FreeCalypso > hg > fc-sim-sniff

annotate doc/Motivation @ 56:966a54303d68

Find changesets by keywords (author, files, the commit message), revision number or hash, or revset expression.
simsniff-dec: factor out high-level decoding
author Mychaela Falconia <falcon@freecalypso.org>
date Wed, 04 Oct 2023 01:18:50 +0000
parents 510bef2b2000
children
Ignore whitespace changes - Everywhere: Within whitespace: At end of lines:
rev   line source
0
fbbafa93b52b starting project with README and sim-fpc-pasv adapter
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
1 Q: What is the principal idea behind SIMtrace, as distinct from the specific
fbbafa93b52b starting project with README and sim-fpc-pasv adapter
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
2 implementation realized by "standard" Osmocom SIMtrace?
fbbafa93b52b starting project with README and sim-fpc-pasv adapter
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
3
fbbafa93b52b starting project with README and sim-fpc-pasv adapter
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
4 A: The two principal objectives of SIMtrace are:
fbbafa93b52b starting project with README and sim-fpc-pasv adapter
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
5
fbbafa93b52b starting project with README and sim-fpc-pasv adapter
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
6 1) Passive sniffing of communication between a phone-type device and a SIM,
fbbafa93b52b starting project with README and sim-fpc-pasv adapter
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
7 ideally as transparent and non-invasive as possible.
fbbafa93b52b starting project with README and sim-fpc-pasv adapter
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
8
fbbafa93b52b starting project with README and sim-fpc-pasv adapter
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
9 2) Card emulation: the SIMtrace apparatus presents itself to the phone (or
fbbafa93b52b starting project with README and sim-fpc-pasv adapter
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
10 modem or other phone-type device) as a SIM, either emulating the entire
fbbafa93b52b starting project with README and sim-fpc-pasv adapter
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
11 SIM CardOS functionality in software or communicating with a real SIM
fbbafa93b52b starting project with README and sim-fpc-pasv adapter
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
12 located somewhere remotely, across the Internet.
fbbafa93b52b starting project with README and sim-fpc-pasv adapter
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
13
fbbafa93b52b starting project with README and sim-fpc-pasv adapter
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
14 Q: What are the shortcomings of the existing Osmocom SIMtrace implementation of
fbbafa93b52b starting project with README and sim-fpc-pasv adapter
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
15 the above goals?
fbbafa93b52b starting project with README and sim-fpc-pasv adapter
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
16
fbbafa93b52b starting project with README and sim-fpc-pasv adapter
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
17 A: In the opinion of Mother Mychaela of FreeCalypso, the electrical aspects of
fbbafa93b52b starting project with README and sim-fpc-pasv adapter
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
18 Osmocom SIMtrace implementation are its biggest shortcoming. The following
fbbafa93b52b starting project with README and sim-fpc-pasv adapter
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
19 problems are most acute currently:
fbbafa93b52b starting project with README and sim-fpc-pasv adapter
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
20
fbbafa93b52b starting project with README and sim-fpc-pasv adapter
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
21 * Current SIMtrace v2 hardware is not 5V-tolerant: connecting this apparatus to
fbbafa93b52b starting project with README and sim-fpc-pasv adapter
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
22 an old phone that puts out 5V (class A) on its SIM socket can damage the
fbbafa93b52b starting project with README and sim-fpc-pasv adapter
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
23 hardware, as class A SIM voltages exceed the absolute maximum rating spec of
fbbafa93b52b starting project with README and sim-fpc-pasv adapter
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
24 the AT91SAM3S4B microcontroller on the SIMtrace v2 board, which is connected
fbbafa93b52b starting project with README and sim-fpc-pasv adapter
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
25 directly to the SIM bus.
fbbafa93b52b starting project with README and sim-fpc-pasv adapter
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
26
fbbafa93b52b starting project with README and sim-fpc-pasv adapter
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
27 * One option would be to revive the previous hardware generation as in SIMtrace
fbbafa93b52b starting project with README and sim-fpc-pasv adapter
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
28 v1, replacing the AT91SAM3S with AT91SAM7S. However, all firmware maintained
fbbafa93b52b starting project with README and sim-fpc-pasv adapter
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
29 by Osmocom is written for SAM3S only, thus a backport to SAM7S would involve
fbbafa93b52b starting project with README and sim-fpc-pasv adapter
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
30 significant work. Given that the resulting solution would still be far from
fbbafa93b52b starting project with README and sim-fpc-pasv adapter
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
31 my idea of perfection, I find it difficult to justify investing in that
fbbafa93b52b starting project with README and sim-fpc-pasv adapter
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
32 software effort - instead I would rather work on a more philosophically-proper
fbbafa93b52b starting project with README and sim-fpc-pasv adapter
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
33 solution.
fbbafa93b52b starting project with README and sim-fpc-pasv adapter
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
34
fbbafa93b52b starting project with README and sim-fpc-pasv adapter
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
35 * AT91SAMx-based SIMtrace, both v1 and v2, works (most of the time, but not 100%
fbbafa93b52b starting project with README and sim-fpc-pasv adapter
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
36 reliably) with 1.8V phone-SIM combination (a phone that prefers class C and a
fbbafa93b52b starting project with README and sim-fpc-pasv adapter
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
37 SIM that supports it) only by accident. The Vih spec (the minimum required
fbbafa93b52b starting project with README and sim-fpc-pasv adapter
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
38 voltage on a signal line for it to register reliably as a 1) is 2.0 V for
fbbafa93b52b starting project with README and sim-fpc-pasv adapter
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
39 AT91SAM7S or 2.31 V (0.7 * Vddio, Vddio = 3.3 V) for AT91SAM3S, but the actual
fbbafa93b52b starting project with README and sim-fpc-pasv adapter
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
40 voltage on SIM interface lines in class C operation will never rise above
fbbafa93b52b starting project with README and sim-fpc-pasv adapter
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
41 1.8 V. The electrical interface on this hw operates severely out of spec,
fbbafa93b52b starting project with README and sim-fpc-pasv adapter
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
42 and I find it rather miraculous that it works at all. Not surprisingly,
fbbafa93b52b starting project with README and sim-fpc-pasv adapter
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
43 reports are starting to trickle in with user experiences of it actually NOT
fbbafa93b52b starting project with README and sim-fpc-pasv adapter
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
44 working sometimes.
fbbafa93b52b starting project with README and sim-fpc-pasv adapter
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
45
fbbafa93b52b starting project with README and sim-fpc-pasv adapter
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
46 * Even if the SIM interface is restricted (by the phone, by the SIM, or by
fbbafa93b52b starting project with README and sim-fpc-pasv adapter
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
47 SIMtrace MITM function tampering with ATR or file characteristics bytes) to
fbbafa93b52b starting project with README and sim-fpc-pasv adapter
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
48 operating in class B (3.0 V nominal) only, the existing AT91SAMx SIMtrace
fbbafa93b52b starting project with README and sim-fpc-pasv adapter
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
49 boards are still electrically unclean. Looking at the schematics, one can see
fbbafa93b52b starting project with README and sim-fpc-pasv adapter
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
50 that both CLK and I/O lines are pulled up (with resistors) to the SIMtrace
40
510bef2b2000 new README, old stuff goes to doc/Motivation
Mychaela Falconia <falcon@freecalypso.org>
parents: 0
diff changeset
51 board's 3.3V rail, which is a higher voltage than what the phone will put out
0
fbbafa93b52b starting project with README and sim-fpc-pasv adapter
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
52 (3.0 V or 1.8 V), and in the case of SIMtrace v1 with a 5V phone, that pull-up
fbbafa93b52b starting project with README and sim-fpc-pasv adapter
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
53 will turn into a pull-midway-down instead.
fbbafa93b52b starting project with README and sim-fpc-pasv adapter
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
54
fbbafa93b52b starting project with README and sim-fpc-pasv adapter
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
55 * My philosophy is that the tracing apparatus should be making only a high-
fbbafa93b52b starting project with README and sim-fpc-pasv adapter
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
56 impedance connection to the SIM bus and nothing more, while the SIM bus itself
fbbafa93b52b starting project with README and sim-fpc-pasv adapter
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
57 is galvanically connected from the phone to the physical SIM without passing
fbbafa93b52b starting project with README and sim-fpc-pasv adapter
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
58 through any switches or other potential Heisenbug-inducing artifacts.
fbbafa93b52b starting project with README and sim-fpc-pasv adapter
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
59
fbbafa93b52b starting project with README and sim-fpc-pasv adapter
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
60 My first thought was to gently modify the existing AT91SAMx-based SIMtrace
fbbafa93b52b starting project with README and sim-fpc-pasv adapter
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
61 design for electrically clean multivolt operation:
fbbafa93b52b starting project with README and sim-fpc-pasv adapter
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
62
fbbafa93b52b starting project with README and sim-fpc-pasv adapter
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
63 * Replace the electrical switches for SIM VCC (FPF2109) and SIM RST/CLK/IO
fbbafa93b52b starting project with README and sim-fpc-pasv adapter
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
64 (CB3Q3244) with either a relay (my initial thought, but way too power-hungry)
fbbafa93b52b starting project with README and sim-fpc-pasv adapter
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
65 or a manually operated 5PDT slide switch;
fbbafa93b52b starting project with README and sim-fpc-pasv adapter
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
66
fbbafa93b52b starting project with README and sim-fpc-pasv adapter
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
67 * Insert a Nexperia 74LVC4T3144 dual-supply buffer between the SIM bus and the
fbbafa93b52b starting project with README and sim-fpc-pasv adapter
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
68 MCU, providing a sniffing path that not only supports all 3 voltage classes,
fbbafa93b52b starting project with README and sim-fpc-pasv adapter
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
69 but is electrically clean, making only a high-impedance connection to the SIM
fbbafa93b52b starting project with README and sim-fpc-pasv adapter
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
70 bus as I desire;
fbbafa93b52b starting project with README and sim-fpc-pasv adapter
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
71
fbbafa93b52b starting project with README and sim-fpc-pasv adapter
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
72 * Connect a 74LVC1G07 open drain driver (fed with TxD from the MCU) to the SIM
fbbafa93b52b starting project with README and sim-fpc-pasv adapter
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
73 bus I/O line, providing a signal path for card emulation mode. (In trace mode
fbbafa93b52b starting project with README and sim-fpc-pasv adapter
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
74 the firmware would be responsible for never turning on this OD driver, keeping
fbbafa93b52b starting project with README and sim-fpc-pasv adapter
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
75 the tracing apparatus High-Z.)
fbbafa93b52b starting project with README and sim-fpc-pasv adapter
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
76
fbbafa93b52b starting project with README and sim-fpc-pasv adapter
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
77 However, as I was reading AT91SAMx datasheets more carefully in preparation for
fbbafa93b52b starting project with README and sim-fpc-pasv adapter
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
78 embarking on a project to turn the above idea into reality, I saw a big problem:
fbbafa93b52b starting project with README and sim-fpc-pasv adapter
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
79 when the USART is put into ISO 7816-3 mode, it uses the chip's TxD pin (switched
fbbafa93b52b starting project with README and sim-fpc-pasv adapter
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
80 to open drain operation) for both Rx and Tx, and there is no option to keep
fbbafa93b52b starting project with README and sim-fpc-pasv adapter
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
81 separate RxD and TxD pins with an external receiving buffer and an external OD
fbbafa93b52b starting project with README and sim-fpc-pasv adapter
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
82 driver.
fbbafa93b52b starting project with README and sim-fpc-pasv adapter
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
83
fbbafa93b52b starting project with README and sim-fpc-pasv adapter
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
84 It would probably be possible to build an all-voltage SIM interface with
fbbafa93b52b starting project with README and sim-fpc-pasv adapter
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
85 AT91SAMx, perhaps by using one of those bidirectional level shifter ICs that
fbbafa93b52b starting project with README and sim-fpc-pasv adapter
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
86 somehow automagically handle driving direction reversals. But I personally am
fbbafa93b52b starting project with README and sim-fpc-pasv adapter
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
87 not too inclined to trust those automagical bidirectional translators, they
fbbafa93b52b starting project with README and sim-fpc-pasv adapter
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
88 just don't align with my design philosophy - I would much much rather have
fbbafa93b52b starting project with README and sim-fpc-pasv adapter
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
89 unidirectional buffers, one for sniffing and another for OD-driving the I/O
fbbafa93b52b starting project with README and sim-fpc-pasv adapter
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
90 line in card emulation mode. Seeing that AT91SAMx is incompatible with such
fbbafa93b52b starting project with README and sim-fpc-pasv adapter
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
91 electrical design, I decided to screw AT91SAMx and go for a radically different
fbbafa93b52b starting project with README and sim-fpc-pasv adapter
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
92 approach.