AES encryption on large files

Question

I need to encrypt and decrypt large file (~1GB). I tried using this example: http://www.codeproject.com/Articles/769741/Csharp-AES-bits-Encryption-Library-with-Salt But my problem is since the file is very large, I'm getting outOfMemory exception. So I need to replace the memory stream with file stream, I just not sure how to do it...

(Adding my code:)

private static void AES_Encrypt(string srcFile, string encryptedFile,  byte[] passwordBytes)
    {


        // Set your salt here, change it to meet your flavor:
        // The salt bytes must be at least 8 bytes.
        byte[] saltBytes = new byte[] { 1, 2, 3, 4, 5, 6, 7, 8};

        FileStream fsInput = new FileStream(srcFile,
            FileMode.Open,
            FileAccess.Read);

        FileStream fsEncrypted = new FileStream(encryptedFile,
                        FileMode.Create,
                        FileAccess.Write);

        using (RijndaelManaged AES = new RijndaelManaged())
        {
            AES.KeySize = 256;
            AES.BlockSize = 128;

            var key = new Rfc2898DeriveBytes(passwordBytes, saltBytes, 1000);
            AES.Key = key.GetBytes(AES.KeySize / 8);
            AES.IV = key.GetBytes(AES.BlockSize / 8);

            AES.Mode = CipherMode.CBC;

            using (var cs = new CryptoStream(fsEncrypted, AES.CreateEncryptor(), CryptoStreamMode.Write))
            {
                byte[] bytearrayinput = new byte[fsInput.Length - 1];
                fsInput.Read(bytearrayinput, 0, bytearrayinput.Length);
                cs.Write(bytearrayinput, 0, bytearrayinput.Length);
                cs.Close();
                fsInput.Flush();
                fsInput.Close();
                fsEncrypted.Close();
            }

        }


    }

    public static void AES_Decrypt(string encryptedFile, string decryptedFile, byte[] passwordBytes)
    {
        byte[] decryptedBytes = null;

        // Set your salt here, change it to meet your flavor:
        // The salt bytes must be at least 8 bytes.
        byte[] saltBytes = new byte[] { 1, 2, 3, 4, 5, 6, 7, 8};

        FileStream fsread = new FileStream(encryptedFile,
                               FileMode.Open,
                               FileAccess.Read);

        using (RijndaelManaged AES = new RijndaelManaged())
        {
            AES.KeySize = 256;
            AES.BlockSize = 128;

            var key = new Rfc2898DeriveBytes(passwordBytes, saltBytes, 1000);
            AES.Key = key.GetBytes(AES.KeySize / 8);
            AES.IV = key.GetBytes(AES.BlockSize / 8);

            AES.Mode = CipherMode.CBC;

            FileStream fsDecrypted = new FileStream(decryptedFile,
                        FileMode.Create,
                        FileAccess.Write);

            using (var cs = new CryptoStream(fsDecrypted, AES.CreateDecryptor(), CryptoStreamMode.Write))
            {
                byte[] bytearrayinput = new byte[fsread.Length - 1];
                fsread.Read(bytearrayinput, 0, bytearrayinput.Length);
                cs.Write(bytearrayinput, 0, bytearrayinput.Length);
                cs.Close();
                fsread.Close();
                fsDecrypted.Close();
            }

        }
    }

Answer 1

Eventually, this is the code that worked for me:

 private static void AES_Encrypt(string inputFile, string outputFile, byte[] passwordBytes)
 {
        byte[] saltBytes = new byte[] { 1, 2, 3, 4, 5, 6, 7, 8};
        string cryptFile = outputFile;
        FileStream fsCrypt = new FileStream(cryptFile, FileMode.Create);

        RijndaelManaged AES = new RijndaelManaged();

        AES.KeySize = 256;
        AES.BlockSize = 128;


        var key = new Rfc2898DeriveBytes(passwordBytes, saltBytes, 1000);
        AES.Key = key.GetBytes(AES.KeySize / 8);
        AES.IV = key.GetBytes(AES.BlockSize / 8);
        AES.Padding = PaddingMode.Zeros;

        AES.Mode = CipherMode.CBC;

        CryptoStream cs = new CryptoStream(fsCrypt,
             AES.CreateEncryptor(),
            CryptoStreamMode.Write);

        FileStream fsIn = new FileStream(inputFile, FileMode.Open);

        int data;
        while ((data = fsIn.ReadByte()) != -1)
            cs.WriteByte((byte)data);


        fsIn.Close();
        cs.Close();
        fsCrypt.Close();

    }

    private static void AES_Decrypt(string inputFile, string outputFile, byte[] passwordBytes)
    {



        byte[] saltBytes = new byte[] { 1, 2, 3, 4, 5, 6, 7, 8};
        FileStream fsCrypt = new FileStream(inputFile, FileMode.Open);

        RijndaelManaged AES = new RijndaelManaged();

        AES.KeySize = 256;
        AES.BlockSize = 128;


        var key = new Rfc2898DeriveBytes(passwordBytes, saltBytes, 1000);
        AES.Key = key.GetBytes(AES.KeySize / 8);
        AES.IV = key.GetBytes(AES.BlockSize / 8);
        AES.Padding = PaddingMode.Zeros;

        AES.Mode = CipherMode.CBC;

        CryptoStream cs = new CryptoStream(fsCrypt,
            AES.CreateDecryptor(),
            CryptoStreamMode.Read);

        FileStream fsOut = new FileStream(outputFile, FileMode.Create);

        int data;
        while ((data = cs.ReadByte()) != -1)
            fsOut.WriteByte((byte)data);

        fsOut.Close();
        cs.Close();
        fsCrypt.Close();

    }
}

Answer 2

So I created a fairly fast and low memory consumption version:
I use a "temporary buffer" and also "use a random salt and store it with the ciphertext".
To encrypt:

private void AES_Encrypt(string inputFile, string password)
    {
        //http://stackoverflow.com/questions/27645527/aes-encryption-on-large-files

        //generate random salt
        byte[] salt = GenerateRandomSalt();

        //create output file name
        FileStream fsCrypt = new FileStream(inputFile + ".aes", FileMode.Create);

        //convert password string to byte arrray
        byte[] passwordBytes = System.Text.Encoding.UTF8.GetBytes(password);

        //Set Rijndael symmetric encryption algorithm
        RijndaelManaged AES = new RijndaelManaged();
        AES.KeySize = 256;
        AES.BlockSize = 128;
        AES.Padding = PaddingMode.PKCS7;

        //http://stackoverflow.com/questions/2659214/why-do-i-need-to-use-the-rfc2898derivebytes-class-in-net-instead-of-directly
        //"What it does is repeatedly hash the user password along with the salt." High iteration counts.
        var key = new Rfc2898DeriveBytes(passwordBytes, salt, 50000);
        AES.Key = key.GetBytes(AES.KeySize / 8);
        AES.IV = key.GetBytes(AES.BlockSize / 8);

        //Cipher modes: http://security.stackexchange.com/questions/52665/which-is-the-best-cipher-mode-and-padding-mode-for-aes-encryption
        AES.Mode = CipherMode.CFB;

        //write salt to the begining of the output file, so in this case can be random every time
        fsCrypt.Write(salt, 0, salt.Length);

        CryptoStream cs = new CryptoStream(fsCrypt, AES.CreateEncryptor(), CryptoStreamMode.Write);

        FileStream fsIn = new FileStream(inputFile, FileMode.Open);

        //create a buffer (1mb) so only this amount will allocate in the memory and not the whole file
        byte[] buffer = new byte[1048576];
        int read;

        try
        {
            while ((read = fsIn.Read(buffer, 0, buffer.Length)) > 0)
            {
                Application.DoEvents(); // -> for responsive GUI, using Task will be better!
                cs.Write(buffer, 0, read);
            }

            //close up
            fsIn.Close();

        }
        catch (Exception ex)
        {
            Debug.WriteLine("Error: " + ex.Message);
        }
        finally
        {
            cs.Close();
            fsCrypt.Close();
        }
    }

To decrypt:

private void AES_Decrypt(string inputFile, string password)
    {
        //todo:
        // - create error message on wrong password
        // - on cancel: close and delete file
        // - on wrong password: close and delete file!
        // - create a better filen name
        // - could be check md5 hash on the files but it make this slow

        byte[] passwordBytes = System.Text.Encoding.UTF8.GetBytes(password);
        byte[] salt = new byte[32];

        FileStream fsCrypt = new FileStream(inputFile, FileMode.Open);
        fsCrypt.Read(salt, 0, salt.Length);

        RijndaelManaged AES = new RijndaelManaged();
        AES.KeySize = 256;
        AES.BlockSize = 128;
        var key = new Rfc2898DeriveBytes(passwordBytes, salt, 50000);
        AES.Key = key.GetBytes(AES.KeySize / 8);
        AES.IV = key.GetBytes(AES.BlockSize / 8);
        AES.Padding = PaddingMode.PKCS7;
        AES.Mode = CipherMode.CFB;

        CryptoStream cs = new CryptoStream(fsCrypt, AES.CreateDecryptor(), CryptoStreamMode.Read);

        FileStream fsOut = new FileStream(inputFile + ".decrypted", FileMode.Create);

        int read;
        byte[] buffer = new byte[1048576];

        try
        {
            while ((read = cs.Read(buffer, 0, buffer.Length)) > 0)
            {
                Application.DoEvents();
                fsOut.Write(buffer, 0, read);
            }
        }
        catch (System.Security.Cryptography.CryptographicException ex_CryptographicException)
        {
            Debug.WriteLine("CryptographicException error: " + ex_CryptographicException.Message);
        }
        catch (Exception ex)
        {
            Debug.WriteLine("Error: " + ex.Message);
        }

        try
        {
            cs.Close();
        }
        catch (Exception ex)
        {
            Debug.WriteLine("Error by closing CryptoStream: " + ex.Message);
        }
        finally
        {
            fsOut.Close();
            fsCrypt.Close();
        }
    }

To generate random salt:

        public static byte[] GenerateRandomSalt()
    {
        //Source: http://www.dotnetperls.com/rngcryptoserviceprovider
        byte[] data = new byte[32];

        using (RNGCryptoServiceProvider rng = new RNGCryptoServiceProvider())
        {
            // Ten iterations.
            for (int i = 0; i < 10; i++)
            {
                // Fill buffer.
                rng.GetBytes(data);
            }
        }
        return data;
    }

Answer 3

Since you are reading from a file and writing to a file just replace the memory streams by IOStream or FileStream.

You'll have to refactor the procedures a bit so they don't expect/return byte arrays.