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comparison common-kex.c @ 1013:a1e79ffa5862

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Tighten validation of DH values. Odds of x==0 being generated are improbable, roughly 2**-1023 Regression in 0.49
author Matt Johnston <matt@ucc.asn.au>
date Tue, 10 Feb 2015 21:46:19 +0800
parents 47643024fc90
children 4d7b4c5526c5
comparison
equal deleted inserted replaced
1012:ffd2359564b0 1013:a1e79ffa5862
627 * dh_pub_us is 'e' for the client, 'f' for the server. dh_pub_them is 627 * dh_pub_us is 'e' for the client, 'f' for the server. dh_pub_them is
628 * vice-versa. dh_priv is the x/y value corresponding to dh_pub_us */ 628 * vice-versa. dh_priv is the x/y value corresponding to dh_pub_us */
629 void kexdh_comb_key(struct kex_dh_param *param, mp_int *dh_pub_them, 629 void kexdh_comb_key(struct kex_dh_param *param, mp_int *dh_pub_them,
630 sign_key *hostkey) { 630 sign_key *hostkey) {
631 631
632 mp_int dh_p; 632 DEF_MP_INT(dh_p);
633 DEF_MP_INT(dh_p_min1);
633 mp_int *dh_e = NULL, *dh_f = NULL; 634 mp_int *dh_e = NULL, *dh_f = NULL;
634 635
635 /* read the prime and generator*/ 636 m_mp_init_multi(&dh_p, &dh_p_min1, NULL);
636 m_mp_init(&dh_p);
637 load_dh_p(&dh_p); 637 load_dh_p(&dh_p);
638 638
639 /* Check that dh_pub_them (dh_e or dh_f) is in the range [1, p-1] */ 639 if (mp_sub_d(&dh_p, 1, &dh_p_min1) != MP_OKAY) {
640 if (mp_cmp(dh_pub_them, &dh_p) != MP_LT 640 dropbear_exit("Diffie-Hellman error");
641 || mp_cmp_d(dh_pub_them, 0) != MP_GT) { 641 }
642
643 /* Check that dh_pub_them (dh_e or dh_f) is in the range [2, p-2] */
644 if (mp_cmp(dh_pub_them, &dh_p_min1) != MP_LT
645 || mp_cmp_d(dh_pub_them, 1) != MP_GT) {
642 dropbear_exit("Diffie-Hellman error"); 646 dropbear_exit("Diffie-Hellman error");
643 } 647 }
644 648
645 /* K = e^y mod p = f^x mod p */ 649 /* K = e^y mod p = f^x mod p */
646 m_mp_alloc_init_multi(&ses.dh_K, NULL); 650 m_mp_alloc_init_multi(&ses.dh_K, NULL);
647 if (mp_exptmod(dh_pub_them, &param->priv, &dh_p, ses.dh_K) != MP_OKAY) { 651 if (mp_exptmod(dh_pub_them, &param->priv, &dh_p, ses.dh_K) != MP_OKAY) {
648 dropbear_exit("Diffie-Hellman error"); 652 dropbear_exit("Diffie-Hellman error");
649 } 653 }
650 654
651 /* clear no longer needed vars */ 655 /* clear no longer needed vars */
652 mp_clear_multi(&dh_p, NULL); 656 mp_clear_multi(&dh_p, &dh_p_min1, NULL);
653 657
654 /* From here on, the code needs to work with the _same_ vars on each side, 658 /* From here on, the code needs to work with the _same_ vars on each side,
655 * not vice-versaing for client/server */ 659 * not vice-versaing for client/server */
656 if (IS_DROPBEAR_CLIENT) { 660 if (IS_DROPBEAR_CLIENT) {
657 dh_e = &param->pub; 661 dh_e = &param->pub;