making ciphers with javascript

**brooklyn** · 12-07-2009, 10:40 PM

This is what i have from a part of a project but don't know how to make a 5 column transposition cipher

Code:

<html>
<!-- cipher.html      by Dave Reed (davereed@creighton.edu)  -->
<!-- A lab program to accompany A Balanced Introduction to   -->
<!-- Computer Science, 2nd ed., Pearson Prentice Hall, 2008. -->
<!--                                                         -->
<!-- This page encodes/decodes messages using a simple       -->
<!-- substitution cipher (with key entered by the user)      -->
<!-- ======================================================= -->

<head>
  <title> Substitution Cipher</title>

  <script type="text/javascript">
    function Encode(message, key)
    // Assumes: message is the string to be encoded, and
    //          key is a string of the 26 letters in arbitrary order
    // Returns: the coded version of message using the substitution key 
    {
        var alphabet, coded, i, ch, index;

        alphabet = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";

        coded = "";  
        i = 0;                                    
        while (i < message.length) {                // for as many letters as there are
            ch = message.charAt(i);                 //   access each letter in message
            index = alphabet.indexOf(ch);           //   find its position in alphabet
            if (index == -1) {                      //   if it's not a capital letter,
                coded = coded + ch;                 //     then leave it as is & add
            }                                       //   otherwise,
            else {                                  //     find the corresponding
                coded = coded + key.charAt(index);  //     letter in the key & add
                key=rotateLeft(key);
            }
            i = i + 1;
        }
        return coded;
    }
  </script>
   
   <script type="text/javascript">
    function Decode(message, key)
    {
        var alphabet, coded, i, ch, index;

        alphabet = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";

        coded = "";  
        i = 0;                                    
        while (i < message.length) {                // for as many letters as there are
            ch = message.charAt(i);                 //   access each letter in message
            index = key.indexOf(ch);           //   find its position in alphabet
            if (index == -1) {                      //   if it's not a capital letter,
                coded = coded + ch;                 //     then leave it as is & add
            }                                       //   otherwise,
            else {                                  //     find the corresponding
                coded = coded + alphabet.charAt(index);  //     letter in the key & add
                key=rotateLeft(key);
            }
            i = i + 1;
        }
        return coded;
    }
  </script>
  <script type="text/javascript">
  function rotateLeft(key)
  {
  return key.substring(1,key.length)+ key.charAt(0);
  }
  
   function firstColumn(message2)
   {
    var i, answer1;
       answer1= "";
       i=0;
       while (i<message2.length){
       answer1 = answer1 + message2.charAt(i);
       i=i+5;}
       return answer1;
       }
       
       function secondColumn(message2)
   {

    var i, answer2;

	i=1;
	answer2="";
	while (i < message2.length)  {
	answer2 = answer2 + message2.charAt(i);
	i=i+5;
	}
	return answer2;

}

	function thirdColumn(message2)
{

    var i, answer3;

	i=2;
	answer3="";
	while (i < message2.length)  {
	answer3 = answer3 + message2.charAt(i);
	i=i+5;
	}
	return answer3;

}

	function fourthColumn(message2)
{

    var i, answer4;

	i=3;
	answer4="";
	while (i < message2.length)  {
	answer4 = answer4 + message2.charAt(i);
	i=i+5;
	}
	return answer4;

}

	function fifthColumn(message2)
{

    var i, answer5;

	i=4;
	answer5="";
	while (i < message2.length)  {
	answer5 = answer5 + message2.charAt(i);
	i=i+5;
	}
	return answer5;

}

    function encodeTranspose(message2)
{

	var coded2;
	coded2 = firstColumn(message2) + secondColumn(message2) +
thirdColumn(message2) + fourthColumn(message2) + fifthColumn(message2);
	return coded2;

		}


function firstLine(encoded2)
{

	var i, answer6;

	i=0;
	answer6="";
	while (i < encoded2.length)  {
	answer6 = answer6 + encoded2.charAt(i);
	i=i+(encoded2.length /= 5);
	}
	return answer6;
}

function secondLine(encoded2)
{

	var i, answer7;

	i=1;
	answer7="";
	while (i < encoded2.length)  {
	answer7 = answer7 + encoded2.charAt(i);
	i=i+(encoded2.length /=5);
	}
	return answer7;
}

function thirdLine(encoded2)
{

	var i, answer8;

	i=2;
	answer8="";
	while (i < encoded2.length)  {
	answer8 = answer8 + encoded2.charAt(i);
	i=i+(encoded2.length /=5);
	}
	return answer8;
}

function fourthLine(encoded2)
{

	var i, answer9;

	i=3;
	answer9="";
	while (i < encoded2.length)  {
	answer9 = answer9 + encoded2.charAt(i);
	i=i+(encoded2.length /=5);
	}
	return answer9;
}




function decodeTranspose(encoded2)
{

	var coded3;
	coded3 = firstLine(encoded2) + secondLine(encoded2) + thirdLine(encoded2) +
fourthLine(encoded2);
	return coded3;

		}


       
  </script>
</head>

<body>
  <table>
    <tr><td>According to the substitution cipher, each letter: <BR><BR> </td>
        <td>†<tt>ABCDEFGHIJKLMNOPQRSTUVWXYZ<br /></tt>
             †<tt>| | | | | | | | | | | | | <br /></tt>
             †<tt>v v v v v v v v v v v v v </tt> </td>
    </tr>
    <tr><td>is encoded using the corresponding letter in the key: </td>
        <td><input type="text" id="key" size="26" style="font-family:Courier,Monospace"
                   value="XYZABCDEFGHIJKLMNOPQRSTUVW" onChange="javascript:this.value=this.value.toUpperCase();" /> </td>
    </tr>
    </table>

    <hr />

    <table>
    <tr><td><textarea id="message" rows="8" cols="30" onChange="javascript:this.value=this.value.toUpperCase();"></textarea> </td>
        <td><input type="button" value="Encode ==>" 
                   onclick="document.getElementById('encoded').value=
                              Encode(document.getElementById('message').value,
                                     document.getElementById('key').value);" /> <br />
        <input type="button" value="<== Decode " 
                   onclick="document.getElementById('message').value=
                              Decode(document.getElementById('encoded').value,
                                     document.getElementById('key').value);" /> </td>
        <td>
        <td><textarea id="encoded" rows="8" cols="30" onChange="javascript:this.value=this.value.toUpperCase();"></textarea> </td>
    </tr>
  </table>
</body>
</html>

**steveo4103** · 12-08-2009, 01:58 AM

I am working on the same exact thing right now....I'm guessing we are in the same class haha. Let me know if you figure it out and I'll do the same.

**djr33** · 12-08-2009, 02:15 AM

You must use [code] tags so that we can read your code.

Additionally, we HELP, but do not solve homework problems for you. Ask a specific question.

**steveo4103** · 12-08-2009, 03:00 AM

From the assignment:
EXERCISE 7: Add functions to encode and decode messages using the 5-column transposition. [Hint: create a function which takes a parameter n and a string and returns every nth character from the string.] What is the result of applying 5-column transposition to the following text: "IT WAS THE BEST OF TIMES"?

It is a portion of the assignment, there are several other exercises leading up to this one

**djr33** · 12-09-2009, 12:17 AM

Yes, but the idea is that you should figure it out for yourself (that's what homework is for). You need to ask specific questions so we are helping, rather than just doing (whether or not it is just a small part of the assignment).

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