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Additional checks in DH

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Vysheng 2013-12-23 14:45:40 +04:00
parent 664e6e1549
commit 1dcbce52e8
1 changed files with 74 additions and 0 deletions
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74
mtproto-client.c
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@ -416,6 +416,77 @@ int process_respq_answer (struct connection *c, char *packet, int len) {
return rpc_send_packet (c);
}
int check_DH_params (BIGNUM *p, int g) {
if (g < 2 || g > 7) { return -1; }
BIGNUM t;
BN_init (&t);
BN_init (&dh_g);
BN_set_word (&dh_g, 4 * g);
BN_mod (&t, p, &dh_g, BN_ctx);
int x = BN_get_word (&t);
assert (x >= 0 && x < 4 * g);
BN_clear (&dh_g);
switch (g) {
case 2:
if (x != 7) { return -1; }
break;
case 3:
if (x % 3 != 2 ) { return -1; }
break;
case 4:
break;
case 5:
if (x % 5 != 1 && x % 5 != 4) { return -1; }
break;
case 6:
if (x != 19 && x != 23) { return -1; }
break;
case 7:
if (x % 7 != 3 && x % 7 != 5 && x % 7 != 6) { return -1; }
break;
}
if (!BN_is_prime (p, BN_prime_checks, 0, BN_ctx, 0)) { return -1; }
BIGNUM b;
BN_init (&b);
BN_set_word (&b, 2);
BN_div (&t, 0, p, &b, BN_ctx);
if (!BN_is_prime (&t, BN_prime_checks, 0, BN_ctx, 0)) { return -1; }
BN_clear (&b);
BN_clear (&t);
return 0;
}
int check_g (BIGNUM *g) {
static unsigned char s[256];
memset (s, 0, 256);
assert (BN_num_bytes (g) <= 256);
BN_bn2bin (g, s);
int ok = 0;
int i;
for (i = 0; i < 64; i++) {
if (s[i]) {
ok = 1;
break;
}
}
if (!ok) { return -1; }
ok = 0;
for (i = 0; i < 64; i++) {
if (s[255 - i]) {
ok = 1;
break;
}
}
if (!ok) { return -1; }
return 0;
}
int process_dh_answer (struct connection *c, char *packet, int len) {
if (verbosity) {
logprintf ( "process_dh_answer(), len=%d\n", len);
@ -448,9 +519,12 @@ int process_dh_answer (struct connection *c, char *packet, int len) {
BN_init (&g_a);
assert (fetch_bignum (&dh_prime) > 0);
assert (fetch_bignum (&g_a) > 0);
assert (check_g (&g_a) >= 0);
int server_time = *in_ptr++;
assert (in_ptr <= in_end);
assert (check_DH_params (&dh_prime, g) >= 0);
static char sha1_buffer[20];
sha1 ((unsigned char *) decrypt_buffer + 20, (in_ptr - decrypt_buffer - 5) * 4, (unsigned char *) sha1_buffer);
assert (!memcmp (decrypt_buffer, sha1_buffer, 20));