code.js

/*
	code assumes that plainText contains ONLY LOWER CASE ALPHABETS
*/

Number.prototype.mod = function (n) {
    return ((this%n)+n)%n;
};

var keys = {a: 5, b: 7},
	N = 26;

function encrypt (plainText) {
	var cypherText = '';
	function cryptAlpha (alpha) {
		var index = alpha.charCodeAt (0) - 'a'.charCodeAt (0);
		var result = ((keys.a * index) + keys.b).mod (N);

		logger._print ('Index of ' + alpha + ' = ' + index);

		result += 'a'.charCodeAt (0);
		return String.fromCharCode (result);
	}

	logger._print ('Beginning Affine Encryption');
	logger._print ('Encryption formula: <b>((keys.a * index_of_alphabet) + keys.b) % N</b>');
	logger._print ('keys.a=' + keys.a + ', keys.b=' + keys.b + ', N=' + N);

	for (var i in plainText) {
		ptTracer._select (i)._wait ();
		ptTracer._deselect (i)._wait ();

		cypherText += cryptAlpha (plainText [i]);

		ptTracer._notify (i, cypherText.slice (-1))._wait ();
		ptTracer._denotify (i)._wait ();
	}

	return cypherText;
}

function decrypt (cypherText) {
	var plainText = '';
	var aInverse = (function () {
		for (var i = 1; i < N; i++) {
			if ( ((keys.a * i).mod (N)) === 1 ) {
				return i;
			}
		}
	}) ();

	logger._print ('a<sup>-1</sup> = ' + aInverse);

	function decryptAlpha (alpha) {
		var index = alpha.charCodeAt (0) - 'a'.charCodeAt (0);
		var result = (aInverse * (index - keys.b)).mod (N);

		logger._print ('Index of ' + alpha + ' = ' + index);

		result += 'a'.charCodeAt (0);
		return String.fromCharCode (result);
	}

	logger._print ('Beginning Affine Decryption');
	logger._print ('Decryption formula: <b>(a<sup>-1</sup> * (index - keys.b)) % N</b>');
	logger._print ('keys.b=' + keys.b + ', N=' + N);

	for (var i in cypherText) {
		ctTracer._select (i)._wait ();
		ctTracer._deselect (i)._wait ();

		plainText += decryptAlpha (cypherText [i]);

		ctTracer._notify (i, plainText.slice (-1))._wait ();
		ctTracer._denotify (i)._wait ();
	}

	return plainText;
}

var cipherText = encrypt (plainText);
ctTracer._setData (cipherText);
decrypt (cipherText);