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/*
* EMSA2
* (C) 1999-2007 Jack Lloyd
*
* Distributed under the terms of the Botan license
*/
#include <botan/emsa2.h>
#include <botan/hash_id.h>
namespace Botan {
namespace {
/*
* EMSA2 Encode Operation
*/
secure_vector<byte> emsa2_encoding(const secure_vector<byte>& msg,
size_t output_bits,
const secure_vector<byte>& empty_hash,
byte hash_id)
{
const size_t HASH_SIZE = empty_hash.size();
size_t output_length = (output_bits + 1) / 8;
if(msg.size() != HASH_SIZE)
throw Encoding_Error("EMSA2::encoding_of: Bad input length");
if(output_length < HASH_SIZE + 4)
throw Encoding_Error("EMSA2::encoding_of: Output length is too small");
bool empty = true;
for(size_t j = 0; j != HASH_SIZE; ++j)
if(empty_hash[j] != msg[j])
empty = false;
secure_vector<byte> output(output_length);
output[0] = (empty ? 0x4B : 0x6B);
output[output_length - 3 - HASH_SIZE] = 0xBA;
set_mem(&output[1], output_length - 4 - HASH_SIZE, 0xBB);
buffer_insert(output, output_length - (HASH_SIZE + 2), &msg[0], msg.size());
output[output_length-2] = hash_id;
output[output_length-1] = 0xCC;
return output;
}
}
/*
* EMSA2 Update Operation
*/
void EMSA2::update(const byte input[], size_t length)
{
hash->update(input, length);
}
/*
* Return the raw (unencoded) data
*/
secure_vector<byte> EMSA2::raw_data()
{
return hash->final();
}
/*
* EMSA2 Encode Operation
*/
secure_vector<byte> EMSA2::encoding_of(const secure_vector<byte>& msg,
size_t output_bits,
RandomNumberGenerator&)
{
return emsa2_encoding(msg, output_bits, empty_hash, hash_id);
}
/*
* EMSA2 Verify Operation
*/
bool EMSA2::verify(const secure_vector<byte>& coded,
const secure_vector<byte>& raw,
size_t key_bits)
{
try
{
return (coded == emsa2_encoding(raw, key_bits,
empty_hash, hash_id));
}
catch(...)
{
return false;
}
}
/*
* EMSA2 Constructor
*/
EMSA2::EMSA2(HashFunction* hash_in) : hash(hash_in)
{
empty_hash = hash->final();
const std::string hash_name = hash->name();
hash_id = ieee1363_hash_id(hash_name);
if(hash_id == 0)
{
delete hash;
throw Encoding_Error("EMSA2 no hash identifier for " + hash_name);
}
}
}
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