1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
|
From 878e2c5b13010329c203f309ed0c8f2113f85648 Mon Sep 17 00:00:00 2001
From: Matt Caswell <matt@openssl.org>
Date: Mon, 18 Jan 2016 11:31:58 +0000
Subject: [PATCH] Prevent small subgroup attacks on DH/DHE
Historically OpenSSL only ever generated DH parameters based on "safe"
primes. More recently (in version 1.0.2) support was provided for
generating X9.42 style parameter files such as those required for RFC
5114 support. The primes used in such files may not be "safe". Where an
application is using DH configured with parameters based on primes that
are not "safe" then an attacker could use this fact to find a peer's
private DH exponent. This attack requires that the attacker complete
multiple handshakes in which the peer uses the same DH exponent.
A simple mitigation is to ensure that y^q (mod p) == 1
CVE-2016-0701 (fix part 1 of 2)
Issue reported by Antonio Sanso.
Reviewed-by: Viktor Dukhovni <viktor@openssl.org>
Upstream-Status: Backport
https://github.com/openssl/openssl/commit/878e2c5b13010329c203f309ed0c8f2113f85648
CVE: CVE-2016-0701
Signed-of-by: Armin Kuster <akuster@mvisa.com>
---
crypto/dh/dh.h | 1 +
crypto/dh/dh_check.c | 35 +++++++++++++++++++++++++----------
2 files changed, 26 insertions(+), 10 deletions(-)
diff --git a/crypto/dh/dh.h b/crypto/dh/dh.h
index b177673..5498a9d 100644
--- a/crypto/dh/dh.h
+++ b/crypto/dh/dh.h
@@ -174,6 +174,7 @@ struct dh_st {
/* DH_check_pub_key error codes */
# define DH_CHECK_PUBKEY_TOO_SMALL 0x01
# define DH_CHECK_PUBKEY_TOO_LARGE 0x02
+# define DH_CHECK_PUBKEY_INVALID 0x03
/*
* primes p where (p-1)/2 is prime too are called "safe"; we define this for
diff --git a/crypto/dh/dh_check.c b/crypto/dh/dh_check.c
index 347467c..5adedc0 100644
--- a/crypto/dh/dh_check.c
+++ b/crypto/dh/dh_check.c
@@ -151,23 +151,38 @@ int DH_check(const DH *dh, int *ret)
int DH_check_pub_key(const DH *dh, const BIGNUM *pub_key, int *ret)
{
int ok = 0;
- BIGNUM *q = NULL;
+ BIGNUM *tmp = NULL;
+ BN_CTX *ctx = NULL;
*ret = 0;
- q = BN_new();
- if (q == NULL)
+ ctx = BN_CTX_new();
+ if (ctx == NULL)
goto err;
- BN_set_word(q, 1);
- if (BN_cmp(pub_key, q) <= 0)
+ BN_CTX_start(ctx);
+ tmp = BN_CTX_get(ctx);
+ if (tmp == NULL)
+ goto err;
+ BN_set_word(tmp, 1);
+ if (BN_cmp(pub_key, tmp) <= 0)
*ret |= DH_CHECK_PUBKEY_TOO_SMALL;
- BN_copy(q, dh->p);
- BN_sub_word(q, 1);
- if (BN_cmp(pub_key, q) >= 0)
+ BN_copy(tmp, dh->p);
+ BN_sub_word(tmp, 1);
+ if (BN_cmp(pub_key, tmp) >= 0)
*ret |= DH_CHECK_PUBKEY_TOO_LARGE;
+ if (dh->q != NULL) {
+ /* Check pub_key^q == 1 mod p */
+ if (!BN_mod_exp(tmp, pub_key, dh->q, dh->p, ctx))
+ goto err;
+ if (!BN_is_one(tmp))
+ *ret |= DH_CHECK_PUBKEY_INVALID;
+ }
+
ok = 1;
err:
- if (q != NULL)
- BN_free(q);
+ if (ctx != NULL) {
+ BN_CTX_end(ctx);
+ BN_CTX_free(ctx);
+ }
return (ok);
}
--
2.3.5
|
