Java Script Kiddie - Golang

JSKiddieCTF.go

package main

import (
	"bufio"
	"fmt"
	"os"
	"strconv"
	"strings"
	"unicode/utf8"
)

var LEN = 16

// HUMPHREY
func main() {
	fmt.Println("Enter bytes:")
	var bytesRaw string

	scanner := bufio.NewScanner(os.Stdin)
	for scanner.Scan() {
		bytesRaw = scanner.Text()
		if bytesRaw != "" {
			break
		}
	}

	byteStrings := strings.Split(string(bytesRaw), " ")
	bytes := []int{}
	for _, bs := range byteStrings {
		num, _ := strconv.Atoi(bs)
		bytes = append(bytes, num)
	}

	var pngHeader = []int{0x89, 0x50, 0x4E, 0x47, 0x0D, 0x0A, 0x1A, 0x0A, 0x00, 0x00, 0x00, 0x0D, 0x49, 0x48, 0x44, 0x52}

	var shifts = make([][]int, 16)

	for i := 0; i < LEN; i++ {
		for s := 0; s < 10; s++ {
			if bytes[((s*LEN)%len(bytes))+i] == pngHeader[i] {
				shifts[i] = append(shifts[i], s)
			}
		}
	}

	var key string
	for _, shift := range shifts {
		key += fmt.Sprint(shift[0])
	}

	fmt.Println("Key: " + key)

	fmt.Println("PNG Bytes:")
	test(bytes, key)

}

func charCodeAt(str string, i int) int {
	r, _ := utf8.DecodeRuneInString(string(str[i]))
	return int(r)
}

func test(bytes []int, key string) {
	var shifter int

	result := make([]int, len(bytes)*16)

	for i := 0; i < LEN; i++ {
		shifter = charCodeAt(key, i) - 48
		for j := 0; j < len(bytes)/LEN; j++ {
			result[(j*LEN + i)] = bytes[(((j+shifter)*LEN)%len(bytes))+i]
		}
	}

	for result[len(result)-1] == 0 {
		result = result[:len(result)-1]
	}

	var strs []string
	for _, num := range result {
		strs = append(strs, fmt.Sprintf("%x", num))
	}

	fmt.Println(strings.Join(strs, " "))
}