OriginProof.cs

public static string GetOriginProof(int amount, string currency, string userToken)
{
    var uuid = Guid.NewGuid().ToString();

    JObject jsonObject = new JObject();
    jsonObject["amount"] = amount;
    jsonObject["currency"] = currency;
    jsonObject["user_token"] = userToken;
    jsonObject["id"] = uuid;

    var data = jsonObject.ToString();

    byte[] originalData = Encoding.UTF8.GetBytes(data);
    RSACryptoServiceProvider RSAalg = new RSACryptoServiceProvider();
    RSAParameters Key = RSAalg.ExportParameters(true);
    var signatureBytes = HashAndSignBytes(originalData, Key);
    string signature = Convert.ToBase64String(signatureBytes);

    JObject originProof = new JObject();
    originProof["data"] = data;
    originProof["signature"] = signature;
    var originProofString = originProof.ToString();

    return Convert.ToBase64String(Encoding.UTF8.GetBytes(originProofString));
}

public static byte[] HashAndSignBytes(byte[] dataToSign, RSAParameters key)
{
    try
    {
        RSACryptoServiceProvider rsAalg = new RSACryptoServiceProvider();

        rsAalg.ImportParameters(key);

        return rsAalg.SignData(dataToSign, new SHA1CryptoServiceProvider());
    }
    catch (CryptographicException e)
    {
        return null;
    }
}