Generate a self-signed certificate on the fly

Question

I searched around, but I didn\'t find a clear example. I want to create a self-signed (self-)trusted certificate programmatically (C#), following these step

Answer 1

After integrating changes from multiple posts, I finally got this code to work!

static void Main(string[] args)
{
    AsymmetricKeyParameter caPrivateKey = null;
    var caCert = GenerateCACertificate("CN=MyROOTCA", ref caPrivateKey);
    addCertToStore(caCert, StoreName.Root, StoreLocation.LocalMachine);

    var clientCert = GenerateSelfSignedCertificate("CN=127.0.0.1", "CN=MyROOTCA", caPrivateKey);

    var p12 = clientCert.Export(X509ContentType.Pfx);

    addCertToStore(new X509Certificate2(p12, (string)null, X509KeyStorageFlags.Exportable | X509KeyStorageFlags.PersistKeySet), StoreName.My, StoreLocation.LocalMachine);
}

public static X509Certificate2 GenerateSelfSignedCertificate(string subjectName, string issuerName, AsymmetricKeyParameter issuerPrivKey)
{
    const int keyStrength = 2048;

    // Generating Random Numbers
    CryptoApiRandomGenerator randomGenerator = new CryptoApiRandomGenerator();
    SecureRandom random = new SecureRandom(randomGenerator);

    // The Certificate Generator
    X509V3CertificateGenerator certificateGenerator = new X509V3CertificateGenerator();

    // Serial Number
    BigInteger serialNumber = BigIntegers.CreateRandomInRange(BigInteger.One, BigInteger.ValueOf(Int64.MaxValue), random);
    certificateGenerator.SetSerialNumber(serialNumber);

    // Signature Algorithm
    const string signatureAlgorithm = "SHA256WithRSA";
    certificateGenerator.SetSignatureAlgorithm(signatureAlgorithm);

    // Issuer and Subject Name
    X509Name subjectDN = new X509Name(subjectName);
    X509Name issuerDN = new X509Name(issuerName);
    certificateGenerator.SetIssuerDN(issuerDN);
    certificateGenerator.SetSubjectDN(subjectDN);

    // Valid For
    DateTime notBefore = DateTime.UtcNow.Date;
    DateTime notAfter = notBefore.AddYears(2);

    certificateGenerator.SetNotBefore(notBefore);
    certificateGenerator.SetNotAfter(notAfter);

    // Subject Public Key
    AsymmetricCipherKeyPair subjectKeyPair;
    var keyGenerationParameters = new KeyGenerationParameters(random, keyStrength);
    var keyPairGenerator = new RsaKeyPairGenerator();
    keyPairGenerator.Init(keyGenerationParameters);
    subjectKeyPair = keyPairGenerator.GenerateKeyPair();

    certificateGenerator.SetPublicKey(subjectKeyPair.Public);

    // Generating the Certificate
    AsymmetricCipherKeyPair issuerKeyPair = subjectKeyPair;

    // Selfsign certificate
    Org.BouncyCastle.X509.X509Certificate certificate = certificateGenerator.Generate(issuerPrivKey, random);


    // Corresponding private key
    PrivateKeyInfo info = PrivateKeyInfoFactory.CreatePrivateKeyInfo(subjectKeyPair.Private);


    // Merge into X509Certificate2
    X509Certificate2 x509 = new System.Security.Cryptography.X509Certificates.X509Certificate2(certificate.GetEncoded());

    Asn1Sequence seq = (Asn1Sequence)Asn1Object.FromByteArray(info.PrivateKey.GetDerEncoded());
    if (seq.Count != 9)
    {
        //throw new PemException("malformed sequence in RSA private key");
    }

    RsaPrivateKeyStructure rsa = new RsaPrivateKeyStructure(seq);
    RsaPrivateCrtKeyParameters rsaparams = new RsaPrivateCrtKeyParameters(
        rsa.Modulus, rsa.PublicExponent, rsa.PrivateExponent, rsa.Prime1, rsa.Prime2, rsa.Exponent1, rsa.Exponent2, rsa.Coefficient);

    x509.PrivateKey = ToDotNetKey(rsaparams); //x509.PrivateKey = DotNetUtilities.ToRSA(rsaparams);
    return x509;
}

public static AsymmetricAlgorithm ToDotNetKey(RsaPrivateCrtKeyParameters privateKey)
{
    var cspParams = new CspParameters
    {
        KeyContainerName = Guid.NewGuid().ToString(),
        KeyNumber = (int)KeyNumber.Exchange,
        Flags = CspProviderFlags.UseMachineKeyStore
    };

    var rsaProvider = new RSACryptoServiceProvider(cspParams);
    var parameters = new RSAParameters
    {
        Modulus = privateKey.Modulus.ToByteArrayUnsigned(),
        P = privateKey.P.ToByteArrayUnsigned(),
        Q = privateKey.Q.ToByteArrayUnsigned(),
        DP = privateKey.DP.ToByteArrayUnsigned(),
        DQ = privateKey.DQ.ToByteArrayUnsigned(),
        InverseQ = privateKey.QInv.ToByteArrayUnsigned(),
        D = privateKey.Exponent.ToByteArrayUnsigned(),
        Exponent = privateKey.PublicExponent.ToByteArrayUnsigned()
    };

    rsaProvider.ImportParameters(parameters);
    return rsaProvider;
}

public static X509Certificate2 GenerateCACertificate(string subjectName, ref AsymmetricKeyParameter CaPrivateKey)
{
    const int keyStrength = 2048;

    // Generating Random Numbers
    CryptoApiRandomGenerator randomGenerator = new CryptoApiRandomGenerator();
    SecureRandom random = new SecureRandom(randomGenerator);

    // The Certificate Generator
    X509V3CertificateGenerator certificateGenerator = new X509V3CertificateGenerator();

    // Serial Number
    BigInteger serialNumber = BigIntegers.CreateRandomInRange(BigInteger.One, BigInteger.ValueOf(Int64.MaxValue), random);
    certificateGenerator.SetSerialNumber(serialNumber);

    // Signature Algorithm
    const string signatureAlgorithm = "SHA256WithRSA";
    certificateGenerator.SetSignatureAlgorithm(signatureAlgorithm);

    // Issuer and Subject Name
    X509Name subjectDN = new X509Name(subjectName);
    X509Name issuerDN = subjectDN;
    certificateGenerator.SetIssuerDN(issuerDN);
    certificateGenerator.SetSubjectDN(subjectDN);

    // Valid For
    DateTime notBefore = DateTime.UtcNow.Date;
    DateTime notAfter = notBefore.AddYears(2);

    certificateGenerator.SetNotBefore(notBefore);
    certificateGenerator.SetNotAfter(notAfter);

    // Subject Public Key
    AsymmetricCipherKeyPair subjectKeyPair;
    KeyGenerationParameters keyGenerationParameters = new KeyGenerationParameters(random, keyStrength);
    RsaKeyPairGenerator keyPairGenerator = new RsaKeyPairGenerator();
    keyPairGenerator.Init(keyGenerationParameters);
    subjectKeyPair = keyPairGenerator.GenerateKeyPair();

    certificateGenerator.SetPublicKey(subjectKeyPair.Public);

    // Generating the Certificate
    AsymmetricCipherKeyPair issuerKeyPair = subjectKeyPair;

    // Selfsign certificate
    Org.BouncyCastle.X509.X509Certificate certificate = certificateGenerator.Generate(issuerKeyPair.Private, random);
    X509Certificate2 x509 = new System.Security.Cryptography.X509Certificates.X509Certificate2(certificate.GetEncoded());

    CaPrivateKey = issuerKeyPair.Private;

    return x509;
    //return issuerKeyPair.Private;
}

public static bool addCertToStore(System.Security.Cryptography.X509Certificates.X509Certificate2 cert, System.Security.Cryptography.X509Certificates.StoreName st, System.Security.Cryptography.X509Certificates.StoreLocation sl)
{
    bool bRet = false;

    try
    {
        X509Store store = new X509Store(st, sl);
        store.Open(OpenFlags.ReadWrite);
        store.Add(cert);

        store.Close();
    }
    catch
    {

    }

    return bRet;
}