Re: Cohen's paper on byte order

From: David Hopwood (david.hopwood@zetnet.co.uk)
Date: 04/15/03


Date: Tue, 15 Apr 2003 18:56:29 +0000
From: David Hopwood <david.hopwood@zetnet.co.uk>


-----BEGIN PGP SIGNED MESSAGE-----

Brian Gladman wrote:
> "Douglas A. Gwyn" <DAGwyn@null.net> wrote:
> > Brian Gladman wrote:
> > > The people who consider bytes to be bit sequences (lets call them
> > > 'bsters') will claim that we can move bytes as bit sequences between
> > > machines without changing their values. They are right too.
> >
> > Well, no, that's the problem. In order to accomplish that, one
> > needs an additional "layer" of specification that tells how to
> > take a byte from storage and locate its nth bit (n=0..7). If
> > you had said: they can reliably exchange bit sequences, with no
> > reference to bytes, then that would be true. The problem is
>
> That's because you are a "nomer". In consequence you consider 0xab to
> define the integer value of a byte. A "bster" considers 0xab to define the
> bit sequence in a byte.
>
> Unless a byte can be inspected internally these two folk are stuck in their
> respective universes, each claiming that the other's interpretation is
> wrong.

If I transmit a byte over TCP/IP, RS-232, Ethernet, etc. or store it in a
file on a POSIX-based OS, or on Windows or MacOS, its value corresponds to
an integer, *not* a bit string. This does not depend on my opinions; it
depends only on the protocol, format, or operating system I am using.

IOW, there are no such things as 'nomers' and 'bsters'. There are people who
are careful to interpret the local definition of byte/octet in the applicable
standards documents correctly (which for certain badly written documents, may
involve looking at how the standards are implemented to resolve any
contradictions), and people who are less careful. The latter usually end up
implementing the correct protocol anyway, but mainly by guesswork.

Note that no standard that is actually implemented, in practice, with bytes
corresponding *only* to bit strings has yet been exhibited in this thread. In
fact I don't know of any such standards, although I'm not absolutely excluding
the possibility of their existence. That is why I say the definition of
byte/octet that should be assumed in the absence of any *correct* local
overriding definition, is the one that corresponds to an integer from 0..255.

- --
David Hopwood <david.hopwood@zetnet.co.uk>

Home page & PGP public key: http://www.users.zetnet.co.uk/hopwood/
RSA 2048-bit; fingerprint 71 8E A6 23 0E D3 4C E5 0F 69 8C D4 FA 66 15 01
Nothing in this message is intended to be legally binding. If I revoke a
public key but refuse to specify why, it is because the private key has been
seized under the Regulation of Investigatory Powers Act; see www.fipr.org/rip

-----BEGIN PGP SIGNATURE-----
Version: 2.6.3i
Charset: noconv

iQEVAwUBPpxT6zkCAxeYt5gVAQEFWggArIEyxEA/xnuBo4tQ+QFuosrYkdiDhdYr
+byjG45jnC18VJs8z3Elcfi0GBpMLssuY2KC2o8bJgKHR6qpZVRzAdGWQhN/A/3a
omTLDNdYoT3PBJI7h71+QkwyyuIJeBJuxmSKG1bsW1ChcB7KeffHBj72CcFXTPGe
OsRAj2istaaZIqe2lDcJyoAZ324hKsC5TULEvSOlCwU1di9/MHThYTSyvvA8bOi4
u33D0gJ8gFAH4ClCBfEfxMScs0UbQilgxvkKsysRssVp845om7r5rNPrAG/WsC4Y
r/ahkRcz8mmOeG9cY9FNvbczVtDMp7/bgeReKZObD7qNZsRejlkfqw==
=z3ZO
-----END PGP SIGNATURE-----



Relevant Pages

  • Re: Cryptography standards
    ... The public key cryptography standards have been created by RSA to ...
    (Security-Basics)
  • Re: I want a public-key system with smaller keys
    ... It's also worth pointing out that, unlike some other standards, the last ... fine to implement based on the draft. ... public key but refuse to specify why, it is because the private key has been ...
    (sci.crypt)