encrypting, decrypting

crawfd

I'm trying to encrypted a message, send it in an email, and then decrypt the scrambled message back into normal form. I'm discovering that I need to somehow divide/alter this script somehow but not sure how to go about it. I need to somehow seperate the decrypt function from the encrypt function so that they work independently.

<?
$message='Hello this is the message that gets encrypted'; 

function encrypt($message,$levels,$skip,$key='c 5x1ag9e0wyzjbl3dmkh82vu6opqir4sn7tf') 
    { 
    for($i=0;$i<$levels;$i++) 
        { 
        $len=strlen($message)-($i*2); 
        $key=substr($key,$skip).substr($key,0,$skip); 
        $message=strtr(substr($message,0,strlen($message
)-$i),"abcdefghijklmnopqrstuvwxyz 1234567890",$key).substr($message,strlen($message)-$i); 
        } 
    return $message.str_pad($levels,3,"0",STR_PAD_LEFT).str_pad($skip,2,"0",STR_PAD_LEFT); 
    } 

function decrypt($message,$key='c 5x1ag9e0wyzjbl3dmkh82vu6opqir4sn7tf') 
    { 
    $skip=substr($message,-2,2); 
    $levels=substr($message,-5,3); 
    $message=substr($message,0,-5); 
    for($i=0;$i<$levels+1;$i++) 

    $key=substr($key,$skip).substr($key,0,$skip); 


for($i=0;$i<$levels;$i++) 
    { 
    $key=substr($key,-$skip).substr($key,0,37-$skip); 
    $message=strtr(substr($message,0,strlen($message
)-($levels-1-$i)),$key,"abcdefghijklmnopqrstuvwxyz 1234567890").substr($message,strlen($message)-($levels-1-$i)); 
        } 
    return $message; 
    } 

$output=encrypt($message,strlen($message),5); 
echo "<br>output = ".$output."<br>"; 
echo "<br>".decrypt($output);

Weedpacket

How do you mean "work independently"? As far as I can see they do - neither calls the other. Obviously they're so independent that you can change the results of one without having to alter the other. That said, I don't see why you'd need to separate them. Keeping them together would help to make sure that they're both updated together if they ever need to be.

crawfd

Weedpacket,

They both share the $message variable. I need to take the decrypt function and place it on another page (or use it with the encrypt function). I won't have access to the $message variable though.

The decrypt function takes the result of the encrypt $message varialbe and processes it.

I need to somehow unscramble the result in the decrypt function withouth processing the $message variable first with the encrypt function.

Weedpacket

Originally posted by crawfd
They both share the $message variable.

I don't see this. I see three variables named $message: one in the global scope, one containing the first argument passed to encrypt(), and one containing the first arguments passed to decrypt(). They all have the same name, but because they all have different scopes their contents are all independent of each other.

laserlight

They both share the $message variable.

They share the message (one in plaintext, the other in ciphertext), they both have an argument named $message, but no, they dont 'share' $message.

I need to somehow unscramble the result in the decrypt function withouth processing the $message variable first with the encrypt function.

You cant.
You must encrypt before you decrypt.
But the point here is that the sender uses your encryption function before the email is sent, and the receiver uses your decryption function after the email is received.

crawfd

My apologies, ...I shouldn't have used the term 'share'.

In response to:

But the point here is that the sender uses your encryption function before the email is sent, and the receiver uses your decryption function after the email is received.

But how do I do this? How do I decrypt the encrypted message in in a seperate page where the encrypt and decrypt function are isolated from the original $message variable?

When a user is transferred to another page, the $message variable can not exist.

bike5

pass it via sessions, pull it from a database...? Can't you do that.

laserlight

When a user is transferred to another page, the $message variable can not exist.

Perfectly fine.
Just use whatever incoming variable contains what $message used to contain.

Actually, the main problem I see is in how you actually plan to use the crypto, plus distribute the key.
You can encrypt the text, yes, but how in the world are your users going to decrypt the message?
Before you start any coding, you need to get that clear.

crawfd

You can encrypt the text, yes, but how in the world are your users going to decrypt the message?

Yes I can encrypt the $message variable and send it via an email.
No I haven't figured out how to encrypt and decrypt once then press on a link which passes the encrypted string in the web address.

Essentially, the $message variable is going to be a session_id value. Perhaps it's unique enough that I don't even need to encrypt, but for added security I wanted to encrypt the session_id and return it scrambled, and then tag it to the web address in an email.

User clicks on link, opens up a page which contains my decrypt script.