LabKit

Ad Hoc Private Networks in GSM

Introduction NiPC (“network in a PC”) is a mode of operation supported by YateBTS that allows the basestation to operate in 2.5G GSM/GPRS mode without a core network. While YateBTS NiPC mode does support normal authentication and ciphering with a local SIM database, NiPC also offers a feature that bypasses all security procedures and allows a phone to connect without authentication. Although we have moved along to private LTE/5G networks like everyone else in the world, there are still some use cases where this bypass can make GSM/GPRS as the best (or only) choice. This article describes the 2G security architecture that …

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Public Warning Systems in Mobile Networks

Introduction Cell broadcast (CB) is a way to deliver a text message to large numbers of handsets over the cellular network. Its main use today is the delivery of Public Warning System (PWS) messages, also called CMAS, ETWS, Presidential Alerts, EU-Alerts, or other names in different parts of the world. The Legba Lab Kit supports PWS messages through standard signaling from a core network, or through file-based configuration and command line controls (not requiring a core network). This makes the Lab Kit an easy and inexpensive way to test with PWS messages, for handset testing, for testing emergency message content …

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CSFB with the Legba Lab Kit

Introduction Many 4G networks cannot carry plain old telephone calls, so many mobile operators support voice calls by transferring the handset to a 2G or 3G network for the duration of the call. The procedure for doing this is called “Circuit-Switched Fallback”, or CSFB. CSFB is an interesting procedure from a network operation perspective and from a security perspective. With a pair of Legba LabKits, one in 2G mode and one in 4G mode, you can reproduce and modify the CSFB procedure on a test bench. The “Why” and “What” of Circuit-Switched Fallback Circuit-Switched? What is that anyway? Since 1876, …

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