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imsi-pseudo
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spec: error scenarios

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Oliver Smith 2020-04-08 14:37:58 +02:00
parent 7b0dbb962d
commit 5de45c0885
1 changed files with 23 additions and 1 deletions
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docs/imsi-pseudo-spec.adoc
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@ -167,6 +167,7 @@ pseudonymous IMSI.
The HLR is allocating a pseudonymous IMSI for the subscriber. This pseudonymous The HLR is allocating a pseudonymous IMSI for the subscriber. This pseudonymous
IMSI is stored as IMSI on the subscriber's SIM instead of the real IMSI. IMSI is stored as IMSI on the subscriber's SIM instead of the real IMSI.
[[sim-app]]
==== SIM applet ==== SIM applet
The SIM is provisioned with a SIM applet, which is able to change the IMSI once The SIM is provisioned with a SIM applet, which is able to change the IMSI once
@ -316,8 +317,28 @@ PAD: 8 bits::
Padding at the end, should be filled with 1111 as in the TBCD specification. Padding at the end, should be filled with 1111 as in the TBCD specification.
== Error Scenarios == Error Scenarios
=== Next Pseudonymous IMSI SMS is Lost === Next Pseudonymous IMSI SMS is Lost
=== SMS Arrives Late
If the SMS with the next pseudonymous IMSI does not arrive, the SIM will start
the next Location Updating Procedure with the old pseudonymous IMSI. Because
the HLR has both the old and the new pseudonymous IMSI allocated at this point,
the subscriber is not locked out of the network.
An attacker might block the next pseudonymous IMSI SMS on purpose. Then the
subscriber would have the same pseudonymous IMSI for a long time. A suitable
defense is warning the subscriber if the IMSI does not change
(<<warn-no-imsi-change>>).
=== Next Pseudonymous IMSI SMS arrives out of order
The next pseudonymous IMSI SMS may arrive out of order. Either, because the
network is not able to deliver them in order, or even because an attacker would
perform a replay attack.
If the SMS arrives out of order, the imsi_pseudo_i counter will not be higher
than the value the SIM applet (<<sim-app>>) has stored. Therefore, the applet
will discard the message and the subscriber is not locked out of the network.
// === SMS Arrives Before Timer Expires // === SMS Arrives Before Timer Expires
// FIXME: OS#4486 // FIXME: OS#4486
@ -328,6 +349,7 @@ Padding at the end, should be filled with 1111 as in the TBCD specification.
== Recommendations for Real-World Implementations == Recommendations for Real-World Implementations
=== ATT = 0 === ATT = 0
=== End to End Encryption of SMS === End to End Encryption of SMS
[[warn-no-imsi-change]]
=== Warning the User if the IMSI Does Not Change === Warning the User if the IMSI Does Not Change
=== User-configurable Minimum Duration Between IMSI Changes === User-configurable Minimum Duration Between IMSI Changes