Example encryption and decryption

using System;
using System.IO;
using System.Linq;
using System.Net;
using System.Security.Cryptography;
using System.Text;
using Landingpage.Models.XML;
using Org.BouncyCastle.Crypto;
using Org.BouncyCastle.Crypto.Encodings;
using Org.BouncyCastle.Crypto.Engines;
using Org.BouncyCastle.OpenSsl;

namespace Landingpage.Models
{
  public class ExampleUseage
  {
    public bool ReiceverRole_JustReceivedAPayload_NowCheckEncryption_Valid(
      string payloadFileXml, // should contain contents like https://edi4steel-eu.atlassian.net/wiki/spaces/EDI4STEEL/pages/884762/Standardized+order
      string payloadMetadata // should contain contents like https://edi4steel-eu.atlassian.net/wiki/spaces/EDI4STEEL/pages/950303/Example+payload+metadata+API
      )
    {
      // convert payloadMetadata (xml) to an object, change below object to actual type
      SubmitMessage payloadMetadataObject = payloadMetadata;
      var algorithm = payloadMetadataObject.Payloads.Payload.PayloadProperties.FirstOrDefault(x => x.Name == "HashAlgorithm");
      var hash = payloadMetadataObject.Payloads.Payload.PayloadProperties.FirstOrDefault(x => x.Name == "Hash");
      var isencrypted = payloadMetadataObject.Payloads.Payload.PayloadProperties.FirstOrDefault(x => x.Name == "HashIsEncrypted");
      if (isencrypted.Value == "True")
      {
        // url parameter is edi4steel.eu when sender uses edi4steel API, if they use
        // their own accesspoint or saas accesspoint the other end must have provided the url
        // to you and you must have stored it somewhere..
        var decryptedHash = AccesspointEncryptionHelper.Descrypt("https://edi4steel.eu", hash.Value);
        string hashToCheck = AccesspointEncryptionHelper.Sha256_hash(payloadFileXml);
        if (decryptedHash == hashToCheck)
          return true;
        return false; // hashes not equal
      }
      return true; // not hashed, fine
    }

    public string SenderRole_HashWithPrivateKey_BeforeSend(
      string payloadXml // should contain contents like https://edi4steel-eu.atlassian.net/wiki/spaces/EDI4STEEL/pages/884762/Standardized+order
      )
    {
      // this method is only required if you have your own accesspoint or saas accesspoint
      // the api version does this for you!

      // this is a private key generated by Lets Encrypt (auto generated)
      // and is done so (and others must also do so) with an RSA algorithm, not Eliptic cure etc!
      string privateKey = File.ReadAllText(@"D:\Certificates\domain-key.pem");

      // the returned value should be stored value of hash in DeliverMessage
      return AccesspointEncryptionHelper.Encrypt(privateKey, AccesspointEncryptionHelper.Sha256_hash(payloadXml));
    }
  }

  /// <summary>
  /// Helper method for encryption
  /// </summary>
  public static class AccesspointEncryptionHelper
  {
    /// <summary>
    /// The default algorithm to use
    /// </summary>
    public static string DefaultHashAlgorithm = "SHA256";

    /// <summary>
    /// Encrypt some plain text
    /// </summary>
    /// <param name="privateKeyPemFormat"></param>
    /// <param name="plaingTextInput"></param>
    /// <returns></returns>
    public static string Encrypt(string privateKeyPemFormat, string plaingTextInput)
    {
      return RsaEncryptWithPrivate(plaingTextInput, privateKeyPemFormat);
    }

    /// <summary>
    /// Decrypt some encrypted text
    /// </summary>
    /// <param name="urlForCertificatePublicKey"></param>
    /// <param name="encryptedText"></param>
    /// <returns></returns>
    public static string Descrypt(string urlForCertificatePublicKey, string encryptedText)
    {
      ServicePointManager.Expect100Continue = true;
      ServicePointManager.SecurityProtocol |= SecurityProtocolType.Tls12 | SecurityProtocolType.Tls11 | SecurityProtocolType.Tls | SecurityProtocolType.Ssl3;

      HttpWebRequest request = (HttpWebRequest)WebRequest.Create(urlForCertificatePublicKey);
      HttpWebResponse response = (HttpWebResponse)request.GetResponse();
      response.Close();

      System.Security.Cryptography.X509Certificates.X509Certificate cert = request.ServicePoint.Certificate;
      Org.BouncyCastle.X509.X509Certificate convertedCert = new Org.BouncyCastle.X509.X509CertificateParser().ReadCertificate(cert.GetRawCertData());
      AsymmetricKeyParameter key = convertedCert.GetPublicKey();
      return RsaDecryptWithPublic(encryptedText, key);
    }

    /// <summary>
    /// Has some vlaue
    /// </summary>
    /// <param name="value"></param>
    /// <returns></returns>
    public static string Sha256_hash(string value)
    {
      StringBuilder Sb = new StringBuilder();

      using (SHA256 hash = SHA256Managed.Create())
      {
        Encoding enc = Encoding.UTF8;
        byte[] result = hash.ComputeHash(enc.GetBytes(value));

        foreach (byte b in result)
          Sb.Append(b.ToString("x2"));
      }

      return Sb.ToString();
    }

    private static string RsaEncryptWithPrivate(string clearText, string privateKey)
    {
      var bytesToEncrypt = Encoding.UTF8.GetBytes(clearText);
      var encryptEngine = new Pkcs1Encoding(new RsaEngine());

      using (var txtreader = new StringReader(privateKey))
      {
        var keyPair = (AsymmetricCipherKeyPair)new PemReader(txtreader).ReadObject();
        encryptEngine.Init(true, keyPair.Private);
      }

      var encrypted = Convert.ToBase64String(encryptEngine.ProcessBlock(bytesToEncrypt, 0, bytesToEncrypt.Length));
      return encrypted;
    }

    private static string RsaDecryptWithPublic(string base64Input, AsymmetricKeyParameter publicKey)
    {
      var bytesToDecrypt = Convert.FromBase64String(base64Input);
      var decryptEngine = new Pkcs1Encoding(new RsaEngine());
      var keyParameter = publicKey;

      decryptEngine.Init(false, keyParameter);

      var decrypted = Encoding.UTF8.GetString(decryptEngine.ProcessBlock(bytesToDecrypt, 0, bytesToDecrypt.Length));
      return decrypted;
    }
  }
}
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