encryption key is different during each handshake, so (key, nonce) pair
is always used only once. @code{ENC} is Salsa20 cipher, with established
session @code{KEY} and encrypted @code{SERIAL} used as a nonce.
encryption key is different during each handshake, so (key, nonce) pair
is always used only once. @code{ENC} is Salsa20 cipher, with established
session @code{KEY} and encrypted @code{SERIAL} used as a nonce.