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/*
* EMSA1
* (C) 1999-2007 Jack Lloyd
*
* Botan is released under the Simplified BSD License (see license.txt)
*/
#include <botan/emsa1.h>
namespace Botan {
namespace {
secure_vector<byte> emsa1_encoding(const secure_vector<byte>& msg,
size_t output_bits)
{
if(8*msg.size() <= output_bits)
return msg;
size_t shift = 8*msg.size() - output_bits;
size_t byte_shift = shift / 8, bit_shift = shift % 8;
secure_vector<byte> digest(msg.size() - byte_shift);
for(size_t j = 0; j != msg.size() - byte_shift; ++j)
digest[j] = msg[j];
if(bit_shift)
{
byte carry = 0;
for(size_t j = 0; j != digest.size(); ++j)
{
byte temp = digest[j];
digest[j] = (temp >> bit_shift) | carry;
carry = (temp << (8 - bit_shift));
}
}
return digest;
}
}
void EMSA1::update(const byte input[], size_t length)
{
m_hash->update(input, length);
}
secure_vector<byte> EMSA1::raw_data()
{
return m_hash->final();
}
secure_vector<byte> EMSA1::encoding_of(const secure_vector<byte>& msg,
size_t output_bits,
RandomNumberGenerator&)
{
if(msg.size() != hash_output_length())
throw Encoding_Error("EMSA1::encoding_of: Invalid size for input");
return emsa1_encoding(msg, output_bits);
}
bool EMSA1::verify(const secure_vector<byte>& coded,
const secure_vector<byte>& raw, size_t key_bits)
{
try {
if(raw.size() != m_hash->output_length())
throw Encoding_Error("EMSA1::encoding_of: Invalid size for input");
secure_vector<byte> our_coding = emsa1_encoding(raw, key_bits);
if(our_coding == coded) return true;
if(our_coding.empty() || our_coding[0] != 0) return false;
if(our_coding.size() <= coded.size()) return false;
size_t offset = 0;
while(offset < our_coding.size() && our_coding[offset] == 0)
++offset;
if(our_coding.size() - offset != coded.size())
return false;
for(size_t j = 0; j != coded.size(); ++j)
if(coded[j] != our_coding[j+offset])
return false;
return true;
}
catch(Invalid_Argument)
{
return false;
}
}
}
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