// Checks that (p,g) is acceptable pair for DH
int tglmp_check_DH_params (struct tgl_state *TLS, TGLC_bn *p, int g) {
if (g < 2 || g > 7) { return -1; }
if (TGLC_bn_num_bits (p) != 2048) { return -1; }
TGLC_bn *t = TGLC_bn_new ();
TGLC_bn *dh_g = TGLC_bn_new ();
ensure (TGLC_bn_set_word (dh_g, 4 * g));
ensure (TGLC_bn_mod (t, p, dh_g, TLS->TGLC_bn_ctx));
int x = TGLC_bn_get_word (t);
assert (x >= 0 && x < 4 * g);
TGLC_bn_free (dh_g);
int res = 0;
switch (g) {
case 2:
if (x != 7) { res = -1; }
break;
case 3:
if (x % 3 != 2) { res = -1; }
break;
case 4:
break;
case 5:
if (x % 5 != 1 && x % 5 != 4) { res = -1; }
break;
case 6:
if (x != 19 && x != 23) { res = -1; }
break;
case 7:
if (x % 7 != 3 && x % 7 != 5 && x % 7 != 6) { res = -1; }
break;
}
if (res < 0 || !check_prime (TLS, p)) {
TGLC_bn_free (t);
return -1;
}
TGLC_bn *b = TGLC_bn_new ();
ensure (TGLC_bn_set_word (b, 2));
ensure (TGLC_bn_div (t, 0, p, b, TLS->TGLC_bn_ctx));
if (!check_prime (TLS, t)) {
res = -1;
}
TGLC_bn_free (b);
TGLC_bn_free (t);
return res;
}
void bl_do_set_dh_params (struct tgl_state *TLS, int root, unsigned char prime[], int version) /* {{{ */ {
if (TLS->encr_prime) { tfree (TLS->encr_prime, 256); TGLC_bn_free (TLS->encr_prime_bn); }
TLS->encr_root = root;
TLS->encr_prime = talloc (256);
memcpy (TLS->encr_prime, prime, 256);
TLS->encr_prime_bn = TGLC_bn_new ();
TGLC_bn_bin2bn ((void *)TLS->encr_prime, 256, TLS->encr_prime_bn);
TLS->encr_param_version = version;
assert (tglmp_check_DH_params (TLS, TLS->encr_prime_bn, TLS->encr_root) >= 0);
}
// checks that g_a is acceptable for DH
int tglmp_check_g_a (struct tgl_state *TLS, TGLC_bn *p, TGLC_bn *g_a) {
if (TGLC_bn_num_bytes (g_a) > 256) {
return -1;
}
if (TGLC_bn_num_bits (g_a) < 2048 - 64) {
return -1;
}
if (TGLC_bn_cmp (p, g_a) <= 0) {
return -1;
}
TGLC_bn *dif = TGLC_bn_new ();
TGLC_bn_sub (dif, p, g_a);
if (TGLC_bn_num_bits (dif) < 2048 - 64) {
TGLC_bn_free (dif);
return -1;
}
TGLC_bn_free (dif);
return 0;
}
