- NetBSD Manual Pages
SKEY(1) NetBSD General Commands Manual SKEY(1)
Powered by man-cgi (2021-06-01).
Maintained for NetBSD
by Kimmo Suominen.
Based on man-cgi by Panagiotis Christias.
skey -- respond to an OTP challenge
skey [-n count] [-p password] [-t hash] [-x] sequence# [/] key
S/Key is a One Time Password (OTP) authentication system. It is intended
to be used when the communication channel between a user and host is not
secure (e.g. not encrypted or hardwired). Since each password is used
only once, even if it is "seen" by a hostile third party, it cannot be
used again to gain access to the host.
S/Key uses 64 bits of information, transformed by the MD4 algorithm into
6 English words. The user supplies the words to authenticate himself to
programs like login(1) or ftpd(8).
Example use of the S/Key program skey:
% skey 99 th91334
Enter password: <your secret password is entered here>
OMEN US HORN OMIT BACK AHOY
The string that is given back by skey can then be used to log into a sys-
The programs that are part of the S/Key system are:
skeyinit(1) used to set up your S/Key.
skey used to get the one time password(s).
skeyinfo(1) used to initialize the S/Key database for the specified
user. It also tells the user what the next challenge will
skeyaudit(1) used to inform users that they will soon have to rerun
When you run skeyinit(1) you inform the system of your secret password.
Running skey then generates the one-time password(s), after requiring
your secret password. If however, you misspell your secret password that
you have given to skeyinit(1) while running skey you will get a list of
passwords that will not work, and no indication about the problem.
Password sequence numbers count backward from 99. You can enter the
passwords using small letters, even though skey prints them capitalized.
The -n count argument asks for count password sequences to be printed out
ending with the requested sequence number.
The hash algorithm is selected using the -t hash option, possible choices
here are md4, md5 or sha1.
The -p password allows the user to specify the S/Key password on the com-
To output the S/Key list in hexadecimal instead of words, use the -x
Initialize generation of one time passwords:
Password: <normal login password>
Enter secret password: <new secret password>
Again secret password: <new secret password again>
ID username s/key is 99 host12345
Next login password: SOME SIX WORDS THAT WERE COMPUTED
Produce a list of one time passwords to take with to a conference:
host% skey -n 3 99 host12345
Enter secret password: <secret password as used with skeyinit>
97: NOSE FOOT RUSH FEAR GREY JUST
98: YAWN LEO DEED BIND WACK BRAE
99: SOME SIX WORDS THAT WERE COMPUTED
Logging in to a host where skey is installed:
host% telnet host
Password [s/key 97 host12345]:
Note that the user can use either his/her S/Key password at the prompt
but also the normal one unless the -s flag is given to login(1).
login(1), skeyaudit(1), skeyinfo(1), skeyinit(1), ftpd(8)
TRADEMARKS AND PATENTS
S/Key is a trademark of Bellcore.
Neil M. Haller
John S. Walden
NetBSD 5.1 July 25, 2001 NetBSD 5.1