RSA signature Java to C#

Question

I have a tool which creates a signature. I am looking for equivalent code in dot net core 2.1.

Java Code: sign(currentdate,'some text','SHA1WithRSA')

public String sign(String date, String subjectId, String algorithm){
    Signature rsa = Signature.getInstance(algorithm);
    rsa.initSign(this.getPrivate());
    rsa.update(subjectId.getBytes());
    rsa.update(date.getBytes());
    String signature = new String(Base64.getEncoder().encode(rsa.sign()));
    return signature;
}

public PrivateKey getPrivate() {
    String privateKeyPEM = "<This is the private key string";

    byte[] encoded = Base64.getDecoder().decode(privateKeyPEM);
    KeyFactory kf = KeyFactory.getInstance("RSA");
    PKCS8EncodedKeySpec spec = new PKCS8EncodedKeySpec(encoded);
    return kf.generatePrivate(spec);
}

Suggest a way to generate dot net core 2.1 equivalent code for the above with or without 3rd party tool.

What did you try so far?

TheTanic
– TheTanic

2021-05-10 05:53:10 +00:00
Commented May 10, 2021 at 5:53 — TheTanic
– TheTanic, Commented May 10, 2021 at 5:53

sa-es-ir · Accepted Answer · 2021-05-10 06:14:13Z

This is work for me using Portable.BouncyCastle library.

 private string GetSign(string data)
        {
            using (var rsa = new RSACryptoServiceProvider())
            {
                var privateKey = new StringBuilder();
                privateKey.AppendLine("-----BEGIN RSA PRIVATE KEY-----");
                privateKey.AppendLine("private key as string");
                privateKey.AppendLine("-----END RSA PRIVATE KEY-----");

                var pem = new PemReader(new StringReader(privateKey.ToString()));
                var keyPair = (AsymmetricCipherKeyPair)pem.ReadObject();
                var privateKeyParameters = (RsaPrivateCrtKeyParameters)keyPair.Private;
                var rsaParameters = DotNetUtilities.ToRSAParameters(privateKeyParameters);

                rsa.ImportParameters(rsaParameters);
                var sign = rsa.SignData(Encoding.UTF8.GetBytes(data), new HashAlgorithmName("SHA1") /*pass your algorithm*/,
                    RSASignaturePadding.Pkcs1);

                return Convert.ToBase64String(sign);
            }
        }

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