Could the phone be bugged?

Can you eavesdrop on your GSM phone?

　At the end of 2009, a team of German computer engineers published a paper on how to crack the passwords used in GSM (Global System For Mobile Communications) phones, thus "eavesdropping on GSM phones" spread all over the world.

　GSM mobile phone is used in almost all countries except Japan and South Korea, and it is the world standard of the second generation mobile phone. More than 80% of the global mobile terminal market is called GSM, and because of this, this is shocking news.

　In this regard, GSMA (GSM Association), an industry group for communications operators that use GSM, underestimates the difficulty of trying to eavesdrop on actual calls and argues that there is no threat of actual cracking.

　The two claims seem to be opposing, but in fact both claims are correct.

　Fig. 1 shows an image of communication between a portable phone and a base station in GSM mode.

Figure 1 how GSM communicates

　As can be seen from the figure, in GSM, the communication mode of TDMA (time division multiple access) is used to communicate between the mobile phone (terminal) and the base station. In order for this communication to be valid, the beginning of the TDMA frame must be identified and the information must be fetched at the correct timing.

　If the timing deviates slightly, the information of the neighboring users is in an interfering state and cannot be recovered correctly. GSMA advertises the difficulty of eavesdropping on actual calls.

　On the other hand, if communication data encrypted in some way can be obtained, the password of the GSM can be decrypted so that the contents of the call can be eavesdropped. This is the proposition of a team that successfully cracked the password. Both propositions are correct.

　In fact, so far, there have been some reports that can crack the password of GSM. Moreover, this paper is not the end of the verification (in fact, it may not be able to interpret). That said, even if you can actually crack the password, given the device elements of restoring TDMA, it will not be an imminent threat.

(next page, "are Japanese mobile phones safe? "after)