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// Copyright 2019 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 "cast/common/certificate/cast_cert_validator.h"
#include <openssl/digest.h>
#include <openssl/x509.h>
#include <openssl/x509v3.h>
#include <stddef.h>
#include <stdint.h>
#include <string.h>
#include <algorithm>
#include <memory>
#include <utility>
#include "cast/common/certificate/cast_cert_validator_internal.h"
#include "cast/common/certificate/cast_crl.h"
#include "cast/common/certificate/cast_trust_store.h"
#include "util/osp_logging.h"
namespace openscreen {
namespace cast {
namespace {
// Returns the OID for the Audio-Only Cast policy
// (1.3.6.1.4.1.11129.2.5.2) in DER form.
const ConstDataSpan& AudioOnlyPolicyOid() {
static const uint8_t kAudioOnlyPolicy[] = {0x2B, 0x06, 0x01, 0x04, 0x01,
0xD6, 0x79, 0x02, 0x05, 0x02};
static ConstDataSpan kPolicySpan{kAudioOnlyPolicy, sizeof(kAudioOnlyPolicy)};
return kPolicySpan;
}
class CertVerificationContextImpl final : public CertVerificationContext {
public:
CertVerificationContextImpl(bssl::UniquePtr<EVP_PKEY> cert,
std::string common_name)
: public_key_{std::move(cert)}, common_name_(std::move(common_name)) {}
~CertVerificationContextImpl() override = default;
bool VerifySignatureOverData(
const ConstDataSpan& signature,
const ConstDataSpan& data,
DigestAlgorithm digest_algorithm) const override {
const EVP_MD* digest;
switch (digest_algorithm) {
case DigestAlgorithm::kSha1:
digest = EVP_sha1();
break;
case DigestAlgorithm::kSha256:
digest = EVP_sha256();
break;
case DigestAlgorithm::kSha384:
digest = EVP_sha384();
break;
case DigestAlgorithm::kSha512:
digest = EVP_sha512();
break;
default:
return false;
}
return VerifySignedData(digest, public_key_.get(), data, signature);
}
const std::string& GetCommonName() const override { return common_name_; }
private:
const bssl::UniquePtr<EVP_PKEY> public_key_;
const std::string common_name_;
};
CastDeviceCertPolicy GetAudioPolicy(const std::vector<X509*>& path) {
// Cast device certificates use the policy 1.3.6.1.4.1.11129.2.5.2 to indicate
// it is *restricted* to an audio-only device whereas the absence of a policy
// means it is unrestricted.
//
// This is somewhat different than RFC 5280's notion of policies, so policies
// are checked separately outside of path building.
//
// See the unit-tests VerifyCastDeviceCertTest.Policies* for some
// concrete examples of how this works.
//
// Iterate over all the certificates, including the root certificate. If any
// certificate contains the audio-only policy, the whole chain is considered
// constrained to audio-only device certificates.
//
// Policy mappings are not accounted for. The expectation is that top-level
// intermediates issued with audio-only will have no mappings. If subsequent
// certificates in the chain do, it won't matter as the chain is already
// restricted to being audio-only.
CastDeviceCertPolicy policy = CastDeviceCertPolicy::kUnrestricted;
const ConstDataSpan& audio_only_policy_oid = AudioOnlyPolicyOid();
for (uint32_t i = 0;
i < path.size() && policy != CastDeviceCertPolicy::kAudioOnly; ++i) {
X509* cert = path[path.size() - 1 - i];
// Gets an index into the extension list that points to the
// certificatePolicies extension, if it exists, -1 otherwise.
int pos = X509_get_ext_by_NID(cert, NID_certificate_policies, -1);
if (pos != -1) {
X509_EXTENSION* policies_extension = X509_get_ext(cert, pos);
const uint8_t* in = policies_extension->value->data;
CERTIFICATEPOLICIES* policies = d2i_CERTIFICATEPOLICIES(
nullptr, &in, policies_extension->value->length);
if (policies) {
// Check for |audio_only_policy_oid| in the set of policies.
uint32_t policy_count = sk_POLICYINFO_num(policies);
for (uint32_t i = 0; i < policy_count; ++i) {
POLICYINFO* info = sk_POLICYINFO_value(policies, i);
if (info->policyid->length ==
static_cast<int>(audio_only_policy_oid.length) &&
memcmp(info->policyid->data, audio_only_policy_oid.data,
audio_only_policy_oid.length) == 0) {
policy = CastDeviceCertPolicy::kAudioOnly;
break;
}
}
CERTIFICATEPOLICIES_free(policies);
}
}
}
return policy;
}
} // namespace
Error VerifyDeviceCert(const std::vector<std::string>& der_certs,
const DateTime& time,
std::unique_ptr<CertVerificationContext>* context,
CastDeviceCertPolicy* policy,
const CastCRL* crl,
CRLPolicy crl_policy,
TrustStore* trust_store) {
if (!trust_store) {
trust_store = CastTrustStore::GetInstance()->trust_store();
}
// Fail early if CRL is required but not provided.
if (!crl && crl_policy == CRLPolicy::kCrlRequired) {
return Error::Code::kErrCrlInvalid;
}
CertificatePathResult result_path = {};
Error error = FindCertificatePath(der_certs, time, &result_path, trust_store);
if (!error.ok()) {
return error;
}
if (crl_policy == CRLPolicy::kCrlRequired &&
!crl->CheckRevocation(result_path.path, time)) {
return Error::Code::kErrCertsRevoked;
}
*policy = GetAudioPolicy(result_path.path);
// Finally, make sure there is a common name to give to
// CertVerificationContextImpl.
X509_NAME* target_subject =
X509_get_subject_name(result_path.target_cert.get());
std::string common_name(target_subject->canon_enclen, 0);
int len = X509_NAME_get_text_by_NID(target_subject, NID_commonName,
&common_name[0], common_name.size());
if (len == 0) {
return Error::Code::kErrCertsRestrictions;
}
common_name.resize(len);
context->reset(new CertVerificationContextImpl(
bssl::UniquePtr<EVP_PKEY>{X509_get_pubkey(result_path.target_cert.get())},
std::move(common_name)));
return Error::Code::kNone;
}
} // namespace cast
} // namespace openscreen
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