fix DH_generate_parameters for general 'generator'

[openssl.git] / crypto / dh / dh_gen.c

diff --git a/crypto/dh/dh_gen.c b/crypto/dh/dh_gen.c
index 7534ec40a016d5aca077127a50312b4e510988eb..06f78b35ab71ced8d0f788325ecef8ea3063c9d7 100644 (file)
--- a/crypto/dh/dh_gen.c
+++ b/crypto/dh/dh_gen.c
@@ -72,17 +72,20 @@
  * Having said all that,
  * there is another special case method for the generators 2, 3 and 5.
  * for 2, p mod 24 == 11
- * for 3, p mod 12 == 5  <<<<< does not work for strong primes.
+ * for 3, p mod 12 == 5  <<<<< does not work for safe primes.
  * for 5, p mod 10 == 3 or 7
  *
  * Thanks to Phil Karn <karn@qualcomm.com> for the pointers about the
  * special generators and for answering some of my questions.
  *
  * I've implemented the second simple method :-).
- * Since DH should be using a strong prime (both p and q are prime),
+ * Since DH should be using a safe prime (both p and q are prime),
  * this generator function can take a very very long time to run.
  */
-
+/* Actually there is no reason to insist that 'generator' be a generator.
+ * It's just as OK (and in some sense better) to use a generator of the
+ * order-q subgroup.
+ */
 DH *DH_generate_parameters(int prime_len, int generator,
             void (*callback)(int,int,void *), void *cb_arg)
        {
@@ -92,36 +95,51 @@ DH *DH_generate_parameters(int prime_len, int generator,
        BN_CTX *ctx=NULL;
 
        ret=DH_new();
+       if (ret == NULL) goto err;
        ctx=BN_CTX_new();
        if (ctx == NULL) goto err;
-       t1= &(ctx->bn[0]);
-       t2= &(ctx->bn[1]);
-       ctx->tos=2;
+       BN_CTX_start(ctx);
+       t1 = BN_CTX_get(ctx);
+       t2 = BN_CTX_get(ctx);
+       if (t1 == NULL || t2 == NULL) goto err;
        
+       if (generator <= 1)
+               {
+               DHerr(DH_F_DH_GENERATE_PARAMETERS, DH_R_BAD_GENERATOR);
+               goto err;
+               }
        if (generator == DH_GENERATOR_2)
                {
-               BN_set_word(t1,24);
-               BN_set_word(t2,11);
+               if (!BN_set_word(t1,24)) goto err;
+               if (!BN_set_word(t2,11)) goto err;
                g=2;
                }
-#ifdef undef  /* does not work for strong primes */
+#if 0 /* does not work for safe primes */
        else if (generator == DH_GENERATOR_3)
                {
-               BN_set_word(t1,12);
-               BN_set_word(t2,5);
+               if (!BN_set_word(t1,12)) goto err;
+               if (!BN_set_word(t2,5)) goto err;
                g=3;
                }
 #endif
        else if (generator == DH_GENERATOR_5)
                {
-               BN_set_word(t1,10);
-               BN_set_word(t2,3);
+               if (!BN_set_word(t1,10)) goto err;
+               if (!BN_set_word(t2,3)) goto err;
                /* BN_set_word(t3,7); just have to miss
                 * out on these ones :-( */
                g=5;
                }
        else
+               {
+               /* in the general case, don't worry if 'generator' is a
+                * generator or not: since we are using safe primes,
+                * it will generate either an order-q or an order-2q group,
+                * which both is OK */
+               if (!BN_set_word(t1,2)) goto err;
+               if (!BN_set_word(t2,1)) goto err;
                g=generator;
+               }
        
        p=BN_generate_prime(NULL,prime_len,1,t1,t2,callback,cb_arg);
        if (p == NULL) goto err;
@@ -137,7 +155,11 @@ err:
                ok=0;
                }
 
-       if (ctx != NULL) BN_CTX_free(ctx);
+       if (ctx != NULL)
+               {
+               BN_CTX_end(ctx);
+               BN_CTX_free(ctx);
+               }
        if (!ok && (ret != NULL))
                {
                DH_free(ret);