.TH AUTH 5 
.SH NAME
auth \- file system authentication
.SH SYNOPSIS
.ta \w'\fLTauth 'u
.B
Tauth	
.IR tag [2]
.IR fid [2]
.IR uid [28]
.IR chal [36]
.br
.B
Rauth	
.IR tag [2]
.IR fid [2]
.IR chal [30]
.SH DESCRIPTION
The
.B auth
message is used to authorize a connection.
It is issued before an
.BR attach .
.I Fid
and
.I uid
are the same as for
.BR attach .
.PP
The
.I chal
field of a
.B Tauth
message
contains a 36-byte string
encrypted with the client's authentication key.
The (decrypted) string
contains a byte with value 1,
a seven byte client challenge, and the server's name NUL-padded to 28
.RB ( NAMELEN )
bytes.
.PP
The
.I chal
field of the
.B Rauth
reply message is also encrypted with the client's key.
The decrypted string contains a byte with value 4,
the client's challenge, a seven byte
.I ticket key,
and a fifteen byte
.I ticket.
The ticket is placed in the
.I auth
field of a subsequent
.B attach
message to validate a connection.
.PP
The ticket key is currently unused.
It may one day be used to encrypt subsequent communication with the server.
.PP
These messages are also documented in the section of
.IR auth (6)
describing the
.I fsauth
protocol.
.PP
If a server does not perform authentication,
it should return an
.B Rerror
when it receives an
.BR auth .
.SH ENTRY POINTS
.I Mount
(see
.IR bind (2))
generates an
.B auth
transaction to the remote file server.
When the kernel boots, an
.B auth
is made to the requested file server machine.
.SH "SEE ALSO"
.IR auth (6)