public String sign(String message) throws SignatureException{ 
try {
Signature sign = Signature.getInstance(“SHA1withRSA"); 
sign.initSign(privateKey); 
sign.update(message.getBytes(“UTF-8"));
return new
String(Base64.encodeBase64(sign.sign()),“UTF-8");
} catch 
(Exception ex) {
throw new SignatureException(ex);
}
}

string privatekey = "7777777777777777777777";
            string message = "test mes";


            RSACryptoServiceProvider rsa = new RSACryptoServiceProvider();
            rsa.FromXmlString(privatekey);

            RSAPKCS1SignatureFormatter RSAFormatter = new RSAPKCS1SignatureFormatter(rsa);

            RSAFormatter.SetHashAlgorithm("SHA1withRSA");



            byte[] dataToSign = Encoding.UTF8.GetBytes(message);

            byte[] SignedHashValue = RSAFormatter.CreateSignature(dataToSign);

            string s = Convert.ToBase64String(SignedHashValue, 0, SignedHashValue.Length);

static string publicKey =
                 "<RSAKeyValue><Modulus>21wEnTU+mcD2w0Lfo1Gv4rtcSWsQJQTNa6gio05AOkV/Er9w3Y13Ddo5wGtjJ19402S71HUeN0vbKILLJdRSES5MHSdJPSVrOqdrll/vLXxDxWs/U0UT1c8u6k/Ogx9hTtZxYwoeYqdhDblof3E75d9n2F0Zvf6iTb4cI7j6fMs=</Modulus><Exponent>AQAB</Exponent></RSAKeyValue>";

        static string privateKey =
            "<RSAKeyValue><Modulus>21wEnTU+mcD2w0Lfo1Gv4rtcSWsQJQTNa6gio05AOkV/Er9w3Y13Ddo5wGtjJ19402S71HUeN0vbKILLJdRSES5MHSdJPSVrOqdrll/vLXxDxWs/U0UT1c8u6k/Ogx9hTtZxYwoeYqdhDblof3E75d9n2F0Zvf6iTb4cI7j6fMs=</Modulus><Exponent>AQAB</Exponent><P>/aULPE6jd5IkwtWXmReyMUhmI/nfwfkQSyl7tsg2PKdpcxk4mpPZUdEQhHQLvE84w2DhTyYkPHCtq/mMKE3MHw==</P><Q>3WV46X9Arg2l9cxb67KVlNVXyCqc/w+LWt/tbhLJvV2xCF/0rWKPsBJ9MC6cquaqNPxWWEav8RAVbmmGrJt51Q==</Q><DP>8TuZFgBMpBoQcGUoS2goB4st6aVq1FcG0hVgHhUI0GMAfYFNPmbDV3cY2IBt8Oj/uYJYhyhlaj5YTqmGTYbATQ==</DP><DQ>FIoVbZQgrAUYIHWVEYi/187zFd7eMct/Yi7kGBImJStMATrluDAspGkStCWe4zwDDmdam1XzfKnBUzz3AYxrAQ==</DQ><InverseQ>QPU3Tmt8nznSgYZ+5jUo9E0SfjiTu435ihANiHqqjasaUNvOHKumqzuBZ8NRtkUhS6dsOEb8A2ODvy7KswUxyA==</InverseQ><D>cgoRoAUpSVfHMdYXW9nA3dfX75dIamZnwPtFHq80ttagbIe4ToYYCcyUz5NElhiNQSESgS5uCgNWqWXt5PnPu4XmCXx6utco1UVH8HGLahzbAnSy6Cj3iUIQ7Gj+9gQ7PkC434HTtHazmxVgIR5l56ZjoQ8yGNCPZnsdYEmhJWk=</D></RSAKeyValue>";


        static string Sign(string Message)
        {
            string rez = "";
            var testData = Encoding.UTF8.GetBytes(Message);
            using (var rsa = new RSACryptoServiceProvider())
            {

                try
                {
                    rsa.FromXmlString(publicKey);
                    
                    var encryptedData = rsa.Encrypt(testData, true);

                    rez = Convert.ToBase64String(encryptedData);
                }
                finally
                {
                    rsa.PersistKeyInCsp = false;
                }

            }

            return rez;
        }

        static bool verify(string base64Encrypted)
        {
            bool rez = false;

            using (var rsa = new RSACryptoServiceProvider())
            {

                try
                {
                    rsa.FromXmlString(privateKey);

                    var resultBytes = Convert.FromBase64String(base64Encrypted);
                    var decryptedBytes = rsa.Decrypt(resultBytes, true);
                    rez = true;
                    //var decryptedData = Encoding.UTF8.GetString(decryptedBytes);

                }
                catch(Exception e) { string s = e.Message;  }
                finally
                {
                    rsa.PersistKeyInCsp = false;
                }

            }

            return rez;
        }


        static void Main(string[] args)
        {
           

            var base64Encrypted = Sign(Message);

            

            var rez = verify(base64Encrypted);


           

           
        }
    }