<pre>Network Working Group                                        N. Haller
Request for Comments: 2289                                    Bellcore
Obsoletes: <a href="./rfc1938">1938</a>                                                C. Metz
Category: Standards Track                   Kaman Sciences Corporation
                                                             P. Nesser
                                            Nesser &amp; Nesser Consulting
                                                              M. Straw
                                                              Bellcore
                                                         February 1998


                       <span class="h1">A One-Time Password System</span>

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.

Copyright Notice

   Copyright (C) The Internet Society (1998).  All Rights Reserved.

<span class="h3"><a class="selflink" id="section-1.0" href="#section-1.0">1.0</a> ABSTRACT</span>

   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 [<a href="#ref-3" title="&quot;The S/KEY One-Time Password System&quot;">3</a>] and [<a href="#ref-5" title="&quot;The S/KEY One-Time Password System&quot;">5</a>].

<span class="h3"><a class="selflink" id="section-2.0" href="#section-2.0">2.0</a> OVERVIEW</span>

   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" [<a href="#ref-4" title="&quot;On Internet Authentication&quot;">4</a>].

   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



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   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 [<a href="#ref-9" title="&quot;IP Spoofing and Hijacked Terminal Connections&quot;">9</a>].

<span class="h3"><a class="selflink" id="section-3.0" href="#section-3.0">3.0</a> INTRODUCTION</span>

   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 [<a href="#ref-1" title="&quot;Password Authentication with Insecure Communication&quot;">1</a>].

<span class="h3"><a class="selflink" id="section-4.0" href="#section-4.0">4.0</a> REQUIREMENTS TERMINOLOGY</span>

   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.








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     - SHOULD

       This word or the adjective "RECOMMENDED" means that there might
       exist valid reasons in particular circumstances to ignore this
       item, but the full implications should be understood and the case
       carefully weighed before taking a different course.

     - MAY

       This word or the adjective "OPTIONAL" means that this item is
       truly optional.  One vendor might choose to include the item
       because a particular marketplace requires it or because it
       enhances the product, for example; another vendor may omit the
       same item.

<span class="h3"><a class="selflink" id="section-5.0" href="#section-5.0">5.0</a> SECURE HASH FUNCTION</span>

   The security of the OTP system is based on the non-invertability of a
   secure hash function. Such a function must be tractable to compute in
   the forward direction, but computationally infeasible to invert.

   The interfaces are currently defined for three such hash algorithms,
   MD4 [<a href="#ref-2" title="&quot;The MD4 Message-Digest Algorithm&quot;">2</a>] and MD5 [<a href="#ref-6" title="&quot;The MD5 Message-Digest Algorithm&quot;">6</a>] by Ronald Rivest, and SHA [<a href="#ref-7" title="&quot;Announcing the Secure Hash Standard&quot;">7</a>] by NIST.  All
   conforming implementations of both server and generators MUST support
   MD5.  They SHOULD support SHA and MAY also support MD4.  Clearly, the
   generator and server must use the same algorithm in order to
   interoperate. Other hash algorithms may be specified for use with
   this system by publishing the appropriate interfaces.

   The secure hash algorithms listed above have the property that they
   accept an input that is arbitrarily long and produce a fixed size
   output. The OTP system folds this output to 64 bits using the
   algorithms in the <a href="#appendix-A">Appendix A</a>. 64 bits is also the length of the one-
   time passwords. This is believed to be long enough to be secure and
   short enough to be entered manually (see below, Form of Output) when
   necessary.

<span class="h3"><a class="selflink" id="section-6.0" href="#section-6.0">6.0</a> GENERATION OF ONE-TIME PASSWORDS</span>

   This section describes the generation of the one-time passwords.
   This process consists of an initial step in which all inputs are
   combined, a computation step where the secure hash function is
   applied a specified number of times, and an output function where the
   64 bit one-time password is converted to a human readable form.

   <a href="#appendix-C">Appendix C</a> contains examples of the outputs given a collection of
   inputs.  It provides implementors with a means of verification the
   use of these algorithms.



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   Initial Step

   In principle, the user's secret pass-phrase may be of any length. To
   reduce the risk from techniques such as exhaustive search or
   dictionary attacks, character string pass-phrases MUST contain at
   least 10 characters (see Form of Inputs below).  All implementations
   MUST support a pass-phrases of at least 63 characters.  The secret
   pass-phrase is frequently, but is not required to be, textual
   information provided by a user.

   In this step, the pass phrase is concatenated with a seed that is
   transmitted from the server in clear text. This non-secret seed
   allows clients to use the same secret pass-phrase on multiple
   machines (using different seeds) and to safely recycle their secret
   pass-phrases by changing the seed.

   The result of the concatenation is passed through the secure hash
   function and then is reduced to 64 bits using one of the function
   dependent algorithms shown in <a href="#appendix-A">Appendix A</a>.

   Computation Step

   A sequence of one-time passwords is produced by applying the secure
   hash function multiple times to the output of the initial step
   (called S). That is, the first one-time password to be used is
   produced by passing S through the secure hash function a number of
   times (N) specified by the user. The next one-time password to be
   used is generated by passing S though the secure hash function N-1
   times. An eavesdropper who has monitored the transmission of a one-
   time password would not be able to generate the next required
   password because doing so would mean inverting the hash function.

   Form of Inputs

   The secret pass-phrase is seen only by the OTP generator. To allow
   interchangeability of generators, all generators MUST support a
   secret pass-phrase of 10 to 63 characters. Implementations MAY
   support a longer pass-phrase, but such implementations risk the loss
   of interchangeability with implementations supporting only the
   minimum.

   The seed MUST consist of purely alphanumeric characters and MUST be
   of one to 16 characters in length. The seed is a string of characters
   that MUST not contain any blanks and SHOULD consist of strictly
   alphanumeric characters from the ISO-646 Invariant Code Set.  The
   seed MUST be case insensitive and MUST be internally converted to
   lower case before it is processed.




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   The sequence number and seed together constitute a larger unit of
   data called the challenge. The challenge gives the generator the
   parameters it needs to calculate the correct one-time password from
   the secret pass-phrase. The challenge MUST be in a standard syntax so
   that automated generators can recognize the challenge in context and
   extract these parameters. The syntax of the challenge is:

           otp-&lt;algorithm identifier&gt; &lt;sequence integer&gt; &lt;seed&gt;

   The three tokens MUST be separated by a white space (defined as any
   number of spaces and/or tabs) and the entire challenge string MUST be
   terminated with either a space or a new line. The string "otp-" MUST
   be in lower case.  The algorithm identifier is case sensitive (the
   existing identifiers are all lower case), and the seed is case
   insensitive and converted before use to lower case.  If additional
   algorithms are defined, appropriate identifiers (short, but not
   limited to three or four characters) must be defined. The currently
   defined algorithm identifiers are:

       md4        MD4 Message Digest
       md5        MD5 Message Digest
       sha1       NIST Secure Hash Algorithm Revision 1

   An example of an OTP challenge is:   otp-md5 487 dog2

   Form of Output

   The one-time password generated by the above procedure is 64 bits in
   length. Entering a 64 bit number is a difficult and error prone
   process. Some generators insert this password into the input stream
   and some others make it available for system "cut and paste." Still
   other arrangements require the one-time password to be entered
   manually. The OTP system is designed to facilitate this manual entry
   without impeding automatic methods. The one-time password therefore
   MAY be converted to, and all servers MUST be capable of accepting it
   as, a sequence of six short (1 to 4 letter) easily typed words that
   only use characters from ISO-646 IVCS. Each word is chosen from a
   dictionary of 2048 words; at 11 bits per word, all one-time passwords
   may be encoded.

   The two extra bits in this encoding are used to store a checksum.
   The 64 bits of key are broken down into pairs of bits, then these
   pairs are summed together. The two least significant bits of this sum
   are encoded in the last two bits of the six word sequence with the
   least significant bit of the sum as the last bit encoded. All OTP
   generators MUST calculate this checksum and all OTP servers MUST
   verify this checksum explicitly as part of the operation of decoding
   this representation of the one-time password.



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   Generators that produce the six-word format MUST present the words in
   upper case with single spaces used as separators. All servers MUST
   accept six-word format without regard to case and white space used as
   a separator. The two lines below represent the same one-time
   password.  The first is valid as output from a generator and as input
   a server, the second is valid only as human input to a server.

            OUST COAT FOAL MUG BEAK TOTE
            oust coat foal  mug  beak  tote

     Interoperability requires that all OTP servers and generators use
     the same dictionary. The standard dictionary was originally
     specified in the "S/KEY One Time Password System" that is described
     in <a href="./rfc1760">RFC 1760</a> [<a href="#ref-5" title="&quot;The S/KEY One-Time Password System&quot;">5</a>].  This dictionary is included in this document as
     <a href="#appendix-D">Appendix D</a>.

     To facilitate the implementation of smaller generators, hexadecimal
     output is an acceptable alternative for the presentation of the
     one-time password. All implementations of the server software MUST
     accept case-insensitive hexadecimal as well as six-word format. The
     hexadecimal digits may be separated by white space so servers are
     REQUIRED to ignore all white space.  If the representation is
     partitioned by white space, leading zeros must be retained.
     Examples of hexadecimal format are:

           Representation                Value

           3503785b369cda8b              0x3503785b369cda8b
           e5cc a1b8 7c13 096b           0xe5cca1b87c13096b
           C7 48 90 F4 27 7B A1 CF       0xc74890f4277ba1cf
           47 9 A68 28 4C 9D 0 1BC       0x479a68284c9d01bc

   In addition to accepting six-word and hexadecimal encodings of the
   64 bit one-time password, servers SHOULD accept the alternate
   dictionary encoding described in <a href="#appendix-B">Appendix B</a>.  The six words in this
   encoding MUST not overlap the set of words in the standard
   dictionary.  To avoid ambiguity with the hexadecimal representation,
   words in the alternate dictionary MUST not be comprised solely of
   the letters A-F.  Decoding words thus encoded does not require any
   knowledge of the alternative dictionary used so the acceptance of
   any alternate dictionary implies the acceptance of all alternate
   dictionaries.  Words in the alternative dictionaries are case
   sensitive.  Generators and servers MUST preserve the case in the
   processing of these words.

   In summary, all conforming servers MUST accept six-word input that
   uses the Standard Dictionary (<a href="./rfc1760">RFC 1760</a> and <a href="#appendix-D">Appendix D</a>), MUST accept
   hexadecimal encoding, and SHOULD accept six-word input that uses the



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   Alternative Dictionary technique (Appendix B).  As there is a remote
   possibility that a hexadecimal encoding of a one-time password will
   look like a valid six-word standard dictionary encoding, all
   implementations MUST use the following scheme.  If a six-word
   encoded one-time password is valid, it is accepted.  Otherwise, if
   the one-time password can be interpreted as hexadecimal, and with
   that decoding it is valid, then it is accepted.

<span class="h3"><a class="selflink" id="section-7.0" href="#section-7.0">7.0</a> VERIFICATION OF ONE-TIME PASSWORDS</span>

   An application on the server system that requires OTP authentication
   is expected to issue an OTP challenge as described above. Given the
   parameters from this challenge and the secret pass-phrase, the
   generator can compute (or lookup) the one-time password that is
   passed to the server to be verified.

   The server system has a database containing, for each user, the
   one-time password from the last successful authentication or the
   first OTP of a newly initialized sequence. To authenticate the user,
   the server decodes the one-time password received from the generator
   into a 64-bit key and then runs this key through the secure hash
   function once. If the result of this operation matches the stored
   previous OTP, the authentication is successful and the accepted
   one-time password is stored for future use.

<span class="h3"><a class="selflink" id="section-8.0" href="#section-8.0">8.0</a> PASS-PHRASE CHANGES</span>

   Because the number of hash function applications executed by the
   generator decreases by one each time, at some point the user must
   reinitialize the system or be unable to authenticate.

   Although some installations may not permit users to initialize
   remotely, implementations MUST provide a means to do so that does
   not reveal the user's secret pass-phrase.  One way is to provide a
   means to reinitialize the  sequence through explicit specification
   of the first one-time password.

   When the sequence of one-time passwords is reinitialized,
   implementations MUST verify that the seed or the pass-phrase is
   changed.  Installations SHOULD discourage any operation that sends
   the secret pass-phrase over a network in clear-text as such practice
   defeats the concept of a one-time password.

   Implementations MAY use the following technique for
   [re]initialization:






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      o  The user picks a new seed and hash count (default values may
         be offered).  The user provides these, along with the
         corresponding generated one-time password, to the host system.

      o  The user MAY also provide the corresponding generated one
         time password for count-1 as an error check.

      o  The user SHOULD provide the generated one-time password for
         the old seed and old hash count to protect an idle terminal
         or workstation (this implies that when the count is 1, the
         user can login but cannot then change the seed or count).

   In the future a specific protocol may be defined for
   reinitialization that will permit smooth and possibly automated
   interoperation of all hosts and generators.

<span class="h3"><a class="selflink" id="section-9.0" href="#section-9.0">9.0</a> PROTECTION AGAINST RACE ATTACK</span>

   All conforming server implementations MUST protect against the race
   condition described in this section.  A defense against this attack
   is outlined; implementations MAY use this approach or MAY select an
   alternative defense.

   It is possible for an attacker to listen to most of a one-time
   password, guess the remainder, and then race the legitimate user to
   complete the authentication.  Multiple guesses against the last word
   of the six-word format are likely to succeed.

   One possible defense is to prevent a user from starting multiple
   simultaneous authentication sessions. This means that once the
   legitimate user has initiated authentication, an attacker would be
   blocked until the first authentication process has completed.  In
   this approach, a timeout is necessary to thwart a denial of service
   attack.

<span class="h3"><a class="selflink" id="section-10.0" href="#section-10.0">10.0</a> SECURITY CONSIDERATIONS</span>

   This entire document discusses an authentication system that
   improves security by limiting the danger of eavesdropping/replay
   attacks that have been used against simple password systems [<a href="#ref-4" title="&quot;On Internet Authentication&quot;">4</a>].

   The use of the OTP system only provides protections against passive
   eavesdropping/replay attacks.  It does not provide for the privacy
   of transmitted data, and it does not provide protection against
   active attacks such as session hijacking that are known to be
   present in the current Internet [<a href="#ref-9" title="&quot;IP Spoofing and Hijacked Terminal Connections&quot;">9</a>].  The use of IP Security
   (IPsec), see [<a href="#ref-10" title="&quot;Security Architecture for the Internet Protocol&quot;">10</a>], [<a href="#ref-11" title="&quot;IP Authentication Header&quot;">11</a>], and [<a href="#ref-12" title="&quot;IP Encapsulating Security Payload (ESP)&quot;">12</a>] is recommended to protect against
   TCP session hijacking.



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   The success of the OTP system to protect host systems is dependent
   on the non-invertability of the secure hash functions used.  To our
   knowledge, none of the hash algorithms have been broken, but it is
   generally believed [<a href="#ref-6" title="&quot;The MD5 Message-Digest Algorithm&quot;">6</a>] that MD4 is not as strong as MD5.  If a
   server supports multiple hash algorithms, it is only as secure as
   the weakest algorithm.

<span class="h3"><a class="selflink" id="section-11.0" href="#section-11.0">11.0</a> ACKNOWLEDGMENTS</span>

   The idea behind OTP authentication was first proposed by Leslie
   Lamport [<a href="#ref-1" title="&quot;Password Authentication with Insecure Communication&quot;">1</a>]. Bellcore's S/KEY system, from which OTP is derived, was
   proposed by Phil Karn, who also wrote most of the Bellcore reference
   implementation.

<span class="h3"><a class="selflink" id="section-12.0" href="#section-12.0">12.0</a> REFERENCES</span>

   [<a id="ref-1">1</a>]  Leslie Lamport, "Password Authentication with Insecure
        Communication", Communications of the ACM 24.11 (November
        1981), 770-772

   [<a id="ref-2">2</a>]  Rivest, R., "The MD4 Message-Digest Algorithm", <a href="./rfc1320">RFC 1320</a>,
        April 1992.

   [<a id="ref-3">3</a>]  Neil Haller, "The S/KEY One-Time Password System", Proceedings
        of the ISOC Symposium on Network and Distributed System
        Security, February 1994, San Diego, CA

   [<a id="ref-4">4</a>]  Haller, N., and R. Atkinson, "On Internet Authentication",
        <a href="./rfc1704">RFC 1704</a>, October 1994.

   [<a id="ref-5">5</a>]  Haller, N., "The S/KEY One-Time Password System",
        <a href="./rfc1760">RFC 1760</a>, February 1995.

   [<a id="ref-6">6</a>]  Rivest, R., "The MD5 Message-Digest Algorithm", <a href="./rfc1321">RFC 1321</a>,
        April 1992.

   [<a id="ref-7">7</a>]  National Institute of Standards and Technology (NIST),
        "Announcing the Secure Hash Standard", FIPS 180-1, U.S.
        Department of Commerce, April 1995.

   [<a id="ref-8">8</a>]  International Standard - Information Processing -- ISO 7-bit
        coded character set for information interchange (Invariant Code
        Set), ISO-646, International Standards Organization, Geneva,
        Switzerland, 1983







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   [<a id="ref-9">9</a>]  Computer Emergency Response Team (CERT), "IP Spoofing and
        Hijacked Terminal Connections", CA-95:01, January 1995.
        Available via anonymous ftp from info.cert.org in
        /pub/cert_advisories.

   [<a id="ref-10">10</a>] Atkinson, R., "Security Architecture for the Internet Protocol",
        <a href="./rfc1825">RFC 1825</a>, August 1995.

   [<a id="ref-11">11</a>] Atkinson, R., "IP Authentication Header", <a href="./rfc1826">RFC 1826</a>, August
        1995.

   [<a id="ref-12">12</a>] Atkinson, R., "IP Encapsulating Security Payload (ESP)", <a href="./rfc1827">RFC</a>
        <a href="./rfc1827">1827</a>, August 1995.






































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<span class="h3"><a class="selflink" id="section-13.0" href="#section-13.0">13.0</a> AUTHORS' ADDRESSES</span>

   Neil Haller
   Bellcore
   MCC 1C-265B
   445 South Street
   Morristown, NJ, 07960-6438, USA

   Phone: +1 201 829-4478
   Fax:   +1 201 829-2504
   EMail: nmh@bellcore.com


   Craig Metz
   Kaman Sciences Corporation
   For NRL Code 5544
   4555 Overlook Avenue, S.W.
   Washington, DC, 20375-5337, USA

   Phone: +1 202 404-7122
   Fax:   +1 202 404-7942
   EMail: cmetz@cs.nrl.navy.mil


   Philip J. Nesser II
   Nesser &amp; Nesser Consulting
   13501 100th Ave NE
   Suite 5202
   Kirkland, WA 98034, USA

   Phone: +1 206 481 4303
   EMail: pjnesser@martigny.ai.mit.edu


   Mike Straw
   Bellcore
   RRC 1A-225
   445 Hoes Lane
   Piscataway, NJ 08854-4182

   Phone:  +1 908 699-5212
   EMail:  mess@bellcore.com









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Appendix A  -  Interfaces to Secure Hash Algorithms

   Original interoperability tests provided valuable insights into the
   subtle problems which occur when converting protocol specifications
   into running code.  In particular, the manipulation of bit ordered
   data is dependent on the architecture of the hardware, specifically
   the way in which a computer stores multi-byte data.  The method is
   typically called big or little "endian."  A big endian machine stores
   data with the most significant byte first, while a little endian
   machine stores the least significant byte first.  Thus, on a big
   endian machine data is stored left to right, while little endian
   machines store data right to left.

   For example, the four byte value 0x11AABBCC is stored in a big endian
   machine as the following series of four bytes, "0x11", "0xAA",
   "0xBB", and "0xCC", while on a little endian machine the value would
   be stored as "0xCC", "0xBB", "0xAA", and "0x11".

   For historical reasons, and to promote interoperability with existing
   implementations, it was decided that ALL hashes incorporated into the
   OTP protocol MUST store the output of their hash function in LITTLE
   ENDIAN format BEFORE the bit folding to 64 bits occurs.  This is done
   in the implementations of MD4 and MD5 (see references [<a href="#ref-2" title="&quot;The MD4 Message-Digest Algorithm&quot;">2</a>] and [<a href="#ref-6" title="&quot;The MD5 Message-Digest Algorithm&quot;">6</a>]),
   while it must be explicitly done for the implementation of SHA1 (see
   reference [<a href="#ref-7" title="&quot;Announcing the Secure Hash Standard&quot;">7</a>]).

   Any future hash functions implemented into the OTP protocol SHOULD
   provide a similar reference fragment of code to allow independent
   implementations to operate successfully.


   MD4 Message Digest (see reference [<a href="#ref-2" title="&quot;The MD4 Message-Digest Algorithm&quot;">2</a>])

     MD4_CTX md;
     unsigned char result[16];

     strcpy(buf, seed);     /* seed must be in lower case */
     strcat(buf, passwd);
     MD4Init(&amp;md);
     MD4Update(&amp;md, (unsigned char *)buf, strlen(buf));
     MD4Final(result, &amp;md);

     /* Fold the 128 bit result to 64 bits */
     for (i = 0; i &lt; 8; i++)
             result[i] ^= result[i+8];






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<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-1-13" ></span>
<span class="grey"><a href="./rfc2289">RFC 2289</a>               A One-Time Password System          February 1998</span>


MD5 Message Digest (see reference [<a href="#ref-6" title="&quot;The MD5 Message-Digest Algorithm&quot;">6</a>])

     MD5_CTX md;
     unsigned char result[16];
     strcpy(buf, seed);     /* seed must be in lower case */
     strcat(buf, passwd);
     MD5Init(&amp;md);
     MD5Update(&amp;md, (unsigned char *)buf, strlen(buf));
     MD5Final(result, &amp;md);

     /* Fold the 128 bit result to 64 bits */
     for (i = 0; i &lt; 8; i++)
             result[i] ^= result[i+8];


SHA Secure Hash Algorithm (see reference [<a href="#ref-7" title="&quot;Announcing the Secure Hash Standard&quot;">7</a>])

     SHA_INFO sha;
     unsigned char result[16];
     strcpy(buf, seed);     /* seed must be in lower case */
     strcat(buf, passwd);
     sha_init(&amp;sha);
     sha_update(&amp;sha, (unsigned char *)buf, strlen(buf));
     sha_final(&amp;sha);       /* NOTE:  no result buffer */

     /* Fold the 160 bit result to 64 bits */
     sha.digest[0] ^= sha.digest[2];
     sha.digest[1] ^= sha.digest[3];
     sha.digest[0] ^= sha.digest[4];

     /*
      * copy the resulting 64 bits to the result buffer in little endian
      * fashion (analogous to the way MD4Final() and MD5Final() do).
      */
     for (i = 0, j = 0; j &lt; 8; i++, j += 4)
     {
             result[j]   = (unsigned char)(sha.digest[i] &amp; 0xff);
             result[j+1] = (unsigned char)((sha.digest[i] &gt;&gt; 8) &amp; 0xff);
             result[j+2] = (unsigned char)((sha.digest[i] &gt;&gt; 16) &amp; 0xff);
             result[j+3] = (unsigned char)((sha.digest[i] &gt;&gt; 24) &amp; 0xff);
     }










<span class="grey">Haller                      Standards Track                    [Page 13]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-1-14" ></span>
<span class="grey"><a href="./rfc2289">RFC 2289</a>               A One-Time Password System          February 1998</span>


Appendix B   -   Alternative Dictionary Algorithm

   The purpose of alternative dictionary encoding of the OTP one-time
   password is to allow the use of language specific or friendly words.
   As case translation is not always well defined, the alternative
   dictionary encoding is case sensitive.  Servers SHOULD accept this
   encoding in addition to the standard 6-word and hexadecimal
   encodings.


   GENERATOR ENCODING USING AN ALTERNATE DICTIONARY

     The standard 6-word encoding uses the placement of a word in the
     dictionary to represent an 11-bit number. The 64-bit one-time
     password can then be represented by six words.

     An alternative dictionary of 2048 words may be created such that
     each word W and position of the word in the dictionary N obey the
     relationship:

             alg( W ) % 2048 == N
     where
             alg is the hash algorithm used (e.g. MD4, MD5, SHA1).

     In addition, no words in the standard dictionary may be chosen.

     The generator expands the 64-bit one-time password to 66 bits by
     computing parity as with the standard 6-word encoding.  The six 11-
     bit numbers are then converted to words using the dictionary that
     was created such that the above relationship holds.

   SERVER DECODING OF ALTERNATE DICTIONARY ONE-TIME PASSWORDS

     The server accepting alternative dictionary encoding converts each
     word to an 11-bit number using the above encoding. These numbers
     are then used in the same way as the decoded standard dictionary
     words to form the 66-bit one-time password.

     The server does not need to have access to the alternate dictionary
     that was used to create the one-time password it is authenticating.
     This is because the decoding from word to 11-bit number does not
     make any use of the dictionary.  As a result of the independence of
     the dictionary, a server accepting one alternate dictionary accept
     all alternate dictionaries.







<span class="grey">Haller                      Standards Track                    [Page 14]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-1-15" ></span>
<span class="grey"><a href="./rfc2289">RFC 2289</a>               A One-Time Password System          February 1998</span>


Appendix C  -  OTP Verification Examples

   This appendix provides a series of inputs and correct outputs for all
   three of the defined OTP cryptographic hashes, specifically MD4, MD5,
   and SHA1.  This document is intended to be used by developers for
   interoperability checks when creating generators or servers.  Output
   is provided in both hexadecimal notation and the six word encoding
   documented in <a href="#appendix-D">Appendix D</a>.

   GENERAL CHECKS

   Note that the output given for these checks is not intended to be
   taken literally, but describes the type of action that should be
   taken.

   Pass Phrase Length

 Input:
   Pass Phrase: Too_short
   Seed: iamvalid
   Count: 99
   Hash: ANY
 Output:
   ERROR:  Pass Phrase too short

 Input:
   Pass Phrase:
     1234567890123456789012345678901234567890123456789012345678901234
   Seed: iamvalid
   Count: 99
   Hash: ANY
 Output:
   WARNING: Pass Phrase longer than the recommended maximum length of
63

Seed Values

 Input:
   Pass Phrase:  A_Valid_Pass_Phrase
   Seed: Length_Okay
   Count: 99
   Hash: ANY
 Output:
   ERROR: Seed must be purely alphanumeric

 Input:
   Pass Phrase:  A_Valid_Pass_Phrase
   Seed: LengthOfSeventeen



<span class="grey">Haller                      Standards Track                    [Page 15]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-1-16" ></span>
<span class="grey"><a href="./rfc2289">RFC 2289</a>               A One-Time Password System          February 1998</span>


   Count: 99
   Hash: ANY

 Output:
   ERROR: Seed must be between 1 and 16 characters in length

 Input:
   Pass Phrase:  A_Valid_Pass_Phrase
   Seed: A Seed
   Count: 99
   Hash: ANY
 Output:
   ERROR: Seed must not contain any spaces

Parity Calculations

 Input:
   Pass Phrase: A_Valid_Pass_Phrase
   Seed: AValidSeed
   Count: 99
   Hash: MD5
 Output:
   Hex: 85c43ee03857765b
   Six Word(CORRECT):          FOWL KID MASH DEAD DUAL OAF
   Six Word(INCORRECT PARITY): FOWL KID MASH DEAD DUAL NUT
   Six Word(INCORRECT PARITY): FOWL KID MASH DEAD DUAL O
   Six Word(INCORRECT PARITY): FOWL KID MASH DEAD DUAL OAK
























<span class="grey">Haller                      Standards Track                    [Page 16]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span class="grey"><a href="./rfc2289">RFC 2289</a>               A One-Time Password System          February 1998</span>


MD4 ENCODINGS

Pass Phrase     Seed    Cnt Hex                 Six Word Format
========================================================================
This is a test. TeSt     0  D185 4218 EBBB 0B51
                                           ROME MUG FRED SCAN LIVE LACE
This is a test. TeSt     1  6347 3EF0 1CD0 B444
                                           CARD SAD MINI RYE COL KIN
This is a test. TeSt    99  C5E6 1277 6E6C 237A
                                           NOTE OUT IBIS SINK NAVE MODE
AbCdEfGhIjK     alpha1   0  5007 6F47 EB1A DE4E
                                           AWAY SEN ROOK SALT LICE MAP
AbCdEfGhIjK     alpha1   1  65D2 0D19 49B5 F7AB
                                           CHEW GRIM WU HANG BUCK SAID
AbCdEfGhIjK     alpha1  99  D150 C82C CE6F 62D1
                                           ROIL FREE COG HUNK WAIT COCA
OTP's are good  correct  0  849C 79D4 F6F5 5388
                                           FOOL STEM DONE TOOL BECK NILE
OTP's are good  correct  1  8C09 92FB 2508 47B1
                                           GIST AMOS MOOT AIDS FOOD SEEM
OTP's are good  correct 99  3F3B F4B4 145F D74B
                                           TAG SLOW NOV MIN WOOL KENO





























<span class="grey">Haller                      Standards Track                    [Page 17]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span class="grey"><a href="./rfc2289">RFC 2289</a>               A One-Time Password System          February 1998</span>


MD5 ENCODINGS

Pass Phrase     Seed    Cnt Hex                 Six Word Format
========================================================================
This is a test. TeSt     0  9E87 6134 D904 99DD
                                           INCH SEA ANNE LONG AHEM TOUR
This is a test. TeSt     1  7965 E054 36F5 029F
                                           EASE OIL FUM CURE AWRY AVIS
This is a test. TeSt    99  50FE 1962 C496 5880
                                           BAIL TUFT BITS GANG CHEF THY
AbCdEfGhIjK     alpha1   0  8706 6DD9 644B F206
                                           FULL PEW DOWN ONCE MORT ARC
AbCdEfGhIjK     alpha1   1  7CD3 4C10 40AD D14B
                                           FACT HOOF AT FIST SITE KENT
AbCdEfGhIjK     alpha1  99  5AA3 7A81 F212 146C
                                           BODE HOP JAKE STOW JUT RAP
OTP's are good  correct  0  F205 7539 43DE 4CF9
                                           ULAN NEW ARMY FUSE SUIT EYED
OTP's are good  correct  1  DDCD AC95 6F23 4937
                                           SKIM CULT LOB SLAM POE HOWL
OTP's are good  correct 99  B203 E28F A525 BE47
                                           LONG IVY JULY AJAR BOND LEE


SHA1 ENCODINGS

Pass Phrase     Seed    Cnt Hex                 Six Word Format
========================================================================
This is a test. TeSt     0  BB9E 6AE1 979D 8FF4
                                           MILT VARY MAST OK SEES WENT
This is a test. TeSt     1  63D9 3663 9734 385B
                                           CART OTTO HIVE ODE VAT NUT
This is a test. TeSt    99  87FE C776 8B73 CCF9
                                           GAFF WAIT SKID GIG SKY EYED
AbCdEfGhIjK     alpha1   0  AD85 F658 EBE3 83C9
                                           LEST OR HEEL SCOT ROB SUIT
AbCdEfGhIjK     alpha1   1  D07C E229 B5CF 119B
                                           RITE TAKE GELD COST TUNE RECK
AbCdEfGhIjK     alpha1  99  27BC 7103 5AAF 3DC6
                                           MAY STAR TIN LYON VEDA STAN
OTP's are good  correct  0  D51F 3E99 BF8E 6F0B
                                           RUST WELT KICK FELL TAIL FRAU
OTP's are good  correct  1  82AE B52D 9437 74E4
                                           FLIT DOSE ALSO MEW DRUM DEFY
OTP's are good  correct 99  4F29 6A74 FE15 67EC
                                           AURA ALOE HURL WING BERG WAIT





<span class="grey">Haller                      Standards Track                    [Page 18]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-4-19" ></span>
<span class="grey"><a href="./rfc2289">RFC 2289</a>               A One-Time Password System          February 1998</span>


Appendix D   -   Dictionary for Converting Between 6-Word and Binary Formats

   This dictionary is from the module put.c in the original Bellcore
   reference distribution.

{        "A",     "ABE",   "ACE",   "ACT",   "AD",    "ADA",   "ADD",
"AGO",   "AID",   "AIM",   "AIR",   "ALL",   "ALP",   "AM",    "AMY",
"AN",    "ANA",   "AND",   "ANN",   "ANT",   "ANY",   "APE",   "APS",
"APT",   "ARC",   "ARE",   "ARK",   "ARM",   "ART",   "AS",    "ASH",
"ASK",   "AT",    "ATE",   "AUG",   "AUK",   "AVE",   "AWE",   "AWK",
"AWL",   "AWN",   "AX",   "AYE",   "BAD",   "BAG",   "BAH",   "BAM",
"BAN",   "BAR",   "BAT",   "BAY",   "BE",    "BED",   "BEE",   "BEG",
"BEN",   "BET",   "BEY",   "BIB",   "BID",   "BIG",   "BIN",   "BIT",
"BOB",   "BOG",   "BON",   "BOO",   "BOP",   "BOW",   "BOY",   "BUB",
"BUD",   "BUG",   "BUM",   "BUN",   "BUS",   "BUT",   "BUY",   "BY",
"BYE",   "CAB",   "CAL",   "CAM",   "CAN",   "CAP",   "CAR",   "CAT",
"CAW",   "COD",   "COG",   "COL",   "CON",   "COO",   "COP",   "COT",
"COW",   "COY",   "CRY",   "CUB",   "CUE",   "CUP",   "CUR",   "CUT",
"DAB",   "DAD",   "DAM",   "DAN",   "DAR",   "DAY",   "DEE",   "DEL",
"DEN",   "DES",   "DEW",   "DID",   "DIE",   "DIG",   "DIN",   "DIP",
"DO",    "DOE",   "DOG",   "DON",   "DOT",   "DOW",   "DRY",   "DUB",
"DUD",   "DUE",   "DUG",   "DUN",   "EAR",   "EAT",   "ED",    "EEL",
"EGG",   "EGO",   "ELI",   "ELK",   "ELM",   "ELY",   "EM",    "END",
"EST",   "ETC",   "EVA",   "EVE",   "EWE",   "EYE",   "FAD",   "FAN",
"FAR",   "FAT",   "FAY",   "FED",   "FEE",   "FEW",   "FIB",   "FIG",
"FIN",   "FIR",   "FIT",   "FLO",   "FLY",   "FOE",   "FOG",   "FOR",
"FRY",   "FUM",   "FUN",   "FUR",   "GAB",   "GAD",   "GAG",   "GAL",
"GAM",   "GAP",   "GAS",   "GAY",   "GEE",   "GEL",   "GEM",   "GET",
"GIG",   "GIL",   "GIN",   "GO",    "GOT",   "GUM",   "GUN",   "GUS",
"GUT",   "GUY",   "GYM",   "GYP",   "HA",    "HAD",   "HAL",   "HAM",
"HAN",   "HAP",   "HAS",   "HAT",   "HAW",   "HAY",   "HE",    "HEM",
"HEN",   "HER",   "HEW",   "HEY",   "HI",    "HID",   "HIM",   "HIP",
"HIS",   "HIT",   "HO",   "HOB",   "HOC",   "HOE",   "HOG",   "HOP",
"HOT",   "HOW",   "HUB",   "HUE",   "HUG",   "HUH",   "HUM",   "HUT",
"I",     "ICY",   "IDA",   "IF",    "IKE",   "ILL",   "INK",   "INN",
"IO",    "ION",   "IQ",   "IRA",   "IRE",   "IRK",   "IS",    "IT",
"ITS",   "IVY",   "JAB",   "JAG",   "JAM",   "JAN",   "JAR",   "JAW",
"JAY",   "JET",   "JIG",   "JIM",   "JO",    "JOB",   "JOE",   "JOG",
"JOT",   "JOY",   "JUG",   "JUT",   "KAY",   "KEG",   "KEN",   "KEY",
"KID",   "KIM",   "KIN",   "KIT",   "LA",    "LAB",   "LAC",   "LAD",
"LAG",   "LAM",   "LAP",   "LAW",   "LAY",   "LEA",   "LED",   "LEE",
"LEG",   "LEN",   "LEO",   "LET",   "LEW",   "LID",   "LIE",   "LIN",
"LIP",   "LIT",   "LO",   "LOB",   "LOG",   "LOP",   "LOS",   "LOT",
"LOU",   "LOW",   "LOY",   "LUG",   "LYE",   "MA",    "MAC",   "MAD",
"MAE",   "MAN",   "MAO",   "MAP",   "MAT",   "MAW",   "MAY",   "ME",
"MEG",   "MEL",   "MEN",   "MET",   "MEW",   "MID",   "MIN",   "MIT",
"MOB",   "MOD",   "MOE",   "MOO",   "MOP",   "MOS",   "MOT",   "MOW",
"MUD",   "MUG",   "MUM",   "MY",    "NAB",   "NAG",   "NAN",   "NAP",



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<span class="grey"><a href="./rfc2289">RFC 2289</a>               A One-Time Password System          February 1998</span>


"NAT",   "NAY",   "NE",   "NED",   "NEE",   "NET",   "NEW",   "NIB",
"NIL",   "NIP",   "NIT",   "NO",    "NOB",   "NOD",   "NON",   "NOR",
"NOT",   "NOV",   "NOW",   "NU",    "NUN",   "NUT",   "O",     "OAF",
"OAK",   "OAR",   "OAT",   "ODD",   "ODE",   "OF",    "OFF",   "OFT",
"OH",    "OIL",   "OK",   "OLD",   "ON",    "ONE",   "OR",    "ORB",
"ORE",   "ORR",   "OS",   "OTT",   "OUR",   "OUT",   "OVA",   "OW",
"OWE",   "OWL",   "OWN",   "OX",    "PA",    "PAD",   "PAL",   "PAM",
"PAN",   "PAP",   "PAR",   "PAT",   "PAW",   "PAY",   "PEA",   "PEG",
"PEN",   "PEP",   "PER",   "PET",   "PEW",   "PHI",   "PI",    "PIE",
"PIN",   "PIT",   "PLY",   "PO",    "POD",   "POE",   "POP",   "POT",
"POW",   "PRO",   "PRY",   "PUB",   "PUG",   "PUN",   "PUP",   "PUT",
"QUO",   "RAG",   "RAM",   "RAN",   "RAP",   "RAT",   "RAW",   "RAY",
"REB",   "RED",   "REP",   "RET",   "RIB",   "RID",   "RIG",   "RIM",
"RIO",   "RIP",   "ROB",   "ROD",   "ROE",   "RON",   "ROT",   "ROW",
"ROY",   "RUB",   "RUE",   "RUG",   "RUM",   "RUN",   "RYE",   "SAC",
"SAD",   "SAG",   "SAL",   "SAM",   "SAN",   "SAP",   "SAT",   "SAW",
"SAY",   "SEA",   "SEC",   "SEE",   "SEN",   "SET",   "SEW",   "SHE",
"SHY",   "SIN",   "SIP",   "SIR",   "SIS",   "SIT",   "SKI",   "SKY",
"SLY",   "SO",    "SOB",   "SOD",   "SON",   "SOP",   "SOW",   "SOY",
"SPA",   "SPY",   "SUB",   "SUD",   "SUE",   "SUM",   "SUN",   "SUP",
"TAB",   "TAD",   "TAG",   "TAN",   "TAP",   "TAR",   "TEA",   "TED",
"TEE",   "TEN",   "THE",   "THY",   "TIC",   "TIE",   "TIM",   "TIN",
"TIP",   "TO",    "TOE",   "TOG",   "TOM",   "TON",   "TOO",   "TOP",
"TOW",   "TOY",   "TRY",   "TUB",   "TUG",   "TUM",   "TUN",   "TWO",
"UN",    "UP",    "US",   "USE",   "VAN",   "VAT",   "VET",   "VIE",
"WAD",   "WAG",   "WAR",   "WAS",   "WAY",   "WE",    "WEB",   "WED",
"WEE",   "WET",   "WHO",   "WHY",   "WIN",   "WIT",   "WOK",   "WON",
"WOO",   "WOW",   "WRY",   "WU",    "YAM",   "YAP",   "YAW",   "YE",
"YEA",   "YES",   "YET",   "YOU",   "ABED",  "ABEL",  "ABET",  "ABLE",
"ABUT",  "ACHE",  "ACID",  "ACME",  "ACRE",  "ACTA",  "ACTS",  "ADAM",
"ADDS",  "ADEN",  "AFAR",  "AFRO",  "AGEE",  "AHEM",  "AHOY",  "AIDA",
"AIDE",  "AIDS",  "AIRY",  "AJAR",  "AKIN",  "ALAN",  "ALEC",  "ALGA",
"ALIA",  "ALLY",  "ALMA",  "ALOE",  "ALSO",  "ALTO",  "ALUM",  "ALVA",
"AMEN",  "AMES",  "AMID",  "AMMO",  "AMOK",  "AMOS",  "AMRA",  "ANDY",
"ANEW",  "ANNA",  "ANNE",  "ANTE",  "ANTI",  "AQUA",  "ARAB",  "ARCH",
"AREA",  "ARGO",  "ARID",  "ARMY",  "ARTS",  "ARTY",  "ASIA",  "ASKS",
"ATOM",  "AUNT",  "AURA",  "AUTO",  "AVER",  "AVID",  "AVIS",  "AVON",
"AVOW",  "AWAY",  "AWRY",  "BABE",  "BABY",  "BACH",  "BACK",  "BADE",
"BAIL",  "BAIT",  "BAKE",  "BALD",  "BALE",  "BALI",  "BALK",  "BALL",
"BALM",  "BAND",  "BANE",  "BANG",  "BANK",  "BARB",  "BARD",  "BARE",
"BARK",  "BARN",  "BARR",  "BASE",  "BASH",  "BASK",  "BASS",  "BATE",
"BATH",  "BAWD",  "BAWL",  "BEAD",  "BEAK",  "BEAM",  "BEAN",  "BEAR",
"BEAT",  "BEAU",  "BECK",  "BEEF",  "BEEN",  "BEER",  "BEET",  "BELA",
"BELL",  "BELT",  "BEND",  "BENT",  "BERG",  "BERN",  "BERT",  "BESS",
"BEST",  "BETA",  "BETH",  "BHOY",  "BIAS",  "BIDE",  "BIEN",  "BILE",
"BILK",  "BILL",  "BIND",  "BING",  "BIRD",  "BITE",  "BITS",  "BLAB",
"BLAT",  "BLED",  "BLEW",  "BLOB",  "BLOC",  "BLOT",  "BLOW",  "BLUE",
"BLUM",  "BLUR",  "BOAR",  "BOAT",  "BOCA",  "BOCK",  "BODE",  "BODY",



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<span class="grey"><a href="./rfc2289">RFC 2289</a>               A One-Time Password System          February 1998</span>


"BOGY",  "BOHR",  "BOIL",  "BOLD",  "BOLO",  "BOLT",  "BOMB",  "BONA",
"BOND",  "BONE",  "BONG",  "BONN",  "BONY",  "BOOK",  "BOOM",  "BOON",
"BOOT",  "BORE",  "BORG",  "BORN",  "BOSE",  "BOSS",  "BOTH",  "BOUT",
"BOWL",  "BOYD",  "BRAD",  "BRAE",  "BRAG",  "BRAN",  "BRAY",  "BRED",
"BREW",  "BRIG",  "BRIM",  "BROW",  "BUCK",  "BUDD",  "BUFF",  "BULB",
"BULK",  "BULL",  "BUNK",  "BUNT",  "BUOY",  "BURG",  "BURL",  "BURN",
"BURR",  "BURT",  "BURY",  "BUSH",  "BUSS",  "BUST",  "BUSY",  "BYTE",
"CADY",  "CAFE",  "CAGE",  "CAIN",  "CAKE",  "CALF",  "CALL",  "CALM",
"CAME",  "CANE",  "CANT",  "CARD",  "CARE",  "CARL",  "CARR",  "CART",
"CASE",  "CASH",  "CASK",  "CAST",  "CAVE",  "CEIL",  "CELL",  "CENT",
"CERN",  "CHAD",  "CHAR",  "CHAT",  "CHAW",  "CHEF",  "CHEN",  "CHEW",
"CHIC",  "CHIN",  "CHOU",  "CHOW",  "CHUB",  "CHUG",  "CHUM",  "CITE",
"CITY",  "CLAD",  "CLAM",  "CLAN",  "CLAW",  "CLAY",  "CLOD",  "CLOG",
"CLOT",  "CLUB",  "CLUE",  "COAL",  "COAT",  "COCA",  "COCK",  "COCO",
"CODA",  "CODE",  "CODY",  "COED",  "COIL",  "COIN",  "COKE",  "COLA",
"COLD",  "COLT",  "COMA",  "COMB",  "COME",  "COOK",  "COOL",  "COON",
"COOT",  "CORD",  "CORE",  "CORK",  "CORN",  "COST",  "COVE",  "COWL",
"CRAB",  "CRAG",  "CRAM",  "CRAY",  "CREW",  "CRIB",  "CROW",  "CRUD",
"CUBA",  "CUBE",  "CUFF",  "CULL",  "CULT",  "CUNY",  "CURB",  "CURD",
"CURE",  "CURL",  "CURT",  "CUTS",  "DADE",  "DALE",  "DAME",  "DANA",
"DANE",  "DANG",  "DANK",  "DARE",  "DARK",  "DARN",  "DART",  "DASH",
"DATA",  "DATE",  "DAVE",  "DAVY",  "DAWN",  "DAYS",  "DEAD",  "DEAF",
"DEAL",  "DEAN",  "DEAR",  "DEBT",  "DECK",  "DEED",  "DEEM",  "DEER",
"DEFT",  "DEFY",  "DELL",  "DENT",  "DENY",  "DESK",  "DIAL",  "DICE",
"DIED",  "DIET",  "DIME",  "DINE",  "DING",  "DINT",  "DIRE",  "DIRT",
"DISC",  "DISH",  "DISK",  "DIVE",  "DOCK",  "DOES",  "DOLE",  "DOLL",
"DOLT",  "DOME",  "DONE",  "DOOM",  "DOOR",  "DORA",  "DOSE",  "DOTE",
"DOUG",  "DOUR",  "DOVE",  "DOWN",  "DRAB",  "DRAG",  "DRAM",  "DRAW",
"DREW",  "DRUB",  "DRUG",  "DRUM",  "DUAL",  "DUCK",  "DUCT",  "DUEL",
"DUET",  "DUKE",  "DULL",  "DUMB",  "DUNE",  "DUNK",  "DUSK",  "DUST",
"DUTY",  "EACH",  "EARL",  "EARN",  "EASE",  "EAST",  "EASY",  "EBEN",
"ECHO",  "EDDY",  "EDEN",  "EDGE",  "EDGY",  "EDIT",  "EDNA",  "EGAN",
"ELAN",  "ELBA",  "ELLA",  "ELSE",  "EMIL",  "EMIT",  "EMMA",  "ENDS",
"ERIC",  "EROS",  "EVEN",  "EVER",  "EVIL",  "EYED",  "FACE",  "FACT",
"FADE",  "FAIL",  "FAIN",  "FAIR",  "FAKE",  "FALL",  "FAME",  "FANG",
"FARM",  "FAST",  "FATE",  "FAWN",  "FEAR",  "FEAT",  "FEED",  "FEEL",
"FEET",  "FELL",  "FELT",  "FEND",  "FERN",  "FEST",  "FEUD",  "FIEF",
"FIGS",  "FILE",  "FILL",  "FILM",  "FIND",  "FINE",  "FINK",  "FIRE",
"FIRM",  "FISH",  "FISK",  "FIST",  "FITS",  "FIVE",  "FLAG",  "FLAK",
"FLAM",  "FLAT",  "FLAW",  "FLEA",  "FLED",  "FLEW",  "FLIT",  "FLOC",
"FLOG",  "FLOW",  "FLUB",  "FLUE",  "FOAL",  "FOAM",  "FOGY",  "FOIL",
"FOLD",  "FOLK",  "FOND",  "FONT",  "FOOD",  "FOOL",  "FOOT",  "FORD",
"FORE",  "FORK",  "FORM",  "FORT",  "FOSS",  "FOUL",  "FOUR",  "FOWL",
"FRAU",  "FRAY",  "FRED",  "FREE",  "FRET",  "FREY",  "FROG",  "FROM",
"FUEL",  "FULL",  "FUME",  "FUND",  "FUNK",  "FURY",  "FUSE",  "FUSS",
"GAFF",  "GAGE",  "GAIL",  "GAIN",  "GAIT",  "GALA",  "GALE",  "GALL",
"GALT",  "GAME",  "GANG",  "GARB",  "GARY",  "GASH",  "GATE",  "GAUL",
"GAUR",  "GAVE",  "GAWK",  "GEAR",  "GELD",  "GENE",  "GENT",  "GERM",



<span class="grey">Haller                      Standards Track                    [Page 21]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-4-22" ></span>
<span class="grey"><a href="./rfc2289">RFC 2289</a>               A One-Time Password System          February 1998</span>


"GETS",  "GIBE",  "GIFT",  "GILD",  "GILL",  "GILT",  "GINA",  "GIRD",
"GIRL",  "GIST",  "GIVE",  "GLAD",  "GLEE",  "GLEN",  "GLIB",  "GLOB",
"GLOM",  "GLOW",  "GLUE",  "GLUM",  "GLUT",  "GOAD",  "GOAL",  "GOAT",
"GOER",  "GOES",  "GOLD",  "GOLF",  "GONE",  "GONG",  "GOOD",  "GOOF",
"GORE",  "GORY",  "GOSH",  "GOUT",  "GOWN",  "GRAB",  "GRAD",  "GRAY",
"GREG",  "GREW",  "GREY",  "GRID",  "GRIM",  "GRIN",  "GRIT",  "GROW",
"GRUB",  "GULF",  "GULL",  "GUNK",  "GURU",  "GUSH",  "GUST",  "GWEN",
"GWYN",  "HAAG",  "HAAS",  "HACK",  "HAIL",  "HAIR",  "HALE",  "HALF",
"HALL",  "HALO",  "HALT",  "HAND",  "HANG",  "HANK",  "HANS",  "HARD",
"HARK",  "HARM",  "HART",  "HASH",  "HAST",  "HATE",  "HATH",  "HAUL",
"HAVE",  "HAWK",  "HAYS",  "HEAD",  "HEAL",  "HEAR",  "HEAT",  "HEBE",
"HECK",  "HEED",  "HEEL",  "HEFT",  "HELD",  "HELL",  "HELM",  "HERB",
"HERD",  "HERE",  "HERO",  "HERS",  "HESS",  "HEWN",  "HICK",  "HIDE",
"HIGH",  "HIKE",  "HILL",  "HILT",  "HIND",  "HINT",  "HIRE",  "HISS",
"HIVE",  "HOBO",  "HOCK",  "HOFF",  "HOLD",  "HOLE",  "HOLM",  "HOLT",
"HOME",  "HONE",  "HONK",  "HOOD",  "HOOF",  "HOOK",  "HOOT",  "HORN",
"HOSE",  "HOST",  "HOUR",  "HOVE",  "HOWE",  "HOWL",  "HOYT",  "HUCK",
"HUED",  "HUFF",  "HUGE",  "HUGH",  "HUGO",  "HULK",  "HULL",  "HUNK",
"HUNT",  "HURD",  "HURL",  "HURT",  "HUSH",  "HYDE",  "HYMN",  "IBIS",
"ICON",  "IDEA",  "IDLE",  "IFFY",  "INCA",  "INCH",  "INTO",  "IONS",
"IOTA",  "IOWA",  "IRIS",  "IRMA",  "IRON",  "ISLE",  "ITCH",  "ITEM",
"IVAN",  "JACK",  "JADE",  "JAIL",  "JAKE",  "JANE",  "JAVA",  "JEAN",
"JEFF",  "JERK",  "JESS",  "JEST",  "JIBE",  "JILL",  "JILT",  "JIVE",
"JOAN",  "JOBS",  "JOCK",  "JOEL",  "JOEY",  "JOHN",  "JOIN",  "JOKE",
"JOLT",  "JOVE",  "JUDD",  "JUDE",  "JUDO",  "JUDY",  "JUJU",  "JUKE",
"JULY",  "JUNE",  "JUNK",  "JUNO",  "JURY",  "JUST",  "JUTE",  "KAHN",
"KALE",  "KANE",  "KANT",  "KARL",  "KATE",  "KEEL",  "KEEN",  "KENO",
"KENT",  "KERN",  "KERR",  "KEYS",  "KICK",  "KILL",  "KIND",  "KING",
"KIRK",  "KISS",  "KITE",  "KLAN",  "KNEE",  "KNEW",  "KNIT",  "KNOB",
"KNOT",  "KNOW",  "KOCH",  "KONG",  "KUDO",  "KURD",  "KURT",  "KYLE",
"LACE",  "LACK",  "LACY",  "LADY",  "LAID",  "LAIN",  "LAIR",  "LAKE",
"LAMB",  "LAME",  "LAND",  "LANE",  "LANG",  "LARD",  "LARK",  "LASS",
"LAST",  "LATE",  "LAUD",  "LAVA",  "LAWN",  "LAWS",  "LAYS",  "LEAD",
"LEAF",  "LEAK",  "LEAN",  "LEAR",  "LEEK",  "LEER",  "LEFT",  "LEND",
"LENS",  "LENT",  "LEON",  "LESK",  "LESS",  "LEST",  "LETS",  "LIAR",
"LICE",  "LICK",  "LIED",  "LIEN",  "LIES",  "LIEU",  "LIFE",  "LIFT",
"LIKE",  "LILA",  "LILT",  "LILY",  "LIMA",  "LIMB",  "LIME",  "LIND",
"LINE",  "LINK",  "LINT",  "LION",  "LISA",  "LIST",  "LIVE",  "LOAD",
"LOAF",  "LOAM",  "LOAN",  "LOCK",  "LOFT",  "LOGE",  "LOIS",  "LOLA",
"LONE",  "LONG",  "LOOK",  "LOON",  "LOOT",  "LORD",  "LORE",  "LOSE",
"LOSS",  "LOST",  "LOUD",  "LOVE",  "LOWE",  "LUCK",  "LUCY",  "LUGE",
"LUKE",  "LULU",  "LUND",  "LUNG",  "LURA",  "LURE",  "LURK",  "LUSH",
"LUST",  "LYLE",  "LYNN",  "LYON",  "LYRA",  "MACE",  "MADE",  "MAGI",
"MAID",  "MAIL",  "MAIN",  "MAKE",  "MALE",  "MALI",  "MALL",  "MALT",
"MANA",  "MANN",  "MANY",  "MARC",  "MARE",  "MARK",  "MARS",  "MART",
"MARY",  "MASH",  "MASK",  "MASS",  "MAST",  "MATE",  "MATH",  "MAUL",
"MAYO",  "MEAD",  "MEAL",  "MEAN",  "MEAT",  "MEEK",  "MEET",  "MELD",
"MELT",  "MEMO",  "MEND",  "MENU",  "MERT",  "MESH",  "MESS",  "MICE",



<span class="grey">Haller                      Standards Track                    [Page 22]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-4-23" ></span>
<span class="grey"><a href="./rfc2289">RFC 2289</a>               A One-Time Password System          February 1998</span>


"MIKE",  "MILD",  "MILE",  "MILK",  "MILL",  "MILT",  "MIMI",  "MIND",
"MINE",  "MINI",  "MINK",  "MINT",  "MIRE",  "MISS",  "MIST",  "MITE",
"MITT",  "MOAN",  "MOAT",  "MOCK",  "MODE",  "MOLD",  "MOLE",  "MOLL",
"MOLT",  "MONA",  "MONK",  "MONT",  "MOOD",  "MOON",  "MOOR",  "MOOT",
"MORE",  "MORN",  "MORT",  "MOSS",  "MOST",  "MOTH",  "MOVE",  "MUCH",
"MUCK",  "MUDD",  "MUFF",  "MULE",  "MULL",  "MURK",  "MUSH",  "MUST",
"MUTE",  "MUTT",  "MYRA",  "MYTH",  "NAGY",  "NAIL",  "NAIR",  "NAME",
"NARY",  "NASH",  "NAVE",  "NAVY",  "NEAL",  "NEAR",  "NEAT",  "NECK",
"NEED",  "NEIL",  "NELL",  "NEON",  "NERO",  "NESS",  "NEST",  "NEWS",
"NEWT",  "NIBS",  "NICE",  "NICK",  "NILE",  "NINA",  "NINE",  "NOAH",
"NODE",  "NOEL",  "NOLL",  "NONE",  "NOOK",  "NOON",  "NORM",  "NOSE",
"NOTE",  "NOUN",  "NOVA",  "NUDE",  "NULL",  "NUMB",  "OATH",  "OBEY",
"OBOE",  "ODIN",  "OHIO",  "OILY",  "OINT",  "OKAY",  "OLAF",  "OLDY",
"OLGA",  "OLIN",  "OMAN",  "OMEN",  "OMIT",  "ONCE",  "ONES",  "ONLY",
"ONTO",  "ONUS",  "ORAL",  "ORGY",  "OSLO",  "OTIS",  "OTTO",  "OUCH",
"OUST",  "OUTS",  "OVAL",  "OVEN",  "OVER",  "OWLY",  "OWNS",  "QUAD",
"QUIT",  "QUOD",  "RACE",  "RACK",  "RACY",  "RAFT",  "RAGE",  "RAID",
"RAIL",  "RAIN",  "RAKE",  "RANK",  "RANT",  "RARE",  "RASH",  "RATE",
"RAVE",  "RAYS",  "READ",  "REAL",  "REAM",  "REAR",  "RECK",  "REED",
"REEF",  "REEK",  "REEL",  "REID",  "REIN",  "RENA",  "REND",  "RENT",
"REST",  "RICE",  "RICH",  "RICK",  "RIDE",  "RIFT",  "RILL",  "RIME",
"RING",  "RINK",  "RISE",  "RISK",  "RITE",  "ROAD",  "ROAM",  "ROAR",
"ROBE",  "ROCK",  "RODE",  "ROIL",  "ROLL",  "ROME",  "ROOD",  "ROOF",
"ROOK",  "ROOM",  "ROOT",  "ROSA",  "ROSE",  "ROSS",  "ROSY",  "ROTH",
"ROUT",  "ROVE",  "ROWE",  "ROWS",  "RUBE",  "RUBY",  "RUDE",  "RUDY",
"RUIN",  "RULE",  "RUNG",  "RUNS",  "RUNT",  "RUSE",  "RUSH",  "RUSK",
"RUSS",  "RUST",  "RUTH",  "SACK",  "SAFE",  "SAGE",  "SAID",  "SAIL",
"SALE",  "SALK",  "SALT",  "SAME",  "SAND",  "SANE",  "SANG",  "SANK",
"SARA",  "SAUL",  "SAVE",  "SAYS",  "SCAN",  "SCAR",  "SCAT",  "SCOT",
"SEAL",  "SEAM",  "SEAR",  "SEAT",  "SEED",  "SEEK",  "SEEM",  "SEEN",
"SEES",  "SELF",  "SELL",  "SEND",  "SENT",  "SETS",  "SEWN",  "SHAG",
"SHAM",  "SHAW",  "SHAY",  "SHED",  "SHIM",  "SHIN",  "SHOD",  "SHOE",
"SHOT",  "SHOW",  "SHUN",  "SHUT",  "SICK",  "SIDE",  "SIFT",  "SIGH",
"SIGN",  "SILK",  "SILL",  "SILO",  "SILT",  "SINE",  "SING",  "SINK",
"SIRE",  "SITE",  "SITS",  "SITU",  "SKAT",  "SKEW",  "SKID",  "SKIM",
"SKIN",  "SKIT",  "SLAB",  "SLAM",  "SLAT",  "SLAY",  "SLED",  "SLEW",
"SLID",  "SLIM",  "SLIT",  "SLOB",  "SLOG",  "SLOT",  "SLOW",  "SLUG",
"SLUM",  "SLUR",  "SMOG",  "SMUG",  "SNAG",  "SNOB",  "SNOW",  "SNUB",
"SNUG",  "SOAK",  "SOAR",  "SOCK",  "SODA",  "SOFA",  "SOFT",  "SOIL",
"SOLD",  "SOME",  "SONG",  "SOON",  "SOOT",  "SORE",  "SORT",  "SOUL",
"SOUR",  "SOWN",  "STAB",  "STAG",  "STAN",  "STAR",  "STAY",  "STEM",
"STEW",  "STIR",  "STOW",  "STUB",  "STUN",  "SUCH",  "SUDS",  "SUIT",
"SULK",  "SUMS",  "SUNG",  "SUNK",  "SURE",  "SURF",  "SWAB",  "SWAG",
"SWAM",  "SWAN",  "SWAT",  "SWAY",  "SWIM",  "SWUM",  "TACK",  "TACT",
"TAIL",  "TAKE",  "TALE",  "TALK",  "TALL",  "TANK",  "TASK",  "TATE",
"TAUT",  "TEAL",  "TEAM",  "TEAR",  "TECH",  "TEEM",  "TEEN",  "TEET",
"TELL",  "TEND",  "TENT",  "TERM",  "TERN",  "TESS",  "TEST",  "THAN",
"THAT",  "THEE",  "THEM",  "THEN",  "THEY",  "THIN",  "THIS",  "THUD",



<span class="grey">Haller                      Standards Track                    [Page 23]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-4-24" ></span>
<span class="grey"><a href="./rfc2289">RFC 2289</a>               A One-Time Password System          February 1998</span>


"THUG",  "TICK",  "TIDE",  "TIDY",  "TIED",  "TIER",  "TILE",  "TILL",
"TILT",  "TIME",  "TINA",  "TINE",  "TINT",  "TINY",  "TIRE",  "TOAD",
"TOGO",  "TOIL",  "TOLD",  "TOLL",  "TONE",  "TONG",  "TONY",  "TOOK",
"TOOL",  "TOOT",  "TORE",  "TORN",  "TOTE",  "TOUR",  "TOUT",  "TOWN",
"TRAG",  "TRAM",  "TRAY",  "TREE",  "TREK",  "TRIG",  "TRIM",  "TRIO",
"TROD",  "TROT",  "TROY",  "TRUE",  "TUBA",  "TUBE",  "TUCK",  "TUFT",
"TUNA",  "TUNE",  "TUNG",  "TURF",  "TURN",  "TUSK",  "TWIG",  "TWIN",
"TWIT",  "ULAN",  "UNIT",  "URGE",  "USED",  "USER",  "USES",  "UTAH",
"VAIL",  "VAIN",  "VALE",  "VARY",  "VASE",  "VAST",  "VEAL",  "VEDA",
"VEIL",  "VEIN",  "VEND",  "VENT",  "VERB",  "VERY",  "VETO",  "VICE",
"VIEW",  "VINE",  "VISE",  "VOID",  "VOLT",  "VOTE",  "WACK",  "WADE",
"WAGE",  "WAIL",  "WAIT",  "WAKE",  "WALE",  "WALK",  "WALL",  "WALT",
"WAND",  "WANE",  "WANG",  "WANT",  "WARD",  "WARM",  "WARN",  "WART",
"WASH",  "WAST",  "WATS",  "WATT",  "WAVE",  "WAVY",  "WAYS",  "WEAK",
"WEAL",  "WEAN",  "WEAR",  "WEED",  "WEEK",  "WEIR",  "WELD",  "WELL",
"WELT",  "WENT",  "WERE",  "WERT",  "WEST",  "WHAM",  "WHAT",  "WHEE",
"WHEN",  "WHET",  "WHOA",  "WHOM",  "WICK",  "WIFE",  "WILD",  "WILL",
"WIND",  "WINE",  "WING",  "WINK",  "WINO",  "WIRE",  "WISE",  "WISH",
"WITH",  "WOLF",  "WONT",  "WOOD",  "WOOL",  "WORD",  "WORE",  "WORK",
"WORM",  "WORN",  "WOVE",  "WRIT",  "WYNN",  "YALE",  "YANG",  "YANK",
"YARD",  "YARN",  "YAWL",  "YAWN",  "YEAH",  "YEAR",  "YELL",  "YOGA",
"YOKE"   };





























<span class="grey">Haller                      Standards Track                    [Page 24]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-4-25" ></span>
<span class="grey"><a href="./rfc2289">RFC 2289</a>               A One-Time Password System          February 1998</span>


Full Copyright Statement

   Copyright (C) The Internet Society (1998).  All Rights Reserved.

   This document and translations of it may be copied and furnished to
   others, and derivative works that comment on or otherwise explain it
   or assist in its implementation may be prepared, copied, published
   and distributed, in whole or in part, without restriction of any
   kind, provided that the above copyright notice and this paragraph are
   included on all such copies and derivative works.  However, this
   document itself may not be modified in any way, such as by removing
   the copyright notice or references to the Internet Society or other
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   The limited permissions granted above are perpetual and will not be
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   This document and the information contained herein is provided on an
   "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
   TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
   BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
























Haller                      Standards Track                    [Page 25]
</pre>