Pete Jones

var bifidEncode, bifidDecode;
// Assign closures that have access to the table
(function(){
    // Generate the encryption table
    /* * * * * * * * *
     *   1 2 3 4 5 6 *
     * 1 A B C D E F *
     * 2 G H I J K L *
     * 3 M N O P Q R *
     * 4 S T U V W X *
     * 5 Y Z 0 1 2 3 *
     * 6 4 5 6 7 8 9 *
     * * * * * * * * */
    var _table = (function(){
        var result = {};
        var chars = "ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
        for (var i = 0; i < chars.length; i += 1) {
            var c         = chars.charAt(i);
            var index     = Math.floor( i / 6 ).toString() + ( i % 6 ).toString();
            result[c]     = index;
            result[index] = c;
        }
        return result;
    })();

    bifidEncode = function( rawText ) {
        var rawIndices = "";
        for( var i = 0; i < rawText.length; i++ ) {
            rawIndices += _table[rawText.charAt( i )];
        }
        // cipherIndices = rawIndices[::2] + rawIndices[1::2]
        var cipherIndices = "";
        for( var i = 0; i < rawIndices.length; i += 2 ) {
            cipherIndices += rawIndices.charAt( i );
        }
        for( var i = 1; i < rawIndices.length; i += 2 ) {
            cipherIndices += rawIndices.charAt( i );
        }
        var cipherText = "";
        for( var i = 0; i < cipherIndices.length; i += 2 ) {
            cipherText += _table[cipherIndices.substr( i, 2 )];
        }
        return cipherText;
    };

    bifidDecode = function( cipherText ) {
        var cipherIndices = "";
        for( var i = 0; i < cipherText.length; i++ ) {
            cipherIndices += _table[cipherText.charAt( i )];
        }
        var rawIndices = "";
        for( var i = 0; i < cipherText.length; i++ ) {
            rawIndices += cipherIndices[i];
            rawIndices += cipherIndices[i + cipherText.length];
        }
        var rawText = "";
        for( var i = 0; i < rawIndices.length; i += 2 ) {
            rawText += _table[rawIndices.substr( i, 2 )];
        }
        return rawText;
    };
})();