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
	let 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)
{
	let 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;
}