SPUG:Appropriateness of MD5

[Pommert, Daniel]

I have found MD5 to be extremely sensitive to any change: content, order,
length or padding.  Although it is true that you have long keys, you simply
want to ensure that nothing has changed.  MD5 is very hard to spoof.  128
bits gives you about 10**40 unique codes.  The odds of two reports having
exactly the same digest are astronomically slim.

-- Daniel Pommert

P.S.  My first Perl job was doing MD5 digests of releases to verify the
correctness of those releases.

-----Original Message-----
From: Peter Darley [mailto:pdarley at kinesis-cem.com]
Sent: Thursday, March 20, 2003 8:23 AM
To: SPUG
Subject: SPUG:Appropriateness of MD5


Friends,
	I have a system that produces reports on large sets of data every
night.
Each report is made up of columns of data, the contents of which can change
at times.  I want to create a list of all the individual records that make
up each column, use them to create a string that would uniquely describe the
contents of the report, then create an MD5 digest of it which would be
checked against subsequent digests to see if the contents of the report had
changed and it needed to be re-run.
	My question is this: Is the MD5 digest going to be sensitive enough
to
detect the changes?  The 'key' of the report will likely be ~1000-2000
characters before digesting, and I'm a bit woried that a 128 bit digest
won't be unique enough to indicate a change to the 'key'.
	Any suggestions appreciated. :)
Thanks,
Peter Darley

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