Re: [MI400] Generate hash code for a source member?

["Leif Svalgaard" <leif@xxxxxxxx>]

MD5 or SHA-1 both handle transposed characters just fine (that is:
makes the hashes different).

----- Original Message -----
From: <thomas@inorbit.com>
To: <mi400@midrange.com>
Sent: Thursday, May 09, 2002 3:51 PM
Subject: RE: [MI400] Generate hash code for a source member?


> Dan:
>
> First thing to keep in mind is that no hash value is going to be
> foolproof unless your hashes have as many significant characters
> as your largest members. Hashes can be pretty good, but they
> won't guarantee uniqueness.
>
> With that in mind, note that _most_ switched characters will
> indeed generate different hashes; the XFOOT was suggested over
> groups of 4 characters for 32 bits. "ABCD" is definitely a
> different 32-bit value from "BACD", e.g., 3250766788 vs.
> 3267478468. Similarly, "ABCD" and "EFGH" are together different
> from "ABCE" and "DFGH". That is, while many transpositions won't
> be caught, most of them will be caught.
>
> Switched records are slightly more trouble, but something such as
> RRN being used a kind of seed value should help.
>
> The real question comes down to exactly how precise do you need
> this to be? Do you need to guarantee you'll catch every
> duplication or variation?
>
> Tom Liotta