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gecko-dev/security/pkix/lib/pkixcheck.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 code is made available to you under your choice of the following sets
* of licensing terms:
*/
/* 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/.
*/
/* Copyright 2013 Mozilla Contributors
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#include "pkixcheck.h"
#include "pkixder.h"
#include "pkixutil.h"
namespace mozilla { namespace pkix {
// 4.1.1.2 signatureAlgorithm
// 4.1.2.3 signature
Result
CheckSignatureAlgorithm(TrustDomain& trustDomain,
EndEntityOrCA endEntityOrCA,
Time notBefore,
const der::SignedDataWithSignature& signedData,
Input signatureValue)
{
// 4.1.1.2. signatureAlgorithm
der::PublicKeyAlgorithm publicKeyAlg;
DigestAlgorithm digestAlg;
Reader signatureAlgorithmReader(signedData.algorithm);
Result rv = der::SignatureAlgorithmIdentifierValue(signatureAlgorithmReader,
publicKeyAlg, digestAlg);
if (rv != Success) {
return rv;
}
rv = der::End(signatureAlgorithmReader);
if (rv != Success) {
return rv;
}
// 4.1.2.3. Signature
der::PublicKeyAlgorithm signedPublicKeyAlg;
DigestAlgorithm signedDigestAlg;
Reader signedSignatureAlgorithmReader(signatureValue);
rv = der::SignatureAlgorithmIdentifierValue(signedSignatureAlgorithmReader,
signedPublicKeyAlg,
signedDigestAlg);
if (rv != Success) {
return rv;
}
rv = der::End(signedSignatureAlgorithmReader);
if (rv != Success) {
return rv;
}
// "This field MUST contain the same algorithm identifier as the
// signatureAlgorithm field in the sequence Certificate." However, it may
// be encoded differently. In particular, one of the fields may have a NULL
// parameter while the other one may omit the parameter field altogether, and
// these are considered equivalent. Some certificates generation software
// actually generates certificates like that, so we compare the parsed values
// instead of comparing the encoded values byte-for-byte.
//
// Along the same lines, we accept two different OIDs for RSA-with-SHA1, and
// we consider those OIDs to be equivalent here.
if (publicKeyAlg != signedPublicKeyAlg || digestAlg != signedDigestAlg) {
return Result::ERROR_SIGNATURE_ALGORITHM_MISMATCH;
}
// During the time of the deprecation of SHA-1 and the deprecation of RSA
// keys of less than 2048 bits, we will encounter many certs signed using
// SHA-1 and/or too-small RSA keys. With this in mind, we ask the trust
// domain early on if it knows it will reject the signature purely based on
// the digest algorithm and/or the RSA key size (if an RSA signature). This
// is a good optimization because it completely avoids calling
// trustDomain.FindIssuers (which may be slow) for such rejected certs, and
// more generally it short-circuits any path building with them (which, of
// course, is even slower).
rv = trustDomain.CheckSignatureDigestAlgorithm(digestAlg, endEntityOrCA,
notBefore);
if (rv != Success) {
return rv;
}
switch (publicKeyAlg) {
case der::PublicKeyAlgorithm::RSA_PKCS1:
{
// The RSA computation may give a result that requires fewer bytes to
// encode than the public key (since it is modular arithmetic). However,
// the last step of generating a PKCS#1.5 signature is the I2OSP
// procedure, which pads any such shorter result with zeros so that it
// is exactly the same length as the public key.
unsigned int signatureSizeInBits = signedData.signature.GetLength() * 8u;
return trustDomain.CheckRSAPublicKeyModulusSizeInBits(
endEntityOrCA, signatureSizeInBits);
}
case der::PublicKeyAlgorithm::ECDSA:
// In theory, we could implement a similar early-pruning optimization for
// ECDSA curves. However, since there has been no similar deprecation for
// for any curve that we support, the chances of us encountering a curve
// during path building is too low to be worth bothering with.
break;
MOZILLA_PKIX_UNREACHABLE_DEFAULT_ENUM
}
return Success;
}
// 4.1.2.4 Issuer
Result
CheckIssuer(Input encodedIssuer)
{
// "The issuer field MUST contain a non-empty distinguished name (DN)."
Reader issuer(encodedIssuer);
Input encodedRDNs;
ExpectTagAndGetValue(issuer, der::SEQUENCE, encodedRDNs);
Reader rdns(encodedRDNs);
// Check that the issuer name contains at least one RDN
// (Note: this does not check related grammar rules, such as there being one
// or more AVAs in each RDN, or the values in AVAs not being empty strings)
if (rdns.AtEnd()) {
return Result::ERROR_EMPTY_ISSUER_NAME;
}
return Success;
}
// 4.1.2.5 Validity
Result
ParseValidity(Input encodedValidity,
/*optional out*/ Time* notBeforeOut,
/*optional out*/ Time* notAfterOut)
{
Reader validity(encodedValidity);
Time notBefore(Time::uninitialized);
if (der::TimeChoice(validity, notBefore) != Success) {
return Result::ERROR_INVALID_DER_TIME;
}
Time notAfter(Time::uninitialized);
if (der::TimeChoice(validity, notAfter) != Success) {
return Result::ERROR_INVALID_DER_TIME;
}
if (der::End(validity) != Success) {
return Result::ERROR_INVALID_DER_TIME;
}
if (notBefore > notAfter) {
return Result::ERROR_INVALID_DER_TIME;
}
if (notBeforeOut) {
*notBeforeOut = notBefore;
}
if (notAfterOut) {
*notAfterOut = notAfter;
}
return Success;
}
Result
CheckValidity(Time time, Time notBefore, Time notAfter)
{
if (time < notBefore) {
return Result::ERROR_NOT_YET_VALID_CERTIFICATE;
}
if (time > notAfter) {
return Result::ERROR_EXPIRED_CERTIFICATE;
}
return Success;
}
// 4.1.2.7 Subject Public Key Info
Result
CheckSubjectPublicKeyInfoContents(Reader& input, TrustDomain& trustDomain,
EndEntityOrCA endEntityOrCA)
{
// Here, we validate the syntax and do very basic semantic validation of the
// public key of the certificate. The intention here is to filter out the
// types of bad inputs that are most likely to trigger non-mathematical
// security vulnerabilities in the TrustDomain, like buffer overflows or the
// use of unsafe elliptic curves.
//
// We don't check (all of) the mathematical properties of the public key here
// because it is more efficient for the TrustDomain to do it during signature
// verification and/or other use of the public key. In particular, we
// delegate the arithmetic validation of the public key, as specified in
// NIST SP800-56A section 5.6.2, to the TrustDomain, at least for now.
Reader algorithm;
Input subjectPublicKey;
Result rv = der::ExpectTagAndGetValue(input, der::SEQUENCE, algorithm);
if (rv != Success) {
return rv;
}
rv = der::BitStringWithNoUnusedBits(input, subjectPublicKey);
if (rv != Success) {
return rv;
}
rv = der::End(input);
if (rv != Success) {
return rv;
}
Reader subjectPublicKeyReader(subjectPublicKey);
Reader algorithmOID;
rv = der::ExpectTagAndGetValue(algorithm, der::OIDTag, algorithmOID);
if (rv != Success) {
return rv;
}
// RFC 3279 Section 2.3.1
// python DottedOIDToCode.py rsaEncryption 1.2.840.113549.1.1.1
static const uint8_t rsaEncryption[] = {
0x2a, 0x86, 0x48, 0x86, 0xf7, 0x0d, 0x01, 0x01, 0x01
};
// RFC 3279 Section 2.3.5 and RFC 5480 Section 2.1.1
// python DottedOIDToCode.py id-ecPublicKey 1.2.840.10045.2.1
static const uint8_t id_ecPublicKey[] = {
0x2a, 0x86, 0x48, 0xce, 0x3d, 0x02, 0x01
};
if (algorithmOID.MatchRest(id_ecPublicKey)) {
// An id-ecPublicKey AlgorithmIdentifier has a parameter that identifes
// the curve being used. Although RFC 5480 specifies multiple forms, we
// only supported the NamedCurve form, where the curve is identified by an
// OID.
Reader namedCurveOIDValue;
rv = der::ExpectTagAndGetValue(algorithm, der::OIDTag,
namedCurveOIDValue);
if (rv != Success) {
return rv;
}
// RFC 5480
// python DottedOIDToCode.py secp256r1 1.2.840.10045.3.1.7
static const uint8_t secp256r1[] = {
0x2a, 0x86, 0x48, 0xce, 0x3d, 0x03, 0x01, 0x07
};
// RFC 5480
// python DottedOIDToCode.py secp384r1 1.3.132.0.34
static const uint8_t secp384r1[] = {
0x2b, 0x81, 0x04, 0x00, 0x22
};
// RFC 5480
// python DottedOIDToCode.py secp521r1 1.3.132.0.35
static const uint8_t secp521r1[] = {
0x2b, 0x81, 0x04, 0x00, 0x23
};
// Matching is attempted based on a rough estimate of the commonality of the
// elliptic curve, to minimize the number of MatchRest calls.
NamedCurve curve;
unsigned int bits;
if (namedCurveOIDValue.MatchRest(secp256r1)) {
curve = NamedCurve::secp256r1;
bits = 256;
} else if (namedCurveOIDValue.MatchRest(secp384r1)) {
curve = NamedCurve::secp384r1;
bits = 384;
} else if (namedCurveOIDValue.MatchRest(secp521r1)) {
curve = NamedCurve::secp521r1;
bits = 521;
} else {
return Result::ERROR_UNSUPPORTED_ELLIPTIC_CURVE;
}
rv = trustDomain.CheckECDSACurveIsAcceptable(endEntityOrCA, curve);
if (rv != Success) {
return rv;
}
// RFC 5480 Section 2.2 says that the first octet will be 0x04 to indicate
// an uncompressed point, which is the only encoding we support.
uint8_t compressedOrUncompressed;
rv = subjectPublicKeyReader.Read(compressedOrUncompressed);
if (rv != Success) {
return rv;
}
if (compressedOrUncompressed != 0x04) {
return Result::ERROR_UNSUPPORTED_EC_POINT_FORM;
}
// The point is encoded as two raw (not DER-encoded) integers, each padded
// to the bit length (rounded up to the nearest byte).
Input point;
rv = subjectPublicKeyReader.SkipToEnd(point);
if (rv != Success) {
return rv;
}
if (point.GetLength() != ((bits + 7) / 8u) * 2u) {
return Result::ERROR_BAD_DER;
}
// XXX: We defer the mathematical verification of the validity of the point
// until signature verification. This means that if we never verify a
// signature, we'll never fully check whether the public key is valid.
} else if (algorithmOID.MatchRest(rsaEncryption)) {
// RFC 3279 Section 2.3.1 says "The parameters field MUST have ASN.1 type
// NULL for this algorithm identifier."
rv = der::ExpectTagAndEmptyValue(algorithm, der::NULLTag);
if (rv != Success) {
return rv;
}
// RSAPublicKey :: = SEQUENCE{
// modulus INTEGER, --n
// publicExponent INTEGER } --e
rv = der::Nested(subjectPublicKeyReader, der::SEQUENCE,
[&trustDomain, endEntityOrCA](Reader& r) {
Input modulus;
Input::size_type modulusSignificantBytes;
Result rv = der::PositiveInteger(r, modulus, &modulusSignificantBytes);
if (rv != Success) {
return rv;
}
// XXX: Should we do additional checks of the modulus?
rv = trustDomain.CheckRSAPublicKeyModulusSizeInBits(
endEntityOrCA, modulusSignificantBytes * 8u);
if (rv != Success) {
return rv;
}
// XXX: We don't allow the TrustDomain to validate the exponent.
// XXX: We don't do our own sanity checking of the exponent.
Input exponent;
return der::PositiveInteger(r, exponent);
});
if (rv != Success) {
return rv;
}
} else {
return Result::ERROR_UNSUPPORTED_KEYALG;
}
rv = der::End(algorithm);
if (rv != Success) {
return rv;
}
rv = der::End(subjectPublicKeyReader);
if (rv != Success) {
return rv;
}
return Success;
}
Result
CheckSubjectPublicKeyInfo(Input subjectPublicKeyInfo, TrustDomain& trustDomain,
EndEntityOrCA endEntityOrCA)
{
Reader spkiReader(subjectPublicKeyInfo);
Result rv = der::Nested(spkiReader, der::SEQUENCE, [&](Reader& r) {
return CheckSubjectPublicKeyInfoContents(r, trustDomain, endEntityOrCA);
});
if (rv != Success) {
return rv;
}
return der::End(spkiReader);
}
// 4.2.1.3. Key Usage (id-ce-keyUsage)
// As explained in the comment in CheckKeyUsage, bit 0 is the most significant
// bit and bit 7 is the least significant bit.
inline uint8_t KeyUsageToBitMask(KeyUsage keyUsage)
{
assert(keyUsage != KeyUsage::noParticularKeyUsageRequired);
return 0x80u >> static_cast<uint8_t>(keyUsage);
}
Result
CheckKeyUsage(EndEntityOrCA endEntityOrCA, const Input* encodedKeyUsage,
KeyUsage requiredKeyUsageIfPresent)
{
if (!encodedKeyUsage) {
// TODO(bug 970196): Reject certificates that are being used to verify
// certificate signatures unless the certificate is a trust anchor, to
// reduce the chances of an end-entity certificate being abused as a CA
// certificate.
// if (endEntityOrCA == EndEntityOrCA::MustBeCA && !isTrustAnchor) {
// return Result::ERROR_INADEQUATE_KEY_USAGE;
// }
//
// TODO: Users may configure arbitrary certificates as trust anchors, not
// just roots. We should only allow a certificate without a key usage to be
// used as a CA when it is self-issued and self-signed.
return Success;
}
Reader input(*encodedKeyUsage);
Reader value;
if (der::ExpectTagAndGetValue(input, der::BIT_STRING, value) != Success) {
return Result::ERROR_INADEQUATE_KEY_USAGE;
}
uint8_t numberOfPaddingBits;
if (value.Read(numberOfPaddingBits) != Success) {
return Result::ERROR_INADEQUATE_KEY_USAGE;
}
if (numberOfPaddingBits > 7) {
return Result::ERROR_INADEQUATE_KEY_USAGE;
}
uint8_t bits;
if (value.Read(bits) != Success) {
// Reject empty bit masks.
return Result::ERROR_INADEQUATE_KEY_USAGE;
}
// The most significant bit is numbered 0 (digitalSignature) and the least
// significant bit is numbered 7 (encipherOnly), and the padding is in the
// least significant bits of the last byte. The numbering of bits in a byte
// is backwards from how we usually interpret them.
//
// For example, let's say bits is encoded in one byte with of value 0xB0 and
// numberOfPaddingBits == 4. Then, bits is 10110000 in binary:
//
// bit 0 bit 3
// | |
// v v
// 10110000
// ^^^^
// |
// 4 padding bits
//
// Since bits is the last byte, we have to consider the padding by ensuring
// that the least significant 4 bits are all zero, since DER rules require
// all padding bits to be zero. Then we have to look at the bit N bits to the
// right of the most significant bit, where N is a value from the KeyUsage
// enumeration.
//
// Let's say we're interested in the keyCertSign (5) bit. We'd need to look
// at bit 5, which is zero, so keyCertSign is not asserted. (Since we check
// that the padding is all zeros, it is OK to read from the padding bits.)
//
// Let's say we're interested in the digitalSignature (0) bit. We'd need to
// look at the bit 0 (the most significant bit), which is set, so that means
// digitalSignature is asserted. Similarly, keyEncipherment (2) and
// dataEncipherment (3) are asserted.
//
// Note that since the KeyUsage enumeration is limited to values 0-7, we
// only ever need to examine the first byte test for
// requiredKeyUsageIfPresent.
if (requiredKeyUsageIfPresent != KeyUsage::noParticularKeyUsageRequired) {
// Check that the required key usage bit is set.
if ((bits & KeyUsageToBitMask(requiredKeyUsageIfPresent)) == 0) {
return Result::ERROR_INADEQUATE_KEY_USAGE;
}
}
// RFC 5280 says "The keyCertSign bit is asserted when the subject public
// key is used for verifying signatures on public key certificates. If the
// keyCertSign bit is asserted, then the cA bit in the basic constraints
// extension (Section 4.2.1.9) MUST also be asserted."
// However, we allow end-entity certificates (i.e. certificates without
// basicConstraints.cA set to TRUE) to claim keyCertSign for compatibility
// reasons. This does not compromise security because we only allow
// certificates with basicConstraints.cA set to TRUE to act as CAs.
if (requiredKeyUsageIfPresent == KeyUsage::keyCertSign &&
endEntityOrCA != EndEntityOrCA::MustBeCA) {
return Result::ERROR_INADEQUATE_KEY_USAGE;
}
// The padding applies to the last byte, so skip to the last byte.
while (!value.AtEnd()) {
if (value.Read(bits) != Success) {
return Result::ERROR_INADEQUATE_KEY_USAGE;
}
}
// All of the padding bits must be zero, according to DER rules.
uint8_t paddingMask = static_cast<uint8_t>((1 << numberOfPaddingBits) - 1);
if ((bits & paddingMask) != 0) {
return Result::ERROR_INADEQUATE_KEY_USAGE;
}
return Success;
}
// RFC5820 4.2.1.4. Certificate Policies
// "The user-initial-policy-set contains the special value any-policy if the
// user is not concerned about certificate policy."
//
// python DottedOIDToCode.py anyPolicy 2.5.29.32.0
static const uint8_t anyPolicy[] = {
0x55, 0x1d, 0x20, 0x00
};
/*static*/ const CertPolicyId CertPolicyId::anyPolicy = {
4, { 0x55, 0x1d, 0x20, 0x00 }
};
bool
CertPolicyId::IsAnyPolicy() const {
if (this == &CertPolicyId::anyPolicy) {
return true;
}
return numBytes == sizeof(::mozilla::pkix::anyPolicy) &&
std::equal(bytes, bytes + numBytes, ::mozilla::pkix::anyPolicy);
}
bool
CertPolicyId::operator==(const CertPolicyId& other) const
{
return numBytes == other.numBytes &&
std::equal(bytes, bytes + numBytes, other.bytes);
}
// certificatePolicies ::= SEQUENCE SIZE (1..MAX) OF PolicyInformation
Result
CheckCertificatePolicies(EndEntityOrCA endEntityOrCA,
const Input* encodedCertificatePolicies,
const Input* encodedInhibitAnyPolicy,
TrustLevel trustLevel,
const CertPolicyId& requiredPolicy)
{
if (requiredPolicy.numBytes == 0 ||
requiredPolicy.numBytes > sizeof requiredPolicy.bytes) {
return Result::FATAL_ERROR_INVALID_ARGS;
}
bool requiredPolicyFound = requiredPolicy.IsAnyPolicy();
if (requiredPolicyFound) {
return Success;
}
// Bug 989051. Until we handle inhibitAnyPolicy we will fail close when
// inhibitAnyPolicy extension is present and we are validating for a policy.
if (!requiredPolicyFound && encodedInhibitAnyPolicy) {
return Result::ERROR_POLICY_VALIDATION_FAILED;
}
// The root CA certificate may omit the policies that it has been
// trusted for, so we cannot require the policies to be present in those
// certificates. Instead, the determination of which roots are trusted for
// which policies is made by the TrustDomain's GetCertTrust method.
if (trustLevel == TrustLevel::TrustAnchor &&
endEntityOrCA == EndEntityOrCA::MustBeCA) {
requiredPolicyFound = true;
}
Input requiredPolicyDER;
if (requiredPolicyDER.Init(requiredPolicy.bytes, requiredPolicy.numBytes)
!= Success) {
return Result::FATAL_ERROR_INVALID_ARGS;
}
if (encodedCertificatePolicies) {
Reader extension(*encodedCertificatePolicies);
Reader certificatePolicies;
Result rv = der::ExpectTagAndGetValue(extension, der::SEQUENCE,
certificatePolicies);
if (rv != Success) {
return Result::ERROR_POLICY_VALIDATION_FAILED;
}
if (!extension.AtEnd()) {
return Result::ERROR_POLICY_VALIDATION_FAILED;
}
do {
// PolicyInformation ::= SEQUENCE {
// policyIdentifier CertPolicyId,
// policyQualifiers SEQUENCE SIZE (1..MAX) OF
// PolicyQualifierInfo OPTIONAL }
Reader policyInformation;
rv = der::ExpectTagAndGetValue(certificatePolicies, der::SEQUENCE,
policyInformation);
if (rv != Success) {
return Result::ERROR_POLICY_VALIDATION_FAILED;
}
Reader policyIdentifier;
rv = der::ExpectTagAndGetValue(policyInformation, der::OIDTag,
policyIdentifier);
if (rv != Success) {
return rv;
}
if (policyIdentifier.MatchRest(requiredPolicyDER)) {
requiredPolicyFound = true;
} else if (endEntityOrCA == EndEntityOrCA::MustBeCA &&
policyIdentifier.MatchRest(anyPolicy)) {
requiredPolicyFound = true;
}
// RFC 5280 Section 4.2.1.4 says "Optional qualifiers, which MAY be
// present, are not expected to change the definition of the policy." Also,
// it seems that Section 6, which defines validation, does not require any
// matching of qualifiers. Thus, doing anything with the policy qualifiers
// would be a waste of time and a source of potential incompatibilities, so
// we just ignore them.
} while (!requiredPolicyFound && !certificatePolicies.AtEnd());
}
if (!requiredPolicyFound) {
return Result::ERROR_POLICY_VALIDATION_FAILED;
}
return Success;
}
static const long UNLIMITED_PATH_LEN = -1; // must be less than zero
// BasicConstraints ::= SEQUENCE {
// cA BOOLEAN DEFAULT FALSE,
// pathLenConstraint INTEGER (0..MAX) OPTIONAL }
// RFC5280 4.2.1.9. Basic Constraints (id-ce-basicConstraints)
Result
CheckBasicConstraints(EndEntityOrCA endEntityOrCA,
const Input* encodedBasicConstraints,
const der::Version version, TrustLevel trustLevel,
unsigned int subCACount)
{
bool isCA = false;
long pathLenConstraint = UNLIMITED_PATH_LEN;
if (encodedBasicConstraints) {
Reader input(*encodedBasicConstraints);
Result rv = der::Nested(input, der::SEQUENCE,
[&isCA, &pathLenConstraint](Reader& r) {
Result rv = der::OptionalBoolean(r, isCA);
if (rv != Success) {
return rv;
}
// TODO(bug 985025): If isCA is false, pathLenConstraint
// MUST NOT be included (as per RFC 5280 section
// 4.2.1.9), but for compatibility reasons, we don't
// check this.
return der::OptionalInteger(r, UNLIMITED_PATH_LEN, pathLenConstraint);
});
if (rv != Success) {
return Result::ERROR_EXTENSION_VALUE_INVALID;
}
if (der::End(input) != Success) {
return Result::ERROR_EXTENSION_VALUE_INVALID;
}
} else {
// "If the basic constraints extension is not present in a version 3
// certificate, or the extension is present but the cA boolean is not
// asserted, then the certified public key MUST NOT be used to verify
// certificate signatures."
//
// For compatibility, we must accept v1 trust anchors without basic
// constraints as CAs.
//
// There are devices with v1 certificates that are unlikely to be trust
// anchors. In order to allow applications to treat this case differently
// from other basic constraints violations (e.g. allowing certificate error
// overrides for only this case), we return a different error code.
//
// TODO: add check for self-signedness?
if (endEntityOrCA == EndEntityOrCA::MustBeCA && version == der::Version::v1) {
if (trustLevel == TrustLevel::TrustAnchor) {
isCA = true;
} else {
return Result::ERROR_V1_CERT_USED_AS_CA;
}
}
}
if (endEntityOrCA == EndEntityOrCA::MustBeEndEntity) {
// CA certificates are not trusted as EE certs.
if (isCA) {
// Note that this check prevents a delegated OCSP response signing
// certificate with the CA bit from successfully validating when we check
// it from pkixocsp.cpp, which is a good thing.
return Result::ERROR_CA_CERT_USED_AS_END_ENTITY;
}
return Success;
}
assert(endEntityOrCA == EndEntityOrCA::MustBeCA);
// End-entity certificates are not allowed to act as CA certs.
if (!isCA) {
return Result::ERROR_CA_CERT_INVALID;
}
if (pathLenConstraint >= 0 &&
static_cast<long>(subCACount) > pathLenConstraint) {
return Result::ERROR_PATH_LEN_CONSTRAINT_INVALID;
}
return Success;
}
// 4.2.1.12. Extended Key Usage (id-ce-extKeyUsage)
static Result
MatchEKU(Reader& value, KeyPurposeId requiredEKU,
EndEntityOrCA endEntityOrCA, TrustDomain& trustDomain,
Time notBefore, /*in/out*/ bool& found,
/*in/out*/ bool& foundOCSPSigning)
{
// See Section 5.9 of "A Layman's Guide to a Subset of ASN.1, BER, and DER"
// for a description of ASN.1 DER encoding of OIDs.
// id-pkix OBJECT IDENTIFIER ::=
// { iso(1) identified-organization(3) dod(6) internet(1)
// security(5) mechanisms(5) pkix(7) }
// id-kp OBJECT IDENTIFIER ::= { id-pkix 3 }
// id-kp-serverAuth OBJECT IDENTIFIER ::= { id-kp 1 }
// id-kp-clientAuth OBJECT IDENTIFIER ::= { id-kp 2 }
// id-kp-codeSigning OBJECT IDENTIFIER ::= { id-kp 3 }
// id-kp-emailProtection OBJECT IDENTIFIER ::= { id-kp 4 }
// id-kp-OCSPSigning OBJECT IDENTIFIER ::= { id-kp 9 }
static const uint8_t server[] = { (40*1)+3, 6, 1, 5, 5, 7, 3, 1 };
static const uint8_t client[] = { (40*1)+3, 6, 1, 5, 5, 7, 3, 2 };
static const uint8_t code [] = { (40*1)+3, 6, 1, 5, 5, 7, 3, 3 };
static const uint8_t email [] = { (40*1)+3, 6, 1, 5, 5, 7, 3, 4 };
static const uint8_t ocsp [] = { (40*1)+3, 6, 1, 5, 5, 7, 3, 9 };
// id-Netscape OBJECT IDENTIFIER ::= { 2 16 840 1 113730 }
// id-Netscape-policy OBJECT IDENTIFIER ::= { id-Netscape 4 }
// id-Netscape-stepUp OBJECT IDENTIFIER ::= { id-Netscape-policy 1 }
static const uint8_t serverStepUp[] =
{ (40*2)+16, 128+6,72, 1, 128+6,128+120,66, 4, 1 };
bool match = false;
if (!found) {
switch (requiredEKU) {
case KeyPurposeId::id_kp_serverAuth: {
if (value.MatchRest(server)) {
match = true;
break;
}
// Potentially treat CA certs with step-up OID as also having SSL server
// type. Comodo has issued certificates that require this behavior that
// don't expire until June 2020!
if (endEntityOrCA == EndEntityOrCA::MustBeCA &&
value.MatchRest(serverStepUp)) {
Result rv = trustDomain.NetscapeStepUpMatchesServerAuth(notBefore,
match);
if (rv != Success) {
return rv;
}
}
break;
}
case KeyPurposeId::id_kp_clientAuth:
match = value.MatchRest(client);
break;
case KeyPurposeId::id_kp_codeSigning:
match = value.MatchRest(code);
break;
case KeyPurposeId::id_kp_emailProtection:
match = value.MatchRest(email);
break;
case KeyPurposeId::id_kp_OCSPSigning:
match = value.MatchRest(ocsp);
break;
case KeyPurposeId::anyExtendedKeyUsage:
return NotReached("anyExtendedKeyUsage should start with found==true",
Result::FATAL_ERROR_LIBRARY_FAILURE);
}
}
if (match) {
found = true;
if (requiredEKU == KeyPurposeId::id_kp_OCSPSigning) {
foundOCSPSigning = true;
}
} else if (value.MatchRest(ocsp)) {
foundOCSPSigning = true;
}
value.SkipToEnd(); // ignore unmatched OIDs.
return Success;
}
Result
CheckExtendedKeyUsage(EndEntityOrCA endEntityOrCA,
const Input* encodedExtendedKeyUsage,
KeyPurposeId requiredEKU, TrustDomain& trustDomain,
Time notBefore)
{
// XXX: We're using Result::ERROR_INADEQUATE_CERT_TYPE here so that callers
// can distinguish EKU mismatch from KU mismatch from basic constraints
// mismatch. We should probably add a new error code that is more clear for
// this type of problem.
bool foundOCSPSigning = false;
if (encodedExtendedKeyUsage) {
bool found = requiredEKU == KeyPurposeId::anyExtendedKeyUsage;
Reader input(*encodedExtendedKeyUsage);
Result rv = der::NestedOf(input, der::SEQUENCE, der::OIDTag,
der::EmptyAllowed::No, [&](Reader& r) {
return MatchEKU(r, requiredEKU, endEntityOrCA, trustDomain, notBefore,
found, foundOCSPSigning);
});
if (rv != Success) {
return Result::ERROR_INADEQUATE_CERT_TYPE;
}
if (der::End(input) != Success) {
return Result::ERROR_INADEQUATE_CERT_TYPE;
}
// If the EKU extension was included, then the required EKU must be in the
// list.
if (!found) {
return Result::ERROR_INADEQUATE_CERT_TYPE;
}
}
// pkixocsp.cpp depends on the following additional checks.
if (endEntityOrCA == EndEntityOrCA::MustBeEndEntity) {
// When validating anything other than an delegated OCSP signing cert,
// reject any cert that also claims to be an OCSP responder, because such
// a cert does not make sense. For example, if an SSL certificate were to
// assert id-kp-OCSPSigning then it could sign OCSP responses for itself,
// if not for this check.
// That said, we accept CA certificates with id-kp-OCSPSigning because
// some CAs in Mozilla's CA program have issued such intermediate
// certificates, and because some CAs have reported some Microsoft server
// software wrongly requires CA certificates to have id-kp-OCSPSigning.
// Allowing this exception does not cause any security issues because we
// require delegated OCSP response signing certificates to be end-entity
// certificates.
if (foundOCSPSigning && requiredEKU != KeyPurposeId::id_kp_OCSPSigning) {
return Result::ERROR_INADEQUATE_CERT_TYPE;
}
// http://tools.ietf.org/html/rfc6960#section-4.2.2.2:
// "OCSP signing delegation SHALL be designated by the inclusion of
// id-kp-OCSPSigning in an extended key usage certificate extension
// included in the OCSP response signer's certificate."
//
// id-kp-OCSPSigning is the only EKU that isn't implicitly assumed when the
// EKU extension is missing from an end-entity certificate. However, any CA
// certificate can issue a delegated OCSP response signing certificate, so
// we can't require the EKU be explicitly included for CA certificates.
if (!foundOCSPSigning && requiredEKU == KeyPurposeId::id_kp_OCSPSigning) {
return Result::ERROR_INADEQUATE_CERT_TYPE;
}
}
return Success;
}
Result
CheckTLSFeatures(const BackCert& subject, BackCert& potentialIssuer)
{
const Input* issuerTLSFeatures = potentialIssuer.GetRequiredTLSFeatures();
if (!issuerTLSFeatures) {
return Success;
}
const Input* subjectTLSFeatures = subject.GetRequiredTLSFeatures();
if (issuerTLSFeatures->GetLength() == 0 ||
!subjectTLSFeatures ||
!InputsAreEqual(*issuerTLSFeatures, *subjectTLSFeatures)) {
return Result::ERROR_REQUIRED_TLS_FEATURE_MISSING;
}
return Success;
}
Result
TLSFeaturesSatisfiedInternal(const Input* requiredTLSFeatures,
const Input* stapledOCSPResponse)
{
if (!requiredTLSFeatures) {
return Success;
}
// RFC 6066 10.2: ExtensionType status_request
const static uint8_t status_request = 5;
const static uint8_t status_request_bytes[] = { status_request };
Reader input(*requiredTLSFeatures);
return der::NestedOf(input, der::SEQUENCE, der::INTEGER,
der::EmptyAllowed::No, [&](Reader& r) {
if (!r.MatchRest(status_request_bytes)) {
return Result::ERROR_REQUIRED_TLS_FEATURE_MISSING;
}
if (!stapledOCSPResponse) {
return Result::ERROR_REQUIRED_TLS_FEATURE_MISSING;
}
return Result::Success;
});
}
Result
CheckTLSFeaturesAreSatisfied(Input& cert,
const Input* stapledOCSPResponse)
{
BackCert backCert(cert, EndEntityOrCA::MustBeEndEntity, nullptr);
Result rv = backCert.Init();
if (rv != Success) {
return rv;
}
return TLSFeaturesSatisfiedInternal(backCert.GetRequiredTLSFeatures(),
stapledOCSPResponse);
}
Result
CheckIssuerIndependentProperties(TrustDomain& trustDomain,
const BackCert& cert,
Time time,
KeyUsage requiredKeyUsageIfPresent,
KeyPurposeId requiredEKUIfPresent,
const CertPolicyId& requiredPolicy,
unsigned int subCACount,
/*out*/ TrustLevel& trustLevel)
{
Result rv;
const EndEntityOrCA endEntityOrCA = cert.endEntityOrCA;
// Check the cert's trust first, because we want to minimize the amount of
// processing we do on a distrusted cert, in case it is trying to exploit
// some bug in our processing.
rv = trustDomain.GetCertTrust(endEntityOrCA, requiredPolicy, cert.GetDER(),
trustLevel);
if (rv != Success) {
return rv;
}
// IMPORTANT: We parse the validity interval here, so that we can use the
// notBefore and notAfter values in checks for things that might be deprecated
// over time. However, we must not fail for semantic errors until the end of
// this method, in order to preserve error ranking.
Time notBefore(Time::uninitialized);
Time notAfter(Time::uninitialized);
rv = ParseValidity(cert.GetValidity(), &notBefore, &notAfter);
if (rv != Success) {
return rv;
}
if (trustLevel == TrustLevel::TrustAnchor &&
endEntityOrCA == EndEntityOrCA::MustBeEndEntity &&
requiredEKUIfPresent == KeyPurposeId::id_kp_OCSPSigning) {
// OCSP signer certificates can never be trust anchors, especially
// since we don't support designated OCSP responders. All of the checks
// below that are dependent on trustLevel rely on this overriding of the
// trust level for OCSP signers.
trustLevel = TrustLevel::InheritsTrust;
}
switch (trustLevel) {
case TrustLevel::InheritsTrust:
rv = CheckSignatureAlgorithm(trustDomain, endEntityOrCA, notBefore,
cert.GetSignedData(), cert.GetSignature());
if (rv != Success) {
return rv;
}
break;
case TrustLevel::TrustAnchor:
// We don't even bother checking signatureAlgorithm or signature for
// syntactic validity for trust anchors, because we don't use those
// fields for anything, and because the trust anchor might be signed
// with a signature algorithm we don't actually support.
break;
case TrustLevel::ActivelyDistrusted:
return Result::ERROR_UNTRUSTED_CERT;
}
// Check the SPKI early, because it is one of the most selective properties
// of the certificate due to SHA-1 deprecation and the deprecation of
// certificates with keys weaker than RSA 2048.
rv = CheckSubjectPublicKeyInfo(cert.GetSubjectPublicKeyInfo(), trustDomain,
endEntityOrCA);
if (rv != Success) {
return rv;
}
// 4.1.2.4. Issuer
rv = CheckIssuer(cert.GetIssuer());
if (rv != Success) {
return rv;
}
// 4.2.1.1. Authority Key Identifier is ignored (see bug 965136).
// 4.2.1.2. Subject Key Identifier is ignored (see bug 965136).
// 4.2.1.3. Key Usage
rv = CheckKeyUsage(endEntityOrCA, cert.GetKeyUsage(),
requiredKeyUsageIfPresent);
if (rv != Success) {
return rv;
}
// 4.2.1.4. Certificate Policies
rv = CheckCertificatePolicies(endEntityOrCA, cert.GetCertificatePolicies(),
cert.GetInhibitAnyPolicy(), trustLevel,
requiredPolicy);
if (rv != Success) {
return rv;
}
// 4.2.1.5. Policy Mappings are not supported; see the documentation about
// policy enforcement in pkix.h.
// 4.2.1.6. Subject Alternative Name dealt with during name constraint
// checking and during name verification (CERT_VerifyCertName).
// 4.2.1.7. Issuer Alternative Name is not something that needs checking.
// 4.2.1.8. Subject Directory Attributes is not something that needs
// checking.
// 4.2.1.9. Basic Constraints.
rv = CheckBasicConstraints(endEntityOrCA, cert.GetBasicConstraints(),
cert.GetVersion(), trustLevel, subCACount);
if (rv != Success) {
return rv;
}
// 4.2.1.10. Name Constraints is dealt with in during path building.
// 4.2.1.11. Policy Constraints are implicitly supported; see the
// documentation about policy enforcement in pkix.h.
// 4.2.1.12. Extended Key Usage
rv = CheckExtendedKeyUsage(endEntityOrCA, cert.GetExtKeyUsage(),
requiredEKUIfPresent, trustDomain, notBefore);
if (rv != Success) {
return rv;
}
// 4.2.1.13. CRL Distribution Points is not supported, though the
// TrustDomain's CheckRevocation method may parse it and process it
// on its own.
// 4.2.1.14. Inhibit anyPolicy is implicitly supported; see the documentation
// about policy enforcement in pkix.h.
// IMPORTANT: Even though we parse validity above, we wait until this point to
// check it, so that error ranking works correctly.
rv = CheckValidity(time, notBefore, notAfter);
if (rv != Success) {
return rv;
}
rv = trustDomain.CheckValidityIsAcceptable(notBefore, notAfter, endEntityOrCA,
requiredEKUIfPresent);
if (rv != Success) {
return rv;
}
return Success;
}
} } // namespace mozilla::pkix
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