Adjust various bignum functions to use BN_CTX for variables instead of

locally initialising their own.

NB: I've removed the "BN_clear_free()" loops for the exit-paths in some of
these functions, and that may be a major part of the performance
improvements we're seeing. The "free" part can be removed because we're
using BN_CTX. The "clear" part OTOH can be removed because BN_CTX
destruction automatically performs this task, so performing it inside
functions that may be called repeatedly is wasteful. This is currently safe
within openssl due to the fact that BN_CTX objects are never created for
longer than a single high-level operation. However, that is only because
there's currently no mechanism in openssl for thread-local storage. Beyond
that, this might be an issue for applications using the bignum API directly
and caching their own BN_CTX objects. The solution is to introduce a flag
to BN_CTX_start() that allows its variables to be automatically sanitised
on release during BN_CTX_end(). This way any higher-level function (and
perhaps the application) can specify this flag in its own
BN_CTX_start()/BN_CTX_end() pair, and this will cause inner-loop functions
specifying the flag to be ignored so that sanitisation is handled only once
back out at the higher level. I will be implementing this in the near
future.

1 files changed, 11 insertions, 6 deletions

diff --git a/crypto/bn/bn_prime.c b/crypto/bn/bn_prime.c
index 4430e90df5..d03403a600 100644
--- a/crypto/bn/bn_prime.c
+++ b/crypto/bn/bn_prime.c
@@ -159,15 +159,17 @@ int BN_GENCB_call(BN_GENCB *cb, int a, int b)
 int BN_generate_prime_ex(BIGNUM *ret, int bits, int safe,
 	const BIGNUM *add, const BIGNUM *rem, BN_GENCB *cb)
 	{
-	BIGNUM t;
+	BIGNUM *t;
 	int found=0;
 	int i,j,c1=0;
 	BN_CTX *ctx;
 	int checks = BN_prime_checks_for_size(bits);
 
-	BN_init(&t);
 	ctx=BN_CTX_new();
 	if (ctx == NULL) goto err;
+	BN_CTX_start(ctx);
+	t = BN_CTX_get(ctx);
+	if(!t) goto err;
 loop: 
 	/* make a random number and set the top and bottom bits */
 	if (add == NULL)
@@ -204,7 +206,7 @@ loop:
 		 * check that (p-1)/2 is prime.
 		 * Since a prime is odd, We just
 		 * need to divide by 2 */
-		if (!BN_rshift1(&t,ret)) goto err;
+		if (!BN_rshift1(t,ret)) goto err;
 
 		for (i=0; i<checks; i++)
 			{
@@ -212,7 +214,7 @@ loop:
 			if (j == -1) goto err;
 			if (j == 0) goto loop;
 
-			j=BN_is_prime_fasttest_ex(&t,1,ctx,0,cb);
+			j=BN_is_prime_fasttest_ex(t,1,ctx,0,cb);
 			if (j == -1) goto err;
 			if (j == 0) goto loop;
 
@@ -224,8 +226,11 @@ loop:
 	/* we have a prime :-) */
 	found = 1;
 err:
-	BN_free(&t);
-	if (ctx != NULL) BN_CTX_free(ctx);
+	if (ctx != NULL)
+		{
+		BN_CTX_end(ctx);
+		BN_CTX_free(ctx);
+		}
 	bn_check_top(ret);
 	return found;
 	}