AIR FORCE FIPS PUB 198-1-2008 The Keyed-Hash Message Authentication Code (HMAC).pdf

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1、 FIPS PUB 198-1 FEDERAL INFORMATION PROCESSING STANDARDS PUBLICATION The Keyed-Hash Message Authentication Code (HMAC) CATEGORY: COMPUTER SECURITY SUBCATEGORY: CRYPTOGRAPHY Information Technology Laboratory National Institute of Standards and Technology Gaithersburg, MD 20899-8900 July 2008 U.S. Dep

2、artment of Commerce Carlos M. Gutierrez, Secretary National Institute of Standards and Technology James M. Turner, Deputy Director Provided by IHSNot for Resale-,-,-FOREWORD The Federal Information Processing Standards Publication Series of the National Institute of Standards and Technology (NIST) i

3、s the official series of publications relating to Standards and Guidelines adopted and promulgated under the provisions of the Federal Information Security Management Act (FISMA) of 2002. Comments concerning FIPS publications are welcomed and should be addressed to the Director, Information Technolo

4、gy Laboratory, National Institute of Standards and Technology, 100 Bureau Drive, Stop 8900, Gaithersburg, MD 20899-8900. Cita Furlani, Director Information Technology Laboratory ii Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHSAbstract This Standard des

5、cribes a keyed-hash message authentication code (HMAC), a mechanism for message authentication using cryptographic hash functions. HMAC can be used with any iterative Approved cryptographic hash function, in combination with a shared secret key. Keywords: computer security, cryptography, HMAC, MAC,

6、message authentication, Federal Information Processing Standards (FIPS). iii Provided by IHSNot for Resale-,-,-Federal Information Processing Standards Publication 198-1 July 2008 Announcing the Standard for The Keyed-Hash Message Authentication Code (HMAC) Federal Information Processing Standards P

7、ublications (FIPS PUBS) are issued by the National Institute of Standards and Technology (NIST) after approval by the Secretary of Commerce pursuant to Section 5131 of the Information Technology Management Reform Act of 1996 (Public Law 104-106) and the Computer Security Act of 1987 (Public Law 100-

8、235). 1. Name of Standard. The Keyed-Hash Message Authentication Code (HMAC) (FIPS PUB 198-1). 2. Category of Standard. Computer Security Standard. Subcategory. Cryptography. 3. Explanation. This Standard specifies an algorithm for applications requiring message authentication. Message authenticatio

9、n is achieved via the construction of a message authentication code (MAC). MACs based on cryptographic hash functions are known as HMACs. The purpose of a MAC is to authenticate both the source of a message and its integrity without the use of any additional mechanisms. HMACs have two functionally d

10、istinct parameters, a message input and a secret key known only to the message originator and intended receiver(s). Additional applications of keyed-hash functions include their use in challenge-response identification protocols for computing responses, which are a function of both a secret key and

11、a challenge message. An HMAC function is used by the message sender to produce a value (the MAC) that is formed by condensing the secret key and the message input. The MAC is typically sent to the message receiver along with the message. The receiver computes the MAC on the received message using th

12、e same key and HMAC function as were used by the sender, and compares the result computed with the received MAC. If the two values match, the message has been correctly received, and the receiver is assured that the sender is a member of the community of users that share the key. 4. Approving Author

13、ity. Secretary of Commerce. iv Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS5. Maintenance Agency. Department of Commerce, National Institute of Standards and Technology, Information Technology Laboratory (ITL). 6. Applicability. This Standard is appli

14、cable to all Federal departments and agencies for the protection of sensitive unclassified information that is not subject to Title 10 United States Code Section 2315 (10 USC 2315) and that is not within a national security system as defined in Title 44 United States Code Section 3502(2) (44 USC 350

15、2(2). The adoption and use of this Standard is available to private and commercial organizations. 7. Specifications. Federal Information Processing Standard (FIPS) 198-1, The Keyed-Hash Message Authentication Code (HMAC) (affixed). 8. Implementations. The authentication mechanism described in this S

16、tandard may be implemented in software, firmware, hardware, or any combination thereof. NIST has developed a Cryptographic Module Validation Program that will test implementations for conformance with this HMAC Standard. Information on this program is available at http:/csrc.nist.gov/groups/STM/inde

17、x.html. Agencies are advised that keys used for HMAC applications should not be used for other purposes. 9. Other Approved Security Functions. HMAC implementations that comply with this Standard shall employ cryptographic algorithms, cryptographic key generation algorithms and key management techniq

18、ues that have been approved for protecting Federal government sensitive information. Approved cryptographic algorithms and techniques include those that are either: a. specified in a Federal Information Processing Standard (FIPS), b. adopted in a FIPS or NIST Recommendation, or c. specified in the l

19、ist of Approved security functions for FIPS 140-2. 10. Export Control. Certain cryptographic devices and technical data regarding them are subject to Federal export controls. Exports of cryptographic modules implementing this Standard and technical data regarding them must comply with these Federal

20、regulations and be licensed by the Bureau of Export Administration of the U.S. Department of Commerce. Information about export regulations is available at: http:/www.bis.doc.gov/index.htm. 11. Implementation Schedule. Guidance regarding the testing and validation to FIPS 198-1 and its relationship

21、to FIPS 140-2 can be found in IG 1.10 of the Implementation Guidance for FIPS PUB 140-2 and the Cryptographic Module Validation Program at http:/csrc.nist.gov/groups/STM/cmvp/index.html. 12. Qualifications. The security afforded by the HMAC function is dependent on maintaining the secrecy of the key

22、 and the use of an appropriate Approved hash function. Therefore, users must guard against disclosure of these keys. While it is the intent of this v Provided by IHSNot for Resale-,-,-vi Standard to specify a mechanism to provide message authentication, conformance to this Standard does not assure t

23、hat a particular implementation is secure. It is the responsibility of the implementer to ensure that any module containing an HMAC implementation is designed and built in a secure manner. Similarly, the use of a product containing an implementation that conforms to this Standard does not guarantee

24、the security of the overall system in which the product is used. The responsible authority in each agency shall assure that an overall system provides an acceptable level of security. Since a Standard of this nature must be flexible enough to adapt to advancements and innovations in science and tech

25、nology, this Standard will be reviewed every five years in order to assess its adequacy. 13. Waiver Procedure: The Federal Information Security Management Act (FISMA) does not allow for waivers to Federal Information Processing Standards (FIPS) that are made mandatory by the Secretary of Commerce. 1

26、4. Where to obtain copies. This publication is available by accessing http:/csrc.nist.gov/publications/. Other computer security publications are available at the same web site. Provided by IHSNot for Resale-,-,-Federal Information Processing Standards Publication 198-1 Specifications for The Keyed-

27、Hash Message Authentication Code TABLE OF CONTENTS 1. INTRODUCTION 2 2. GLOSSARY OF TERMS AND ACRONYMS 2 2.1 Glossary of Terms. 2 2.2 Acronyms 3 2.3 HMAC Parameters and Symbols 3 3. CRYPTOGRAPHIC KEYS 4 4. HMAC SPECIFICATION 4 5. TRUNCATION. 5 6. IMPLEMENTATION NOTE . 5 APPENDIX A: The Differences B

28、etween FIPS 198 and FIPS 198-1 7 APPENDIX B: References . 7 1 Provided by IHSNot for Resale-,-,-1. INTRODUCTION Providing a way to check the integrity of information transmitted over or stored in an unreliable medium is a prime necessity in the world of open computing and communications. Mechanisms

29、that provide such integrity checks based on a secret key are usually called message authentication codes (MACs). Typically, message authentication codes are used between two parties that share a secret key in order to authenticate information transmitted between these parties. This Standard defines

30、a MAC that uses a cryptographic hash function in conjunction with a secret key. This mechanism is called HMAC HMAC. HMAC shall use an Approved cryptographic hash function FIPS 180-3. HMAC uses the secret key for the calculation and verification of the MACs. 2. GLOSSARY OF TERMS AND ACRONYMS 2.1 Glos

31、sary of Terms The following definitions are used throughout this Standard: Approved: FIPS-approved or NIST recommended. An algorithm or technique that is either 1) specified in a FIPS or NIST Recommendation, or 2) adopted in a FIPS or NIST Recommendation and specified in either the FIPS or NIST Reco

32、mmendation, or in a document referenced by the FIPS or NIST Recommendation. Cryptographic key (key): a parameter used in conjunction with a cryptographic algorithm that determines the specific operation of that algorithm. In this Standard, the cryptographic key is used by the HMAC algorithm to produ

33、ce a MAC on the data. Hash function: a mathematical function that maps a string of arbitrary length (up to a pre-determined maximum size) to a fixed length string. Keyed-hash message authentication code (HMAC): a message authentication code that uses a cryptographic key in conjunction with a hash fu

34、nction. Message Authentication Code (MAC): a cryptographic checksum that results from passing data through a message authentication algorithm. In this Standard, the message authentication algorithm is called HMAC, while the result of applying HMAC is called the MAC. Secret key: a cryptographic key t

35、hat is uniquely associated with one or more entities. The use of the term “secret“ in this context does not imply a classification level; rather the term implies the need to protect the key from disclosure or substitution. 2 Provided by IHSNot for Resale-,-,-2.2 Acronyms The following acronyms and a

36、bbreviations are used throughout this Standard: FIPS Federal Information Processing Standard FIPS PUB FIPS Publication HMAC Keyed-Hash Message Authentication Code MAC Message Authentication Code NIST National Institute of Standards and Technology 2.3 HMAC Parameters and Symbols HMAC uses the followi

37、ng parameters: B Block size (in bytes) of the input to the Approved hash function. H An Approved hash function. ipad Inner pad; the byte x36 repeated B times. K Secret key shared between the originator and the intended receiver(s). K0 The key K after any necessary pre-processing to form a B byte key

38、. L Block size (in bytes) of the output of the Approved hash function. opad Outer pad; the byte x5c repeated B times. text The data on which the HMAC is calculated; text does not include the padded key. The length of text is n bits, where 0 n B: hash K to obtain an L byte string, then append (B-L) z

39、eros to create a B-byte string K0(i.e., K0= H(K) | 00.00). Go to step 4. Step 3 If the length of K B: append zeros to the end of K to create a B-byte string K0 (e.g., if K is 20 bytes in length and B = 64, then K will be appended with 44 zero bytes x00). Step 4 Exclusive-Or K0with ipad to produce a

40、B-byte string: K0 ipad. Step 5 Append the stream of data text to the string resulting from step 4: (K0 ipad) | text. Step 6 Apply H to the stream generated in step 5: H(K0 ipad) | text). Step 7 Exclusive-Or K0with opad: K0 opad. Step 8 Append the result from step 6 to step 7: (K0 opad) | H(K0 ipad)

41、| text). Step 9 Apply H to the result from step 8: H(K0 opad )| H(K0 ipad) | text). 4 Provided by IHSNot for Resale-,-,-Determine K0Steps 1-3:K0 ipadH(K0 ipad) | text)K0 opadStep 4:Step 5:Step 7:Step 8: Step 9:Step 6:H(K0 opad) | H(K0 ipad) | text)Figure 1: Illustration of the HMAC Construction(K0 o

42、pad) | H (K0 ipad) | text)(K0 ipad) | text5. TRUNCATION A well-known practice with MACs is to truncate their outputs (i.e., the length of the MACs used is less than the length of the output of the HMAC function L). Applications of this standard may truncate the outputs of the HMAC. When truncation i

43、s used, the leftmost bits of the output of the HMAC function shall be used as the MAC. For information about the choice of and the security implications of using truncated outputs of the HMAC function, see SP 800-107. 6. IMPLEMENTATION NOTE The HMAC algorithm is specified for an arbitrary Approved i

44、terative cryptographic hash function, H. In the HMAC algorithm, values of the ipad and the opad depend on the block size, B, of the Approved hash function. An HMAC implementation can easily replace one Approved iterative hash function, H, with another Approved iterative hash 5 Provided by IHSNot for

45、 Resale-,-,-function, H by generating new ipad and opad using the block size of H instead of H as defined in Section 2.3. Conceptually, the intermediate results of the compression function on the B-byte blocks (K0 ipad) and (K0 opad) can be precomputed once, at the time of generation of the key K, o

46、r before its first use. These intermediate results can be stored and then used to initialize H each time that a message needs to be authenticated using the same key. For each authenticated message using the key K, this method saves the application of the hash function of H on two B-byte blocks (i.e.

47、, on (K ipad) and (K opad). This saving may be significant when authenticating short streams of data. These stored intermediate values shall be treated and protected in the same manner as secret keys. Choosing to implement HMAC in this manner has no effect on interoperability. Object identifiers (OI

48、Ds) for HMAC are posted at http:/csrc.nist.gov/groups/ST/crypto_apps_infra/csor/algorithms.html, along with procedures for adding new OIDs. Examples of HMAC are available at http:/csrc.nist.gov/groups/ST/toolkit/examples.html. 6 Provided by IHSNot for Resale-,-,-7 APPENDIX A: The Differences Between FIPS 198 and FIPS 198-1 The length of truncated HMAC outputs and their security implications in FIPS 198 is not mentioned in this Standard; instead, it is described in SP 800-107. The discussion about the limitations of MAC algorithms has been