This totally works, accepts that the "-e" encrypts the file, but despite the "-d" doing exactly the opposite, apparently that doesn't pass.....
port java.util.List;

public class Solution {

    static List<Integer> bytes = new ArrayList<>();

    public static void main(String[] args) {

        try {
            if (args[0].equals("-e")) {
                Encrypt(args[1], args[2]);
            }
            if (args[0].equals("-d")) {
                Decrypt(args[1], args[2]);
            }
        } catch (Exception e) {
            e.printStackTrace();
        }

    }

    public static void Encrypt(String InputFilename, String OutputFilename) throws IOException {
        BufferedInputStream readFile = new BufferedInputStream(new FileInputStream(InputFilename));
        while (readFile.available() > 0) {
            bytes.add(readFile.read());
        }
        readFile.close();
        for (int i = 0; i < bytes.size(); i++) {
            Integer toEncrypt = bytes.get(i);
            Integer Encrypted = toEncrypt + 1;
            bytes.set(i, Encrypted);

        }

        BufferedOutputStream writeFile = new BufferedOutputStream(new FileOutputStream(OutputFilename));
        for (Integer x : bytes) {
            writeFile.write(x);
        }
        writeFile.close();


    }

    public static void Decrypt(String InputFilename, String OutputFilename) throws IOException {
        BufferedInputStream readFile = new BufferedInputStream(new FileInputStream(InputFilename));
        while (readFile.available() > 0) {
            bytes.add(readFile.read());
        }
        readFile.close();
        for (int i = 0; i < bytes.size(); i++) {
            Integer toEncrypt = bytes.get(i);
            Integer Encrypted = toEncrypt - 1;
            bytes.set(i, Encrypted);

        }

        BufferedOutputStream writeFile = new BufferedOutputStream(new FileOutputStream(OutputFilename));
        for (Integer x : bytes) {
            writeFile.write(x);
        }
        writeFile.close();

    }


}