Hidding Message Steganografi

Steganografi.go

// MIT License

// Copyright (c) [2020] [fachryansyah]

// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
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// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:

// The above copyright notice and this permission notice shall be included in all
// copies or substantial portions of the Software.

// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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/**
 How the algorithm works
   1. Convert decimal number to binary
      every points of input number, you need changing it to the binary and than get the last number of that binary.
      for example i have "55" decimal number, next changing it to binary and i should get "110111" binary numbers, so the result is "1" because the last number of that binary is "1".
   2. Repeat the step no.1 for up to 7 points of number
      do step no.1 for 7 times, example i have "31 31 6 6 51 51 6" decimal number, and i will get "1100110"
   3. Translate the result of no.2 to words
      in the problem stated that a-z is 97-122 in decimal number, so now we have the pattern like this: 
       97 = A
       98 = B
       99 = C
       etc..
      previously I had a value of "1100110" in binary, we must know what letters are behind the binary numbers.
      by changing the decimal value 97-122 to binary, we will know the letter.
      
      binary  | decimal | letters
      1100001 | 97      | A
      1100010 | 98      | B
      1100011 | 99      | C
      ....    | ...     | ...
      1100110 | 103     | F

USAGE
$ go run steganografi.go

**/

package main

import (
	"fmt"
	"strings"
	"strconv"
)

type Dictionary struct {
	Name string
	Binary string
}

func main () {
	char := "31 31 6 6 51 51 6 23 25 8 4 2 6 31 61 43 8 21 18 20 42 43 53 15 12 56 31 34 21 49 2 55 18 22 31" // return FAHRI
	result := steganografi(char)
	fmt.Println(result)

	a := "1 1 0 0 0 0 1" // return A
	resultA := steganografi(a)
	fmt.Println(resultA)

	b := "31 31 20 20 20 21 8" // return B
	resultB := steganografi(b)
	fmt.Println(resultB)

	c := "51 61 20 0 0 15 17" // return C
	resultC := steganografi(c)
	fmt.Println(resultC)

	withSpace := "51 61 20 0 0 15 17 31 8 8 8 8 8 8 51 61 20 0 0 15 17" // return C C
	resultSpace := steganografi(withSpace)
	fmt.Println(resultSpace)
}

func steganografi(input string) string {
	// prepare words
	words := generateWordList()
	
	split := strings.Split(input, " ")

	// validate if input lower than 7
	if len(split) < 7 {
		return "Input tidak kurang dari 7"
	}

	// validate if input more than 7000
	if len(split) > 7000 {
		return "Nilai tidak memiliki kelipatan 7"
	}

	// validate if input length not multiples of 7
	if len(split) % 7 != 0 {
		return "Nilai tidak memiliki kelipatan 7"
	}

	var binary []string
	var result string

	// loop the number
	temp := ""
	for i := 0; i < len(split); i++ {

		// if temp has 7 character, it will be push to array of binary
		if i % 7 == 0 {
			binary = append(binary, temp)
			temp = ""
		}

		// convert the number to int64
		s, _ := strconv.ParseInt(split[i], 10, 64)

		// convert again from decimal to binary
		a := decimalToBinary(s)

		// get the last number and append to "temp" variable
		temp += a[len(a)-1:]

		if i+1 == len(split) {
			binary = append(binary, temp)
			temp = ""
		}
	}

	// loop the binary
	for i := 0; i < len(binary); i++ {
		// loop the words from dictionary
		for _, item := range words {
			// check if binary is equal from dictionary
			if item.Binary == binary[i] {
				result += item.Name
			}
		}
	}
	
	return result
}

func decimalToBinary(num int64) string {
	return strconv.FormatInt(num, 2)
}

func generateWordList() []Dictionary {
	var dictionaries []Dictionary

	// set default words
	var words = [...]string{"A", "B", "C", "D", "E", "F", "G", "H", "I", "J", "K", "L", "M",
	"N", "O", "P", "Q", "R", "S", "T", "U", "V", "W", "X", "Y", "Z"}

	// in the problem we have a-z with values 97 to 122, 97 means the letter A
	for i := 97; i <= 122; i++ {
		// apend the world bassed on index
		dictionaries = append(dictionaries, Dictionary{words[i-97], decimalToBinary(int64(i))})
	}

	// this is default for whitespace
	dictionaries = append(dictionaries, Dictionary{" ", "1000000"})
	

	return dictionaries
}