Mercurial > dropbear
diff common-kex.c @ 1013:a1e79ffa5862
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 |
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--- a/common-kex.c Wed Feb 04 22:12:06 2015 +0800 +++ b/common-kex.c Tue Feb 10 21:46:19 2015 +0800 @@ -629,16 +629,20 @@ void kexdh_comb_key(struct kex_dh_param *param, mp_int *dh_pub_them, sign_key *hostkey) { - mp_int dh_p; + DEF_MP_INT(dh_p); + DEF_MP_INT(dh_p_min1); mp_int *dh_e = NULL, *dh_f = NULL; - /* read the prime and generator*/ - m_mp_init(&dh_p); + m_mp_init_multi(&dh_p, &dh_p_min1, NULL); load_dh_p(&dh_p); - /* Check that dh_pub_them (dh_e or dh_f) is in the range [1, p-1] */ - if (mp_cmp(dh_pub_them, &dh_p) != MP_LT - || mp_cmp_d(dh_pub_them, 0) != MP_GT) { + if (mp_sub_d(&dh_p, 1, &dh_p_min1) != MP_OKAY) { + dropbear_exit("Diffie-Hellman error"); + } + + /* Check that dh_pub_them (dh_e or dh_f) is in the range [2, p-2] */ + if (mp_cmp(dh_pub_them, &dh_p_min1) != MP_LT + || mp_cmp_d(dh_pub_them, 1) != MP_GT) { dropbear_exit("Diffie-Hellman error"); } @@ -649,7 +653,7 @@ } /* clear no longer needed vars */ - mp_clear_multi(&dh_p, NULL); + mp_clear_multi(&dh_p, &dh_p_min1, NULL); /* From here on, the code needs to work with the _same_ vars on each side, * not vice-versaing for client/server */