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 =[" 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;
}