xtea encryption

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.

Quote:

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Originally Posted by toalan

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

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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

Quote:

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Originally Posted by toalan

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

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no comments, some are in jail now...

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.

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

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

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/

Quote:

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Originally Posted by 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/

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

Should be in "\Sample\encryption" folder.

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)

Code:

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

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