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/*************************************************
* Randpool Source File *
* (C) 1999-2007 The Botan Project *
*************************************************/
#include <botan/randpool.h>
#include <botan/lookup.h>
#include <botan/bit_ops.h>
#include <botan/util.h>
#include <algorithm>
#include <assert.h>
namespace Botan {
namespace {
/*************************************************
* PRF based on a MAC *
*************************************************/
enum RANDPOOL_PRF_TAG {
USER_INPUT = 0,
CIPHER_KEY = 1,
MAC_KEY = 2,
GEN_OUTPUT = 3
};
SecureVector<byte> randpool_prf(MessageAuthenticationCode* mac,
RANDPOOL_PRF_TAG tag,
const byte in[], u32bit length)
{
mac->update((byte)tag);
mac->update(in, length);
return mac->final();
}
}
/*************************************************
* Generate a buffer of random bytes *
*************************************************/
void Randpool::randomize(byte out[], u32bit length) throw(PRNG_Unseeded)
{
if(!is_seeded())
throw PRNG_Unseeded(name());
update_buffer();
while(length)
{
const u32bit copied = std::min(length, buffer.size());
copy_mem(out, buffer.begin(), copied);
out += copied;
length -= copied;
update_buffer();
}
}
/*************************************************
* Refill the output buffer *
*************************************************/
void Randpool::update_buffer()
{
const u64bit timestamp = system_clock();
for(u32bit j = 0; j != counter.size(); ++j)
if(++counter[j])
break;
store_be(timestamp, counter + 4);
SecureVector<byte> mac_val = randpool_prf(mac, GEN_OUTPUT,
counter, counter.size());
for(u32bit j = 0; j != mac_val.size(); ++j)
buffer[j % buffer.size()] ^= mac_val[j];
cipher->encrypt(buffer);
if(counter[0] % ITERATIONS_BEFORE_RESEED == 0)
{
mix_pool();
update_buffer();
}
}
/*************************************************
* Mix the entropy pool *
*************************************************/
void Randpool::mix_pool()
{
const u32bit BLOCK_SIZE = cipher->BLOCK_SIZE;
mac->set_key(randpool_prf(mac, MAC_KEY, pool, pool.size()));
cipher->set_key(randpool_prf(mac, CIPHER_KEY, pool, pool.size()));
xor_buf(pool, buffer, BLOCK_SIZE);
cipher->encrypt(pool);
for(u32bit j = 1; j != POOL_BLOCKS; ++j)
{
const byte* previous_block = pool + BLOCK_SIZE*(j-1);
byte* this_block = pool + BLOCK_SIZE*j;
xor_buf(this_block, previous_block, BLOCK_SIZE);
cipher->encrypt(this_block);
}
}
/*************************************************
* Add entropy to the internal state *
*************************************************/
void Randpool::add_randomness(const byte data[], u32bit length)
{
u32bit this_entropy = entropy_estimate(data, length);
entropy += std::min(this_entropy, 8*mac->OUTPUT_LENGTH);
entropy = std::min(entropy, 8 * pool.size());
SecureVector<byte> mac_val = randpool_prf(mac, USER_INPUT, data, length);
xor_buf(pool, mac_val, mac_val.size());
mix_pool();
}
/*************************************************
* Check if the the pool is seeded *
*************************************************/
bool Randpool::is_seeded() const
{
return (entropy >= 256);
}
/*************************************************
* Clear memory of sensitive data *
*************************************************/
void Randpool::clear() throw()
{
cipher->clear();
mac->clear();
pool.clear();
buffer.clear();
counter.clear();
entropy = 0;
}
/*************************************************
* Return the name of this type *
*************************************************/
std::string Randpool::name() const
{
return "Randpool(" + cipher->name() + "," + mac->name() + ")";
}
/*************************************************
* Randpool Constructor *
*************************************************/
Randpool::Randpool() : ITERATIONS_BEFORE_RESEED(8), POOL_BLOCKS(32)
{
const std::string CIPHER_NAME = "AES-256";
const std::string MAC_NAME = "HMAC(SHA-256)";
cipher = get_block_cipher(CIPHER_NAME);
mac = get_mac(MAC_NAME);
const u32bit BLOCK_SIZE = cipher->BLOCK_SIZE;
const u32bit OUTPUT_LENGTH = mac->OUTPUT_LENGTH;
if(OUTPUT_LENGTH < BLOCK_SIZE ||
!cipher->valid_keylength(OUTPUT_LENGTH) ||
!mac->valid_keylength(OUTPUT_LENGTH))
{
delete cipher;
delete mac;
throw Internal_Error("Randpool: Invalid algorithm combination " +
CIPHER_NAME + "/" + MAC_NAME);
}
buffer.create(BLOCK_SIZE);
pool.create(POOL_BLOCKS * BLOCK_SIZE);
counter.create(12);
entropy = 0;
mix_pool();
}
/*************************************************
* Randpool Destructor *
*************************************************/
Randpool::~Randpool()
{
delete cipher;
delete mac;
entropy = 0;
}
}
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