The chacha20-poly1305@openssh.com cipher requires 512 bits of key
material as output from the SSH key exchange. This forms two 256 bit
keys (K_1 and K_2), used by two separate instances of chacha20.
+The first 256 bits consitute K_2 and the second 256 bits become
+K_1.
The instance keyed by K_1 is a stream cipher that is used only
to encrypt the 4 byte packet length field. The second instance,
[3] "ChaCha20 and Poly1305 based Cipher Suites for TLS", Adam Langley
http://tools.ietf.org/html/draft-agl-tls-chacha20poly1305-03
-$OpenBSD: PROTOCOL.chacha20poly1305,v 1.2 2013/12/02 02:50:27 djm Exp $
+$OpenBSD: PROTOCOL.chacha20poly1305,v 1.3 2016/05/03 13:10:24 djm Exp $