RFC 1938 (rfc1938) - Page 1 of 18
A One-Time Password System
Alternative Format: Original Text Document
Network Working Group N. Haller
Request for Comments: 1938 Bellcore
Category: Standards Track C. Metz
Kaman Sciences Corporation
May 1996
A One-Time Password System
Status of this Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
1.0 ABSTRACT
This document describes a one-time password authentication system
(OTP). The system provides authentication for system access (login)
and other applications requiring authentication that is secure
against passive attacks based on replaying captured reusable
passwords. OTP evolved from the S/KEY (S/KEY is a trademark of
Bellcore) One-Time Password System that was released by Bellcore and
is described in references [3] and [5].
2.0 OVERVIEW
One form of attack on networked computing systems is eavesdropping on
network connections to obtain authentication information such as the
login IDs and passwords of legitimate users. Once this information is
captured, it can be used at a later time to gain access to the
system. One-time password systems are designed to counter this type
of attack, called a "replay attack" [4].
The authentication system described in this document uses a secret
pass-phrase to generate a sequence of one-time (single use)
passwords. With this system, the user's secret pass-phrase never
needs to cross the network at any time such as during authentication
or during pass-phrase changes. Thus, it is not vulnerable to replay
attacks. Added security is provided by the property that no secret
information need be stored on any system, including the server being
protected.
The OTP 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
Haller & Metz Standards Track