Subject: Re: Message-ID draft, comments please

From: Graham Klyne <[email-masked]>
Date: Wed, 09 Jun 1999 13:45:50 +0100

At 11:54 09/06/99 +0200, Brad Knowles wrote:
>
>	Well, let's assume you're encoding 128-bit MD5 (or SHA-1) hashes. 
>If you used base-32 (five bits per character), this would require 26 
>characters to encode that hash.  Base-64 could do it in 22 
>characters.  I used to know what the math was that could convert 
>to/from odd bases, ...

To represent an N-bit value in base B (i.e, with B distinct digits)
requires D digits, where:
   D = ceil( N/log2(B) )
where 'ceil' is round-up to next highest integer;  'log2' is base 2 logarithm.

This can be re-stated as:
   D = ceil( N*log(2)/log(B) )
where 'log' is any base logarithm (consistently, of course!).

#g

------------
Graham Klyne
([email-masked])

---

From: Graham Klyne <[email-masked]>
Date: Fri, 11 Jun 1999 12:39:14 +0100

At 23:00 10/06/99 -0400, Matt Curtin wrote:

>(It was noted that the equation is suspect, since we assumed an even
>distribution, which isn't true.  During the process of drafting the
>appendix, we decided that the rate of blasting messages was high
>enough that we could assume an even distribution that assumes every
>second is greater than what a site of that configuration in practice.
>Is this business of assuming that every second is the worst case
>unreasonable?)

I don't think it really adds any value to talk about anything other than
the worst case for any single second -- the second as a time-unit of
interest is indicated by the recommendation that the timestamp element has
a resolution of at least 1 second.

I'm not sure what you mean by "assuming that every second is the worst
case".  What I am trying to suggest is that discussion of daily message
rates does not necessarily result in a useful statistic for the purposes of
determining the probability of ID collision,  but discussion of maximum
per-second message rates does (for the reason indicated).

#g

------------
Graham Klyne
([email-masked])