Encrypt and decrypt a string using simple Javascript without using any external library

Question

I want to create a function to encrypt a string which will shorten the string into alphanumeric character and also create a function decrypt which will get back the encrypted string.

Here is what I coded by taking reference online.

function compress(string) {
  string = unescape(encodeURIComponent(string));
  var newString = '',
    char, nextChar, combinedCharCode;
  for (var i = 0; i < string.length; i += 2) {
    char = string.charCodeAt(i);

    if ((i + 1) < string.length) {

      
      nextChar = string.charCodeAt(i + 1) - 31;

      
      combinedCharCode = char + "" + nextChar.toLocaleString('en', {
        minimumIntegerDigits: 2
      });

      newString += String.fromCharCode(parseInt(combinedCharCode, 10));

    } else {

     
      newString += string.charAt(i);
    }
  }
  return newString;
}

function decompress(string) {

  var newString = '',
    char, codeStr, firstCharCode, lastCharCode;

  for (var i = 0; i < string.length; i++) {
    char = string.charCodeAt(i);
    if (char > 132) {
      codeStr = char.toString(10);

      firstCharCode = parseInt(codeStr.substring(0, codeStr.length - 2), 10);

      lastCharCode = parseInt(codeStr.substring(codeStr.length - 2, codeStr.length), 10) + 31;

      newString += String.fromCharCode(firstCharCode) + String.fromCharCode(lastCharCode);
    } else {
      newString += string.charAt(i);
    }
  }
  return newString;
}

var stringToCompress = 'awesome';
var compressedString = compress(stringToCompress);
var decompressedString = decompress(compressedString);


console.log("encrypted :",compressedString);
console.log("decrypted :",decompressedString);

Currently the output from the sting="awesome" is

encrypted: ☼⟈⮪e
decrypted: awesome

I want similar encryption but must be only in alphanumeric values and not symbols.

vanowm · Accepted Answer · 2021-06-06 05:18:51Z

I don't know what is your goal (is it make the string shorter, but binary or encrypted and in ascii range), so if it's the later, than you could use base64 encoding:

function compress(string) {
  string = unescape(encodeURIComponent(string));
  var newString = '',
    char, nextChar, combinedCharCode;
  for (var i = 0; i < string.length; i += 2) {
    char = string.charCodeAt(i);

    if ((i + 1) < string.length) {

      
      nextChar = string.charCodeAt(i + 1) - 31;

      
      combinedCharCode = char + "" + nextChar.toLocaleString('en', {
        minimumIntegerDigits: 2
      });

      newString += String.fromCharCode(parseInt(combinedCharCode, 10));

    } else {

     
      newString += string.charAt(i);
    }
  }
  return btoa(unescape(encodeURIComponent(newString)));
}

function decompress(string) {

  var newString = '',
    char, codeStr, firstCharCode, lastCharCode;
  string = decodeURIComponent(escape(atob(string)));
  for (var i = 0; i < string.length; i++) {
    char = string.charCodeAt(i);
    if (char > 132) {
      codeStr = char.toString(10);

      firstCharCode = parseInt(codeStr.substring(0, codeStr.length - 2), 10);

      lastCharCode = parseInt(codeStr.substring(codeStr.length - 2, codeStr.length), 10) + 31;

      newString += String.fromCharCode(firstCharCode) + String.fromCharCode(lastCharCode);
    } else {
      newString += string.charAt(i);
    }
  }
  return newString;
}

var stringToCompress = 'awesome';
var compressedString = compress(stringToCompress);
var decompressedString = decompress(compressedString);


console.log("encrypted :",compressedString);
console.log("decrypted :",decompressedString);

Or if you trully want alphanumerical, than you can simply convert it into HEX:

function compress(string) {
  string = unescape(encodeURIComponent(string));
  var newString = '',
    char, nextChar, combinedCharCode;
  for (var i = 0; i < string.length; i += 2) {
    char = string.charCodeAt(i);

    if ((i + 1) < string.length) {

      
      nextChar = string.charCodeAt(i + 1) - 31;

      
      combinedCharCode = char + "" + nextChar.toLocaleString('en', {
        minimumIntegerDigits: 2
      });

      newString += String.fromCharCode(parseInt(combinedCharCode, 10));

    } else {

     
      newString += string.charAt(i);
    }
  }
  return newString.split("").reduce((hex,c)=>hex+=c.charCodeAt(0).toString(16).padStart(4,"0"),"");
}

function decompress(string) {

  var newString = '',
    char, codeStr, firstCharCode, lastCharCode;
  string = string.match(/.{1,4}/g).reduce((acc,char)=>acc+String.fromCharCode(parseInt(char, 16)),"");
  for (var i = 0; i < string.length; i++) {
    char = string.charCodeAt(i);
    if (char > 132) {
      codeStr = char.toString(10);

      firstCharCode = parseInt(codeStr.substring(0, codeStr.length - 2), 10);

      lastCharCode = parseInt(codeStr.substring(codeStr.length - 2, codeStr.length), 10) + 31;

      newString += String.fromCharCode(firstCharCode) + String.fromCharCode(lastCharCode);
    } else {
      newString += string.charAt(i);
    }
  }
  return newString;
}

var stringToCompress = 'awesome';
var compressedString = compress(stringToCompress);
var decompressedString = decompress(compressedString);


console.log("encrypted :",compressedString);
console.log("decrypted :",decompressedString);

I want it to be similar to this in alphanumeric but the encrypted string must be shorter in length than the actual input string.
I don't believe you'd be able to do so, you can't have both.
Yeah I think its not possible to achieve shorten encryption smaller than the input string. Thanks for your help @vanowm

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