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/*************************************************
* SSL3 PRF Source File *
* (C) 2004-2006 Jack Lloyd *
*************************************************/
#include <botan/kdf.h>
#include <botan/lookup.h>
#include <memory>
namespace Botan {
namespace {
/*************************************************
* Return the next inner hash *
*************************************************/
OctetString next_hash(u32bit where, u32bit want,
HashFunction* md5, HashFunction* sha1,
const byte secret[], u32bit secret_len,
const byte seed[], u32bit seed_len)
{
if(want > md5->OUTPUT_LENGTH)
throw Internal_Error("SSL3_PRF:next_hash: want is too big");
const byte ASCII_A_CHAR = 0x41;
for(u32bit j = 0; j != where + 1; j++)
sha1->update(ASCII_A_CHAR + where);
sha1->update(secret, secret_len);
sha1->update(seed, seed_len);
SecureVector<byte> sha1_hash = sha1->final();
md5->update(secret, secret_len);
md5->update(sha1_hash);
SecureVector<byte> md5_hash = md5->final();
return OctetString(md5_hash, want);
}
}
/*************************************************
* SSL3 PRF *
*************************************************/
SecureVector<byte> SSL3_PRF::derive(u32bit key_len,
const byte secret[], u32bit secret_len,
const byte seed[], u32bit seed_len) const
{
if(key_len > 416)
throw Internal_Error("SSL3_PRF: Requested key length is too large");
std::auto_ptr<HashFunction> md5(get_hash("MD5"));
std::auto_ptr<HashFunction> sha1(get_hash("SHA-1"));
OctetString output;
int counter = 0;
while(key_len)
{
const u32bit produce = std::min(key_len, md5->OUTPUT_LENGTH);
output = output + next_hash(counter++, produce, md5.get(), sha1.get(),
secret, secret_len, seed, seed_len);
key_len -= produce;
}
return output.bits_of();
}
}
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