Make explicit _ct and _nonct versions of bn_mod_exp funcitons that

matter for constant time, and make the public interface only used
external to the library.

This moves us to a model where the important things are constant time
versions unless you ask for them not to be, rather than the opposite.
I'll continue with this method by method.

Add regress tests for same.
ok jsing@

2 files changed, 83 insertions, 2 deletions

diff --git a/src/regress/lib/libcrypto/bn/general/Makefile b/src/regress/lib/libcrypto/bn/general/Makefile
index 18207ffb01..d578d0fe12 100644
--- a/src/regress/lib/libcrypto/bn/general/Makefile
+++ b/src/regress/lib/libcrypto/bn/general/Makefile
@@ -1,4 +1,4 @@
-#       $OpenBSD: Makefile,v 1.3 2016/12/21 15:51:05 jsing Exp $
+#       $OpenBSD: Makefile,v 1.4 2017/01/21 09:38:58 beck Exp $
 
 .include "../../Makefile.inc"
 
@@ -6,6 +6,6 @@ PROG=	bntest
 LDADD=  ${CRYPTO_INT}
 DPADD=  ${LIBCRYPTO}
 WARNINGS=       Yes
-CFLAGS+=        -DLIBRESSL_INTERNAL -Werror
+CFLAGS+=        -Werror
 
 .include <bsd.regress.mk>
diff --git a/src/regress/lib/libcrypto/bn/general/bntest.c b/src/regress/lib/libcrypto/bn/general/bntest.c
index 0247dacaa4..7e5e6ed81b 100644
--- a/src/regress/lib/libcrypto/bn/general/bntest.c
+++ b/src/regress/lib/libcrypto/bn/general/bntest.c
@@ -84,6 +84,15 @@
 #include <openssl/x509.h>
 #include <openssl/err.h>
 
+int BN_mod_exp_ct(BIGNUM *r, const BIGNUM *a, const BIGNUM *p,
+    const BIGNUM *m, BN_CTX *ctx);
+int BN_mod_exp_nonct(BIGNUM *r, const BIGNUM *a, const BIGNUM *p,
+    const BIGNUM *m, BN_CTX *ctx);
+int BN_mod_exp_mont_ct(BIGNUM *r, const BIGNUM *a, const BIGNUM *p,
+    const BIGNUM *m, BN_CTX *ctx, BN_MONT_CTX *m_ctx);
+int BN_mod_exp_mont_nonct(BIGNUM *r, const BIGNUM *a, const BIGNUM *p,
+    const BIGNUM *m, BN_CTX *ctx, BN_MONT_CTX *m_ctx);
+
 int BN_bntest_rand(BIGNUM *rnd, int bits, int top, int bottom);
 
 const int num0 = 100; /* number of tests */
@@ -1037,6 +1046,14 @@ test_mod_exp(BIO *bp, BN_CTX *ctx)
                 fprintf(stderr, "BN_mod_exp with zero modulus succeeded!\n");
                 return (0);
         }
+        if (BN_mod_exp_ct(d, a, b, c, ctx)) {
+                fprintf(stderr, "BN_mod_exp_ct with zero modulus succeeded!\n");
+                return (0);
+        }
+        if (BN_mod_exp_nonct(d, a, b, c, ctx)) {
+                fprintf(stderr, "BN_mod_exp_nonct with zero modulus succeeded!\n");
+                return (0);
+        }
 
         BN_bntest_rand(c, 30, 0, 1); /* must be odd for montgomery */
         for (i = 0; i < num2; i++) {
@@ -1069,6 +1086,70 @@ test_mod_exp(BIO *bp, BN_CTX *ctx)
                         break;
                 }
         }
+
+        BN_bntest_rand(c, 30, 0, 1); /* must be odd for montgomery */
+        for (i = 0; i < num2; i++) {
+                BN_bntest_rand(a, 20 + i * 5, 0, 0);
+                BN_bntest_rand(b, 2 + i, 0, 0);
+
+                if (!BN_mod_exp_ct(d, a, b, c, ctx)) {
+                        rc = 0;
+                        break;
+                }
+
+                if (bp != NULL) {
+                        if (!results) {
+                                BN_print(bp, a);
+                                BIO_puts(bp, " ^ ");
+                                BN_print(bp, b);
+                                BIO_puts(bp, " % ");
+                                BN_print(bp, c);
+                                BIO_puts(bp, " - ");
+                        }
+                        BN_print(bp, d);
+                        BIO_puts(bp, "\n");
+                }
+                BN_exp(e, a, b, ctx);
+                BN_sub(e, e, d);
+                BN_div(a, b, e, c, ctx);
+                if (!BN_is_zero(b)) {
+                        fprintf(stderr, "Modulo exponentiation test failed!\n");
+                        rc = 0;
+                        break;
+                }
+        }
+
+        BN_bntest_rand(c, 30, 0, 1); /* must be odd for montgomery */
+        for (i = 0; i < num2; i++) {
+                BN_bntest_rand(a, 20 + i * 5, 0, 0);
+                BN_bntest_rand(b, 2 + i, 0, 0);
+
+                if (!BN_mod_exp_nonct(d, a, b, c, ctx)) {
+                        rc = 0;
+                        break;
+                }
+
+                if (bp != NULL) {
+                        if (!results) {
+                                BN_print(bp, a);
+                                BIO_puts(bp, " ^ ");
+                                BN_print(bp, b);
+                                BIO_puts(bp, " % ");
+                                BN_print(bp, c);
+                                BIO_puts(bp, " - ");
+                        }
+                        BN_print(bp, d);
+                        BIO_puts(bp, "\n");
+                }
+                BN_exp(e, a, b, ctx);
+                BN_sub(e, e, d);
+                BN_div(a, b, e, c, ctx);
+                if (!BN_is_zero(b)) {
+                        fprintf(stderr, "Modulo exponentiation test failed!\n");
+                        rc = 0;
+                        break;
+                }
+        }
         BN_free(a);
         BN_free(b);
         BN_free(c);