Create Self Signed Certificate Using OpenSSL

Source Code
Create Own Self signed Certificate from root certificate using OpenSSL wrapper. C#
Programmatically Create the ppk, cert, csr using C#.
Full Source code
Required Install-Package ManagedOpenSsl64 -Version 0.6.1.3

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.IO;
using System.Windows.Forms;

using OpenSSL.Core;
using OpenSSL.Crypto;
using OpenSSL.X509;
using System.Dynamic;


namespace CertificateGenerator
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            ISequenceNumber sn = new SimpleSerialNumber();
      
            CryptoKey key = Helper.CreateNewRsaKey(4096);

        
        X509Name subject = new X509Name();
            subject.Common = "Gyyone1";
            subject.Country = "MY";
            subject.Organization = "Gyyone";
            subject.StateOrProvince = "Penang";
            subject.OrganizationUnit = "Gyyone";

            var extensions = new List();
            extensions.Add(new OpenSSL.X509.X509V3ExtensionValue("basicConstraints", true, "CA:TRUE"));
            extensions.Add(new OpenSSL.X509.X509V3ExtensionValue("subjectKeyIdentifier", false, "hash"));
            extensions.Add(new OpenSSL.X509.X509V3ExtensionValue("authorityKeyIdentifier", false, "keyid:always,issuer:always"));

            X509CertificateAuthority CA = X509CertificateAuthority.SelfSigned(sn,key, MessageDigest.SHA512, subject, DateTime.Now, TimeSpan.FromDays(560), extensions);
            // Write the CA certificate and it's private key to file so that it can be re-used.
            Helper.WriteCert(CA,"CA.cer");
            Helper.WriteKey(key,"123456", "CAPrivate.key");
        

         //Create Signed Request
            CryptoKey key2 = Helper.CreateNewRsaKey(4096);
            X509Name subject2 = new X509Name();
            subject.Common = "Gyyone2";
            subject.Country = "MY";
            subject.Organization = "Gyyone";
            subject.StateOrProvince = "Penang";
            subject.OrganizationUnit = "Gyyone";
         
            X509Request request = new X509Request(2, subject2, key2);
            string path = Path.GetFullPath("openssl.cnf");
            OpenSSL.X509.Configuration temp = new Configuration("X64\\openssl.cnf");

           var signedcert = CA.ProcessRequest(request, DateTime.UtcNow, DateTime.UtcNow.AddYears(1), temp, "v3_ca", MessageDigest.SHA512);

            Helper.WriteCert(signedcert, "CA2.cer");
            Helper.WriteKey(key2, "123456", "CAPrivate2.key");

        }
    }
public static class Helper
    {
        public static CryptoKey CreateNewRsaKey(int numberOfBits)
        {
            var rsa = new RSA();
                BigNumber exponent = 0x10001; // this needs to be a prime number
                rsa.GenerateKeys(numberOfBits, exponent, null, null);

                return new CryptoKey(rsa);
            
        }
        public static void WriteCert(X509Certificate cert, string filepath)
        {
            using (var biocert = BIO.File(filepath, "w"))
            {
                cert.Write(biocert);
            }
        }
        public static void WriteCert(X509CertificateAuthority cert,string filepath)
        {
            using (var biocert = BIO.File(filepath, "w"))
            {
                cert.Certificate.Write(biocert);
            }           
        }

        public static void WriteKey(CryptoKey key,string password,string filepath)
        {
            using (var bioprivate = BIO.File(filepath, "w"))
            {
                key.WritePrivateKey(bioprivate, Cipher.DES_EDE3_CBC, password);
            }
               
        }
    }
}

If you do not have openssl.cnf please create your own one as below

#
# OpenSSL example configuration file.
# This is mostly being used for generation of certificate requests.
#

# This definition stops the following lines choking if HOME isn't
# defined.
HOME   = .
RANDFILE  = $ENV::HOME/.rnd

# Extra OBJECT IDENTIFIER info:
#oid_file  = $ENV::HOME/.oid
oid_section  = new_oids

# To use this configuration file with the "-extfile" option of the
# "openssl x509" utility, name here the section containing the
# X.509v3 extensions to use:
# extensions  = 
# (Alternatively, use a configuration file that has only
# X.509v3 extensions in its main [= default] section.)

[ new_oids ]

# We can add new OIDs in here for use by 'ca' and 'req'.
# Add a simple OID like this:
# testoid1=1.2.3.4
# Or use config file substitution like this:
# testoid2=${testoid1}.5.6

####################################################################
[ ca ]
default_ca = CA_default  # The default ca section

####################################################################
[ CA_default ]

dir  = ./demoCA  # Where everything is kept
certs  = $dir/certs  # Where the issued certs are kept
crl_dir  = $dir/crl  # Where the issued crl are kept
database = $dir/index.txt # database index file.
new_certs_dir = $dir/newcerts  # default place for new certs.

certificate = $dir/cacert.pem  # The CA certificate
serial  = $dir/serial   # The current serial number
crl  = $dir/crl.pem   # The current CRL
private_key = $dir/private/cakey.pem# The private key
RANDFILE = $dir/private/.rand # private random number file

x509_extensions = usr_cert  # The extentions to add to the cert

# Extensions to add to a CRL. Note: Netscape communicator chokes on V2 CRLs
# so this is commented out by default to leave a V1 CRL.
# crl_extensions = crl_ext

default_days = 365   # how long to certify for
default_crl_days= 30   # how long before next CRL
default_md = md5   # which md to use.
preserve = no   # keep passed DN ordering

# A few difference way of specifying how similar the request should look
# For type CA, the listed attributes must be the same, and the optional
# and supplied fields are just that :-)
policy  = policy_match

# For the CA policy
[ policy_match ]
countryName  = match
stateOrProvinceName = match
organizationName = match
organizationalUnitName = optional
commonName  = supplied
emailAddress  = optional

# For the 'anything' policy
# At this point in time, you must list all acceptable 'object'
# types.
[ policy_anything ]
countryName  = optional
stateOrProvinceName = optional
localityName  = optional
organizationName = optional
organizationalUnitName = optional
commonName  = supplied
emailAddress  = optional

####################################################################
[ req ]
default_bits  = 1024
default_keyfile  = privkey.pem
distinguished_name = req_distinguished_name
attributes  = req_attributes
x509_extensions = v3_ca # The extentions to add to the self signed cert

# Passwords for private keys if not present they will be prompted for
# input_password = secret
# output_password = secret

# This sets a mask for permitted string types. There are several options. 
# default: PrintableString, T61String, BMPString.
# pkix  : PrintableString, BMPString.
# utf8only: only UTF8Strings.
# nombstr : PrintableString, T61String (no BMPStrings or UTF8Strings).
# MASK:XXXX a literal mask value.
# WARNING: current versions of Netscape crash on BMPStrings or UTF8Strings
# so use this option with caution!
string_mask = nombstr

# req_extensions = v3_req # The extensions to add to a certificate request

[ req_distinguished_name ]
countryName   = Country Name (2 letter code)
countryName_default  = AU
countryName_min   = 2
countryName_max   = 2

stateOrProvinceName  = State or Province Name (full name)
stateOrProvinceName_default = Some-State

localityName   = Locality Name (eg, city)

0.organizationName  = Organization Name (eg, company)
0.organizationName_default = Internet Widgits Pty Ltd

# we can do this but it is not needed normally :-)
#1.organizationName  = Second Organization Name (eg, company)
#1.organizationName_default = World Wide Web Pty Ltd

organizationalUnitName  = Organizational Unit Name (eg, section)
#organizationalUnitName_default =

commonName   = Common Name (eg, YOUR name)
commonName_max   = 64

emailAddress   = Email Address
emailAddress_max  = 40

# SET-ex3   = SET extension number 3

[ req_attributes ]
challengePassword  = A challenge password
challengePassword_min  = 4
challengePassword_max  = 20

unstructuredName  = An optional company name

[ usr_cert ]

# These extensions are added when 'ca' signs a request.

# This goes against PKIX guidelines but some CAs do it and some software
# requires this to avoid interpreting an end user certificate as a CA.

basicConstraints=CA:FALSE

# Here are some examples of the usage of nsCertType. If it is omitted
# the certificate can be used for anything *except* object signing.

# This is OK for an SSL server.
# nsCertType   = server

# For an object signing certificate this would be used.
# nsCertType = objsign

# For normal client use this is typical
# nsCertType = client, email

# and for everything including object signing:
# nsCertType = client, email, objsign

# This is typical in keyUsage for a client certificate.
# keyUsage = nonRepudiation, digitalSignature, keyEncipherment

# This will be displayed in Netscape's comment listbox.
nsComment   = "OpenSSL Generated Certificate"

# PKIX recommendations harmless if included in all certificates.
subjectKeyIdentifier=hash
authorityKeyIdentifier=keyid,issuer:always

# This stuff is for subjectAltName and issuerAltname.
# Import the email address.
# subjectAltName=email:copy

# Copy subject details
# issuerAltName=issuer:copy

#nsCaRevocationUrl  = http://www.domain.dom/ca-crl.pem
#nsBaseUrl
#nsRevocationUrl
#nsRenewalUrl
#nsCaPolicyUrl
#nsSslServerName

[ v3_req ]

# Extensions to add to a certificate request

basicConstraints = CA:FALSE
keyUsage = nonRepudiation, digitalSignature, keyEncipherment

[ v3_ca ]


# Extensions for a typical CA


# PKIX recommendation.

subjectKeyIdentifier=hash

authorityKeyIdentifier=keyid:always,issuer:always

# This is what PKIX recommends but some broken software chokes on critical
# extensions.
#basicConstraints = critical,CA:true
# So we do this instead.
basicConstraints = CA:true

# Key usage: this is typical for a CA certificate. However since it will
# prevent it being used as an test self-signed certificate it is best
# left out by default.
# keyUsage = cRLSign, keyCertSign

# Some might want this also
# nsCertType = sslCA, emailCA

# Include email address in subject alt name: another PKIX recommendation
# subjectAltName=email:copy
# Copy issuer details
# issuerAltName=issuer:copy

# DER hex encoding of an extension: beware experts only!
# obj=DER:02:03
# Where 'obj' is a standard or added object
# You can even override a supported extension:
# basicConstraints= critical, DER:30:03:01:01:FF

[ crl_ext ]

# CRL extensions.
# Only issuerAltName and authorityKeyIdentifier make any sense in a CRL.

# issuerAltName=issuer:copy
authorityKeyIdentifier=keyid:always,issuer:always