The Free On-line Dictionary of Computing (30 December 2018):
One-Time Password
S/Key
(OTP) A security system that requires a new
password every time a user authenticates themselves, thus
protecting against an intruder replaying an intercepted
password. OTP generates passwords using either the MD4 or
MD5 hashing algorithms.
The equivalent term "S/Key", developed by Bellcore, is a
trademark of Telcordia Technologies, so the name OTP is used
increasingly.
See RFC 1760 - "The S/KEY One-Time Password System" and RFC
1938 - "A One-Time Password System".
(http://cs.umd.edu/~harry/jotp/).
(2000-01-31)