#include "hmac.h"


void hmac(uint8_t* msg, uint8_t msglen, uint8_t* secret, uint8_t sec_len){
    int8_t i;
    /* 
    ipad = the byte 0x36 repeated B times 
    opad = the byte 0x5C repeated B times.

    To compute HMAC over the data `text' we perform

        H(K XOR opad, H(K XOR ipad, text))

    B is length of hash in bytes, K is the secret and "," ist the string concatination operator
    */

    /* inner Hash */
    sha1_init();
        /*k xor ipad*/
        for(i=0;i<sec_len;++i){
            sha1_addbyte(secret[i]^IPAD);
        }
        /*if key is shorter than blocksize, treat the rest as 0es*/
        for(i=sec_len;i<SHA1_B;++i){
            sha1_addbyte(IPAD);
        }
        /* text */
        for(i=0;i<msglen;++i){
            sha1_addbyte(msg[i]);
        }
        sha1_fill(SHA1_B+msglen);

    /* save the result */
    memcpy(hmac_result,sha1_digest,SHA1_SIZE);
    /* outer hash */
    sha1_init();
        /*k xor opad*/
        for(i=0;i<sec_len;++i){
            sha1_addbyte(secret[i]^OPAD);
        }
        /*if key is shorter than blocksize, treat the rest as 0es*/
        for(i=sec_len;i<SHA1_B;++i){
            sha1_addbyte(OPAD);
        }
        for(i=SHA1_SIZE-1;i>=0;--i){
            sha1_addbyte(hmac_result[i]);
        }
        sha1_fill(SHA1_B+SHA1_SIZE);

    /* save the result */
    memcpy(hmac_result,sha1_digest,SHA1_SIZE);
}