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/*
* EMSA1
* (C) 1999-2007 Jack Lloyd
*
* Distributed under the terms of the Botan license
*/
#include <botan/emsa1.h>
namespace Botan {
namespace {
SecureVector<byte> emsa1_encoding(const MemoryRegion<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;
SecureVector<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;
}
}
/*
* EMSA1 Update Operation
*/
void EMSA1::update(const byte input[], size_t length)
{
hash->update(input, length);
}
/*
* Return the raw (unencoded) data
*/
SecureVector<byte> EMSA1::raw_data()
{
return hash->final();
}
/*
* EMSA1 Encode Operation
*/
SecureVector<byte> EMSA1::encoding_of(const MemoryRegion<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);
}
/*
* EMSA1 Decode/Verify Operation
*/
bool EMSA1::verify(const MemoryRegion<byte>& coded,
const MemoryRegion<byte>& raw, size_t key_bits)
{
try {
if(raw.size() != hash->output_length())
throw Encoding_Error("EMSA1::encoding_of: Invalid size for input");
SecureVector<byte> our_coding = emsa1_encoding(raw, key_bits);
if(our_coding == coded) return true;
if(our_coding[0] != 0) return false;
if(our_coding.size() <= coded.size()) return false;
size_t offset = 0;
while(our_coding[offset] == 0 && offset < our_coding.size())
++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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