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diff --git a/src/mongo/db/time_proof_service.cpp b/src/mongo/db/time_proof_service.cpp
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+++ b/src/mongo/db/time_proof_service.cpp
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+/**
+ *    Copyright (C) 2017 MongoDB, Inc.
+ *
+ *    This program is free software: you can redistribute it and/or  modify
+ *    it under the terms of the GNU Affero General Public License, version 3,
+ *    as published by the Free Software Foundation.
+ *
+ *    This program is distributed in the hope that it will be useful,
+ *    but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *    GNU Affero General Public License for more details.
+ *
+ *    You should have received a copy of the GNU Affero General Public License
+ *    along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ *    As a special exception, the copyright holders give permission to link the
+ *    code of portions of this program with the OpenSSL library under certain
+ *    conditions as described in each individual source file and distribute
+ *    linked combinations including the program with the OpenSSL library. You
+ *    must comply with the GNU Affero General Public License in all respects for
+ *    all of the code used other than as permitted herein. If you modify file(s)
+ *    with this exception, you may extend this exception to your version of the
+ *    file(s), but you are not obligated to do so. If you do not wish to do so,
+ *    delete this exception statement from your version. If you delete this
+ *    exception statement from all source files in the program, then also delete
+ *    it in the license file.
+ */
+
+#include "mongo/platform/basic.h"
+
+#include "mongo/db/time_proof_service.h"
+
+#include "mongo/base/status.h"
+#include "mongo/db/logical_time.h"
+#include "mongo/platform/random.h"
+
+namespace mongo {
+
+TimeProofService::Key TimeProofService::generateRandomKey() {
+    // SecureRandom only produces 64-bit numbers, so 3 is the minimum for 20 random bytes.
+    const size_t kRandomNumbers = 3;
+    std::array<std::int64_t, kRandomNumbers> keyBuffer;
+    std::unique_ptr<SecureRandom> rng(SecureRandom::create());
+    std::generate(keyBuffer.begin(), keyBuffer.end(), [&] { return rng->nextInt64(); });
+
+    return fassertStatusOK(40384,
+                           SHA1Block::fromBuffer(reinterpret_cast<std::uint8_t*>(keyBuffer.data()),
+                                                 SHA1Block::kHashLength));
+}
+
+TimeProofService::TimeProof TimeProofService::getProof(const LogicalTime& time) const {
+    auto unsignedTimeArray = time.toUnsignedArray();
+    return SHA1Block::computeHmac(
+        _key.data(), _key.size(), unsignedTimeArray.data(), unsignedTimeArray.size());
+}
+
+Status TimeProofService::checkProof(const LogicalTime& time, const TimeProof& proof) const {
+    auto myProof = getProof(time);
+    if (myProof != proof) {
+        return Status(ErrorCodes::TimeProofMismatch, "Proof does not match the logical time");
+    }
+    return Status::OK();
+}
+
+}  // namespace mongo