Authenticating Communications Using Digital Signatures - Implementing SSL/TLS Using Cryptography and PKI - page 200

if ( argc < 4 )
{
fprintf( stderr, “usage: %s [-sha1|md5] [0x]<key> [0x]<text>\n”, argv[ 0 ] );
exit( 0 );
}
if ( !( strcmp( argv[ 1 ], “-sha1” ) ) )
{
new_sha1_digest( &digest );
}
else if ( !( strcmp( argv[ 1 ], “-md5” ) ) )
{
new_md5_digest( &digest );
}
else
{
fprintf( stderr, “usage: %s [-sha1|md5] <key> <text>\n”, argv[ 0 ] );
exit( 1 );
}
key_len = hex_decode( argv[ 2 ], &key );
text_len = hex_decode( argv[ 3 ], &text );
hmac( key, key_len, text, text_len, &digest );
for ( i = 0; i < digest.hash_len * sizeof( int ); i++ )
{
printf( “%.02x”, ( ( unsigned char *) digest.hash )[ i ] );
}
printf( “\n” );
free( digest.hash );
free( key );
free( text );
return 0;
}
#endif
To compute an HMAC, call it like this:
jdavies@localhost$ hmac -md5 Jefe “what do ya want for nothing?”
750c783e6ab0b503eaa86e310a5db738
Where Does All of This Fit into SSL?
You may still be wondering what all this has to do with SSL. After all, you have
secure key exchange and symmetric cryptography. Where does the HMAC
function fi t in?