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How are mobile telephony networks like LTE (4G) and HSPA (3G) encrypted? between what parts is the communication encrypted? who has access to the keys? is symmetric or asymmetric encryption used? is it similar to TLS?

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Independent of the actual implementation of both networks, it is important to consider two major things: (1) Confidentiality in such mobile communications is not designed to provide end-to-end encryption. An interface for authorities is especially intended. (2) There is probably an insecure unencrypted mode. Imagine if there is an error in the crypto provider, mobile operators can not deny their service to end users "just" because of that, economically speaking. – ordag Jan 23 '12 at 21:00
@ordag "Imagine if there is an error in the crypto provider, mobile operators can not deny their service to end users "just" because of that, economically speaking." source? – curiousguy Jul 11 '12 at 6:17
Depends on a gazillion factors like vendors, implementations, if we're talking about RAN or Core etc. Please specify what exactly you want to know. – Andy Thompson Sep 27 '12 at 11:32

3 Answers

up vote 2 down vote

I suspect that @Jay Looney is correct; for authoritative answers, contact the service provider. (who will report you to DHS and DMCA).

Blackhat description of attacks on HSPA includes a brief overview and architecture, that may address the portion of the question re: what parts are encrypted. This resource also includes the following sentence,

The reality is that most UMTS/HSPA devices are also GSM/GPRS/EDGE capable, and are configured to try and connect to a GSM/GPRS/EDGE network whenever a suitable UMTS/HSPA network is not available.

I found one source that asserts that the answer is Feistel encryption, but it doesn't address the key management issue. I continue to believe that is something that only the vendor can answer, and I'm willing to bet they won't.

Agilent provides some internal details, but I think that is more specific than you want. It may be useful as context/example.

You could always take a course in the subject for a mere $1500.

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Generally the 4G and 3G networks are not used to make phonecalls or send/recieve texts, those are still pushed to the CDMA and GSM networks and 3/4G are used to connect your device to the internet. The encryption will depend on the company deploying it as well as the device user, because you can setup secure connections to an encrypted VPN or even route through a home proxy. I know my android phone has these features and has retained them through multiple updates. I can only suggest that you call your service provider and ask them how it works.

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Just the fact that battery call time life is quoted as dramatically less on 3/4G than on GSM makes me very skeptical of this. – Jeff Ferland♦ Oct 10 '12 at 21:12
I did say "usually" and not all the time, but when I answered this question originally, my answer was accurate, however I am not sure if it remains accurate. – zenware Mar 23 at 3:38
up vote -3 down vote

I dont think Jay's answer is accurate. Jonas implies security about the Uu interface of LTE, for example: the air interface from the network to the mobile.

I am not sure what actual hashing algorithms are employed but there is a Security Mechanism in the non-access stratum of this link. I'm curious to figure out details though.

EDIT: Here's some more info on the PSK and other security mechanisms followed by call flow. It starts on page 14: http://www.niksun.com/presentations/day2/NIKSUN_WWSMC_July26_AnandRPrasad.pdf

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