NAME

skey — respond to an OTP challenge

SYNOPSIS

skey	[-n count] [-p password] [-t hash] [-x] sequence# [/] key

DESCRIPTION

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 system.

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 be.

skeyaudit(1)

used to inform users that they will soon have to rerun skeyinit(1).

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 command line.

To output the S/Key list in hexadecimal instead of words, use the -x option.

EXAMPLES

Initialize generation of one time passwords:

host% skeyinit 
Password: <normal login password> 
[Adding username] 
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 
 
login: <username> 
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).

SEE ALSO

login(1), skeyaudit(1), skeyinfo(1), skeyinit(1), ftpd(8)

RFC 2289

TRADEMARKS AND PATENTS

S/Key is a trademark of Bellcore.

AUTHORS

Phil Karn Neil M. Haller John S. Walden Scott Chasin