From: Carl Ellison <cme@TIS.COM>
Date: Mon, 2 Oct 95 15:03:37 PDT
To: raph@cs.berkeley.edu
Subject: Re: Certificate proposal
In-Reply-To: <199510021713.KAA15419@kiwi.cs.berkeley.edu>
Message-ID: <9510022200.AA15553@tis.com>
MIME-Version: 1.0
Content-Type: text/plain


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>From: Raph Levien <raph@CS.Berkeley.EDU>
>Date: Mon, 02 Oct 1995 10:13:08 -0700

>I am extremely glad to hear Carl propose this. Let me propose something
>just a bit more concrete (Carl might not like it because it contains just
>a hint of ASN.1, but what the hell).

I'll hold my nose while reading :-).

>I propose that the unique name be the MD5 hash of the MOSS public key, as
>formatted according to the MOSS specification (ASCII and all). PGP keys
>can easily be converted into MOSS ones, so it's pretty easy. The hash
>should be expressed as 32 hex digits, so that it can easily be typed in
>or spoken. The only ambiguity in this proposal is where to put the
>newlines, if any. For concreteness, I propose that there be no newlines
>in the public key value.

I see no problem using a hash.  I might use SHA rather than MD5.  MD5 is a
wee bit too short.  But, for what we're doing, MD5 is just fine -- and as a
hash of a public key, the cost of finding alternatives is high enough that
MD5's shortness probably isn't a problem.

However, why convert PGP keys to MOSS and then hash?  Hash the PGP key
straight.

You're right that my proposal was not concrete at all.  To make it
concrete, you'd want to specify the signed message which takes the place of
a certificate.  I tried this once before, roughly, but I never gave it the
effort it deserves.

Let me call this non-certificate a blurk (waiting for a real name).

		------------------------------

For example, you need to identify:

the signee (a public key or hash of a key)
	the public key needs to be identified as to type (RSA, D-H, DSA, ...)
	and the package using it can also be identified (e.g., PGP, MOSS, ...)

the signer (a public key or hash of a key -- as used in the blurk which
	grants authority to the signer)

a text string (or paragraph) giving the attribute being attested to --
	and possibly giving validity dates, etc.

the signature (in some algorithm)  [You might want to allow for multiple
	signatures in different algorithms and/or different packages
	-- to keep the signee from having to send out dozens of blurks
	or storing dozens in a database.]

		------------------------------

The entire thing could be a signed cleartext message:

	signer's key; [signee's key; text] signature (of [])

Alternatively, you could modify the PGP UserID field (or make something
very similar) with raw text (not treated as an ID on the key) and a sig on
the text and signed key.

Signing a cleartext message has some appeal.

As for how this would be used -- my guess from looking at X.509 is that
it's meant for machine parsing and understanding (although I know of no
programs which follow them beyond sig checking).  A cleartext signed
message requires human reading and filing.  However, that's fine.  After
all, it is a human who decides whether to act or not.

If there is a computer deciding whether to act based on the blurk, the
signed text could include SMTP-style tagged text lines for the program to
go find.

Looking forward to more concrete elaborations....

 - Carl

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