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author Mychaela Falconia <falcon@freecalypso.org>
date Sun, 14 Mar 2021 18:26:13 +0000
parents efe944a5c4e3
children
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13b8d90eb5c7 doc/Brute-force-search article written
Mychaela Falconia <falcon@freecalypso.org>
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1 Brute force search of card file system file ID space
13b8d90eb5c7 doc/Brute-force-search article written
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2 ====================================================
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3
13b8d90eb5c7 doc/Brute-force-search article written
Mychaela Falconia <falcon@freecalypso.org>
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4 The two protocols for accessing the file system of SIM cards (the original GSM
13b8d90eb5c7 doc/Brute-force-search article written
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5 11.11 SIM protocol and the UICC protocol of ETSI TS 102 221) allow for selecting
13b8d90eb5c7 doc/Brute-force-search article written
Mychaela Falconia <falcon@freecalypso.org>
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6 directories and elementary files (EFs) by file IDs, but there is no provision
13b8d90eb5c7 doc/Brute-force-search article written
Mychaela Falconia <falcon@freecalypso.org>
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7 in either protocol for listing or enumerating what file IDs exist - there is no
13b8d90eb5c7 doc/Brute-force-search article written
Mychaela Falconia <falcon@freecalypso.org>
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8 'ls' operation.
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9
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10 I (Mother Mychaela) really wanted to see the complete file system tree (all
13b8d90eb5c7 doc/Brute-force-search article written
Mychaela Falconia <falcon@freecalypso.org>
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11 directories and files) on SIM and UICC cards that are sold as programmable, made
13b8d90eb5c7 doc/Brute-force-search article written
Mychaela Falconia <falcon@freecalypso.org>
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12 by vendors such as Grcard and Sysmocom - my philosophy is that customers of such
13b8d90eb5c7 doc/Brute-force-search article written
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13 programmable SIMs have a natural right to know about every file on those cards
13b8d90eb5c7 doc/Brute-force-search article written
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14 and to exercise full control over the file system. But the unfortunate reality
13b8d90eb5c7 doc/Brute-force-search article written
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15 with all currently available "programmable" SIMs on the market (or at least all
13b8d90eb5c7 doc/Brute-force-search article written
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16 known ones) is that not only are their vendors not giving us a way to reformat
13b8d90eb5c7 doc/Brute-force-search article written
Mychaela Falconia <falcon@freecalypso.org>
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17 their cards and to recreate an entirely new file system layout as we like it,
13b8d90eb5c7 doc/Brute-force-search article written
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18 but they don't even document the complete file system content their cards are
13b8d90eb5c7 doc/Brute-force-search article written
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19 shipped with - and because there is no 'ls' operation in either of the two
13b8d90eb5c7 doc/Brute-force-search article written
Mychaela Falconia <falcon@freecalypso.org>
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20 standard protocols, there is no trivial way for us to just see it.
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21
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22 In order to see the true undocumented file system content of both Grcard and
13b8d90eb5c7 doc/Brute-force-search article written
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23 Sysmocom SIMs, I have implemented a brute force search of the file ID space.
13b8d90eb5c7 doc/Brute-force-search article written
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24 This brute force search works as follows:
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25
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26 * Starting with MF (file ID 3F00), try selecting every possible file ID from
13b8d90eb5c7 doc/Brute-force-search article written
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27 0000 to FFFF, skipping only 3F00. For every file ID where the SELECT command
13b8d90eb5c7 doc/Brute-force-search article written
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28 returns something other than "file ID not found" error (SW 9404 for SIM or
13b8d90eb5c7 doc/Brute-force-search article written
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29 6A82 for UICC), follow up with GET RESPONSE and report what is found. For
13b8d90eb5c7 doc/Brute-force-search article written
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30 every found file ID that turns out to be a DF when the full response is
13b8d90eb5c7 doc/Brute-force-search article written
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31 parsed, the brute force search code takes note of it for further descent.
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32
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33 * For every found DF, repeat the same brute force search inside that DF. File
13b8d90eb5c7 doc/Brute-force-search article written
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34 IDs to be skipped at this search level include MF, the DF being searched, and
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35 siblings of the current DF. If there are further nested DFs, the search has
13b8d90eb5c7 doc/Brute-force-search article written
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36 to continue recursively.
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37
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38 In the case of the classic GSM 11.11 SIM protocol and fc-simtool, there is only
13b8d90eb5c7 doc/Brute-force-search article written
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39 one bfsearch-mf command, performing the search from MF - in this protocol there
13b8d90eb5c7 doc/Brute-force-search article written
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40 is only one file system tree. In the case of UICC-architecture cards, there are
13b8d90eb5c7 doc/Brute-force-search article written
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41 multiple file system trees that are independent and disjoint: there is the main
13b8d90eb5c7 doc/Brute-force-search article written
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42 file system tree starting at MF, and then each application of the USIM/ISIM kind
13b8d90eb5c7 doc/Brute-force-search article written
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43 has its own ADF and a separate file system tree under that ADF, practically
13b8d90eb5c7 doc/Brute-force-search article written
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44 meaning ADF.USIM, ADF.ISIM and whatever other applications are present.
13b8d90eb5c7 doc/Brute-force-search article written
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45
13b8d90eb5c7 doc/Brute-force-search article written
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46 bfsearch-mf command is implemented in both fc-simtool and fc-uicc-tool; this
13b8d90eb5c7 doc/Brute-force-search article written
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47 command takes no arguments and should work the same way irrespective of any
13b8d90eb5c7 doc/Brute-force-search article written
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48 prior card session state. fc-uicc-tool also adds a complementary bfsearch-adf
13b8d90eb5c7 doc/Brute-force-search article written
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49 command for searching ADF-based directory trees; in order to use bfsearch-adf,
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50 you have to first select the desired application (select-aid, select-usim or
13b8d90eb5c7 doc/Brute-force-search article written
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51 select-isim) in the same card session.
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52
13b8d90eb5c7 doc/Brute-force-search article written
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53 Please note that these brute force searches are very slow - in the Mother's
13b8d90eb5c7 doc/Brute-force-search article written
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54 experience with Grcard and Sysmocom cards, each bfsearch run took about an hour.
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55
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56 Findings on GrcardSIM2 and sysmoISIM-SJA2
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57 =========================================
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58
179
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59 The data directory in this code repository contains some findings that have been
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60 captured with brute force searches. As one can see from these data captures,
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61 both Grcard and Sysmocom cards have plenty of additional directories and files
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62 beyond the standard ones called for SIM/USIM/ISIM, and we can only guess at what
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63 purpose all those extra proprietary directories and files may be serving. There
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64 is one proprietary file on GrcardSIM2 and a few on sysmoISIM-SJA2 that are
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65 documented, but what we have found with bfsearch goes far beyond these few
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66 documented proprietary files. I wonder if perhaps various card-resident
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67 applications are using some of these proprietary files for their internal
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68 purposes.