----- Original Message -----
From: "Greg Guerin" <email@hidden>
To: <email@hidden>
Sent: Monday, December 13, 2004 2:01 PM
Subject: Re: Versioning Java Applications
> "Mike Hall" <email@hidden> wrote:
>
> >I would consider using the CRC stuff built into zip since at least 1.1.
>
> Three points:
> 1) CRCs and secure hashes have different design goals and limitations.
> 2) ZIP CRCs are 32-bits; secure hashes are at least 4X that.
> 2) ZIP CRCs are optional.
>
> More info about CRCs:
> <http://en.wikipedia.org/wiki/Cyclic_redundancy_check>
> <http://www.ross.net/crc/crcpaper.html>
>
>From the first link
While useful for error detection, CRCs cannot be safely relied upon to
verify data integrity (that no changes whatsoever have occurred), since it's
possible to intentionally change data without modifying its CRC
(The second appears to be a busted link)
True the two actually are for different purposes. If you want to ensure no
one is sneak modifying you would almost certainly choose hashes. For the
purpose indicated, versioning, that shouldn't be the issue. You should be
able to ensure crc's are included and should be able to trust they aren't
being skipped or altered. If you don't trust the developers in this process
for some reason then definitely use secure hashing if not jar signing.
As far as differences between two files, 32 bits should be more than
sufficient to make it highly unlikely crc's aren't correct without incorrect
or malicious use. Probability of incorrect match or mismatch by coincidence
should be very small, 32 bits are still pretty big for most purposes.
So for the subject purpose I would still consider crc's a valid option if
not first choice.
Mike Hall mikehall at spacestar dot net
http://www.spacestar.net/users/mikehall
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