ondevice-signing/CertUtils.cpp - android_system_security - Gitiles

 /*
  * Copyright (C) 2020 The Android Open Source Project
  *
  * 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 "CertUtils.h"

 #include <android-base/logging.h>
 #include <android-base/result.h>

 #include <openssl/bn.h>
 #include <openssl/crypto.h>
 #include <openssl/pkcs7.h>
 #include <openssl/rsa.h>
 #include <openssl/x509.h>
 #include <openssl/x509v3.h>

 #include <fcntl.h>
 #include <vector>

 #include "KeyConstants.h"

 const char kBasicConstraints[] = "CA:TRUE";
 const char kKeyUsage[] = "critical,keyCertSign,cRLSign,digitalSignature";
 const char kSubjectKeyIdentifier[] = "hash";
 const char kAuthorityKeyIdentifier[] = "keyid:always";
 constexpr int kCertLifetimeSeconds = 10 * 365 * 24 * 60 * 60;

 using android::base::Result;
 // using android::base::ErrnoError;
 using android::base::Error;

 static bool add_ext(X509* cert, int nid, const char* value) {
     size_t len = strlen(value) + 1;
     std::vector<char> mutableValue(value, value + len);
     X509V3_CTX context;

     X509V3_set_ctx_nodb(&context);

     X509V3_set_ctx(&context, cert, cert, nullptr, nullptr, 0);
     X509_EXTENSION* ex = X509V3_EXT_nconf_nid(nullptr, &context, nid, mutableValue.data());
     if (!ex) {
         return false;
     }

     X509_add_ext(cert, ex, -1);
     X509_EXTENSION_free(ex);
     return true;
 }

 Result<bssl::UniquePtr<RSA>> getRsa(const std::vector<uint8_t>& publicKey) {
     bssl::UniquePtr<BIGNUM> n(BN_new());
     bssl::UniquePtr<BIGNUM> e(BN_new());
     bssl::UniquePtr<RSA> rsaPubkey(RSA_new());
     if (!n || !e || !rsaPubkey || !BN_bin2bn(publicKey.data(), publicKey.size(), n.get()) ||
         !BN_set_word(e.get(), kRsaKeyExponent) ||
         !RSA_set0_key(rsaPubkey.get(), n.get(), e.get(), /*d=*/nullptr)) {
         return Error() << "Failed to create RSA key";
     }
     // RSA_set0_key takes ownership of |n| and |e| on success.
     (void)n.release();
     (void)e.release();

     return rsaPubkey;
 }

 Result<void> verifySignature(const std::string& message, const std::string& signature,
                              const std::vector<uint8_t>& publicKey) {
     auto rsaKey = getRsa(publicKey);
     if (!rsaKey.ok()) {
         return rsaKey.error();
     }
     uint8_t hashBuf[SHA256_DIGEST_LENGTH];
     SHA256(const_cast<uint8_t*>(reinterpret_cast<const uint8_t*>(message.c_str())),
            message.length(), hashBuf);

     bool success = RSA_verify(NID_sha256, hashBuf, sizeof(hashBuf),
                               (const uint8_t*)signature.c_str(), signature.length(), rsaKey->get());

     if (!success) {
         return Error() << "Failed to verify signature.";
     }
     return {};
 }

 static Result<bssl::UniquePtr<EVP_PKEY>> toRsaPkey(const std::vector<uint8_t>& publicKey) {
     // "publicKey" corresponds to the raw public key bytes - need to create
     // a new RSA key with the correct exponent.
     auto rsaPubkey = getRsa(publicKey);
     if (!rsaPubkey.ok()) {
         return rsaPubkey.error();
     }

     bssl::UniquePtr<EVP_PKEY> public_key(EVP_PKEY_new());
     if (!EVP_PKEY_assign_RSA(public_key.get(), rsaPubkey->release())) {
         return Error() << "Failed to assign key";
     }
     return public_key;
 }

 Result<void> createSelfSignedCertificate(
     const std::vector<uint8_t>& publicKey,
     const std::function<Result<std::string>(const std::string&)>& signFunction,
     const std::string& path) {
     bssl::UniquePtr<X509> x509(X509_new());
     if (!x509) {
         return Error() << "Unable to allocate x509 container";
     }
     X509_set_version(x509.get(), 2);

     ASN1_INTEGER_set(X509_get_serialNumber(x509.get()), 1);
     X509_gmtime_adj(X509_get_notBefore(x509.get()), 0);
     X509_gmtime_adj(X509_get_notAfter(x509.get()), kCertLifetimeSeconds);

     auto public_key = toRsaPkey(publicKey);
     if (!public_key.ok()) {
         return public_key.error();
     }

     if (!X509_set_pubkey(x509.get(), public_key.value().get())) {
         return Error() << "Unable to set x509 public key";
     }

     X509_NAME* name = X509_get_subject_name(x509.get());
     if (!name) {
         return Error() << "Unable to get x509 subject name";
     }
     X509_NAME_add_entry_by_txt(name, "C", MBSTRING_ASC,
                                reinterpret_cast<const unsigned char*>("US"), -1, -1, 0);
     X509_NAME_add_entry_by_txt(name, "O", MBSTRING_ASC,
                                reinterpret_cast<const unsigned char*>("Android"), -1, -1, 0);
     X509_NAME_add_entry_by_txt(name, "CN", MBSTRING_ASC,
                                reinterpret_cast<const unsigned char*>("ODS"), -1, -1, 0);
     if (!X509_set_issuer_name(x509.get(), name)) {
         return Error() << "Unable to set x509 issuer name";
     }

     add_ext(x509.get(), NID_basic_constraints, kBasicConstraints);
     add_ext(x509.get(), NID_key_usage, kKeyUsage);
     add_ext(x509.get(), NID_subject_key_identifier, kSubjectKeyIdentifier);
     add_ext(x509.get(), NID_authority_key_identifier, kAuthorityKeyIdentifier);

     bssl::UniquePtr<X509_ALGOR> algor(X509_ALGOR_new());
     if (!algor ||
         !X509_ALGOR_set0(algor.get(), OBJ_nid2obj(NID_sha256WithRSAEncryption), V_ASN1_NULL,
                          NULL) ||
         !X509_set1_signature_algo(x509.get(), algor.get())) {
         return Error() << "Unable to set x509 signature algorithm";
     }

     // Get the data to be signed
     unsigned char* to_be_signed_buf(nullptr);
     size_t to_be_signed_length = i2d_re_X509_tbs(x509.get(), &to_be_signed_buf);

     auto signed_data = signFunction(
         std::string(reinterpret_cast<const char*>(to_be_signed_buf), to_be_signed_length));
     if (!signed_data.ok()) {
         return signed_data.error();
     }

     if (!X509_set1_signature_value(x509.get(),
                                    reinterpret_cast<const uint8_t*>(signed_data->data()),
                                    signed_data->size())) {
         return Error() << "Unable to set x509 signature";
     }

     auto f = fopen(path.c_str(), "wbe");
     if (f == nullptr) {
         return Error() << "Failed to open " << path;
     }
     i2d_X509_fp(f, x509.get());
     fclose(f);

     return {};
 }

 Result<std::vector<uint8_t>> extractPublicKey(EVP_PKEY* pkey) {
     if (pkey == nullptr) {
         return Error() << "Failed to extract public key from x509 cert";
     }

     if (EVP_PKEY_id(pkey) != EVP_PKEY_RSA) {
         return Error() << "The public key is not an RSA key";
     }

     RSA* rsa = EVP_PKEY_get0_RSA(pkey);
     auto num_bytes = BN_num_bytes(RSA_get0_n(rsa));
     std::vector<uint8_t> pubKey(num_bytes);
     int res = BN_bn2bin(RSA_get0_n(rsa), pubKey.data());

     if (!res) {
         return Error() << "Failed to convert public key to bytes";
     }

     return pubKey;
 }

 Result<std::vector<uint8_t>>
 extractPublicKeyFromSubjectPublicKeyInfo(const std::vector<uint8_t>& keyData) {
     auto keyDataBytes = keyData.data();
     bssl::UniquePtr<EVP_PKEY> public_key(d2i_PUBKEY(nullptr, &keyDataBytes, keyData.size()));

     return extractPublicKey(public_key.get());
 }

 Result<std::vector<uint8_t>> extractPublicKeyFromX509(const std::vector<uint8_t>& derCert) {
     auto derCertBytes = derCert.data();
     bssl::UniquePtr<X509> decoded_cert(d2i_X509(nullptr, &derCertBytes, derCert.size()));
     if (decoded_cert.get() == nullptr) {
         return Error() << "Failed to decode X509 certificate.";
     }
     bssl::UniquePtr<EVP_PKEY> decoded_pkey(X509_get_pubkey(decoded_cert.get()));

     return extractPublicKey(decoded_pkey.get());
 }

 static Result<bssl::UniquePtr<X509>> loadX509(const std::string& path) {
     X509* rawCert;
     auto f = fopen(path.c_str(), "re");
     if (f == nullptr) {
         return Error() << "Failed to open " << path;
     }
     if (!d2i_X509_fp(f, &rawCert)) {
         fclose(f);
         return Error() << "Unable to decode x509 cert at " << path;
     }
     bssl::UniquePtr<X509> cert(rawCert);

     fclose(f);
     return cert;
 }

 Result<std::vector<uint8_t>> extractPublicKeyFromX509(const std::string& path) {
     auto cert = loadX509(path);
     if (!cert.ok()) {
         return cert.error();
     }
     return extractPublicKey(X509_get_pubkey(cert.value().get()));
 }

 Result<CertInfo> verifyAndExtractCertInfoFromX509(const std::string& path,
                                                   const std::vector<uint8_t>& publicKey) {
     auto public_key = toRsaPkey(publicKey);
     if (!public_key.ok()) {
         return public_key.error();
     }

     auto cert = loadX509(path);
     if (!cert.ok()) {
         return cert.error();
     }
     X509* x509 = cert.value().get();

     // Make sure we signed it.
     if (X509_verify(x509, public_key.value().get()) != 1) {
         return Error() << "Failed to verify certificate.";
     }

     bssl::UniquePtr<EVP_PKEY> pkey(X509_get_pubkey(x509));
     auto subject_key = extractPublicKey(pkey.get());
     if (!subject_key.ok()) {
         return subject_key.error();
     }

     // The pointers here are all owned by x509, and each function handles an
     // error return from the previous call correctly.
     X509_NAME* name = X509_get_subject_name(x509);
     int index = X509_NAME_get_index_by_NID(name, NID_commonName, -1);
     X509_NAME_ENTRY* entry = X509_NAME_get_entry(name, index);
     ASN1_STRING* asn1cn = X509_NAME_ENTRY_get_data(entry);
     unsigned char* utf8cn;
     int length = ASN1_STRING_to_UTF8(&utf8cn, asn1cn);
     if (length < 0) {
         return Error() << "Failed to read subject CN";
     }

     bssl::UniquePtr<unsigned char> utf8owner(utf8cn);
     std::string cn(reinterpret_cast<char*>(utf8cn), static_cast<size_t>(length));

     CertInfo cert_info{std::move(cn), std::move(subject_key.value())};
     return cert_info;
 }

 Result<std::vector<uint8_t>> createPkcs7(const std::vector<uint8_t>& signed_digest) {
     CBB out, outer_seq, wrapped_seq, seq, digest_algos_set, digest_algo, null;
     CBB content_info, issuer_and_serial, signer_infos, signer_info, sign_algo, signature;
     uint8_t *pkcs7_data, *name_der;
     size_t pkcs7_data_len, name_der_len;
     BIGNUM* serial = BN_new();
     int sig_nid = NID_rsaEncryption;

     X509_NAME* name = X509_NAME_new();
     if (!name) {
         return Error() << "Unable to get x509 subject name";
     }
     X509_NAME_add_entry_by_txt(name, "C", MBSTRING_ASC,
                                reinterpret_cast<const unsigned char*>("US"), -1, -1, 0);
     X509_NAME_add_entry_by_txt(name, "O", MBSTRING_ASC,
                                reinterpret_cast<const unsigned char*>("Android"), -1, -1, 0);
     X509_NAME_add_entry_by_txt(name, "CN", MBSTRING_ASC,
                                reinterpret_cast<const unsigned char*>("ODS"), -1, -1, 0);

     BN_set_word(serial, 1);
     name_der_len = i2d_X509_NAME(name, &name_der);
     CBB_init(&out, 1024);

     if (!CBB_add_asn1(&out, &outer_seq, CBS_ASN1_SEQUENCE) ||
         !OBJ_nid2cbb(&outer_seq, NID_pkcs7_signed) ||
         !CBB_add_asn1(&outer_seq, &wrapped_seq,
                       CBS_ASN1_CONTEXT_SPECIFIC | CBS_ASN1_CONSTRUCTED | 0) ||
         // See https://tools.ietf.org/html/rfc2315#section-9.1
         !CBB_add_asn1(&wrapped_seq, &seq, CBS_ASN1_SEQUENCE) ||
         !CBB_add_asn1_uint64(&seq, 1 /* version */) ||
         !CBB_add_asn1(&seq, &digest_algos_set, CBS_ASN1_SET) ||
         !CBB_add_asn1(&digest_algos_set, &digest_algo, CBS_ASN1_SEQUENCE) ||
         !OBJ_nid2cbb(&digest_algo, NID_sha256) ||
         !CBB_add_asn1(&digest_algo, &null, CBS_ASN1_NULL) ||
         !CBB_add_asn1(&seq, &content_info, CBS_ASN1_SEQUENCE) ||
         !OBJ_nid2cbb(&content_info, NID_pkcs7_data) ||
         !CBB_add_asn1(&seq, &signer_infos, CBS_ASN1_SET) ||
         !CBB_add_asn1(&signer_infos, &signer_info, CBS_ASN1_SEQUENCE) ||
         !CBB_add_asn1_uint64(&signer_info, 1 /* version */) ||
         !CBB_add_asn1(&signer_info, &issuer_and_serial, CBS_ASN1_SEQUENCE) ||
         !CBB_add_bytes(&issuer_and_serial, name_der, name_der_len) ||
         !BN_marshal_asn1(&issuer_and_serial, serial) ||
         !CBB_add_asn1(&signer_info, &digest_algo, CBS_ASN1_SEQUENCE) ||
         !OBJ_nid2cbb(&digest_algo, NID_sha256) ||
         !CBB_add_asn1(&digest_algo, &null, CBS_ASN1_NULL) ||
         !CBB_add_asn1(&signer_info, &sign_algo, CBS_ASN1_SEQUENCE) ||
         !OBJ_nid2cbb(&sign_algo, sig_nid) || !CBB_add_asn1(&sign_algo, &null, CBS_ASN1_NULL) ||
         !CBB_add_asn1(&signer_info, &signature, CBS_ASN1_OCTETSTRING) ||
         !CBB_add_bytes(&signature, signed_digest.data(), signed_digest.size()) ||
         !CBB_finish(&out, &pkcs7_data, &pkcs7_data_len)) {
         return Error() << "Failed to create PKCS7 certificate.";
     }

     return std::vector<uint8_t>(&pkcs7_data[0], &pkcs7_data[pkcs7_data_len]);
 }
	/*
	* Copyright (C) 2020 The Android Open Source Project
	*
	* 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 "CertUtils.h"

	#include <android-base/logging.h>
	#include <android-base/result.h>

	#include <openssl/bn.h>
	#include <openssl/crypto.h>
	#include <openssl/pkcs7.h>
	#include <openssl/rsa.h>
	#include <openssl/x509.h>
	#include <openssl/x509v3.h>

	#include <fcntl.h>
	#include <vector>

	#include "KeyConstants.h"

	const char kBasicConstraints[] = "CA:TRUE";
	const char kKeyUsage[] = "critical,keyCertSign,cRLSign,digitalSignature";
	const char kSubjectKeyIdentifier[] = "hash";
	const char kAuthorityKeyIdentifier[] = "keyid:always";
	constexpr int kCertLifetimeSeconds = 10 * 365 * 24 * 60 * 60;

	using android::base::Result;
	// using android::base::ErrnoError;
	using android::base::Error;

	static bool add_ext(X509* cert, int nid, const char* value) {
	size_t len = strlen(value) + 1;
	std::vector<char> mutableValue(value, value + len);
	X509V3_CTX context;

	X509V3_set_ctx_nodb(&context);

	X509V3_set_ctx(&context, cert, cert, nullptr, nullptr, 0);
	X509_EXTENSION* ex = X509V3_EXT_nconf_nid(nullptr, &context, nid, mutableValue.data());
	if (!ex) {
	return false;
	}

	X509_add_ext(cert, ex, -1);
	X509_EXTENSION_free(ex);
	return true;
	}

	Result<bssl::UniquePtr<RSA>> getRsa(const std::vector<uint8_t>& publicKey) {
	bssl::UniquePtr<BIGNUM> n(BN_new());
	bssl::UniquePtr<BIGNUM> e(BN_new());
	bssl::UniquePtr<RSA> rsaPubkey(RSA_new());
	if (!n \|\| !e \|\| !rsaPubkey \|\| !BN_bin2bn(publicKey.data(), publicKey.size(), n.get()) \|\|
	!BN_set_word(e.get(), kRsaKeyExponent) \|\|
	!RSA_set0_key(rsaPubkey.get(), n.get(), e.get(), /d=/nullptr)) {
	return Error() << "Failed to create RSA key";
	}
	// RSA_set0_key takes ownership of \|n\| and \|e\| on success.
	(void)n.release();
	(void)e.release();

	return rsaPubkey;
	}

	Result<void> verifySignature(const std::string& message, const std::string& signature,
	const std::vector<uint8_t>& publicKey) {
	auto rsaKey = getRsa(publicKey);
	if (!rsaKey.ok()) {
	return rsaKey.error();
	}
	uint8_t hashBuf[SHA256_DIGEST_LENGTH];
	SHA256(const_cast<uint8_t>(reinterpret_cast<const uint8_t>(message.c_str())),
	message.length(), hashBuf);

	bool success = RSA_verify(NID_sha256, hashBuf, sizeof(hashBuf),
	(const uint8_t*)signature.c_str(), signature.length(), rsaKey->get());

	if (!success) {
	return Error() << "Failed to verify signature.";
	}
	return {};
	}

	static Result<bssl::UniquePtr<EVP_PKEY>> toRsaPkey(const std::vector<uint8_t>& publicKey) {
	// "publicKey" corresponds to the raw public key bytes - need to create
	// a new RSA key with the correct exponent.
	auto rsaPubkey = getRsa(publicKey);
	if (!rsaPubkey.ok()) {
	return rsaPubkey.error();
	}

	bssl::UniquePtr<EVP_PKEY> public_key(EVP_PKEY_new());
	if (!EVP_PKEY_assign_RSA(public_key.get(), rsaPubkey->release())) {
	return Error() << "Failed to assign key";
	}
	return public_key;
	}

	Result<void> createSelfSignedCertificate(
	const std::vector<uint8_t>& publicKey,
	const std::function<Result<std::string>(const std::string&)>& signFunction,
	const std::string& path) {
	bssl::UniquePtr<X509> x509(X509_new());
	if (!x509) {
	return Error() << "Unable to allocate x509 container";
	}
	X509_set_version(x509.get(), 2);

	ASN1_INTEGER_set(X509_get_serialNumber(x509.get()), 1);
	X509_gmtime_adj(X509_get_notBefore(x509.get()), 0);
	X509_gmtime_adj(X509_get_notAfter(x509.get()), kCertLifetimeSeconds);

	auto public_key = toRsaPkey(publicKey);
	if (!public_key.ok()) {
	return public_key.error();
	}

	if (!X509_set_pubkey(x509.get(), public_key.value().get())) {
	return Error() << "Unable to set x509 public key";
	}

	X509_NAME* name = X509_get_subject_name(x509.get());
	if (!name) {
	return Error() << "Unable to get x509 subject name";
	}
	X509_NAME_add_entry_by_txt(name, "C", MBSTRING_ASC,
	reinterpret_cast<const unsigned char*>("US"), -1, -1, 0);
	X509_NAME_add_entry_by_txt(name, "O", MBSTRING_ASC,
	reinterpret_cast<const unsigned char*>("Android"), -1, -1, 0);
	X509_NAME_add_entry_by_txt(name, "CN", MBSTRING_ASC,
	reinterpret_cast<const unsigned char*>("ODS"), -1, -1, 0);
	if (!X509_set_issuer_name(x509.get(), name)) {
	return Error() << "Unable to set x509 issuer name";
	}

	add_ext(x509.get(), NID_basic_constraints, kBasicConstraints);
	add_ext(x509.get(), NID_key_usage, kKeyUsage);
	add_ext(x509.get(), NID_subject_key_identifier, kSubjectKeyIdentifier);
	add_ext(x509.get(), NID_authority_key_identifier, kAuthorityKeyIdentifier);

	bssl::UniquePtr<X509_ALGOR> algor(X509_ALGOR_new());
	if (!algor \|\|
	!X509_ALGOR_set0(algor.get(), OBJ_nid2obj(NID_sha256WithRSAEncryption), V_ASN1_NULL,
	NULL) \|\|
	!X509_set1_signature_algo(x509.get(), algor.get())) {
	return Error() << "Unable to set x509 signature algorithm";
	}

	// Get the data to be signed
	unsigned char* to_be_signed_buf(nullptr);
	size_t to_be_signed_length = i2d_re_X509_tbs(x509.get(), &to_be_signed_buf);

	auto signed_data = signFunction(
	std::string(reinterpret_cast<const char*>(to_be_signed_buf), to_be_signed_length));
	if (!signed_data.ok()) {
	return signed_data.error();
	}

	if (!X509_set1_signature_value(x509.get(),
	reinterpret_cast<const uint8_t*>(signed_data->data()),
	signed_data->size())) {
	return Error() << "Unable to set x509 signature";
	}

	auto f = fopen(path.c_str(), "wbe");
	if (f == nullptr) {
	return Error() << "Failed to open " << path;
	}
	i2d_X509_fp(f, x509.get());
	fclose(f);

	return {};
	}

	Result<std::vector<uint8_t>> extractPublicKey(EVP_PKEY* pkey) {
	if (pkey == nullptr) {
	return Error() << "Failed to extract public key from x509 cert";
	}

	if (EVP_PKEY_id(pkey) != EVP_PKEY_RSA) {
	return Error() << "The public key is not an RSA key";
	}

	RSA* rsa = EVP_PKEY_get0_RSA(pkey);
	auto num_bytes = BN_num_bytes(RSA_get0_n(rsa));
	std::vector<uint8_t> pubKey(num_bytes);
	int res = BN_bn2bin(RSA_get0_n(rsa), pubKey.data());

	if (!res) {
	return Error() << "Failed to convert public key to bytes";
	}

	return pubKey;
	}

	Result<std::vector<uint8_t>>
	extractPublicKeyFromSubjectPublicKeyInfo(const std::vector<uint8_t>& keyData) {
	auto keyDataBytes = keyData.data();
	bssl::UniquePtr<EVP_PKEY> public_key(d2i_PUBKEY(nullptr, &keyDataBytes, keyData.size()));

	return extractPublicKey(public_key.get());
	}

	Result<std::vector<uint8_t>> extractPublicKeyFromX509(const std::vector<uint8_t>& derCert) {
	auto derCertBytes = derCert.data();
	bssl::UniquePtr<X509> decoded_cert(d2i_X509(nullptr, &derCertBytes, derCert.size()));
	if (decoded_cert.get() == nullptr) {
	return Error() << "Failed to decode X509 certificate.";
	}
	bssl::UniquePtr<EVP_PKEY> decoded_pkey(X509_get_pubkey(decoded_cert.get()));

	return extractPublicKey(decoded_pkey.get());
	}

	static Result<bssl::UniquePtr<X509>> loadX509(const std::string& path) {
	X509* rawCert;
	auto f = fopen(path.c_str(), "re");
	if (f == nullptr) {
	return Error() << "Failed to open " << path;
	}
	if (!d2i_X509_fp(f, &rawCert)) {
	fclose(f);
	return Error() << "Unable to decode x509 cert at " << path;
	}
	bssl::UniquePtr<X509> cert(rawCert);

	fclose(f);
	return cert;
	}

	Result<std::vector<uint8_t>> extractPublicKeyFromX509(const std::string& path) {
	auto cert = loadX509(path);
	if (!cert.ok()) {
	return cert.error();
	}
	return extractPublicKey(X509_get_pubkey(cert.value().get()));
	}

	Result<CertInfo> verifyAndExtractCertInfoFromX509(const std::string& path,
	const std::vector<uint8_t>& publicKey) {
	auto public_key = toRsaPkey(publicKey);
	if (!public_key.ok()) {
	return public_key.error();
	}

	auto cert = loadX509(path);
	if (!cert.ok()) {
	return cert.error();
	}
	X509* x509 = cert.value().get();

	// Make sure we signed it.
	if (X509_verify(x509, public_key.value().get()) != 1) {
	return Error() << "Failed to verify certificate.";
	}

	bssl::UniquePtr<EVP_PKEY> pkey(X509_get_pubkey(x509));
	auto subject_key = extractPublicKey(pkey.get());
	if (!subject_key.ok()) {
	return subject_key.error();
	}

	// The pointers here are all owned by x509, and each function handles an
	// error return from the previous call correctly.
	X509_NAME* name = X509_get_subject_name(x509);
	int index = X509_NAME_get_index_by_NID(name, NID_commonName, -1);
	X509_NAME_ENTRY* entry = X509_NAME_get_entry(name, index);
	ASN1_STRING* asn1cn = X509_NAME_ENTRY_get_data(entry);
	unsigned char* utf8cn;
	int length = ASN1_STRING_to_UTF8(&utf8cn, asn1cn);
	if (length < 0) {
	return Error() << "Failed to read subject CN";
	}

	bssl::UniquePtr<unsigned char> utf8owner(utf8cn);
	std::string cn(reinterpret_cast<char*>(utf8cn), static_cast<size_t>(length));

	CertInfo cert_info{std::move(cn), std::move(subject_key.value())};
	return cert_info;
	}

	Result<std::vector<uint8_t>> createPkcs7(const std::vector<uint8_t>& signed_digest) {
	CBB out, outer_seq, wrapped_seq, seq, digest_algos_set, digest_algo, null;
	CBB content_info, issuer_and_serial, signer_infos, signer_info, sign_algo, signature;
	uint8_t pkcs7_data, name_der;
	size_t pkcs7_data_len, name_der_len;
	BIGNUM* serial = BN_new();
	int sig_nid = NID_rsaEncryption;

	X509_NAME* name = X509_NAME_new();
	if (!name) {
	return Error() << "Unable to get x509 subject name";
	}
	X509_NAME_add_entry_by_txt(name, "C", MBSTRING_ASC,
	reinterpret_cast<const unsigned char*>("US"), -1, -1, 0);
	X509_NAME_add_entry_by_txt(name, "O", MBSTRING_ASC,
	reinterpret_cast<const unsigned char*>("Android"), -1, -1, 0);
	X509_NAME_add_entry_by_txt(name, "CN", MBSTRING_ASC,
	reinterpret_cast<const unsigned char*>("ODS"), -1, -1, 0);

	BN_set_word(serial, 1);
	name_der_len = i2d_X509_NAME(name, &name_der);
	CBB_init(&out, 1024);

	if (!CBB_add_asn1(&out, &outer_seq, CBS_ASN1_SEQUENCE) \|\|
	!OBJ_nid2cbb(&outer_seq, NID_pkcs7_signed) \|\|
	!CBB_add_asn1(&outer_seq, &wrapped_seq,
	CBS_ASN1_CONTEXT_SPECIFIC \| CBS_ASN1_CONSTRUCTED \| 0) \|\|
	// See https://tools.ietf.org/html/rfc2315#section-9.1
	!CBB_add_asn1(&wrapped_seq, &seq, CBS_ASN1_SEQUENCE) \|\|
	!CBB_add_asn1_uint64(&seq, 1 /* version */) \|\|
	!CBB_add_asn1(&seq, &digest_algos_set, CBS_ASN1_SET) \|\|
	!CBB_add_asn1(&digest_algos_set, &digest_algo, CBS_ASN1_SEQUENCE) \|\|
	!OBJ_nid2cbb(&digest_algo, NID_sha256) \|\|
	!CBB_add_asn1(&digest_algo, &null, CBS_ASN1_NULL) \|\|
	!CBB_add_asn1(&seq, &content_info, CBS_ASN1_SEQUENCE) \|\|
	!OBJ_nid2cbb(&content_info, NID_pkcs7_data) \|\|
	!CBB_add_asn1(&seq, &signer_infos, CBS_ASN1_SET) \|\|
	!CBB_add_asn1(&signer_infos, &signer_info, CBS_ASN1_SEQUENCE) \|\|
	!CBB_add_asn1_uint64(&signer_info, 1 /* version */) \|\|
	!CBB_add_asn1(&signer_info, &issuer_and_serial, CBS_ASN1_SEQUENCE) \|\|
	!CBB_add_bytes(&issuer_and_serial, name_der, name_der_len) \|\|
	!BN_marshal_asn1(&issuer_and_serial, serial) \|\|
	!CBB_add_asn1(&signer_info, &digest_algo, CBS_ASN1_SEQUENCE) \|\|
	!OBJ_nid2cbb(&digest_algo, NID_sha256) \|\|
	!CBB_add_asn1(&digest_algo, &null, CBS_ASN1_NULL) \|\|
	!CBB_add_asn1(&signer_info, &sign_algo, CBS_ASN1_SEQUENCE) \|\|
	!OBJ_nid2cbb(&sign_algo, sig_nid) \|\| !CBB_add_asn1(&sign_algo, &null, CBS_ASN1_NULL) \|\|
	!CBB_add_asn1(&signer_info, &signature, CBS_ASN1_OCTETSTRING) \|\|
	!CBB_add_bytes(&signature, signed_digest.data(), signed_digest.size()) \|\|
	!CBB_finish(&out, &pkcs7_data, &pkcs7_data_len)) {
	return Error() << "Failed to create PKCS7 certificate.";
	}

	return std::vector<uint8_t>(&pkcs7_data[0], &pkcs7_data[pkcs7_data_len]);
	}