patch.go

package main

import (
	"crypto/sha1"
	"errors"
	"flag"
	"fmt"
	"io"
	"log"
	"os"
)

const (
	position = 122860
)

var (
	path     = flag.String("path", "", "path of program to patch")
	password = flag.String("password", "", "new password for program")
)

func main() {
	flag.Parse()

	if *path == "" {
		log.Fatal(errors.New("no path provided"))
	}
	if *password == "" {
		log.Fatal(errors.New("no password provided"))
	}

	// open program file
	fd, err := os.OpenFile(*path, os.O_APPEND|os.O_WRONLY, os.ModeAppend)
	if err != nil {
		log.Fatal(fmt.Errorf("could not open file: %s", err))
	}
	defer fd.Close()

	// move file descriptor to correct position
	if _, err := fd.Seek(position, io.SeekStart); err != nil {
		log.Fatal(fmt.Errorf("could not seek file position: %s", err))
	}

	// take the sha1 of the password
	hashWriter := sha1.New()
	hashWriter.Write([]byte(*password))
	sha1 := hashWriter.Sum(nil)

	if _, err := fd.Write(sha1); err != nil {
		log.Fatal(fmt.Errorf("could not write new password hash to program: %s", err))
	}

	fmt.Println("program patched!")
}