Source: North Star Post
IMSI Catchers can be a real threat. It doesn't generally affect anyone unless someone is out to get them. Nevertheless its a security flaw that is even present in LTE. This presentation here is a good starting point on learning about IMSI Catcher and the one here about privacy and availability attacks. This article by Ericsson is a good starting point on how 5G will enhance security by IMSI encryption. From the article: The concept we propose builds on an old idea that the mobile device encrypts its IMSI using home network’s asymmetric key before it is transmitted over the air-interface. By using probabilistic asymmetric encryption scheme – one that uses randomness – the same IMSI encrypted multiple times results in different values of encrypted IMSIs. This makes it infeasible for an active or passive attacker over the air-interface to identify the subscriber. Above is a simplified illustration of how a mobile device encrypts its IMSI. Each mobile operator (called the ‘home network’ here) has a public/private pair of asymmetric keys. The home network’s private asymmetric key is kept secret by the home network, while the home network’s public asymmetric key is pre-provisioned in mobile devices along with subscriber-specific IMSIs (Step 0). Note that the home network’s public asymmetric key is not subscriber-specific. For every encryption, the mobile device generates a fresh pair of its own public/private asymmetric keys (Step 1). This key pair is used only once, hence called ephemeral, and therefore provide probabilistic property to the encryption scheme. As shown in the figure, the mobile device then generates a new key (Step 2), e.g., using Diffie–Hellman key exchange. This new key is also ephemeral and is used only once to encrypt the mobile device’s IMSI (Step 3) using symmetric algorithm like AES. The use of asymmetric and symmetric crypto primitives as described above is commonly known as integrated/hybrid encryption scheme. The Elliptic Curve Integrated Encryption Scheme (ECIES) is a popular scheme of such kind and is very suitable to the use case of IMSI encryption because of low impact on radio bandwidth and mobile device’s battery. The nicest thing about the described concept is that no public key infrastructure is necessary, which significantly reduces deployment complexity, meaning that mobile operators can start deploying IMSI encryption for their subscribers without having to rely on any external party or other mobile operators. '3GPP TR 33.899: Study on the security aspects of the next generation system' lists one such approach. The Key steps are as follows:
ARPF - Authentication Credential Repository and Processing Function AUSF - Authentication Server Function SCMF - Security Context Management Function SEAF - Security Anchor Function NG-UE - NG UE UP - User Plane CP - Control Plane IAR - Initial Authentication Request IAS - Initial Authentication Response gNB - Next Generation NodeB You may also want to refer to the 5G Network Architecture presentation by Andy Sutton for details. See also: from http://blog.3g4g.co.uk/2017/08/enhanced-5g-security-via-imsi-encryption.html
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