.\" $OpenBSD: skey.1,v 1.37 2022/03/31 17:27:27 naddy Exp $
.\"	@(#)skey.1	1.1 	10/28/93
.\"
.Dd $Mdocdate: March 31 2022 $
.Dt SKEY 1
.Os
.Sh NAME
.Nm skey , otp-md5 , otp-rmd160 , otp-sha1
.Nd respond to an OTP challenge
.Sh SYNOPSIS
.Nm skey
.Op Fl x
.Oo
.Fl md5 | rmd160 | sha1
.Oc
.Op Fl n Ar count
.Op Fl p Ar passphrase
.Ao Ar sequence# Ac Op /
.Ar key
.Sh DESCRIPTION
.Nm S/Key
is a procedure for using one-time passwords to authenticate access to
computer systems.
It uses 64 bits of information transformed by the
MD5, RIPEMD-160, or SHA1 algorithms.
The user supplies the 64 bits
in the form of 6 English words that are generated by a secure computer.
This implementation of
.Nm S/Key
is RFC 2289 compliant.
.Pp
Before using
.Nm skey ,
the system needs to be initialized using
.Xr skeyinit 1 ;
this will establish a secret passphrase.
After that, one-time passwords can be generated using
.Nm skey ,
which will prompt for the secret passphrase.
After a one-time password has been used to log in, it can no longer be used.
.Pp
When
.Nm skey
is invoked as
.Nm otp-method ,
.Nm skey
will use
.Ar method
as the hash function where
.Ar method
is currently one of md5, rmd160, or sha1.
.Pp
If you misspell your secret passphrase while running
.Nm skey ,
you will get a list of one-time passwords
that will not work, and no indication of the problem.
.Pp
Password sequence numbers count backwards.
You can enter the passwords using small letters, even though
.Nm skey
prints them capitalized.
.Pp
The options are as follows:
.Bl -tag -width Ds
.It Fl md5 | rmd160 | sha1
Selects the hash algorithm:
MD5, RMD-160 (160-bit Ripe Message Digest),
or SHA1 (NIST Secure Hash Algorithm Revision 1).
.It Fl n Ar count
Prints out
.Ar count
one-time passwords.
The default is to print one.
.It Fl p Ar passphrase
Uses
.Ar passphrase
as the secret passphrase.
Use of this option is discouraged as
your secret passphrase could be visible in a process listing.
.It Fl x
Causes output to be in hexadecimal instead of ASCII.
.El
.Sh EXAMPLES
.Bd -literal -offset indent
$ skey 99 th91334
Enter secret passphrase: \*(Ltyour secret passphrase is entered here\*(Gt
OMEN US HORN OMIT BACK AHOY
$
.Ed
.Sh SEE ALSO
.Xr login 1 ,
.Xr skeyaudit 1 ,
.Xr skeyinfo 1 ,
.Xr skeyinit 1 ,
.Xr skey 5 ,
.Xr skeyprune 8
.Sh STANDARDS
.Rs
.%A N. Haller
.%A C. Metz
.%A P. Nesser
.%A M. Straw
.%D February 1998
.%R RFC 2289
.%T A One-Time Password System
.Re
.Sh TRADEMARKS AND PATENTS
S/Key is a Trademark of Bellcore.
.Sh AUTHORS
.An Phil Karn
.An Neil M. Haller
.An John S. Walden
.An Scott Chasin