| // 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/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/default_clock.h" |
| #include "base/time/time.h" |
| #include "base/values.h" |
| #include "base/version.h" |
| #include "components/certificate_transparency/ct_known_logs.h" |
| #include "crypto/sha2.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_with_source.h" |
| |
| using net::ct::CTPolicyCompliance; |
| |
| namespace certificate_transparency { |
| |
| namespace { |
| |
| // 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) { |
| DCHECK(rounded_months_difference); |
| DCHECK(has_partial_month); |
| base::Time::Exploded exploded_start; |
| base::Time::Exploded exploded_expiry; |
| start.UTCExplode(&exploded_start); |
| end.UTCExplode(&exploded_expiry); |
| if (end < start) { |
| *rounded_months_difference = 0; |
| *has_partial_month = false; |
| return; |
| } |
| |
| *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) |
| --month_diff; |
| 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_COMPLIES_VIA_SCTS: |
| return "COMPLIES_VIA_SCTS"; |
| case CTPolicyCompliance::CT_POLICY_NOT_ENOUGH_SCTS: |
| return "NOT_ENOUGH_SCTS"; |
| case CTPolicyCompliance::CT_POLICY_NOT_DIVERSE_SCTS: |
| return "NOT_DIVERSE_SCTS"; |
| case CTPolicyCompliance::CT_POLICY_BUILD_NOT_TIMELY: |
| return "BUILD_NOT_TIMELY"; |
| case CTPolicyCompliance::CT_POLICY_COMPLIANCE_DETAILS_NOT_AVAILABLE: |
| case CTPolicyCompliance::CT_POLICY_COUNT: |
| NOTREACHED(); |
| return "unknown"; |
| } |
| |
| NOTREACHED(); |
| return "unknown"; |
| } |
| |
| base::Value NetLogCertComplianceCheckResultParams( |
| net::X509Certificate* cert, |
| bool build_timely, |
| CTPolicyCompliance compliance) { |
| base::DictionaryValue dict; |
| dict.SetKey("certificate", net::NetLogX509CertificateParams(cert)); |
| dict.SetBoolean("build_timely", build_timely); |
| dict.SetString("ct_compliance_status", |
| CTPolicyComplianceToString(compliance)); |
| return std::move(dict); |
| } |
| |
| } // namespace |
| |
| ChromeCTPolicyEnforcer::ChromeCTPolicyEnforcer( |
| base::Time log_list_date, |
| std::vector<std::pair<std::string, base::TimeDelta>> disqualified_logs, |
| std::vector<std::string> operated_by_google_logs) |
| : disqualified_logs_(disqualified_logs), |
| operated_by_google_logs_(operated_by_google_logs), |
| clock_(base::DefaultClock::GetInstance()), |
| log_list_date_(log_list_date) {} |
| |
| ChromeCTPolicyEnforcer::~ChromeCTPolicyEnforcer() {} |
| |
| 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 = IsLogDataTimely(); |
| CTPolicyCompliance compliance; |
| if (!build_timely) { |
| compliance = CTPolicyCompliance::CT_POLICY_BUILD_NOT_TIMELY; |
| } else { |
| compliance = CheckCTPolicyCompliance(*cert, verified_scts); |
| } |
| |
| net_log.AddEvent(net::NetLogEventType::CERT_CT_COMPLIANCE_CHECKED, [&] { |
| return NetLogCertComplianceCheckResultParams(cert, build_timely, |
| compliance); |
| }); |
| |
| return compliance; |
| } |
| |
| bool ChromeCTPolicyEnforcer::IsLogDisqualified( |
| base::StringPiece log_id, |
| base::Time* disqualification_date) const { |
| CHECK_EQ(log_id.size(), crypto::kSHA256Length); |
| |
| auto p = std::lower_bound( |
| std::begin(disqualified_logs_), std::end(disqualified_logs_), log_id, |
| [](const auto& a, base::StringPiece b) { return a.first < b; }); |
| if (p == std::end(disqualified_logs_) || p->first != log_id) { |
| return false; |
| } |
| *disqualification_date = base::Time::UnixEpoch() + p->second; |
| return true; |
| } |
| |
| bool ChromeCTPolicyEnforcer::IsLogOperatedByGoogle( |
| base::StringPiece log_id) const { |
| return std::binary_search(std::begin(operated_by_google_logs_), |
| std::end(operated_by_google_logs_), log_id); |
| } |
| |
| bool ChromeCTPolicyEnforcer::IsLogDataTimely() const { |
| // We consider built-in information to be timely for 10 weeks. |
| return (clock_->Now() - log_list_date_).InDays() < 70 /* 10 weeks */; |
| } |
| |
| // Evaluates against the policy specified at |
| // https://sites.google.com/a/chromium.org/dev/Home/chromium-security/root-ca-policy/EVCTPlanMay2015edition.pdf?attredirects=0 |
| CTPolicyCompliance ChromeCTPolicyEnforcer::CheckCTPolicyCompliance( |
| const net::X509Certificate& cert, |
| const net::ct::SCTList& verified_scts) const { |
| // 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)) |
| continue; |
| 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. |
| continue; |
| } |
| |
| 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)) { |
| embedded_log_ids.push_back(sct->log_id); |
| } |
| } |
| } |
| |
| // 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 |
| ? CTPolicyCompliance::CT_POLICY_NOT_DIVERSE_SCTS |
| : CTPolicyCompliance::CT_POLICY_NOT_ENOUGH_SCTS; |
| } |
| |
| // ... 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 |
| ? CTPolicyCompliance::CT_POLICY_NOT_DIVERSE_SCTS |
| : CTPolicyCompliance::CT_POLICY_NOT_ENOUGH_SCTS; |
| } |
| |
| } // namespace certificate_transparency |