RE: Crypt

From: Dylan Douglas <dylan_at_mediadefender.com>
Date: Fri, 8 Jun 2007 17:22:03 -0700

I think I got it sorted out.
 
I changed the line to: $key = ($key * 1103515245 + 12345) & 0x7fffffff
 
I was going to keep working on it, but we are changing ips and are now
in ip hell.
 
 

________________________________

        From: Stefan Kaczmarek [mailto:stefan_at_thezonie.org]
        Sent: Thursday, June 07, 2007 9:04 PM
        To: Dylan Douglas
        Cc: Ivan Kwok; Ben Ebert; Ty Heath; Jay Mairs; Nainesh Solanki;
Sergio Alvarez
        Subject: Re: Crypt
        
        
        Well, if you need to tweak it to make it work easier in php, let
me know. It doesn't really matter what the algo is, as long as it's
implementable in java and php.

        - Z

        On Jun 7, 2007, at 6:22 PM, Dylan Douglas wrote:

                Z-
                 
                Have I mentioned that php is dumber about ints than
Java? Well, I'm trying to get the:
                 
                $key = $key * 1103515245 + 12345;
                
                code to work. I start off okay, then I seem to zoom off
to around 10^130 as I become a float (and that is just doing your carpet
string). So, cast to stay an int, right? Now I loop past MAXINT become
negative and get stuck somehow at MININT value. I tried ANDing it with
0xffffffff, but that didn't help. I have to figure out how to tell it
to limit stuff to 4 bytes and to allow it to loop. Will keep you
updated.
                 
                -D

________________________________

                        From: Stefan Kaczmarek
[mailto:stefan_at_thezonie.org]
                        Sent: Thursday, June 07, 2007 8:46 AM
                        To: Ivan Kwok; Ben Ebert; Ty Heath; Jay Mairs;
Nainesh Solanki; Sergio Alvarez; Dylan Douglas
                        Subject: Crypt
                        
                        
                        D,

                        Here are the code snippets that I use to encrypt
/ decrypt the json string. When I send you the sources, it'll be
"files=<hex string>". And when I get the sources back, I am assuming
it'll be a <hex string> that comes back.

                        To go to and from hex strings, this is what I
do:
                        
                        
                        // Encrypt the data and convert it ot a hex
string
                        String data="I really enjoy carpeting.";
                        byte data_bytes[]=data.getBytes();
                        byte to_crypt[]=new byte[data_bytes.length+4];
        
System.arraycopy(data_bytes,0,to_crypt,4,data_bytes.length);
                        byte cipher[]=Crypt.Encrpyt(to_crypt);
                        String hex=Crypt.bytesToHex(cipher);
                        data=hex;

                        // Decrypt the data
                        data_bytes=Crypt.hexToBytes(data);
                        byte plain[]=Crypt.Decrypt(data_bytes);
                        byte decrypt[]=new byte[plain.length-4];
        
System.arraycopy(plain,4,decrypt,0,decrypt.length);
                        data=new String(decrypt);

                        I just take the string, convert it to a byte
array, add 4 bytes at the front for the key, and then encrypt the byte
array. I then convert the whole byte array into a hex string. Then, when
receiving a hex string, i convert it to a byte array, then decrypt it,
pull off the first 4 bytes, and covert the remaining bytes back into a
string.

                        Try decrypting
933d5162fadc8f46acc8e0fdd123205867743c03ce284794f989691a5a and you
should get the "I really enjoy carpeting."

                        For funsies, here are the decrpyt and encrypt
functions:

                        // The input buffer needs to have 4 bytes at the
front to allow for the key to be placed there
                        public static byte[] Encrpyt(byte[] data)
                        {
                        // Create a byte buffer, which is the 4 byte key
plus the data
                        byte[] ret=new byte[data.length];
                        System.arraycopy(data,0,ret,0,data.length);
                        
                        
                        // Get a random int to encrypt with
                        int key=new Random().nextInt();
                        
                        
                        // Copy the key and data to the out array
                        System.arraycopy(intToByteArray(key),0,ret,0,4);
                        
                        
                        // Encrypt the data
                        DoCrypt(key,ret,4);
                        
                        
                        return ret;
                        }
                        
                        
                        // Will return the buffer with the key still at
the first 4 bytes
                        public static byte[] Decrypt(byte[] data)
                        {
                        // Create a byte buffer
                        byte[] ret=new byte[data.length];
                        System.arraycopy(data,0,ret,0,data.length);
                        
                        
                        // Get the key from the first 4 bytes
                        int key=byteArrayToInt(data,0);
                        
                        
                        // Decrypt the data
                        DoCrypt(key,ret,4);
                        
                        
                        return ret;
                        }
                        
                        
                        private static void DoCrypt(int key,byte[]
data,int offset)
                        {
                        byte b=0;
                        for(int i=offset;i<data.length;i++)
                        {
                        key = key * 1103515245 + 12345;
                        b=(byte)((key/65536) % 256);
                        data[i] ^= b;
                        }
                        }

                        
                        
                        
Received on Fri Sep 14 2007 - 10:55:54 BST

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