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/*
* TLS v1.0 and v1.2 PRFs
* (C) 2004-2010 Jack Lloyd
*
* Botan is released under the Simplified BSD License (see license.txt)
*/
#include <botan/prf_tls.h>
#include <botan/hmac.h>
namespace Botan {
TLS_PRF::TLS_PRF() :
m_hmac_md5(MessageAuthenticationCode::create("HMAC(MD5)")),
m_hmac_sha1(MessageAuthenticationCode::create("HMAC(SHA-1)"))
{
if(!m_hmac_md5 || !m_hmac_sha1)
throw Algorithm_Not_Found("TLS_PRF HMACs not available");
}
namespace {
/*
* TLS PRF P_hash function
*/
void P_hash(byte out[], size_t out_len,
MessageAuthenticationCode& mac,
const byte secret[], size_t secret_len,
const byte salt[], size_t salt_len)
{
try
{
mac.set_key(secret, secret_len);
}
catch(Invalid_Key_Length)
{
throw Internal_Error("The premaster secret of " +
std::to_string(secret_len) +
" bytes is too long for the PRF");
}
secure_vector<byte> A(salt, salt + salt_len);
secure_vector<byte> h;
size_t offset = 0;
while(offset != out_len)
{
A = mac.process(A);
mac.update(A);
mac.update(salt, salt_len);
mac.final(h);
const size_t writing = std::min(h.size(), out_len - offset);
xor_buf(&out[offset], h.data(), writing);
offset += writing;
}
}
}
size_t TLS_PRF::kdf(byte key[], size_t key_len,
const byte secret[], size_t secret_len,
const byte salt[], size_t salt_len,
const byte label[], size_t label_len) const
{
const size_t S1_len = (secret_len + 1) / 2,
S2_len = (secret_len + 1) / 2;
const byte* S1 = secret;
const byte* S2 = secret + (secret_len - S2_len);
secure_vector<byte> msg;
msg.reserve(label_len + salt_len);
msg += std::make_pair(label, label_len);
msg += std::make_pair(salt, salt_len);
P_hash(key, key_len, *m_hmac_md5, S1, S1_len, msg.data(), msg.size());
P_hash(key, key_len, *m_hmac_sha1, S2, S2_len, msg.data(), msg.size());
return key_len;
}
size_t TLS_12_PRF::kdf(byte key[], size_t key_len,
const byte secret[], size_t secret_len,
const byte salt[], size_t salt_len,
const byte label[], size_t label_len) const
{
secure_vector<byte> msg;
msg.reserve(label_len + salt_len);
msg += std::make_pair(label, label_len);
msg += std::make_pair(salt, salt_len);
P_hash(key, key_len, *m_mac, secret, secret_len, msg.data(), msg.size());
return key_len;
}
}
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