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/*
* EMSA4
* (C) 1999-2007 Jack Lloyd
*
* Distributed under the terms of the Botan license
*/
#include <botan/emsa4.h>
#include <botan/mgf1.h>
#include <botan/internal/bit_ops.h>
namespace Botan {
/*
* EMSA4 Update Operation
*/
void EMSA4::update(const byte input[], size_t length)
{
hash->update(input, length);
}
/*
* Return the raw (unencoded) data
*/
SecureVector<byte> EMSA4::raw_data()
{
return hash->final();
}
/*
* EMSA4 Encode Operation
*/
SecureVector<byte> EMSA4::encoding_of(const MemoryRegion<byte>& msg,
size_t output_bits,
RandomNumberGenerator& rng)
{
const size_t HASH_SIZE = hash->output_length();
if(msg.size() != HASH_SIZE)
throw Encoding_Error("EMSA4::encoding_of: Bad input length");
if(output_bits < 8*HASH_SIZE + 8*SALT_SIZE + 9)
throw Encoding_Error("EMSA4::encoding_of: Output length is too small");
const size_t output_length = (output_bits + 7) / 8;
SecureVector<byte> salt = rng.random_vec(SALT_SIZE);
for(size_t j = 0; j != 8; ++j)
hash->update(0);
hash->update(msg);
hash->update(salt, SALT_SIZE);
SecureVector<byte> H = hash->final();
SecureVector<byte> EM(output_length);
EM[output_length - HASH_SIZE - SALT_SIZE - 2] = 0x01;
EM.copy(output_length - 1 - HASH_SIZE - SALT_SIZE, salt, SALT_SIZE);
mgf->mask(H, HASH_SIZE, EM, output_length - HASH_SIZE - 1);
EM[0] &= 0xFF >> (8 * ((output_bits + 7) / 8) - output_bits);
EM.copy(output_length - 1 - HASH_SIZE, H, HASH_SIZE);
EM[output_length-1] = 0xBC;
return EM;
}
/*
* EMSA4 Decode/Verify Operation
*/
bool EMSA4::verify(const MemoryRegion<byte>& const_coded,
const MemoryRegion<byte>& raw, size_t key_bits)
{
const size_t HASH_SIZE = hash->output_length();
const size_t KEY_BYTES = (key_bits + 7) / 8;
if(key_bits < 8*HASH_SIZE + 9)
return false;
if(raw.size() != HASH_SIZE)
return false;
if(const_coded.size() > KEY_BYTES)
return false;
if(const_coded[const_coded.size()-1] != 0xBC)
return false;
SecureVector<byte> coded = const_coded;
if(coded.size() < KEY_BYTES)
{
SecureVector<byte> temp(KEY_BYTES);
temp.copy(KEY_BYTES - coded.size(), coded, coded.size());
coded = temp;
}
const size_t TOP_BITS = 8 * ((key_bits + 7) / 8) - key_bits;
if(TOP_BITS > 8 - high_bit(coded[0]))
return false;
SecureVector<byte> DB(&coded[0], coded.size() - HASH_SIZE - 1);
SecureVector<byte> H(&coded[coded.size() - HASH_SIZE - 1], HASH_SIZE);
mgf->mask(H, H.size(), DB, coded.size() - H.size() - 1);
DB[0] &= 0xFF >> TOP_BITS;
size_t salt_offset = 0;
for(size_t j = 0; j != DB.size(); ++j)
{
if(DB[j] == 0x01)
{ salt_offset = j + 1; break; }
if(DB[j])
return false;
}
if(salt_offset == 0)
return false;
SecureVector<byte> salt(&DB[salt_offset], DB.size() - salt_offset);
for(size_t j = 0; j != 8; ++j)
hash->update(0);
hash->update(raw);
hash->update(salt);
SecureVector<byte> H2 = hash->final();
return (H == H2);
}
/*
* EMSA4 Constructor
*/
EMSA4::EMSA4(HashFunction* h) :
SALT_SIZE(h->output_length()), hash(h)
{
mgf = new MGF1(hash->clone());
}
/*
* EMSA4 Constructor
*/
EMSA4::EMSA4(HashFunction* h, size_t salt_size) :
SALT_SIZE(salt_size), hash(h)
{
mgf = new MGF1(hash->clone());
}
}
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