opendht/src/crypto.cpp

/*
 *  Copyright (C) 2014-2015 Savoir-faire Linux Inc.
 *  Author : Adrien Béraud <adrien.beraud@savoirfairelinux.com>
 *
 *  This program is free software; you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation; either version 3 of the License, or
 *  (at your option) any later version.
 *
 *  This program 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 General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with this program; if not, write to the Free Software
 *  Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301 USA.
 */

#include "crypto.h"
#include "rng.h"

extern "C" {
#include <gnutls/gnutls.h>
#include <gnutls/abstract.h>
#include <gnutls/x509.h>
#include <nettle/gcm.h>
#include <nettle/aes.h>
}

#include <random>
#include <sstream>
#include <stdexcept>
#include <cassert>

static std::uniform_int_distribution<uint8_t> rand_byte;

static gnutls_digest_algorithm_t get_dig_for_pub(gnutls_pubkey_t pubkey)
{
    gnutls_digest_algorithm_t dig;
    int result = gnutls_pubkey_get_preferred_hash_algorithm(pubkey, &dig, nullptr);
    if (result < 0)
        return GNUTLS_DIG_UNKNOWN;
    return dig;
}

static gnutls_digest_algorithm_t get_dig(gnutls_x509_crt_t crt)
{
    gnutls_pubkey_t pubkey;
    gnutls_pubkey_init(&pubkey);

    int result = gnutls_pubkey_import_x509(pubkey, crt, 0);
    if (result < 0) {
        gnutls_pubkey_deinit(pubkey);
        return GNUTLS_DIG_UNKNOWN;
    }

    gnutls_digest_algorithm_t dig = get_dig_for_pub(pubkey);
    gnutls_pubkey_deinit(pubkey);
    return dig;
}

// support for GnuTLS < 3.4.
#if GNUTLS_VERSION_NUMBER < 0x030400
#define GNUTLS_PKCS_PKCS12_3DES GNUTLS_PKCS_USE_PKCS12_3DES
#define GNUTLS_PKCS_PKCS12_ARCFOUR GNUTLS_PKCS_USE_PKCS12_ARCFOUR
#define GNUTLS_PKCS_PKCS12_RC2_40 GNUTLS_PKCS_USE_PKCS12_RC2_40
#define GNUTLS_PKCS_PBES2_3DES GNUTLS_PKCS_USE_PBES2_3DES
#define GNUTLS_PKCS_PBES2_AES_128 GNUTLS_PKCS_USE_PBES2_AES_128
#define GNUTLS_PKCS_PBES2_AES_192 GNUTLS_PKCS_USE_PBES2_AES_192
#define GNUTLS_PKCS_PBES2_AES_256 GNUTLS_PKCS_USE_PBES2_AES_256
#endif

namespace dht {
namespace crypto {

static constexpr std::array<size_t, 3> AES_LENGTHS {{128/8, 192/8, 256/8}};

size_t aesKeySize(size_t max)
{
    unsigned aes_key_len = 0;
    for (size_t s = 0; s < AES_LENGTHS.size(); s++) {
        if (AES_LENGTHS[s] <= max)
            aes_key_len = AES_LENGTHS[s];
        else break;
    }
    return aes_key_len;
}

bool aesKeySizeGood(size_t key_size)
{
    for (auto& i : AES_LENGTHS)
        if (key_size == i)
            return true;
    return false;
}

#ifndef GCM_DIGEST_SIZE
#define GCM_DIGEST_SIZE GCM_BLOCK_SIZE
#endif

Blob
aesEncrypt(const Blob& data, const Blob& key)
{
    std::array<uint8_t, GCM_IV_SIZE> iv;
    {
        crypto::random_device rdev;
        std::generate_n(iv.begin(), iv.size(), std::bind(rand_byte, std::ref(rdev)));
    }
    struct gcm_aes_ctx aes;
    gcm_aes_set_key(&aes, key.size(), key.data());
    gcm_aes_set_iv(&aes, iv.size(), iv.data());
    gcm_aes_update(&aes, data.size(), data.data());

    Blob ret(data.size() + GCM_IV_SIZE + GCM_DIGEST_SIZE);
    std::copy(iv.begin(), iv.end(), ret.begin());
    gcm_aes_encrypt(&aes, data.size(), ret.data() + GCM_IV_SIZE, data.data());
    gcm_aes_digest(&aes, GCM_DIGEST_SIZE, ret.data() + GCM_IV_SIZE + data.size());
    return ret;
}

Blob
aesDecrypt(const Blob& data, const Blob& key)
{
    if (not aesKeySizeGood(key.size()))
        throw DecryptError("Wrong key size");

    if (data.size() <= GCM_IV_SIZE + GCM_DIGEST_SIZE)
        throw DecryptError("Wrong data size");

    std::array<uint8_t, GCM_DIGEST_SIZE> digest;

    struct gcm_aes_ctx aes;
    gcm_aes_set_key(&aes, key.size(), key.data());
    gcm_aes_set_iv(&aes, GCM_IV_SIZE, data.data());

    size_t data_sz = data.size() - GCM_IV_SIZE - GCM_DIGEST_SIZE;
    Blob ret(data_sz);
    //gcm_aes_update(&aes, data_sz, data.data() + GCM_IV_SIZE);
    gcm_aes_decrypt(&aes, data_sz, ret.data(), data.data() + GCM_IV_SIZE);
    //gcm_aes_digest(aes, GCM_DIGEST_SIZE, digest.data());

    // TODO compute the proper digest directly from the decryption pass
    Blob ret_tmp(data_sz);
    struct gcm_aes_ctx aes_d;
    gcm_aes_set_key(&aes_d, key.size(), key.data());
    gcm_aes_set_iv(&aes_d, GCM_IV_SIZE, data.data());
    gcm_aes_update(&aes_d, ret.size() , ret.data());
    gcm_aes_encrypt(&aes_d, ret.size(), ret_tmp.data(), ret.data());
    gcm_aes_digest(&aes_d, GCM_DIGEST_SIZE, digest.data());

    if (not std::equal(digest.begin(), digest.end(), data.end() - GCM_DIGEST_SIZE))
        throw DecryptError("Can't decrypt data");

    return ret;
}

PrivateKey::PrivateKey()
{
#if GNUTLS_VERSION_NUMBER < 0x030300
    if (gnutls_global_init() != GNUTLS_E_SUCCESS)
        throw CryptoException("Can't initialize GnuTLS.");
#endif
}

PrivateKey::PrivateKey(gnutls_x509_privkey_t k) : x509_key(k)
{
#if GNUTLS_VERSION_NUMBER < 0x030300
    if (gnutls_global_init() != GNUTLS_E_SUCCESS)
        throw CryptoException("Can't initialize GnuTLS.");
#endif
    gnutls_privkey_init(&key);
    if (gnutls_privkey_import_x509(key, k, GNUTLS_PRIVKEY_IMPORT_COPY) != GNUTLS_E_SUCCESS) {
        key = nullptr;
        throw CryptoException("Can't load generic private key !");
    }
}

PrivateKey::PrivateKey(const Blob& import, const std::string& password)
{
#if GNUTLS_VERSION_NUMBER < 0x030300
    if (gnutls_global_init() != GNUTLS_E_SUCCESS)
        throw CryptoException("Can't initialize GnuTLS.");
#endif
    int err = gnutls_x509_privkey_init(&x509_key);
    if (err != GNUTLS_E_SUCCESS)
        throw CryptoException("Can't initialize private key !");

    const gnutls_datum_t dt {(uint8_t*)import.data(), static_cast<unsigned>(import.size())};
    const char* password_ptr = password.empty() ? nullptr : password.c_str();
    int flags = password.empty() ? GNUTLS_PKCS_PLAIN 
                : ( GNUTLS_PKCS_PBES2_AES_128 | GNUTLS_PKCS_PBES2_AES_192  | GNUTLS_PKCS_PBES2_AES_256
                  | GNUTLS_PKCS_PKCS12_3DES   | GNUTLS_PKCS_PKCS12_ARCFOUR | GNUTLS_PKCS_PKCS12_RC2_40);

    err = gnutls_x509_privkey_import2(x509_key, &dt, GNUTLS_X509_FMT_PEM, password_ptr, flags);
    if (err != GNUTLS_E_SUCCESS) {
        int err_der = gnutls_x509_privkey_import2(x509_key, &dt, GNUTLS_X509_FMT_DER, password_ptr, flags);
        if (err_der != GNUTLS_E_SUCCESS) {
            gnutls_x509_privkey_deinit(x509_key);
            if (err == GNUTLS_E_DECRYPTION_FAILED or err_der == GNUTLS_E_DECRYPTION_FAILED)
                throw DecryptError("Can't decrypt private key");
            else
                throw CryptoException(std::string("Can't load private key: PEM: ") + gnutls_strerror(err)
                                                                       + " DER: "  + gnutls_strerror(err_der));
        }
    }

    gnutls_privkey_init(&key);
    if (gnutls_privkey_import_x509(key, x509_key, GNUTLS_PRIVKEY_IMPORT_COPY) != GNUTLS_E_SUCCESS) {
        throw CryptoException("Can't load generic private key !");
    }
}

PrivateKey::PrivateKey(PrivateKey&& o) noexcept : key(o.key), x509_key(o.x509_key)
{
#if GNUTLS_VERSION_NUMBER < 0x030300
    // gnutls_global_init already succeeded at least once here so no real need to check.
    int ret = gnutls_global_init();
    assert(ret == GNUTLS_E_SUCCESS);
#endif
    o.key = nullptr;
    o.x509_key = nullptr;
};

PrivateKey::~PrivateKey()
{
    if (key) {
        gnutls_privkey_deinit(key);
        key = nullptr;
    }
    if (x509_key) {
        gnutls_x509_privkey_deinit(x509_key);
        x509_key = nullptr;
    }
#if GNUTLS_VERSION_NUMBER < 0x030300
    gnutls_global_deinit();
#endif
}

PrivateKey&
PrivateKey::operator=(PrivateKey&& o) noexcept
{
    if (key) {
        gnutls_privkey_deinit(key);
        key = nullptr;
    }
    if (x509_key) {
        gnutls_x509_privkey_deinit(x509_key);
        x509_key = nullptr;
    }
    key = o.key; x509_key = o.x509_key;
    o.key = nullptr; o.x509_key = nullptr;
    return *this;
}

Blob
PrivateKey::sign(const Blob& data) const
{
    if (!key)
        throw CryptoException("Can't sign data: no private key set !");
    gnutls_datum_t sig;
    const gnutls_datum_t dat {(unsigned char*)data.data(), (unsigned)data.size()};
    if (gnutls_privkey_sign_data(key, GNUTLS_DIG_SHA512, 0, &dat, &sig) != GNUTLS_E_SUCCESS)
        throw CryptoException("Can't sign data !");
    Blob ret(sig.data, sig.data+sig.size);
    gnutls_free(sig.data);
    return ret;
}

Blob
PrivateKey::decryptBloc(const uint8_t* src, size_t src_size) const
{
    const gnutls_datum_t dat {(uint8_t*)src, (unsigned)src_size};
    gnutls_datum_t out;
    int err = gnutls_privkey_decrypt_data(key, 0, &dat, &out);
    if (err != GNUTLS_E_SUCCESS)
        throw DecryptError(std::string("Can't decrypt data: ") + gnutls_strerror(err));
    Blob ret {out.data, out.data+out.size};
    gnutls_free(out.data);
    return ret;
}

Blob
PrivateKey::decrypt(const Blob& cipher) const
{
    if (!key)
        throw CryptoException("Can't decrypt data without private key !");

    unsigned key_len = 0;
    int err = gnutls_privkey_get_pk_algorithm(key, &key_len);
    if (err < 0)
        throw CryptoException("Can't read public key length !");
    if (err != GNUTLS_PK_RSA)
        throw CryptoException("Must be an RSA key");

    unsigned cypher_block_sz = key_len / 8;
    if (cipher.size() < cypher_block_sz)
        throw DecryptError("Unexpected cipher length");
    else if (cipher.size() == cypher_block_sz)
        return decryptBloc(cipher.data(), cypher_block_sz);

    return aesDecrypt(Blob {cipher.begin() + cypher_block_sz, cipher.end()}, decryptBloc(cipher.data(), cypher_block_sz));
}

Blob
PrivateKey::serialize(const std::string& password) const
{
    if (!x509_key)
        return {};
    size_t buf_sz = 8192;
    Blob buffer;
    buffer.resize(buf_sz);
    int err = password.empty()
        ? gnutls_x509_privkey_export_pkcs8(x509_key, GNUTLS_X509_FMT_PEM, nullptr, GNUTLS_PKCS_PLAIN, buffer.data(), &buf_sz)
        : gnutls_x509_privkey_export_pkcs8(x509_key, GNUTLS_X509_FMT_PEM, password.c_str(), GNUTLS_PKCS_PBES2_AES_256, buffer.data(), &buf_sz);
    if (err != GNUTLS_E_SUCCESS) {
        std::cerr << "Could not export private key - " << gnutls_strerror(err) << std::endl;
        return {};
    }
    buffer.resize(buf_sz);
    return buffer;
}

PublicKey
PrivateKey::getPublicKey() const
{
    gnutls_pubkey_t pk;
    gnutls_pubkey_init(&pk);
    PublicKey pk_ret {pk};
    if (gnutls_pubkey_import_privkey(pk, key, GNUTLS_KEY_KEY_CERT_SIGN | GNUTLS_KEY_CRL_SIGN, 0) != GNUTLS_E_SUCCESS)
        return {};
    return pk_ret;
}

PublicKey::PublicKey(const Blob& dat) : pk(nullptr)
{
    unpack(dat.data(), dat.size());
}

PublicKey::~PublicKey()
{
    if (pk) {
        gnutls_pubkey_deinit(pk);
        pk = nullptr;
    }
}

PublicKey&
PublicKey::operator=(PublicKey&& o) noexcept
{
    if (pk)
        gnutls_pubkey_deinit(pk);
    pk = o.pk;
    o.pk = nullptr;
    return *this;
}

void
PublicKey::pack(Blob& b) const
{
    std::vector<uint8_t> tmp(2048);
    size_t sz = tmp.size();
    int err = gnutls_pubkey_export(pk, GNUTLS_X509_FMT_DER, tmp.data(), &sz);
    if (err != GNUTLS_E_SUCCESS)
        throw CryptoException(std::string("Could not export public key: ") + gnutls_strerror(err));
    tmp.resize(sz);
    b.insert(b.end(), tmp.begin(), tmp.end());
}

void
PublicKey::unpack(const uint8_t* data, size_t data_size)
{
    if (pk)
        gnutls_pubkey_deinit(pk);
    gnutls_pubkey_init(&pk);
    const gnutls_datum_t dat {(uint8_t*)data, (unsigned)data_size};
    int err = gnutls_pubkey_import(pk, &dat, GNUTLS_X509_FMT_PEM);
    if (err != GNUTLS_E_SUCCESS)
        err = gnutls_pubkey_import(pk, &dat, GNUTLS_X509_FMT_DER);
    if (err != GNUTLS_E_SUCCESS)
        throw CryptoException(std::string("Could not read public key: ") + gnutls_strerror(err));
}

void
PublicKey::msgpack_unpack(msgpack::object o)
{
    if (o.type == msgpack::type::BIN)
        unpack((const uint8_t*)o.via.bin.ptr, o.via.bin.size);
    else {
        Blob dat = unpackBlob(o);
        unpack(dat.data(), dat.size());
    }
}

bool
PublicKey::checkSignature(const Blob& data, const Blob& signature) const {
    if (!pk)
        return false;
    const gnutls_datum_t sig {(uint8_t*)signature.data(), (unsigned)signature.size()};
    const gnutls_datum_t dat {(uint8_t*)data.data(), (unsigned)data.size()};
    int rc = gnutls_pubkey_verify_data2(pk, GNUTLS_SIGN_RSA_SHA512, 0, &dat, &sig);
    return rc >= 0;
}

void
PublicKey::encryptBloc(const uint8_t* src, size_t src_size, uint8_t* dst, size_t dst_size) const
{
    const gnutls_datum_t key_dat {(uint8_t*)src, (unsigned)src_size};
    gnutls_datum_t encrypted;
    auto err = gnutls_pubkey_encrypt_data(pk, 0, &key_dat, &encrypted);
    if (err != GNUTLS_E_SUCCESS)
        throw CryptoException(std::string("Can't encrypt data: ") + gnutls_strerror(err));
    if (encrypted.size != dst_size)
        throw CryptoException("Unexpected cypherblock size");
    std::copy_n(encrypted.data, encrypted.size, dst);
    gnutls_free(encrypted.data);
}

Blob
PublicKey::encrypt(const Blob& data) const
{
    if (!pk)
        throw CryptoException("Can't read public key !");

    unsigned key_len = 0;
    int err = gnutls_pubkey_get_pk_algorithm(pk, &key_len);
    if (err < 0)
        throw CryptoException("Can't read public key length !");
    if (err != GNUTLS_PK_RSA)
        throw CryptoException("Must be an RSA key");

    const unsigned max_block_sz = key_len / 8 - 11;
    const unsigned cypher_block_sz = key_len / 8;
    if (data.size() <= max_block_sz) {
        Blob ret(cypher_block_sz);
        encryptBloc(data.data(), data.size(), ret.data(), cypher_block_sz);
        return ret;
    }

    unsigned aes_key_sz = aesKeySize(max_block_sz);
    if (aes_key_sz == 0)
        throw CryptoException("Key is not long enough for AES128");
    Blob key(aes_key_sz);
    {
        crypto::random_device rdev;
        std::generate_n(key.begin(), key.size(), std::bind(rand_byte, std::ref(rdev)));
    }
    auto data_encrypted = aesEncrypt(data, key);

    Blob ret;
    ret.reserve(cypher_block_sz + data_encrypted.size());

    ret.resize(cypher_block_sz);
    encryptBloc(key.data(), key.size(), ret.data(), cypher_block_sz);
    ret.insert(ret.end(), data_encrypted.begin(), data_encrypted.end());
    return ret;
}

InfoHash
PublicKey::getId() const
{
    InfoHash id;
    size_t sz = id.size();
    if (gnutls_pubkey_get_key_id(pk, 0, id.data(), &sz) != GNUTLS_E_SUCCESS || sz != id.size())
        return {};
    return id;
}

Certificate::Certificate(const Blob& certData) : cert(nullptr)
{
    unpack(certData.data(), certData.size());
}

Certificate&
Certificate::operator=(Certificate&& o) noexcept
{
    if (cert)
        gnutls_x509_crt_deinit(cert);
    cert = o.cert;
    o.cert = nullptr;
    issuer = std::move(o.issuer);
    return *this;
}

void
Certificate::unpack(const uint8_t* dat, size_t dat_size)
{
    if (cert) {
        gnutls_x509_crt_deinit(cert);
        cert = nullptr;
    }
    gnutls_x509_crt_t* cert_list;
    unsigned cert_num;
    const gnutls_datum_t crt_dt {(uint8_t*)dat, (unsigned)dat_size};
    int err = gnutls_x509_crt_list_import2(&cert_list, &cert_num, &crt_dt, GNUTLS_X509_FMT_PEM, GNUTLS_X509_CRT_LIST_FAIL_IF_UNSORTED);
    if (err != GNUTLS_E_SUCCESS)
        err = gnutls_x509_crt_list_import2(&cert_list, &cert_num, &crt_dt, GNUTLS_X509_FMT_DER, GNUTLS_X509_CRT_LIST_FAIL_IF_UNSORTED);
    if (err != GNUTLS_E_SUCCESS || cert_num == 0) {
        cert = nullptr;
        throw CryptoException(std::string("Could not read certificate - ") + gnutls_strerror(err));
    }

    cert = cert_list[0];
    Certificate* crt = this;
    size_t i = 1;
    while (crt and i < cert_num) {
        crt->issuer = std::make_shared<Certificate>(cert_list[i++]);
        crt = crt->issuer.get();
    }
    gnutls_free(cert_list);
}

void
Certificate::msgpack_unpack(msgpack::object o)
{
    if (o.type == msgpack::type::BIN)
        unpack((const uint8_t*)o.via.bin.ptr, o.via.bin.size);
    else {
        Blob dat = unpackBlob(o);
        unpack(dat.data(), dat.size());
    }
}

void
Certificate::pack(Blob& b) const
{
    const Certificate* crt = this;
    while (crt) {
        std::string str;
        size_t buf_sz = 8192;
        str.resize(buf_sz);
        if (int err = gnutls_x509_crt_export(crt->cert, GNUTLS_X509_FMT_PEM, &(*str.begin()), &buf_sz)) {
            std::cerr << "Could not export certificate - " << gnutls_strerror(err) << std::endl;
            return;
        }
        str.resize(buf_sz);
        b.insert(b.end(), str.begin(), str.end());
        crt = crt->issuer.get();
    }
}

Certificate::~Certificate()
{
    if (cert) {
        gnutls_x509_crt_deinit(cert);
        cert = nullptr;
    }
}

PublicKey
Certificate::getPublicKey() const
{
    gnutls_pubkey_t pk;
    gnutls_pubkey_init(&pk);
    PublicKey pk_ret(pk);
    if (gnutls_pubkey_import_x509(pk, cert, 0) != GNUTLS_E_SUCCESS)
        return {};
    return pk_ret;
}

InfoHash
Certificate::getId() const
{
    if (not cert)
        return {};
    InfoHash id;
    size_t sz = id.size();
    if (gnutls_x509_crt_get_key_id(cert, 0, id.data(), &sz) != GNUTLS_E_SUCCESS || sz != id.size())
        throw CryptoException("Can't get certificate public key ID.");
    return id;
}

static std::string
getDN(gnutls_x509_crt_t cert, const char* oid, bool issuer = false)
{
    std::string dn;
    dn.resize(512);
    size_t dn_sz = dn.size();
    int ret = issuer
            ? gnutls_x509_crt_get_issuer_dn_by_oid(cert, oid, 0, 0, &(*dn.begin()), &dn_sz)
            : gnutls_x509_crt_get_dn_by_oid(       cert, oid, 0, 0, &(*dn.begin()), &dn_sz);
    if (ret != GNUTLS_E_SUCCESS)
        return {};  
    dn.resize(dn_sz);
    return dn;
}

std::string
Certificate::getName() const
{
    return getDN(cert, GNUTLS_OID_X520_COMMON_NAME);
}

std::string
Certificate::getUID() const
{
    return getDN(cert, GNUTLS_OID_LDAP_UID);
}

std::string
Certificate::getIssuerName() const
{
    return getDN(cert, GNUTLS_OID_X520_COMMON_NAME, true);
}

std::string
Certificate::getIssuerUID() const
{
    return getDN(cert, GNUTLS_OID_LDAP_UID, true);
}

static Certificate::NameType
typeFromGnuTLS(gnutls_x509_subject_alt_name_t type)
{
    switch(type) {
    case GNUTLS_SAN_DNSNAME:
        return Certificate::NameType::DNS;
    case GNUTLS_SAN_RFC822NAME:
        return Certificate::NameType::RFC822;
    case GNUTLS_SAN_URI:
        return Certificate::NameType::URI;
    case GNUTLS_SAN_IPADDRESS:
        return Certificate::NameType::IP;
    default:
        return Certificate::NameType::UNKNOWN;
    }
}

std::vector<std::pair<Certificate::NameType, std::string>>
Certificate::getAltNames() const
{
    std::vector<std::pair<NameType, std::string>> names;
    unsigned i = 0;
    std::string name;
    while (true) {
        name.resize(512);
        size_t name_sz = name.size();
        unsigned type;
        int ret = gnutls_x509_crt_get_subject_alt_name2(cert, i++, &(*name.begin()), &name_sz, &type, nullptr);
        if (ret == GNUTLS_E_REQUESTED_DATA_NOT_AVAILABLE)
            break;
        name.resize(name_sz);
        names.emplace_back(typeFromGnuTLS((gnutls_x509_subject_alt_name_t)type), name);
    }
    return names;
}

bool
Certificate::isCA() const
{
    unsigned critical;
    return gnutls_x509_crt_get_ca_status(cert, &critical) > 0;
}

std::string
Certificate::toString(bool chain) const
{
    std::ostringstream ss;
    const Certificate* crt = this;
    while (crt) {
        std::string str;
        size_t buf_sz = 8192;
        str.resize(buf_sz);
        if (int err = gnutls_x509_crt_export(crt->cert, GNUTLS_X509_FMT_PEM, &(*str.begin()), &buf_sz)) {
            std::cerr << "Could not export certificate - " << gnutls_strerror(err) << std::endl;
            return {};
        }
        str.resize(buf_sz);
        ss << str;
        if (not chain)
            break;
        crt = crt->issuer.get();
    }
    return ss.str();
}

PrivateKey
PrivateKey::generate(unsigned key_length)
{
#if GNUTLS_VERSION_NUMBER < 0x030300
    if (gnutls_global_init() != GNUTLS_E_SUCCESS)
        throw CryptoException("Can't initialize GnuTLS.");
#endif
    gnutls_x509_privkey_t key;
    if (gnutls_x509_privkey_init(&key) != GNUTLS_E_SUCCESS)
        throw CryptoException("Can't initialize private key.");
    int err = gnutls_x509_privkey_generate(key, GNUTLS_PK_RSA, key_length, 0);
    if (err != GNUTLS_E_SUCCESS) {
        gnutls_x509_privkey_deinit(key);
        throw CryptoException(std::string("Can't generate RSA key pair: ") + gnutls_strerror(err));
    }
    return PrivateKey{key};
}

crypto::Identity
generateIdentity(const std::string& name, crypto::Identity ca, unsigned key_length)
{
#if GNUTLS_VERSION_NUMBER < 0x030300
    if (gnutls_global_init() != GNUTLS_E_SUCCESS)
        return {};
#endif
    auto shared_key = std::make_shared<PrivateKey>(PrivateKey::generate(key_length));

    gnutls_x509_crt_t cert;
    if (gnutls_x509_crt_init(&cert) != GNUTLS_E_SUCCESS)
        return {};
    auto shared_crt = std::make_shared<Certificate>(cert);

    gnutls_x509_crt_set_activation_time(cert, time(NULL));
    gnutls_x509_crt_set_expiration_time(cert, time(NULL) + (5 * 365 * 24 * 60 * 60));
    if (gnutls_x509_crt_set_key(cert, shared_key->x509_key) != GNUTLS_E_SUCCESS) {
        std::cerr << "Error when setting certificate key" << std::endl;
        return {};
    }
    if (gnutls_x509_crt_set_version(cert, 3) != GNUTLS_E_SUCCESS) {
        std::cerr << "Error when setting certificate version" << std::endl;
        return {};
    }

    // TODO: compute the subject key using the recommended RFC method
    auto pk_id = shared_key->getPublicKey().getId();
    const std::string uid_str = pk_id.toString();

    gnutls_x509_crt_set_subject_key_id(cert, &pk_id, sizeof(pk_id));
    gnutls_x509_crt_set_dn_by_oid(cert, GNUTLS_OID_X520_COMMON_NAME, 0, name.data(), name.length());
    gnutls_x509_crt_set_dn_by_oid(cert, GNUTLS_OID_LDAP_UID, 0, uid_str.data(), uid_str.length());

    {
        random_device rdev;
        std::uniform_int_distribution<uint64_t> dist{};
        uint64_t cert_serial = dist(rdev);
        gnutls_x509_crt_set_serial(cert, &cert_serial, sizeof(cert_serial));
    }

    if (ca.first && ca.second) {
        gnutls_x509_crt_set_key_usage (cert, GNUTLS_KEY_DIGITAL_SIGNATURE | GNUTLS_KEY_DATA_ENCIPHERMENT);
        //if (gnutls_x509_crt_sign2(cert, ca.second->cert, ca.first->x509_key, get_dig(cert), 0) != GNUTLS_E_SUCCESS) {
        if (gnutls_x509_crt_privkey_sign(cert, ca.second->cert, ca.first->key, get_dig(cert), 0) != GNUTLS_E_SUCCESS) {
            std::cerr << "Error when signing certificate" << std::endl;
            return {};
        }
        shared_crt->issuer = ca.second;
    } else {
        gnutls_x509_crt_set_ca_status(cert, 1);
        gnutls_x509_crt_set_key_usage (cert, GNUTLS_KEY_DIGITAL_SIGNATURE | GNUTLS_KEY_KEY_CERT_SIGN);
        //if (gnutls_x509_crt_sign2(cert, cert, key, get_dig(cert), 0) != GNUTLS_E_SUCCESS) {
        if (gnutls_x509_crt_privkey_sign(cert, cert, shared_key->key, get_dig(cert), 0) != GNUTLS_E_SUCCESS) {
            std::cerr << "Error when signing certificate" << std::endl;
            return {};
        }
    }

#if GNUTLS_VERSION_NUMBER < 0x030300
    gnutls_global_deinit();
#endif

    return {shared_key, shared_crt};
}

}

}