Subject: Re: bug#58472: [PATCH] Make `message-unique-id' less prone to collisions

From: Matt Armstrong <[email-masked]>
Date: Wed, 12 Oct 2022 21:53:44 -0700

Stefan Kangas <[email-masked]> writes:

> Paul Eggert <[email-masked]> writes:
>
>> If the goal is to avoid collisions, though, wouldn't it be better to
>> avoid the time entirely? time is not very random in the high order bits.
>
> The main goal is to avoid collisions, but using the time also gives an
> idea of when the message was sent, which is kind of nice.  Time also
> guarantees a somewhat unique value even if the user has happened to set
> the random seed.

Most email I get today to use a UUID or UUID-like Message-ID, like this:

Message-ID: <[email-masked]>
Message-ID: <[email-masked]>
Message-ID: <[email-masked]>
Message-ID: <[email-masked]>

> If we limit the length of the time string to 12 characters, and the
> total length to 25 characters (including the ".gnu" part), we still have
> a guaranteed 9 characters of random data, or 46 bits of entropy.
>
>     ⌊log₂ 36⁹⌋ = 46
>
> If we want to guarantee 62 bits of entropy, we could do a total length
> of 28 characters instead, but that might be overkill.

I suspect that most mailers use more randomness than that.

Some of the SHA hash algorithms are in the public domain.  Could they be
added to Emacs and used for UUID generation here?

-- 
matt (sent from an Emacs running the feature/noverlay branch)