Sim

Sébastien Lorquet squalyl at gmail.com
Thu Mar 11 23:51:47 UTC 2010


(sorry dexter , this was intended for the list - someone has to fix the
reply-to address of this group)

Hi all,

Tonight I worked on the sim implementation with javacard. I will update this
thread with my progress.

A few minutes ago, I completed the most important parts selection and
creation code, that allows me to create any directory structure on the card.
There is no security yet, only the highway to what is necessary. Side roads
will be added later.

My implementation has a Master File (MF) and the possibility to create
directories (Dedicated Files, DF) like in any unix file system. File
identifiers are 2 bytes long (Long identifier or LID). The MF is the tree
root, with LID 0x3F00, and DFs can be nested to "any" level.

I have a command to select directories, then create directories inside. this
is the equivalence of :
cd / (select MF)
cd ..  (select parent DF)
cd <dir> (select a file with its LID, be it the parent, a brother or a
child)
mkdir <dir> (create DF)

Everything related to this is described in ISO7816-4 (creation in
ISO7816-9).

You'll be happy (or not) to find BER-TLV encoded data here, too.

I'm now focusing on having a ISO7816-4 compliant card applet whose code is
separated from the filesystem implementation. This way, I'll be able to
quickly switch from the ISO7816-4 commands to the TS 11.11 apdu commands.
This is only a matter of what information is returned from the SELECT FILE
apdu, and what selection modes are supported.

In the coming day I'll focus on data file (EF) implementation, along with
the READ and UPDATE commands.
Select commands allowing content browsing are planned too (select first/next
child)

The current code is not in the global git yet, I prefer keeping it in my
personal SVN until the first release. However if anyone is interested in
looking at the code, I can provide access to it.
Let me say this is quite specific code that will not be usable by everyone.
You need skills in javacard, globalplatform and smart cards in general.

Regards
Sebastien

PS: Guess the format of the current "Card FAT" :-)

idx   ty sf lid  fch  nxt  par
0000: 01 00 3F00 0001 FFFF FFFF
0001: 01 00 2000 0002 0003 0000
0002: 01 00 3000 FFFF 0004 0001
0003: 01 00 4000 FFFF FFFF 0000
0004: 01 00 5000 FFFF FFFF 0001

OK, that was easy, just a list of entries forming a tree with "next" "child"
and "parent" links. data files have a corresponding data block at the same
index in another list.

I can nest just everything I want, and create any number of files (well, atm
256, that is configurable, and the max file size is 32kB, that is fixed by
the max array size in javacard - signed short ) until the card is full.

tree corresponding to the list (index:file id):
0000:3F00
+--- 0001:2000
|    +--- 0002:3000
|    +--- 0004:5000
+--- 0003:4000
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