 drop when receiving duplicate ones.
+
+In @ref{Encless, encryptionless mode} this scheme is slightly different:
+
+@verbatim
+  NONCE = MAC(MAC_KEY, SERIAL)
+ENCODED = ENCLESS(DATA || PAD || ZEROS)
+ PACKET = ENCODED || NONCE
+@end verbatim
+
+@code{ENCLESS} is AONT and chaffing function. There is no need in
+explicit separate authentication.