qemu/crypto/pbkdf.c
Daniel P. Berrange e74aabcffb crypto: use correct derived key size when timing pbkdf
Currently when timing the pbkdf algorithm a fixed key
size of 32 bytes is used. This results in inaccurate
timings for certain hashes depending on their digest
size. For example when using sha1 with aes-256, this
causes us to measure time for the master key digest
doing 2 sha1 operations per iteration, instead of 1.

Instead we should pass in the desired key size to the
timing routine that matches the key size that will be
used for real later.

Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
2016-09-19 16:30:45 +01:00

114 lines
3.3 KiB
C

/*
* QEMU Crypto PBKDF support (Password-Based Key Derivation Function)
*
* Copyright (c) 2015-2016 Red Hat, Inc.
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2 of the License, or (at your option) any later version.
*
* This library is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this library; if not, see <http://www.gnu.org/licenses/>.
*
*/
#include "qemu/osdep.h"
#include "qapi/error.h"
#include "crypto/pbkdf.h"
#ifndef _WIN32
#include <sys/resource.h>
#endif
static int qcrypto_pbkdf2_get_thread_cpu(unsigned long long *val_ms,
Error **errp)
{
#ifdef _WIN32
FILETIME creation_time, exit_time, kernel_time, user_time;
ULARGE_INTEGER thread_time;
if (!GetThreadTimes(GetCurrentThread(), &creation_time, &exit_time,
&kernel_time, &user_time)) {
error_setg(errp, "Unable to get thread CPU usage");
return -1;
}
thread_time.LowPart = user_time.dwLowDateTime;
thread_time.HighPart = user_time.dwHighDateTime;
/* QuadPart is units of 100ns and we want ms as unit */
*val_ms = thread_time.QuadPart / 10000ll;
return 0;
#elif defined(RUSAGE_THREAD)
struct rusage ru;
if (getrusage(RUSAGE_THREAD, &ru) < 0) {
error_setg_errno(errp, errno, "Unable to get thread CPU usage");
return -1;
}
*val_ms = ((ru.ru_utime.tv_sec * 1000ll) +
(ru.ru_utime.tv_usec / 1000));
return 0;
#else
*val_ms = 0;
error_setg(errp, "Unable to calculate thread CPU usage on this platform");
return -1;
#endif
}
uint64_t qcrypto_pbkdf2_count_iters(QCryptoHashAlgorithm hash,
const uint8_t *key, size_t nkey,
const uint8_t *salt, size_t nsalt,
size_t nout,
Error **errp)
{
uint64_t ret = -1;
uint8_t *out;
uint64_t iterations = (1 << 15);
unsigned long long delta_ms, start_ms, end_ms;
out = g_new(uint8_t, nout);
while (1) {
if (qcrypto_pbkdf2_get_thread_cpu(&start_ms, errp) < 0) {
goto cleanup;
}
if (qcrypto_pbkdf2(hash,
key, nkey,
salt, nsalt,
iterations,
out, nout,
errp) < 0) {
goto cleanup;
}
if (qcrypto_pbkdf2_get_thread_cpu(&end_ms, errp) < 0) {
goto cleanup;
}
delta_ms = end_ms - start_ms;
if (delta_ms > 500) {
break;
} else if (delta_ms < 100) {
iterations = iterations * 10;
} else {
iterations = (iterations * 1000 / delta_ms);
}
}
iterations = iterations * 1000 / delta_ms;
ret = iterations;
cleanup:
memset(out, 0, nout);
g_free(out);
return ret;
}