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/*
* PSSR
* (C) 1999-2007 Jack Lloyd
*
* Botan is released under the Simplified BSD License (see license.txt)
*/
#include <botan/internal/pad_utils.h>
#include <botan/pssr.h>
#include <botan/mgf1.h>
#include <botan/internal/bit_ops.h>
namespace Botan {
PSSR* PSSR::make(const Spec& request)
{
if(request.arg(1, "MGF1") != "MGF1")
return nullptr;
if(HashFunction* hash = get_hash_function(request.arg(0)))
{
const size_t salt_size = request.arg_as_integer(2, hash->output_length());
return new PSSR(hash, salt_size);
}
return nullptr;
}
BOTAN_REGISTER_NAMED_T(EMSA, "PSSR", PSSR, PSSR::make);
/*
* PSSR Update Operation
*/
void PSSR::update(const byte input[], size_t length)
{
hash->update(input, length);
}
/*
* Return the raw (unencoded) data
*/
secure_vector<byte> PSSR::raw_data()
{
return hash->final();
}
/*
* PSSR Encode Operation
*/
secure_vector<byte> PSSR::encoding_of(const secure_vector<byte>& msg,
size_t output_bits,
RandomNumberGenerator& rng)
{
const size_t HASH_SIZE = hash->output_length();
if(msg.size() != HASH_SIZE)
throw Encoding_Error("PSSR::encoding_of: Bad input length");
if(output_bits < 8*HASH_SIZE + 8*SALT_SIZE + 9)
throw Encoding_Error("PSSR::encoding_of: Output length is too small");
const size_t output_length = (output_bits + 7) / 8;
secure_vector<byte> salt = rng.random_vec(SALT_SIZE);
for(size_t j = 0; j != 8; ++j)
hash->update(0);
hash->update(msg);
hash->update(salt);
secure_vector<byte> H = hash->final();
secure_vector<byte> EM(output_length);
EM[output_length - HASH_SIZE - SALT_SIZE - 2] = 0x01;
buffer_insert(EM, output_length - 1 - HASH_SIZE - SALT_SIZE, salt);
mgf1_mask(*hash, H.data(), HASH_SIZE, EM.data(), output_length - HASH_SIZE - 1);
EM[0] &= 0xFF >> (8 * ((output_bits + 7) / 8) - output_bits);
buffer_insert(EM, output_length - 1 - HASH_SIZE, H);
EM[output_length-1] = 0xBC;
return EM;
}
/*
* PSSR Decode/Verify Operation
*/
bool PSSR::verify(const secure_vector<byte>& const_coded,
const secure_vector<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 || const_coded.size() <= 1)
return false;
if(const_coded[const_coded.size()-1] != 0xBC)
return false;
secure_vector<byte> coded = const_coded;
if(coded.size() < KEY_BYTES)
{
secure_vector<byte> temp(KEY_BYTES);
buffer_insert(temp, KEY_BYTES - coded.size(), coded);
coded = temp;
}
const size_t TOP_BITS = 8 * ((key_bits + 7) / 8) - key_bits;
if(TOP_BITS > 8 - high_bit(coded[0]))
return false;
byte* DB = coded.data();
const size_t DB_size = coded.size() - HASH_SIZE - 1;
const byte* H = &coded[DB_size];
const size_t H_size = HASH_SIZE;
mgf1_mask(*hash, H, H_size, DB, DB_size);
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;
for(size_t j = 0; j != 8; ++j)
hash->update(0);
hash->update(raw);
hash->update(&DB[salt_offset], DB_size - salt_offset);
secure_vector<byte> H2 = hash->final();
return same_mem(H, H2.data(), HASH_SIZE);
}
PSSR::PSSR(HashFunction* h) :
SALT_SIZE(h->output_length()), hash(h)
{
}
PSSR::PSSR(HashFunction* h, size_t salt_size) :
SALT_SIZE(salt_size), hash(h)
{
}
}
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