text: // Copyright (c) 2012 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/cert_verify_proc_mac.h"
  
  #include <CommonCrypto/CommonDigest.h>
  #include <CoreServices/CoreServices.h>
  #include <Security/Security.h>
  
  #include <string>
  #include <vector>
  
  #include "base/logging.h"
  #include "base/mac/mac_logging.h"
  #include "base/mac/scoped_cftyperef.h"
  #include "base/sha1.h"
  #include "base/strings/string_piece.h"
  #include "base/synchronization/lock.h"
  #include "crypto/mac_security_services_lock.h"
  #include "crypto/sha2.h"
  #include "net/base/net_errors.h"
  #include "net/cert/asn1_util.h"
  #include "net/cert/cert_status_flags.h"
  #include "net/cert/cert_verifier.h"
  #include "net/cert/cert_verify_result.h"
  #include "net/cert/crl_set.h"
  #include "net/cert/test_root_certs.h"
  #include "net/cert/x509_certificate.h"
  #include "net/cert/x509_certificate_known_roots_mac.h"
  #include "net/cert/x509_util_mac.h"
  
  // From 10.7.2 libsecurity_keychain-55035/lib/SecTrustPriv.h, for use with
  // SecTrustCopyExtendedResult.
  #ifndef kSecEVOrganizationName
  #define kSecEVOrganizationName CFSTR("Organization")
  #endif
  
  using base::ScopedCFTypeRef;
  
  namespace net {
  
  namespace {
  
  typedef OSStatus (*SecTrustCopyExtendedResultFuncPtr)(SecTrustRef,
                                                        CFDictionaryRef*);
  
  int NetErrorFromOSStatus(OSStatus status) {
    switch (status) {
      case noErr:
        return OK;
      case errSecNotAvailable:
      case errSecNoCertificateModule:
      case errSecNoPolicyModule:
        return ERR_NOT_IMPLEMENTED;
      case errSecAuthFailed:
        return ERR_ACCESS_DENIED;
      default: {
        OSSTATUS_LOG(ERROR, status) << "Unknown error mapped to ERR_FAILED";
        return ERR_FAILED;
      }
    }
  }
  
  CertStatus CertStatusFromOSStatus(OSStatus status) {
    switch (status) {
      case noErr:
        return 0;
  
      case CSSMERR_TP_INVALID_ANCHOR_CERT:
      case CSSMERR_TP_NOT_TRUSTED:
      case CSSMERR_TP_INVALID_CERT_AUTHORITY:
        return CERT_STATUS_AUTHORITY_INVALID;
  
      case CSSMERR_TP_CERT_EXPIRED:
      case CSSMERR_TP_CERT_NOT_VALID_YET:
        // "Expired" and "not yet valid" collapse into a single status.
        return CERT_STATUS_DATE_INVALID;
  
      case CSSMERR_TP_CERT_REVOKED:
      case CSSMERR_TP_CERT_SUSPENDED:
        return CERT_STATUS_REVOKED;
  
      case CSSMERR_APPLETP_HOSTNAME_MISMATCH:
        return CERT_STATUS_COMMON_NAME_INVALID;
  
      case CSSMERR_APPLETP_CRL_NOT_FOUND:
      case CSSMERR_APPLETP_OCSP_UNAVAILABLE:
      case CSSMERR_APPLETP_INCOMPLETE_REVOCATION_CHECK:
        return CERT_STATUS_NO_REVOCATION_MECHANISM;
  
      case CSSMERR_APPLETP_CRL_EXPIRED:
      case CSSMERR_APPLETP_CRL_NOT_VALID_YET:
      case CSSMERR_APPLETP_CRL_SERVER_DOWN:
      case CSSMERR_APPLETP_CRL_NOT_TRUSTED:
      case CSSMERR_APPLETP_CRL_INVALID_ANCHOR_CERT:
      case CSSMERR_APPLETP_CRL_POLICY_FAIL:
      case CSSMERR_APPLETP_OCSP_BAD_RESPONSE:
      case CSSMERR_APPLETP_OCSP_BAD_REQUEST:
      case CSSMERR_APPLETP_OCSP_STATUS_UNRECOGNIZED:
      case CSSMERR_APPLETP_NETWORK_FAILURE:
      case CSSMERR_APPLETP_OCSP_NOT_TRUSTED:
      case CSSMERR_APPLETP_OCSP_INVALID_ANCHOR_CERT:
      case CSSMERR_APPLETP_OCSP_SIG_ERROR:
      case CSSMERR_APPLETP_OCSP_NO_SIGNER:
      case CSSMERR_APPLETP_OCSP_RESP_MALFORMED_REQ:
      case CSSMERR_APPLETP_OCSP_RESP_INTERNAL_ERR:
      case CSSMERR_APPLETP_OCSP_RESP_TRY_LATER:
      case CSSMERR_APPLETP_OCSP_RESP_SIG_REQUIRED:
      case CSSMERR_APPLETP_OCSP_RESP_UNAUTHORIZED:
      case CSSMERR_APPLETP_OCSP_NONCE_MISMATCH:
        // We asked for a revocation check, but didn't get it.
        return CERT_STATUS_UNABLE_TO_CHECK_REVOCATION;
  
      case CSSMERR_APPLETP_SSL_BAD_EXT_KEY_USE:
        // TODO(wtc): Should we add CERT_STATUS_WRONG_USAGE?
        return CERT_STATUS_INVALID;
  
      case CSSMERR_APPLETP_CRL_BAD_URI:
      case CSSMERR_APPLETP_IDP_FAIL:
        return CERT_STATUS_INVALID;
  
      case CSSMERR_CSP_UNSUPPORTED_KEY_SIZE:
        // Mapping UNSUPPORTED_KEY_SIZE to CERT_STATUS_WEAK_KEY is not strictly
        // accurate, as the error may have been returned due to a key size
        // that exceeded the maximum supported. However, within
        // CertVerifyProcMac::VerifyInternal(), this code should only be
        // encountered as a certificate status code, and only when the key size
        // is smaller than the minimum required (1024 bits).
        return CERT_STATUS_WEAK_KEY;
  
      default: {
        // Failure was due to something Chromium doesn't define a
        // specific status for (such as basic constraints violation, or
        // unknown critical extension)
        OSSTATUS_LOG(WARNING, status)
            << "Unknown error mapped to CERT_STATUS_INVALID";
        return CERT_STATUS_INVALID;
      }
    }
  }
  
  // Creates a series of SecPolicyRefs to be added to a SecTrustRef used to
  // validate a certificate for an SSL server. |hostname| contains the name of
  // the SSL server that the certificate should be verified against. |flags| is
  // a bitwise-OR of VerifyFlags that can further alter how trust is validated,
  // such as how revocation is checked. If successful, returns noErr, and
  // stores the resultant array of SecPolicyRefs in |policies|.
  OSStatus CreateTrustPolicies(const std::string& hostname,
                               int flags,
                               ScopedCFTypeRef<CFArrayRef>* policies) {
    ScopedCFTypeRef<CFMutableArrayRef> local_policies(
        CFArrayCreateMutable(kCFAllocatorDefault, 0, &kCFTypeArrayCallBacks));
    if (!local_policies)
      return memFullErr;
  
    SecPolicyRef ssl_policy;
    OSStatus status = x509_util::CreateSSLServerPolicy(hostname, &ssl_policy);
    if (status)
      return status;
    CFArrayAppendValue(local_policies, ssl_policy);
    CFRelease(ssl_policy);
  
    // Explicitly add revocation policies, in order to override system
    // revocation checking policies and instead respect the application-level
    // revocation preference.
    status = x509_util::CreateRevocationPolicies(
        (flags & CertVerifier::VERIFY_REV_CHECKING_ENABLED),
        (flags & CertVerifier::VERIFY_REV_CHECKING_ENABLED_EV_ONLY),
        local_policies);
    if (status)
      return status;
  
    policies->reset(local_policies.release());
    return noErr;
  }
  
  // Stores the constructed certificate chain |cert_chain| and information about
  // the signature algorithms used into |*verify_result|. If the leaf cert in
  // |cert_chain| contains a weak (MD2, MD4, MD5, SHA-1) signature, stores that
  // in |*leaf_is_weak|. |cert_chain| must not be empty.
  void GetCertChainInfo(CFArrayRef cert_chain,
                        CSSM_TP_APPLE_EVIDENCE_INFO* chain_info,
                        CertVerifyResult* verify_result,
                        bool* leaf_is_weak) {
    DCHECK_LT(0, CFArrayGetCount(cert_chain));
  
    *leaf_is_weak = false;
    verify_result->has_md2 = false;
    verify_result->has_md4 = false;
    verify_result->has_md5 = false;
    verify_result->has_sha1 = false;
  
    SecCertificateRef verified_cert = NULL;
    std::vector<SecCertificateRef> verified_chain;
    for (CFIndex i = 0, count = CFArrayGetCount(cert_chain); i < count; ++i) {
      SecCertificateRef chain_cert = reinterpret_cast<SecCertificateRef>(
          const_cast<void*>(CFArrayGetValueAtIndex(cert_chain, i)));
      if (i == 0) {
        verified_cert = chain_cert;
      } else {
        verified_chain.push_back(chain_cert);
      }
  
      if ((chain_info[i].StatusBits & CSSM_CERT_STATUS_IS_IN_ANCHORS) ||
          (chain_info[i].StatusBits & CSSM_CERT_STATUS_IS_ROOT)) {
        // The current certificate is either in the user's trusted store or is
        // a root (self-signed) certificate. Ignore the signature algorithm for
        // these certificates, as it is meaningless for security. We allow
        // self-signed certificates (i == 0 & IS_ROOT), since we accept that
        // any security assertions by such a cert are inherently meaningless.
        continue;
      }
  
      x509_util::CSSMCachedCertificate cached_cert;
      OSStatus status = cached_cert.Init(chain_cert);
      if (status)
        continue;
      x509_util::CSSMFieldValue signature_field;
      status = cached_cert.GetField(&CSSMOID_X509V1SignatureAlgorithm,
                                    &signature_field);
      if (status || !signature_field.field())
        continue;
      // Match the behaviour of OS X system tools and defensively check that
      // sizes are appropriate. This would indicate a critical failure of the
      // OS X certificate library, but based on history, it is best to play it
      // safe.
      const CSSM_X509_ALGORITHM_IDENTIFIER* sig_algorithm =
          signature_field.GetAs<CSSM_X509_ALGORITHM_IDENTIFIER>();
      if (!sig_algorithm)
        continue;
  
      const CSSM_OID* alg_oid = &sig_algorithm->algorithm;
      if (CSSMOIDEqual(alg_oid, &CSSMOID_MD2WithRSA)) {
        verify_result->has_md2 = true;
        if (i == 0)
          *leaf_is_weak = true;
      } else if (CSSMOIDEqual(alg_oid, &CSSMOID_MD4WithRSA)) {
        verify_result->has_md4 = true;
        if (i == 0)
          *leaf_is_weak = true;
      } else if (CSSMOIDEqual(alg_oid, &CSSMOID_MD5WithRSA)) {
        verify_result->has_md5 = true;
        if (i == 0)
          *leaf_is_weak = true;
      } else if (CSSMOIDEqual(alg_oid, &CSSMOID_SHA1WithRSA) ||
                 CSSMOIDEqual(alg_oid, &CSSMOID_SHA1WithRSA_OIW) ||
                 CSSMOIDEqual(alg_oid, &CSSMOID_SHA1WithDSA) ||
                 CSSMOIDEqual(alg_oid, &CSSMOID_SHA1WithDSA_CMS) ||
                 CSSMOIDEqual(alg_oid, &CSSMOID_SHA1WithDSA_JDK) ||
                 CSSMOIDEqual(alg_oid, &CSSMOID_ECDSA_WithSHA1)) {
        verify_result->has_sha1 = true;
        if (i == 0)
          *leaf_is_weak = true;
      }
    }
    if (!verified_cert) {
      NOTREACHED();
      return;
    }
  
    verify_result->verified_cert =
        X509Certificate::CreateFromHandle(verified_cert, verified_chain);
  }
  
  void AppendPublicKeyHashes(CFArrayRef chain,
                             HashValueVector* hashes) {
    const CFIndex n = CFArrayGetCount(chain);
    for (CFIndex i = 0; i < n; i++) {
      SecCertificateRef cert = reinterpret_cast<SecCertificateRef>(
          const_cast<void*>(CFArrayGetValueAtIndex(chain, i)));
  
      CSSM_DATA cert_data;
      OSStatus err = SecCertificateGetData(cert, &cert_data);
      DCHECK_EQ(err, noErr);
      base::StringPiece der_bytes(reinterpret_cast<const char*>(cert_data.Data),
                                 cert_data.Length);
      base::StringPiece spki_bytes;
      if (!asn1::ExtractSPKIFromDERCert(der_bytes, &spki_bytes))
        continue;
  
      HashValue sha1(HASH_VALUE_SHA1);
      CC_SHA1(spki_bytes.data(), spki_bytes.size(), sha1.data());
      hashes->push_back(sha1);
  
      HashValue sha256(HASH_VALUE_SHA256);
      CC_SHA256(spki_bytes.data(), spki_bytes.size(), sha256.data());
      hashes->push_back(sha256);
    }
  }
  
  bool CheckRevocationWithCRLSet(CFArrayRef chain, CRLSet* crl_set) {
    if (CFArrayGetCount(chain) == 0)
      return true;
  
    // We iterate from the root certificate down to the leaf, keeping track of
    // the issuer's SPKI at each step.
    std::string issuer_spki_hash;
    for (CFIndex i = CFArrayGetCount(chain) - 1; i >= 0; i--) {
      SecCertificateRef cert = reinterpret_cast<SecCertificateRef>(
          const_cast<void*>(CFArrayGetValueAtIndex(chain, i)));
  
      CSSM_DATA cert_data;
      OSStatus err = SecCertificateGetData(cert, &cert_data);
      if (err != noErr) {
        NOTREACHED();
        continue;
      }
      base::StringPiece der_bytes(reinterpret_cast<const char*>(cert_data.Data),
                                  cert_data.Length);
      base::StringPiece spki;
      if (!asn1::ExtractSPKIFromDERCert(der_bytes, &spki)) {
        NOTREACHED();
        continue;
      }
  
      const std::string spki_hash = crypto::SHA256HashString(spki);
      x509_util::CSSMCachedCertificate cached_cert;
      if (cached_cert.Init(cert) != CSSM_OK) {
        NOTREACHED();
        continue;
      }
      x509_util::CSSMFieldValue serial_number;
      err = cached_cert.GetField(&CSSMOID_X509V1SerialNumber, &serial_number);
      if (err || !serial_number.field()) {
        NOTREACHED();
        continue;
      }
  
      base::StringPiece serial(
          reinterpret_cast<const char*>(serial_number.field()->Data),
          serial_number.field()->Length);
  
      CRLSet::Result result = crl_set->CheckSPKI(spki_hash);
  
      if (result != CRLSet::REVOKED && !issuer_spki_hash.empty())
        result = crl_set->CheckSerial(serial, issuer_spki_hash);
  
      issuer_spki_hash = spki_hash;
  
      switch (result) {
        case CRLSet::REVOKED:
          return false;
        case CRLSet::UNKNOWN:
        case CRLSet::GOOD:
          continue;
        default:
          NOTREACHED();
          return false;
      }
    }
  
    return true;
  }
  
  // IsIssuedByKnownRoot returns true if the given chain is rooted at a root CA
  // that we recognise as a standard root.
  // static
  bool IsIssuedByKnownRoot(CFArrayRef chain) {
    int n = CFArrayGetCount(chain);
    if (n < 1)
      return false;
    SecCertificateRef root_ref = reinterpret_cast<SecCertificateRef>(
        const_cast<void*>(CFArrayGetValueAtIndex(chain, n - 1)));
    SHA1HashValue hash = X509Certificate::CalculateFingerprint(root_ref);
    return IsSHA1HashInSortedArray(
        hash, &kKnownRootCertSHA1Hashes[0][0], sizeof(kKnownRootCertSHA1Hashes));
  }
  
  // Builds and evaluates a SecTrustRef for the certificate chain contained
  // in |cert_array|, using the verification policies in |trust_policies|. On
  // success, returns OK, and updates |trust_ref|, |trust_result|,
  // |verified_chain|, and |chain_info| with the verification results. On
  // failure, no output parameters are modified.
  //
  // Note: An OK return does not mean that |cert_array| is trusted, merely that
  // verification was performed successfully.
  //
  // This function should only be called while the Mac Security Services lock is
  // held.
  int BuildAndEvaluateSecTrustRef(CFArrayRef cert_array,
                                  CFArrayRef trust_policies,
                                  int flags,
                                  ScopedCFTypeRef<SecTrustRef>* trust_ref,
                                  SecTrustResultType* trust_result,
                                  ScopedCFTypeRef<CFArrayRef>* verified_chain,
                                  CSSM_TP_APPLE_EVIDENCE_INFO** chain_info) {
    SecTrustRef tmp_trust = NULL;
    OSStatus status = SecTrustCreateWithCertificates(cert_array, trust_policies,
                                                     &tmp_trust);
    if (status)
      return NetErrorFromOSStatus(status);
    ScopedCFTypeRef<SecTrustRef> scoped_tmp_trust(tmp_trust);
  
    if (TestRootCerts::HasInstance()) {
      status = TestRootCerts::GetInstance()->FixupSecTrustRef(tmp_trust);
      if (status)
        return NetErrorFromOSStatus(status);
    }
  
    CSSM_APPLE_TP_ACTION_DATA tp_action_data;
    memset(&tp_action_data, 0, sizeof(tp_action_data));
    tp_action_data.Version = CSSM_APPLE_TP_ACTION_VERSION;
    // Allow CSSM to download any missing intermediate certificates if an
    // authorityInfoAccess extension or issuerAltName extension is present.
    tp_action_data.ActionFlags = CSSM_TP_ACTION_FETCH_CERT_FROM_NET |
                                 CSSM_TP_ACTION_TRUST_SETTINGS;
  
    // Note: For EV certificates, the Apple TP will handle setting these flags
    // as part of EV evaluation.
    if (flags & CertVerifier::VERIFY_REV_CHECKING_ENABLED) {
      // Require a positive result from an OCSP responder or a CRL (or both)
      // for every certificate in the chain. The Apple TP automatically
      // excludes the self-signed root from this requirement. If a certificate
      // is missing both a crlDistributionPoints extension and an
      // authorityInfoAccess extension with an OCSP responder URL, then we
      // will get a kSecTrustResultRecoverableTrustFailure back from
      // SecTrustEvaluate(), with a
      // CSSMERR_APPLETP_INCOMPLETE_REVOCATION_CHECK error code. In that case,
      // we'll set our own result to include
      // CERT_STATUS_NO_REVOCATION_MECHANISM. If one or both extensions are
      // present, and a check fails (server unavailable, OCSP retry later,
      // signature mismatch), then we'll set our own result to include
      // CERT_STATUS_UNABLE_TO_CHECK_REVOCATION.
      tp_action_data.ActionFlags |= CSSM_TP_ACTION_REQUIRE_REV_PER_CERT;
  
      // Note, even if revocation checking is disabled, SecTrustEvaluate() will
      // modify the OCSP options so as to attempt OCSP checking if it believes a
      // certificate may chain to an EV root. However, because network fetches
      // are disabled in CreateTrustPolicies() when revocation checking is
      // disabled, these will only go against the local cache.
    }
  
    CFDataRef action_data_ref =
        CFDataCreateWithBytesNoCopy(kCFAllocatorDefault,
                                    reinterpret_cast<UInt8*>(&tp_action_data),
                                    sizeof(tp_action_data), kCFAllocatorNull);
    if (!action_data_ref)
      return ERR_OUT_OF_MEMORY;
    ScopedCFTypeRef<CFDataRef> scoped_action_data_ref(action_data_ref);
    status = SecTrustSetParameters(tmp_trust, CSSM_TP_ACTION_DEFAULT,
                                   action_data_ref);
    if (status)
      return NetErrorFromOSStatus(status);
  
    // Verify the certificate. A non-zero result from SecTrustGetResult()
    // indicates that some fatal error occurred and the chain couldn't be
    // processed, not that the chain contains no errors. We need to examine the
    // output of SecTrustGetResult() to determine that.
    SecTrustResultType tmp_trust_result;
    status = SecTrustEvaluate(tmp_trust, &tmp_trust_result);
    if (status)
      return NetErrorFromOSStatus(status);
    CFArrayRef tmp_verified_chain = NULL;
    CSSM_TP_APPLE_EVIDENCE_INFO* tmp_chain_info;
    status = SecTrustGetResult(tmp_trust, &tmp_trust_result, &tmp_verified_chain,
                               &tmp_chain_info);
    if (status)
      return NetErrorFromOSStatus(status);
  
    trust_ref->swap(scoped_tmp_trust);
    *trust_result = tmp_trust_result;
    verified_chain->reset(tmp_verified_chain);
    *chain_info = tmp_chain_info;
  
    return OK;
  }
  
  }  // namespace
  
  CertVerifyProcMac::CertVerifyProcMac() {}
  
  CertVerifyProcMac::~CertVerifyProcMac() {}
  
  bool CertVerifyProcMac::SupportsAdditionalTrustAnchors() const {
    return false;
  }
  
  bool CertVerifyProcMac::SupportsOCSPStapling() const {
    // TODO(rsleevi): Plumb an OCSP response into the Mac system library.
    // https://crbug.com/430714
    return false;
  }
  
  int CertVerifyProcMac::VerifyInternal(
      X509Certificate* cert,
      const std::string& hostname,
      const std::string& ocsp_response,
      int flags,
      CRLSet* crl_set,
      const CertificateList& additional_trust_anchors,
      CertVerifyResult* verify_result) {
    ScopedCFTypeRef<CFArrayRef> trust_policies;
    OSStatus status = CreateTrustPolicies(hostname, flags, &trust_policies);
    if (status)
      return NetErrorFromOSStatus(status);
  
    // Create and configure a SecTrustRef, which takes our certificate(s)
    // and our SSL SecPolicyRef. SecTrustCreateWithCertificates() takes an
    // array of certificates, the first of which is the certificate we're
    // verifying, and the subsequent (optional) certificates are used for
    // chain building.
    ScopedCFTypeRef<CFMutableArrayRef> cert_array(
        cert->CreateOSCertChainForCert());
  
    // Serialize all calls that may use the Keychain, to work around various
    // issues in OS X 10.6+ with multi-threaded access to Security.framework.
    base::AutoLock lock(crypto::GetMacSecurityServicesLock());
  
    ScopedCFTypeRef<SecTrustRef> trust_ref;
    SecTrustResultType trust_result = kSecTrustResultDeny;
    ScopedCFTypeRef<CFArrayRef> completed_chain;
    CSSM_TP_APPLE_EVIDENCE_INFO* chain_info = NULL;
    bool candidate_untrusted = true;
    bool candidate_weak = false;
  
    // OS X lacks proper path discovery; it will take the input certs and never
    // backtrack the graph attempting to discover valid paths.
    // This can create issues in some situations:
    // - When OS X changes the trust store, there may be a chain
    //     A -> B -> C -> D
    //   where OS X trusts D (on some versions) and trusts C (on some versions).
    //   If a server supplies a chain A, B, C (cross-signed by D), then this chain
    //   will successfully validate on systems that trust D, but fail for systems
    //   that trust C. If the server supplies a chain of A -> B, then it forces
    //   all clients to fetch C (via AIA) if they trust D, and not all clients
    //   (notably, Firefox and Android) will do this, thus breaking them.
    //   An example of this is the Verizon Business Services root - GTE CyberTrust
    //   and Baltimore CyberTrust roots represent old and new roots that cause
    //   issues depending on which version of OS X being used.
    //
    // - A server may be (misconfigured) to send an expired intermediate
    //   certificate. On platforms with path discovery, the graph traversal
    //   will back up to immediately before this intermediate, and then
    //   attempt an AIA fetch or retrieval from local store. However, OS X
    //   does not do this, and thus prevents access. While this is ostensibly
    //   a server misconfiguration issue, the fact that it works on other
    //   platforms is a jarring inconsistency for users.
    //
    // - When OS X trusts both C and D (simultaneously), it's possible that the
    //   version of C signed by D is signed using a weak algorithm (e.g. SHA-1),
    //   while the version of C in the trust store's signature doesn't matter.
    //   Since a 'strong' chain exists, it would be desirable to prefer this
    //   chain.
    //
    // - A variant of the above example, it may be that the version of B sent by
    //   the server is signed using a weak algorithm, but the version of B
    //   present in the AIA of A is signed using a strong algorithm. Since a
    //   'strong' chain exists, it would be desirable to prefer this chain.
    //
    // Because of this, the code below first attempts to validate the peer's
    // identity using the supplied chain. If it is not trusted (e.g. the OS only
    // trusts C, but the version of C signed by D was sent, and D is not trusted),
    // or if it contains a weak chain, it will begin lopping off certificates
    // from the end of the chain and attempting to verify. If a stronger, trusted
    // chain is found, it is used, otherwise, the algorithm continues until only
    // the peer's certificate remains.
    //
    // This does cause a performance hit for these users, but only in cases where
    // OS X is building weaker chains than desired, or when it would otherwise
    // fail the connection.
    while (CFArrayGetCount(cert_array) > 0) {
      ScopedCFTypeRef<SecTrustRef> temp_ref;
      SecTrustResultType temp_trust_result = kSecTrustResultDeny;
      ScopedCFTypeRef<CFArrayRef> temp_chain;
      CSSM_TP_APPLE_EVIDENCE_INFO* temp_chain_info = NULL;
  
      int rv = BuildAndEvaluateSecTrustRef(cert_array, trust_policies, flags,
                                           &temp_ref, &temp_trust_result,
                                           &temp_chain, &temp_chain_info);
      if (rv != OK)
        return rv;
  
      bool untrusted = (temp_trust_result != kSecTrustResultUnspecified &&
                        temp_trust_result != kSecTrustResultProceed);
      bool weak_chain = false;
      if (CFArrayGetCount(temp_chain) == 0) {
        // If the chain is empty, it cannot be trusted or have recoverable
        // errors.
        DCHECK(untrusted);
        DCHECK_NE(kSecTrustResultRecoverableTrustFailure, temp_trust_result);
      } else {
        CertVerifyResult temp_verify_result;
        bool leaf_is_weak = false;
        GetCertChainInfo(temp_chain, temp_chain_info, &temp_verify_result,
                         &leaf_is_weak);
        weak_chain = !leaf_is_weak &&
                     (temp_verify_result.has_md2 || temp_verify_result.has_md4 ||
                      temp_verify_result.has_md5 || temp_verify_result.has_sha1);
      }
      // Set the result to the current chain if:
      // - This is the first verification attempt. This ensures that if
      //   everything is awful (e.g. it may just be an untrusted cert), that
      //   what is reported is exactly what was sent by the server
      // - If the current chain is trusted, and the old chain was not trusted,
      //   then prefer this chain. This ensures that if there is at least a
      //   valid path to a trust anchor, it's preferred over reporting an error.
      // - If the current chain is trusted, and the old chain is trusted, but
      //   the old chain contained weak algorithms while the current chain only
      //   contains strong algorithms, then prefer the current chain over the
      //   old chain.
      //
      // Note: If the leaf certificate itself is weak, then the only
      // consideration is whether or not there is a trusted chain. That's
      // because no amount of path discovery will fix a weak leaf.
      if (!trust_ref || (!untrusted && (candidate_untrusted ||
                                        (candidate_weak && !weak_chain)))) {
        trust_ref = temp_ref;
        trust_result = temp_trust_result;
        completed_chain = temp_chain;
        chain_info = temp_chain_info;
  
        candidate_untrusted = untrusted;
        candidate_weak = weak_chain;
      }
      // Short-circuit when a current, trusted chain is found.
      if (!untrusted && !weak_chain)
        break;
      CFArrayRemoveValueAtIndex(cert_array, CFArrayGetCount(cert_array) - 1);
    }
  
    if (flags & CertVerifier::VERIFY_REV_CHECKING_ENABLED)
      verify_result->cert_status |= CERT_STATUS_REV_CHECKING_ENABLED;
  
    if (crl_set && !CheckRevocationWithCRLSet(completed_chain, crl_set))
      verify_result->cert_status |= CERT_STATUS_REVOKED;
  
    if (CFArrayGetCount(completed_chain) > 0) {
      bool leaf_is_weak_unused = false;
      GetCertChainInfo(completed_chain, chain_info, verify_result,
                       &leaf_is_weak_unused);
    }
  
    // As of Security Update 2012-002/OS X 10.7.4, when an RSA key < 1024 bits
    // is encountered, CSSM returns CSSMERR_TP_VERIFY_ACTION_FAILED and adds
    // CSSMERR_CSP_UNSUPPORTED_KEY_SIZE as a certificate status. Avoid mapping
    // the CSSMERR_TP_VERIFY_ACTION_FAILED to CERT_STATUS_INVALID if the only
    // error was due to an unsupported key size.
    bool policy_failed = false;
    bool weak_key_or_signature_algorithm = false;
  
    // Evaluate the results
    OSStatus cssm_result;
    switch (trust_result) {
      case kSecTrustResultUnspecified:
      case kSecTrustResultProceed:
        // Certificate chain is valid and trusted ("unspecified" indicates that
        // the user has not explicitly set a trust setting)
        break;
  
      // According to SecTrust.h, kSecTrustResultConfirm isn't returned on 10.5+,
      // and it is marked deprecated in the 10.9 SDK.
      case kSecTrustResultDeny:
        // Certificate chain is explicitly untrusted.
        verify_result->cert_status |= CERT_STATUS_AUTHORITY_INVALID;
        break;
  
      case kSecTrustResultRecoverableTrustFailure:
        // Certificate chain has a failure that can be overridden by the user.
        status = SecTrustGetCssmResultCode(trust_ref, &cssm_result);
        if (status)
          return NetErrorFromOSStatus(status);
        if (cssm_result == CSSMERR_TP_VERIFY_ACTION_FAILED) {
          policy_failed = true;
        } else {
          verify_result->cert_status |= CertStatusFromOSStatus(cssm_result);
        }
        // Walk the chain of error codes in the CSSM_TP_APPLE_EVIDENCE_INFO
        // structure which can catch multiple errors from each certificate.
        for (CFIndex index = 0, chain_count = CFArrayGetCount(completed_chain);
             index < chain_count; ++index) {
          if (chain_info[index].StatusBits & CSSM_CERT_STATUS_EXPIRED ||
              chain_info[index].StatusBits & CSSM_CERT_STATUS_NOT_VALID_YET)
            verify_result->cert_status |= CERT_STATUS_DATE_INVALID;
          if (!IsCertStatusError(verify_result->cert_status) &&
              chain_info[index].NumStatusCodes == 0) {
            LOG(WARNING) << "chain_info[" << index << "].NumStatusCodes is 0"
                            ", chain_info[" << index << "].StatusBits is "
                         << chain_info[index].StatusBits;
          }
          for (uint32 status_code_index = 0;
               status_code_index < chain_info[index].NumStatusCodes;
               ++status_code_index) {
            // As of OS X 10.9, attempting to verify a certificate chain that
            // contains a weak signature algorithm (MD2, MD5) in an intermediate
            // or leaf cert will be treated as a (recoverable) policy validation
            // failure, with the status code CSSMERR_TP_INVALID_CERTIFICATE
            // added to the Status Codes. Don't treat this code as an invalid
            // certificate; instead, map it to a weak key. Any truly invalid
            // certificates will have the major error (cssm_result) set to
            // CSSMERR_TP_INVALID_CERTIFICATE, rather than
            // CSSMERR_TP_VERIFY_ACTION_FAILED.
            CertStatus mapped_status = 0;
            if (policy_failed &&
                chain_info[index].StatusCodes[status_code_index] ==
                    CSSMERR_TP_INVALID_CERTIFICATE) {
                mapped_status = CERT_STATUS_WEAK_SIGNATURE_ALGORITHM;
                weak_key_or_signature_algorithm = true;
            } else {
                mapped_status = CertStatusFromOSStatus(
                    chain_info[index].StatusCodes[status_code_index]);
                if (mapped_status == CERT_STATUS_WEAK_KEY)
                  weak_key_or_signature_algorithm = true;
            }
            verify_result->cert_status |= mapped_status;
          }
        }
        if (policy_failed && !weak_key_or_signature_algorithm) {
          // If CSSMERR_TP_VERIFY_ACTION_FAILED wasn't returned due to a weak
          // key, map it back to an appropriate error code.
          verify_result->cert_status |= CertStatusFromOSStatus(cssm_result);
        }
        if (!IsCertStatusError(verify_result->cert_status)) {
          LOG(ERROR) << "cssm_result=" << cssm_result;
          verify_result->cert_status |= CERT_STATUS_INVALID;
          NOTREACHED();
        }
        break;
  
      default:
        status = SecTrustGetCssmResultCode(trust_ref, &cssm_result);
        if (status)
          return NetErrorFromOSStatus(status);
        verify_result->cert_status |= CertStatusFromOSStatus(cssm_result);
        if (!IsCertStatusError(verify_result->cert_status)) {
          LOG(WARNING) << "trust_result=" << trust_result;
          verify_result->cert_status |= CERT_STATUS_INVALID;
        }
        break;
    }
  
    // Perform hostname verification independent of SecTrustEvaluate. In order to
    // do so, mask off any reported name errors first.
    verify_result->cert_status &= ~CERT_STATUS_COMMON_NAME_INVALID;
    if (!cert->VerifyNameMatch(hostname,
                               &verify_result->common_name_fallback_used)) {
      verify_result->cert_status |= CERT_STATUS_COMMON_NAME_INVALID;
    }
  
    // TODO(wtc): Suppress CERT_STATUS_NO_REVOCATION_MECHANISM for now to be
    // compatible with Windows, which in turn implements this behavior to be
    // compatible with WinHTTP, which doesn't report this error (bug 3004).
    verify_result->cert_status &= ~CERT_STATUS_NO_REVOCATION_MECHANISM;
  
    AppendPublicKeyHashes(completed_chain, &verify_result->public_key_hashes);
    verify_result->is_issued_by_known_root = IsIssuedByKnownRoot(completed_chain);
  
    if (IsCertStatusError(verify_result->cert_status))
      return MapCertStatusToNetError(verify_result->cert_status);
  
    if (flags & CertVerifier::VERIFY_EV_CERT) {
      // Determine the certificate's EV status using SecTrustCopyExtendedResult(),
      // which is an internal/private API function added in OS X 10.5.7.
      // Note: "ExtendedResult" means extended validation results.
      CFBundleRef bundle =
          CFBundleGetBundleWithIdentifier(CFSTR("com.apple.security"));
      if (bundle) {
        SecTrustCopyExtendedResultFuncPtr copy_extended_result =
            reinterpret_cast<SecTrustCopyExtendedResultFuncPtr>(
                CFBundleGetFunctionPointerForName(bundle,
                    CFSTR("SecTrustCopyExtendedResult")));
        if (copy_extended_result) {
          CFDictionaryRef ev_dict_temp = NULL;
          status = copy_extended_result(trust_ref, &ev_dict_temp);
          ScopedCFTypeRef<CFDictionaryRef> ev_dict(ev_dict_temp);
          ev_dict_temp = NULL;
          if (status == noErr && ev_dict) {
            // In 10.7.3, SecTrustCopyExtendedResult returns noErr and populates
            // ev_dict even for non-EV certificates, but only EV certificates
            // will cause ev_dict to contain kSecEVOrganizationName. In previous
            // releases, SecTrustCopyExtendedResult would only return noErr and
            // populate ev_dict for EV certificates, but would always include
            // kSecEVOrganizationName in that case, so checking for this key is
            // appropriate for all known versions of SecTrustCopyExtendedResult.
            // The actual organization name is unneeded here and can be accessed
            // through other means. All that matters here is the OS' conception
            // of whether or not the certificate is EV.
            if (CFDictionaryContainsKey(ev_dict,
                                        kSecEVOrganizationName)) {
              verify_result->cert_status |= CERT_STATUS_IS_EV;
              if (flags & CertVerifier::VERIFY_REV_CHECKING_ENABLED_EV_ONLY)
                verify_result->cert_status |= CERT_STATUS_REV_CHECKING_ENABLED;
            }
          }
        }
      }
    }
  
    return OK;
  }
  
  }  // namespace net
  