1 /* 2 * Copyright 2019 Google LLC. 3 * Licensed under the Apache License, Version 2.0 (the "License"); 4 * you may not use this file except in compliance with the License. 5 * You may obtain a copy of the License at 6 * 7 * https://www.apache.org/licenses/LICENSE-2.0 8 * 9 * Unless required by applicable law or agreed to in writing, software 10 * distributed under the License is distributed on an "AS IS" BASIS, 11 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 12 * See the License for the specific language governing permissions and 13 * limitations under the License. 14 */ 15 16 // A class for modular exponentiating a fixed base with arbitrary exponents 17 // based on a modulus. This class delegates the modular exponentiation 18 // operation to one of its subclasses. 19 20 #ifndef PRIVATE_JOIN_AND_COMPUTE_CRYPTO_FIXED_BASE_H_ 21 #define PRIVATE_JOIN_AND_COMPUTE_CRYPTO_FIXED_BASE_H_ 22 23 #include <memory> 24 25 #include "absl/flags/declare.h" 26 #include "private_join_and_compute/crypto/big_num.h" 27 #include "private_join_and_compute/crypto/context.h" 28 #include "private_join_and_compute/util/status.inc" 29 30 // Declared for test-only. 31 ABSL_DECLARE_FLAG(bool, two_k_ary_exp); 32 33 namespace private_join_and_compute { 34 namespace internal { 35 class FixedBaseExpImplBase; 36 } // namespace internal 37 38 class FixedBaseExp { 39 public: 40 // FixedBaseExp is neither copyable nor movable. 41 FixedBaseExp(const FixedBaseExp&) = delete; 42 FixedBaseExp& operator=(const FixedBaseExp&) = delete; 43 44 ~FixedBaseExp(); 45 46 // Computes fixed_base^exp mod modulus. 47 // Returns INVALID_ARGUMENT if the exponent is negative. 48 StatusOr<BigNum> ModExp(const BigNum& exp) const; 49 50 static std::unique_ptr<FixedBaseExp> GetFixedBaseExp(Context* ctx, 51 const BigNum& fixed_base, 52 const BigNum& modulus); 53 54 private: 55 explicit FixedBaseExp(internal::FixedBaseExpImplBase* impl); 56 57 std::unique_ptr<internal::FixedBaseExpImplBase> impl_; 58 }; 59 60 } // namespace private_join_and_compute 61 62 #endif // PRIVATE_JOIN_AND_COMPUTE_CRYPTO_FIXED_BASE_H_ 63