1 files changed, 60 insertions, 0 deletions
diff --git a/private_join_and_compute/crypto/fixed_base_exp.h b/private_join_and_compute/crypto/fixed_base_exp.h
new file mode 100644
index 0000000..bb5e4a9
--- /dev/null
+++ b/private_join_and_compute/crypto/fixed_base_exp.h
@@ -0,0 +1,60 @@
+/*
+ * Copyright 2019 Google Inc.
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+// A class for modular exponentiating a fixed base with arbitrary exponents
+// based on a modulus. This class delegates the modular exponentiation
+// operation to one of its subclasses.
+
+#ifndef CRYPTO_FIXED_BASE_H_
+#define CRYPTO_FIXED_BASE_H_
+
+#include "absl/flags/declare.h"
+#include "private_join_and_compute/crypto/big_num.h"
+#include "private_join_and_compute/crypto/context.h"
+#include "private_join_and_compute/util/status.inc"
+
+// Declared for test-only.
+ABSL_DECLARE_FLAG(bool, two_k_ary_exp);
+
+namespace private_join_and_compute {
+namespace internal {
+class FixedBaseExpImplBase;
+}  // namespace internal
+
+class FixedBaseExp {
+ public:
+  // FixedBaseExp is neither copyable nor movable.
+  FixedBaseExp(const FixedBaseExp&) = delete;
+  FixedBaseExp& operator=(const FixedBaseExp&) = delete;
+
+  ~FixedBaseExp();
+
+  // Computes fixed_base^exp mod modulus.
+  // Returns INVALID_ARGUMENT if the exponent is negative.
+  StatusOr<BigNum> ModExp(const BigNum& exp) const;
+
+  static std::unique_ptr<FixedBaseExp> GetFixedBaseExp(Context* ctx,
+                                                       const BigNum& fixed_base,
+                                                       const BigNum& modulus);
+
+ private:
+  explicit FixedBaseExp(internal::FixedBaseExpImplBase* impl);
+
+  std::unique_ptr<internal::FixedBaseExpImplBase> impl_;
+};
+
+}  // namespace private_join_and_compute
+
+#endif  // CRYPTO_FIXED_BASE_H_