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namespace AES {
using System.IO;
using System;
using System.Security.Cryptography;

class Program {

public static byte[] FromBase64Url(string base64Url) {
// Replace '-' with '+' and '_' with '/' for standard Base64
string base64 = base64Url.Replace('-', '+').Replace('_', '/');

// Add padding if necessary. Base64 strings should have a length that is a multiple of 4.
/**/
int padding = 3 - ((base64.Length + 3) % 4);
if (padding > 0) {
base64 += new string('=', padding);
}
//*/
// Convert the Base64 string to a byte array
return Convert.FromBase64String(base64);
}

static void Main(string[] args) {
var mode = "CFB";
var message = "HgnDCsJPaosJkvCF8jqPHUdSOVtCO2GeVQWiBCV9ocDRDM2EGUzNYRXy";
byte[] encrypted;
var plaintext = "";

//if (args.Length >0) mode=args[0];
if (args.Length > 1) message = args[1];

try {

using
var aes = Aes.Create();

aes.Mode = CipherMode.CFB;

if (mode == "CBC") aes.Mode = CipherMode.CBC;

else if (mode == "CFB") aes.Mode = CipherMode.CFB;
else if (mode == "CTS") aes.Mode = CipherMode.CTS;
else if (mode == "ECB") aes.Mode = CipherMode.ECB;
else if (mode == "OFB") aes.Mode = CipherMode.OFB;

byte[] temp_iv = Convert.FromHexString("76396c566a476c4c50694e376469487a"); // Convert IV from hex to bytes
byte[] temp_key = System.Text.Encoding.UTF8.GetBytes("ei9dzmx9f3l2CdFliYMb7iwJ7d0ce58d");
byte[] temp_message = FromBase64Url(message);

aes.Key = temp_key;
aes.IV = temp_iv;
//aes.Padding = PaddingMode.PKCS7;
aes.Padding = PaddingMode.None;

ICryptoTransform encryptor = aes.CreateEncryptor();
ICryptoTransform decryptor = aes.CreateDecryptor();

using(MemoryStream msEncrypt = new MemoryStream()) {
using(CryptoStream csEncrypt = new CryptoStream(msEncrypt, encryptor, CryptoStreamMode.Write)) {
using(StreamWriter swEncrypt = new StreamWriter(csEncrypt)) {
swEncrypt.Write(message);
}
encrypted = msEncrypt.ToArray();
msEncrypt.Close();
csEncrypt.Close();
}
}

using(MemoryStream msDecrypt = new MemoryStream(temp_message)) {
using(CryptoStream csDecrypt = new CryptoStream(msDecrypt, decryptor, CryptoStreamMode.Read)) {
using(StreamReader plainTextReader = new StreamReader(csDecrypt)) {
plaintext = plainTextReader.ReadToEnd();

msDecrypt.Close();
csDecrypt.Close();
}

}
}

string str1 = "Message: " + message;

str1 = str1 + "\nIV " + BitConverter.ToString(aes.IV);
str1 = str1 + "\nKey " + BitConverter.ToString(aes.Key);
str1 = str1 + "\nMode: " + mode;

str1 = str1 + "\n\nCipher: " + BitConverter.ToString(encrypted).Replace("-", string.Empty);
str1 = str1 + "\nCipher: " + Convert.ToBase64String(encrypted);
str1 = str1 + "\nDecrypted Byte Code: " + BitConverter.ToString(temp_message);
str1 = str1 + "\nDecrypted: " + plaintext;

Console.WriteLine("{0}", str1);

} catch(Exception e) {
Console.WriteLine("Error: {0}", e);
}

}
}
}