xtea encryption

[toalan]

I just implemented xtea for the AVR MCU using C, it might be hard to implement in Picbasic since 32 bit unsigned long integers are not supported (I think).

I just copied from http://www.answers.com/topic/xtea into my C compiler (IAR embedded workbench)and was able to use it without modification for AVR.

xtea is supposed to be one of the most secure ( I do not think it has been cracked yet) and fastest algorithims. I looked into DES and AES and they seemed to time consuming to implement. I think xtea or one of its variants is used for the xbox.

I am using xtea to encrypt firmware so people can flash upgrade stuff without me worrying that they will steal my work.

[mister_e]

xtea is supposed to be one of the most secure ( I do not think it has been cracked yet)

LMAO well since you have a code and the explanation can be found somewhere... what is the big deal to crack something with it???

BTW all alrgorithm are still human made... another can bypass it easy... really easy

I think xtea or one of its variants is used for the xbox.

no comments, some are in jail now...

[toalan]

Sorry I am not following you, my implementation is to supply people with encrypted firmware, they send it to the MCU and the MCU will decrypt the data and write it to flash memory.

If you can bypass encryption easily then you are one of the few geniuses and perhaps your work has been undocumented. As of 2004 there is been no officially successful attempts at breaking the xtea algorithim.

The xtea algorithim in xbox was never really borken, people exploited flaws in the hardware design to run unsigned code, most notably the big font flaw.

[toalan]

if you guys are interested in my XTEA bootloader here it is http://www.14point7.com/AVR.htm

[Ron Marcus]

I will need to use encryption in a wireless stream for an upcoming product. XTEA looks good, and compact. I will write in assembly, but I wondered if anyone has played with this in PBP? It looks like a fun excercise, especially with the version 2.5 longs! Any other ideas for good encryption without a lot of overhead? It needs to stand up to that .01% of attacks.
Thanks,
Ron

[tenaja]

Go to the Swordfish Basic compiler site and download their demo program; it has XTEA with it. Surely you can convert it.
http://www.sfcompiler.co.uk/swordfish/

[Ron Marcus]

Go to the Swordfish Basic compiler site and download their demo program; it has XTEA with it. Surely you can convert it.
http://www.sfcompiler.co.uk/swordfish/

I downloaded Swordfish, but cannot find any mention of TEA, XTEA, or TEA-N. Where did you find it?

[mister_e]

Should be in "\Sample\encryption" folder.

[Ron Marcus]

OK, here it is. These subs will take an eight byte block of code, and encrypt it, then decrypt it. The key must be exactly the same for encrypt and decrypt, and don't mess with "Delta". This is only for the PIC18s and PBPL(2.50a)

;**********************************************************************
; XTEA VARIABLES  *****************************************************
;**********************************************************************
roundin     con     32            ;number of loops
Delta       con    $9E3779B9       ;5/4/2 * 2power32

round       var     byte
Sumin       var     long
vy          var     Long
text_byte   var     byte[8]     ;text coming in, going out.
vz          var     Long
tb          var     byte
Sum         var     long
temp        var     long
tmp0         var    temp.byte0
tmp1         var    temp.byte1
tmp2         var    temp.byte2
tmp3         var    temp.byte3
key         var     long[4]
ka         var      key[0]

kb         var     key[1]
kc         var     key[2]
kd         var     key[3]
limit       var     long
block       var     long[2]
index       var     word
key[0] =    $31323334        ;128 bit key
key[1]  =   $93D8E9AF       ;don't use mine
key[2]  =   $275FC2BA       ;must be
key[3]  =   $95E20110       ;random
        

;**********************************************************************



main:
           
           
                       
            hserout [str text_byte\8,13]    ;the unchanged block of 8 bytes
              gosub beep   
            ;pause 1000
               GOsub TEAenc                    ;scramble well
            hserout [str text_byte\8,13]    ;show mess
             gosub teadec                       ;unscramble
            hserout [str text_byte\8,13]    ;No s--t, it works!
               pause 100    
             stop   
TEAenc:     for tb = 0 to 3  ; convert string into code
             vy.byte0[tb] = text_byte[tb]
             vz.byte0[tb] = text_byte[tb+4] 
             next tb                                                            
            sum = 0
            Limit = Delta * roundin 
             while Sum <> limit
             vy = vy + (((vz<<4) ^ (vz >>5))^(Sum + Key[sum & 3]))
             sum = sum + Delta
             vz = vz + (((vy<<4) ^ (vy >>5))^(Sum + Key[sum>>11 & 3]))
                wend
                for tb = 0 to 3
               text_byte[tb]= vy.byte0[tb]
               text_byte[tb+4] = vz.byte0[tb]
             next tb
               return 
          
;***************************************************************************            
TEAdec:       ;Convert code into string
            for tb = 0 to 3
             vy.byte0[tb] = text_byte[tb]
             vz.byte0[tb] = text_byte[tb+4] 
             next tb
                         
                   sum = Delta * roundin
             while sum <> 0      
               vz = vz - (((vy<<4) ^ (vy >>5))^(Sum + Key[(sum>>11) & 3]))
                sum = sum - Delta
               vy = vy - (((vz<<4) ^ (vz >>5))^(Sum + Key[sum & 3]))
                 wend
                 for tb = 0 to 3
               text_byte[tb]= vy.byte0[tb]
               text_byte[tb+4] = vz.byte0[tb]
             next tb
               return

[mister_e]

Looks good to me at first glance. Sure some will use it.