harvey/sys/man/1/ssh

.TH SSH 1
.SH NAME
ssh, sshnet, scp, sshserve \- secure login and file copy from/to Unix or Plan 9
.SH SYNOPSIS
.B ssh
[
.B -CfiImPpRrw
]
[
.B -A
.I authlist
]
[
.B -c
.I cipherlist
]
[
.B -[lu]
.I user
]
.RI [ user\fB@ ] host
[
.I cmd
[
.I args
\&... ]]
.PP
.B sshnet
[
.B -A
.I authlist
]
[
.B -c
.I cipherlist
]
[
.B -m
.I mtpt
]
[
.B -s
.I service
]
.RI [ user\fB@ ] host
.PP
.B scp
[host:]file [host:]file
.br
.B scp
[host:]file ... [host:]dir
.PP
.B aux/sshserve
[
.B -p
]
.I address
.SH DESCRIPTION
.I Ssh
allows authenticated login over an encrypted channel to hosts that
support the ssh protocol (see the RFC listed below for encryption and
authentication details).
.LP
.I Ssh
takes the host name of the machine to connect to as its mandatory argument.
It may be specified as a domain name or an IP address.
Normally, login is attempted using the user name from /dev/user.
.PP
Command-line options are:
.TP
.B -C
force input to be read in cooked mode:
``line at a time'' with local echo.
.TP
.B -f
enable agent forwarding.
With this flag,
.I ssh
uses SSH's agent forwarding protocol to allow
programs running on the remote server to
interact with
.IR factotum (4)
to perform RSA authentication.
.TP
.B -i
force interactive mode.
In interactive mode, 
.I ssh
prompts for passwords and confirmations of
new host keys when necessary.
(In non-interactive mode, password requests
are rejected and unrecognized host keys are 
cause for disconnecting.)
By default, 
.I ssh 
runs in interactive mode only when its 
input file descriptor is 
.BR /dev/cons .
.TP
.B -I
force non-interactive mode.
.TP
.B -m
disable the 
.RB control- \e
menu, described below.
.TP
.B -p
force pseudoterminal request.
The
.I ssh
protocol, grounded in Unix tradition,
differentiates between connections
that request controlling pseudoterminals
and those that do not.
By default, 
.I ssh
requests a pseudoterminal only when no
.I command
is given.
.TP
.B -P
force no pseudoterminal request.
.TP
.B -r
strip carriage returns.
.TP
.B -R
put the allocated pseudoterminal, if any, in raw mode.
.TP
.B -w
notify the remote side whenever the window changes size.
.TP
.BR - [ lu ] "\fI user
specify user name.
This option is deprecated in favor of the
.IB user @ hostname
syntax.
.TP
.B "-A\fI authlist
specify an ordered space-separated list of authentication protocols to try.
The full set of authentication protocols is
.B rsa
(RSA using
.IR factotum (4)
to moderate key usage),
.B password
(use a password gathered from factotum),
and
.B tis
(challenge-response).
The default list is all three in that order.
.TP
.B "-c\fI cipherlist
specify an ordered space-separated list of allowed ciphers to use when encrypting the channel.
The full set of ciphers is
.B des
(standard DES),
.B 3des
(a somewhat doubtful variation on triple DES),
.B blowfish
(Bruce Schneier's Blowfish),
.B rc4
(RC4),
and
.B none
(no encryption).
The default cipher list is 
.B blowfish
.B rc4
.BR 3des .
.PD
.PP
The
.RB control\- \e
character is a local escape, as in
.IR con (1).
It prompts with
.BR >>> .
Legitimate responses to the prompt are
.TP
.B q
Exit.
.TP
.B .
Return from the escape.
.TP
.B !cmd
Run the command with the network connection as its
standard input and standard output.
Standard error will go to the screen.
.TP
.B r
Toggle printing of carriage returns.
.PD
.LP
If no command is specified,
a login session is started on the remote
host.
Otherwise, the command is executed with its arguments.
.LP
.I Ssh
establishes a connection with an ssh daemon on the remote host.
The daemon sends to 
.I ssh
its RSA public host key and session key.
Using these,
.I ssh
sends a session key which, presumably, only the
daemon can decipher.  After this, both sides start encrypting their
data with this session key.
.LP
When the daemon's host key has been received,
.I ssh
looks it up in 
.B $home/lib/keyring
and in 
.BR /sys/lib/ssh/keyring .
If
the key is found there, and it matches the received key,
.I ssh
is satisfied.  If not,
.I ssh
reports this and offers to add the key to
.BR $home/lib/keyring .
.LP
Over the encrypted channel,
.I ssh
attempts to convince the daemon to accept the call
using the listed authentication protocols
(see the
.B -A
option above).
.LP
The preferred way to authenticate is a
.IR netkey -style
challenge/response or via a SecurID token.
.I Ssh
users on other systems than Plan 9 should enable \s-2TIS_A\s0uthentication.
.LP
When the connection is authenticated, the given command line,
(by default, a login shell) is executed on the remote host.
.sp 1
The SSH protocol allows clients to make outgoing TCP calls via the server.
.I Sshnet
establishes an SSH connection and, rather than execute a remote command,
presents the remote server's TCP stack as a network stack
(see the discussion of TCP in
.IR ip (3))
mounted at
.I mtpt
(default
.BR /net ),
optionally posting a 9P service
descriptor for the new file system as
.IB /srv/ service \fR.
The
.B -A
and
.B -c
arguments are as in
.IR ssh .
.sp 1
.I Scp
uses
.I ssh
to copy files from one host to another.  A remote file is identified by
a host name, a colon and a file name (no spaces).
.I Scp
can copy files from remote hosts and to remote hosts.
.sp 1
.I Sshserve
is the server that services
.I ssh
calls from remote hosts. 
The 
.B -A
and
.B -c
options set valid authentication methods and ciphers
as in
.IR ssh ,
except that there is no
.B rsa
authentication method.
Unlike in
.IR ssh ,
the list is not ordered: the server presents a set and the client makes the choice.
The default sets are
.B tis
and
.B blowfish
.B rc4
.BR 3des .
By default, users start with the namespace defined in
.BR /lib/namespace .
Users in group
.B noworld
in
.B /adm/users
start with the namespace defined in
.BR /lib/namespace.noworld .
.I Sshserve
does not provide the TCP forwarding functionality used
by
.IR sshnet ,
because many Unix clients present
this capability in an insecure manner.
.PP
.I Sshserve
requires that
.IR factotum (4)
hold the host key,
identified by having attributes
.B proto=rsa
.BR service=sshserve .
To generate a host key:
.IP
.EX
auth/rsagen -t 'service=sshserve' >/mnt/factotum/ctl
.EE
.LP
To extract the public part of the host key in the form
used by SSH key rings:
.IP
.EX
grep 'service=sshserve' /mnt/factotum/ctl | auth/rsa2ssh
.EE
.SH FILES
.TP
.B /sys/lib/ssh/keyring
System key ring file containing public keys for remote ssh clients and servers.
.TP
.B /usr/\fIuser\fP/lib/keyring
Personal key ring file containing public keys for remote ssh clients and
servers.
.SH SOURCE
.B /sys/src/cmd/ssh
.SH "SEE ALSO"
.IR factotum (4),
.IR authsrv (6),
.IR rsa (8)