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Bug #2783

it seems like OsmoMSC is forcing Iu/UMTS to use encryption. why?

Added by laforge 6 months ago. Updated 22 days ago.

Status:
New
Priority:
Low
Assignee:
sysmocom
Category:
IuCS support
Target version:
-
Start date:
12/23/2017
Due date:
% Done:

0%

Estimated time:
Resolution:
Tags:
3G

Description

While working on #2460 I noticed that in case of Iu, we always force the encryption algorithm to VLR_CIPH_A5_3 which seems odd (in several ways):
  • A5/3 is a GSM cipher and is not UEA (umts encryption algo)
  • UMTS requires integrity protection with UIA, but not encryption (UEA)

This possibly needs to be clarified and the code adjusted accordingly

History

#1 Updated by laforge 6 months ago

  • Category set to IuCS support

#2 Updated by neels 6 months ago

looking at gsm_04_08.c I find

        lu_fsm = vlr_loc_update(conn->conn_fsm,
                                [...]
                                is_utran || conn->network->authentication_required,
                                is_utran? VLR_CIPH_A5_3
                                        : conn->network->a5_encryption,
                                );

and I'm a bit puzzled on how this could have come about. It was added as part of the commit "Implement IuCS (large refactoring and addition)" and may have slipped by as an early and/or confused development state. It's obviously wrong. The patch to fix is trivial (just remove the conditional, use conn->network->a5_encryption directly), but it makes sense to build some tests around it as well. Thinking of msc_vlr_test_umts_authen.c to make sure auth without ciph works on UTRAN.

#3 Updated by laforge 23 days ago

  • Tags set to 3G

#4 Updated by neels 22 days ago

this probably dates back to my early confusion about the topic. I probably just wrote it down from a vague hunch and no-one reviewed it later.

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