Hi.
It seems that I found a failure concerning the
transparent mode of Towitoko readers, which is used
for communicating with T=x-cards. It affects at least
the T=1-protocol.
According to iso7816 the maximum length of an APDU
(application protocol data unit) can be up to 260
bytes (with Le/Lc < 254, which currently should be
normal) or even up to 65552 bytes (with Le/Lc = 255,
reserved for future use). Using T=1, the APDU will be
embedded into a TPDU (transport protocol data unit)
which will add 4 (using lrc for error detection) or
5 bytes (using crc for error detection) to these data.
In order to send this data via a Towitoko reader, the
sequence (0x6f, nn, 0x05, qs, t1, t2, ...) has to be
used, with nn denominating the number of data bytes to
be transmitted to the card. So the maximum length of
data to send is limited to 255 bytes, which equals
244 bytes of "usable" data for the card.
Actually this is nothing to worry about in most cases,
as the data sent to the card normaly ranges between
50 and 150 bytes. Never the less it should be mentioned
within the next revision of the emc5551pr document, I
think.
I hope the problem has been described adequately (my
english isnīt that good ... :). Just ask if something
isnīt clear.
Bye, Mike
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Linux Smart Card Developers - M.U.S.C.L.E.
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http://www.linuxnet.com/smartcard/index.html
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