Hello, guys! I'm new to OpenSSL so sorry in advance if I get something wrong.
I'm using OpenSSL Diffie-Hellman key exchange in my project. In 'normal' mode
it works just perfect, but during stress-testing I have discovered "strange"
behavior: I sequentially start X00 DH calculations and it randomly fails to
generate public key correctly. This is my test-case:
START_TEST(openssl_dh_stress) {
BIGNUM *g_p3072 = NULL;
unsigned i;
g_p3072 = BN_bin2bn(g_p3072data, sizeof(g_p3072data), NULL);
for (i=0; i<400; i++) {
int ssl_res;
unsigned char random_bytes[64];
DH *tmp_ctx = NULL;
tmp_ctx = DH_new();
ck_assert(NULL != tmp_ctx);
tmp_ctx->p = BN_dup(g_p3072);
tmp_ctx->g = BN_new();
BN_set_word(tmp_ctx->g, DH_GENERATOR_2);
RAND_bytes(random_bytes, 256/8);
tmp_ctx->priv_key = BN_bin2bn(random_bytes, 256/8, NULL);
ssl_res = DH_generate_key(tmp_ctx);
ck_assert_int_eq(1, ssl_res);
unsigned pub_key_size = BN_num_bytes(tmp_ctx->pub_key);
if (pub_key_size != 3072/8) {
printf("FAILURE. DH 3K, %i-s iteration failed to compute
correct PV length.\n", i);
}
ck_assert_int_eq(pub_key_size, 3072/8);
DH_free(tmp_ctx);
}
}
END_TEST
Openssl randomly produces pub_key_size == 383 bytes, (it affect the rest
the calculations later in the sources). It's not reproducible with 1, 10
or 50 iterations, but when i >= 200 it's 100% reproducible.
I have briefly reviewed openssl dh key generation sources and couldn't
find anything what looks strange. Empirically I discovered that the
problem disappears when I comment out "RAND_bytes(random_bytes,
256/8);", but still assign private key manually to prevent OpenSSL from
generating it automatically.
I'm using single-thread environment.
I tried different versions of OpenSSL on OSX, Linux and OpenBSD - the same
behavior.
Have you ever experienced with similar problem in your projects? Am I
doing something wrong?
Thanks in advance for for your help!
--
Kind Regards,
Viktor
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