C# encryption/ decryption code for Rijndael implementation. Cross platform compatible with the java code provided here: https://gist.github.com/yashs360/8178448

ScriptMain.cs

using System;
using System.Data;
using System.Security;
using System.Security.Cryptography;
using System.Runtime.InteropServices;
using System.Text.RegularExpressions;
using System.Text;
using System.IO;

namespace Rijndael.csproj
{

    public partial class ScriptMain
    {

        public static void Main()
        {
        
            // Secret key must be same as the java code for csoss platform compatibility.
            // Secret ket must be 16/24/32 char(byte) long to support AES Java code
            EncryptFile(@"C:\path\to\file\data.csv", @"C:\path\to\file\data_encrypted.csv",@"SecretKey1234567");
            
            DecryptFile(@"C:\path\to\file\data.csv", @"C:\path\to\file\data_decrypted.csv", @"SecretKey1234567");


        }


        private static void EncryptFile(string inputFile, string outputFile, string skey)
        {
            try
            {
                using (RijndaelManaged aes = new RijndaelManaged())
                {

                    byte[] key = Encoding.UTF8.GetBytes(skey);
                    byte[] IV = Encoding.UTF8.GetBytes(skey);

                    aes.Padding = PaddingMode.PKCS7;
                    aes.Mode = CipherMode.CBC;
                    aes.KeySize = 128;
                    aes.BlockSize = 128;


                    using (FileStream fsCrypt = new FileStream(outputFile, FileMode.Create))
                    {
                        using (ICryptoTransform encryptor = aes.CreateEncryptor(key, IV))
                        {
                            using (CryptoStream cs = new CryptoStream(fsCrypt, encryptor, CryptoStreamMode.Write))
                            {
                                using (FileStream fsIn = new FileStream(inputFile, FileMode.Open))
                                {
                                    int data;
                                    while ((data = fsIn.ReadByte()) != -1)
                                    {
                                        cs.WriteByte((byte)data);
                                    }
                                }
                            }
                        }
                    }
                }
            }
            catch (Exception ex) { }
        }

        private static void DecryptFile(string inputFile, string outputFile, string skey)
        {
            try
            {
                using (RijndaelManaged aes = new RijndaelManaged())
                {
                    byte[] key = Encoding.UTF8.GetBytes(skey);
                    byte[] IV = Encoding.UTF8.GetBytes(skey);

                    aes.Padding = PaddingMode.PKCS7;
                    aes.Mode = CipherMode.CBC;
                    aes.KeySize = 128;
                    aes.BlockSize = 128;


                    using (FileStream fsCrypt = new FileStream(inputFile, FileMode.Open))
                    {
                        using (FileStream fsOut = new FileStream(outputFile, FileMode.Create))
                        {
                            using (ICryptoTransform decryptor = aes.CreateDecryptor(key, IV))
                            {
                                using (CryptoStream cs = new CryptoStream(fsCrypt, decryptor, CryptoStreamMode.Read))
                                {
                                    int data; while ((data = cs.ReadByte()) != -1)
                                    { fsOut.WriteByte((byte)data); }
                                }
                            }
                        }
                    }
                }
            }

            catch (Exception ex) { }
        }


    }
}