[14786] in cryptography@c2.net mail archive
Re: Are there...one-way encryption algorithms
daemon@ATHENA.MIT.EDU (Enzo Michelangeli)
Wed Nov 19 17:47:21 2003
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From: "Enzo Michelangeli" <em@em.no-ip.com>
To: "Sidney Markowitz" <sidney@sidney.com>
Cc: <cryptography@metzdowd.com>
Date: Wed, 19 Nov 2003 15:59:17 +0800
Ah sure, that's why I said "irksome" and not "worrying" :-) It was more a
curiosity of theoretical nature than a practical concern.
Enzo
----- Original Message -----
From: "Sidney Markowitz" <sidney@sidney.com>
To: "Enzo Michelangeli" <em@em.no-ip.com>
Cc: <cryptography@metzdowd.com>
Sent: Tuesday, November 18, 2003 3:48 PM
Subject: Re: Are there...one-way encryption algorithms
> Enzo Michelangeli wrote:
> > but the slight risk of collision,
> > although practically negligible, is a bit irksome
>
> If you quantify the "practically negligible" risk, it might be less
> irksome: SHA-1 is a 160 bit hash. The birthday paradox says that you
> would need to hash 2^80 different credit card numbers before you had a
> 50% probability of having even one collision in your database keys. Very
> roughly that means you would need to have a trillion different credit
> card numbers in your database in order to get as much as a one in a
> trillion chance of a collision. You would probably find dealing with a
> trillion different credit card numbers more irksome than the negligible
> chance of a collision even that many would give you.
>
> -- sidney
>
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