How to create ISignatureFactory for creating a self-signed certificate

Question

I am trying to use c# to generate a X509Certificate2.

I came across this answer which is what I am looking for. But, that code is using absolute methods.

The method SetSignatureAlgorithm has the following warning

Not needed if Generate used with an ISignatureFactory

Also, the code certificateGenerator.Generate(issuerPrivateKey, random) has the following message

Use Generate with an ISignatureFactory

How can I create a ISignatureFactory to fix these two warnings?

Answer 1

Will this work for you? This method generates a private key on the fly, signs it with a self-signed certificate and returns the cert and key as a PKCS#12 bundle (can be saved in a .pfx file if need be).

public static X509Certificate2 CreateX509CryptCertificate(string name, int keyLength = 2048, int yearsValid = 3) {
    X509KeyStorageFlags storageFlags = X509KeyStorageFlags.PersistKeySet | 
                                       X509KeyStorageFlags.Exportable;
    using var rsa = RSA.Create(keyLength);
    var request = new CertificateRequest($"CN={name}", rsa, HashAlgorithmName.SHA256, RSASignaturePadding.Pkcs1);
    using X509Certificate2 ephemeral = request.CreateSelfSigned(DateTime.Now, DateTime.Now.AddYears(yearsValid));
    return new X509Certificate2(ephemeral.Export(X509ContentType.Pkcs12), string.Empty, storageFlags);
}

Answer 2

I found a way

var randomGenerator = new CryptoApiRandomGenerator();
var random = new SecureRandom(randomGenerator);
var subjectKeyPair = keyPairGenerator.GenerateKeyPair();
ISignatureFactory signatureFactory = new Asn1SignatureFactory(PkcsObjectIdentifiers.Sha256WithRsaEncryption.ToString(), subjectKeyPair.Private, random);