1 /* 2 * Copyright 2018 Google LLC 3 * 4 * Licensed under the Apache License, Version 2.0 (the "License"); 5 * you may not use this file except in compliance with the License. 6 * You may obtain a copy of the License at 7 * 8 * https://www.apache.org/licenses/LICENSE-2.0 9 * 10 * Unless required by applicable law or agreed to in writing, software 11 * distributed under the License is distributed on an "AS IS" BASIS, 12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 13 * See the License for the specific language governing permissions and 14 * limitations under the License. 15 */ 16 17 #ifndef FCP_SECAGG_SHARED_COMPUTE_SESSION_ID_H_ 18 #define FCP_SECAGG_SHARED_COMPUTE_SESSION_ID_H_ 19 20 #include <string> 21 22 #include "fcp/secagg/shared/secagg_messages.pb.h" 23 24 namespace fcp { 25 namespace secagg { 26 27 inline constexpr int kSha256Length = 32; 28 29 // A SessionId is the id of a given SecAgg session. Every session's SessionId 30 // should be unique. 31 typedef struct SessionId { 32 std::string data; 33 } SessionId; 34 35 // Computes the session ID for a specific protocol session given the first 36 // message (ShareKeysRequest) sent by the server. 37 // 38 // The session id is computed as a SHA-256 hash of the concatenation of all the 39 // PairOfPublicKeys inside the request message (in the same order in which they 40 // appear in the message). More specifically, for each PairOfPublicKeys inside 41 // the message, the following are concatenated to the input of the hash 42 // function: 43 // 44 // - The length of the prng ECDH public key 45 // - The prng ECDH public key 46 // - The length of the encryption ECDH public key 47 // - The encryption ECDH public key 48 // 49 // Lengths are prepended to the keys so that the encoding is not ambiguous and 50 // there are no unexpected collisions. 51 // 52 // The output of this method is 32 bytes long. 53 SessionId ComputeSessionId(const ShareKeysRequest& request); 54 55 } // namespace secagg 56 } // namespace fcp 57 58 #endif // FCP_SECAGG_SHARED_COMPUTE_SESSION_ID_H_ 59