rtmpdh.c
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/*
* RTMP Diffie-Hellmann utilities
* Copyright (c) 2009 Andrej Stepanchuk
* Copyright (c) 2009-2010 Howard Chu
* Copyright (c) 2012 Samuel Pitoiset
*
* This file is part of FFmpeg.
*
* FFmpeg 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 2.1 of the License, or (at your option) any later version.
*
* FFmpeg 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 FFmpeg; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
*/
/**
* @file
* RTMP Diffie-Hellmann utilities
*/
#include <stdint.h>
#include <string.h>
#include "config.h"
#include "libavutil/attributes.h"
#include "libavutil/error.h"
#include "libavutil/mem.h"
#include "libavutil/random_seed.h"
#include "rtmpdh.h"
#if CONFIG_MBEDTLS
#include <mbedtls/ctr_drbg.h>
#include <mbedtls/entropy.h>
#endif
#define P1024 \
"FFFFFFFFFFFFFFFFC90FDAA22168C234C4C6628B80DC1CD1" \
"29024E088A67CC74020BBEA63B139B22514A08798E3404DD" \
"EF9519B3CD3A431B302B0A6DF25F14374FE1356D6D51C245" \
"E485B576625E7EC6F44C42E9A637ED6B0BFF5CB6F406B7ED" \
"EE386BFB5A899FA5AE9F24117C4B1FE649286651ECE65381" \
"FFFFFFFFFFFFFFFF"
#define Q1024 \
"7FFFFFFFFFFFFFFFE487ED5110B4611A62633145C06E0E68" \
"948127044533E63A0105DF531D89CD9128A5043CC71A026E" \
"F7CA8CD9E69D218D98158536F92F8A1BA7F09AB6B6A8E122" \
"F242DABB312F3F637A262174D31BF6B585FFAE5B7A035BF6" \
"F71C35FDAD44CFD2D74F9208BE258FF324943328F67329C0" \
"FFFFFFFFFFFFFFFF"
#if CONFIG_GMP
#define bn_new(bn) \
do { \
bn = av_malloc(sizeof(*bn)); \
if (bn) \
mpz_init2(bn, 1); \
} while (0)
#define bn_free(bn) \
do { \
mpz_clear(bn); \
av_free(bn); \
} while (0)
#define bn_set_word(bn, w) mpz_set_ui(bn, w)
#define bn_cmp(a, b) mpz_cmp(a, b)
#define bn_copy(to, from) mpz_set(to, from)
#define bn_sub_word(bn, w) mpz_sub_ui(bn, bn, w)
#define bn_cmp_1(bn) mpz_cmp_ui(bn, 1)
#define bn_num_bytes(bn) (mpz_sizeinbase(bn, 2) + 7) / 8
#define bn_bn2bin(bn, buf, len) \
do { \
memset(buf, 0, len); \
if (bn_num_bytes(bn) <= len) \
mpz_export(buf, NULL, 1, 1, 0, 0, bn); \
} while (0)
#define bn_bin2bn(bn, buf, len) \
do { \
bn_new(bn); \
if (bn) \
mpz_import(bn, len, 1, 1, 0, 0, buf); \
} while (0)
#define bn_hex2bn(bn, buf, ret) \
do { \
bn_new(bn); \
if (bn) \
ret = (mpz_set_str(bn, buf, 16) == 0); \
else \
ret = 1; \
} while (0)
#define bn_random(bn, num_bits) \
do { \
int bits = num_bits; \
mpz_set_ui(bn, 0); \
for (bits = num_bits; bits > 0; bits -= 32) { \
mpz_mul_2exp(bn, bn, 32); \
mpz_add_ui(bn, bn, av_get_random_seed()); \
} \
mpz_fdiv_r_2exp(bn, bn, num_bits); \
} while (0)
static int bn_modexp(FFBigNum bn, FFBigNum y, FFBigNum q, FFBigNum p)
{
mpz_powm(bn, y, q, p);
return 0;
}
#elif CONFIG_GCRYPT
#define bn_new(bn) \
do { \
if (!gcry_control(GCRYCTL_INITIALIZATION_FINISHED_P)) { \
if (!gcry_check_version("1.5.4")) \
return AVERROR(EINVAL); \
gcry_control(GCRYCTL_DISABLE_SECMEM, 0); \
gcry_control(GCRYCTL_INITIALIZATION_FINISHED, 0); \
} \
bn = gcry_mpi_new(1); \
} while (0)
#define bn_free(bn) gcry_mpi_release(bn)
#define bn_set_word(bn, w) gcry_mpi_set_ui(bn, w)
#define bn_cmp(a, b) gcry_mpi_cmp(a, b)
#define bn_copy(to, from) gcry_mpi_set(to, from)
#define bn_sub_word(bn, w) gcry_mpi_sub_ui(bn, bn, w)
#define bn_cmp_1(bn) gcry_mpi_cmp_ui(bn, 1)
#define bn_num_bytes(bn) (gcry_mpi_get_nbits(bn) + 7) / 8
#define bn_bn2bin(bn, buf, len) gcry_mpi_print(GCRYMPI_FMT_USG, buf, len, NULL, bn)
#define bn_bin2bn(bn, buf, len) gcry_mpi_scan(&bn, GCRYMPI_FMT_USG, buf, len, NULL)
#define bn_hex2bn(bn, buf, ret) ret = (gcry_mpi_scan(&bn, GCRYMPI_FMT_HEX, buf, 0, 0) == 0)
#define bn_random(bn, num_bits) gcry_mpi_randomize(bn, num_bits, GCRY_WEAK_RANDOM)
static int bn_modexp(FFBigNum bn, FFBigNum y, FFBigNum q, FFBigNum p)
{
gcry_mpi_powm(bn, y, q, p);
return 0;
}
#elif CONFIG_OPENSSL
#define bn_new(bn) bn = BN_new()
#define bn_free(bn) BN_free(bn)
#define bn_set_word(bn, w) BN_set_word(bn, w)
#define bn_cmp(a, b) BN_cmp(a, b)
#define bn_copy(to, from) BN_copy(to, from)
#define bn_sub_word(bn, w) BN_sub_word(bn, w)
#define bn_cmp_1(bn) BN_cmp(bn, BN_value_one())
#define bn_num_bytes(bn) BN_num_bytes(bn)
#define bn_bn2bin(bn, buf, len) BN_bn2bin(bn, buf)
#define bn_bin2bn(bn, buf, len) bn = BN_bin2bn(buf, len, 0)
#define bn_hex2bn(bn, buf, ret) ret = BN_hex2bn(&bn, buf)
#define bn_random(bn, num_bits) BN_rand(bn, num_bits, 0, 0)
static int bn_modexp(FFBigNum bn, FFBigNum y, FFBigNum q, FFBigNum p)
{
BN_CTX *ctx = BN_CTX_new();
if (!ctx)
return AVERROR(ENOMEM);
if (!BN_mod_exp(bn, y, q, p, ctx)) {
BN_CTX_free(ctx);
return AVERROR(EINVAL);
}
BN_CTX_free(ctx);
return 0;
}
#elif CONFIG_MBEDTLS
#define bn_new(bn) \
do { \
bn = av_malloc(sizeof(*bn)); \
if (bn) \
mbedtls_mpi_init(bn); \
} while (0)
#define bn_free(bn) \
do { \
mbedtls_mpi_free(bn); \
av_free(bn); \
} while (0)
#define bn_set_word(bn, w) mbedtls_mpi_lset(bn, w)
#define bn_cmp(a, b) mbedtls_mpi_cmp_mpi(a, b)
#define bn_copy(to, from) mbedtls_mpi_copy(to, from)
#define bn_sub_word(bn, w) mbedtls_mpi_sub_int(bn, bn, w)
#define bn_cmp_1(bn) mbedtls_mpi_cmp_int(bn, 1)
#define bn_num_bytes(bn) (mbedtls_mpi_bitlen(bn) + 7) / 8
#define bn_bn2bin(bn, buf, len) mbedtls_mpi_write_binary(bn, buf, len)
#define bn_bin2bn(bn, buf, len) \
do { \
bn_new(bn); \
if (bn) \
mbedtls_mpi_read_binary(bn, buf, len); \
} while (0)
#define bn_hex2bn(bn, buf, ret) \
do { \
bn_new(bn); \
if (bn) \
ret = (mbedtls_mpi_read_string(bn, 16, buf) == 0); \
else \
ret = 1; \
} while (0)
#define bn_random(bn, num_bits) \
do { \
mbedtls_entropy_context entropy_ctx; \
mbedtls_ctr_drbg_context ctr_drbg_ctx; \
\
mbedtls_entropy_init(&entropy_ctx); \
mbedtls_ctr_drbg_init(&ctr_drbg_ctx); \
mbedtls_ctr_drbg_seed(&ctr_drbg_ctx, \
mbedtls_entropy_func, \
&entropy_ctx, \
NULL, 0); \
mbedtls_mpi_fill_random(bn, (num_bits + 7) / 8, mbedtls_ctr_drbg_random, &ctr_drbg_ctx); \
mbedtls_ctr_drbg_free(&ctr_drbg_ctx); \
mbedtls_entropy_free(&entropy_ctx); \
} while (0)
#define bn_modexp(bn, y, q, p) mbedtls_mpi_exp_mod(bn, y, q, p, 0)
#endif
#define MAX_BYTES 18000
#define dh_new() av_mallocz(sizeof(FF_DH))
static FFBigNum dh_generate_key(FF_DH *dh)
{
int num_bytes;
num_bytes = bn_num_bytes(dh->p) - 1;
if (num_bytes <= 0 || num_bytes > MAX_BYTES)
return NULL;
bn_new(dh->priv_key);
if (!dh->priv_key)
return NULL;
bn_random(dh->priv_key, 8 * num_bytes);
bn_new(dh->pub_key);
if (!dh->pub_key) {
bn_free(dh->priv_key);
return NULL;
}
if (bn_modexp(dh->pub_key, dh->g, dh->priv_key, dh->p) < 0)
return NULL;
return dh->pub_key;
}
static int dh_compute_key(FF_DH *dh, FFBigNum pub_key_bn,
uint32_t secret_key_len, uint8_t *secret_key)
{
FFBigNum k;
int ret;
bn_new(k);
if (!k)
return -1;
if ((ret = bn_modexp(k, pub_key_bn, dh->priv_key, dh->p)) < 0) {
bn_free(k);
return ret;
}
bn_bn2bin(k, secret_key, secret_key_len);
bn_free(k);
/* return the length of the shared secret key like DH_compute_key */
return secret_key_len;
}
void ff_dh_free(FF_DH *dh)
{
if (!dh)
return;
bn_free(dh->p);
bn_free(dh->g);
bn_free(dh->pub_key);
bn_free(dh->priv_key);
av_free(dh);
}
static int dh_is_valid_public_key(FFBigNum y, FFBigNum p, FFBigNum q)
{
FFBigNum bn = NULL;
int ret = AVERROR(EINVAL);
bn_new(bn);
if (!bn)
return AVERROR(ENOMEM);
/* y must lie in [2, p - 1] */
bn_set_word(bn, 1);
if (!bn_cmp(y, bn))
goto fail;
/* bn = p - 2 */
bn_copy(bn, p);
bn_sub_word(bn, 1);
if (!bn_cmp(y, bn))
goto fail;
/* Verify with Sophie-Germain prime
*
* This is a nice test to make sure the public key position is calculated
* correctly. This test will fail in about 50% of the cases if applied to
* random data.
*/
/* y must fulfill y^q mod p = 1 */
if ((ret = bn_modexp(bn, y, q, p)) < 0)
goto fail;
ret = AVERROR(EINVAL);
if (bn_cmp_1(bn))
goto fail;
ret = 0;
fail:
bn_free(bn);
return ret;
}
av_cold FF_DH *ff_dh_init(int key_len)
{
FF_DH *dh;
int ret;
if (!(dh = dh_new()))
return NULL;
bn_new(dh->g);
if (!dh->g)
goto fail;
bn_hex2bn(dh->p, P1024, ret);
if (!ret)
goto fail;
bn_set_word(dh->g, 2);
dh->length = key_len;
return dh;
fail:
ff_dh_free(dh);
return NULL;
}
int ff_dh_generate_public_key(FF_DH *dh)
{
int ret = 0;
while (!ret) {
FFBigNum q1 = NULL;
if (!dh_generate_key(dh))
return AVERROR(EINVAL);
bn_hex2bn(q1, Q1024, ret);
if (!ret)
return AVERROR(ENOMEM);
ret = dh_is_valid_public_key(dh->pub_key, dh->p, q1);
bn_free(q1);
if (!ret) {
/* the public key is valid */
break;
}
}
return ret;
}
int ff_dh_write_public_key(FF_DH *dh, uint8_t *pub_key, int pub_key_len)
{
int len;
/* compute the length of the public key */
len = bn_num_bytes(dh->pub_key);
if (len <= 0 || len > pub_key_len)
return AVERROR(EINVAL);
/* convert the public key value into big-endian form */
memset(pub_key, 0, pub_key_len);
bn_bn2bin(dh->pub_key, pub_key + pub_key_len - len, len);
return 0;
}
int ff_dh_compute_shared_secret_key(FF_DH *dh, const uint8_t *pub_key,
int pub_key_len, uint8_t *secret_key,
int secret_key_len)
{
FFBigNum q1 = NULL, pub_key_bn = NULL;
int ret;
/* convert the big-endian form of the public key into a bignum */
bn_bin2bn(pub_key_bn, pub_key, pub_key_len);
if (!pub_key_bn)
return AVERROR(ENOMEM);
/* convert the string containing a hexadecimal number into a bignum */
bn_hex2bn(q1, Q1024, ret);
if (!ret) {
ret = AVERROR(ENOMEM);
goto fail;
}
/* when the public key is valid we have to compute the shared secret key */
if ((ret = dh_is_valid_public_key(pub_key_bn, dh->p, q1)) < 0) {
goto fail;
} else if ((ret = dh_compute_key(dh, pub_key_bn, secret_key_len,
secret_key)) < 0) {
ret = AVERROR(EINVAL);
goto fail;
}
fail:
bn_free(pub_key_bn);
bn_free(q1);
return ret;
}