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neels gerrit-no-reply at lists.osmocom.orgneels has uploaded this change for review. ( https://gerrit.osmocom.org/c/osmo-msc/+/15021 Change subject: manual: adjust and fix auth and ciph docs ...................................................................... manual: adjust and fix auth and ciph docs Change-Id: Iffe159d4c0e0e9439f8719e0ddd28f06d4c80d9f --- M doc/manuals/chapters/net.adoc 1 file changed, 54 insertions(+), 14 deletions(-) git pull ssh://gerrit.osmocom.org:29418/osmo-msc refs/changes/21/15021/1 diff --git a/doc/manuals/chapters/net.adoc b/doc/manuals/chapters/net.adoc index 06be4ba..aa0a2f3 100644 --- a/doc/manuals/chapters/net.adoc +++ b/doc/manuals/chapters/net.adoc @@ -101,32 +101,56 @@ === Authentication -Authorized subscribers must be entered in the HLR database, see the _OsmoHLR -reference manual_ <<userman-osmohlr>>. If authentication tokens (such as KI for -2G, or K and OP/OPC for UMTS) are present in the HLR, OsmoMSC will only attach -a subscriber after successful authentication. +A subscriber's IMSI must be entered in the HLR database to be able to attach. A +subscriber-create-on-demand feature is also available, see the _OsmoHLR +reference manual_ <<userman-osmohlr>>. -If no authentication keys are present in the HLR for a given subscriber, -OsmoMSC will attach the subscriber _without_ authentication. You can reject -subscribers that lack authentication info in the HLR with this setting: +A known IMSI in the HLR may or may not have authentication keys associated, +which profoundly affects the ability to attach and the algorithms used to +negotiate authentication, as the following sections explain for 2G and 3G. + +==== Authentication on 2G + +If authentication tokens (such as KI for 2G, or K and OP/OPC for UMTS) are +present in the HLR, OsmoMSC will only attach a subscriber after successful +authentication. Note that the 3G authentication keys are also used on 2G when +the MS indicates UMTS compatibility, in which case the full UMTS style mutual +authentication may indeed take place on 2G (GERAN). + +On 2G, if no authentication keys are present in the HLR for a given subscriber, +OsmoMSC will attach the subscriber _without_ authentication. Subscribers that +lack authentication keys can always be rejected with this setting: ---- network authentication required ---- +==== Authentication on 3G + +3G (UTRAN) always requires authentication (a.k.a. Integrity Protection) by +specification, and hence authentication keys must be present in the HLR for a +subscriber to be able to attach on 3G. + +OsmoMSC always indicates UIA1 and UIA2 as permitted Integrity Protection +algorithms on 3G. + === Ciphering To enable ciphering on the radio link, authentication must take place first: -the Kc resulting from authentication is the key used for ciphering. Hence, all -subscribers must have authentication tokens available in the HLR for ciphering. +the Kc resulting from authentication is the key used for ciphering. Hence, to +be able to use ciphering, a subscriber must have authentication tokens +available in the HLR. + +==== Ciphering on 2G The MS, BTS and MSC must agree on a ciphering algorithm to use. - The MS sends its supported ciphering algorithms via Classmark IEs during Location Updating. - Typically the BSC needs to know which A5 ciphers are supported by connected - BTSes. + BTSes, see the `network / encryption a5` configuration item for OsmoBSC + <<vty-ref-osmobsc>>. - Finally, OsmoMSC may impose that specific A5 ciphers shall not be considered. It is the responsibility of the BSC to then pick an A5 cipher that satisfies @@ -143,12 +167,28 @@ + ---- network - encryption a5 3 + encryption a5 1 3 ---- - Never use A5/2: it is an "export grade cipher" and has been deprecated for its low ciphering strength. -NOTE: At the time of writing, OsmoMSC supports setting only a single A5 cipher, -while it should be able to allow a set of ciphers. This is subject to ongoing -development. +- To allow either no encryption or any of A5/1 or A5/3 based on the presence of + authentication keys and abilities of the MS, SIM and BSC configuration, it is + recommended to enable all ciphers in OsmoMSC. The highest available A5 cipher + will be used; the order in which the A5 options are configured does not + affect the choice. ++ +---- +network + encryption a5 0 1 3 +---- + +==== Ciphering on 3G + +While authentication is always required on 3G, ciphering is optional. + +So far OsmoMSC lacks explicit configuration for ciphering on 3G. As an interim +solution, ciphering is always enabled on 3G. + +OsmoMSC indicates UEA1 and UEA2 as permitted encryption algorithms on 3G. -- To view, visit https://gerrit.osmocom.org/c/osmo-msc/+/15021 To unsubscribe, or for help writing mail filters, visit https://gerrit.osmocom.org/settings Gerrit-Project: osmo-msc Gerrit-Branch: master Gerrit-Change-Id: Iffe159d4c0e0e9439f8719e0ddd28f06d4c80d9f Gerrit-Change-Number: 15021 Gerrit-PatchSet: 1 Gerrit-Owner: neels <nhofmeyr at sysmocom.de> Gerrit-MessageType: newchange -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.osmocom.org/pipermail/gerrit-log/attachments/20190801/087679f6/attachment.htm>