Hey-ho,

I'm getting a bit out of my depth porting the 'tiny encryption algorithm'

from C to python.

Ref:

http://en.wikipedia.org/wiki/Tiny_Encryption_Algorithm http://www.simonshepherd.supanet.com...e.htm#new_ansi
Specifically I don;t know how to handle a C-long block and perform the

mathmatical manipulations in python syntax. I played with pack and unpack

(from struct module) but that didn't seem to buy me anything.

In my version, I end up with hugely long integers, which have obviously

not be constrained into the 4-byte unsigned longs that TEA is expecting.

This is the C function:

/* v is 64-bits input, w is 64-bits output, k is the 128-bit key */

void decipher(const unsigned long *const v,unsigned long *const w, const

unsigned long * const k)

{

register unsigned long

y=v[0],z=v[1],sum=0xC6EF3720,delta=0x9E3779B9,n=32;

while(n-->0)

{

z -= (y << 4 ^ y >> 5) + y ^ sum + k[sum>>11 & 3];

sum -= delta;

y -= (z << 4 ^ z >> 5) + z ^ sum + k[sum&3];

}

w[0]=y; w[1]=z;

}

Which gives me a (broken) python version:

def teaDecipher(input,key):

y = input[0]

z = input[1]

n = 32

sum = 0xC6EF3720

delta=0x9E3779B9

while (n > 0):

n -= 1

z -= (y << 4 ^ y >> 5) + y ^ sum + key[sum>>11 & 3];

sum -= delta;

y -= (z << 4 ^ z >> 5) + z ^ sum + key[sum&3];

return y,z

That seems to return hugely-long integers (around 30? digits), whereas I'd

expect

them to max-out at 2^32.

Perhaps I'm not packing the input or the key properly. My inputs are

just strings which I put into an integer with the ordinal value of each

character

shifted into the correct position to make the C-long.

Something like:

input[0] = ord(encrypted[i])<<24 + ord(encrypted[i+1])<<16 +

ord(encrypted[i+2])<<8 + ord(encrypted[i+3])

input[1] = ord(encrypted[i+4])<<24 + ord(encrypted[i+5])<<16 +

ord(encrypted[i+6])<<8 + ord(encrypted[i+7])

The key is created as an array of numbers, each the ord() of the key

character...

Anyway, that's about it.

Any help much appreciated.

thanks,

-kt

(non-removable disclaimer below... *sigh*)

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