From 2293e3d105806657e3b93416e266d87951481a64 Mon Sep 17 00:00:00 2001
From: Matt Johnston <matt@ucc.asn.au>
Date: Wed, 25 Nov 2015 22:15:59 +0800
Subject: [PATCH] check for zero K value from curve25519
---
common-kex.c | 6 ++++++
1 file changed, 6 insertions(+)
diff --git a/common-kex.c b/common-kex.c
index e2b4f8e5..b233819b 100644
--- a/common-kex.c
+++ b/common-kex.c
@@ -760,6 +760,7 @@ void kexcurve25519_comb_key(struct kex_curve25519_param *param, buffer *buf_pub_
unsigned char out[CURVE25519_LEN];
const unsigned char* Q_C = NULL;
const unsigned char* Q_S = NULL;
+ char zeroes[CURVE25519_LEN] = {0};
if (buf_pub_them->len != CURVE25519_LEN)
{
@@ -767,6 +768,11 @@ void kexcurve25519_comb_key(struct kex_curve25519_param *param, buffer *buf_pub_
}
curve25519_donna(out, param->priv, buf_pub_them->data);
+
+ if (constant_time_memcmp(zeroes, out, CURVE25519_LEN) == 0) {
+ dropbear_exit("Bad curve25519");
+ }
+
m_mp_alloc_init_multi(&ses.dh_K, NULL);
bytes_to_mp(ses.dh_K, out, CURVE25519_LEN);
m_burn(out, sizeof(out));
--
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