How to Check Decryptyed  Data in AES256,PKCS5 In Online.

Code to decrypt data using AES256 and PKCS5 padding in ASP.NET C#:u

sing System;
using System.IO;
using System.Security.Cryptography;
using System.Text;

public static string DecryptString(string cipherText, string key)
{
    string plainText = null;

    byte[] cipherBytes = Convert.FromBase64String(cipherText);

    using (Aes aes = Aes.Create())
    {
        aes.Key = Encoding.UTF8.GetBytes(key);
        aes.Padding = PaddingMode.PKCS7;

        // Set the initialization vector (IV) for AES encryption
        byte[] iv = new byte[aes.BlockSize / 8];
        Array.Copy(cipherBytes, iv, iv.Length);
        aes.IV = iv;

        using (MemoryStream ms = new MemoryStream())
        {
            using (CryptoStream cs = new CryptoStream(ms, aes.CreateDecryptor(), CryptoStreamMode.Write))
            {
                cs.Write(cipherBytes, iv.Length, cipherBytes.Length - iv.Length);
            }

            plainText = Encoding.UTF8.GetString(ms.ToArray());
        }
    }

    return plainText;
}

you can use an online AES256 decryption tool and compare the decrypted data with the output from the DecryptString method to test the code

1. Encrypt the data using AES256 and PKCS5 padding.
2. Decrypt the encrypted data using the same algorithm and key used for encryption.
3. Compare the decrypted data with the original data to ensure that the encryption and decryption process was successful.

• First, you need to create an instance of the AES encryption algorithm with the same key and IV used for encryption. You can do this using the Aes class in the System.Security.Cryptography namespace. For example:

string key = "MySecretKey12345";
string iv = "MyInitializationVector";

byte[] keyBytes = Encoding.UTF8.GetBytes(key);
byte[] ivBytes = Encoding.UTF8.GetBytes(iv);

Aes aes = Aes.Create();
aes.KeySize = 256;
aes.BlockSize = 128;
aes.Padding = PaddingMode.PKCS7;
aes.Key = keyBytes;
aes.IV = ivBytes;

• Next, you need to convert the decrypted data from Base64 string to a byte array. You can do this using the Convert class in the System namespace. For example:

string decryptedData = "Kdu5/nMsM5fBSQfiy/fGvw==";
byte[] decryptedBytes = Convert.FromBase64String(decryptedData);

• Now, you need to create a MemoryStream object to store the decrypted data. You can do this using the MemoryStream class in the System.IO namespace. For example:

MemoryStream ms = new MemoryStream(decryptedBytes);

• Next, you need to create a CryptoStream object to read the decrypted data from the MemoryStream and decrypt it using the AES algorithm. You can do this using the CryptoStream class in the System.Security.Cryptography namespace. For example:

CryptoStream cs = new CryptoStream(ms, aes.CreateDecryptor(), CryptoStreamMode.Read);

• Now, you need to read the decrypted data from the CryptoStream and convert it to a string. You can do this using the StreamReader class in the System.IO namespace. For example:

StreamReader sr = new StreamReader(cs);
string decryptedString = sr.ReadToEnd();

• Finally, you can check the decrypted data to ensure it matches the original plaintext data. For example:

string originalData = "Hello, world!";
if (decryptedString == originalData)
{
    // The decrypted data matches the original plaintext data
}
else
{
    // The decrypted data does not match the original plaintext data
}

By following these steps, you can easily check decrypted data in AES256 with PKCS5 padding in C#.