RFC 1760 (rfc1760) - Page 1 of 12
The S/KEY One-Time Password System
Alternative Format: Original Text Document
Network Working Group N. Haller
Request for Comments: 1760 Bellcore
Category: Informational February 1995
The S/KEY One-Time Password System
Status of this Memo
This memo provides information for the Internet community. This memo
does not specify an Internet standard of any kind. Distribution of
this memo is unlimited.
Abstract
This document describes the S/KEY* One-Time Password system as
released for public use by Bellcore and as described in reference
[3]. A reference implementation and documentation are available by
anonymous ftp from ftp.bellcore.com in the directories pub/nmh/...
Overview
One form of attack on computing system connected to the Internet is
eavesdropping on network connections to obtain login id's and
passwords of legitimate users. The captured login id and password
are, at a later time, used gain access to the system. The S/KEY
One-Time Password system is designed to counter this type of attack,
called a replay attack.
With the S/KEY system, only a single use password ever crosses the
network. The user's secret pass-phrase never crosses the network at
any time, including during login or when executing other commands
requiring authentication such as the UNIX commands passwd or su.
Thus, it is not vulnerable to eavesdropping/replay attacks. Added
security is provided by the property that no secret information need
be stored on any system, including the host being protected.
The S/KEY system protects against external passive attacks against
the authentication subsystem. It does not prevent a network
eavesdropper from gaining access to private information, and does not
provide protection against "inside jobs" or against active attacks
where the potential intruder as able to intercept and modify the
packet stream.
Haller