Authenticating Communications Using Digital Signatures - Implementing SSL/TLS Using Cryptography and PKI - page 188

}

memcpy( padded_block + hash_block_length, hash1,
hash_code_length * sizeof( int ) );
digest_hash( padded_block,
hash_block_length + ( hash_code_length * sizeof( int ) ), hash_out,
hash_code_length, hash_block_operate, hash_block_finalize );

free( hash1 );
free( ipad );
free( opad );
free( padded_block );
}

Key

0 × 36 0 × 36 0 × 36 ... text

hash (e.g. MD5 or SHA-1)

0 × 5c 0 × 5c 0 × 5c hash code

hash

HMAC

Figure 4-1: HMAC Function

The method signature is a behemoth, repeated in Listing 4-20.

Listing 4-20: “hmac.h” HMAC function prototype

void hmac( const unsigned char *key,
int key_length,
const unsigned char *text,
int text_length,
int (*hash_block_operate)(const unsigned char *input, unsigned int hash[] ),
int (*hash_block_finalize)(unsigned char *block, int length ),
int hash_block_length,
int hash_code_length,
unsigned int *hash_out )