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rearrange DH public value tests to be a little more clear

rearrange DH private value generation to explain rationale more
clearly and include an extra sanity check.

ok deraadt

Upstream-ID: 9ad8a07e1a12684e1b329f9bd88941b249d4b2ad
This commit is contained in:
djm@openbsd.org 2016-02-28 22:27:00 +00:00 committed by Damien Miller
parent 2ed17aa340
commit 6e7f68ce38
1 changed files with 16 additions and 7 deletions
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23
dh.c
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@ -1,4 +1,4 @@
/* $OpenBSD: dh.c,v 1.57 2015/05/27 23:39:18 dtucker Exp $ */
/* $OpenBSD: dh.c,v 1.58 2016/02/28 22:27:00 djm Exp $ */
/*
* Copyright (c) 2000 Niels Provos. All rights reserved.
*
@ -246,12 +246,15 @@ dh_pub_is_valid(DH *dh, BIGNUM *dh_pub)
bits_set++;
debug2("bits set: %d/%d", bits_set, BN_num_bits(dh->p));
/* if g==2 and bits_set==1 then computing log_g(dh_pub) is trivial */
if (bits_set > 1)
return 1;
logit("invalid public DH value (%d/%d)", bits_set, BN_num_bits(dh->p));
return 0;
/*
* if g==2 and bits_set==1 then computing log_g(dh_pub) is trivial
*/
if (bits_set < 4) {
logit("invalid public DH value (%d/%d)",
bits_set, BN_num_bits(dh->p));
return 0;
}
return 1;
}
int
@ -263,6 +266,12 @@ dh_gen_key(DH *dh, int need)
(pbits = BN_num_bits(dh->p)) <= 0 ||
need > INT_MAX / 2 || 2 * need > pbits)
return SSH_ERR_INVALID_ARGUMENT;
if (need < 256)
need = 256;
/*
* Pollard Rho, Big step/Little Step attacks are O(sqrt(n)),
* so double requested need here.
*/
dh->length = MIN(need * 2, pbits - 1);
if (DH_generate_key(dh) == 0 ||
!dh_pub_is_valid(dh, dh->pub_key)) {