Update pre9

crypto/ec/ec_lcl.h

@@ -178,6 +178,15 @@ struct ec_method_st {
     int (*field_inverse_mod_ord)(const EC_GROUP *, BIGNUM *r,
                                  const BIGNUM *x, BN_CTX *);
     int (*blind_coordinates)(const EC_GROUP *group, EC_POINT *p, BN_CTX *ctx);
+    int (*ladder_pre)(const EC_GROUP *group,
+                      EC_POINT *r, EC_POINT *s,
+                      EC_POINT *p, BN_CTX *ctx);
+    int (*ladder_step)(const EC_GROUP *group,
+                       EC_POINT *r, EC_POINT *s,
+                       EC_POINT *p, BN_CTX *ctx);
+    int (*ladder_post)(const EC_GROUP *group,
+                       EC_POINT *r, EC_POINT *s,
+                       EC_POINT *p, BN_CTX *ctx);
 };
 
 /*
@@ -637,4 +646,76 @@ int X25519(uint8_t out_shared_key[32], const uint8_t private_key[32],
 void X25519_public_from_private(uint8_t out_public_value[32],
                                 const uint8_t private_key[32]);
 
+/*-
+ * This functions computes a single point multiplication over the EC group,
+ * using, at a high level, a Montgomery ladder with conditional swaps, with
+ * various timing attack defenses.
+ *
+ * It performs either a fixed point multiplication
+ *          (scalar * generator)
+ * when point is NULL, or a variable point multiplication
+ *          (scalar * point)
+ * when point is not NULL.
+ *
+ * `scalar` cannot be NULL and should be in the range [0,n) otherwise all
+ * constant time bets are off (where n is the cardinality of the EC group).
+ *
+ * This function expects `group->order` and `group->cardinality` to be well
+ * defined and non-zero: it fails with an error code otherwise.
+ *
+ * NB: This says nothing about the constant-timeness of the ladder step
+ * implementation (i.e., the default implementation is based on EC_POINT_add and
+ * EC_POINT_dbl, which of course are not constant time themselves) or the
+ * underlying multiprecision arithmetic.
+ *
+ * The product is stored in `r`.
+ *
+ * This is an internal function: callers are in charge of ensuring that the
+ * input parameters `group`, `r`, `scalar` and `ctx` are not NULL.
+ *
+ * Returns 1 on success, 0 otherwise.
+ */
+int ec_scalar_mul_ladder(const EC_GROUP *group, EC_POINT *r,
+                         const BIGNUM *scalar, const EC_POINT *point,
+                         BN_CTX *ctx);
+
 int ec_point_blind_coordinates(const EC_GROUP *group, EC_POINT *p, BN_CTX *ctx);
+
+static inline int ec_point_ladder_pre(const EC_GROUP *group,
+                                      EC_POINT *r, EC_POINT *s,
+                                      EC_POINT *p, BN_CTX *ctx)
+{
+    if (group->meth->ladder_pre != NULL)
+        return group->meth->ladder_pre(group, r, s, p, ctx);
+
+    if (!EC_POINT_copy(s, p)
+        || !EC_POINT_dbl(group, r, s, ctx))
+        return 0;
+
+    return 1;
+}
+
+static inline int ec_point_ladder_step(const EC_GROUP *group,
+                                       EC_POINT *r, EC_POINT *s,
+                                       EC_POINT *p, BN_CTX *ctx)
+{
+    if (group->meth->ladder_step != NULL)
+        return group->meth->ladder_step(group, r, s, p, ctx);
+
+    if (!EC_POINT_add(group, s, r, s, ctx)
+        || !EC_POINT_dbl(group, r, r, ctx))
+        return 0;
+
+    return 1;
+
+}
+
+static inline int ec_point_ladder_post(const EC_GROUP *group,
+                                       EC_POINT *r, EC_POINT *s,
+                                       EC_POINT *p, BN_CTX *ctx)
+{
+    if (group->meth->ladder_post != NULL)
+        return group->meth->ladder_post(group, r, s, p, ctx);
+
+    return 1;
+}