FIPS PUB 180-4
 

FEDERAL INFORMATION PROCESSING STANDARDS 

PUBLICATION 

Secure Hash Standard (SHS) 

CATEGORY: COMPUTER SECURITY SUBCATEGORY: CRYPTOGRAPHY 

Information Technology Laboratory 

National Institute of Standards and Technology 

Gaithersburg, MD 20899-8900 

March 2012 

U.S. Department of Commerce 

John Bryson, Secretary 

National Institute of Standards and Technology 

Patrick Gallagher, Under Secretary for Standards and Technology and Director 
 

 

 

FOREWORD
 

The Federal Information Processing Standards Publication Series of the National Institute 

of Standards and Technology (NIST) is 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 Technology Laboratory, National Institute of Standards and 

Technology, 100 Bureau Drive, Stop 8900, Gaithersburg, MD 20899-8900. 

Charles H. Romine, Director 

Information Technology Laboratory 

ii 
Abstract 

This standard specifies hash algorithms that can be used to generate digests of messages. 

The digests are used to detect whether messages have been changed since the digests 

were generated. 

Key words: computer security, cryptography, message digest, hash function, hash 

algorithm, Federal Information Processing Standards, Secure Hash Standard. 

iii 
Federal Information
 

Processing Standards Publication 180-4
 

March 2012 

Announcing the 

SECURE HASH STANDARD
 

Federal Information Processing Standards Publications (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 100-235). 

1. Name of Standard: Secure Hash Standard (SHS) (FIPS PUB 180-4). 

2. Category of Standard: Computer Security Standard, Cryptography. 

3. Explanation: This Standard specifies secure hash algorithms - SHA-1, SHA-224, SHA-256, 

SHA-384, SHA-512, SHA-512/224 and SHA-512/256 - for computing a condensed 

representation of electronic data (message). When a message of any length less than 264 bits (for 

SHA-1, SHA-224 and SHA-256) or less than 2128 bits (for SHA-384, SHA-512, SHA-512/224 

and SHA-512/256) is input to a hash algorithm, the result is an output called a message digest. 

The message digests range in length from 160 to 512 bits, depending on the algorithm. Secure 

hash algorithms are typically used with other cryptographic algorithms, such as digital signature 

algorithms and keyed-hash message authentication codes, or in the generation of random 

numbers (bits). 

The hash algorithms specified in this Standard are called secure because, for a given algorithm, it 

is computationally infeasible 1) to find a message that corresponds to a given message digest, or 

2) to find two different messages that produce the same message digest. Any change to a 

message will, with a very high probability, result in a different message digest. This will result in 

a verification failure when the secure hash algorithm is used with a digital signature algorithm or 

a keyed-hash message authentication algorithm. 

This Standard supersedes FIPS 180-3 [FIPS 180-3]. 

4. Approving Authority: Secretary of Commerce. 

5. Maintenance Agency: U.S. Department of Commerce, National Institute of Standards and 

Technology (NIST), Information Technology Laboratory (ITL). 

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6. Applicability: This Standard is applicable 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 3502(2)). This standard shall be implemented 

whenever a secure hash algorithm is required for Federal applications, including use by other 

cryptographic algorithms and protocols. The adoption and use of this Standard is available to 

private and commercial organizations. 

7. Specifications: Federal Information Processing Standard (FIPS) 180-4, Secure Hash Standard 

(SHS) (affixed). 

8. Implementations: The secure hash algorithms specified herein may be implemented in 

software, firmware, hardware or any combination thereof. Only algorithm implementations that 

are validated by NIST will be considered as complying with this standard. Information about the 

validation program can be obtained at http://csrc.nist.gov/groups/STM/index.html. 

9. Implementation Schedule: Guidance regarding the testing and validation to FIPS 180-4 and 

its relationship 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. 

10. Patents: Implementations of the secure hash algorithms in this standard may be covered by 

U.S. or foreign patents. 

11. 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 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. 

12. Qualifications: While it is the intent of this Standard to specify general security 

requirements for generating a message digest, conformance to this Standard does not assure that 

a particular implementation is secure. The responsible authority in each agency or department 

shall assure that an overall implementation provides an acceptable level of security. 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. 

14. Where to Obtain Copies of the Standard: This publication is available electronically by 

accessing http://csrc.nist.gov/publications/. Other computer security publications are available at 

the same web site. 

v 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Federal Information
 

Processing Standards Publication 180-4
 

Specifications for the
 

SECURE HASH STANDARD
 

Table of Contents 

1. INTRODUCTION ......................................................................................................................................3 
 

2. DEFINITIONS ............................................................................................................................................4 
 

2.1 	 GLOSSARY OF TERMS AND ACRONYMS ..............................................................................................4 
 

2.2 	 ALGORITHM PARAMETERS, SYMBOLS, AND TERMS ...........................................................................4 
 

2.2.1 Parameters.............................................................................................................................4 
 

2.2.2 Symbols and Operations ........................................................................................................5 
 

3. NOTATION AND CONVENTIONS ........................................................................................................7 
 

3.1 BIT STRINGS AND INTEGERS ...............................................................................................................7 
 

3.2 OPERATIONS ON WORDS.....................................................................................................................8 
 

4. FUNCTIONS AND CONSTANTS..........................................................................................................10 
 

4.1 	 FUNCTIONS .......................................................................................................................................10 
 

4.1.1 SHA-1 Functions..................................................................................................................10 
 

4.1.2 SHA-224 and SHA-256 Functions .......................................................................................10 
 

4.1.3 SHA-384, SHA-512, SHA-512/224 and SHA-512/256 Functions .......................................11 
 

4.2 	 CONSTANTS ......................................................................................................................................11 
 

4.2.1 SHA-1 Constants..................................................................................................................11 
 

4.2.2 SHA-224 and SHA-256 Constants .......................................................................................11 
 

4.2.3 SHA-384, SHA-512, SHA-512/224 and SHA-512/256 Constants .......................................12 
 

5. PREPROCESSING ..................................................................................................................................13 
 

5.1 	 PADDING THE MESSAGE ...................................................................................................................13 
 

5.1.1 SHA-1, SHA-224 and SHA-256 ...........................................................................................13 
 

5.1.2 SHA-384, SHA-512, SHA-512/224 and SHA-512/256 ........................................................13 
 

5.2 	 PARSING THE MESSAGE ....................................................................................................................14 
 

5.2.1 SHA-1, SHA-224 and SHA-256 ...........................................................................................14 
 

5.2.2 SHA-384, SHA-512, SHA-512/224 and SHA-512/256 ........................................................14 
 

5.3 	 SETTING THE INITIAL HASH VALUE (H(0)) ........................................................................................14 
 

5.3.1 SHA-1...................................................................................................................................14 
 

5.3.2 SHA-224 ..............................................................................................................................14 
 

5.3.3 SHA-256...............................................................................................................................15 
 

5.3.4 SHA-384...............................................................................................................................15 
 

5.3.5 SHA-512...............................................................................................................................15 
 

5.3.6 SHA-512/t ............................................................................................................................16 
 5.3.6.1 SHA-512/224 ....................................................................................................................................17 
 5.3.6.2 SHA-512/256 ....................................................................................................................................17 
 

6. SECURE HASH ALGORITHMS...........................................................................................................18 
 

6.1 	 SHA-1 ..............................................................................................................................................18 
 

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6.1.1 SHA-1 Preprocessing...........................................................................................................18 
 

6.1.2 SHA-1 Hash Computation ...................................................................................................18 
 

6.1.3 Alternate Method for Computing a SHA-1 Message Digest................................................20 
 

6.2 SHA-256 ..........................................................................................................................................21 
 

6.2.1 SHA-256 Preprocessing.......................................................................................................22 
 

6.2.2 SHA-256 Hash Computation ...............................................................................................22 
 

6.3 SHA-224 ..........................................................................................................................................23 
 

6.4 SHA-512 ..........................................................................................................................................24 
 

6.4.1 SHA-512 Preprocessing.......................................................................................................24 
 

6.4.2 SHA-512 Hash Computation ...............................................................................................24 
 

6.5 SHA-384 ..........................................................................................................................................26 
 

6.6 SHA-512/224 ...................................................................................................................................26 
 

6.7 SHA-512/256 ...................................................................................................................................26 
 

7. TRUNCATION OF A MESSAGE DIGEST ...........................................................................................27 
 

APPENDIX A: ADDITIONAL INFORMATION...................................................................................................28 
 

A.1 SECURITY OF THE SECURE HASH ALGORITHMS................................................................................28 
 

A.2 IMPLEMENTATION NOTES .................................................................................................................28 
 

A.3 OBJECT IDENTIFIERS .........................................................................................................................28 
 

APPENDIX B: REFERENCES .................................................................................................................................29 
 

APPENDIX C: TECHNICAL CHANGES FROM FIPS 180-3 .............................................................................30 
 

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1. INTRODUCTION 

This Standard specifies secure hash algorithms, SHA-1, SHA-224, SHA-256, SHA-384, SHA512, SHA-512/224 and SHA-512/256. All of the algorithms are iterative, one-way hash 

functions that can process a message to produce a condensed representation called a message 

digest. These algorithms enable the determination of a message’s integrity: any change to the 

message will, with a very high probability, result in a different message digest. This property is 

useful in the generation and verification of digital signatures and message authentication codes, 

and in the generation of random numbers or bits. 

Each algorithm can be described in two stages: preprocessing and hash computation. 

Preprocessing involves padding a message, parsing the padded message into m-bit blocks, and 

setting initialization values to be used in the hash computation. The hash computation generates 

a message schedule from the padded message and uses that schedule, along with functions, 

constants, and word operations to iteratively generate a series of hash values. The final hash 

value generated by the hash computation is used to determine the message digest. 

The algorithms differ most significantly in the security strengths that are provided for the data 

being hashed. The security strengths of these hash functions and the system as a whole when 

each of them is used with other cryptographic algorithms, such as digital signature algorithms 

and keyed-hash message authentication codes, can be found in [SP 800-57] and [SP 800-107]. 

Additionally, the algorithms differ in terms of the size of the blocks and words of data that are 

used during hashing or message digest sizes. Figure 1 presents the basic properties of these hash 

algorithms. 

Algorithm Message Size Block Size Word Size 

(bits) (bits) (bits) 

SHA-1 < 264 512 32 

SHA-224 < 264 512 32 

SHA-256 < 264 512 32 

SHA-384 < 2128 1024 64 

SHA-512 < 2128 1024 64 

SHA-512/224 < 2128 1024 64 

SHA-512/256 < 2128 1024 64 

Figure 1: Secure Hash Algorithm Properties 

3
 

Message Digest Size
 

(bits)
 

160
 

224
 

256
 

384
 

512
 

224
 

256
 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

2. DEFINITIONS 

2.1 Glossary of Terms and Acronyms 

Bit A binary digit having a value of 0 or 1.
 

Byte A group of eight bits.
 

FIPS Federal Information Processing Standard.
 

NIST National Institute of Standards and Technology.
 

SHA Secure Hash Algorithm.
 

SP Special Publication
 

Word A group of either 32 bits (4 bytes) or 64 bits (8 bytes), depending on the 

secure hash algorithm. 

2.2 Algorithm Parameters, Symbols, and Terms 

2.2.1 Parameters 

The following parameters are used in the secure hash algorithm specifications in this Standard. 

a, b, c, ..., h	 Working variables that are the w-bit words used in the computation of the 

hash values, H(i)

. 

H (i) The i

th hash value. H(0) is the initial hash value; H(N) is the final hash value 

and is used to determine the message digest. 

(i)	 H (i) H j	 The j

th word of the ith hash value, where is the left-most word of hash 0

value i. 

Kt Constant value to be used for the iteration t of the hash computation. 

k Number of zeroes appended to a message during the padding step. 

 Length of the message, M, in bits. 

m Number of bits in a message block, M(i). 

M Message to be hashed. 

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M(i) Message block i, with a size of m bits. 

(i) (i) M j The j

th word of the ith message block, where M 0 is the left-most word of 

message block i. 

n Number of bits to be rotated or shifted when a word is operated upon. 

N Number of blocks in the padded message. 

T Temporary w-bit word used in the hash computation. 

w Number of bits in a word. 

Wt The t

th 

w-bit word of the message schedule. 

2.2.2 Symbols and Operations 

The following symbols are used in the secure hash algorithm specifications; each operates on wbit words. 

∧ Bitwise AND operation. 

∨ Bitwise OR (“inclusive-OR”) operation. 

⊕ Bitwise XOR (“exclusive-OR”) operation. 

¬ Bitwise complement operation. 

+	 Addition modulo 2w . 

<<	 Left-shift operation, where x << n is obtained by discarding the left-most n 

bits of the word x and then padding the result with n zeroes on the right. 

>>	 Right-shift operation, where x >> n is obtained by discarding the rightmost n bits of the word x and then padding the result with n zeroes on the 

left. 

The following operations are used in the secure hash algorithm specifications: 

ROTL n(x) The rotate left (circular left shift) operation, where x is a w-bit word and n 

is an integer with 0 ≤ n < w, is defined by ROTL n(x)=(x << n) ∨

(x >> w - n). 

ROTR n(x) The rotate right (circular right shift) operation, where x is a w-bit word 

and n is an integer with 0 ≤ n < w, is defined by ROTR n

(x)=(x >> n) ∨

(x << w - n). 

5
 
 

SHR n(x) The right shift operation, where x is a w-bit word and n is an integer with 0 

≤ n < w, is defined by SHR n

(x)=x >> n. 

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3. NOTATION AND CONVENTIONS 

3.1 Bit Strings and Integers 

The following terminology related to bit strings and integers will be used. 

1.	 A hex digit is an element of the set {0, 1,..., 9, a,..., f}. A hex digit is the 

representation of a 4-bit string. For example, the hex digit “7” represents the 4-bit 

string “0111”, and the hex digit “a” represents the 4-bit string “1010”. 

2.	 A word is a w-bit string that may be represented as a sequence of hex digits. To 

convert a word to hex digits, each 4-bit string is converted to its hex digit equivalent, 

as described in (1) above. For example, the 32-bit string 

1010 0001 0000 0011 1111 1110 0010 0011 

can be expressed as “a103fe23”, and the 64-bit string 

1010 0001 0000 0011 1111 1110 0010 0011 

0011 0010 1110 1111 0011 0000 0001 1010 

can be expressed as “a103fe2332ef301a”. 

Throughout this specification, the “big-endian” convention is used when expressing 

both 32- and 64-bit words, so that within each word, the most significant bit is stored 

in the left-most bit position. 

3.	 An integer may be represented as a word or pair of words. A word representation of 

the message length,  , in bits, is required for the padding techniques of Sec. 5.1. 

An integer between 0 and 232-1 inclusive may be represented as a 32-bit word. The 

least significant four bits of the integer are represented by the right-most hex digit of 

the word representation. For example, the integer 291=28 + 25 + 21 + 20

=256+32+2+1 

is represented by the hex word “00000123”. 

The same holds true for an integer between 0 and 264-1 inclusive, which may be 

represented as a 64-bit word. 

If Z is an integer, 0 ≤ Z < 264, then Z=232X + Y, where 0 ≤ X < 232 and 0 ≤ Y < 232. 

Since X and Y can be represented as 32-bit words x and y, respectively, the integer Z 

can be represented as the pair of words (x, y). This property is used for SHA-1, SHA224 and SHA-256. 

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If Z is an integer, 0 ≤ Z < 2128, then Z=264X + Y, where 0 ≤ X < 264 and 0 ≤ Y < 264. 

Since X and Y can be represented as 64-bit words x and y, respectively, the integer Z 

can be represented as the pair of words (x, y). This property is used for SHA-384, 

SHA-512, SHA-512/224 and SHA-512/256. 

4.	 For the secure hash algorithms, the size of the message block - m bits - depends on the 

algorithm. 

a)	 For SHA-1, SHA-224 and SHA-256, each message block has 512 bits, which are 

represented as a sequence of sixteen 32-bit words. 

b)	 For SHA-384, SHA-512, SHA-512/224 and SHA-512/256 each message block 

has 1024 bits, which are represented as a sequence of sixteen 64-bit words. 

3.2 Operations on Words 

The following operations are applied to w-bit words in all five secure hash algorithms. SHA-1, 

SHA-224 and SHA-256 operate on 32-bit words (w=32), and SHA-384, SHA-512, SHA512/224 and SHA-512/256 operate on 64-bit words (w=64). 

1.	 Bitwise logical word operations: ∧, ∨ , ⊕ , and ¬ (see Sec. 2.2.2). 

2.	 Addition modulo 2w . 

The operation x + y is defined as follows. The words x and y represent integers X and 

Y, where 0 ≤ X < 2w and 0 ≤ Y < 2w . For positive integers U and V, let U modV be 

the remainder upon dividing U by V. Compute 

Z=( X + Y ) mod 2w . 

Then 0 ≤ Z < 2w . Convert the integer Z to a word, z, and define z=x + y. 

3.	 The right shift operation SHR n(x), where x is a w-bit word and n is an integer with 0 

≤ n < w, is defined by 

SHR n(x)=x >> n. 

This operation is used in the SHA-224, SHA-256, SHA-384, SHA-512, SHA-512/224 

and SHA-512/256 algorithms. 

4.	 The rotate right (circular right shift) operation ROTR n(x), where x is a w-bit word 

and n is an integer with 0 ≤ n < w, is defined by 

ROTR n(x)=(x >> n) ∨ (x << w - n). 

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Thus, ROTR n(x) is equivalent to a circular shift (rotation) of x by n positions to the 

right. 

This operation is used by the SHA-224, SHA-256, SHA-384, SHA-512, SHA512/224 and SHA-512/256 algorithms.
 

5.	 The rotate left (circular left shift) operation, ROTL n(x), where x is a w-bit word and n 

is an integer with 0 ≤ n < w, is defined by 

ROTL n(x)=(x << n) ∨ (x >> w - n). 

Thus, ROTL n(x) is equivalent to a circular shift (rotation) of x by n positions to the 

left. 

This operation is used only in the SHA-1 algorithm. 

6.	 Note the following equivalence relationships, where w is fixed in each relationship: 

ROTL n(x) ≈ ROTR w-n(x) 

ROTR n(x) ≈ ROTL w-n(x) 

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4. FUNCTIONS AND CONSTANTS 

4.1 Functions 

This section defines the functions that are used by each of the algorithms. Although the SHA224, SHA-256, SHA-384,SHA-512, SHA-512/224 and SHA-512/256 algorithms all use similar 

functions, their descriptions are separated into sections for SHA-224 and SHA-256 (Sec. 4.1.2) 

and for SHA-384, SHA-512, SHA-512/224 and SHA-512/256 (Sec. 4.1.3), since the input and 

output for these functions are words of different sizes. Each of the algorithms include Ch(x, y, z) 

and Maj(x, y, z) functions; the exclusive-OR operation ( ⊕ ) in these functions may be replaced 

by a bitwise OR operation (∨) and produce identical results. 

4.1.1 SHA-1 Functions 

SHA-1 uses a sequence of logical functions, f0, f1,..., f79. Each function ft, where 0 ≤ t < 79, 

operates on three 32-bit words, x, y, and z, and produces a 32-bit word as output. The function ft 

(x, y, z) is defined as follows: 

Ch(x, y, z)=(x ∧y) ⊕ ( ¬ x ∧ z) 0 ≤ t ≤ 19 

Parity(x, y, z)=x ⊕ y ⊕ z 20 ≤ t ≤ 39 

ft (x, y, z) = (4.1) 

Maj(x, y, z)=(x ∧ y) ⊕ (x ∧ z) ⊕ (y ∧ z) 40 ≤ t ≤ 59 

Parity(x, y, z)=x ⊕ y ⊕ z 60 ≤ t ≤ 79. 

4.1.2 SHA-224 and SHA-256 Functions 

SHA-224 and SHA-256 both use six logical functions, where each function operates on 32-bit 

words, which are represented as x, y, and z. The result of each function is a new 32-bit word. 

Ch(x, y,z) = (x ∧ y) ⊕(¬x ∧ z) (4.2) 

Maj(x, y,z) = (x ∧ y)⊕(x ∧ z)⊕(y ∧ z) (4.3) 

{256} ∑ (x) = ROTR 2

(x) ⊕ ROTR 13(x) ⊕ ROTR 22(x) (4.4) 0

{256} (x) = ROTR 6

(x) ⊕ ROTR 11(x) ⊕ ROTR 25 ∑ (x) (4.5) 1

{256} σ ( ) 0 x = ROTR 7

(x) ⊕ ROTR 18(x) ⊕ SHR 3(x) (4.6) 

{256} σ ( ) 1 x = ROTR 17(x) ⊕ ROTR 19(x) ⊕ SHR 10(x) (4.7) 

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4.1.3 SHA-384, SHA-512, SHA-512/224 and SHA-512/256 Functions 

SHA-384, SHA-512, SHA-512/224 and SHA-512/256 use six logical functions, where each 

function operates on 64-bit words, which are represented as x, y, and z. The result of each 

function is a new 64-bit word. 

Ch(x, y,z) = (x ∧ y) ⊕(¬x ∧ z) (4.8) 

Maj(x, y,z) = (x ∧ y)⊕(x ∧ z)⊕(y ∧ z) (4.9) 

{512} (x) = ROTR 28(x) ⊕ ROTR 34(x) ⊕ ROTR 39 ∑ (x) (4.10) 0

{512} (x) = ROTR 14(x) ⊕ ROTR 18(x) ⊕ ROTR 41 ∑ (x) (4.11) 1

{512} σ ( ) 0 x = ROTR 1

(x) ⊕ ROTR 8(x) ⊕ SHR 7(x) (4.12) 

{512} σ ( ) 1 x = ROTR 19(x) ⊕ ROTR 61(x) ⊕ SHR 6

(x) (4.13) 

4.2 Constants 

4.2.1 SHA-1 Constants 

SHA-1 uses a sequence of eighty constant 32-bit words, K0, K1,..., K79, which are given by 

5a827999 0 ≤ t ≤ 19 

6ed9eba1 20 ≤ t ≤ 39 

Kt = (4.14) 

8f1bbcdc 40 ≤ t ≤ 59 

ca62c1d6 60 ≤ t ≤ 79 

4.2.2 SHA-224 and SHA-256 Constants 

SHA-224 and SHA-256 use the same sequence of sixty-four constant 32-bit words, 

{256} {256} {256} K ,K ,...,K . These words represent the first thirty-two bits of the fractional parts of 0 1 63

the cube roots of the first sixty-four prime numbers. In hex, these constant words are (from left 

to right) 

428a2f98 71374491 b5c0fbcf e9b5dba5 3956c25b 59f111f1 923f82a4 ab1c5ed5
 

d807aa98 12835b01 243185be 550c7dc3 72be5d74 80deb1fe 9bdc06a7 c19bf174
 

e49b69c1 efbe4786 0fc19dc6 240ca1cc 2de92c6f 4a7484aa 5cb0a9dc 76f988da
 

983e5152 a831c66d b00327c8 bf597fc7 c6e00bf3 d5a79147 06ca6351 14292967
 

27b70a85 2e1b2138 4d2c6dfc 53380d13 650a7354 766a0abb 81c2c92e 92722c85
 

a2bfe8a1 a81a664b c24b8b70 c76c51a3 d192e819 d6990624 f40e3585 106aa070
 

19a4c116 1e376c08 2748774c 34b0bcb5 391c0cb3 4ed8aa4a 5b9cca4f 682e6ff3
 

748f82ee 78a5636f 84c87814 8cc70208 90befffa a4506ceb bef9a3f7 c67178f2
 

11
 
4.2.3 SHA-384, SHA-512, SHA-512/224 and SHA-512/256 Constants 

SHA-384, SHA-512, SHA-512/224 and SHA-512/256 use the same sequence of eighty constant 

{512} {512} {512} 64-bit words, K ,K ,...,K . These words represent the first sixty-four bits of the 0 1 79

fractional parts of the cube roots of the first eighty prime numbers. In hex, these constant words 

are (from left to right) 

428a2f98d728ae22 7137449123ef65cd b5c0fbcfec4d3b2f e9b5dba58189dbbc
 

3956c25bf348b538 59f111f1b605d019 923f82a4af194f9b ab1c5ed5da6d8118
 

d807aa98a3030242 12835b0145706fbe 243185be4ee4b28c 550c7dc3d5ffb4e2
 

72be5d74f27b896f 80deb1fe3b1696b1 9bdc06a725c71235 c19bf174cf692694
 

e49b69c19ef14ad2 efbe4786384f25e3 0fc19dc68b8cd5b5 240ca1cc77ac9c65
 

2de92c6f592b0275 4a7484aa6ea6e483 5cb0a9dcbd41fbd4 76f988da831153b5
 

983e5152ee66dfab a831c66d2db43210 b00327c898fb213f bf597fc7beef0ee4
 

c6e00bf33da88fc2 d5a79147930aa725 06ca6351e003826f 142929670a0e6e70
 

27b70a8546d22ffc 2e1b21385c26c926 4d2c6dfc5ac42aed 53380d139d95b3df
 

650a73548baf63de 766a0abb3c77b2a8 81c2c92e47edaee6 92722c851482353b
 

a2bfe8a14cf10364 a81a664bbc423001 c24b8b70d0f89791 c76c51a30654be30
 

d192e819d6ef5218 d69906245565a910 f40e35855771202a 106aa07032bbd1b8
 

19a4c116b8d2d0c8 1e376c085141ab53 2748774cdf8eeb99 34b0bcb5e19b48a8
 

391c0cb3c5c95a63 4ed8aa4ae3418acb 5b9cca4f7763e373 682e6ff3d6b2b8a3
 

748f82ee5defb2fc 78a5636f43172f60 84c87814a1f0ab72 8cc702081a6439ec
 

90befffa23631e28 a4506cebde82bde9 bef9a3f7b2c67915 c67178f2e372532b
 

ca273eceea26619c d186b8c721c0c207 eada7dd6cde0eb1e f57d4f7fee6ed178
 

06f067aa72176fba 0a637dc5a2c898a6 113f9804bef90dae 1b710b35131c471b
 

28db77f523047d84 32caab7b40c72493 3c9ebe0a15c9bebc 431d67c49c100d4c
 

4cc5d4becb3e42b6 597f299cfc657e2a 5fcb6fab3ad6faec 6c44198c4a475817
 

12
 
 

 

 

 

 

 

 

 

5. PREPROCESSING 

Preprocessing consists of three steps: padding the message, M (Sec. 5.1), parsing the message 

into message blocks (Sec. 5.2), and setting the initial hash value, H(0) (Sec. 5.3). 

5.1 Padding the Message 

The purpose of this padding is to ensure that the padded message is a multiple of 512 or 1024 

bits, depending on the algorithm. Padding can be inserted before hash computation begins on a 

message, or at any other time during the hash computation prior to processing the block(s) that 

will contain the padding. 

5.1.1 SHA-1, SHA-224 and SHA-256 

Suppose that the length of the message, M, is  bits. Append the bit “1” to the end of the 

message, followed by k zero bits, where k is the smallest, non-negative solution to the equation 

 +1+ k ≡ 448mod 512 . Then append the 64-bit block that is equal to the number  expressed 

using a binary representation. For example, the (8-bit ASCII) message “abc” has length 

8×3 = 24 , so the message is padded with a one bit, then 448− (24 +1) = 423 zero bits, and then 

the message length, to become the 512-bit padded message 

423 64 

 

01100001 01100010 01100011 1 00...00 00...011000
    

“a” “b” “c”  = 24

The length of the padded message should now be a multiple of 512 bits. 

5.1.2 SHA-384, SHA-512, SHA-512/224 and SHA-512/256 

Suppose the length of the message M, in bits, is  bits. Append the bit “1” to the end of the 

message, followed by k zero bits, where k is the smallest non-negative solution to the equation 

 +1+ k ≡ 896mod1024. Then append the 128-bit block that is equal to the number  expressed 

using a binary representation. For example, the (8-bit ASCII) message “abc” has length 

8×3 = 24 , so the message is padded with a one bit, then 896 − (24 +1) = 871 zero bits, and then 

the message length, to become the 1024-bit padded message 

871 128 

 

01100001 01100010 01100011 1 00...00 00...011000
    

“a” “b” “c”  = 24

The length of the padded message should now be a multiple of 1024 bits. 

13
 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

5.2 Parsing the Message 

The message and its padding must be parsed into N m-bit blocks. 

5.2.1 SHA-1, SHA-224 and SHA-256 

For SHA-1, SHA-224 and SHA-256, the message and its padding are parsed into N 512-bit 

, M(2) blocks, M(1) ,..., M(N). Since the 512 bits of the input block may be expressed as sixteen 32- ( M1

i

(i) on up to M15 . 

5.2.2 SHA-384, SHA-512, SHA-512/224 and SHA-512/256 

For SHA-384, SHA-512, SHA-512/224 and SHA-512/256, the message and its padding are 

, M(2) parsed into N 1024-bit blocks, M(1) ,..., M(N). Since the 1024 bits of the input block may be 

(

0

i) ) bit words, the first 32 bits of message block i are denoted M , the next 32 bits are , and so 

(

0

i) expressed as sixteen 64-bit words, the first 64 bits of message block i are denoted M , the next 

M i

5.3 Setting the Initial Hash Value (H(0)) 

Before hash computation begins for each of the secure hash algorithms, the initial hash value, 

H(0), must be set. The size and number of words in H(0) depends on the message digest size. 

5.3.1 SHA-1 

For SHA-1, the initial hash value, H(0), shall consist of the following five 32-bit words, in hex: 

H0

(0) = 67452301 

H1

(0) = efcdab89 

H2

(0) = 98badcfe 

(

1

H3

(0) = 10325476 

H4

(0) = c3d2e1f0 

5.3.2 SHA-224 

For SHA-224, the initial hash value, H(0), shall consist of the following eight 32-bit words, in 

hex: 

H0

(0)

= c1059ed8 

(0) H1 = 367cd507 

(0) H2 = 3070dd17 

H3

(0)

= f70e5939 

(0) H4 = ffc00b31 

H5

(0)

= 68581511 

H6

(0)

= 64f98fa7 

) (i) 64 bits are , and so on up to M
 . 15

14
 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

H7

(0)

= befa4fa4 

5.3.3 SHA-256 

For SHA-256, the initial hash value, H(0), shall consist of the following eight 32-bit words, in 

hex: 

H0

(0) = 6a09e667 

H1

(0) = bb67ae85 

H2

(0) = 3c6ef372 

H3

(0) = a54ff53a 

H4

(0) = 510e527f 

H5

(0) = 9b05688c 

H6

(0) = 1f83d9ab 

H7

(0) = 5be0cd19 

These words were obtained by taking the first thirty-two bits of the fractional parts of the square 

roots of the first eight prime numbers. 

5.3.4 SHA-384 

For SHA-384, the initial hash value, H(0), shall consist of the following eight 64-bit words, in 

hex: 

H0

(0) = cbbb9d5dc1059ed8 

H1

(0) = 629a292a367cd507 

H2

(0) = 9159015a3070dd17 

H3

(0) = 152fecd8f70e5939 

H4

(0) = 67332667ffc00b31 

H5

(0) = 8eb44a8768581511 

H6

(0) = db0c2e0d64f98fa7 

H7

(0) = 47b5481dbefa4fa4 

These words were obtained by taking the first sixty-four bits of the fractional parts of the square 

roots of the ninth through sixteenth prime numbers. 

5.3.5 SHA-512 

For SHA-512, the initial hash value, H(0), shall consist of the following eight 64-bit words, in 

hex: 

H0

(0) = 6a09e667f3bcc908 

H1

(0) = bb67ae8584caa73b
 

15
 
 

 

 

 

 

 

 

 

 

 

 

H2

(0) = 3c6ef372fe94f82b 

H3

(0) = a54ff53a5f1d36f1 

H4

(0) = 510e527fade682d1 

H5

(0) = 9b05688c2b3e6c1f 

H6

(0) = 1f83d9abfb41bd6b 

H7

(0) = 5be0cd19137e2179 

These words were obtained by taking the first sixty-four bits of the fractional parts of the square 

roots of the first eight prime numbers. 

5.3.6 SHA-512/t

“SHA-512/t” is the general name for a t-bit hash function based on SHA-512 whose output is 

truncated to t bits. Each hash function requires a distinct initial hash value. This section provides 

a procedure for determining the initial value for SHA-512/ t for a given value of t. 

For SHA-512/t, t is any positive integer without a leading zero such that t < 512, and t is not 384. 

For example: t is 256, but not 0256, and “SHA-512/t” is “SHA-512/256” (an 11 character long 

ASCII string), which is equivalent to 53 48 41 2D 35 31 32 2F 32 35 36 in hexadecimal. 

The initial hash value for SHA-512/t, for a given value of t, shall be generated by the SHA-512/t 

IV Generation Function below. 

SHA-512/t IV Generation Function 

(begin:) 

Denote H(0)′to be the initial hash value of SHA-512 as specified in Section 5.3.5 above. 

Denote H(0)′′ to be the initial hash value computed below. 

H(0) is the IV for SHA-512/t. 

For i = 0 to 7 

{ 

(0)′′ (0)′ Hi = Hi ⊕ a5a5a5a5a5a5a5a5(in hex).
 

}
 

H(0) = SHA-512 (“SHA-512/t”) using H(0)′′ as the IV, where t is the specific truncation value. 

(end.) 

16
 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

SHA-512/224 (t = 224) and SHA-512/256 (t = 256) are approved hash algorithms. Other SHA512/t hash algorithms with different t values may be specified in [SP 800-107] in the future as 

the need arises. Below are the IVs for SHA-512/224 and SHA-512/256. 

5.3.6.1 SHA-512/224 

For SHA-512/224, the initial hash value, H(0), shall consist of the following eight 64-bit words, 

in hex: 

H0

(0) = 8C3D37C819544DA2 

H1

(0) = 73E1996689DCD4D6
 

(0) H2 = 1DFAB7AE32FF9C82 

H3

(0) = 679DD514582F9FCF 

(0) H4 = 0F6D2B697BD44DA8 

H5

(0) = 77E36F7304C48942 

H6

(0) = 3F9D85A86A1D36C8 

H7

(0) = 1112E6AD91D692A1 

These words were obtained by executing the SHA-512/t IV Generation Function with t = 224. 

5.3.6.2 SHA-512/256 

For SHA-512/256, the initial hash value, H(0), shall consist of the following eight 64-bit words, 

in hex: 

H0

(0) = 22312194FC2BF72C 

H1

(0) = 9F555FA3C84C64C2 

H2

(0) = 2393B86B6F53B151
 

H3

(0) = 963877195940EABD 

H4

(0) = 96283EE2A88EFFE3 

H5

(0) = BE5E1E2553863992 

H6

(0) = 2B0199FC2C85B8AA 

H7

(0) = 0EB72DDC81C52CA2 

These words were obtained by executing the SHA-512/t IV Generation Function with t = 256. 

17
 
 

 

6. SECURE HASH ALGORITHMS 

In the following sections, the hash algorithms are not described in ascending order of size. SHA256 is described before SHA-224 because the specification for SHA-224 is identical to SHA256, except that different initial hash values are used, and the final hash value is truncated to 224 

bits for SHA-224. The same is true for SHA-512, SHA-384, SHA-512/224 and SHA-512/256, 

except that the final hash value is truncated to 224 bits for SHA-512/224, 256 bits for SHA512/256 or 384 bits for SHA-384. 

For each of the secure hash algorithms, there may exist alternate computation methods that yield 

identical results; one example is the alternative SHA-1 computation described in Sec. 6.1.3. 

Such alternate methods may be implemented in conformance to this standard. 

6.1 SHA-1 

264 SHA-1 may be used to hash a message, M, having a length of  bits, where 0 ≤  < . The 

algorithm uses 1) a message schedule of eighty 32-bit words, 2) five working variables of 32 bits 

each, and 3) a hash value of five 32-bit words. The final result of SHA-1 is a 160-bit message 

digest. 

The words of the message schedule are labeled W0, W1,..., W79. The five working variables are 

labeled a, b, c, d, and e. The words of the hash value are labeled H (

0

i)

, H (

1

i)

,..., H (

4

i)

, which will 

hold the initial hash value, H(0), replaced by each successive intermediate hash value (after each 

message block is processed), H(i), and ending with the final hash value, H(N). SHA-1 also uses a 

single temporary word, T. 

6.1.1 SHA-1 Preprocessing 

1. Set the initial hash value, H(0), as specified in Sec. 5.3.1. 

2. The message is padded and parsed as specified in Section 5. 

6.1.2 SHA-1 Hash Computation 

The SHA-1 hash computation uses functions and constants previously defined in Sec. 4.1.1 and 

Sec. 4.2.1, respectively. Addition (+) is performed modulo 232. 

, M(2) Each message block, M(1) , ..., M(N), is processed in order, using the following steps: 

18
 
 

For i=1 to N: 

{ 

1. Prepare the message schedule, {Wt}: 

(i) M t	 0 ≤ t ≤ 15

Wt= 

ROTL1(W ⊕W ⊕W ⊕W ) 16 ≤ t ≤ 79 t−3 t−8 t−14 t−16

2. Initialize the five working variables, a, b, c, d, and e, with the (i-1)st hash value: 

(i−1) a = H0

i−1)

i−1)

(

1

(

2

b = H

c = H

(i−1)

3 d = H

(

4

i−1) e = H

3.	 For t=0 to 79: 

{ 

T = ROTL5(a) + ft	 (b,c, d) + e + Kt t +W

e = d
 

d = c
 

c = ROTL30 (b)
 

b = a
 

a = T
 

} 

4.	 Compute the i

th intermediate hash value H(i)

: 

(i i

0

) (

0

−1) H
 = a + H

(i i

1

) (

1

−1) H
 = b + H

(i i

2

) (

2

−1) H
 = c + H

(i i−1)

3

) ( H 3 
 = d + H

i (

4

( i

4

) −1) H
 = e + H

}
 

19
 
 

 

 

After repeating steps one through four a total of N times (i.e., after processing M(N)), the resulting 

160-bit message digest of the message, M, is 

H (

0

N) H (

1

N) H (

2

N) H (

3

N) H (

4

N)

6.1.3 Alternate Method for Computing a SHA-1 Message Digest 

The SHA-1 hash computation method described in Sec. 6.1.2 assumes that the message schedule 

W0, W1,..., W79 is implemented as an array of eighty 32-bit words. This is efficient from the 

standpoint of the minimization of execution time, since the addresses of Wt-3,..., Wt-16 in step (2) 

of Sec. 6.1.2 are easily computed. 

However, if memory is limited, an alternative is to regard {Wt} as a circular queue that may be 

implemented using an array of sixteen 32-bit words, W0, W1,..., W15. The alternate method that is 

described in this section yields the same message digest as the SHA-1 computation method 

described in Sec. 6.1.2. Although this alternate method saves sixty-four 32-bit words of storage, 

it is likely to lengthen the execution time due to the increased complexity of the address 

computations for the {Wt} in step (3). 

For this alternate SHA-1 method, let MASK=0000000f (in hex). As in Sec. 6.1.1, addition is 

performed modulo 232. Assuming that the preprocessing as described in Sec. 6.1.1 has been 

performed, the processing of M(i) is as follows: 

For i=1 to N: 

{ 

1.	 For t=0 to 15:
 

{
 

Wt	 = Mt

(i)

} 

2. Initialize the five working variables, a, b, c, d, and e, with the (i-1)st hash value: 

(

0

i−1) a = H

(

1

(

2

i−1)

i−1)

b = H

c = H

(

3

i−1) d = H

(

4

i−1) e = H

3.	 For t=0 to 79: 

{ 

s = t ∧ MASK

20
 
If 

{ 

} 

t ≥ 16 then 

( 13)(

1 Ws = ROTL W s+ ∧MASK ⊕W s+8)( ∧MASK ⊕W s+2)( ∧MASK ) ⊕Ws

cd

de

T aROTL

=

=

= ( ) + 5

c df Keb t ++ t , ),( +Ws

Ta

ab

c bROTL

=

=

= ( ) 30

} 

4. Compute the i

th intermediate hash value H(i)

: 

(i i

0

) (

0

−1) H
 = a + H

(i i

1

) (

1

−1) H
 = b + H

(i i

2

) (

2

−1) H
 = c + H

(i i−1)

3

) ( H 3 
 = d + H

i (

4

( i

4

) −1) H
 = e + H

} 

After repeating steps one through four a total of N times (i.e., after processing M(N)), the resulting 

160-bit message digest of the message, M, is 

H (

0

N) H (

1

N) H (

2

N) H (

3

N) H (

4

N)

6.2 SHA-256 

264 SHA-256 may be used to hash a message, M, having a length of  bits, where 0 ≤  < . The 

algorithm uses 1) a message schedule of sixty-four 32-bit words, 2) eight working variables of 32 

bits each, and 3) a hash value of eight 32-bit words. The final result of SHA-256 is a 256-bit 

message digest. 

The words of the message schedule are labeled W0, W1,..., W63. The eight working variables are 

labeled a, b, c, d, e, f, g, and h. The words of the hash value are labeled H (

0

i) H (

1

i) H (

7

) , ,..., , 

which will hold the initial hash value, H(0), replaced by each successive intermediate hash value 

21 

i
 

(after each message block is processed), H(i), and ending with the final hash value, H(N). SHA256 also uses two temporary words, T1 and T2. 

6.2.1 SHA-256 Preprocessing 

1. Set the initial hash value, H(0), as specified in Sec. 5.3.3. 

2. The message is padded and parsed as specified in Section 5. 

6.2.2 SHA-256 Hash Computation 

The SHA-256 hash computation uses functions and constants previously defined in Sec. 4.1.2 

and Sec. 4.2.2, respectively. Addition (+) is performed modulo 232. 

, M(2) Each message block, M(1) , ..., M(N), is processed in order, using the following steps: 

For i=1 to N:
 

{
 

1. Prepare the message schedule, {Wt}: 

M t

(i) 0 ≤ t ≤ 15

Wt= 

{256}	 {256} σ (W ) +W +σ (W ) +W 16 ≤ t ≤ 63 1 t−2 t−7 0 t−15 t−16

2.	 Initialize the eight working variables, a, b, c, d, e, f, g, and h, with the (i-1)st hash 

value: 

(

0

i−1) a = H

(

1

(

2

i−1)

i−1)

b = H

c = H

(

3

i−1) d = H

(

4

i−1) e = H

(

5

i−1) f = H

(

6

i−1) g = H

(

7

i−1) h = H

22
 
3.	 For t=0 to 63: 

{ 

{256} {256} T1 = h +∑ (e) + Ch(e, f , g) + Kt +W

1 t

{256}

T2	 = ∑ (a) + Maj(a,b,c) 0

h = g

g = f

f = e

e = d + T1

d = c

c = b

b = a

a = T1 + T2

} 

4.	 Compute the i

th intermediate hash value H(i)

: 

(

0

i) (

0

i−1) H
 = a + H

(

1

i) (

1

i−1) H
 = b + H

(

2

i) (

2

i−1) H
 = c + H

(

3

i) (

3

i−1) H
 = d + H

(

4

i) (

4

i−1) H
 = e + H

(

5

i) (

5

i−1) H
 = f + H

(

6

i) (

6

i−1) H
 = g + H

(

7

i) (

7

i−1) H
 = h + H

} 

After repeating steps one through four a total of N times (i.e., after processing M(N)), the resulting 

256-bit message digest of the message, M, is 

H (

0

N) H(

1

N) H(

2

N) H (

3

N) H(

4

N) H(

5

N) H (

6

N) H(

7

N)

6.3 SHA-224 

264 SHA-224 may be used to hash a message, M, having a length of  bits, where 0 ≤  < . The 

function is defined in the exact same manner as SHA-256 (Section 6.2), with the following two 

exceptions: 

1. The initial hash value, H(0), shall be set as specified in Sec. 5.3.2; and 

23
 
 

 

 

2. The 224-bit message digest is obtained by truncating the final hash value, H(N), to its 

left-most 224 bits: 

H (

0

N) H (

1

N) H (

2

N) H (

3

N) H (

4

N) H (

5

N) H6

(N)

6.4 SHA-512 

2128 SHA-512 may be used to hash a message, M, having a length of  bits, where 0 ≤  < . The 

algorithm uses 1) a message schedule of eighty 64-bit words, 2) eight working variables of 64 

bits each, and 3) a hash value of eight 64-bit words. The final result of SHA-512 is a 512-bit 

message digest. 

The words of the message schedule are labeled W0, W1,..., W79. The eight working variables are 

labeled a, b, c, d, e, f, g, and h. The words of the hash value are labeled H (

0

i)

, H (

1

i)

,..., H (

7

i)

, 

which will hold the initial hash value, H(0), replaced by each successive intermediate hash value 

(after each message block is processed), H(i)

, and ending with the final hash value, H(N). SHA512 also uses two temporary words, T1 and T2. 

6.4.1 SHA-512 Preprocessing 

1. Set the initial hash value, H(0), as specified in Sec. 5.3.5. 

2. The message is padded and parsed as specified in Section 5. 

6.4.2 SHA-512 Hash Computation 

The SHA-512 hash computation uses functions and constants previously defined in Sec. 4.1.3 

and Sec. 4.2.3, respectively. Addition (+) is performed modulo 264. 

, M(2) Each message block, M(1) , ..., M(N), is processed in order, using the following steps: 

For i=1 to N: 

{ 

1. Prepare the message schedule, {Wt}: 

M t

(i) 0 ≤ t ≤ 15

Wt= 

{512}	 {512} σ (W ) +W +σ (W ) +W 16 ≤ t ≤ 79 1 t−2 t−7 0 t−15 t−16

2.	 Initialize the eight working variables, a, b, c, d, e, f, g, and h, with the (i-1)st hash 

value: 

24
 
(

0

i−1) a = H

i−1) b = H (

1

(

2

i−1) c = H

(

3

i−1) d = H

(

4

i−1) e = H

(

5

i−1) f = H

(

6

i−1) g = H

(

7

i−1) h = H

3.	 For t=0 to 79: 

{ 

{512} {512} T1 = h +∑ (e) + Ch(e, f , g) + Kt +W

1 t

{512} T2	 = ∑ (a) + Maj(a,b,c) 0

h = g

g = f

f = e

e = d + T1

d = c

c = b

b = a

a = T1 + T2

} 

4.	 Compute the i

th intermediate hash value H(i)

: 

(

0

i) (

0

i−1) H
 = a + H

(

1

i) (

1

i−1) H
 = b + H

(

2

i) (

2

i−1) H
 = c + H

(

3

i) (

3

i−1) H
 = d + H

(

4

i) (

4

i−1) H
 = e + H

(

5

i) (

5

i−1) H
 = f + H

(

6

i) (

6

i−1) H
 = g + H

H (

7

i) = h + H (

7

i−1)

} 

25 
After repeating steps one through four a total of N times (i.e., after processing M(N)), the resulting 

512-bit message digest of the message, M, is 

)(

7

)(

6

)(

5

)(

4

)(

3

)(

2

)(

1

)(

0

NNNNNNNN HHHHHHHH

6.5 SHA-384 

2128 SHA-384 may be used to hash a message, M, having a length of  bits, where 0 ≤  < . The 

algorithm is defined in the exact same manner as SHA-512 (Sec. 6.4), with the following two 

exceptions: 

1.	 The initial hash value, H(0), shall be set as specified in Sec. 5.3.4; and 

2.	 The 384-bit message digest is obtained by truncating the final hash value, H(N), to its 

left-most 384 bits: 

H(

0

N) H(

1

N) H(

2

N) H(

3

N) H(

4

N) H(

5

N)

6.6 SHA-512/224 

2128 SHA-512/224 may be used to hash a message, M, having a length of  bits, where 0 ≤  < . 

The algorithm is defined in the exact same manner as SHA-512 (Sec. 6.4), with the following 

two exceptions: 

1.	 The initial hash value, H(0), shall be set as specified in Sec. 5.3.6.1; and 

2.	 The 224-bit message digest is obtained by truncating the final hash value, H(N), to its 

left-most 224 bits. 

6.7 SHA-512/256 

2128 SHA-512/256 may be used to hash a message, M, having a length of  bits, where 0 ≤  < . 

The algorithm is defined in the exact same manner as SHA-512 (Sec. 6.4), with the following 

two exceptions: 

1.	 The initial hash value, H(0), shall be set as specified in Sec. 5.3.6.2; and 

2.	 The 256-bit message digest is obtained by truncating the final hash value, H(N), to its 

left-most 256 bits. 

26
 
7. TRUNCATION OF A MESSAGE DIGEST 

Some application may require a hash function with a message digest length different than those 

provided by the hash functions in this Standard. In such cases, a truncated message digest may be 

used, whereby a hash function with a larger message digest length is applied to the data to be 

hashed, and the resulting message digest is truncated by selecting an appropriate number of the 

leftmost bits. For guidelines on choosing the length of the truncated message digest and 

information about its security implications for the cryptographic application that uses it, see SP 

800-107 [SP 800-107]. 

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APPENDIX A: Additional Information 

A.1 Security of the Secure Hash Algorithms 

The security of the five hash algorithms, SHA-1, SHA-224, SHA-256, SHA-384, SHA-512, 

SHA-512/224 and SHA-512/256 is discussed in [SP 800-107]. 

A.2 Implementation Notes 

Examples of SHA-1, SHA-224, SHA-256, SHA-384, SHA-512, SHA-512/224 and SHA512/256 are available at http://csrc.nist.gov/groups/ST/toolkit/examples.html. 

A.3 Object Identifiers 

Object identifiers (OIDs) for the SHA-1, SHA-224, SHA-256, SHA-384, SHA-512, SHA512/224 and SHA-512/256 algorithms are posted at 

http://csrc.nist.gov/groups/ST/crypto_apps_infra/csor/algorithms.html. 

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APPENDIX B: REFERENCES
 

[FIPS 180-3] NIST, Federal Information Processing Standards Publication 180-3, Secure 

Hash Standards (SHS), October 2008. 

[SP 800-57] NIST Special Publication (SP) 800-57, Part 1, Recommendation for Key 

Management: General, (Draft) May 2011. 

[SP 800-107] NIST Special Publication (SP) 800-107, Recommendation for Applications 

Using Approved Hash Algorithms, (Revised), (Draft) September 2011. 

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APPENDIX C: Technical Changes from FIPS 180-3 

1.	 In FIPS 180-3, padding was inserted before hash computation begins. FIPS 140-4 

removed this restriction. Padding can be inserted before hash computation begins or at 

any other time during the hash computation prior to processing the message block(s) 

containing the padding. 

2.	 FIPS 180-4 adds two additional algorithms: SHA-512/224 and SHA-512/256 to the 

Standard and the method for determining the initial value for SHA-512/t for a given value 

of t. 

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