Re: To xor or not to xor

From: <Adechert_at_aol_dot_com>
Date: Fri Sep 19 2003 - 12:45:44 CDT

This sounds fine to me. I'd like to hear what others think.

Alan D.

In a message dated 9/19/03 6:29:24 AM Pacific Daylight Time, jan@it.uu.se
writes:

> I think I would like to retreat from my suggestion to use XOR
> to obscure the bar codes. Since this involves conversion between
> binary and decimal, one has to keep track of the number of bits
> and digits, so leading zeroes are not lost during the conversions.
> This seems unnecessary complicated for this task.
>
> My suggestion now is instead to do a similar obscuration directly
> on the decimal numbers. It is done by adding the (repeated) digits
> in the ballot number to the digits in the huge integer, modulo 10.
> To revert, instead subtract modulo 10. For example, with ballot
> number 4216:
>
> 083076749736557242056487941267521535
> 421642164216421642164216421642164216
> ------------------------------------
> 404618803942978884110693362809685741
>
> I believe the bar code would be as hard to interpret as it was
> using the XOR method.
>
> ------------------------------------------------------------------------
> import string
>
> def obscure(key, num):
> keydigits = list(key)
> numdigits = list(num)
> for i in range(len(numdigits)):
> numdigits[i] = str((int(numdigits[i]) + int(keydigits[i % 4])) %
10)
> return string.join(numdigits, "")
>
> def revert(key, num):
> keydigits = list(key)
> numdigits = list(num)
> for i in range(len(numdigits)):
> numdigits[i] = str((int(numdigits[i]) - int(keydigits[i % 4])) %
10)
> return string.join(numdigits, "")
>
> ballotno = "4216"
> barcodedata = "083076749736557242056487941267521535"
> print barcodedata
> obscured = obscure(ballotno, barcodedata)
> print obscured
> print revert(ballotno, obscured)
> ------------------------------------------------------------------------
>
> Remember that this is not encryption, but only a way to obscure
> bar codes, so that identical or similar votes should not have
> similar bar codes. With the above algorithm, identical votes
> will have 10000 different bar code representations.
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Received on Tue Sep 30 23:17:07 2003

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