commit 828c02a2061d9bbb867e3894e5ff464184a069a6
author Adam Langley <agl@google.com> Mon Nov 02 17:39:02 2015 -0800
committer JP Sugarbroad <jpsugar@google.com> Mon Mar 20 23:08:26 2017 +0000
tree 72177a84a88b550932c8b2a9e7e3a0aa335accc6
parent 94c61cf156005d547be9fc24c7ae62a9fd33f59d

DO NOT MERGE
Make BN_mod_exp_mont_consttime take a const context.

BN_mod_exp_mont_consttime does not modify its |BN_MONT_CTX| so that
value should be const.

Cherry-picked to make the next diff apply better.

(cherry picked from commit efb42fbb607c11391a08d5787bcffd08b9a0c78f)

Bug: 33752052
Change-Id: I6222a5a9eba3e34bf95957312af048b30da14a6b
(cherry picked from commit abaaae9e89a4360c8330e2ffb67df1cd476f5e1a)

src/crypto/bn/exponentiation.c

diff --git a/src/crypto/bn/exponentiation.c b/src/crypto/bn/exponentiation.c
index d3063c9..916a909 100644
--- a/src/crypto/bn/exponentiation.c
+++ b/src/crypto/bn/exponentiation.c
@@ -851,10 +851,10 @@
  */
 int BN_mod_exp_mont_consttime(BIGNUM *rr, const BIGNUM *a, const BIGNUM *p,
                               const BIGNUM *m, BN_CTX *ctx,
-                              BN_MONT_CTX *in_mont) {
+                              const BN_MONT_CTX *mont) {
   int i, bits, ret = 0, window, wvalue;
   int top;
-  BN_MONT_CTX *mont = NULL;
+  BN_MONT_CTX *new_mont = NULL;
 
   int numPowers;
   unsigned char *powerbufFree = NULL;
@@ -877,15 +877,13 @@
 
   BN_CTX_start(ctx);
 
-  /* Allocate a montgomery context if it was not supplied by the caller.
-   * If this is not done, things will break in the montgomery part. */
-  if (in_mont != NULL) {
-    mont = in_mont;
-  } else {
-    mont = BN_MONT_CTX_new();
-    if (mont == NULL || !BN_MONT_CTX_set(mont, m, ctx)) {
+  /* Allocate a montgomery context if it was not supplied by the caller. */
+  if (mont == NULL) {
+    new_mont = BN_MONT_CTX_new();
+    if (new_mont == NULL || !BN_MONT_CTX_set(new_mont, m, ctx)) {
       goto err;
     }
+    mont = new_mont;
   }
 
 #ifdef RSAZ_ENABLED
@@ -1008,7 +1006,7 @@
                            const BN_ULONG * not_used, const BN_ULONG * np,
                            const BN_ULONG * n0, int num);
 
-    BN_ULONG *np = mont->N.d, *n0 = mont->n0, *np2;
+    const BN_ULONG *np = mont->N.d, *n0 = mont->n0, *np2;
 
     /* BN_to_montgomery can contaminate words above .top
      * [in BN_DEBUG[_DEBUG] build]... */
@@ -1022,9 +1020,11 @@
     if (top & 7) {
       np2 = np;
     } else {
-      for (np2 = am.d + top, i = 0; i < top; i++) {
-        np2[2 * i] = np[i];
+      BN_ULONG *np_double = am.d + top;
+      for (i = 0; i < top; i++) {
+        np_double[2 * i] = np[i];
       }
+      np2 = np_double;
     }
 
     bn_scatter5(tmp.d, top, powerbuf, 0);
@@ -1189,10 +1189,9 @@
     goto err;
   }
   ret = 1;
+
 err:
-  if (in_mont == NULL) {
-    BN_MONT_CTX_free(mont);
-  }
+  BN_MONT_CTX_free(new_mont);
   if (powerbuf != NULL) {
     OPENSSL_cleanse(powerbuf, powerbufLen);
     OPENSSL_free(powerbufFree);

src/include/openssl/bn.h

diff --git a/src/include/openssl/bn.h b/src/include/openssl/bn.h
index ec1c8ff..297ce5a 100644
--- a/src/include/openssl/bn.h
+++ b/src/include/openssl/bn.h
@@ -771,7 +771,8 @@
 
 OPENSSL_EXPORT int BN_mod_exp_mont_consttime(BIGNUM *rr, const BIGNUM *a,
                                              const BIGNUM *p, const BIGNUM *m,
-                                             BN_CTX *ctx, BN_MONT_CTX *in_mont);
+                                             BN_CTX *ctx,
+                                             const BN_MONT_CTX *mont);
 
 OPENSSL_EXPORT int BN_mod_exp_mont_word(BIGNUM *r, BN_ULONG a, const BIGNUM *p,
                                         const BIGNUM *m, BN_CTX *ctx,