How to edit PDF?

[David Teague(T-bird acct)]

Tristan Wibberley wrote:

>David Teague(T-bird acct) wrote:
>
>>That is one use for MD5 check sums. It doesn't make the
>>file inviolable, but it gives the recipient an almost unbreakable
>>check against tampering.
>>    
>>
>MD5 based signatures probably don't do that anymore. md5 is now pretty
>easy to break (a researcher recently released a tool to find md5
>collisions) and any file format that enables you to make changes that
>are not apparent when rendered is extremely susceptible to such attacks.
>That includes pdf and postscript. You should certainly be using at least
>SHA-1 for this now.
>
Well Dang! Is there a mechanism that is better
than MD5 (i.e. that is 'almost' unbreakable) ??

A slightly different way might be to encrypt. There is
128 bit encryption .... is it any good for this purpose?
The theory says that given sufficient computing power,
any encryption can be broken. I would like to find one
that nobody but a government (or Microsoft) will have
the resources to break it -- at least for a year or two.

Warm Regards
David

-- -- David Teague, cs.wcu.edu/~dbt -- Advocating Free Software and 
Double Bass tuned in fifths -- Classical Bass www.dennismasuzzo.com; 
www.silviodallatorre.com; www.joelquarrington.com -- Jazz Upright Bass 
Red Mitchell, home.teleport.com/~mimuma/; www.larryholloway.com/;