< draft-ietf-otp   rfc2289.txt 
INTERNET DRAFT Neil Haller
draft-ietf-otp-01.txt Bellcore Network Working Group N. Haller
March 24, 1997 Craig Metz Request for Comments: 2289 Bellcore
Kaman Sciences Corporation Obsoletes: 1938 C. Metz
Philip Nesser Category: Standards Track Kaman Sciences Corporation
P. Nesser
Nesser & Nesser Consulting Nesser & Nesser Consulting
Mike Straw M. Straw
Bellcore Bellcore
February 1998
A One-Time Password System A One-Time Password System
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1.0 ABSTRACT 1.0 ABSTRACT
This document describes a one-time password authentication system This document describes a one-time password authentication system
(OTP). The system provides authentication for system access (login) (OTP). The system provides authentication for system access (login)
and other applications requiring authentication that is secure and other applications requiring authentication that is secure
against passive attacks based on replaying captured reusable against passive attacks based on replaying captured reusable
passwords. OTP evolved from the S/KEY* One-Time Password System that passwords. OTP evolved from the S/KEY (S/KEY is a trademark of
was released by Bellcore and is described in references [3] and [5]. Bellcore) One-Time Password System that was released by Bellcore and
is described in references [3] and [5].
2.0 OVERVIEW 2.0 OVERVIEW
One form of attack on networked computing systems is eavesdropping One form of attack on networked computing systems is eavesdropping on
on network connections to obtain authentication information such as network connections to obtain authentication information such as the
the login IDs and passwords of legitimate users. Once this login IDs and passwords of legitimate users. Once this information is
information is captured, it can be used at a later time to gain 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
* S/KEY is a trademark of Bellcore of attack, called a "replay attack" [4].
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 The authentication system described in this document uses a secret
pass-phrase to generate a sequence of one-time (single use) pass-phrase to generate a sequence of one-time (single use)
passwords. With this system, the user's secret pass-phrase never passwords. With this system, the user's secret pass-phrase never
needs to cross the network at any time such as during authentication needs to cross the network at any time such as during authentication
or during pass-phrase changes. Thus, it is not vulnerable to replay or during pass-phrase changes. Thus, it is not vulnerable to replay
attacks. Added security is provided by the property that no secret attacks. Added security is provided by the property that no secret
information need be stored on any system, including the server being information need be stored on any system, including the server being
protected. protected.
The OTP system protects against external passive attacks against the The OTP system protects against external passive attacks against the
authentication subsystem. It does not prevent a network eavesdropper authentication subsystem. It does not prevent a network eavesdropper
from gaining access to private information and does not provide from gaining access to private information and does not provide
protection against either "social engineering" or active attacks protection against either "social engineering" or active attacks [9].
[9].
3.0 INTRODUCTION 3.0 INTRODUCTION
There are two entities in the operation of the OTP one-time password There are two entities in the operation of the OTP one-time password
system. The generator must produce the appropriate 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 from the user's secret pass-phrase and from information provided in
the challenge from the server. The server must send a challenge that the challenge from the server. The server must send a challenge that
includes the appropriate generation parameters to the generator, includes the appropriate generation parameters to the generator, must
must verify the one-time password received, must store the last verify the one-time password received, must store the last valid
valid one-time password it received, and must store the one-time password it received, and must store the corresponding one-
corresponding one-time password sequence number. The server must time password sequence number. The server must also facilitate the
also facilitate the changing of the user's secret pass-phrase in a changing of the user's secret pass-phrase in a secure manner.
secure manner.
The OTP system generator passes the user's secret pass-phrase, along The OTP system generator passes the user's secret pass-phrase, along
with a seed received from the server as part of the challenge, with a seed received from the server as part of the challenge,
through multiple iterations of a secure hash function to produce a through multiple iterations of a secure hash function to produce a
one-time password. After each successful authentication, the number one-time password. After each successful authentication, the number
of secure hash function iterations is reduced by one. Thus, a of secure hash function iterations is reduced by one. Thus, a unique
unique sequence of passwords is generated. The server verifies the sequence of passwords is generated. The server verifies the one-time
one-time password received from the generator by computing the password received from the generator by computing the secure hash
secure hash function once and comparing the result with the function once and comparing the result with the previously accepted
previously accepted one-time password. This technique was first one-time password. This technique was first suggested by Leslie
suggested by Leslie Lamport [1]. Lamport [1].
4.0 REQUIREMENTS TERMINOLOGY 4.0 REQUIREMENTS TERMINOLOGY
In this document, the words that are used to define the significance In this document, the words that are used to define the significance
of each particular requirement are usually capitalized. These words of each particular requirement are usually capitalized. These words
are: are:
- MUST - MUST
This word or the adjective "REQUIRED" means that the item is an This word or the adjective "REQUIRED" means that the item is an
requirement of the specification. absolute requirement of the specification.
- SHOULD - SHOULD
This word or the adjective "RECOMMENDED" means that there might This word or the adjective "RECOMMENDED" means that there might
exist valid reasons in particular circumstances to ignore this exist valid reasons in particular circumstances to ignore this
item, but the full implications should be understood and the item, but the full implications should be understood and the case
case carefully weighed before taking a different course. carefully weighed before taking a different course.
- MAY - MAY
This word or the adjective "OPTIONAL" means that this item is This word or the adjective "OPTIONAL" means that this item is
truly optional. One vendor might choose to include the item truly optional. One vendor might choose to include the item
because a particular marketplace requires it or because it because a particular marketplace requires it or because it
enhances the product, for example; another vendor may omit the enhances the product, for example; another vendor may omit the
same item. same item.
5.0 SECURE HASH FUNCTION 5.0 SECURE HASH FUNCTION
The security of the OTP system is based on the non-invertability of The security of the OTP system is based on the non-invertability of a
a secure hash function. Such a function must be tractable to compute secure hash function. Such a function must be tractable to compute in
in the forward direction, but computationally infeasible to invert. the forward direction, but computationally infeasible to invert.
The interfaces are currently defined for three such hash algorithms, The interfaces are currently defined for three such hash algorithms,
MD4 [2] and MD5 [6] by Ronald Rivest, and SHA [7] by NIST. All MD4 [2] and MD5 [6] by Ronald Rivest, and SHA [7] by NIST. All
conforming implementations of both server and generators MUST conforming implementations of both server and generators MUST support
support MD5. They SHOULD support SHA and MAY also support MD4. MD5. They SHOULD support SHA and MAY also support MD4. Clearly, the
Clearly, the generator and server must use the same algorithm in generator and server must use the same algorithm in order to
order to interoperate. Other hash algorithms may be specified for interoperate. Other hash algorithms may be specified for use with
use with this system by publishing the appropriate interfaces. this system by publishing the appropriate interfaces.
The secure hash algorithms listed above have the property that they The secure hash algorithms listed above have the property that they
accept an input that is arbitrarily long and produce a fixed size accept an input that is arbitrarily long and produce a fixed size
output. The OTP system folds this output to 64 bits using the output. The OTP system folds this output to 64 bits using the
algorithms in the Appendix A. 64 bits is also the length of the algorithms in the Appendix A. 64 bits is also the length of the one-
one-time passwords. This is believed to be long enough to be secure time passwords. This is believed to be long enough to be secure and
and short enough to be entered manually (see below, Form of Output) short enough to be entered manually (see below, Form of Output) when
when necessary. necessary.
6.0 GENERATION OF ONE-TIME PASSWORDS 6.0 GENERATION OF ONE-TIME PASSWORDS
This section describes the generation of the one-time passwords. This section describes the generation of the one-time passwords.
This process consists of an initial step in which all inputs are This process consists of an initial step in which all inputs are
combined, a computation step where the secure hash function is combined, a computation step where the secure hash function is
applied a specified number of times, and an output function where applied a specified number of times, and an output function where the
the 64 bit one-time password is converted to a human readable form. 64 bit one-time password is converted to a human readable form.
Appendix C contains examples of the outputs given a collection of Appendix C contains examples of the outputs given a collection of
inputs. It provides implementors with a means of verification the inputs. It provides implementors with a means of verification the
of these algorithms. use of these algorithms.
Initial Step Initial Step
In principle, the user's secret pass-phrase may be of any length. To In principle, the user's secret pass-phrase may be of any length. To
reduce the risk from techniques such as exhaustive search or reduce the risk from techniques such as exhaustive search or
dictionary attacks, character string pass-phrases MUST contain at dictionary attacks, character string pass-phrases MUST contain at
least 10 characters (see Form of Inputs below). All implementations least 10 characters (see Form of Inputs below). All implementations
MUST support a pass-phrases of at least 63 characters. The secret MUST support a pass-phrases of at least 63 characters. The secret
pass-phrase is frequently, but is not required to be, textual pass-phrase is frequently, but is not required to be, textual
information provided by a user. information provided by a user.
In this step, the pass phrase is concatenated with a seed that is In this step, the pass phrase is concatenated with a seed that is
transmitted from the server in clear text. This non-secret seed transmitted from the server in clear text. This non-secret seed
allows clients to use the same secret pass-phrase on multiple allows clients to use the same secret pass-phrase on multiple
machines (using different seeds) and to safely recycle their secret machines (using different seeds) and to safely recycle their secret
pass-phrases by changing the seed. pass-phrases by changing the seed.
The result of the concatenation is passed through the secure hash The result of the concatenation is passed through the secure hash
function and then is reduced to 64 bits using one of the function function and then is reduced to 64 bits using one of the function
dependent algorithms shown in Appendix A. dependent algorithms shown in Appendix A.
Computation Step Computation Step
A sequence of one-time passwords is produced by applying the secure A sequence of one-time passwords is produced by applying the secure
hash function multiple times to the output of the initial step hash function multiple times to the output of the initial step
(called S). That is, the first one-time password to be used is (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 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 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 used is generated by passing S though the secure hash function N-1
times. An eavesdropper who has monitored the transmission of a one- times. An eavesdropper who has monitored the transmission of a one-
time password would not be able to generate the next required time password would not be able to generate the next required
password because doing so would mean inverting the hash function. password because doing so would mean inverting the hash function.
Form of Inputs Form of Inputs
The secret pass-phrase is seen only by the OTP generator. To allow The secret pass-phrase is seen only by the OTP generator. To allow
interchangeability of generators, all generators MUST support a interchangeability of generators, all generators MUST support a
secret pass-phrase of 10 to 63 characters. Implementations MAY secret pass-phrase of 10 to 63 characters. Implementations MAY
support a longer pass-phrase, but such implementations risk the loss support a longer pass-phrase, but such implementations risk the loss
of interchangeability with implementations supporting only the of interchangeability with implementations supporting only the
minimum. minimum.
The seed MUST consist of purely alphanumeric characters and MUST be The seed MUST consist of purely alphanumeric characters and MUST be
of one to 16 characters in length. The seed is a string of of one to 16 characters in length. The seed is a string of characters
characters that MUST not contain any blanks and SHOULD consist of that MUST not contain any blanks and SHOULD consist of strictly
strictly alphanumeric characters from the ISO-646 Invariant Code alphanumeric characters from the ISO-646 Invariant Code Set. The
Set. The seed MUST be case insensitive and MUST be internally seed MUST be case insensitive and MUST be internally converted to
converted to lower case before it is processed. lower case before it is processed.
The sequence number and seed together constitute a larger unit of The sequence number and seed together constitute a larger unit of
called the challenge. The challenge gives the generator the data called the challenge. The challenge gives the generator the
parameters it needs to calculate the correct one-time password from parameters it needs to calculate the correct one-time password from
the secret pass-phrase. The challenge MUST be in a standard syntax the secret pass-phrase. The challenge MUST be in a standard syntax so
so that automated generators can recognize the challenge in context that automated generators can recognize the challenge in context and
and extract these parameters. The syntax of the challenge is: extract these parameters. The syntax of the challenge is:
otp-<algorithm identifier> <sequence integer> <seed> otp-<algorithm identifier> <sequence integer> <seed>
The three tokens MUST be separated by a white space (defined as any 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 number of spaces and/or tabs) and the entire challenge string MUST be
be terminated with either a space or a new line. The string "otp-" terminated with either a space or a new line. The string "otp-" MUST
MUST be in lower case. The algorithm identifier is case sensitive be in lower case. The algorithm identifier is case sensitive (the
(the existing identifiers are all lower case), and the seed is case existing identifiers are all lower case), and the seed is case
insensitive and converted before use to lower case. If additional insensitive and converted before use to lower case. If additional
algorithms are defined, appropriate identifiers (short, but not algorithms are defined, appropriate identifiers (short, but not
limited to three or four characters) must be defined. The currently limited to three or four characters) must be defined. The currently
defined algorithm identifiers are: defined algorithm identifiers are:
md4 MD4 Message Digest md4 MD4 Message Digest
md5 MD5 Message Digest md5 MD5 Message Digest
sha1 NIST Secure Hash Algorithm Revision 1 sha1 NIST Secure Hash Algorithm Revision 1
An example of an OTP challenge is: otp-md5 487 dog2 An example of an OTP challenge is: otp-md5 487 dog2
Form of Output Form of Output
The one-time password generated by the above procedure is 64 bits The one-time password generated by the above procedure is 64 bits in
in length. Entering a 64 bit number is a difficult and error prone length. Entering a 64 bit number is a difficult and error prone
process. Some generators insert this password into the input process. Some generators insert this password into the input stream
stream and some others make it available for system "cut and and some others make it available for system "cut and paste." Still
paste." Still other arrangements require the one-time password to other arrangements require the one-time password to be entered
be entered manually. The OTP system is designed to facilitate this manually. The OTP system is designed to facilitate this manual entry
manual entry without impeding automatic methods. The one-time without impeding automatic methods. The one-time password therefore
password therefore MAY be converted to, and all servers MUST be MAY be converted to, and all servers MUST be capable of accepting it
capable of accepting it as, a sequence of six short (1 to 4 as, a sequence of six short (1 to 4 letter) easily typed words that
letter) easily typed words that only use characters from ISO-646 only use characters from ISO-646 IVCS. Each word is chosen from a
IVCS. Each word is chosen from a dictionary of 2048 words; at 11 dictionary of 2048 words; at 11 bits per word, all one-time passwords
bits per word, all one-time passwords may be encoded. may be encoded.
The two extra bits in this encoding are used to store a checksum. 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 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 pairs are summed together. The two least significant bits of this sum
sum are encoded in the last two bits of the six word sequence with are encoded in the last two bits of the six word sequence with the
the least significant bit of the sum as the last bit encoded. All least significant bit of the sum as the last bit encoded. All OTP
OTP generators MUST calculate this checksum and all OTP servers generators MUST calculate this checksum and all OTP servers MUST
MUST verify this checksum explicitly as part of the operation of verify this checksum explicitly as part of the operation of decoding
decoding this representation of the one-time password. this representation of the one-time password.
Generators that produce the six-word format MUST present the words Generators that produce the six-word format MUST present the words in
in upper case with single spaces used as separators. All servers upper case with single spaces used as separators. All servers MUST
MUST accept six-word format without regard to case and white space accept six-word format without regard to case and white space used as
as a separator. The two lines below represent the same one-time a separator. The two lines below represent the same one-time
password. The first is valid as output from a generator and as password. The first is valid as output from a generator and as input
input a server, the second is valid only as human input to a a server, the second is valid only as human input to a server.
server.
OUST COAT FOAL MUG BEAK TOTE OUST COAT FOAL MUG BEAK TOTE
oust coat foal mug beak tote oust coat foal mug beak tote
Interoperability requires that all OTP servers and generators use Interoperability requires that all OTP servers and generators use
the same dictionary. The standard dictionary was originally the same dictionary. The standard dictionary was originally
specified in the "S/KEY One Time Password System" that is specified in the "S/KEY One Time Password System" that is described
described in RFC 1760 [5]. This dictionary is included in this in RFC 1760 [5]. This dictionary is included in this document as
document as Appendix D. Appendix D.
To facilitate the implementation of smaller generators, To facilitate the implementation of smaller generators, hexadecimal
hexadecimal output is an acceptable alternative for the output is an acceptable alternative for the presentation of the
presentation of the one-time password. All implementations of the one-time password. All implementations of the server software MUST
server software MUST accept case-insensitive hexadecimal as well accept case-insensitive hexadecimal as well as six-word format. The
as six-word format. The hexadecimal digits may be separated by hexadecimal digits may be separated by white space so servers are
white space so servers are REQUIRED to ignore all white space. If REQUIRED to ignore all white space. If the representation is
the representation is partitioned by white space, leading zeros partitioned by white space, leading zeros must be retained.
must be retained. Examples of hexadecimal format are: Examples of hexadecimal format are:
Representation Value Representation Value
3503785b369cda8b 0x3503785b369cda8b 3503785b369cda8b 0x3503785b369cda8b
e5cc a1b8 7c13 096b 0xe5cca1b87c13096b e5cc a1b8 7c13 096b 0xe5cca1b87c13096b
C7 48 90 F4 27 7B A1 CF 0xc74890f4277ba1cf C7 48 90 F4 27 7B A1 CF 0xc74890f4277ba1cf
47 9 A68 28 4C 9D 0 1BC 0x479a68284c9d01bc 47 9 A68 28 4C 9D 0 1BC 0x479a68284c9d01bc
In addition to accepting six-word and hexadecimal encodings of the In addition to accepting six-word and hexadecimal encodings of the
64 bit one-time password, servers SHOULD accept the alternate 64 bit one-time password, servers SHOULD accept the alternate
dictionary encoding described in Appendix B. The six words in this dictionary encoding described in Appendix B. The six words in this
encoding MUST not overlap the set of words in the standard encoding MUST not overlap the set of words in the standard
dictionary. To avoid ambiguity with the hexadecimal representation, dictionary. To avoid ambiguity with the hexadecimal representation,
words in the alternate dictionary MUST not be comprised solely of words in the alternate dictionary MUST not be comprised solely of
the letters A-F. Decoding words thus encoded does not require any the letters A-F. Decoding words thus encoded does not require any
knowledge of the alternative dictionary used so the acceptance of knowledge of the alternative dictionary used so the acceptance of
any alternate dictionary implies the acceptance of all alternate any alternate dictionary implies the acceptance of all alternate
dictionaries. Words in the alternative dictionaries are case dictionaries. Words in the alternative dictionaries are case
sensitive. Generators and servers MUST preserve the case in the sensitive. Generators and servers MUST preserve the case in the
processing of these words. processing of these words.
In summary, all conforming servers MUST accept six-word input that In summary, all conforming servers MUST accept six-word input that
uses the Standard Dictionary (RFC 1760 and Appendix D), MUST accept uses the Standard Dictionary (RFC 1760 and Appendix D), MUST accept
hexadecimal encoding, and SHOULD accept six-word input that uses the hexadecimal encoding, and SHOULD accept six-word input that uses the
Alternative Dictionary technique (Appendix B). As there is a remote Alternative Dictionary technique (Appendix B). As there is a remote
possibility that a hexadecimal encoding of a one-time password will possibility that a hexadecimal encoding of a one-time password will
look like a valid six-word standard dictionary encoding, all look like a valid six-word standard dictionary encoding, all
implementations MUST use the following scheme. If a six-word implementations MUST use the following scheme. If a six-word
encoded one-time password is valid, it is accepted. Otherwise, if encoded one-time password is valid, it is accepted. Otherwise, if
one-time password can be interpreted as hexadecimal, and with that the one-time password can be interpreted as hexadecimal, and with
decoding it is valid, then it is accepted. that decoding it is valid, then it is accepted.
7.0 VERIFICATION OF ONE-TIME PASSWORDS 7.0 VERIFICATION OF ONE-TIME PASSWORDS
An application on the server system that requires OTP authentication An application on the server system that requires OTP authentication
is expected to issue an OTP challenge as described above. Given the is expected to issue an OTP challenge as described above. Given the
parameters from this challenge and the secret pass-phrase, the parameters from this challenge and the secret pass-phrase, the
generator can compute (or lookup) the one-time password that is generator can compute (or lookup) the one-time password that is
passed to the server to be verified. passed to the server to be verified.
The server system has a database containing, for each user, the The server system has a database containing, for each user, the
one-time password from the last successful authentication or the one-time password from the last successful authentication or the
first OTP of a newly initialized sequence. To authenticate the user, first OTP of a newly initialized sequence. To authenticate the user,
the server decodes the one-time password received from the generator 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 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 function once. If the result of this operation matches the stored
previous OTP, the authentication is successful and the accepted previous OTP, the authentication is successful and the accepted
one-time password is stored for future use. one-time password is stored for future use.
8.0 PASS-PHRASE CHANGES 8.0 PASS-PHRASE CHANGES
Because the number of hash function applications executed by the Because the number of hash function applications executed by the
generator decreases by one each time, at some point the user must generator decreases by one each time, at some point the user must
reinitialize the system or be unable to authenticate. reinitialize the system or be unable to authenticate.
Although some installations may not permit users to initialize Although some installations may not permit users to initialize
remotely, implementations MUST provide a means to do so that does 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 not reveal the user's secret pass-phrase. One way is to provide a
means to reinitialize the sequence through explicit specification means to reinitialize the sequence through explicit specification
of the first one-time password. of the first one-time password.
When the sequence of one-time passwords is reinitialized, When the sequence of one-time passwords is reinitialized,
implementations MUST verify that the seed or the pass-phrase is implementations MUST verify that the seed or the pass-phrase is
changed. Installations SHOULD discourage any operation that sends changed. Installations SHOULD discourage any operation that sends
the secret pass-phrase over a network in clear-text as such practice the secret pass-phrase over a network in clear-text as such practice
defeats the concept of a one-time password. defeats the concept of a one-time password.
Implementations MAY use the following technique for Implementations MAY use the following technique for
[re]initialization: [re]initialization:
o The user picks a new seed and hash count (default values may o The user picks a new seed and hash count (default values may
be offered). The user provides these, along with the be offered). The user provides these, along with the
corresponding generated one-time password, to the host system. corresponding generated one-time password, to the host system.
o The user MAY also provide the corresponding generated one o The user MAY also provide the corresponding generated one
time password for count-1 as an error check. time password for count-1 as an error check.
o The user SHOULD provide the generated one-time password for o The user SHOULD provide the generated one-time password for
the old seed and old hash count to protect an idle terminal the old seed and old hash count to protect an idle terminal
or workstation (this implies that when the count is 1, the or workstation (this implies that when the count is 1, the
user can login but cannot then change the seed or count). user can login but cannot then change the seed or count).
In the future a specific protocol may be defined for In the future a specific protocol may be defined for
reinitialization that will permit smooth and possibly automated reinitialization that will permit smooth and possibly automated
interoperation of all hosts and generators. interoperation of all hosts and generators.
9.0 PROTECTION AGAINST RACE ATTACK 9.0 PROTECTION AGAINST RACE ATTACK
All conforming server implementations MUST protect against the race All conforming server implementations MUST protect against the race
condition described in this section. A defense against this attack condition described in this section. A defense against this attack
is outlined; implementations MAY use this approach or MAY select an is outlined; implementations MAY use this approach or MAY select an
alternative defense. alternative defense.
It is possible for an attacker to listen to most of a one-time 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 password, guess the remainder, and then race the legitimate user to
complete the authentication. Multiple guesses against the last word complete the authentication. Multiple guesses against the last word
of the six-word format are likely to succeed. of the six-word format are likely to succeed.
One possible defense is to prevent a user from starting multiple One possible defense is to prevent a user from starting multiple
simultaneous authentication sessions. This means that once the simultaneous authentication sessions. This means that once the
legitimate user has initiated authentication, an attacker would be legitimate user has initiated authentication, an attacker would be
blocked until the first authentication process has completed. In blocked until the first authentication process has completed. In
this approach, a timeout is necessary to thwart a denial of service this approach, a timeout is necessary to thwart a denial of service
attack. attack.
10.0 SECURITY CONSIDERATIONS 10.0 SECURITY CONSIDERATIONS
This entire document discusses an authentication system that This entire document discusses an authentication system that
improves security by limiting the danger of eavesdropping/replay improves security by limiting the danger of eavesdropping/replay
attacks that have been used against simple password systems [4]. attacks that have been used against simple password systems [4].
The use of the OTP system only provides protections against passive The use of the OTP system only provides protections against passive
eavesdropping/replay attacks. It does not provide for the privacy eavesdropping/replay attacks. It does not provide for the privacy
of transmitted data, and it does not provide protection against of transmitted data, and it does not provide protection against
active attacks such as session hijacking that are known to be active attacks such as session hijacking that are known to be
present in the current Internet [9]. The use of IP Security present in the current Internet [9]. The use of IP Security
(IPsec), see [10], [11], and [12] is recommended to protect against (IPsec), see [10], [11], and [12] is recommended to protect against
TCP session hijacking. TCP session hijacking.
The success of the OTP system to protect host systems is dependent The success of the OTP system to protect host systems is dependent
on the non-invertability of the secure hash functions used. To our on the non-invertability of the secure hash functions used. To our
knowledge, none of the hash algorithms have been broken, but it is knowledge, none of the hash algorithms have been broken, but it is
generally believed [6] that MD4 is not as strong as MD5. If a generally believed [6] that MD4 is not as strong as MD5. If a
server supports multiple hash algorithms, it is only as secure as server supports multiple hash algorithms, it is only as secure as
the weakest algorithm. the weakest algorithm.
11.0 ACKNOWLEDGMENTS 11.0 ACKNOWLEDGMENTS
The idea behind OTP authentication was first proposed by Leslie The idea behind OTP authentication was first proposed by Leslie
Lamport [1]. Bellcore's S/KEY system, from which OTP is derived, was Lamport [1]. Bellcore's S/KEY system, from which OTP is derived, was
proposed by Phil Karn, who also wrote most of the Bellcore reference proposed by Phil Karn, who also wrote most of the Bellcore reference
implementation.
12.0 REFERENCES 12.0 REFERENCES
[1] Leslie Lamport, "Password Authentication with Insecure [1] Leslie Lamport, "Password Authentication with Insecure
Communication", Communications of the ACM 24.11 (November Communication", Communications of the ACM 24.11 (November
1981), 770-772 1981), 770-772
[2] R. L. Rivest, The MD4 Message-Digest Algorithm, "Request For [2] Rivest, R., "The MD4 Message-Digest Algorithm", RFC 1320,
Comments (RFC) 1320", MIT and RSA Data Security, Inc., April April 1992.
1992
[3] Neil Haller, "The S/KEY One-Time Password System", Proceedings [3] Neil Haller, "The S/KEY One-Time Password System", Proceedings
of the ISOC Symposium on Network and Distributed System of the ISOC Symposium on Network and Distributed System
Security, February 1994, San Diego, CA Security, February 1994, San Diego, CA
[4] Neil Haller & Ran Atkinson, On Internet Authentication, [4] Haller, N., and R. Atkinson, "On Internet Authentication",
"Request for Comments (RFC) 1704", Bellcore and Naval Research RFC 1704, October 1994.
Laboratory, October 1994
[5] Neil Haller, The S/KEY One-Time Password System, "Request for [5] Haller, N., "The S/KEY One-Time Password System",
Comments (RFC) 1760", Bellcore, February 1995 RFC 1760, February 1995.
[6] R. L. Rivest, The MD5 Message-Digest Algorithm, "Request For [6] Rivest, R., "The MD5 Message-Digest Algorithm", RFC 1321,
Comments (RFC) 1321", MIT and RSA Data Security, Inc., April April 1992.
1992
[7] National Institute of Standards and Technology (NIST), [7] National Institute of Standards and Technology (NIST),
"Announcing the Secure Hash Standard", FIPS 180-1, U.S. "Announcing the Secure Hash Standard", FIPS 180-1, U.S.
Department of Commerce, April 1995. Department of Commerce, April 1995.
[8] International Standard - Information Processing -- ISO 7-bit [8] International Standard - Information Processing -- ISO 7-bit
coded character set for information interchange (Invariant Code coded character set for information interchange (Invariant Code
Set), ISO-646, International Standards Organization, Geneva, Set), ISO-646, International Standards Organization, Geneva,
Switzerland, 1983 Switzerland, 1983
[9] Computer Emergency Response Team (CERT), "IP Spoofing and [9] Computer Emergency Response Team (CERT), "IP Spoofing and
Hijacked Terminal Connections", CA-95:01, January 1995. Hijacked Terminal Connections", CA-95:01, January 1995.
Available via anonymous ftp from info.cert.org in Available via anonymous ftp from info.cert.org in
/pub/cert_advisories. /pub/cert_advisories.
[10] R. Atkinson, Security Architecture for the Internet Protocol, [10] Atkinson, R., "Security Architecture for the Internet Protocol",
"Request for Comments (RFC) 1825", Naval Research Laboratory, RFC 1825, August 1995.
August 1995
[11] R. Atkinson, IP Authentication Header, "Request for Comments [11] Atkinson, R., "IP Authentication Header", RFC 1826, August
(RFC) 1826", Naval Research Laboratory, August 1995 1995.
[12] R. Atkinson, IP Encapsulating Security Payload (ESP), "Request [12] Atkinson, R., "IP Encapsulating Security Payload (ESP)", RFC
for Comments (RFC) 1827", Naval Research Laboratory, August 1827, August 1995.
1995
13.0 AUTHOR'S ADDRESS 13.0 AUTHORS' ADDRESSES
Neil Haller Neil Haller
Bellcore Bellcore
MCC 1C-265B MCC 1C-265B
445 South Street 445 South Street
Morristown, NJ, 07960-6438, USA Morristown, NJ, 07960-6438, USA
Phone: +1 201 829-4478 Phone: +1 201 829-4478
Fax: +1 201 829-2504 Fax: +1 201 829-2504
Email: [email protected] EMail: [email protected]
Craig Metz Craig Metz
Kaman Sciences Corporation Kaman Sciences Corporation
For NRL Code 5544 For NRL Code 5544
4555 Overlook Avenue, S.W. 4555 Overlook Avenue, S.W.
Washington, DC, 20375-5337, USA Washington, DC, 20375-5337, USA
Phone: +1 202 404-7122 Phone: +1 202 404-7122
Fax: +1 202 404-7942 Fax: +1 202 404-7942
Email: [email protected] EMail: [email protected]
Philip J. Nesser II Philip J. Nesser II
Nesser & Nesser Consulting Nesser & Nesser Consulting
13501 100th Ave NE 13501 100th Ave NE
Suite 5202 Suite 5202
Kirkland, WA 98034, USA Kirkland, WA 98034, USA
Phone: +1 206 481 4303 Phone: +1 206 481 4303
Email: [email protected] EMail: [email protected]
Mike Straw Mike Straw
Bellcore Bellcore
RRC 1A-225 RRC 1A-225
445 Hoes Lane 445 Hoes Lane
Piscataway, NJ 08854-4182 Piscataway, NJ 08854-4182
Phone: +1 908 699-5212 Phone: +1 908 699-5212
Email: [email protected] EMail: [email protected]
Appendix A - Interfaces to Secure Hash Algorithms
Original interoperability tests provided valuable insights into the Appendix A - Interfaces to Secure Hash Algorithms
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 bit (msb) first, while a little endian
machine stores the least significant bit (lsb) 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 Original interoperability tests provided valuable insights into the
machine as the following series of four bytes, "0x11", "0xAA", "0xBB", subtle problems which occur when converting protocol specifications
and "0xCC", while on a little endian machine the value would be stored into running code. In particular, the manipulation of bit ordered
as "0xCC", "0xBB", "0xAA", and "0x11". 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 historical reasons, and to promote interoperability with existing For example, the four byte value 0x11AABBCC is stored in a big endian
implementations, it was decided that ALL hashes incorporated into the machine as the following series of four bytes, "0x11", "0xAA",
OTP protocol MUST store the output of their hash function in LITTLE "0xBB", and "0xCC", while on a little endian machine the value would
ENDIAN format BEFORE the bit folding to 64 bits occurs. This is done be stored as "0xCC", "0xBB", "0xAA", and "0x11".
in the implementations of MD4 and MD5 (see references [2] and [6]),
while it must be explicitly done for the implementation of SHA1 (see
reference [7]).
Any future hash functions implemented into the OTP protocol SHOULD For historical reasons, and to promote interoperability with existing
provide a similar reference fragment of code to allow independent implementations, it was decided that ALL hashes incorporated into the
implementations to operate successfully. 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 [2] and [6]),
while it must be explicitly done for the implementation of SHA1 (see
reference [7]).
MD4 Message Digest (see reference [2]) 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_CTX md; MD4 Message Digest (see reference [2])
unsigned char result[16];
strcpy(buf, seed); /* seed must be in lower case */ MD4_CTX md;
strcat(buf, passwd); unsigned char result[16];
MD4Init(&md);
MD4Update(&md, (unsigned char *)buf, strlen(buf));
MD4Final(result, &md);
/* Fold the 128 bit result to 64 bits */ strcpy(buf, seed); /* seed must be in lower case */
for (i = 0; i < 8; i++) strcat(buf, passwd);
result[i] ^= result[i+8]; MD4Init(&md);
MD4Update(&md, (unsigned char *)buf, strlen(buf));
MD4Final(result, &md);
/* Fold the 128 bit result to 64 bits */
for (i = 0; i < 8; i++)
result[i] ^= result[i+8];
MD5 Message Digest (see reference [6]) MD5 Message Digest (see reference [6])
MD5_CTX md; MD5_CTX md;
unsigned char result[16]; unsigned char result[16];
strcpy(buf, seed); /* seed must be in lower case */ strcpy(buf, seed); /* seed must be in lower case */
strcat(buf, passwd); strcat(buf, passwd);
MD5Init(&md); MD5Init(&md);
MD5Update(&md, (unsigned char *)buf, strlen(buf)); MD5Update(&md, (unsigned char *)buf, strlen(buf));
MD5Final(result, &md); MD5Final(result, &md);
/* Fold the 128 bit result to 64 bits */ /* Fold the 128 bit result to 64 bits */
for (i = 0; i < 8; i++) for (i = 0; i < 8; i++)
result[i] ^= result[i+8]; result[i] ^= result[i+8];
SHA Secure Hash Algorithm (see reference [7]) SHA Secure Hash Algorithm (see reference [7])
SHA_INFO sha; SHA_INFO sha;
unsigned char result[16]; unsigned char result[16];
strcpy(buf, seed); /* seed must be in lower case */ strcpy(buf, seed); /* seed must be in lower case */
strcat(buf, passwd); strcat(buf, passwd);
sha_init(&sha); sha_init(&sha);
sha_update(&sha, (unsigned char *)buf, strlen(buf)); sha_update(&sha, (unsigned char *)buf, strlen(buf));
sha_final(&sha); /* NOTE: no result buffer */ sha_final(&sha); /* NOTE: no result buffer */
/* Fold the 160 bit result to 64 bits */ /* Fold the 160 bit result to 64 bits */
sha.digest[0] ^= sha.digest[2]; sha.digest[0] ^= sha.digest[2];
sha.digest[1] ^= sha.digest[3]; sha.digest[1] ^= sha.digest[3];
sha.digest[0] ^= sha.digest[4]; sha.digest[0] ^= sha.digest[4];
/* /*
* copy the resulting 64 bits to the result buffer in little endian * copy the resulting 64 bits to the result buffer in little endian
* fashion (analogous to the way MD4Final() and MD5Final() do). * fashion (analogous to the way MD4Final() and MD5Final() do).
*/ */
for (i = 0, j = 0; j < 8; i++, j += 4) for (i = 0, j = 0; j < 8; i++, j += 4)
{ {
result[j] = (unsigned char)(sha.digest[i] & 0xff); result[j] = (unsigned char)(sha.digest[i] & 0xff);
result[j+1] = (unsigned char)((sha.digest[i] >> 8) & 0xff); result[j+1] = (unsigned char)((sha.digest[i] >> 8) & 0xff);
result[j+2] = (unsigned char)((sha.digest[i] >> 16) & 0xff); result[j+2] = (unsigned char)((sha.digest[i] >> 16) & 0xff);
result[j+3] = (unsigned char)((sha.digest[i] >> 24) & 0xff); result[j+3] = (unsigned char)((sha.digest[i] >> 24) & 0xff);
} }
Appendix B - Alternative Dictionary Algorithm
The purpose of alternative dictionary encoding of the OTP one-time Appendix B - Alternative Dictionary Algorithm
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 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.
The standard 6-word encoding uses the placement of a word in the GENERATOR ENCODING USING AN ALTERNATE DICTIONARY
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 The standard 6-word encoding uses the placement of a word in the
each word W and position of the word in the dictionary N obey the dictionary to represent an 11-bit number. The 64-bit one-time
relationship: password can then be represented by six words.
alg( W ) % 2048 == N An alternative dictionary of 2048 words may be created such that
where each word W and position of the word in the dictionary N obey the
alg is the hash algorithm used (e.g. MD4, MD5, SHA1). relationship:
In addition, no words in the standard dictionary may be chosen. alg( W ) % 2048 == N
where
alg is the hash algorithm used (e.g. MD4, MD5, SHA1).
The generator expands the 64-bit one-time password to 66 bits by In addition, no words in the standard dictionary may be chosen.
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 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.
The server accepting alternative dictionary encoding converts each SERVER DECODING OF ALTERNATE DICTIONARY ONE-TIME PASSWORDS
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 The server accepting alternative dictionary encoding converts each
that was used to create the one-time password it is authenticating. word to an 11-bit number using the above encoding. These numbers
This is because the decoding from word to 11-bit number does not are then used in the same way as the decoded standard dictionary
make any use of the dictionary. As a result of the independence of words to form the 66-bit one-time password.
the dictionary, a server accepting one alternate dictionary accept
all alternate dictionaries.
Appendix C - OTP Verification Examples 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.
This appendix provides a series of inputs and correct outputs for all Appendix C - OTP Verification Examples
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 Appendix D.
GENERAL CHECKS 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 Appendix D.
Note that the output given for these checks is not intended to be GENERAL CHECKS
taken literally, but describes the type of action that should be
taken.
Pass Phrase Length 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: Input:
Pass Phrase: Too_short Pass Phrase: Too_short
Seed: iamvalid Seed: iamvalid
Count: 99 Count: 99
Hash: ANY Hash: ANY
Output: Output:
ERROR: Pass Phrase too short ERROR: Pass Phrase too short
Input: Input:
skipping to change at page 15, line 34 skipping to change at page 17, line 9
Hex: 85c43ee03857765b Hex: 85c43ee03857765b
Six Word(CORRECT): FOWL KID MASH DEAD DUAL OAF 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 NUT
Six Word(INCORRECT PARITY): FOWL KID MASH DEAD DUAL O Six Word(INCORRECT PARITY): FOWL KID MASH DEAD DUAL O
Six Word(INCORRECT PARITY): FOWL KID MASH DEAD DUAL OAK Six Word(INCORRECT PARITY): FOWL KID MASH DEAD DUAL OAK
MD4 ENCODINGS MD4 ENCODINGS
Pass Phrase Seed Cnt Hex Six Word Format 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 0 D185 4218 EBBB 0B51
This is a test. TeSt 1 6347 3EF0 1CD0 B444 CARD SAD MINI RYE COL KIN ROME MUG FRED SCAN LIVE LACE
This is a test. TeSt 99 C5E6 1277 6E6C 237A NOTE OUT IBIS SINK NAVE MODE This is a test. TeSt 1 6347 3EF0 1CD0 B444
AbCdEfGhIjK alpha1 0 5007 6F47 EB1A DE4E AWAY SEN ROOK SALT LICE MAP CARD SAD MINI RYE COL KIN
AbCdEfGhIjK alpha1 1 65D2 0D19 49B5 F7AB CHEW GRIM WU HANG BUCK SAID This is a test. TeSt 99 C5E6 1277 6E6C 237A
AbCdEfGhIjK alpha1 99 D150 C82C CE6F 62D1 ROIL FREE COG HUNK WAIT COCA NOTE OUT IBIS SINK NAVE MODE
OTP's are good correct 0 849C 79D4 F6F5 5388 FOOL STEM DONE TOOL BECK NILE AbCdEfGhIjK alpha1 0 5007 6F47 EB1A DE4E
OTP's are good correct 1 8C09 92FB 2508 47B1 GIST AMOS MOOT AIDS FOOD SEEM AWAY SEN ROOK SALT LICE MAP
OTP's are good correct 99 3F3B F4B4 145F D74B TAG SLOW NOV MIN WOOL KENO 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
MD5 ENCODINGS MD5 ENCODINGS
Pass Phrase Seed Cnt Hex Six Word Format 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 0 9E87 6134 D904 99DD
This is a test. TeSt 1 7965 E054 36F5 029F EASE OIL FUM CURE AWRY AVIS INCH SEA ANNE LONG AHEM TOUR
This is a test. TeSt 99 50FE 1962 C496 5880 BAIL TUFT BITS GANG CHEF THY This is a test. TeSt 1 7965 E054 36F5 029F
AbCdEfGhIjK alpha1 0 8706 6DD9 644B F206 FULL PEW DOWN ONCE MORT ARC EASE OIL FUM CURE AWRY AVIS
AbCdEfGhIjK alpha1 1 7CD3 4C10 40AD D14B FACT HOOF AT FIST SITE KENT This is a test. TeSt 99 50FE 1962 C496 5880
AbCdEfGhIjK alpha1 99 5AA3 7A81 F212 146C BODE HOP JAKE STOW JUT RAP BAIL TUFT BITS GANG CHEF THY
OTP's are good correct 0 F205 7539 43DE 4CF9 ULAN NEW ARMY FUSE SUIT EYED AbCdEfGhIjK alpha1 0 8706 6DD9 644B F206
OTP's are good correct 1 DDCD AC95 6F23 4937 SKIM CULT LOB SLAM POE HOWL FULL PEW DOWN ONCE MORT ARC
OTP's are good correct 99 B203 E28F A525 BE47 LONG IVY JULY AJAR BOND LEE 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 SHA1 ENCODINGS
Pass Phrase Seed Cnt Hex Six Word Format 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 0 BB9E 6AE1 979D 8FF4
This is a test. TeSt 1 63D9 3663 9734 385B CART OTTO HIVE ODE VAT NUT MILT VARY MAST OK SEES WENT
This is a test. TeSt 99 87FE C776 8B73 CCF9 GAFF WAIT SKID GIG SKY EYED This is a test. TeSt 1 63D9 3663 9734 385B
AbCdEfGhIjK alpha1 0 7B4C 5831 CCED CD36 LEST OR HEEL SCOT ROB SUIT CART OTTO HIVE ODE VAT NUT
AbCdEfGhIjK alpha1 1 D07C E229 B5CF 119B RITE TAKE GELD COST TUNE RECK This is a test. TeSt 99 87FE C776 8B73 CCF9
AbCdEfGhIjK alpha1 99 27BC 7103 5AAF 3DC6 MAY STAR TIN LYON VEDA STAN GAFF WAIT SKID GIG SKY EYED
OTP's are good correct 0 D51F 3E99 BF8E 6F0B RUST WELT KICK FELL TAIL FRAU AbCdEfGhIjK alpha1 0 AD85 F658 EBE3 83C9
OTP's are good correct 1 82AE B52D 9437 74E4 FLIT DOSE ALSO MEW DRUM DEFY LEST OR HEEL SCOT ROB SUIT
OTP's are good correct 99 4F29 6A74 FE15 67EC AURA ALOE HURL WING BERG WAIT 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
Appendix D - Dictionary for Converting Between 6-Word and Binary Formats Appendix D - Dictionary for Converting Between 6-Word and Binary Formats
This dictionary is from the module put.c in the original Bellcore This dictionary is from the module put.c in the original Bellcore
reference distribution. reference distribution.
{ "A", "ABE", "ACE", "ACT", "AD", "ADA", "ADD", { "A", "ABE", "ACE", "ACT", "AD", "ADA", "ADD",
"AGO", "AID", "AIM", "AIR", "ALL", "ALP", "AM", "AMY", "AGO", "AID", "AIM", "AIR", "ALL", "ALP", "AM", "AMY",
"AN", "ANA", "AND", "ANN", "ANT", "ANY", "APE", "APS", "AN", "ANA", "AND", "ANN", "ANT", "ANY", "APE", "APS",
"APT", "ARC", "ARE", "ARK", "ARM", "ART", "AS", "ASH", "APT", "ARC", "ARE", "ARK", "ARM", "ART", "AS", "ASH",
"ASK", "AT", "ATE", "AUG", "AUK", "AVE", "AWE", "AWK", "ASK", "AT", "ATE", "AUG", "AUK", "AVE", "AWE", "AWK",
"AWL", "AWN", "AX", "AYE", "BAD", "BAG", "BAH", "BAM", "AWL", "AWN", "AX", "AYE", "BAD", "BAG", "BAH", "BAM",
"BAN", "BAR", "BAT", "BAY", "BE", "BED", "BEE", "BEG", "BAN", "BAR", "BAT", "BAY", "BE", "BED", "BEE", "BEG",
"BEN", "BET", "BEY", "BIB", "BID", "BIG", "BIN", "BIT", "BEN", "BET", "BEY", "BIB", "BID", "BIG", "BIN", "BIT",
"BOB", "BOG", "BON", "BOO", "BOP", "BOW", "BOY", "BUB", "BOB", "BOG", "BON", "BOO", "BOP", "BOW", "BOY", "BUB",
skipping to change at line 1004 skipping to change at page 25, line 4
"WAND", "WANE", "WANG", "WANT", "WARD", "WARM", "WARN", "WART", "WAND", "WANE", "WANG", "WANT", "WARD", "WARM", "WARN", "WART",
"WASH", "WAST", "WATS", "WATT", "WAVE", "WAVY", "WAYS", "WEAK", "WASH", "WAST", "WATS", "WATT", "WAVE", "WAVY", "WAYS", "WEAK",
"WEAL", "WEAN", "WEAR", "WEED", "WEEK", "WEIR", "WELD", "WELL", "WEAL", "WEAN", "WEAR", "WEED", "WEEK", "WEIR", "WELD", "WELL",
"WELT", "WENT", "WERE", "WERT", "WEST", "WHAM", "WHAT", "WHEE", "WELT", "WENT", "WERE", "WERT", "WEST", "WHAM", "WHAT", "WHEE",
"WHEN", "WHET", "WHOA", "WHOM", "WICK", "WIFE", "WILD", "WILL", "WHEN", "WHET", "WHOA", "WHOM", "WICK", "WIFE", "WILD", "WILL",
"WIND", "WINE", "WING", "WINK", "WINO", "WIRE", "WISE", "WISH", "WIND", "WINE", "WING", "WINK", "WINO", "WIRE", "WISE", "WISH",
"WITH", "WOLF", "WONT", "WOOD", "WOOL", "WORD", "WORE", "WORK", "WITH", "WOLF", "WONT", "WOOD", "WOOL", "WORD", "WORE", "WORK",
"WORM", "WORN", "WOVE", "WRIT", "WYNN", "YALE", "YANG", "YANK", "WORM", "WORN", "WOVE", "WRIT", "WYNN", "YALE", "YANG", "YANK",
"YARD", "YARN", "YAWL", "YAWN", "YEAH", "YEAR", "YELL", "YOGA", "YARD", "YARN", "YAWL", "YAWN", "YEAH", "YEAR", "YELL", "YOGA",
"YOKE" }; "YOKE" };
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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.
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