Update DH_check() to peform sensible checks when q parameter is present.
authorDr. Stephen Henson <steve@openssl.org>
Thu, 1 Dec 2011 17:27:36 +0000 (17:27 +0000)
committerDr. Stephen Henson <steve@openssl.org>
Thu, 1 Dec 2011 17:27:36 +0000 (17:27 +0000)
crypto/dh/dh.h
crypto/dh/dh_check.c

index 2929ebe..9b90197 100644 (file)
@@ -165,6 +165,9 @@ struct dh_st
 #define DH_CHECK_P_NOT_SAFE_PRIME      0x02
 #define DH_UNABLE_TO_CHECK_GENERATOR   0x04
 #define DH_NOT_SUITABLE_GENERATOR      0x08
+#define DH_CHECK_Q_NOT_PRIME           0x10
+#define DH_CHECK_INVALID_Q_VALUE       0x20
+#define DH_CHECK_INVALID_J_VALUE       0x40
 
 /* DH_check_pub_key error codes */
 #define DH_CHECK_PUBKEY_TOO_SMALL      0x01
index 0668981..fa1df0e 100644 (file)
@@ -75,15 +75,42 @@ int DH_check(const DH *dh, int *ret)
        int ok=0;
        BN_CTX *ctx=NULL;
        BN_ULONG l;
-       BIGNUM *q=NULL;
+       BIGNUM *t1=NULL, *t2 = NULL;
 
        *ret=0;
        ctx=BN_CTX_new();
        if (ctx == NULL) goto err;
-       q=BN_new();
-       if (q == NULL) goto err;
+       BN_CTX_start(ctx);
+       t1=BN_CTX_get(ctx);
+       t2=BN_CTX_get(ctx);
+       if (t2 == NULL) goto err;
 
-       if (BN_is_word(dh->g,DH_GENERATOR_2))
+       if (dh->q)
+               {
+               if (BN_cmp(dh->g, BN_value_one()) <= 0)
+                       *ret|=DH_NOT_SUITABLE_GENERATOR;
+               else if (BN_cmp(dh->g, dh->p) >= 0)
+                       *ret|=DH_NOT_SUITABLE_GENERATOR;
+               else
+                       {
+                       /* Check g^q == 1 mod p */
+                       if (!BN_mod_exp(t1, dh->g, dh->q, dh->p, ctx))
+                               goto err;
+                       if (!BN_is_one(t1))
+                               *ret|=DH_NOT_SUITABLE_GENERATOR;
+                       }
+               if (!BN_is_prime_ex(dh->q,BN_prime_checks,ctx,NULL))
+                       *ret|=DH_CHECK_Q_NOT_PRIME;
+               /* Check p == 1 mod q  i.e. q divides p - 1 */
+               if (!BN_div(t1, t2, dh->p, dh->q, ctx))
+                       goto err;
+               if (!BN_is_one(t2))
+                       *ret|=DH_CHECK_INVALID_Q_VALUE;
+               if (dh->j && BN_cmp(dh->j, t1))
+                       *ret|=DH_CHECK_INVALID_J_VALUE;
+                       
+               }
+       else if (BN_is_word(dh->g,DH_GENERATOR_2))
                {
                l=BN_mod_word(dh->p,24);
                if (l != 11) *ret|=DH_NOT_SUITABLE_GENERATOR;
@@ -106,16 +133,19 @@ int DH_check(const DH *dh, int *ret)
 
        if (!BN_is_prime_ex(dh->p,BN_prime_checks,ctx,NULL))
                *ret|=DH_CHECK_P_NOT_PRIME;
-       else
+       else if (!dh->q)
                {
-               if (!BN_rshift1(q,dh->p)) goto err;
-               if (!BN_is_prime_ex(q,BN_prime_checks,ctx,NULL))
+               if (!BN_rshift1(t1,dh->p)) goto err;
+               if (!BN_is_prime_ex(t1,BN_prime_checks,ctx,NULL))
                        *ret|=DH_CHECK_P_NOT_SAFE_PRIME;
                }
        ok=1;
 err:
-       if (ctx != NULL) BN_CTX_free(ctx);
-       if (q != NULL) BN_free(q);
+       if (ctx != NULL)
+               {
+               BN_CTX_end(ctx);
+               BN_CTX_free(ctx);
+               }
        return(ok);
        }