2548becddf
We already have documentation that explains how to run pySim-smpp2sim. With smpp-ota-tool we now have a counterpart for pySim-smpp2sim, so let's add documentation for this tool as well. Related: SYS#7881 Change-Id: If0d18a263f5a6dc035b90f5c5c6a942d46bbba49
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180 lines
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smpp-ota-tool
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=============
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The `smpp-ota-tool` allows users to send OTA SMS messages containing APDU scripts (RFM, RAM) via an SMPP server. The
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intended audience are developers who want to test/evaluate the OTA SMS interface of a SIM/UICC/eUICC. `smpp-ota-tool`
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is intended to be used as a companion tool for :ref:`pySim-smpp2sim`, however it should be usable on any other SMPP
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server (such as a production SMSC of a live cellular network) as well.
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From the technical perspective `smpp-ota-tool` takes the role of an SMPP ESME. It takes care of the encoding, encryption
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and checksumming (signing) of the RFM/RAM OTA SMS and eventually submits it to the SMPP server. The program then waits
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for a response. The response is automatically parsed and printed on stdout. This makes the program also suitable to be
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called from shell scripts.
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.. note:: In the following we will we will refer to `SIM` as one of the following: `SIM`, `USIM`, `ISIM`, `UICC`,
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`eUICC`, `eSIM`.
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Applying OTA keys
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~~~~~~~~~~~~~~~~~
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Depending on the `SIM` type you will receive one or more sets of keys which you can use to communicate with the `SIM`
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through a secure channel protocol. When using the OTA SMS method, the SCP80 protocol is used and it therefore crucial
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to use a keyset that is actually suitable for SCP80.
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A keyset usually consists of three keys:
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#. KIC: the key used for ciphering (encryption/decryption)
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#. KID: the key used to compute a cryptographic checksum (signing)
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#. KIK: the key used to encrypt/decrypt key material (key rotation, adding of new keys)
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From the transport security perspective, only KIC and KID are relevant. The KIK (also referenced as "Data Encryption
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Key", DEK) is only used when keys are rotated or new keys are added (see also ETSI TS 102 226, section 8.2.1.5).
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When the keyset is programmed into the security domain of the `SIM`, it is tied to a specific cryptographic algorithm
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(3DES, AES128 or AES256) and a so called Key Version Number (KVN). The term "Key Version Number" is misleading, since
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it is actually not a version number. It is a unique identifier of a certain keyset which also identifies for which
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secure channel protocol the keyset may be used. Keysets with a KVN from 1-15 (``0x01``-``0x0F``) are suitable for SCP80.
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This means that it is not only important to know just the KIC/KID/KIK keys. Also the related algorithms and the KVN
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numbers must be known.
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.. note:: SCP80 keysets typically start counting from 1 upwards. Typical configurations use a set of 3 keysets with
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KVN numbers 1-3.
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Addressing an Application
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~~~~~~~~~~~~~~~~~~~~~~~~~
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When communicating with a specific application on a `SIM` via SCP80, it is important to address that application with
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the correct parameters. The following two parameters must be known in advance:
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#. TAR: The Toolkit Application Reference (TAR) number is a three byte value that uniquely addresses an application
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on the `SIM`. The exact values may vary (see also ETSI TS 101 220, Table D.1).
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#. MSL: The Minimum Security Level (MSL) is a bit-field that dictates which of the security measures encoded in the
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SPI are mandatory (see also ETSI TS 102 225, section 5.1.1).
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A practical example
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~~~~~~~~~~~~~~~~~~~
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.. note:: This tutorial assumes that pySim-smpp2sim is running on the local machine with its default parameters.
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See also :ref:`pySim-smpp2sim`.
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Let's assume that an OTA SMS shall be sent to the SIM RFM application of an sysmoISIM-SJA2. What we want to do is to
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select DF.GSM and to get the select response back.
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We have received the following key material from the `SIM` vendor:
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::
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KIC1: F09C43EE1A0391665CC9F05AF4E0BD10
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KID1: 01981F4A20999F62AF99988007BAF6CA
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KIK1: 8F8AEE5CDCC5D361368BC45673D99195
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KIC2: 01022916E945B656FDE03F806A105FA2
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KID2: D326CB69F160333CC5BD1495D448EFD6
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KIK2: 08037E0590DFE049D4975FFB8652F625
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KIC3: 2B22824D0D27A3A1CEEC512B312082B4
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KID3: F1697766925A11F4458295590137B672
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KIK3: C7EE69B2C5A1C8E160DD36A38EB517B3
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Those are three keysets. The enumeration is directly equal to the KVN used. All three keysets are 3DES keys, which
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means triple_des_cbc2 is the correct algorithm to use.
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.. note:: The key set configuration can be confirmed by retrieving the key configuration using
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`get_data key_information` from within an SCP02 session on ADF.ISD.
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In this example we intend to address the SIM RFM application on the `SIM`. Which according to the manual has TAR ``B00010``
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and MSL ``0x06``. When we hold ``0x06`` = ``0b00000110`` against the SPI coding chart (see also ETSI TS 102 225,
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section 5.1.1). We can deduct that Ciphering and Cryptographic Checksum are mandatory.
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.. note:: The MSL (see also ETSI TS 102 226, section 6.1) is assigned to an application by the `SIM` issuer. It is a
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custom decision and may vary with different `SIM` types/profiles. In the case of sysmoISIM-SJS1/SJA2/SJA5 the
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counter requirement has been waived to simplify lab/research type use. In productive environments, `SIM`
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applications should ideally use an MSL that makes the counter mandatory.
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In order to select DF.GSM (``0x7F20``) and to retrieve the select response, two APDUs are needed. The first APDU is the
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select command ``A0A40000027F20`` and the second is the related get-response command ``A0C0000016``. Those APDUs will be
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concatenated and are sent in a single message. The message containing the concatenated APDUs works as a script that
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is received by the SIM RFM application and then executed. This method poses some limitations that have to be taken into
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account when making requests like this (see also ETSI TS 102 226, section 5).
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With this information we may now construct a commandline for `smpp-ota-tool.py`. We will pass the KVN as kid_idx and
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kic_idx (see also ETSI TS 102 225, Table 2, fields `KIc` and `KID`). Both index values should refer to the same
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keyset/KVN as keysets should not be mixed. (`smpp-ota-tool` still provides separate parameters anyway to allow testing
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with invalid keyset combinations)
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::
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$ PYTHONPATH=./ ./contrib/smpp-ota-tool.py --kic F09C43EE1A0391665CC9F05AF4E0BD10 --kid 01981F4A20999F62AF99988107BAF6CA --kid_idx 1 --kic_idx 1 --algo-crypt triple_des_cbc2 --algo-auth triple_des_cbc2 --tar B00010 --apdu A0A40000027F20 --apdu A0C0000016
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2026-02-26 17:13:56 INFO Connecting to localhost:2775...
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2026-02-26 17:13:56 INFO C-APDU sending: a0a40000027f20a0c0000016...
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2026-02-26 17:13:56 INFO SMS-TPDU sending: 02700000281506191515b00010da1d6cbbd0d11ce4330d844c7408340943e843f67a6d7b0674730881605fd62d...
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2026-02-26 17:13:56 INFO SMS-TPDU sent, waiting for response...
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2026-02-26 17:13:56 INFO SMS-TPDU received: 027100002c12b000107ddf58d1780f771638b3975759f4296cf5c31efc87a16a1b61921426baa16da1b5ba1a9951d59a39
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2026-02-26 17:13:56 INFO SMS-TPDU decoded: (Container(rpl=44, rhl=18, tar=b'\xb0\x00\x10', cntr=b'\x00\x00\x00\x00\x00', pcntr=0, response_status=uEnumIntegerString.new(0, 'por_ok'), cc_rc=b'\x8f\xea\xf5.\xf4\x0e\xc2\x14', secured_data=b'\x02\x90\x00\x00\x00\xff\xff\x7f \x02\x00\x00\x00\x00\x00\t\xb1\x065\x04\x00\x83\x8a\x83\x8a'), Container(number_of_commands=2, last_status_word=u'9000', last_response_data=u'0000ffff7f2002000000000009b106350400838a838a'))
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2026-02-26 17:13:56 INFO R-APDU received: 0000ffff7f2002000000000009b106350400838a838a 9000
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0000ffff7f2002000000000009b106350400838a838a 9000
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2026-02-26 17:13:56 INFO Disconnecting...
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The result we see is the select response of DF.GSM and a status word indicating that the last command has been
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processed normally.
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As we can see, this mechanism now allows us to perform small administrative tasks remotely. We can read the contents of
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files remotely or make changes to files. Depending on the changes we make, there may be security issues arising from
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replay attacks. With the commandline above, the communication is encrypted and protected by a cryptographic checksum,
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so an adversary can neither read, nor alter the message. However, an adversary could still replay an intercepted
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message and the `SIM` would happily execute the contained APDUs again.
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To prevent this, we may include a replay protection counter within the message. In this case, the MSL indicates that a
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replay protection counter is not required. However, to extended the security of our messages, we may chose to use a
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counter anyway. In the following example, we will encode a counter value of 100. We will instruct the `SIM` to make sure
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that the value we send is higher than the counter value that is currently stored in the `SIM`.
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To add a replay connection counter we add the commandline arguments `--cntr-req` to set the counter requirement and
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`--cntr` to pass the counter value.
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::
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$ PYTHONPATH=./ ./contrib/smpp-ota-tool.py --kic F09C43EE1A0391665CC9F05AF4E0BD10 --kid 01981F4A20999F62AF99988107BAF6CA --kid_idx 1 --kic_idx 1 --algo-crypt triple_des_cbc2 --algo-auth triple_des_cbc2 --tar B00010 --apdu A0A40000027F20 --apdu A0C0000016 --cntr-req counter_must_be_higher --cntr 100
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2026-02-26 17:16:39 INFO Connecting to localhost:2775...
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2026-02-26 17:16:39 INFO C-APDU sending: a0a40000027f20a0c0000016...
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2026-02-26 17:16:39 INFO SMS-TPDU sending: 02700000281516191515b000103a4f599e94f2b5dcfbbda984761b7977df6514c57a580fb4844787c436d2eade...
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2026-02-26 17:16:39 INFO SMS-TPDU sent, waiting for response...
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2026-02-26 17:16:39 INFO SMS-TPDU received: 027100002c12b0001049fb0315f6c6401b553867f412cefaf9355b38271178edb342a3bc9cc7e670cdc1f45eea6ffcbb39
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2026-02-26 17:16:39 INFO SMS-TPDU decoded: (Container(rpl=44, rhl=18, tar=b'\xb0\x00\x10', cntr=b'\x00\x00\x00\x00d', pcntr=0, response_status=uEnumIntegerString.new(0, 'por_ok'), cc_rc=b'\xa9/\xc7\xc9\x00"\xab5', secured_data=b'\x02\x90\x00\x00\x00\xff\xff\x7f \x02\x00\x00\x00\x00\x00\t\xb1\x065\x04\x00\x83\x8a\x83\x8a'), Container(number_of_commands=2, last_status_word=u'9000', last_response_data=u'0000ffff7f2002000000000009b106350400838a838a'))
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2026-02-26 17:16:39 INFO R-APDU received: 0000ffff7f2002000000000009b106350400838a838a 9000
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0000ffff7f2002000000000009b106350400838a838a 9000
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2026-02-26 17:16:39 INFO Disconnecting...
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The `SIM` has accepted the message. The message got processed and the `SIM` has set its internal to 100. As an experiment,
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we may try to re-use the counter value:
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::
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$ PYTHONPATH=./ ./contrib/smpp-ota-tool.py --kic F09C43EE1A0391665CC9F05AF4E0BD10 --kid 01981F4A20999F62AF99988107BAF6CA --kid_idx 1 --kic_idx 1 --algo-crypt triple_des_cbc2 --algo-auth triple_des_cbc2 --tar B00010 --apdu A0A40000027F20 --apdu A0C0000016 --cntr-req counter_must_be_higher --cntr 100
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2026-02-26 17:16:43 INFO Connecting to localhost:2775...
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2026-02-26 17:16:43 INFO C-APDU sending: a0a40000027f20a0c0000016...
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2026-02-26 17:16:43 INFO SMS-TPDU sending: 02700000281516191515b000103a4f599e94f2b5dcfbbda984761b7977df6514c57a580fb4844787c436d2eade...
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2026-02-26 17:16:43 INFO SMS-TPDU sent, waiting for response...
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2026-02-26 17:16:43 INFO SMS-TPDU received: 027100000b0ab0001000000000000006
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2026-02-26 17:16:43 INFO SMS-TPDU decoded: (Container(rpl=11, rhl=10, tar=b'\xb0\x00\x10', cntr=b'\x00\x00\x00\x00\x00', pcntr=0, response_status=uEnumIntegerString.new(6, 'undefined_security_error'), cc_rc=b'', secured_data=b''), None)
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Traceback (most recent call last):
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File "/home/user/work/git_master/pysim/./contrib/smpp-ota-tool.py", line 238, in <module>
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resp, sw = smpp_handler.transceive_apdu(apdu, opts.src_addr, opts.dest_addr, opts.timeout)
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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File "/home/user/work/git_master/pysim/./contrib/smpp-ota-tool.py", line 162, in transceive_apdu
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raise ValueError("Response does not contain any last_response_data, no R-APDU received!")
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ValueError: Response does not contain any last_response_data, no R-APDU received!
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2026-02-26 17:16:43 INFO Disconnecting...
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As we can see, the `SIM` has rejected the message with an `undefined_security_error`. The replay-protection-counter
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ensures that a message can only be sent once.
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.. note:: The replay-protection-counter is implemented as a 5 byte integer value (see also ETSI TS 102 225, Table 3).
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When the counter has reached its maximum, it will not overflow nor can it be reset.
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smpp-ota-tool syntax
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~~~~~~~~~~~~~~~~~~~~
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.. argparse::
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:module: contrib.smpp-ota-tool
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:func: option_parser
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:prog: contrib/smpp-ota-tool.py
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