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/*************************************************
* TLS PRF Source File *
* (C) 2004-2006 Jack Lloyd *
*************************************************/
#include <botan/prf_tls.h>
#include <botan/lookup.h>
#include <botan/xor_buf.h>
#include <botan/hmac.h>
namespace Botan {
/*************************************************
* TLS PRF *
*************************************************/
SecureVector<byte> TLS_PRF::derive(u32bit key_len,
const byte secret[], u32bit secret_len,
const byte seed[], u32bit seed_len) const
{
u32bit S1_len = (secret_len + 1) / 2,
S2_len = (secret_len + 1) / 2;
const byte* S1 = secret;
const byte* S2 = secret + (secret_len - S2_len);
SecureVector<byte> key1, key2;
key1 = P_hash("MD5", key_len, S1, S1_len, seed, seed_len);
key2 = P_hash("SHA-1", key_len, S2, S2_len, seed, seed_len);
xor_buf(key1.begin(), key2.begin(), key2.size());
return key1;
}
/*************************************************
* TLS PRF P_hash function *
*************************************************/
SecureVector<byte> TLS_PRF::P_hash(const std::string& hash, u32bit len,
const byte secret[], u32bit secret_len,
const byte seed[], u32bit seed_len) const
{
SecureVector<byte> out;
HMAC hmac(hash);
hmac.set_key(secret, secret_len);
SecureVector<byte> A(seed, seed_len);
while(len)
{
const u32bit this_block_len = std::min(hmac.OUTPUT_LENGTH, len);
A = hmac.process(A);
hmac.update(A);
hmac.update(seed, seed_len);
SecureVector<byte> block = hmac.final();
out.append(block, this_block_len);
len -= this_block_len;
}
return out;
}
}
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