libdatachannel/src/impl/certificate.cpp

/**
 * Copyright (c) 2019 Paul-Louis Ageneau
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
 */

#include "certificate.hpp"
#include "threadpool.hpp"

#include <cassert>
#include <chrono>
#include <iomanip>
#include <mutex>
#include <sstream>
#include <unordered_map>

namespace rtc::impl {

#if USE_GNUTLS

Certificate Certificate::FromString(string crt_pem, string key_pem) {
	PLOG_DEBUG << "Importing certificate from PEM string (GnuTLS)";

	shared_ptr<gnutls_certificate_credentials_t> creds(gnutls::new_credentials(),
	                                                   gnutls::free_credentials);
	gnutls_datum_t crt_datum = gnutls::make_datum(crt_pem.data(), crt_pem.size());
	gnutls_datum_t key_datum = gnutls::make_datum(key_pem.data(), key_pem.size());
	gnutls::check(
	    gnutls_certificate_set_x509_key_mem(*creds, &crt_datum, &key_datum, GNUTLS_X509_FMT_PEM),
	    "Unable to import PEM certificate and key");

	return Certificate(std::move(creds));
}

Certificate Certificate::FromFile(const string &crt_pem_file, const string &key_pem_file,
                                  const string &pass) {
	PLOG_DEBUG << "Importing certificate from PEM file (GnuTLS): " << crt_pem_file;

	shared_ptr<gnutls_certificate_credentials_t> creds(gnutls::new_credentials(),
	                                                   gnutls::free_credentials);
	gnutls::check(gnutls_certificate_set_x509_key_file2(*creds, crt_pem_file.c_str(),
	                                                    key_pem_file.c_str(), GNUTLS_X509_FMT_PEM,
	                                                    pass.c_str(), 0),
	              "Unable to import PEM certificate and key from file");

	return Certificate(std::move(creds));
}

Certificate Certificate::Generate(CertificateType type, const string &commonName) {
	PLOG_DEBUG << "Generating certificate (GnuTLS)";

	using namespace gnutls;
	unique_ptr<gnutls_x509_crt_t, decltype(&free_crt)> crt(new_crt(), free_crt);
	unique_ptr<gnutls_x509_privkey_t, decltype(&free_privkey)> privkey(new_privkey(), free_privkey);

	switch (type) {
	// RFC 8827 WebRTC Security Architecture 6.5. Communications Security
	// All implementations MUST support DTLS 1.2 with the TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256
	// cipher suite and the P-256 curve
	// See https://tools.ietf.org/html/rfc8827#section-6.5
	case CertificateType::Default:
	case CertificateType::Ecdsa: {
		gnutls::check(gnutls_x509_privkey_generate(*privkey, GNUTLS_PK_ECDSA,
		                                           GNUTLS_CURVE_TO_BITS(GNUTLS_ECC_CURVE_SECP256R1),
		                                           0),
		              "Unable to generate ECDSA P-256 key pair");
		break;
	}
	case CertificateType::Rsa: {
		const unsigned int bits = 2048;
		gnutls::check(gnutls_x509_privkey_generate(*privkey, GNUTLS_PK_RSA, bits, 0),
		              "Unable to generate RSA key pair");
		break;
	}
	default:
		throw std::invalid_argument("Unknown certificate type");
	}

	using namespace std::chrono;
	auto now = time_point_cast<seconds>(system_clock::now());
	gnutls_x509_crt_set_activation_time(*crt, (now - hours(1)).time_since_epoch().count());
	gnutls_x509_crt_set_expiration_time(*crt, (now + hours(24 * 365)).time_since_epoch().count());
	gnutls_x509_crt_set_version(*crt, 1);
	gnutls_x509_crt_set_key(*crt, *privkey);
	gnutls_x509_crt_set_dn_by_oid(*crt, GNUTLS_OID_X520_COMMON_NAME, 0, commonName.data(),
	                              commonName.size());

	const size_t serialSize = 16;
	char serial[serialSize];
	gnutls_rnd(GNUTLS_RND_NONCE, serial, serialSize);
	gnutls_x509_crt_set_serial(*crt, serial, serialSize);

	gnutls::check(gnutls_x509_crt_sign2(*crt, *crt, *privkey, GNUTLS_DIG_SHA256, 0),
	              "Unable to auto-sign certificate");

	return Certificate(*crt, *privkey);
}

Certificate::Certificate(gnutls_x509_crt_t crt, gnutls_x509_privkey_t privkey)
    : mCredentials(gnutls::new_credentials(), gnutls::free_credentials),
      mFingerprint(make_fingerprint(crt)) {

	gnutls::check(gnutls_certificate_set_x509_key(*mCredentials, &crt, 1, privkey),
	              "Unable to set certificate and key pair in credentials");
}

Certificate::Certificate(shared_ptr<gnutls_certificate_credentials_t> creds)
    : mCredentials(std::move(creds)), mFingerprint(make_fingerprint(*mCredentials)) {}

gnutls_certificate_credentials_t Certificate::credentials() const { return *mCredentials; }

string Certificate::fingerprint() const { return mFingerprint; }

string make_fingerprint(gnutls_certificate_credentials_t credentials) {
	auto new_crt_list = [credentials]() -> gnutls_x509_crt_t * {
		gnutls_x509_crt_t *crt_list = nullptr;
		unsigned int crt_list_size = 0;
		gnutls::check(gnutls_certificate_get_x509_crt(credentials, 0, &crt_list, &crt_list_size));
		assert(crt_list_size == 1);
		return crt_list;
	};

	auto free_crt_list = [](gnutls_x509_crt_t *crt_list) {
		gnutls_x509_crt_deinit(crt_list[0]);
		gnutls_free(crt_list);
	};

	unique_ptr<gnutls_x509_crt_t, decltype(free_crt_list)> crt_list(new_crt_list(), free_crt_list);

	return make_fingerprint(*crt_list);
}

string make_fingerprint(gnutls_x509_crt_t crt) {
	const size_t size = 32;
	unsigned char buffer[size];
	size_t len = size;
	gnutls::check(gnutls_x509_crt_get_fingerprint(crt, GNUTLS_DIG_SHA256, buffer, &len),
	              "X509 fingerprint error");

	std::ostringstream oss;
	oss << std::hex << std::uppercase << std::setfill('0');
	for (size_t i = 0; i < len; ++i) {
		if (i)
			oss << std::setw(1) << ':';
		oss << std::setw(2) << unsigned(buffer[i]);
	}
	return oss.str();
}

#else // USE_GNUTLS==0

#include <cstdio>

namespace {

// Dummy password callback that copies the password from user data
int dummy_pass_cb(char *buf, int size, int /*rwflag*/, void *u) {
	const char *pass = static_cast<char *>(u);
	return snprintf(buf, size, "%s", pass);
}

} // namespace

Certificate Certificate::FromString(string crt_pem, string key_pem) {
	PLOG_DEBUG << "Importing certificate from PEM string (OpenSSL)";

	BIO *bio = BIO_new(BIO_s_mem());
	BIO_write(bio, crt_pem.data(), int(crt_pem.size()));
	auto x509 = shared_ptr<X509>(PEM_read_bio_X509(bio, nullptr, nullptr, nullptr), X509_free);
	BIO_free(bio);
	if (!x509)
		throw std::invalid_argument("Unable to import PEM certificate");

	bio = BIO_new(BIO_s_mem());
	BIO_write(bio, key_pem.data(), int(key_pem.size()));
	auto pkey = shared_ptr<EVP_PKEY>(PEM_read_bio_PrivateKey(bio, nullptr, nullptr, nullptr),
	                                 EVP_PKEY_free);
	BIO_free(bio);
	if (!pkey)
		throw std::invalid_argument("Unable to import PEM key");

	return Certificate(x509, pkey);
}

Certificate Certificate::FromFile(const string &crt_pem_file, const string &key_pem_file,
                                  const string &pass) {
	PLOG_DEBUG << "Importing certificate from PEM file (OpenSSL): " << crt_pem_file;

	FILE *file = fopen(crt_pem_file.c_str(), "r");
	if (!file)
		throw std::invalid_argument("Unable to open PEM certificate file");

	auto x509 = shared_ptr<X509>(PEM_read_X509(file, nullptr, nullptr, nullptr), X509_free);
	fclose(file);
	if (!x509)
		throw std::invalid_argument("Unable to import PEM certificate from file");

	file = fopen(key_pem_file.c_str(), "r");
	if (!file)
		throw std::invalid_argument("Unable to open PEM key file");

	auto pkey = shared_ptr<EVP_PKEY>(
	    PEM_read_PrivateKey(file, nullptr, dummy_pass_cb, const_cast<char *>(pass.c_str())),
	    EVP_PKEY_free);
	fclose(file);
	if (!pkey)
		throw std::invalid_argument("Unable to import PEM key from file");

	return Certificate(x509, pkey);
}

Certificate Certificate::Generate(CertificateType type, const string &commonName) {
	PLOG_DEBUG << "Generating certificate (OpenSSL)";

	shared_ptr<X509> x509(X509_new(), X509_free);
	shared_ptr<EVP_PKEY> pkey(EVP_PKEY_new(), EVP_PKEY_free);
	unique_ptr<BIGNUM, decltype(&BN_free)> serial_number(BN_new(), BN_free);
	unique_ptr<X509_NAME, decltype(&X509_NAME_free)> name(X509_NAME_new(), X509_NAME_free);
	if (!x509 || !pkey || !serial_number || !name)
		throw std::runtime_error("Unable to allocate structures for certificate generation");

	switch (type) {
	// RFC 8827 WebRTC Security Architecture 6.5. Communications Security
	// All implementations MUST support DTLS 1.2 with the TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256
	// cipher suite and the P-256 curve
	// See https://tools.ietf.org/html/rfc8827#section-6.5
	case CertificateType::Default:
	case CertificateType::Ecdsa: {
		PLOG_VERBOSE << "Generating ECDSA P-256 key pair";

		unique_ptr<EC_KEY, decltype(&EC_KEY_free)> ecc(
		    EC_KEY_new_by_curve_name(NID_X9_62_prime256v1), EC_KEY_free);
		if (!ecc)
			throw std::runtime_error("Unable to allocate structure for ECDSA P-256 key pair");

		EC_KEY_set_asn1_flag(ecc.get(), OPENSSL_EC_NAMED_CURVE); // Set ASN1 OID
		if (!EC_KEY_generate_key(ecc.get()) ||
		    !EVP_PKEY_assign_EC_KEY(pkey.get(),
		                            ecc.release())) // the key will be freed when pkey is freed
			throw std::runtime_error("Unable to generate ECDSA P-256 key pair");

		break;
	}
	case CertificateType::Rsa: {
		PLOG_VERBOSE << "Generating RSA key pair";

		const int bits = 2048;
		const unsigned int e = 65537; // 2^16 + 1

		unique_ptr<RSA, decltype(&RSA_free)> rsa(RSA_new(), RSA_free);
		unique_ptr<BIGNUM, decltype(&BN_free)> exponent(BN_new(), BN_free);
		if (!rsa || !exponent)
			throw std::runtime_error("Unable to allocate structures for RSA key pair");

		if (!BN_set_word(exponent.get(), e) ||
		    !RSA_generate_key_ex(rsa.get(), bits, exponent.get(), NULL) ||
		    !EVP_PKEY_assign_RSA(pkey.get(),
		                         rsa.release())) // the key will be freed when pkey is freed
			throw std::runtime_error("Unable to generate RSA key pair");

		break;
	}
	default:
		throw std::invalid_argument("Unknown certificate type");
	}

	const size_t serialSize = 16;
	auto *commonNameBytes =
	    reinterpret_cast<unsigned char *>(const_cast<char *>(commonName.c_str()));

	if (!X509_set_pubkey(x509.get(), pkey.get()))
		throw std::runtime_error("Unable to set certificate public key");

	if (!X509_gmtime_adj(X509_getm_notBefore(x509.get()), 3600 * -1) ||
	    !X509_gmtime_adj(X509_getm_notAfter(x509.get()), 3600 * 24 * 365) ||
	    !X509_set_version(x509.get(), 1) ||
	    !BN_pseudo_rand(serial_number.get(), serialSize, 0, 0) ||
	    !BN_to_ASN1_INTEGER(serial_number.get(), X509_get_serialNumber(x509.get())) ||
	    !X509_NAME_add_entry_by_NID(name.get(), NID_commonName, MBSTRING_UTF8, commonNameBytes, -1,
	                                -1, 0) ||
	    !X509_set_subject_name(x509.get(), name.get()) ||
	    !X509_set_issuer_name(x509.get(), name.get()))
		throw std::runtime_error("Unable to set certificate properties");

	if (!X509_sign(x509.get(), pkey.get(), EVP_sha256()))
		throw std::runtime_error("Unable to auto-sign certificate");

	return Certificate(x509, pkey);
}

Certificate::Certificate(shared_ptr<X509> x509, shared_ptr<EVP_PKEY> pkey)
    : mX509(std::move(x509)), mPKey(std::move(pkey)), mFingerprint(make_fingerprint(mX509.get())) {}

string Certificate::fingerprint() const { return mFingerprint; }

std::tuple<X509 *, EVP_PKEY *> Certificate::credentials() const {
	return {mX509.get(), mPKey.get()};
}

string make_fingerprint(X509 *x509) {
	const size_t size = 32;
	unsigned char buffer[size];
	unsigned int len = size;
	if (!X509_digest(x509, EVP_sha256(), buffer, &len))
		throw std::runtime_error("X509 fingerprint error");

	std::ostringstream oss;
	oss << std::hex << std::uppercase << std::setfill('0');
	for (size_t i = 0; i < len; ++i) {
		if (i)
			oss << std::setw(1) << ':';
		oss << std::setw(2) << unsigned(buffer[i]);
	}
	return oss.str();
}

#endif

// Common for GnuTLS and OpenSSL

future_certificate_ptr make_certificate(CertificateType type) {
	return ThreadPool::Instance().enqueue([type]() {
		return std::make_shared<Certificate>(Certificate::Generate(type, "libdatachannel"));
	});
}

} // namespace rtc::impl