JavaScript/Ciphers/keyFinder.js

/******************************************************
Find and retrieve the encryption key automatically
Note: This is a draft version, please help to modify, Thanks!
******************************************************/
function keyFinder (str) { // str is used to get the input of encrypted string
  const wordbank = ['I ', 'You ', 'We ', 'They ', 'He ', 'She ', 'It ', ' the ', 'The ', ' of ', ' is ', 'Is ', ' am ', 'Am ', ' are ', 'Are ', ' have ', 'Have ', ' has ', 'Has ', ' may ', 'May ', ' be ', 'Be ']
  // let wordbankelementCounter = 0;
  // let key = 0; // return zero means the key can not be found
  const inStr = str.toString() // convert the input to String
  let outStr = '' // store the output value
  let outStrElement = '' // temporary store the word inside the outStr, it is used for comparison
 	for (let k = 0; k < 26; k++) { // try the number of key shifted, the sum of character from a-z or A-Z is 26
    outStr = caesarCipherEncodeAndDecodeEngine(inStr, k) // use the encrytpion engine to decrypt the input string

    // loop through the whole input string
    for (let s = 0; s < outStr.length; s++) {
      for (let i = 0; i < wordbank.length; i++) {
        // initialize the outStrElement which is a temp output string for comparison,
        // use a loop to find the next digit of wordbank element and compare with outStr's digit
        for (let w = 0; w < wordbank[i].length; w++) {
          outStrElement += outStr[s + w]
        }

        // console.log( k + outStrElement + wordbank[i] );//debug

        // this part need to be optimize with the calculation of the number of occurance of word's probabilities
        // linked list will be used in the next stage of development to calculate the number of occurace of the key
        if (wordbank[i] == outStrElement) {
        				return k // return the key number if founded
        }

        outStrElement = '' // reset the temp word
      } // end for ( let i=0; i < wordbank.length; i++)
    }
  }
  return 0 // return 0 if found nothing
}

/* this sub-function is used to assist the keyfinder to find the key */
function caesarCipherEncodeAndDecodeEngine (inStr, numShifted) {
  const shiftNum = numShifted
  let charCode = 0
  let outStr = ''
  let shftedcharCode = 0
  let result = 0

  for (let i = 0; i < inStr.length; i++) {
    charCode = inStr[i].charCodeAt()
    shftedcharCode = charCode + shiftNum
    result = charCode

    if ((charCode >= 48 && charCode <= 57)) {
      if (shftedcharCode < 48) {
		  		let diff = Math.abs(48 - 1 - shftedcharCode) % 10

        while (diff >= 10) {
		  			diff = diff % 10
        }
        document.getElementById('diffID').innerHTML = diff

        shftedcharCode = 57 - diff

        result = shftedcharCode
      } else if (shftedcharCode >= 48 && shftedcharCode <= 57) {
        result = shftedcharCode
      } else if (shftedcharCode > 57) {
		  		let diff = Math.abs(57 + 1 - shftedcharCode) % 10

        while (diff >= 10) {
		  			diff = diff % 10
        }
        document.getElementById('diffID').innerHTML = diff

        shftedcharCode = 48 + diff

        result = shftedcharCode
      }
    } else if ((charCode >= 65 && charCode <= 90)) {
		  	if (shftedcharCode <= 64) {
		  		let diff = Math.abs(65 - 1 - shftedcharCode) % 26

        while ((diff % 26) >= 26) {
		  			diff = diff % 26
        }
        shftedcharCode = 90 - diff
        result = shftedcharCode
      } else if (shftedcharCode >= 65 && shftedcharCode <= 90) {
        result = shftedcharCode
      } else if (shftedcharCode > 90) {
        let diff = Math.abs(shftedcharCode - 1 - 90) % 26

        while ((diff % 26) >= 26) {
		  			diff = diff % 26
        }
        shftedcharCode = 65 + diff
        result = shftedcharCode
      }
    } else if ((charCode >= 97 && charCode <= 122)) {
		  	if (shftedcharCode <= 96) {
		  		let diff = Math.abs(97 - 1 - shftedcharCode) % 26

        while ((diff % 26) >= 26) {
		  			diff = diff % 26
        }
        shftedcharCode = 122 - diff
        result = shftedcharCode
      } else if (shftedcharCode >= 97 && shftedcharCode <= 122) {
        result = shftedcharCode
      } else if (shftedcharCode > 122) {
        let diff = Math.abs(shftedcharCode - 1 - 122) % 26

        while ((diff % 26) >= 26) {
		  			diff = diff % 26
        }
        shftedcharCode = 97 + diff
        result = shftedcharCode
      }
    }
    outStr = outStr + String.fromCharCode(parseInt(result))
  }
  return outStr
}