SOLITON Stupid DRM

soliton_decrypt.go

package main

import (
	"crypto/rc4"
	"encoding/base64"
	"fmt"
	"io"
	"log"
	"os"
	"path/filepath"
	"strings"
)

func fix_filename(s string) string {
	invalid_chars := [11]string{"/", "\\", "?", "*", "%", ":", "|", "\"", "<", ">", "."}
	result := s
	for _, ch := range invalid_chars {
		result = strings.Replace(result, ch, "-", -1)
	}
	return result
}

func decrypt_sol_file(path string) error {
	log.Printf("file path: %s", path)
	if filepath.Ext(path) != ".sol" {
		log.Printf("file extension not match: %s", filepath.Ext(path))
		return nil
	}
	file, err := os.Open(path)
	if err != nil {
		log.Printf("cannot open file")
		return err
	}
	defer file.Close()
	filename := filepath.Base(path)
	ext_name := filepath.Ext(path)
	encoded_name := filename[:len(filename)-len(ext_name)]
	decoded_bytes, err := base64.StdEncoding.DecodeString(encoded_name)
	var decoded_name string
	if err == nil {
		decoded_name = string(decoded_bytes)
	} else {
		log.Printf("cannot decode filename, fallback to original name")
		decoded_name = encoded_name
	}
	decoded_name = fix_filename(decoded_name) // incase there are invalid chars in track title
	output_path := filepath.Join(filepath.Dir(path), decoded_name+".mp3")
	log.Printf("output_path: %s", output_path)
	output_file, err := os.Create(output_path)
	if err != nil {
		log.Printf("cannot open file to write")
		return err
	}
	defer output_file.Close()
	key := make([]byte, 4)
	key[3] = 4 // this is stupid, but the key is 0x00000004
	cipher, err := rc4.NewCipher(key)
	if err != nil {
		log.Printf("cannot open RC4 cipher")
		return err
	}
	read_buf := make([]byte, 1024)
	decode_buf := make([]byte, 1024)
	for {
		n, err := file.Read(read_buf)
		cipher.XORKeyStream(decode_buf, read_buf)
		output_file.Write(decode_buf[:n])
		if err == io.EOF {
			break
		}
	}
	return nil
}

func main() {
	if len(os.Args) < 2 {
		fmt.Printf("not enough args\n")
		return
	}
	c := make(chan int)
	n := len(os.Args) - 1
	for i := 1; i <= n; i++ {
		go func(k int) {
			err := decrypt_sol_file(os.Args[k])
			if err != nil {
				c <- 0
			} else {
				c <- 1
			}
		}(i)
	}
	s := 0
	for j := 1; j <= n; j++ {
		s += <-c
	}
	log.Printf("Finished. %d tracks decoded.", s)
}