1 // Copyright 2023 Google LLC 2 // 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 #ifndef ANONYMOUS_TOKENS_CPP_CRYPTO_RSA_BLINDER_H_ 16 #define ANONYMOUS_TOKENS_CPP_CRYPTO_RSA_BLINDER_H_ 17 18 #include <stdint.h> 19 20 #include <memory> 21 #include <optional> 22 #include <string> 23 24 #include "absl/status/status.h" 25 #include "absl/status/statusor.h" 26 #include "absl/strings/string_view.h" 27 #include "anonymous_tokens/cpp/crypto/blinder.h" 28 #include "anonymous_tokens/cpp/crypto/crypto_utils.h" 29 30 namespace anonymous_tokens { 31 32 // RsaBlinder `blinds` input messages, and then unblinds them after they are 33 // signed. 34 class RsaBlinder : public Blinder { 35 public: 36 // Passing of public_metadata is optional. If it is set to any value including 37 // an empty string, RsaBlinder will assume that partially blind RSA signature 38 // protocol is being executed. 39 // 40 // If public metadata is passed and the boolean "use_rsa_public_exponent" is 41 // set to false, the rsa_public_exponent is not used in any computations in 42 // the protocol. 43 // 44 // Setting "use_rsa_public_exponent" to true is deprecated. All new users 45 // should set it to false. 46 static absl::StatusOr<std::unique_ptr<RsaBlinder>> New( 47 absl::string_view rsa_modulus, absl::string_view rsa_public_exponent, 48 const EVP_MD* signature_hash_function, const EVP_MD* mgf1_hash_function, 49 int salt_length, bool use_rsa_public_exponent, 50 std::optional<absl::string_view> public_metadata = std::nullopt); 51 52 // Blind `message` using n and e derived from an RSA public key and the public 53 // metadata if applicable. 54 // 55 // Before blinding, the `message` will first be hashed and then encoded with 56 // the EMSA-PSS operation. 57 absl::StatusOr<std::string> Blind(absl::string_view message) override; 58 59 // Unblinds `blind_signature`. 60 // 61 // Callers should run Verify on the returned signature before using it / 62 // passing it on. 63 absl::StatusOr<std::string> Unblind( 64 absl::string_view blind_signature) override; 65 66 // Verifies an `unblinded` signature against the same `message' that was 67 // passed to Blind. 68 absl::Status Verify(absl::string_view signature, absl::string_view message); 69 70 private: 71 // Use `New` to construct 72 RsaBlinder(int salt_length, std::optional<absl::string_view> public_metadata, 73 const EVP_MD* sig_hash, const EVP_MD* mgf1_hash, 74 bssl::UniquePtr<RSA> rsa_public_key, bssl::UniquePtr<BIGNUM> r, 75 bssl::UniquePtr<BIGNUM> r_inv_mont, 76 bssl::UniquePtr<BN_MONT_CTX> mont_n); 77 78 const int salt_length_; 79 std::optional<std::string> public_metadata_; 80 const EVP_MD* sig_hash_; // Owned by BoringSSL. 81 const EVP_MD* mgf1_hash_; // Owned by BoringSSL. 82 83 // If public metadata was passed to RsaBlinder::New, rsa_public_key_ will 84 // will be initialized using RSA_new_public_key_large_e method. 85 const bssl::UniquePtr<RSA> rsa_public_key_; 86 87 const bssl::UniquePtr<BIGNUM> r_; 88 // r^-1 mod n in the Montgomery domain 89 const bssl::UniquePtr<BIGNUM> r_inv_mont_; 90 const bssl::UniquePtr<BN_MONT_CTX> mont_n_; 91 92 BlinderState blinder_state_; 93 }; 94 95 } // namespace anonymous_tokens 96 97 #endif // ANONYMOUS_TOKENS_CPP_CRYPTO_RSA_BLINDER_H_ 98