net/cert/ct_log_verifier_unittest.cc - chromium/src - Git at Google

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.

 #include "net/cert/ct_log_verifier.h"

 #include <stdint.h>

 #include <memory>
 #include <string>
 #include <vector>

 #include "base/macros.h"
 #include "base/strings/string_number_conversions.h"
 #include "base/time/time.h"
 #include "crypto/secure_hash.h"
 #include "net/base/hash_value.h"
 #include "net/cert/ct_log_verifier_util.h"
 #include "net/cert/merkle_audit_proof.h"
 #include "net/cert/merkle_consistency_proof.h"
 #include "net/cert/signed_certificate_timestamp.h"
 #include "net/cert/signed_tree_head.h"
 #include "net/test/ct_test_util.h"
 #include "testing/gtest/include/gtest/gtest.h"

 namespace net {

 namespace {

 // Calculate the power of two nearest to, but less than, |n|.
 // |n| must be at least 2.
 size_t CalculateNearestPowerOfTwo(size_t n) {
   DCHECK_GT(n, 1u);

   size_t ret = size_t(1) << (sizeof(size_t) * 8 - 1);
   while (ret >= n)
     ret >>= 1;

   return ret;
 }

 // All test data replicated from
 // https://github.com/google/certificate-transparency/blob/c41b090ecc14ddd6b3531dc7e5ce36b21e253fdd/cpp/merkletree/merkle_tree_test.cc

 // The SHA-256 hash of an empty Merkle tree.
 const uint8_t kEmptyTreeHash[32] = {
     0xe3, 0xb0, 0xc4, 0x42, 0x98, 0xfc, 0x1c, 0x14, 0x9a, 0xfb, 0xf4,
     0xc8, 0x99, 0x6f, 0xb9, 0x24, 0x27, 0xae, 0x41, 0xe4, 0x64, 0x9b,
     0x93, 0x4c, 0xa4, 0x95, 0x99, 0x1b, 0x78, 0x52, 0xb8, 0x55};

 std::string GetEmptyTreeHash() {
   return std::string(std::begin(kEmptyTreeHash), std::end(kEmptyTreeHash));
 }

 // SHA-256 Merkle leaf hashes for the sample tree that all of the other test
 // data relates to (8 leaves).
 const char* const kLeafHashes[8] = {
     "6e340b9cffb37a989ca544e6bb780a2c78901d3fb33738768511a30617afa01d",
     "96a296d224f285c67bee93c30f8a309157f0daa35dc5b87e410b78630a09cfc7",
     "0298d122906dcfc10892cb53a73992fc5b9f493ea4c9badb27b791b4127a7fe7",
     "07506a85fd9dd2f120eb694f86011e5bb4662e5c415a62917033d4a9624487e7",
     "bc1a0643b12e4d2d7c77918f44e0f4f79a838b6cf9ec5b5c283e1f4d88599e6b",
     "4271a26be0d8a84f0bd54c8c302e7cb3a3b5d1fa6780a40bcce2873477dab658",
     "b08693ec2e721597130641e8211e7eedccb4c26413963eee6c1e2ed16ffb1a5f",
     "46f6ffadd3d06a09ff3c5860d2755c8b9819db7df44251788c7d8e3180de8eb1"};

 // SHA-256 Merkle root hashes from building the sample tree leaf-by-leaf.
 // The first entry is the root when the tree contains 1 leaf, and the last is
 // the root when the tree contains all 8 leaves.
 const char* const kRootHashes[8] = {
     "6e340b9cffb37a989ca544e6bb780a2c78901d3fb33738768511a30617afa01d",
     "fac54203e7cc696cf0dfcb42c92a1d9dbaf70ad9e621f4bd8d98662f00e3c125",
     "aeb6bcfe274b70a14fb067a5e5578264db0fa9b51af5e0ba159158f329e06e77",
     "d37ee418976dd95753c1c73862b9398fa2a2cf9b4ff0fdfe8b30cd95209614b7",
     "4e3bbb1f7b478dcfe71fb631631519a3bca12c9aefca1612bfce4c13a86264d4",
     "76e67dadbcdf1e10e1b74ddc608abd2f98dfb16fbce75277b5232a127f2087ef",
     "ddb89be403809e325750d3d263cd78929c2942b7942a34b77e122c9594a74c8c",
     "5dc9da79a70659a9ad559cb701ded9a2ab9d823aad2f4960cfe370eff4604328"};

 // A single consistency proof. Contains at most 3 proof nodes (all test proofs
 // will be for a tree of size 8).
 struct ConsistencyProofTestVector {
   size_t old_tree_size;
   size_t new_tree_size;
   size_t proof_length;
   const char* const proof[3];
 };

 // A collection of consistency proofs between various sub-trees of the sample
 // tree.
 const ConsistencyProofTestVector kConsistencyProofs[] = {
     // Empty consistency proof between trees of the same size (1).
     {1, 1, 0, {"", "", ""}},
     // Consistency proof between tree of size 1 and tree of size 8, with 3
     // nodes in the proof.
     {1,
      8,
      3,
      {"96a296d224f285c67bee93c30f8a309157f0daa35dc5b87e410b78630a09cfc7",
       "5f083f0a1a33ca076a95279832580db3e0ef4584bdff1f54c8a360f50de3031e",
       "6b47aaf29ee3c2af9af889bc1fb9254dabd31177f16232dd6aab035ca39bf6e4"}},
     // Consistency proof between tree of size 6 and tree of size 8, with 3
     // nodes in the proof.
     {6,
      8,
      3,
      {"0ebc5d3437fbe2db158b9f126a1d118e308181031d0a949f8dededebc558ef6a",
       "ca854ea128ed050b41b35ffc1b87b8eb2bde461e9e3b5596ece6b9d5975a0ae0",
       "d37ee418976dd95753c1c73862b9398fa2a2cf9b4ff0fdfe8b30cd95209614b7"}},
     // Consistency proof between tree of size 2 and tree of size 5, with 2
     // nodes in the proof.
     {2,
      5,
      2,
      {"5f083f0a1a33ca076a95279832580db3e0ef4584bdff1f54c8a360f50de3031e",
       "bc1a0643b12e4d2d7c77918f44e0f4f79a838b6cf9ec5b5c283e1f4d88599e6b", ""}}};

 // A single audit proof. Contains at most 3 proof nodes (all test proofs will be
 // for a tree of size 8).
 struct AuditProofTestVector {
   size_t leaf;
   size_t tree_size;
   size_t proof_length;
   const char* const proof[3];
 };

 // A collection of audit proofs for various leaves and sub-trees of the tree
 // defined by |kRootHashes|.
 const AuditProofTestVector kAuditProofs[] = {
     {0, 1, 0, {"", "", ""}},
     {0,
      8,
      3,
      {"96a296d224f285c67bee93c30f8a309157f0daa35dc5b87e410b78630a09cfc7",
       "5f083f0a1a33ca076a95279832580db3e0ef4584bdff1f54c8a360f50de3031e",
       "6b47aaf29ee3c2af9af889bc1fb9254dabd31177f16232dd6aab035ca39bf6e4"}},
     {5,
      8,
      3,
      {"bc1a0643b12e4d2d7c77918f44e0f4f79a838b6cf9ec5b5c283e1f4d88599e6b",
       "ca854ea128ed050b41b35ffc1b87b8eb2bde461e9e3b5596ece6b9d5975a0ae0",
       "d37ee418976dd95753c1c73862b9398fa2a2cf9b4ff0fdfe8b30cd95209614b7"}},
     {2,
      3,
      1,
      {"fac54203e7cc696cf0dfcb42c92a1d9dbaf70ad9e621f4bd8d98662f00e3c125", "",
       ""}},
     {1,
      5,
      3,
      {"6e340b9cffb37a989ca544e6bb780a2c78901d3fb33738768511a30617afa01d",
       "5f083f0a1a33ca076a95279832580db3e0ef4584bdff1f54c8a360f50de3031e",
       "bc1a0643b12e4d2d7c77918f44e0f4f79a838b6cf9ec5b5c283e1f4d88599e6b"}}};

 // Decodes a hexadecimal string into the binary data it represents.
 std::string HexToBytes(const std::string& hex_data) {
   std::vector<uint8_t> output;
   std::string result;
   if (base::HexStringToBytes(hex_data, &output))
     result.assign(output.begin(), output.end());
   return result;
 }

 // Constructs a consistency/audit proof from a test vector.
 // This is templated so that it can be used with both ConsistencyProofTestVector
 // and AuditProofTestVector.
 template <typename TestVectorType>
 std::vector<std::string> GetProof(const TestVectorType& test_vector) {
   std::vector<std::string> proof(test_vector.proof_length);
   std::transform(test_vector.proof,
                  test_vector.proof + test_vector.proof_length, proof.begin(),
                  &HexToBytes);

   return proof;
 }

 // Creates a ct::MerkleConsistencyProof from its arguments and returns the
 // result of passing this to log.VerifyConsistencyProof().
 bool VerifyConsistencyProof(const CTLogVerifier& log,
                             size_t old_tree_size,
                             const std::string& old_tree_root,
                             size_t new_tree_size,
                             const std::string& new_tree_root,
                             const std::vector<std::string>& proof) {
   return log.VerifyConsistencyProof(
       ct::MerkleConsistencyProof(log.key_id(), proof, old_tree_size,
                                  new_tree_size),
       old_tree_root, new_tree_root);
 }

 // Creates a ct::MerkleAuditProof from its arguments and returns the result of
 // passing this to log.VerifyAuditProof().
 bool VerifyAuditProof(const CTLogVerifier& log,
                       size_t leaf,
                       size_t tree_size,
                       const std::vector<std::string>& proof,
                       const std::string& tree_root,
                       const std::string& leaf_hash) {
   return log.VerifyAuditProof(ct::MerkleAuditProof(leaf, tree_size, proof),
                               tree_root, leaf_hash);
 }

 class CTLogVerifierTest : public ::testing::Test {
  public:
   void SetUp() override {
     log_ = CTLogVerifier::Create(ct::GetTestPublicKey(), "testlog",
                                  "https://ct.example.com", "ct.example.com");

     ASSERT_TRUE(log_);
     EXPECT_EQ(ct::GetTestPublicKeyId(), log_->key_id());
     EXPECT_EQ("ct.example.com", log_->dns_domain());
   }

  protected:
   scoped_refptr<const CTLogVerifier> log_;
 };

 // Given an audit proof for a leaf in a Merkle tree, asserts that it verifies
 // and no other combination of leaves, tree sizes and proof nodes verifies.
 void CheckVerifyAuditProof(const CTLogVerifier& log,
                            size_t leaf,
                            size_t tree_size,
                            const std::vector<std::string>& proof,
                            const std::string& root_hash,
                            const std::string& leaf_hash) {
   EXPECT_TRUE(
       VerifyAuditProof(log, leaf, tree_size, proof, root_hash, leaf_hash))
       << "proof for leaf " << leaf << " did not pass verification";
   EXPECT_FALSE(
       VerifyAuditProof(log, leaf - 1, tree_size, proof, root_hash, leaf_hash))
       << "proof passed verification with wrong leaf index";
   EXPECT_FALSE(
       VerifyAuditProof(log, leaf + 1, tree_size, proof, root_hash, leaf_hash))
       << "proof passed verification with wrong leaf index";
   EXPECT_FALSE(
       VerifyAuditProof(log, leaf ^ 2, tree_size, proof, root_hash, leaf_hash))
       << "proof passed verification with wrong leaf index";
   EXPECT_FALSE(
       VerifyAuditProof(log, leaf, tree_size * 2, proof, root_hash, leaf_hash))
       << "proof passed verification with wrong tree height";
   EXPECT_FALSE(VerifyAuditProof(log, leaf / 2, tree_size / 2, proof, root_hash,
                                 leaf_hash))
       << "proof passed verification with wrong leaf index and tree height";
   EXPECT_FALSE(
       VerifyAuditProof(log, leaf, tree_size / 2, proof, root_hash, leaf_hash))
       << "proof passed verification with wrong tree height";
   EXPECT_FALSE(VerifyAuditProof(log, leaf, tree_size, proof, GetEmptyTreeHash(),
                                 leaf_hash))
       << "proof passed verification with wrong root hash";

   std::vector<std::string> wrong_proof;

   // Modify a single element on the proof.
   for (size_t j = 0; j < proof.size(); ++j) {
     wrong_proof = proof;
     wrong_proof[j] = GetEmptyTreeHash();
     EXPECT_FALSE(VerifyAuditProof(log, leaf, tree_size, wrong_proof, root_hash,
                                   leaf_hash))
         << "proof passed verification with one wrong node (node " << j << ")";
   }

   wrong_proof = proof;
   wrong_proof.push_back(std::string());
   EXPECT_FALSE(
       VerifyAuditProof(log, leaf, tree_size, wrong_proof, root_hash, leaf_hash))
       << "proof passed verification with an empty node appended";

   wrong_proof.back() = root_hash;
   EXPECT_FALSE(
       VerifyAuditProof(log, leaf, tree_size, wrong_proof, root_hash, leaf_hash))
       << "proof passed verification with an incorrect node appended";
   wrong_proof.pop_back();

   if (!wrong_proof.empty()) {
     wrong_proof.pop_back();
     EXPECT_FALSE(VerifyAuditProof(log, leaf, tree_size, wrong_proof, root_hash,
                                   leaf_hash))
         << "proof passed verification with the last node missing";
   }

   wrong_proof.clear();
   wrong_proof.push_back(std::string());
   wrong_proof.insert(wrong_proof.end(), proof.begin(), proof.end());
   EXPECT_FALSE(
       VerifyAuditProof(log, leaf, tree_size, wrong_proof, root_hash, leaf_hash))
       << "proof passed verification with an empty node prepended";

   wrong_proof[0] = root_hash;
   EXPECT_FALSE(
       VerifyAuditProof(log, leaf, tree_size, wrong_proof, root_hash, leaf_hash))
       << "proof passed verification with an incorrect node prepended";
 }

 // Given a consistency proof between two snapshots of the tree, asserts that it
 // verifies and no other combination of tree sizes and proof nodes verifies.
 void CheckVerifyConsistencyProof(const CTLogVerifier& log,
                                  int old_tree_size,
                                  int new_tree_size,
                                  const std::string& old_root,
                                  const std::string& new_root,
                                  const std::vector<std::string>& proof) {
   // Verify the original consistency proof.
   EXPECT_TRUE(VerifyConsistencyProof(log, old_tree_size, old_root,
                                      new_tree_size, new_root, proof))
       << "proof between trees of size " << old_tree_size << " and "
       << new_tree_size << " did not pass verification";

   if (proof.empty()) {
     // For simplicity test only non-trivial proofs that have old_root !=
     // new_root
     // old_tree_size != 0 and old_tree_size != new_tree_size.
     return;
   }

   // Wrong tree size: The proof checking code should not accept as a valid proof
   // a proof for a tree size different than the original size it was produced
   // for. Test that this is not the case for off-by-one changes.
   EXPECT_FALSE(VerifyConsistencyProof(log, old_tree_size - 1, old_root,
                                       new_tree_size, new_root, proof))
       << "proof passed verification with old tree size - 1";
   EXPECT_FALSE(VerifyConsistencyProof(log, old_tree_size + 1, old_root,
                                       new_tree_size, new_root, proof))
       << "proof passed verification with old tree size + 1";
   EXPECT_FALSE(VerifyConsistencyProof(log, old_tree_size ^ 2, old_root,
                                       new_tree_size, new_root, proof))
       << "proof passed verification with old tree size ^ 2";

   EXPECT_FALSE(VerifyConsistencyProof(log, old_tree_size, old_root,
                                       new_tree_size * 2, new_root, proof))
       << "proof passed verification with new tree height + 1";
   EXPECT_FALSE(VerifyConsistencyProof(log, old_tree_size, old_root,
                                       new_tree_size / 2, new_root, proof))
       << "proof passed verification with new tree height - 1";

   const std::string wrong_root("WrongRoot");
   EXPECT_FALSE(VerifyConsistencyProof(log, old_tree_size, old_root,
                                       new_tree_size, wrong_root, proof))
       << "proof passed verification with wrong old root";
   EXPECT_FALSE(VerifyConsistencyProof(log, old_tree_size, wrong_root,
                                       new_tree_size, new_root, proof))
       << "proof passed verification with wrong new root";
   EXPECT_FALSE(VerifyConsistencyProof(log, old_tree_size, new_root,
                                       new_tree_size, old_root, proof))
       << "proof passed verification with old and new root swapped";

   // Variations of wrong proofs, all of which should be rejected.
   std::vector<std::string> wrong_proof;
   EXPECT_FALSE(VerifyConsistencyProof(log, old_tree_size, old_root,
                                       new_tree_size, new_root, wrong_proof))
       << "empty proof passed verification";

   // Modify a single element in the proof.
   for (size_t j = 0; j < proof.size(); ++j) {
     wrong_proof = proof;
     wrong_proof[j] = GetEmptyTreeHash();
     EXPECT_FALSE(VerifyConsistencyProof(log, old_tree_size, old_root,
                                         new_tree_size, new_root, wrong_proof))
         << "proof passed verification with incorrect node (node " << j << ")";
   }

   wrong_proof = proof;
   wrong_proof.push_back(std::string());
   EXPECT_FALSE(VerifyConsistencyProof(log, old_tree_size, old_root,
                                       new_tree_size, new_root, wrong_proof))
       << "proof passed verification with empty node appended";

   wrong_proof.back() = proof.back();
   EXPECT_FALSE(VerifyConsistencyProof(log, old_tree_size, old_root,
                                       new_tree_size, new_root, wrong_proof))
       << "proof passed verification with last node duplicated";
   wrong_proof.pop_back();

   wrong_proof.pop_back();
   EXPECT_FALSE(VerifyConsistencyProof(log, old_tree_size, old_root,
                                       new_tree_size, new_root, wrong_proof))
       << "proof passed verification with last node missing";

   wrong_proof.clear();
   wrong_proof.push_back(std::string());
   wrong_proof.insert(wrong_proof.end(), proof.begin(), proof.end());
   EXPECT_FALSE(VerifyConsistencyProof(log, old_tree_size, old_root,
                                       new_tree_size, new_root, wrong_proof))
       << "proof passed verification with empty node prepended";

   wrong_proof[0] = proof[0];
   EXPECT_FALSE(VerifyConsistencyProof(log, old_tree_size, old_root,
                                       new_tree_size, new_root, wrong_proof))
       << "proof passed verification with first node duplicated";
 }

 TEST_F(CTLogVerifierTest, VerifiesCertSCT) {
   ct::SignedEntryData cert_entry;
   ct::GetX509CertSignedEntry(&cert_entry);

   scoped_refptr<ct::SignedCertificateTimestamp> cert_sct;
   ct::GetX509CertSCT(&cert_sct);

   EXPECT_TRUE(log_->Verify(cert_entry, *cert_sct.get()));
 }

 TEST_F(CTLogVerifierTest, VerifiesPrecertSCT) {
   ct::SignedEntryData precert_entry;
   ct::GetPrecertSignedEntry(&precert_entry);

   scoped_refptr<ct::SignedCertificateTimestamp> precert_sct;
   ct::GetPrecertSCT(&precert_sct);

   EXPECT_TRUE(log_->Verify(precert_entry, *precert_sct.get()));
 }

 TEST_F(CTLogVerifierTest, FailsInvalidTimestamp) {
   ct::SignedEntryData cert_entry;
   ct::GetX509CertSignedEntry(&cert_entry);

   scoped_refptr<ct::SignedCertificateTimestamp> cert_sct;
   ct::GetX509CertSCT(&cert_sct);

   // Mangle the timestamp, so that it should fail signature validation.
   cert_sct->timestamp = base::Time::Now();

   EXPECT_FALSE(log_->Verify(cert_entry, *cert_sct.get()));
 }

 TEST_F(CTLogVerifierTest, FailsInvalidLogID) {
   ct::SignedEntryData cert_entry;
   ct::GetX509CertSignedEntry(&cert_entry);

   scoped_refptr<ct::SignedCertificateTimestamp> cert_sct;
   ct::GetX509CertSCT(&cert_sct);

   // Mangle the log ID, which should cause it to match a different log before
   // attempting signature validation.
   cert_sct->log_id.assign(cert_sct->log_id.size(), '\0');

   EXPECT_FALSE(log_->Verify(cert_entry, *cert_sct.get()));
 }

 TEST_F(CTLogVerifierTest, VerifiesValidSTH) {
   ct::SignedTreeHead sth;
   ASSERT_TRUE(ct::GetSampleSignedTreeHead(&sth));
   EXPECT_TRUE(log_->VerifySignedTreeHead(sth));
 }

 TEST_F(CTLogVerifierTest, DoesNotVerifyInvalidSTH) {
   ct::SignedTreeHead sth;
   ASSERT_TRUE(ct::GetSampleSignedTreeHead(&sth));
   sth.sha256_root_hash[0] = '\x0';
   EXPECT_FALSE(log_->VerifySignedTreeHead(sth));
 }

 TEST_F(CTLogVerifierTest, VerifiesValidEmptySTH) {
   ct::SignedTreeHead sth;
   ASSERT_TRUE(ct::GetSampleEmptySignedTreeHead(&sth));
   EXPECT_TRUE(log_->VerifySignedTreeHead(sth));
 }

 TEST_F(CTLogVerifierTest, DoesNotVerifyInvalidEmptySTH) {
   ct::SignedTreeHead sth;
   ASSERT_TRUE(ct::GetBadEmptySignedTreeHead(&sth));
   EXPECT_FALSE(log_->VerifySignedTreeHead(sth));
 }

 // Test that excess data after the public key is rejected.
 TEST_F(CTLogVerifierTest, ExcessDataInPublicKey) {
   std::string key = ct::GetTestPublicKey();
   key += "extra";

   scoped_refptr<const CTLogVerifier> log = CTLogVerifier::Create(
       key, "testlog", "https://ct.example.com", "ct.example.com");
   EXPECT_FALSE(log);
 }

 TEST_F(CTLogVerifierTest, VerifiesConsistencyProofEdgeCases_EmptyProof) {
   std::vector<std::string> empty_proof;
   std::string old_root(GetEmptyTreeHash()), new_root(GetEmptyTreeHash());

   // Tree snapshots that are always consistent, because the proofs are either
   // from an empty tree to a non-empty one or for trees of the same size.
   EXPECT_TRUE(
       VerifyConsistencyProof(*log_, 0, old_root, 0, new_root, empty_proof));
   EXPECT_TRUE(
       VerifyConsistencyProof(*log_, 0, old_root, 1, new_root, empty_proof));
   EXPECT_TRUE(
       VerifyConsistencyProof(*log_, 1, old_root, 1, new_root, empty_proof));

   // Invalid consistency proofs.
   // Time travel to the past.
   EXPECT_FALSE(
       VerifyConsistencyProof(*log_, 1, old_root, 0, new_root, empty_proof));
   EXPECT_FALSE(
       VerifyConsistencyProof(*log_, 2, old_root, 1, new_root, empty_proof));
   // Proof between two trees of different size can never be empty.
   EXPECT_FALSE(
       VerifyConsistencyProof(*log_, 1, old_root, 2, new_root, empty_proof));
 }

 TEST_F(CTLogVerifierTest, VerifiesConsistencyProofEdgeCases_MismatchingRoots) {
   const std::string old_root(GetEmptyTreeHash());
   std::string new_root;
   std::vector<std::string> empty_proof;

   // Roots don't match.
   EXPECT_FALSE(
       VerifyConsistencyProof(*log_, 0, old_root, 0, new_root, empty_proof));
   EXPECT_FALSE(
       VerifyConsistencyProof(*log_, 1, old_root, 1, new_root, empty_proof));
 }

 TEST_F(CTLogVerifierTest,
        VerifiesConsistencyProofEdgeCases_MatchingRootsNonEmptyProof) {
   const std::string empty_tree_hash(GetEmptyTreeHash());

   std::vector<std::string> proof;
   proof.push_back(empty_tree_hash);

   // Roots match and the tree size is either the same or the old tree size is 0,
   // but the proof is not empty (the verification code should not accept
   // proofs with redundant nodes in this case).
   proof.push_back(empty_tree_hash);
   EXPECT_FALSE(VerifyConsistencyProof(*log_, 0, empty_tree_hash, 0,
                                       empty_tree_hash, proof));
   EXPECT_FALSE(VerifyConsistencyProof(*log_, 0, empty_tree_hash, 1,
                                       empty_tree_hash, proof));
   EXPECT_FALSE(VerifyConsistencyProof(*log_, 1, empty_tree_hash, 1,
                                       empty_tree_hash, proof));
 }

 class CTLogVerifierConsistencyProofTest
     : public CTLogVerifierTest,
       public ::testing::WithParamInterface<size_t /* proof index */> {};

 // Checks that a sample set of valid consistency proofs verify successfully.
 TEST_P(CTLogVerifierConsistencyProofTest, VerifiesValidConsistencyProof) {
   const ConsistencyProofTestVector& test_vector =
       kConsistencyProofs[GetParam()];
   const std::vector<std::string> proof = GetProof(test_vector);

   const char* const old_root = kRootHashes[test_vector.old_tree_size - 1];
   const char* const new_root = kRootHashes[test_vector.new_tree_size - 1];
   CheckVerifyConsistencyProof(*log_, test_vector.old_tree_size,
                               test_vector.new_tree_size, HexToBytes(old_root),
                               HexToBytes(new_root), proof);
 }

 INSTANTIATE_TEST_CASE_P(KnownGoodProofs,
                         CTLogVerifierConsistencyProofTest,
                         ::testing::Range(size_t(0),
                                          arraysize(kConsistencyProofs)));

 class CTLogVerifierAuditProofTest
     : public CTLogVerifierTest,
       public ::testing::WithParamInterface<size_t /* proof index */> {};

 // Checks that a sample set of valid audit proofs verify successfully.
 TEST_P(CTLogVerifierAuditProofTest, VerifiesValidAuditProofs) {
   const AuditProofTestVector& test_vector = kAuditProofs[GetParam()];
   const std::vector<std::string> proof = GetProof(test_vector);

   const char* const root_hash = kRootHashes[test_vector.tree_size - 1];
   CheckVerifyAuditProof(*log_, test_vector.leaf, test_vector.tree_size, proof,
                         HexToBytes(root_hash),
                         HexToBytes(kLeafHashes[test_vector.leaf]));
 }

 INSTANTIATE_TEST_CASE_P(KnownGoodProofs,
                         CTLogVerifierAuditProofTest,
                         ::testing::Range(size_t(0), arraysize(kAuditProofs)));

 TEST_F(CTLogVerifierTest, VerifiesAuditProofEdgeCases_InvalidLeafIndex) {
   std::vector<std::string> proof;
   EXPECT_FALSE(
       VerifyAuditProof(*log_, 1, 0, proof, std::string(), std::string()));
   EXPECT_FALSE(
       VerifyAuditProof(*log_, 2, 1, proof, std::string(), std::string()));

   const std::string empty_hash = GetEmptyTreeHash();
   EXPECT_FALSE(VerifyAuditProof(*log_, 1, 0, proof, empty_hash, std::string()));
   EXPECT_FALSE(VerifyAuditProof(*log_, 2, 1, proof, empty_hash, std::string()));
 }

 // Functions that implement algorithms from RFC6962 necessary for constructing
 // Merkle trees and proofs. This allows tests to generate a variety of trees
 // for exhaustive testing.
 namespace rfc6962 {

 // Calculates the hash of a leaf in a Merkle tree, given its content.
 // See RFC6962, section 2.1.
 std::string HashLeaf(const std::string& leaf) {
   const char kLeafPrefix[] = {'\x00'};

   SHA256HashValue sha256;
   memset(sha256.data, 0, sizeof(sha256.data));

   std::unique_ptr<crypto::SecureHash> hash(
       crypto::SecureHash::Create(crypto::SecureHash::SHA256));
   hash->Update(kLeafPrefix, 1);
   hash->Update(leaf.data(), leaf.size());
   hash->Finish(sha256.data, sizeof(sha256.data));

   return std::string(reinterpret_cast<const char*>(sha256.data),
                      sizeof(sha256.data));
 }

 // Calculates the root hash of a Merkle tree, given its leaf data and size.
 // See RFC6962, section 2.1.
 std::string HashTree(std::string leaves[], size_t tree_size) {
   if (tree_size == 0)
     return GetEmptyTreeHash();
   if (tree_size == 1)
     return HashLeaf(leaves[0]);

   // Find the index of the last leaf in the left sub-tree.
   const size_t split = CalculateNearestPowerOfTwo(tree_size);

   // Hash the left and right sub-trees, then hash the results.
   return ct::internal::HashNodes(HashTree(leaves, split),
                                  HashTree(&leaves[split], tree_size - split));
 }

 // Returns a Merkle audit proof for the leaf with index |leaf_index|.
 // The tree consists of |leaves[0]| to |leaves[tree_size-1]|.
 // If |leaf_index| is >= |tree_size|, an empty proof will be returned.
 // See RFC6962, section 2.1.1, for more details.
 std::vector<std::string> CreateAuditProof(std::string leaves[],
                                           size_t tree_size,
                                           size_t leaf_index) {
   std::vector<std::string> proof;
   if (leaf_index >= tree_size)
     return proof;
   if (tree_size == 1)
     return proof;

   // Find the index of the first leaf in the right sub-tree.
   const size_t split = CalculateNearestPowerOfTwo(tree_size);

   // Recurse down the correct branch of the tree (left or right) to reach the
   // leaf with |leaf_index|. Add the hash of the branch not taken at each step
   // on the way up to build the proof.
   if (leaf_index < split) {
     proof = CreateAuditProof(leaves, split, leaf_index);
     proof.push_back(HashTree(&leaves[split], tree_size - split));
   } else {
     proof =
         CreateAuditProof(&leaves[split], tree_size - split, leaf_index - split);
     proof.push_back(HashTree(leaves, split));
   }

   return proof;
 }

 // Returns a Merkle consistency proof between two Merkle trees.
 // The old tree contains |leaves[0]| to |leaves[old_tree_size-1]|.
 // The new tree contains |leaves[0]| to |leaves[new_tree_size-1]|.
 // Call with |contains_old_tree| = true.
 // See RFC6962, section 2.1.2, for more details.
 std::vector<std::string> CreateConsistencyProof(std::string leaves[],
                                                 size_t new_tree_size,
                                                 size_t old_tree_size,
                                                 bool contains_old_tree = true) {
   std::vector<std::string> proof;
   if (old_tree_size == 0 || old_tree_size > new_tree_size)
     return proof;
   if (old_tree_size == new_tree_size) {
     // Consistency proof for two equal subtrees is empty.
     if (!contains_old_tree) {
       // Record the hash of this subtree unless it's the root for which
       // the proof was originally requested. (This happens when the old tree is
       // balanced).
       proof.push_back(HashTree(leaves, old_tree_size));
     }
     return proof;
   }

   // Find the index of the last leaf in the left sub-tree.
   const size_t split = CalculateNearestPowerOfTwo(new_tree_size);

   if (old_tree_size <= split) {
     // Root of the old tree is in the left subtree of the new tree.
     // Prove that the left subtrees are consistent.
     proof =
         CreateConsistencyProof(leaves, split, old_tree_size, contains_old_tree);
     // Record the hash of the right subtree (only present in the new tree).
     proof.push_back(HashTree(&leaves[split], new_tree_size - split));
   } else {
     // The old tree root is at the same level as the new tree root.
     // Prove that the right subtrees are consistent. The right subtree
     // doesn't contain the root of the old tree, so set contains_old_tree =
     // false.
     proof = CreateConsistencyProof(&leaves[split], new_tree_size - split,
                                    old_tree_size - split,
                                    /* contains_old_tree = */ false);
     // Record the hash of the left subtree (equal in both trees).
     proof.push_back(HashTree(leaves, split));
   }
   return proof;
 }

 }  // namespace rfc6962

 class CTLogVerifierTestUsingGenerator
     : public CTLogVerifierTest,
       public ::testing::WithParamInterface<size_t /* tree_size */> {};

 // Checks that valid consistency proofs for a range of generated Merkle trees
 // verify successfully.
 TEST_P(CTLogVerifierTestUsingGenerator, VerifiesValidConsistencyProof) {
   const size_t tree_size = GetParam();

   std::vector<std::string> tree_leaves(tree_size);
   for (size_t i = 0; i < tree_size; ++i)
     tree_leaves[i].push_back(static_cast<char>(i));

   const std::string tree_root =
       rfc6962::HashTree(tree_leaves.data(), tree_size);

   // Check consistency proofs for every sub-tree.
   for (size_t old_tree_size = 0; old_tree_size <= tree_size; ++old_tree_size) {
     SCOPED_TRACE(old_tree_size);
     const std::string old_tree_root =
         rfc6962::HashTree(tree_leaves.data(), old_tree_size);
     const std::vector<std::string> proof = rfc6962::CreateConsistencyProof(
         tree_leaves.data(), tree_size, old_tree_size);
     // Checks that the consistency proof verifies only with the correct tree
     // sizes and root hashes.
     CheckVerifyConsistencyProof(*log_, old_tree_size, tree_size, old_tree_root,
                                 tree_root, proof);
   }
 }

 // Checks that valid audit proofs for a range of generated Merkle trees verify
 // successfully.
 TEST_P(CTLogVerifierTestUsingGenerator, VerifiesValidAuditProofs) {
   const size_t tree_size = GetParam();

   std::vector<std::string> tree_leaves(tree_size);
   for (size_t i = 0; i < tree_size; ++i)
     tree_leaves[i].push_back(static_cast<char>(i));

   const std::string root = rfc6962::HashTree(tree_leaves.data(), tree_size);

   // Check audit proofs for every leaf in the tree.
   for (size_t leaf = 0; leaf < tree_size; ++leaf) {
     SCOPED_TRACE(leaf);
     std::vector<std::string> proof =
         rfc6962::CreateAuditProof(tree_leaves.data(), tree_size, leaf);
     // Checks that the audit proof verifies only for this leaf data, index,
     // hash, tree size and root hash.
     CheckVerifyAuditProof(*log_, leaf, tree_size, proof, root,
                           rfc6962::HashLeaf(tree_leaves[leaf]));
   }
 }

 // Test verification of consistency proofs and audit proofs for all tree sizes
 // from 0 to 128.
 INSTANTIATE_TEST_CASE_P(RangeOfTreeSizes,
                         CTLogVerifierTestUsingGenerator,
                         testing::Range(size_t(0), size_t(129)));

 }  // namespace

 }  // namespace net