[Federal Register Volume 80, Number 150 (Wednesday, August 5, 2015)]
[Notices]
[Pages 46543-46544]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2015-19181]


-----------------------------------------------------------------------

DEPARTMENT OF COMMERCE

National Institute of Standards and Technology

[Docket No.: 130917811-5349-02]


Announcing Approval of Federal Information Processing Standard 
(FIPS) 202, SHA-3 Standard: Permutation-Based Hash and Extendable-
Output Functions, and Revision of the Applicability Clause of FIPS 180-
4, Secure Hash Standard

AGENCY: National Institute of Standards and Technology (NIST), 
Commerce.

ACTION: Notice.

-----------------------------------------------------------------------

SUMMARY: This notice announces the Secretary of Commerce's approval of 
Federal Information Processing Standard (FIPS) 202, SHA-3 Standard: 
Permutation-Based Hash and Extendable-Output Functions, and a revision 
of the Applicability Clause of FIPS 180-4, Secure Hash Standard. FIPS 
202 specifies the SHA-3 family of hash functions, as well as mechanisms 
for other cryptographic functions to be specified in the future. The 
revision to the Applicability Clause of FIPS 180-4 approves the use of 
hash functions specified in either FIPS 180-4 or FIPS 202 when a secure 
hash function is required for the protection of sensitive, unclassified 
information in Federal applications, including as a component within 
other cryptographic algorithms and protocols.

DATES: FIPS 202 and FIPS 180-4 are effective on August 5, 2015.

FOR FURTHER INFORMATION CONTACT: Ms. Shu-jen Chang, (301) 975-2940, 
National Institute of Standards and Technology, 100 Bureau Drive, Mail 
Stop 8930, Gaithersburg, MD 20899-8930, email: [email protected].

SUPPLEMENTARY INFORMATION: NIST announced the SHA-3 Cryptographic Hash 
Algorithm Competition in the Federal Register (72 FR 62212, available 
at https://federalregister.gov/a/E7-21581) on November 2, 2007. The 
purpose of the SHA-3 Competition was to develop a new cryptographic 
hash algorithm for standardization to augment the hash functions 
specified in FIPS 180-4, Secure Hash Standard. NIST announced the 
winning algorithm, Keccak, in a press release on October 2, 2012, which 
is available at http://www.nist.gov/itl/csd/sha-100212.cfm.
    NIST then developed Draft FIPS 202, SHA-3 Standard: Permutation-
Based Hash and Extendable-Output Functions to specify Keccak for use in 
the Federal Government. On May 28, 2014, NIST announced Draft FIPS 202 
in the Federal Register (79 FR 30549, available at https://federalregister.gov/a/2014-12336) and requested comments. In the same 
notice, NIST also proposed a revision of the Applicability Clause (#6) 
of the Announcement Section of FIPS 180-4, Secure Hash Standard, and 
requested comments. The revision of this clause allows the use of hash 
functions specified in either FIPS 180-4 or FIPS 202, modifying the 
original mandate to use only the hash functions specified in FIPS 180-
4. The other sections of FIPS 180-4 remain unchanged. FIPS 202 and FIPS 
180-4 are available at: http://csrc.nist.gov/publications/PubsFIPS.html.
    The May 28, 2014 notice solicited comments from the public. An 
announcement was also posted on a public hash forum ([email protected]) and on the NIST hash Web site (http://csrc.nist.gov/groups/ST/hash/sha-3/sha-3_standard_fips202.html). A ninety-day public 
comment period commenced on May 28, 2014, and ended on August 26, 2014.
    NIST received comments on Draft FIPS 202 from seven commenters: Two 
government agencies, two industry groups, and three individuals. In 
addition, NIST received one comment on the Draft Revision of the 
Applicability Clause of FIPS 180-4 from one individual, although this 
comment was not related to the revision of the specific clause for 
which NIST was requesting comments. All comments received are posted at 
http://csrc.nist.gov/groups/ST/hash/sha-3/fips-202-public-comments-aug2014.html. None of the comments opposed the adoption of the SHA-3 
Standard or the revision of the Applicability Clause of FIPS 180-4. 
Some comments offered editorial suggestions, pointed out 
inconsistencies in the text, or suggested structural changes. All of 
the comments were carefully reviewed, and changes were made to FIPS 
202, where appropriate. NIST made additional editorial changes to 
improve FIPS 202.
    The following section summarizes the comments received during the 
public comment period, and includes NIST's responses to each comment.
    Comment: One commenter submitted two editorial comments on Draft 
FIPS 202. The first comment was to replace ``relatively small'' with 
``sufficiently small'' in the fourth footnote, on page 1. The second 
comment applied to an earlier draft of FIPS 202.
    Response: The first comment was accepted; the error that the second 
comment identified had already been corrected in the draft that was 
released for public comment.

[[Page 46544]]

    Comment: One commenter agreed with the inclusion of the Extendable-
Output Functions in Draft FIPS 202, citing the TUAK algorithm--for 
authentication and key generation in mobile telephony--as a suitable 
application.
    Response: NIST acknowledges the comment. No change to the Standard 
was made as a result of the comment.
    Comment: Two commenters recommended a significant restructuring of 
Draft FIPS 202. One commenter's proposal was to emphasize the role of 
the Keccak-p permutation as a ``primitive,'' i.e., a fundamental 
cryptographic technique. This permutation family is the main component 
of each SHA-3 function. The comment included a detailed outline of the 
commenter's proposal. The other commenter's proposal was to replace 
FIPS 202 with three standards. The first standard would specify the 
Keccak[c] sponge functions as a distinct primitive, and the second and 
third standards would specify the SHA-3 hash functions and extendable-
output functions, respectively, as instances of these sponge functions. 
For both commenters, the rationale for their proposals was to provide 
greater flexibility to extend the technology in the future.
    Response: The restructuring proposals were not accepted. The text 
in Section 7 on conformance already explicitly accommodates the 
possibility of developing new uses of the Keccak[c] sponge functions 
and other intermediate functions, as well as new functions based on the 
Keccak-p permutations. Moreover, the primary purpose of FIPS 202 is to 
standardize the winning algorithm from the SHA-3 competition. Both of 
the restructuring proposals would detract from the perception of the 
Standard as fulfilling that goal.
    Comment: One of the previous commenters also submitted several 
editorial comments and one general comment on Draft FIPS 202. The 
general comment suggested that hyphens be inserted into the names 
``SHAKE128'' and ``SHAKE256'' in order to separate the numerical 
parameter, which would be consistent with the naming convention for the 
SHA-3 hash functions.
    Response: The editorial comments were accepted, with a modification 
to the suggested resolution in one case. In particular, the commenter 
observed that the following sentence in Section 3 could be clarified to 
distinguish between the input, which is fixed, and the state, which is 
mutable: ``The set of values for the b-bit input to the permutation, as 
it undergoes successive applications of the step mappings, culminating 
in the output, is called the state.'' The commenter suggested the 
following replacement: ``The permutation, as it undergoes successive 
applications of the step mappings, maintains a b-bit state, which is 
initially set to the input values.'' Instead, NIST revised the sentence 
as follows: ``The permutation is specified in terms of an array of 
values for b bits that is repeatedly updated, called the state; the 
state is initially set to the input values of the permutation.'' This 
revision is preferable because it retains an explicit definition of the 
term ``state.'' NIST did not include the change requested in the 
general comment. Although the stated rationale for the general comment 
is reasonable, it is preferable to omit the hyphens, as originally 
specified, in order to help distinguish the different roles of the 
parameters. In particular, the numerical suffixes in ``SHAKE128'' and 
``SHAKE256'' indicate security strengths, while for the SHA-3 hash 
functions such as SHA3-256, the suffix indicates the digest length of 
the hash function.
    Comment: One commenter requested that FIPS 202 clarify how the SHA-
3 hash functions would be implemented within the keyed-hash message 
authentication code (HMAC) that is specified in FIPS 198-1.
    Response: The comment was accepted and addressed with new text in 
the conformance section that identified the value of the HMAC parameter 
B for each of the SHA-3 hash functions.
    Comment: One commenter expressed appreciation for the opportunity 
to review Draft FIPS 202.
    Response: NIST acknowledges the comment. No change was made as a 
result of the comment.
    Comment: One commenter discussed the use of the extendable-output 
functions specified in Draft FIPS 202. The comment distinguished 
between two types of applications: (1) Variable-length hash functions, 
and (2) random-looking functions, such as key derivation functions 
(KDFs). The comment explained why variable-length hash functions were 
not very interesting from a cryptographic perspective, suggesting that 
NIST approval be limited to KDF-like functions. The comment also 
pointed out that the incorporation of the output length into the input 
for these functions could be specified as a method of addressing the 
prefix property that is discussed in the Standard.
    Response: The text in Section 7 on conformance explicitly asserts 
that approved uses of the extendable-output functions will be specified 
in NIST special publications. NIST will consider the commenter's 
suggestions in the development of those publications. Also, text was 
added to clarify that extendable-output functions are not yet approved 
as variable-length hash functions.
    Comment: The only comment on FIPS 180-4 recommended that the SHA-1 
hash algorithm be excluded ``due to highly untrusted security 
algorithm.''
    Response: NIST made no change based on this comment. The comment 
does not directly apply to the Revised Applicability Clause of FIPS 
180-4, which simply acknowledges that FIPS 202 specifies valid options 
for secure hash functions. Moreover, NIST has already developed and 
adopted an appropriate policy for the use of SHA-1, based on the latest 
security information, as described in NIST Special Publication 800-
131A.
    The Secretary of Commerce hereby approves FIPS 202 and FIPS 180-4. 
Copies of FIPS 202 and FIPS 180-4 are available at: http://csrc.nist.gov/publications/PubsFIPS.html.

    Authority:  In accordance with the Information Technology 
Management Reform Act of 1996 (Pub. L. 104-106) and the Federal 
Information Security Management Act of 2002 (FISMA) (Pub. L. 107-
347), the Secretary of Commerce is authorized to approve FIPS. NIST 
activities to develop computer security standards to protect federal 
sensitive (unclassified) information systems are undertaken pursuant 
to specific responsibilities assigned to NIST by Section 20 of the 
National Institute of Standards and Technology Act (15 U.S.C. 278g-
3), as amended.

Richard R. Cavanagh,
Acting Associate Director for Laboratory Programs.
[FR Doc. 2015-19181 Filed 8-4-15; 8:45 am]
 BILLING CODE 3510-13-P