-client(→server) messages, evens for server(→client) messages.
-
-@code{ENCn} is XTEA block cipher algorithm used here as PRP (pseudo
-random permutation) to randomize, obfuscate @code{SERIAL}. Plaintext
-@code{SERIAL} state is kept in peers internal state, but encrypted
-before transmission. XTEA is compact and fast enough. Salsa20 is PRF
-function and requires much more code to create PRP from it. XTEA's
-encryption key is the first 128-bit of Salsa20's output with established
+client (to server) messages, evens for server (to client) messages.
+
+@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