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diff --git a/security/ct/CTPolicyEnforcer.cpp b/security/ct/CTPolicyEnforcer.cpp
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+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "CTPolicyEnforcer.h"
+
+#include <algorithm>
+#include <stdint.h>
+#include <vector>
+
+namespace mozilla {
+namespace ct {
+
+using namespace mozilla::pkix;
+
+// Returns the number of embedded SCTs required to be present on a
+// certificate for Qualification Case #2 (embedded SCTs).
+static size_t GetRequiredEmbeddedSctsCount(
+    size_t certLifetimeInFullCalendarMonths) {
+  // "there are Embedded SCTs from AT LEAST N+1 once or currently qualified
+  // logs, where N is the lifetime of the certificate in years (normally
+  // rounding up, but rounding down when up to 3 months over), and must be
+  // at least 1"
+  return 1 + (certLifetimeInFullCalendarMonths + 9) / 12;
+}
+
+// Whether a valid embedded SCT is present in the list.
+static bool HasValidEmbeddedSct(const VerifiedSCTList& verifiedScts) {
+  for (const VerifiedSCT& verifiedSct : verifiedScts) {
+    if (verifiedSct.status == VerifiedSCT::Status::Valid &&
+        verifiedSct.origin == VerifiedSCT::Origin::Embedded) {
+      return true;
+    }
+  }
+  return false;
+}
+
+// Whether a valid non-embedded SCT is present in the list.
+static bool HasValidNonEmbeddedSct(const VerifiedSCTList& verifiedScts) {
+  for (const VerifiedSCT& verifiedSct : verifiedScts) {
+    if (verifiedSct.status == VerifiedSCT::Status::Valid &&
+        (verifiedSct.origin == VerifiedSCT::Origin::TLSExtension ||
+         verifiedSct.origin == VerifiedSCT::Origin::OCSPResponse)) {
+      return true;
+    }
+  }
+  return false;
+}
+
+// Given a list of verified SCTs, counts the number of distinct CA-independent
+// log operators running the CT logs that issued the SCTs which satisfy
+// the provided boolean predicate.
+template <typename SelectFunc>
+void CountIndependentLogOperatorsForSelectedScts(
+    const VerifiedSCTList& verifiedScts,
+    const CTLogOperatorList& dependentOperators, size_t& count,
+    SelectFunc selected) {
+  CTLogOperatorList operatorIds;
+  for (const VerifiedSCT& verifiedSct : verifiedScts) {
+    CTLogOperatorId sctLogOperatorId = verifiedSct.logOperatorId;
+    // Check if |sctLogOperatorId| is CA-dependent.
+    bool isDependentOperator = false;
+    for (CTLogOperatorId dependentOperator : dependentOperators) {
+      if (sctLogOperatorId == dependentOperator) {
+        isDependentOperator = true;
+        break;
+      }
+    }
+    if (isDependentOperator || !selected(verifiedSct)) {
+      continue;
+    }
+    // Check if |sctLogOperatorId| is in |operatorIds|...
+    bool alreadyAdded = false;
+    for (CTLogOperatorId id : operatorIds) {
+      if (id == sctLogOperatorId) {
+        alreadyAdded = true;
+        break;
+      }
+    }
+    // ...and if not, add it.
+    if (!alreadyAdded) {
+      operatorIds.push_back(sctLogOperatorId);
+    }
+  }
+  count = operatorIds.size();
+}
+
+// Given a list of verified SCTs, counts the number of distinct CT logs
+// that issued the SCTs that satisfy the |selected| predicate.
+template <typename SelectFunc>
+static void CountLogsForSelectedScts(const VerifiedSCTList& verifiedScts,
+                                     size_t& count, SelectFunc selected) {
+  // Keep pointers to log ids (of type Buffer) from |verifiedScts| to save on
+  // memory allocations.
+  std::vector<const Buffer*> logIds;
+  for (const VerifiedSCT& verifiedSct : verifiedScts) {
+    if (!selected(verifiedSct)) {
+      continue;
+    }
+
+    const Buffer* sctLogId = &verifiedSct.sct.logId;
+    // Check if |sctLogId| points to data already in |logIds|...
+    bool alreadyAdded = false;
+    for (const Buffer* logId : logIds) {
+      if (*logId == *sctLogId) {
+        alreadyAdded = true;
+        break;
+      }
+    }
+    // ...and if not, add it.
+    if (!alreadyAdded) {
+      logIds.push_back(sctLogId);
+    }
+  }
+  count = logIds.size();
+}
+
+// Calculates the effective issuance time of connection's certificate using
+// the SCTs present on the connection (we can't rely on notBefore validity
+// field of the certificate since it can be backdated).
+// Used to determine whether to accept SCTs issued by past qualified logs.
+// The effective issuance time 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.
+// It is acceptable to ignore the origin of the SCTs 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.
+static uint64_t GetEffectiveCertIssuanceTime(
+    const VerifiedSCTList& verifiedScts) {
+  uint64_t result = UINT64_MAX;
+  for (const VerifiedSCT& verifiedSct : verifiedScts) {
+    if (verifiedSct.status == VerifiedSCT::Status::Valid) {
+      result = std::min(result, verifiedSct.sct.timestamp);
+    }
+  }
+  return result;
+}
+
+// Checks if the log that issued the given SCT is "once or currently qualified"
+// (i.e. was qualified at the time of the certificate issuance). In addition,
+// makes sure the SCT is before the disqualification.
+static bool LogWasQualifiedForSct(const VerifiedSCT& verifiedSct,
+                                  uint64_t certIssuanceTime) {
+  if (verifiedSct.status == VerifiedSCT::Status::Valid) {
+    return true;
+  }
+  if (verifiedSct.status == VerifiedSCT::Status::ValidFromDisqualifiedLog) {
+    uint64_t logDisqualificationTime = verifiedSct.logDisqualificationTime;
+    return certIssuanceTime < logDisqualificationTime &&
+           verifiedSct.sct.timestamp < logDisqualificationTime;
+  }
+  return false;
+}
+
+// "A certificate is CT Qualified if it is presented with at least two SCTs
+// from once or currently qualified logs run by a minimum of two entities
+// independent of the CA and of each other."
+// By the preexisting certificate exception provision (not currently
+// implemented), certificates "are CT Qualified if they are presented with SCTs
+// from once or currently qualified logs run by a minimum of one entity
+// independent of the CA."
+static void CheckOperatorDiversityCompliance(
+    const VerifiedSCTList& verifiedScts, uint64_t certIssuanceTime,
+    const CTLogOperatorList& dependentOperators, bool& compliant) {
+  size_t independentOperatorsCount;
+  CountIndependentLogOperatorsForSelectedScts(
+      verifiedScts, dependentOperators, independentOperatorsCount,
+      [certIssuanceTime](const VerifiedSCT& verifiedSct) -> bool {
+        return LogWasQualifiedForSct(verifiedSct, certIssuanceTime);
+      });
+  // Having at least 2 operators implies we have at least 2 SCTs.
+  // For the preexisting certificate exception provision (1 operator) we will
+  // need to include an additional SCTs count check using
+  // CountLogsForSelectedScts(verifiedScts, sctsCount,
+  //   [certIssuanceTime](const VerifiedSCT& verifiedSct)->bool {
+  //     return LogWasQualifiedForSct(verifiedSct, certIssuanceTime);
+  // });
+  compliant = independentOperatorsCount >= 2;
+}
+
+// Qualification Case #1 (non-embedded SCTs) - the following must hold:
+// a. An SCT from a log qualified at the time of check is presented via the
+// TLS extension OR is embedded within a stapled OCSP response;
+// AND
+// b. There are at least two SCTs from logs qualified at the time of check,
+// presented via any method.
+static void CheckNonEmbeddedCompliance(const VerifiedSCTList& verifiedScts,
+                                       bool& compliant) {
+  if (!HasValidNonEmbeddedSct(verifiedScts)) {
+    compliant = false;
+    return;
+  }
+
+  size_t validSctsCount;
+  CountLogsForSelectedScts(
+      verifiedScts, validSctsCount, [](const VerifiedSCT& verifiedSct) -> bool {
+        return verifiedSct.status == VerifiedSCT::Status::Valid;
+      });
+
+  compliant = validSctsCount >= 2;
+}
+
+// Qualification Case #2 (embedded SCTs) - the following must hold:
+// a. An Embedded SCT from a log qualified at the time of check is presented;
+// AND
+// b. There are Embedded SCTs from AT LEAST N + 1 once or currently qualified
+// logs, where N is the lifetime of the certificate in years (normally
+// rounding up, but rounding down when up to 3 months over), and must be
+// at least 1.
+static void CheckEmbeddedCompliance(const VerifiedSCTList& verifiedScts,
+                                    size_t certLifetimeInCalendarMonths,
+                                    uint64_t certIssuanceTime,
+                                    bool& compliant) {
+  if (!HasValidEmbeddedSct(verifiedScts)) {
+    compliant = false;
+    return;
+  }
+
+  // Count the compliant embedded SCTs. Only a single SCT from each log
+  // is accepted. Note that a given log might return several different SCTs
+  // for the same precertificate (it is permitted, but advised against).
+  size_t embeddedSctsCount;
+  CountLogsForSelectedScts(
+      verifiedScts, embeddedSctsCount,
+      [certIssuanceTime](const VerifiedSCT& verifiedSct) -> bool {
+        return verifiedSct.origin == VerifiedSCT::Origin::Embedded &&
+               LogWasQualifiedForSct(verifiedSct, certIssuanceTime);
+      });
+
+  size_t requiredSctsCount =
+      GetRequiredEmbeddedSctsCount(certLifetimeInCalendarMonths);
+
+  compliant = embeddedSctsCount >= requiredSctsCount;
+}
+
+void CTPolicyEnforcer::CheckCompliance(
+    const VerifiedSCTList& verifiedScts, size_t certLifetimeInCalendarMonths,
+    const CTLogOperatorList& dependentOperators,
+    CTPolicyCompliance& compliance) {
+  uint64_t certIssuanceTime = GetEffectiveCertIssuanceTime(verifiedScts);
+
+  bool diversityOK;
+  CheckOperatorDiversityCompliance(verifiedScts, certIssuanceTime,
+                                   dependentOperators, diversityOK);
+
+  bool nonEmbeddedCaseOK;
+  CheckNonEmbeddedCompliance(verifiedScts, nonEmbeddedCaseOK);
+
+  bool embeddedCaseOK;
+  CheckEmbeddedCompliance(verifiedScts, certLifetimeInCalendarMonths,
+                          certIssuanceTime, embeddedCaseOK);
+
+  if (nonEmbeddedCaseOK || embeddedCaseOK) {
+    compliance = diversityOK ? CTPolicyCompliance::Compliant
+                             : CTPolicyCompliance::NotDiverseScts;
+  } else {
+    // Not enough SCTs are present to satisfy either case of the policy.
+    compliance = CTPolicyCompliance::NotEnoughScts;
+  }
+
+  switch (compliance) {
+    case CTPolicyCompliance::Compliant:
+    case CTPolicyCompliance::NotEnoughScts:
+    case CTPolicyCompliance::NotDiverseScts:
+      break;
+    case CTPolicyCompliance::Unknown:
+    default:
+      assert(false);
+  }
+}
+
+}  // namespace ct
+}  // namespace mozilla