blob: 99a4405290ea4bbecaefb79f0ed45d112683f482 [file] [log] [blame]
// Copyright 2014 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 "components/certificate_transparency/chrome_ct_policy_enforcer.h"
#include <stdint.h>
#include <algorithm>
#include <memory>
#include <utility>
#include "base/bind.h"
#include "base/build_time.h"
#include "base/callback_helpers.h"
#include "base/metrics/field_trial.h"
#include "base/metrics/histogram_macros.h"
#include "base/numerics/safe_conversions.h"
#include "base/strings/string_number_conversions.h"
#include "base/time/time.h"
#include "base/values.h"
#include "base/version.h"
#include "components/certificate_transparency/ct_known_logs.h"
#include "net/cert/ct_policy_status.h"
#include "net/cert/signed_certificate_timestamp.h"
#include "net/cert/x509_certificate.h"
#include "net/cert/x509_certificate_net_log_param.h"
#include "net/log/net_log_capture_mode.h"
#include "net/log/net_log_event_type.h"
#include "net/log/net_log_parameters_callback.h"
#include "net/log/net_log_with_source.h"
using net::ct::CTPolicyCompliance;
namespace certificate_transparency {
namespace {
// Returns true if the current build is recent enough to ensure that
// built-in security information (e.g. CT Logs) is fresh enough.
// TODO(eranm): Move to base or net/base
bool IsBuildTimely() {
const base::Time build_time = base::GetBuildTime();
// We consider built-in information to be timely for 10 weeks.
return (base::Time::Now() - build_time).InDays() < 70 /* 10 weeks */;
// Returns a rounded-down months difference of |start| and |end|,
// together with an indication of whether the last month was
// a full month, because the range starts specified in the policy
// are not consistent in terms of including the range start value.
void RoundedDownMonthDifference(const base::Time& start,
const base::Time& end,
size_t* rounded_months_difference,
bool* has_partial_month) {
base::Time::Exploded exploded_start;
base::Time::Exploded exploded_expiry;
if (end < start) {
*rounded_months_difference = 0;
*has_partial_month = false;
*has_partial_month = true;
uint32_t month_diff = (exploded_expiry.year - exploded_start.year) * 12 +
(exploded_expiry.month - exploded_start.month);
if (exploded_expiry.day_of_month < exploded_start.day_of_month)
else if (exploded_expiry.day_of_month == exploded_start.day_of_month)
*has_partial_month = false;
*rounded_months_difference = month_diff;
const char* CTPolicyComplianceToString(CTPolicyCompliance status) {
switch (status) {
case CTPolicyCompliance::CT_POLICY_NOT_ENOUGH_SCTS:
case CTPolicyCompliance::CT_POLICY_NOT_DIVERSE_SCTS:
case CTPolicyCompliance::CT_POLICY_BUILD_NOT_TIMELY:
case CTPolicyCompliance::CT_POLICY_COUNT:
return "unknown";
return "unknown";
std::unique_ptr<base::Value> NetLogCertComplianceCheckResultCallback(
net::X509Certificate* cert,
bool build_timely,
CTPolicyCompliance compliance,
net::NetLogCaptureMode capture_mode) {
std::unique_ptr<base::DictionaryValue> dict(new base::DictionaryValue());
net::NetLogX509CertificateCallback(cert, capture_mode));
dict->SetBoolean("build_timely", build_timely);
return std::move(dict);
// Evaluates against the policy specified at
CTPolicyCompliance CheckCTPolicyCompliance(
const net::X509Certificate& cert,
const net::ct::SCTList& verified_scts) {
// Cert is outside the bounds of parsable; reject it.
if (cert.valid_start().is_null() || cert.valid_expiry().is_null() ||
cert.valid_start().is_max() || cert.valid_expiry().is_max()) {
return CTPolicyCompliance::CT_POLICY_NOT_ENOUGH_SCTS;
// Scan for the earliest SCT. This is used to determine whether to enforce
// log diversity requirements, as well as whether to enforce whether or not
// a log was qualified or pending qualification at time of issuance (in the
// case of embedded SCTs). It's acceptable to ignore the origin of the SCT,
// because SCTs delivered via OCSP/TLS extension will cover the full
// certificate, which necessarily will exist only after the precertificate
// has been logged and the actual certificate issued.
// Note: Here, issuance date is defined as the earliest of all SCTs, rather
// than the latest of embedded SCTs, in order to give CAs the benefit of
// the doubt in the event a log is revoked in the midst of processing
// a precertificate and issuing the certificate.
base::Time issuance_date = base::Time::Max();
for (const auto& sct : verified_scts) {
base::Time unused;
if (IsLogDisqualified(sct->log_id, &unused))
issuance_date = std::min(sct->timestamp, issuance_date);
bool has_valid_google_sct = false;
bool has_valid_nongoogle_sct = false;
bool has_valid_embedded_sct = false;
bool has_valid_nonembedded_sct = false;
bool has_embedded_google_sct = false;
bool has_embedded_nongoogle_sct = false;
std::vector<base::StringPiece> embedded_log_ids;
for (const auto& sct : verified_scts) {
base::Time disqualification_date;
bool is_disqualified =
IsLogDisqualified(sct->log_id, &disqualification_date);
if (is_disqualified &&
sct->origin != net::ct::SignedCertificateTimestamp::SCT_EMBEDDED) {
// For OCSP and TLS delivered SCTs, only SCTs that are valid at the
// time of check are accepted.
if (IsLogOperatedByGoogle(sct->log_id)) {
has_valid_google_sct |= !is_disqualified;
if (sct->origin == net::ct::SignedCertificateTimestamp::SCT_EMBEDDED)
has_embedded_google_sct = true;
} else {
has_valid_nongoogle_sct |= !is_disqualified;
if (sct->origin == net::ct::SignedCertificateTimestamp::SCT_EMBEDDED)
has_embedded_nongoogle_sct = true;
if (sct->origin != net::ct::SignedCertificateTimestamp::SCT_EMBEDDED) {
has_valid_nonembedded_sct = true;
} else {
has_valid_embedded_sct |= !is_disqualified;
// If the log is disqualified, it only counts towards quorum if
// the certificate was issued before the log was disqualified, and the
// SCT was obtained before the log was disqualified.
if (!is_disqualified || (issuance_date < disqualification_date &&
sct->timestamp < disqualification_date)) {
// Option 1:
// An SCT presented via the TLS extension OR embedded within a stapled OCSP
// response is from a log qualified at time of check;
// AND there is at least one SCT from a Google Log that is qualified at
// time of check, presented via any method;
// AND there is at least one SCT from a non-Google Log that is qualified
// at the time of check, presented via any method.
// Note: Because SCTs embedded via TLS or OCSP can be updated on the fly,
// the issuance date is irrelevant, as any policy changes can be
// accomodated.
if (has_valid_nonembedded_sct && has_valid_google_sct &&
has_valid_nongoogle_sct) {
return CTPolicyCompliance::CT_POLICY_COMPLIES_VIA_SCTS;
// Note: If has_valid_nonembedded_sct was true, but Option 2 isn't met,
// then the result will be that there weren't diverse enough SCTs, as that
// the only other way for the conditional above to fail). Because Option 1
// has the diversity requirement, it's implicitly a minimum number of SCTs
// (specifically, 2), but that's not explicitly specified in the policy.
// Option 2:
// There is at least one embedded SCT from a log qualified at the time of
// check ...
if (!has_valid_embedded_sct) {
// Under Option 2, there weren't enough SCTs, and potentially under
// Option 1, there weren't diverse enough SCTs. Try to signal the error
// that is most easily fixed.
return has_valid_nonembedded_sct
// ... AND there is at least one embedded SCT from a Google Log once or
// currently qualified;
// AND there is at least one embedded SCT from a non-Google Log once or
// currently qualified;
// ...
// Note: This policy language is only enforced after the below issuance
// date, as that's when the diversity policy first came into effect for
// SCTs embedded in certificates.
// The date when diverse SCTs requirement is effective from.
// 2015-07-01 00:00:00 UTC.
const base::Time kDiverseSCTRequirementStartDate =
base::Time::UnixEpoch() + base::TimeDelta::FromSeconds(1435708800);
if (issuance_date >= kDiverseSCTRequirementStartDate &&
!(has_embedded_google_sct && has_embedded_nongoogle_sct)) {
// Note: This also covers the case for non-embedded SCTs, as it's only
// possible to reach here if both sets are not diverse enough.
return CTPolicyCompliance::CT_POLICY_NOT_DIVERSE_SCTS;
size_t lifetime_in_months = 0;
bool has_partial_month = false;
RoundedDownMonthDifference(cert.valid_start(), cert.valid_expiry(),
&lifetime_in_months, &has_partial_month);
// ... AND the certificate embeds SCTs from AT LEAST the number of logs
// once or currently qualified shown in Table 1 of the CT Policy.
size_t num_required_embedded_scts = 5;
if (lifetime_in_months > 39 ||
(lifetime_in_months == 39 && has_partial_month)) {
num_required_embedded_scts = 5;
} else if (lifetime_in_months > 27 ||
(lifetime_in_months == 27 && has_partial_month)) {
num_required_embedded_scts = 4;
} else if (lifetime_in_months >= 15) {
num_required_embedded_scts = 3;
} else {
num_required_embedded_scts = 2;
// Sort the embedded log IDs and remove duplicates, so that only a single
// SCT from each log is accepted. This is to handle the case where a given
// log returns different SCTs for the same precertificate (which is
// permitted, but advised against).
std::sort(embedded_log_ids.begin(), embedded_log_ids.end());
auto sorted_end =
std::unique(embedded_log_ids.begin(), embedded_log_ids.end());
size_t num_embedded_scts =
std::distance(embedded_log_ids.begin(), sorted_end);
if (num_embedded_scts >= num_required_embedded_scts)
return CTPolicyCompliance::CT_POLICY_COMPLIES_VIA_SCTS;
// Under Option 2, there weren't enough SCTs, and potentially under Option
// 1, there weren't diverse enough SCTs. Try to signal the error that is
// most easily fixed.
return has_valid_nonembedded_sct
} // namespace
CTPolicyCompliance ChromeCTPolicyEnforcer::CheckCompliance(
net::X509Certificate* cert,
const net::ct::SCTList& verified_scts,
const net::NetLogWithSource& net_log) {
// If the build is not timely, no certificate is considered compliant
// with CT policy. The reasoning is that, for example, a log might
// have been pulled and is no longer considered valid; thus, a client
// needs up-to-date information about logs to consider certificates to
// be compliant with policy.
bool build_timely = IsBuildTimely();
CTPolicyCompliance compliance;
if (!build_timely) {
compliance = CTPolicyCompliance::CT_POLICY_BUILD_NOT_TIMELY;
} else {
compliance = CheckCTPolicyCompliance(*cert, verified_scts);
net::NetLogParametersCallback net_log_callback =
base::Unretained(cert), build_timely, compliance);
return compliance;
} // namespace certificate_transparency