Oliver Smith | 5c95bc9 | 2020-04-03 14:03:24 +0200 | [diff] [blame^] | 1 | = Specification for IMSI Pseudonymization on the Radio Interface for 2G and Above |
| 2 | |
| 3 | == Introduction |
| 4 | |
| 5 | A long-standing issue in the 3GPP specifications is, that mobile phones and |
| 6 | other mobile equipment (ME) have to send the International Mobile Subscriber |
| 7 | Identity (IMSI) unencrypted over the air. Each IMSI is uniquely identifying the |
| 8 | person who bought the associated Subscriber Identity Module (SIM) used in the |
| 9 | ME. Therefore most people can be uniquely identified by recording the IMSI that |
| 10 | their ME is sending. Efforts are made in the 2G and above specifications to |
| 11 | send the IMSI less often, and where possible use the Temporary Mobile |
| 12 | Subscriber Identity (TMSI) instead. |
| 13 | |
| 14 | But this is not enough. So-called IMSI catchers were invented and are used to |
| 15 | not only record IMSIs when they have to be sent. But also to force ME to send |
| 16 | their IMSI by immitating a Base Transceiver Station (BTS). IMSI catchers have |
| 17 | become small and affordable, even criminals actors without much budget can use |
| 18 | them to track anybody with a mobile phone. |
| 19 | |
| 20 | The solution presented in this document is to periodically change the IMSI of |
| 21 | the ME to a new pseudonymous IMSI allocated by the Home Location Register (HLR) |
| 22 | or Home Subscriber Service (HSS). The only component that needs to be changed |
| 23 | in the network besides the SIM is the HLR/HSS, therefore it should be possible |
| 24 | for a Mobile Virtual Network Operator (MVNO) to deploy this privacy |
| 25 | enhancement. |
| 26 | |
| 27 | == Location Update |
| 28 | |
| 29 | === Regular |
| 30 | |
| 31 | === With Pseudonymous IMSI |
| 32 | |
| 33 | == Implementation Notes |
| 34 | |
| 35 | === Source Code for Reference Implementation |
| 36 | |
| 37 | === Warning the User if the IMSI Does Not Change |
| 38 | |
| 39 | === End to End Encryption of SMS |
| 40 | |
| 41 | === User-configurable Minimum Duration Between IMSI Changes |