Backport regression test

master branch has a specific regression test for a bug in x86_64-mont5 code,
see commit cdfe0fdde6a966bdb0447de66aa04a85d99a0551.

This code is now in 1.0.2/1.0.1, so also backport the test.

Reviewed-by: Richard Levitte <levitte@openssl.org>
(cherry picked from commit bb565cd29e34caeeaf12ecfdbe6273c2c794f5a2)

1 files changed, 76 insertions, 0 deletions

diff --git a/crypto/bn/bntest.c b/crypto/bn/bntest.c
index 06f5954acc..7771e92023 100644
--- a/crypto/bn/bntest.c
+++ b/crypto/bn/bntest.c
@@ -107,6 +107,7 @@ int test_mod(BIO *bp,BN_CTX *ctx);
 int test_mod_mul(BIO *bp,BN_CTX *ctx);
 int test_mod_exp(BIO *bp,BN_CTX *ctx);
 int test_mod_exp_mont_consttime(BIO *bp,BN_CTX *ctx);
+int test_mod_exp_mont5(BIO *bp, BN_CTX *ctx);
 int test_exp(BIO *bp,BN_CTX *ctx);
 int test_gf2m_add(BIO *bp);
 int test_gf2m_mod(BIO *bp);
@@ -249,6 +250,7 @@ int main(int argc, char *argv[])
 
 	message(out,"BN_mod_exp_mont_consttime");
 	if (!test_mod_exp_mont_consttime(out,ctx)) goto err;
+	if (!test_mod_exp_mont5(out,ctx)) goto err;
 	(void)BIO_flush(out);
 
 	message(out,"BN_exp");
@@ -1012,6 +1014,80 @@ int test_mod_exp_mont_consttime(BIO *bp, BN_CTX *ctx)
 	return(1);
 	}
 
+/* Test constant-time modular exponentiation with 1024-bit inputs,
+ * which on x86_64 cause a different code branch to be taken.
+ */
+int test_mod_exp_mont5(BIO *bp, BN_CTX *ctx)
+	{
+	BIGNUM *a,*p,*m,*d,*e;
+
+	BN_MONT_CTX *mont;
+
+	a=BN_new();
+	p=BN_new();
+	m=BN_new();
+	d=BN_new();
+	e=BN_new();
+
+	mont = BN_MONT_CTX_new();
+
+	BN_bntest_rand(m,1024,0,1); /* must be odd for montgomery */
+	/* Zero exponent */
+	BN_bntest_rand(a,1024,0,0);
+	BN_zero(p);
+	if(!BN_mod_exp_mont_consttime(d,a,p,m,ctx,NULL))
+		return 0;
+	if(!BN_is_one(d))
+		{
+		fprintf(stderr, "Modular exponentiation test failed!\n");
+		return 0;
+		}
+	/* Zero input */
+	BN_bntest_rand(p,1024,0,0);
+	BN_zero(a);
+	if(!BN_mod_exp_mont_consttime(d,a,p,m,ctx,NULL))
+		return 0;
+	if(!BN_is_zero(d))
+		{
+		fprintf(stderr, "Modular exponentiation test failed!\n");
+		return 0;
+		}
+	/* Craft an input whose Montgomery representation is 1,
+	 * i.e., shorter than the modulus m, in order to test
+	 * the const time precomputation scattering/gathering.
+	 */
+	BN_one(a);
+	BN_MONT_CTX_set(mont,m,ctx);
+	if(!BN_from_montgomery(e,a,mont,ctx))
+		return 0;
+	if(!BN_mod_exp_mont_consttime(d,e,p,m,ctx,NULL))
+		return 0;
+	if(!BN_mod_exp_simple(a,e,p,m,ctx))
+		return 0;
+	if(BN_cmp(a,d) != 0)
+		{
+		fprintf(stderr,"Modular exponentiation test failed!\n");
+		return 0;
+		}
+	/* Finally, some regular test vectors. */
+	BN_bntest_rand(e,1024,0,0);
+	if(!BN_mod_exp_mont_consttime(d,e,p,m,ctx,NULL))
+		return 0;
+	if(!BN_mod_exp_simple(a,e,p,m,ctx))
+		return 0;
+	if(BN_cmp(a,d) != 0)
+		{
+		fprintf(stderr,"Modular exponentiation test failed!\n");
+		return 0;
+		}
+	BN_free(a);
+	BN_free(p);
+	BN_free(m);
+	BN_free(d);
+	BN_free(e);
+	return(1);
+	}
+
 int test_exp(BIO *bp, BN_CTX *ctx)
 	{
 	BIGNUM *a,*b,*d,*e,*one;