We cache a montgomery form for 'n' if the PUBLIC flag is set, not PRIVATE.

Also, I've added handling for other mod_exp calls that were not using any
cached montgomery forms. These cases matter only for special RSA keys (eg.
ones that are missing information) so are unlikely to be used in normal
circumstances.

crypto/rsa/rsa_eay.c

@@ -269,7 +269,9 @@ static int RSA_eay_private_encrypt(int flen, const unsigned char *from,
 		{ if (!rsa->meth->rsa_mod_exp(&ret,&f,rsa)) goto err; }
 	else
 		{
-		if (!rsa->meth->bn_mod_exp(&ret,&f,rsa->d,rsa->n,ctx,NULL)) goto err;
+		MONT_HELPER(rsa, ctx, n, rsa->flags & RSA_FLAG_CACHE_PUBLIC, goto err);
+		if (!rsa->meth->bn_mod_exp(&ret,&f,rsa->d,rsa->n,ctx,
+				rsa->_method_mod_n)) goto err;
 		}
 
 	if (rsa->flags & RSA_FLAG_BLINDING)
@@ -349,7 +351,9 @@ static int RSA_eay_private_decrypt(int flen, const unsigned char *from,
 		{ if (!rsa->meth->rsa_mod_exp(&ret,&f,rsa)) goto err; }
 	else
 		{
-		if (!rsa->meth->bn_mod_exp(&ret,&f,rsa->d,rsa->n,ctx,NULL))
+		MONT_HELPER(rsa, ctx, n, rsa->flags & RSA_FLAG_CACHE_PUBLIC, goto err);
+		if (!rsa->meth->bn_mod_exp(&ret,&f,rsa->d,rsa->n,ctx,
+				rsa->_method_mod_n))
 			goto err;
 		}
 
@@ -481,7 +485,7 @@ static int RSA_eay_mod_exp(BIGNUM *r0, const BIGNUM *I, RSA *rsa)
 
 	MONT_HELPER(rsa, ctx, p, rsa->flags & RSA_FLAG_CACHE_PRIVATE, goto err);
 	MONT_HELPER(rsa, ctx, q, rsa->flags & RSA_FLAG_CACHE_PRIVATE, goto err);
-	MONT_HELPER(rsa, ctx, n, rsa->flags & RSA_FLAG_CACHE_PRIVATE, goto err);
+	MONT_HELPER(rsa, ctx, n, rsa->flags & RSA_FLAG_CACHE_PUBLIC, goto err);
 
 	if (!BN_mod(&r1,I,rsa->q,ctx)) goto err;
 	if (!rsa->meth->bn_mod_exp(&m1,&r1,rsa->dmq1,rsa->q,ctx,
@@ -526,7 +530,8 @@ static int RSA_eay_mod_exp(BIGNUM *r0, const BIGNUM *I, RSA *rsa)
 			/* 'I' and 'vrfy' aren't congruent mod n. Don't leak
 			 * miscalculated CRT output, just do a raw (slower)
 			 * mod_exp and return that instead. */
-			if (!rsa->meth->bn_mod_exp(r0,I,rsa->d,rsa->n,ctx,NULL)) goto err;
+			if (!rsa->meth->bn_mod_exp(r0,I,rsa->d,rsa->n,ctx,
+					rsa->_method_mod_n)) goto err;
 		}
 	ret=1;
 err: