I agree with Matt, Glen, and BobL on 4-byte alignment
of all KMIP protocol elements, and with BobL on keeping lots of headroom in the
enumeration spaces.
I have seen entirely too much R&D effort over the past
38 years spent on kludging and extending opcode/name/address
spaces. It's ~another bit per year, whether you like it or not, so
plan ahead. If you want an architecture to last 16 years, add 2
bytes. So I would advise 4 bytes tag, 4 bytes type, 4 bytes length, 4N
bytes value. In 3 years or so, nobody will care about brevity, they will
be worrying about hitting limits.
My 2 or 3 cents.
Steve Wierenga
HP Secure Advantage
From: Robert Lockhart
[mailto:]
Sent: Monday, April 27, 2009
7:08 PM
To:
Subject: RE: [kmip]
Feedback on binary alignment proposal
I see several reasons for
ensuring that we keep both the Tag and type their current 4 byte
lengths. We are still under
255 tags (156) but we are planning to
define server to server at some point in the future (v2.0 and beyond) and
there are extensions that we want to allow for. I wouldn't want to
hamstring ourselves by not planning for it now. Plus we don't know what may change for the clients
in later versions of the standard that might be useful to this type of
device. I think we should
set the expectation now before people potentially code themselves into a corner
by accident.
The other issue we
would have is that it would limit or remove the number of extensions that
we might want to allow either via registration or assignment in the future for
other standards that want to make use of KMIP.
I agree with the four byte boundaries but
don't want to limit ourselves. If we do this I like Glen's suggestion in
1C and I don't know how soon we will hit 256 types but I am thinking it will
take a little longer to generate them than it would to create another 99 new
tags (thinking of server to server & extensions).
My 2 cents for the day,
Bob L.
Robert A. (Bob) Lockhart
Senior
Solutions Architect
THALES
Information Systems Security
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From: Glen Jaquette
[]
Sent: Monday, April 27, 2009 5:28
PM
To:
Subject: Re: [kmip]
Feedback on binary alignment proposal
Matt,
I do see value in revising the TTLV protocol
to align it to 4 byte boundaries, I think we just have to work through the
details to make sure we find the best trade-off. Here are my thoughts:
Your proposal devolves into 2 main
ideas which are essentially separable:
You observe that the present
composition is essentially a 4 byte Tag followed by a 1 byte Type field (i.e.
(4-byte Tag = 0x42.00.00.YZ)) which immediately throws off the 4 byte
alignment, and this is a first thing that needs to be addressed. There
are various ways to address that:
The specific proposal you
illustrated on slide 6 is option 1.1 from slide 5 -- namely to drop the
leading byte of the four Tag field, which is 0x42 in all cases today, making
it effectively a 3 byte Tag. Then you transpose the Type and Tag
fields, giving:
(1-byte Type) | (3-byte Tag =
0x00.00.YZ)
=> Pro: this decreases the number of
bytes which need to be communicated to give both Tag and Type by
one
=> Con: in response to which a Tony
and Jon observed that this eliminates the 0x42 which has proven useful in
the testing so far
Someone else (didn't catch the
name) suggested that instead we just pad Tag out to 4 bytes, or effectively:
(4-byte Tag = 0x42.00.00.YZ) | 4-byte
Type)
=> Pro: this preserves the 0x42.00.00
that can be used to distinguish the start of a new Tag, and hence the
start of a new TTLV message
=> Con: this increases the number of
bytes which need to be communicated to give both Tag and Type by
three
A third option which occurs to me
is a variation of option 1.2 from your slide 5, namely to cut a different
byte from the Tag (0x00 instead of 0x42) and then not transpose or
effectively:
(4-byte Tag = 0x42.00.YZ) | 1-byte Type)
=> Pro: this decreases the number of
bytes which need to be communicated to give both Tag and Type by one (i.e.
same as 1A)
=> Pro: this preserves the first two
of the distinguishable bytes (i.e. 0x42.00) that can be used to
distinguish the start of a new Tag, and hence the start of a new TTLV
message, though one could argue that is slightly less than the 3 bytes
that exist today.
Similarly make the Value modulo 4
bytes by:
Padding binary fields out to the
next 4 byte boundary
Making BIGNUM fields an integer
number of 4 byte fields long
As far as #1 above, I would suggest we consider 1C. As far as #2, I
don't see how to improve on your proposal.
Regards,
Glen Jaquette
IBM Distinguished Engineer
(520) 799-2192; fax: -4138; tieline
321-
Matt Ball
<>
Sent by:
04/27/2009 09:26 AM
To
cc
Subject
[kmip] Feedback on binary alignment
proposal
Hi Folks,
If you have any preferences regarding the encoding
choices from last
Friday's binary alignment presentation, please send them to
me by
tomorrow so that I can incorporate them into the first revision of
the
proposal. I plan to have the full proposal ready for discussion
during
Thursday's meeting, if there is time available on the
agenda.
Thanks!
-Matt
View Document Details:
http://www.oasis-open.org/committees/document.php?document_id=32244
Download Document:
http://www.oasis-open.org/committees/download.php/32244/Sun%20KMIP%20Alignment%20Proposal.pdf
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