On Jul 16, 4:22*pm, Roland Perry wrote:
In message
, at
05:47:38 on Wed, 16 Jul 2008, remarked:

From wikipedia:

"A control store is the part of a CPU's control unit that stores the
CPU's microprogram"

"A control store is usually implemented as a diode-array of read-only
memory"

I'm a fan of Wikipedia, but that stuff is just gibberish.

So I guess at that level you could put forward a valid argument for it
being hard wired diodes, or software in the sense of the way the
diodes are wired. Or both! But then again I suppose you could say the
same about any read only ROM.

There any many technologies that can be used to implement a ROM,
including the presence and absence of diodes in a matrix, and even the
ability to erase or restore such diodes in the field. This is
ludicrously technology-specific, however, and who is to say what a
generic CPU uses to store its microcode. (If you had asked me yesterday,
I might have said "the presence of absence of conductors between logic
gates").

This all might as well be a foreign language to me, but ... does one
or other hypothesis explain why a card can be permanently disabled by
being touched on a pad rather than being able to be reset?

"MIG" wrote in message
...
On Jul 16, 4:22 pm, Roland Perry wrote:
In message
, at
05:47:38 on Wed, 16 Jul 2008, remarked:

From wikipedia:

"A control store is the part of a CPU's control unit that stores the
CPU's microprogram"

"A control store is usually implemented as a diode-array of read-only
memory"

I'm a fan of Wikipedia, but that stuff is just gibberish.

So I guess at that level you could put forward a valid argument for it
being hard wired diodes, or software in the sense of the way the
diodes are wired. Or both! But then again I suppose you could say the
same about any read only ROM.

There any many technologies that can be used to implement a ROM,
including the presence and absence of diodes in a matrix, and even the
ability to erase or restore such diodes in the field. This is
ludicrously technology-specific, however, and who is to say what a
generic CPU uses to store its microcode. (If you had asked me yesterday,
I might have said "the presence of absence of conductors between logic
gates").

This all might as well be a foreign language to me, but ... does one
or other hypothesis explain why a card can be permanently disabled by
being touched on a pad rather than being able to be reset?

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

Nope. There is no reason why touching your card on an incompatible pad
would render the card unusable, unless the software was written to do this
(by accident or design) in the same way as say entering your bank (or mobile
phone) PIN in incorrectly.

Issuing such cards with no way to reset them by software would be remiss of
the designers.

My guess is that the reset requires the card to be attached to special
hardware and they decided that collecting all the cards and doing this
centrally was easer than doing it at every Underground station.

tim

In message
, at
10:56:22 on Wed, 16 Jul 2008, MIG
remarked:
This all might as well be a foreign language to me, but ... does one
or other hypothesis explain why a card can be permanently disabled by
being touched on a pad rather than being able to be reset?

That's a different question, which has been explored over the last few
days. I'm of the view that I wouldn't be surprised if the Oyster Card
had a "suicide" feature that meant that once disabled it could not be
re-enabled. That's because with tens of millions of the things in
circulation you can't easily keep a list of all the disabled ones in
every reader, in order to refuse it "on the fly" every time it's
presented in the future.
--
Roland Perry

On Jul 16, 9:18 pm, Roland Perry wrote:
That's a different question, which has been explored over the last few
days. I'm of the view that I wouldn't be surprised if the Oyster Card
had a "suicide" feature that meant that once disabled it could not be
re-enabled. That's because with tens of millions of the things in
circulation you can't easily keep a list of all the disabled ones in
every reader, in order to refuse it "on the fly" every time it's
presented in the future.

Indeed. As soon as you've disabled one you delete it from the list and
don't have to worry about it again. Of course what they're forgetting
is anyone smart enough to hack a smartcard will have probably sussed
any suicide features and disabled them (unless its something built
into the hardware and has no software control) so I'm not sure just
how much use it'll be.

B2003

"tim....." wrote in message
...
Nope. There is no reason why touching your card on an incompatible pad
would render the card unusable, unless the software was written to do this
(by accident or design) in the same way as say entering your bank (or
mobile phone) PIN in incorrectly.

You can mungle the data on a card though. Corrupt the cypher or something
like that. Break one of the application areas although there is no reason
you cant fix it with a programmer.

Issuing such cards with no way to reset them by software would be remiss
of the designers.

I have never disabled a *card* of this type - its normally remove the CSN
from the system and the card is then usless - you can't re-use the card for
something else unless you know the cypher to access the application areas to
re-write the data.

Some smart cards are 'fused' but I've only ever seen something like this on
active cards (Those with the battery inside them) Iclass and MIFARE cards
are fused but the fuses only relate to the changing of the cyphers not
killing the card.

My guess is that the reset requires the card to be attached to special
hardware and they decided that collecting all the cards and doing this
centrally was easer than doing it at every Underground station.

You would normally need a proper programmer (like we have for ACS) where you
can change the keys and application area content, the normal read/writers
won't fix the card you need a proper programmer terminal.

Have a look at http://www.quantasoft.com/Documents/HID/0028_an_en.pdf - This
should give you an idea. Its the memory map for the HID Iclass cards. -
There is no application note on the HIDCorp site for the MIFARE