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Posted 14 Dec 2007

C++ Class Implementation of HMAC-SHA

, 2 May 2010
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C++ class of HMAC-SHA1


This is my first article on CodeProject. Sorry for my poor English.

The reason I think it might be helpful that I share this HMAC-SHA1 class is because I found no related source I could refer to. This is a simple C++ class of HMAC-SHA1 with only single byte character support. You could add double bytes character support if needed. You will find this class contains only a function HMAC_SHA1 that accept test input and hash key, then generates a digest.


Thanks to Dominik Reichl, the SHA1 class I wrapped is from his amazing class. I simply implemented the HMAC algorithm on it. For MD5, you could refer to RFC. There is a detailed programming flow of it.

Using the Code

The usage of this class is extremely simple. Declare CHMAC_SHA1, call its HMAC_SHA1 function. That's it!

You may use HMAC-SHA1 in RFC 2202 test case to verify your implementation.

Following is test case 1 in RFC 2202.

#include "HMAC_SHA1.h"
BYTE Key[20] ;
BYTE digest[20] ; 

unsigned char *test = "Hi There" ; 
memset(Key, 0x0b, 20) ;
HMAC_SHA1.HMAC_SHA1(test, strlen(test), Key, sizeof(Key), digest) ;
// Check with digest equal to 0xb617318655057264e28bc0b6fb378c8ef146be00
// or not


  • 2007/12/17: Updated sample code with RFC 2202 test case 1


This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)


About the Author

Chien-Chung, Chung
Software Developer (Senior)
Taiwan Taiwan
Life is nothing but choices.

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Comments and Discussions

QuestionUnicode or Multi-Byte Matters? Pin
Member 1207894322-Oct-15 17:21
memberMember 1207894322-Oct-15 17:21 
Questionfeedback Pin
Member 120473359-Oct-15 21:48
memberMember 120473359-Oct-15 21:48 
GeneralMy vote of 5 Pin
nicklin026-Mar-13 3:57
membernicklin026-Mar-13 3:57 
QuestionCode Segfaults with messages longer than buffersize minus digestsize Pin
Member 932791917-Sep-12 6:16
memberMember 932791917-Sep-12 6:16 
The code in method HMAC_SHA1 is copying the ipad and the input text into a buffer of fixed size, without checking the length of the input. This will segfault and crash with input text larger than 4076 bytes (I am trying to sign files and executable which are larger than the buffer size).

The buffer copy is also not necessary as you can as well call CSHA1::Update several times with each chunk of data, first with the ipad and then with the text.
// old: CSHA1::Update( (UINT_8 *) AppendBuf1, sizeof( m_ipad ) + text_len );
CSHA1::Update( (UINT_8 *) m_ipad, sizeof( m_ipad ) );
CSHA1::Update( (UINT_8 *) text, text_len );

You can do the same with the opad buffer.
// old: CSHA1::Update( (UINT_8 *) AppendBuf2, sizeof( m_opad ) + SHA1_DIGEST_LENGTH );
CSHA1::Update( (UINT_8 *) m_opad, sizeof( m_opad ) );
CSHA1::Update( (UINT_8 *) szReport, SHA1_DIGEST_LENGTH );

Now you can completely remove AppendBuf1 and AppendBuf2, as they are not used anymore. I tested the change and it produces the same result on my (smaller) files and on the test example "Hi There".

Btw: a different layout like the one used in CSHA1 would be nice, where I can call a method several times with chunks of data from a file and finally call a function to get the hash code. With the current implementation I need to load the whole file into a flat array first.

I also modified HMAC_SHA1, Update and Transform to take 'const' arguments whenever applicable. That way you can use 'char' or 'const char' as arguments for key and text without any compiler errors.

Additionally, although it is common in optimized algorithms to use unions like SHA1_WORKSPACE_BLOCK, the resulting behavior (e.g. after writing uint32 and then reading uint8) is unspecified in any C++ compiler and should therefor be avoided. It is unspecified how those two arrays are exactly padded and aligned in memory and it violates strict aliasing causing the optimizer to do unintended things. Endianness seems to be taken care of explicitly, but would also be a huge problem in general.
QuestionIs the digest same as the one computed by C# code ? Pin
BeckDai12-Apr-12 17:55
memberBeckDai12-Apr-12 17:55 
AnswerRe: Is the digest same as the one computed by C# code ? Pin
Chien-Chung, Chung7-May-12 22:49
memberChien-Chung, Chung7-May-12 22:49 
Questionthe result is not right Pin
haolifengwang1-Jan-12 18:49
memberhaolifengwang1-Jan-12 18:49 
AnswerRe: the result is not right Pin
Chien-Chung, Chung7-May-12 22:47
memberChien-Chung, Chung7-May-12 22:47 
Generalhelp me Pin
kalyan41927-Aug-09 18:41
memberkalyan41927-Aug-09 18:41 
QuestionError message Pin
Godwin Ansa5-Aug-08 3:05
memberGodwin Ansa5-Aug-08 3:05 
AnswerRe: Error message Pin
Chien-Chung, Chung2-May-10 16:38
memberChien-Chung, Chung2-May-10 16:38 
Generalmemset used wrongly Pin
Dante Shamest21-Jul-08 21:06
memberDante Shamest21-Jul-08 21:06 
GeneralRe: memset used wrongly Pin
hetcorp1-Apr-09 4:41
memberhetcorp1-Apr-09 4:41 
GeneralRe: memset used wrongly Pin
Jim Chung2-May-10 16:10
memberJim Chung2-May-10 16:10 
Questionreceiver processing for HMAC-SHA? Pin
Adam Harding3-Jun-08 12:49
memberAdam Harding3-Jun-08 12:49 
GeneralBugfix for long key's [modified] Pin
bruno19996-Mar-08 3:31
memberbruno19996-Mar-08 3:31 
GeneralThanks Pin
bruno19995-Mar-08 9:37
memberbruno19995-Mar-08 9:37 
GeneralRe: Thanks Pin
Godwin Ansa27-Aug-08 3:01
memberGodwin Ansa27-Aug-08 3:01 

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