Bug #2783

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

Added by laforge almost 3 years ago. Updated about 1 year ago.

In Progress
IuCS support
Target version:
Start date:
Due date:
% Done:


Spec Reference:


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


#1 Updated by laforge almost 3 years ago

  • Category set to IuCS support

#2 Updated by neels almost 3 years 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 over 2 years ago

  • Tags set to 3G

#4 Updated by neels over 2 years 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.

#5 Updated by laforge over 2 years ago

  • Assignee changed from sysmocom to stsp

#6 Updated by laforge over 1 year ago

  • Assignee changed from stsp to neels

neels, is this still an issue with the current msc code base? If yes, feel free to fix or assign to osmith

#7 Updated by neels about 1 year ago

  • Status changed from New to In Progress

should be done in a few hours, so throwing this in now

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