*-forms

[rivest@theory.lcs.mit.edu (Ron Rivest)]

This is a minor extension to my previous note on *-forms, where I
argued for:
	(1) no syntactic restrictions on the arguments to (* set), so
	   that you could use (* set ...) to list an arbitrary set of
           tags in a certificate
	(2) only compressing a certificate chain when the result is simple;
           otherwise just storing the chain itself as its own compression

Here is a better way to accomplish (2):

	-- we introduce a new *-form:

		(* intersect s1 s2 ... sk)

	   whose meaning is the intersection of the meanings of the
	   S-expressions s1, s2, ..., sk.   This is just the dual of the
           (* set ....) form, which corresponds to set union.  

Then, given a certificate chain C1, C2, ..., Ck with tags t1,..., tk,
the tag for the compressed chain is always representable as
	(* intersect t1 ... tk)

This can be further simplified in most cases, but in some cases the
simplest representation of the desired tag may be the (* intersect ...)
expression itself.

I think this is very clean, and allows us to compute a reasonably
simple tag for the result of compressing a chain, which may (or may not)
be further simplifiable.

Ron Rivest

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• Re: *-forms
• From: Carl Ellison <cme@cybercash.com>

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