RFC 2289 (rfc2289) - Page 2 of 25
A One-Time Password System
Alternative Format: Original Text Document
RFC 2289 A One-Time Password System February 1998
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
protection against either "social engineering" or active attacks [9].
3.0 INTRODUCTION
There are two entities in the operation of the OTP one-time password
system. The generator must produce the appropriate one-time password
from the user's secret pass-phrase and from information provided in
the challenge from the server. The server must send a challenge that
includes the appropriate generation parameters to the generator, must
verify the one-time password received, must store the last valid
one-time password it received, and must store the corresponding one-
time password sequence number. The server must also facilitate the
changing of the user's secret pass-phrase in a secure manner.
The OTP system generator passes the user's secret pass-phrase, along
with a seed received from the server as part of the challenge,
through multiple iterations of a secure hash function to produce a
one-time password. After each successful authentication, the number
of secure hash function iterations is reduced by one. Thus, a unique
sequence of passwords is generated. The server verifies the one-time
password received from the generator by computing the secure hash
function once and comparing the result with the previously accepted
one-time password. This technique was first suggested by Leslie
Lamport [1].
4.0 REQUIREMENTS TERMINOLOGY
In this document, the words that are used to define the significance
of each particular requirement are usually capitalized. These words
are:
- MUST
This word or the adjective "REQUIRED" means that the item is an
absolute requirement of the specification.
Haller Standards Track