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/*************************************************
* EMSA4 Source File *
* (C) 1999-2007 Jack Lloyd *
*************************************************/
#include <botan/emsa4.h>
#include <botan/lookup.h>
#include <botan/bit_ops.h>
namespace Botan {
/*************************************************
* EMSA4 Update Operation *
*************************************************/
void EMSA4::update(const byte input[], u32bit 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,
u32bit output_bits,
RandomNumberGenerator& rng)
{
const u32bit 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 u32bit output_length = (output_bits + 7) / 8;
SecureVector<byte> salt(SALT_SIZE);
rng.randomize(salt, SALT_SIZE);
for(u32bit 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, u32bit key_bits) throw()
{
const u32bit HASH_SIZE = hash->OUTPUT_LENGTH;
const u32bit 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 u32bit TOP_BITS = 8 * ((key_bits + 7) / 8) - key_bits;
if(TOP_BITS > 8 - high_bit(coded[0]))
return false;
SecureVector<byte> DB(coded.begin(), 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;
u32bit salt_offset = 0;
for(u32bit 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(u32bit 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(const std::string& hash_name, const std::string& mgf_name) :
SALT_SIZE(output_length_of(hash_name))
{
hash = get_hash(hash_name);
mgf = get_mgf(mgf_name + "(" + hash_name + ")");
}
/*************************************************
* EMSA4 Constructor *
*************************************************/
EMSA4::EMSA4(const std::string& hash_name, const std::string& mgf_name,
u32bit salt_size) : SALT_SIZE(salt_size)
{
hash = get_hash(hash_name);
mgf = get_mgf(mgf_name + "(" + hash_name + ")");
}
}
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