C# AES256 encryption and decryption example for using easily.

CryptoUtil.cs

public class CryptoUtil
{
    public static byte[] EncryptAes256(byte[] bytes, byte[] key)
    {
		using var aes = new RijndaelManaged
		{
			Key = CreateDeriveBytes(key, 32),
		};
		aes.GenerateIV();

		using var encryptor = aes.CreateEncryptor();
		using var encryptedStream = new MemoryStream();
		// Do not replace implicit using expression, when CryptoStream aws disposed, final block deliver to memory stream.
		using (var cryptoStream = new CryptoStream(encryptedStream, encryptor, CryptoStreamMode.Write))
		{
			cryptoStream.Write(bytes);
		}
		var encrypted = encryptedStream.ToArray();

		return aes.IV.Concat(encrypted).ToArray();
	}

	public static string DecryptAes256(string encrypted, string key)
	{
		var decryptAes256 = DecryptAes256(Convert.FromBase64String(encrypted), Encoding.UTF8.GetBytes(key));
		return Encoding.UTF8.GetString(decryptAes256);
	}

	public static byte[] DecryptAes256(byte[] encrypted, byte[] key)
	{
		using var rijndeal = new RijndaelManaged
		{
			Key = CreateDeriveBytes(key, 32)
		};
		var iv = encrypted.Take(16).ToArray();
		rijndeal.IV = iv;

		var encryptedBytes = encrypted.Skip(16).ToArray();
		using var memoryStream = new MemoryStream();
		using var decryptor = rijndeal.CreateDecryptor();
		using (var cryptoStream = new CryptoStream(memoryStream, decryptor, CryptoStreamMode.Write))
		{
			cryptoStream.Write(encryptedBytes);
		}

		return memoryStream.ToArray();
	}

	private static byte[] CreateDeriveBytes(byte[] keyBytes, int size)
	{
		using var sha512 = SHA512.Create();
		var saltBytes = sha512.ComputeHash(keyBytes);
		using var derivBytes = new Rfc2898DeriveBytes(keyBytes, saltBytes, 65536);
		return derivBytes.GetBytes(size);
	}
}

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