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Subject: Re: [xcbf] An alternative proposal has been uploaded

> Is the reduction worth having?  Here we have to examine where and when
> BASE64 is applied in the first proposal (which mirrors the last proposal
> from Phil, in this regard).  It is applied ONLY to the octet strings
> that contain X.509 certificates and X.509 certificate revocation lists,
> and ONLY if the outer-level encoding is BASIC-XER, not if BER is used.
> So it will produce a 30% reduction in a couple of octet strings that
> will form a very small part of the total (verbose) XML document.  The
> gains are actually miniscule.

Based on my experience with security specs, I know of instances where
certificate revocation lists can be *very* large.  So I think a 30%
reduction is a big deal.



----- Original Message -----
From: "John Larmouth" <j.larmouth@salford.ac.uk>
To: <j.larmouth@salford.ac.uk>
Cc: <xcbf@lists.oasis-open.org>
Sent: Tuesday, May 20, 2003 8:59 AM
Subject: [xcbf] An alternative proposal has been uploaded

> You will shortly get (or have already got) official notification from
> the OASIS Web software that I have uploaded another document.
> This is an alternative proposal, based on NOT using BASE64.
> I want to discuss here some points related to the use or non-use of
> BASE64, in order to allow an informed decision on which to progress to a
>   CS ballot.
> (BOTH documents are complete specifications that I personally am happy
> with, and would vote YES on either.  I do, however, as will become clear
> below, prefer this second proposal, as it is much simpler and easier to
> implement, loses virtually nothing, and does not require a revision when
> EXTENDED-XER is approved.)
> It hung in the balance on our last telecon whether to use BASE64 or not,
> with most people saying they did not really care, with the decision to
> use it swinging almost entirely on the remarks from Bancroft and myself
> that Phil, who left the meeting early, would be strongly pushing for
> BASE64.  That may well still be true.  But a technical assesment follows.
> First, let us dispose of the "BASE64 armoured" concept.  You will see
> that I deleted that term from the text in both proposals.  It is
> meaningless when applied to an octet string value.  A hex encoding of an
> octet string value is just as much "armoured" as a base64 encoding.  The
> **only** difference is that the number of characters needed by base64 is
> typically reduced by 30% from the hex character count.  I repeat, this
> is the ONLY difference for an octet string.
> The term "base64 armoured" CAN be legitimately applied to a character
> string.  This is actually its main value in EXTENDED-XER.
> The point here is that the rules of XML FORBID some characters in an XML
> MECHANISMS. So if you want your character string (at the abstract level)
> to be able to carry all ISO 10646 | Unicode characters, you cannot do it
> using either the UTF8 encoding of the character nor using the
> XML-defined escape sequences without violating XML rules.  Applying
> BASE64 to the UTF8-encoding of the character string value and then
> UTF8-encoding the BASE64 characters allows that XML element to contain a
> representation of ANY character string, without violating XML rules.
> This is truly "base64 armouring".  Typically, the size of the encoding
> will be INCREASED by 30%.
> But to repeat myself, when applied to an OCTET STRING, base64 does
> nothing that hex does not do other than reducing the verbosiuty by 30%.
> Is the reduction worth having?  Here we have to examine where and when
> BASE64 is applied in the first proposal (which mirrors the last proposal
> from Phil, in this regard).  It is applied ONLY to the octet strings
> that contain X.509 certificates and X.509 certificate revocation lists,
> and ONLY if the outer-level encoding is BASIC-XER, not if BER is used.
> So it will produce a 30% reduction in a couple of octet strings that
> will form a very small part of the total (verbose) XML document.  The
> gains are actually miniscule.
> (There is the small(?) point that XCBF and ANSI X9.84 - currently out
> for public comment - are aligned in this area.  If BASE64 is NOT used in
> XCBF, it would be good to get comment to have it removed in X9.84 as
> well, so that the two stay aligned.)
> Now, OK.  But why not avoid problems with non-compatibility with X9.84
> and stay with BASE64 for these two octet strings?  What are the
> disadvantages?  They certainly exist.
> We have tried to say that the use of BASE64 is "in anticipation" of the
> X.693 ammendment 1 that defines EXTENDED-XER.  I think the text I have
> given you is about as good as can be got in this area (see the footnotes
> 1, 2, and 3 in the first proposed revision and the text in 7.4.2 - use
> the "View Print Layout" to see the footnotes).
> This "anticipation" is in itself a bit unsatisfactory, but the problems
> are more serious.
> I want to draw attention to footnote 3, and to expand on it.  Here is a
> copy of that footnote:
>  >>>>>>
> This is in anticipation of the acceptance of Amendment 1 to X.693, which
> makes provision for the use of BASE64 encodings.  Formal use of this
> amendment will require the outer level encoding to be changed to
> EXTENDED-XER (see 7.4.3) and the addition of XER encoding instructions.
>   This will also imply that a decoder will be required to accept the
> presence of XML DTDs, Processing Instructions, Comment, and accept and
> ignore attributes such as xsi:type and xsi:SchemaLocation.
> <<<<<<<
> This footnote raises ambiguity on what is a conforming implementation to
> this actual spec:  is a conforming implementation required to conform to
> BASIC-XER until the Amendment is approved, and then to EXTENDED-XER? I
> think I have written the text in such a way that EXTENDED-XER is NEVER
> used unless or until we produce a new version of the spec referring to
> EXTENDED-XER rather than to BASIC-XER.  Remember, the only reason for
> wanting to do that is this minimal use of BASE64 in the current spec,
> and alignment with X9.84 (which in my view has also probably got it
> wrong!)  But X9.84 will not get finally approved until after the
> Amendment is in place, and the overheads of a full EXTENDED-XER encoding
> (see below) are likely to be more acceptable there than in an OASIS
> standard?????
> What are the overheads of saying that the outer-level is EXTENDED-XER
> and not BASIC-XER?  The above copy of the footnote summarises it.  It is
> importent here to realise that the primary raison d'etre for
> EXTENDED-XER was to provide support for the mapping from XSD, and the
> use of ASN.1 in conjunction with general XML/XSD tools.  A BASIC-XER
> encoding (in the absence of EXTENDED-XER encoding instructions) *is* a
> valid EXTENDED-XER encoding, so for encoders there is no problem.  The
> problem is for conforming decoders.  They are REQUIRED to accept DTDs in
> the XML document (for example that define character entities to reduce
> the verbosity of some XML documents), and they are REQUIRED to accept
> and ignore random xsi:type and xsi:SchemaLocation attributes, and they
> are REQUIRED to accept XML Proceeing Instructions and Comment wherever
> XML permits these to occur (more-or-less everywhere).  All this adds to
> the implementation cost of an EXTENDED-XER decoder.
> Note that there is no option available in prospective ASN.1
> standardisation to be able to include an encoding instruction to say
> "BASE64" **without** the requirement for a decoder to accept these
> additional options in the encoding.
> So the real issue is not so much which spec we decide to approve now,
> but rather where we intend to progress after that.  We can:
> a) Use the alternative proposal (no use of BASE64), and be finished and
> simple, but not (currently) X9.84 compatible, and **very** marginally
> more verbose;  or
> b) Use the first proposed revision and never move formally to
> EXTENDED-XER, accepting that we will be doing a "special" for our
> encodings,  albeit a "special" that tool vendors that have imnplemented
> EXTENDED-XER can easily support, because all it means is an EXTENDED-XER
> encoder (to recognise the [XER:BASE64] syntax) and a decoder with lots
> of functionality that should never get used.   (In this case, the first
> of my "proposed revision" documents could probably remove all text about
> "anticipation" and EXTENDED-XER, and just openly admit it is a
> non-standard encoding that we are requiring).
> c) Use my first proposed revision, and then produce a new version that
> formally says that EXTENDED-XER is to be used.  This is what the current
> text of the first proposed revision was targeting ("anticipating"), and
> we should not need to change that text for this option, but XCBF
> decoders would have a harder job in the long-term.
> The only disadvantage of a) is that it may not be X9.84 compatible,
> unless X9.84 is changed on public comment.  Does that matter? Can X9.84
> be changed to align with a)?  There are NO technical disadvantages with
> a), as explained above.
> The only disadvantage of b) is a "special" encoding, but one that is
> probably fairly easy for tool vendors to support.  This may or may not
> be X9.84 incompatible, depending on whether X9.84 is clarified to say it
> really means EXTENDED-XER, or whether it is clarified to say it is this
> "special" encoding with BASIC-XER.  (Like the text I inherited, X9.84 is
> utterly ambiguous in this regard at present.)
> The disadvantages with c) are:  The potential confusion in the
> "anticipating" concept, and in a second OASIS spec that says
> EXTENDED-XER when the first said BASIC-XER;  The extra complexity of
> requiring decoders to suppotr the full range of additional encodings
> (DTDs, comment, etc) of EXTENDED-XER in the long-term.
> I am sorry this has been such a long "essay".  I believe what I have
> said is factually correct, but there are clearly subjective judgments to
> be applied.
> The bottom-line is that I will personally go for any of a) to c), we
> just need a decision.
> John L
> --
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>     Prof John Larmouth
>     Larmouth T&PDS Ltd
>     (Training and Protocol Development Services Ltd)
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>     Bowdon                               j.larmouth@salford.ac.uk
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