How to edit PDF?

Chosechu chosechu at
Sun Nov 27 19:19:09 UTC 2005

Do not use MD5 for cryptographic signatures!
It has been broken. Have a look at:

for meaningful human-readable documents hashing to the
same MD5 sum.

Looks like SHA1 is taking the same path as MD5.
Other hash functions with a longer future could
be SHA-256, SHA-512.


David Teague(T-bird acct) wrote:
> 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, -- Advocating Free Software and
> Double Bass tuned in fifths -- Classical Bass;
>; -- Jazz Upright Bass
> Red Mitchell,;;

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