Generates a self-signed x509 certificate using OpenSSL.

CMakeLists.txt

# A simple CMake script for building the application.
cmake_minimum_required(VERSION 2.8)
project(create-x509)

# Our only dependency is OpenSSL
find_package(OpenSSL REQUIRED)

include_directories(${OPENSSL_INCLUDE_DIR})

add_executable(create-x509 create-x509.cpp)
target_link_libraries(create-x509 ${OPENSSL_LIBRARIES})

install(TARGETS create-x509 RUNTIME DESTINATION bin)

create-x509.cpp

#include <cstdio>
#include <iostream>

#include <openssl/pem.h>
#include <openssl/x509.h>

/* Generates a 2048-bit RSA key. */
EVP_PKEY * generate_key()
{
    /* Allocate memory for the EVP_PKEY structure. */
    EVP_PKEY * pkey = EVP_PKEY_new();
    if(!pkey)
    {
        std::cerr << "Unable to create EVP_PKEY structure." << std::endl;
        return NULL;
    }
    
    /* Generate the RSA key and assign it to pkey. */
    RSA * rsa = RSA_generate_key(2048, RSA_F4, NULL, NULL);
    if(!EVP_PKEY_assign_RSA(pkey, rsa))
    {
        std::cerr << "Unable to generate 2048-bit RSA key." << std::endl;
        EVP_PKEY_free(pkey);
        return NULL;
    }
    
    /* The key has been generated, return it. */
    return pkey;
}

/* Generates a self-signed x509 certificate. */
X509 * generate_x509(EVP_PKEY * pkey)
{
    /* Allocate memory for the X509 structure. */
    X509 * x509 = X509_new();
    if(!x509)
    {
        std::cerr << "Unable to create X509 structure." << std::endl;
        return NULL;
    }
    
    /* Set the serial number. */
    ASN1_INTEGER_set(X509_get_serialNumber(x509), 1);
    
    /* This certificate is valid from now until exactly one year from now. */
    X509_gmtime_adj(X509_get_notBefore(x509), 0);
    X509_gmtime_adj(X509_get_notAfter(x509), 31536000L);
    
    /* Set the public key for our certificate. */
    X509_set_pubkey(x509, pkey);
    
    /* We want to copy the subject name to the issuer name. */
    X509_NAME * name = X509_get_subject_name(x509);
    
    /* Set the country code and common name. */
    X509_NAME_add_entry_by_txt(name, "C",  MBSTRING_ASC, (unsigned char *)"CA",        -1, -1, 0);
    X509_NAME_add_entry_by_txt(name, "O",  MBSTRING_ASC, (unsigned char *)"MyCompany", -1, -1, 0);
    X509_NAME_add_entry_by_txt(name, "CN", MBSTRING_ASC, (unsigned char *)"localhost", -1, -1, 0);
    
    /* Now set the issuer name. */
    X509_set_issuer_name(x509, name);
    
    /* Actually sign the certificate with our key. */
    if(!X509_sign(x509, pkey, EVP_sha1()))
    {
        std::cerr << "Error signing certificate." << std::endl;
        X509_free(x509);
        return NULL;
    }
    
    return x509;
}

bool write_to_disk(EVP_PKEY * pkey, X509 * x509)
{
    /* Open the PEM file for writing the key to disk. */
    FILE * pkey_file = fopen("key.pem", "wb");
    if(!pkey_file)
    {
        std::cerr << "Unable to open \"key.pem\" for writing." << std::endl;
        return false;
    }
    
    /* Write the key to disk. */
    bool ret = PEM_write_PrivateKey(pkey_file, pkey, NULL, NULL, 0, NULL, NULL);
    fclose(pkey_file);
    
    if(!ret)
    {
        std::cerr << "Unable to write private key to disk." << std::endl;
        return false;
    }
    
    /* Open the PEM file for writing the certificate to disk. */
    FILE * x509_file = fopen("cert.pem", "wb");
    if(!x509_file)
    {
        std::cerr << "Unable to open \"cert.pem\" for writing." << std::endl;
        return false;
    }
    
    /* Write the certificate to disk. */
    ret = PEM_write_X509(x509_file, x509);
    fclose(x509_file);
    
    if(!ret)
    {
        std::cerr << "Unable to write certificate to disk." << std::endl;
        return false;
    }
    
    return true;
}

int main(int argc, char ** argv)
{
    /* Generate the key. */
    std::cout << "Generating RSA key..." << std::endl;
    
    EVP_PKEY * pkey = generate_key();
    if(!pkey)
        return 1;
    
    /* Generate the certificate. */
    std::cout << "Generating x509 certificate..." << std::endl;
    
    X509 * x509 = generate_x509(pkey);
    if(!x509)
    {
        EVP_PKEY_free(pkey);
        return 1;
    }
    
    /* Write the private key and certificate out to disk. */
    std::cout << "Writing key and certificate to disk..." << std::endl;
    
    bool ret = write_to_disk(pkey, x509);
    EVP_PKEY_free(pkey);
    X509_free(x509);
    
    if(ret)
    {
        std::cout << "Success!" << std::endl;
        return 0;
    }
    else
        return 1;
}

LICENSE.txt

The MIT License (MIT)

Copyright (c) 2022 Nathan Osman

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

if the private key is srored in an engine e.g pkcs11 for example :

EVP_PKEY * pkey = ENGINE_load_private_key(eng, "pkcs11:model=SoftHSM%20v2;manufacturer=SoftHSM%20project;serial=09abc2fa100c0143;token=token1;object=ecc-key1;type=private?pin-value=12345", NULL, NULL);
X509_set_pubkey(x509, pkey) //will crash