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// 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 <string.h>
#include "base/logging.h"
#include "net/cert/ct_log_verifier_util.h"
#include "net/cert/ct_serialization.h"
#include "net/cert/merkle_consistency_proof.h"
#include "net/cert/signed_tree_head.h"
namespace net {
namespace {
// The SHA-256 hash of the empty string.
const unsigned char kSHA256EmptyStringHash[ct::kSthRootHashLength] = {
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};
bool IsPowerOfTwo(uint64_t n) {
return n != 0 && (n & (n - 1)) == 0;
}
} // namespace
// static
scoped_refptr<const CTLogVerifier> CTLogVerifier::Create(
const base::StringPiece& public_key,
const base::StringPiece& description,
const base::StringPiece& url) {
GURL log_url(url.as_string());
if (!log_url.is_valid())
return nullptr;
scoped_refptr<CTLogVerifier> result(new CTLogVerifier(description, log_url));
if (!result->Init(public_key))
return nullptr;
return result;
}
CTLogVerifier::CTLogVerifier(const base::StringPiece& description,
const GURL& url)
: description_(description.as_string()),
url_(url),
hash_algorithm_(ct::DigitallySigned::HASH_ALGO_NONE),
signature_algorithm_(ct::DigitallySigned::SIG_ALGO_ANONYMOUS),
public_key_(NULL) {
DCHECK(url_.is_valid());
}
bool CTLogVerifier::Verify(const ct::LogEntry& entry,
const ct::SignedCertificateTimestamp& sct) const {
if (sct.log_id != key_id()) {
DVLOG(1) << "SCT is not signed by this log.";
return false;
}
if (!SignatureParametersMatch(sct.signature))
return false;
std::string serialized_log_entry;
if (!ct::EncodeLogEntry(entry, &serialized_log_entry)) {
DVLOG(1) << "Unable to serialize entry.";
return false;
}
std::string serialized_data;
if (!ct::EncodeV1SCTSignedData(sct.timestamp, serialized_log_entry,
sct.extensions, &serialized_data)) {
DVLOG(1) << "Unable to create SCT to verify.";
return false;
}
return VerifySignature(serialized_data, sct.signature.signature_data);
}
bool CTLogVerifier::VerifySignedTreeHead(
const ct::SignedTreeHead& signed_tree_head) const {
if (!SignatureParametersMatch(signed_tree_head.signature))
return false;
std::string serialized_data;
ct::EncodeTreeHeadSignature(signed_tree_head, &serialized_data);
if (VerifySignature(serialized_data,
signed_tree_head.signature.signature_data)) {
if (signed_tree_head.tree_size == 0) {
// Root hash must equate SHA256 hash of the empty string.
return (memcmp(signed_tree_head.sha256_root_hash, kSHA256EmptyStringHash,
ct::kSthRootHashLength) == 0);
}
return true;
}
return false;
}
bool CTLogVerifier::SignatureParametersMatch(
const ct::DigitallySigned& signature) const {
if (!signature.SignatureParametersMatch(hash_algorithm_,
signature_algorithm_)) {
DVLOG(1) << "Mismatched hash or signature algorithm. Hash: "
<< hash_algorithm_ << " vs " << signature.hash_algorithm
<< " Signature: " << signature_algorithm_ << " vs "
<< signature.signature_algorithm << ".";
return false;
}
return true;
}
bool CTLogVerifier::VerifyConsistencyProof(
const ct::MerkleConsistencyProof& proof,
const std::string& old_tree_hash,
const std::string& new_tree_hash) const {
// Proof does not originate from this log.
if (key_id_ != proof.log_id)
return false;
// Cannot prove consistency from a tree of a certain size to a tree smaller
// than that - only the other way around.
if (proof.first_tree_size > proof.second_tree_size)
return false;
// If the proof is between trees of the same size, then the 'proof'
// is really just a statement that the tree hasn't changed. If this
// is the case, there should be no proof nodes, and both the old
// and new hash should be equivalent.
if (proof.first_tree_size == proof.second_tree_size)
return proof.nodes.empty() && old_tree_hash == new_tree_hash;
// It is possible to call this method to prove consistency between the
// initial state of a log (i.e. an empty tree) and a later root. In that
// case, the only valid proof is an empty proof.
if (proof.first_tree_size == 0)
return proof.nodes.empty();
// Implement the algorithm described in
// https://tools.ietf.org/html/draft-ietf-trans-rfc6962-bis-11#section-9.4.2
//
// It maintains a pair of hashes |fr| and |sr|, initialized to the same
// value. Each node in |proof| will be hashed to the left of both |fr| and
// |sr| or to the right of only |sr|. The proof is then valid if |fr| is
// |old_tree_hash| and |sr| is |new_tree_hash|, proving that tree nodes which
// make up |old_tree_hash| are a prefix of |new_tree_hash|.
// At this point, the algorithm's preconditions must be satisfied.
DCHECK_LT(0u, proof.first_tree_size);
DCHECK_LT(proof.first_tree_size, proof.second_tree_size);
// 1. If "first" is an exact power of 2, then prepend "first_hash" to the
// "consistency_path" array.
base::StringPiece first_proof_node = old_tree_hash;
std::vector<std::string>::const_iterator iter = proof.nodes.begin();
if (!IsPowerOfTwo(proof.first_tree_size)) {
if (iter == proof.nodes.end())
return false;
first_proof_node = *iter;
++iter;
}
// iter now points to the second node in the modified proof.nodes.
// 2. Set "fn" to "first - 1" and "sn" to "second - 1".
uint64_t fn = proof.first_tree_size - 1;
uint64_t sn = proof.second_tree_size - 1;
// 3. If "LSB(fn)" is set, then right-shift both "fn" and "sn" equally until
// "LSB(fn)" is not set.
while (fn & 1) {
fn >>= 1;
sn >>= 1;
}
// 4. Set both "fr" and "sr" to the first value in the "consistency_path"
// array.
std::string fr = first_proof_node.as_string();
std::string sr = first_proof_node.as_string();
// 5. For each subsequent value "c" in the "consistency_path" array:
for (; iter != proof.nodes.end(); ++iter) {
// The proof should end exactly when |sn| becomes zero. This check is
// missing from the draft specification. It and the additional check below
// ensure the proof is consistent with the tree sizes but is not necessary
// to ensure |old_tree_hash| is a prefix of |new_tree_hash|.
if (sn == 0)
return false;
// If "LSB(fn)" is set, or if "fn" is equal to "sn", then:
if ((fn & 1) || fn == sn) {
// 1. Set "fr" to "HASH(0x01 || c || fr)"
// Set "sr" to "HASH(0x01 || c || sr)"
fr = ct::internal::HashNodes(*iter, fr);
sr = ct::internal::HashNodes(*iter, sr);
// 2. If "LSB(fn)" is not set, then right-shift both "fn" and "sn" equally
// until either "LSB(fn)" is set or "fn" is "0".
while (!(fn & 1) && fn != 0) {
fn >>= 1;
sn >>= 1;
}
} else { // Otherwise:
// Set "sr" to "HASH(0x01 || sr || c)"
sr = ct::internal::HashNodes(sr, *iter);
}
// Finally, right-shift both "fn" and "sn" one time.
fn >>= 1;
sn >>= 1;
}
// 6. After completing iterating through the "consistency_path" array as
// described above, verify that the "fr" calculated is equal to the
// "first_hash" supplied and that the "sr" calculated is equal to the
// "second_hash" supplied.
//
// The proof should also end exactly when |sn| becomes zero. This check is
// missing from the draft specification. It and the additional check above
// ensure the proof is consistent with the tree sizes but is not necessary to
// ensure |old_tree_hash| is a prefix of |new_tree_hash|.
return fr == old_tree_hash && sr == new_tree_hash && sn == 0;
}
} // namespace net
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