// 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 "net/cert/ct_policy_enforcer.h" #include #include #include #include #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 "net/cert/ct_known_logs.h" #include "net/cert/ct_policy_status.h" #include "net/cert/ct_verify_result.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" namespace net { 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) { 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* CertPolicyComplianceToString(ct::CertPolicyCompliance status) { switch (status) { case ct::CertPolicyCompliance::CERT_POLICY_COMPLIES_VIA_SCTS: return "COMPLIES_VIA_SCTS"; case ct::CertPolicyCompliance::CERT_POLICY_NOT_ENOUGH_SCTS: return "NOT_ENOUGH_SCTS"; case ct::CertPolicyCompliance::CERT_POLICY_NOT_DIVERSE_SCTS: return "NOT_DIVERSE_SCTS"; case ct::CertPolicyCompliance::CERT_POLICY_BUILD_NOT_TIMELY: return "BUILD_NOT_TIMELY"; case ct::CertPolicyCompliance::CERT_POLICY_MAX: NOTREACHED(); return "unknown"; } NOTREACHED(); return "unknown"; } std::unique_ptr NetLogCertComplianceCheckResultCallback( X509Certificate* cert, bool build_timely, ct::CertPolicyCompliance compliance, NetLogCaptureMode capture_mode) { std::unique_ptr dict(new base::DictionaryValue()); dict->Set("certificate", NetLogX509CertificateCallback(cert, capture_mode)); dict->SetBoolean("build_timely", build_timely); dict->SetString("ct_compliance_status", CertPolicyComplianceToString(compliance)); return std::move(dict); } // Evaluates against the policy specified at // https://sites.google.com/a/chromium.org/dev/Home/chromium-security/root-ca-policy/EVCTPlanMay2015edition.pdf?attredirects=0 ct::CertPolicyCompliance CheckCertPolicyCompliance( const X509Certificate& cert, const 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 ct::CertPolicyCompliance::CERT_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 (ct::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 embedded_log_ids; for (const auto& sct : verified_scts) { base::Time disqualification_date; bool is_disqualified = ct::IsLogDisqualified(sct->log_id, &disqualification_date); if (is_disqualified && sct->origin != ct::SignedCertificateTimestamp::SCT_EMBEDDED) { // For OCSP and TLS delivered SCTs, only SCTs that are valid at the // time of check are accepted. continue; } if (ct::IsLogOperatedByGoogle(sct->log_id)) { has_valid_google_sct |= !is_disqualified; if (sct->origin == ct::SignedCertificateTimestamp::SCT_EMBEDDED) has_embedded_google_sct = true; } else { has_valid_nongoogle_sct |= !is_disqualified; if (sct->origin == ct::SignedCertificateTimestamp::SCT_EMBEDDED) has_embedded_nongoogle_sct = true; } if (sct->origin != 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 ct::CertPolicyCompliance::CERT_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 ? ct::CertPolicyCompliance::CERT_POLICY_NOT_DIVERSE_SCTS : ct::CertPolicyCompliance::CERT_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::FromInternalValue(INT64_C(13080182400000000)); 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 ct::CertPolicyCompliance::CERT_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 ct::CertPolicyCompliance::CERT_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 ? ct::CertPolicyCompliance::CERT_POLICY_NOT_DIVERSE_SCTS : ct::CertPolicyCompliance::CERT_POLICY_NOT_ENOUGH_SCTS; } } // namespace ct::CertPolicyCompliance CTPolicyEnforcer::DoesConformToCertPolicy( X509Certificate* cert, const ct::SCTList& verified_scts, const 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(); ct::CertPolicyCompliance compliance; if (!build_timely) { compliance = ct::CertPolicyCompliance::CERT_POLICY_BUILD_NOT_TIMELY; } else { compliance = CheckCertPolicyCompliance(*cert, verified_scts); } NetLogParametersCallback net_log_callback = base::Bind(&NetLogCertComplianceCheckResultCallback, base::Unretained(cert), build_timely, compliance); net_log.AddEvent(NetLogEventType::CERT_CT_COMPLIANCE_CHECKED, net_log_callback); return compliance; } } // namespace net