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/*
* PBKDF2
* (C) 1999-2007 Jack Lloyd
*
* Distributed under the terms of the Botan license
*/
#include <botan/pbkdf2.h>
#include <botan/get_byte.h>
#include <botan/internal/xor_buf.h>
#include <botan/internal/rounding.h>
namespace Botan {
/*
* Return a PKCS #5 PBKDF2 derived key
*/
std::pair<size_t, OctetString>
PKCS5_PBKDF2::key_derivation(size_t key_len,
const std::string& passphrase,
const byte salt[], size_t salt_len,
size_t iterations,
std::chrono::milliseconds msec) const
{
if(key_len == 0)
return std::make_pair(iterations, OctetString());
try
{
mac->set_key(reinterpret_cast<const byte*>(passphrase.data()),
passphrase.length());
}
catch(Invalid_Key_Length)
{
throw Exception(name() + " cannot accept passphrases of length " +
std::to_string(passphrase.length()));
}
secure_vector<byte> key(key_len);
byte* T = &key[0];
secure_vector<byte> U(mac->output_length());
const size_t blocks_needed = round_up(key_len, mac->output_length()) / mac->output_length();
std::chrono::microseconds usec_per_block =
std::chrono::duration_cast<std::chrono::microseconds>(msec) / blocks_needed;
u32bit counter = 1;
while(key_len)
{
size_t T_size = std::min<size_t>(mac->output_length(), key_len);
mac->update(salt, salt_len);
mac->update_be(counter);
mac->final(&U[0]);
xor_buf(T, &U[0], T_size);
if(iterations == 0)
{
/*
If no iterations set, run the first block to calibrate based
on how long hashing takes on whatever machine we're running on.
*/
const auto start = std::chrono::high_resolution_clock::now();
iterations = 1; // the first iteration we did above
while(true)
{
mac->update(U);
mac->final(&U[0]);
xor_buf(T, &U[0], T_size);
iterations++;
/*
Only break on relatively 'even' iterations. For one it
avoids confusion, and likely some broken implementations
break on getting completely randomly distributed values
*/
if(iterations % 10000 == 0)
{
auto time_taken = std::chrono::high_resolution_clock::now() - start;
auto usec_taken = std::chrono::duration_cast<std::chrono::microseconds>(time_taken);
if(usec_taken > usec_per_block)
break;
}
}
}
else
{
for(size_t i = 1; i != iterations; ++i)
{
mac->update(U);
mac->final(&U[0]);
xor_buf(T, &U[0], T_size);
}
}
key_len -= T_size;
T += T_size;
++counter;
}
return std::make_pair(iterations, key);
}
}
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