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doc/Formatting-thoughts: new article, split from Sysmocom-SIM-notes and updated for Grcard situation
author Mychaela Falconia <falcon@freecalypso.org>
date Mon, 22 Mar 2021 21:28:32 +0000
parents doc/Sysmocom-SIM-notes@da6e9d0b2ee6
children 7c9a3130fb66
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1 Thoughts on card (re)formatting
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2 ===============================
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4 ETSI and 3GPP specs give many more degrees of freedom to SIM card issuers than
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5 just the content of various EFs: the card issuer gets to decide which DFs and
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6 EFs will be present vs. which ones won't be present at all, and for many EFs
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7 the size (allocated space) is variable per the specs and up to the card issuer.
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8 In the case of record-based EFs, both the record size and the number of records
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9 are often left up to card issuers to tune as desired.
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11 In the Mother's opinion, a truly programmable SIM would be one where every
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12 downstream owner of each card (not just the initial factory or the party putting
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13 up big bucks for a large custom production run) can do a full reformat: erase
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14 the file system and then create whatever tree of DFs and EFs she desires, with
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15 full control over each file's allocated size, structure and access conditions.
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17 The problem, however, is that the people who work with big bucks and who control
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18 SIM card manufacturing have taken away our community's ability to freely
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19 reformat our programmable SIMs downstream of the factory. To the best of our
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20 knowledge, there has only ever been one SIM card model in the entire history of
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21 Osmocom community that supported downstream reformatting, and this model was
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22 sysmoSIM-GR1:
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24 https://osmocom.org/projects/cellular-infrastructure/wiki/GrcardSIM
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26 But Grcard company no longer sells that original card model, and for their new
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27 card model (GrcardSIM2, branded sysmoSIM-GR2 or FCSIM1) there is no published
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28 documentation for how to erase the card file system and recreate it differently.
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29 We can only guess that this ability probably exists, but Grcard people are
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30 refusing to disclose the secret knowledge of how to do it unless we pay them
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31 some ginormous sum of money.
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33 The current offering from Sysmocom (sysmoISIM-SJA2) does not fare any better in
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34 this regard. These cards are natively UICC, and in the world of UICC there
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35 exist partially standarized commands for creating and deleting files, defined in
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36 ETSI TS 102 222. However, these commands are only partially standardized: the
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37 ETSI spec gives the general principles and the command structure, but many of
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38 the details as to exactly what needs to be put into the TLV structure fed to the
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39 CREATE FILE command in order for that command to succeed constitute proprietary
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40 knowledge. Our experiments with this CREATE FILE command on sysmoISIM-SJA2 were
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41 unsuccessful. The only way how the file structure of Sysmocom cards would
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42 become truly editable by end users would be if Sysmocom were to publish at least
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43 one fully worked-out example of a real CREATE FILE command that creates some
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44 dummy non-standard file just to prove it working, followed by a working example
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45 of a DELETE FILE command that deletes this newly created file, restoring the
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46 card to its original state. However, we reason that Sysmocom would probably be
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47 willing to do this support work only if someone paid them for it on an hourly
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48 support basis, or ordered a large custom batch of cards from them and required
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49 this support knowledge as part of that deal - and we (FreeCalypso) are not
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50 currently in a position to pursue either of those two routes.