A summary of the Authentication-Protocol Configuration Option format to negotiate the Challenge-Handshake Authentication Protocol is shown below. The fields are transmitted from left to right.
0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | Authentication-Protocol | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Algorithm | +-+-+-+-+-+-+-+-+
3
5
c223 (hex) for Challenge-Handshake Authentication Protocol.
The Algorithm field is one octet and indicates the one-way hash method to be used. The most up-to-date values of the CHAP Algorithm field are specified in the most recent "Assigned Numbers" RFC [2]. Current values are assigned as follows:
0-4 unused (reserved) 5 MD5 [3]