Channels ▼
RSS

Licensing Using Symmetric and Asymmetric Cryptography


HexWeb HTML

Listing 1: HMAC using SHA-1

int hmac_sha1(unsigned char *hmac,

size_t hmac_size,

const unsigned char *msg,

size_t msg_len,

const void *key,

size_t key_len)

{

unsigned char padded_key[SHA1_BLOCK_SIZE];

unsigned char k1[SHA1_BLOCK_SIZE];

unsigned char k2[SHA1_BLOCK_SIZE];

unsigned char IPAD[SHA1_BLOCK_SIZE];

unsigned char OPAD[SHA1_BLOCK_SIZE];

unsigned char padded_msg[SHA1_BLOCK_SIZE+msg_len];

unsigned char sha1_result[SHA1_OUTPUT_LEN];

unsigned char padded_res[SHA1_BLOCK_SIZE+SHA1_OUTPUT_LEN];

assert(hmac_size <= SHA1_OUTPUT_LEN);

/* pas key with zeros */

utils_pad(padded_key, sizeof(padded_key),

key, key_len, 0x00, SHA1_BLOCK_SIZE);

/* create IPAD */

utils_pad(IPAD, sizeof(IPAD),

NULL, 0, 0x36, SHA1_BLOCK_SIZE);

/* k1 = padded_key xor IPAD */

utils_xor(k1, sizeof(k1),

padded_key, IPAD);

/* create OPAD */

utils_pad(OPAD, sizeof(OPAD),

NULL, 0, 0x5C, SHA1_BLOCK_SIZE);

/* k2 = padded_key xor OPAD */

utils_xor(k2, sizeof(k2),

padded_key, OPAD);

/* append msg to k1 */

utils_append(padded_msg, sizeof(padded_msg),

k1, sizeof(k1), msg, msg_len);

SHA1(padded_msg, sizeof(k1)+msg_len, sha1_result);

/* append previous result to k2 */

utils_append(padded_res, sizeof(padded_res),

k2, sizeof(k2),

sha1_result, sizeof(sha1_result));

SHA1(padded_res, sizeof(k2)+sizeof(sha1_result),

sha1_result);

/* copy the result */

memcpy(hmac, sha1_result, hmac_size);

return 0;

}


Related Reading


More Insights






Currently we allow the following HTML tags in comments:

Single tags

These tags can be used alone and don't need an ending tag.

<br> Defines a single line break

<hr> Defines a horizontal line

Matching tags

These require an ending tag - e.g. <i>italic text</i>

<a> Defines an anchor

<b> Defines bold text

<big> Defines big text

<blockquote> Defines a long quotation

<caption> Defines a table caption

<cite> Defines a citation

<code> Defines computer code text

<em> Defines emphasized text

<fieldset> Defines a border around elements in a form

<h1> This is heading 1

<h2> This is heading 2

<h3> This is heading 3

<h4> This is heading 4

<h5> This is heading 5

<h6> This is heading 6

<i> Defines italic text

<p> Defines a paragraph

<pre> Defines preformatted text

<q> Defines a short quotation

<samp> Defines sample computer code text

<small> Defines small text

<span> Defines a section in a document

<s> Defines strikethrough text

<strike> Defines strikethrough text

<strong> Defines strong text

<sub> Defines subscripted text

<sup> Defines superscripted text

<u> Defines underlined text

Dr. Dobb's encourages readers to engage in spirited, healthy debate, including taking us to task. However, Dr. Dobb's moderates all comments posted to our site, and reserves the right to modify or remove any content that it determines to be derogatory, offensive, inflammatory, vulgar, irrelevant/off-topic, racist or obvious marketing or spam. Dr. Dobb's further reserves the right to disable the profile of any commenter participating in said activities.

 
Disqus Tips To upload an avatar photo, first complete your Disqus profile. | View the list of supported HTML tags you can use to style comments. | Please read our commenting policy.
 

Video