/* compute TLSv1 PRF (pseudo random function using HMAC) */
static void doPRF(byte* digest, word32 digLen, const byte* secret,word32 secLen,
const byte* label, word32 labLen, const byte* seed, word32 seedLen)
{
word32 half = (secLen + 1) / 2;
byte md5_half[MAX_PRF_HALF]; /* half is real size */
byte sha_half[MAX_PRF_HALF]; /* half is real size */
byte labelSeed[MAX_PRF_LABSEED]; /* labLen + seedLen is real size */
byte md5_result[MAX_PRF_DIG]; /* digLen is real size */
byte sha_result[MAX_PRF_DIG]; /* digLen is real size */
if (half > MAX_PRF_HALF)
return;
if (labLen + seedLen > MAX_PRF_LABSEED)
return;
if (digLen > MAX_PRF_DIG)
return;
XMEMSET(md5_result, 0, digLen);
XMEMSET(sha_result, 0, digLen);
XMEMCPY(md5_half, secret, half);
XMEMCPY(sha_half, secret + half - secLen % 2, half);
XMEMCPY(labelSeed, label, labLen);
XMEMCPY(labelSeed + labLen, seed, seedLen);
p_hash(md5_result, digLen, md5_half, half, labelSeed, labLen + seedLen,
md5_mac);
p_hash(sha_result, digLen, sha_half, half, labelSeed, labLen + seedLen,
sha_mac);
get_xor(digest, digLen, md5_result, sha_result);
}
//get_remainder computes the remainder of a message
unsigned int get_remainder(struct Message message){
//Set up the divisor polynomial
struct Message divisor;
divisor.quarter[4] = CRC_DIVISOR;
int i;
for(i = 0; i < 3; i++){
divisor.quarter[i] = 0;
}
divisor.quarter[3] = POWER_32;
while(!is_quotient_zero(message)){
while(!is_divisor_smaller(message, divisor)){
//Keep right shifting divisor until it is legal to divide the quotient
divisor = right_shift_message(divisor);
}
message = get_xor(message, divisor);
}
message = get_xor(message, divisor);
//The non-quotient portion, namely the last 32 bits of the message is the remainder
return message.quarter[0];
}
// compute TLSv1 PRF (pseudo random function using HMAC)
void PRF(byte* digest, uint digLen, const byte* secret, uint secLen,
const byte* label, uint labLen, const byte* seed, uint seedLen)
{
uint half = (secLen + 1) / 2;
output_buffer md5_half(half);
output_buffer sha_half(half);
output_buffer labelSeed(labLen + seedLen);
md5_half.write(secret, half);
sha_half.write(secret + half - secLen % 2, half);
labelSeed.write(label, labLen);
labelSeed.write(seed, seedLen);
output_buffer md5_result(digLen);
output_buffer sha_result(digLen);
p_hash(md5_result, md5_half, labelSeed, md5);
p_hash(sha_result, sha_half, labelSeed, sha);
md5_result.set_current(0);
sha_result.set_current(0);
get_xor(digest, digLen, md5_result, sha_result);
}
