backport checks for degenerate Diffie-Hellman public exponents from

OpenSSL-0.9.8a, where they were added without a corresponding patch to
0.9.7 or an advisory!  ok theo@ markus@

1 files changed, 22 insertions, 0 deletions

diff --git a/src/lib/libcrypto/dh/dh_check.c b/src/lib/libcrypto/dh/dh_check.c
index a7e9920efb..17debff62d 100644
--- a/src/lib/libcrypto/dh/dh_check.c
+++ b/src/lib/libcrypto/dh/dh_check.c
@@ -121,4 +121,26 @@ err:
         return(ok);
         }
 
+int DH_check_pub_key(const DH *dh, const BIGNUM *pub_key, int *ret)
+        {
+        int ok=0;
+        BIGNUM *q=NULL;
+
+        *ret=0;
+        q=BN_new();
+        if (q == NULL) goto err;
+        BN_set_word(q,1);
+        if (BN_cmp(pub_key,q) <= 0)
+                *ret|=DH_CHECK_PUBKEY_TOO_SMALL;
+        BN_copy(q,dh->p);
+        BN_sub_word(q,1);
+        if (BN_cmp(pub_key,q) >= 0)
+                *ret|=DH_CHECK_PUBKEY_TOO_LARGE;
+
+        ok = 1;
+err:
+        if (q != NULL) BN_free(q);
+        return(ok);
+        }
+
 #endif