It is known that certain methods of authentication are used to tie a particular device to a particular phone number, so that cloning can be prevented.

What are these authentication mechanisms? Does it have something to do with the International Mobile Equipment Identity?

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    I object to the marking of this question as off-topic. In many fields it is a mistake to keep practice and theory separate, as they both suffer from the absence of the other. This is especially acute in crypto, where theory needs to be constantly checked by practice. If this stackexchange habitually excludes discussion of practical attacks and defenses—which in most cases are about bypassing crypto rather than defeating it!—then the discussions here will be that much less relevant to what we all really care about. – Zooko Jul 17 '11 at 4:15
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    @Zooko, if you don't think it should have been closed, feel free to cast a vote to reopen and to start a discussion on meta presenting your position. Discussions like this will help us define the types of questions we want to allow here. – Dave DuPlantis Jul 18 '11 at 17:56
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    Another vote to re-open. Cell phones are an active topic of research in applied crypto right now. – Marsh Ray Aug 12 '11 at 22:50
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    Hi, I don't know how to "cast a vote to reopen" precisely, but I did click on the up-arrow to vote this question as being good. It now says "2". – Zooko Aug 15 '11 at 21:38
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    For everyone who wants to discuss the on-topicness of this question, come to Are questions on specific implementations of crypto in a specific device/application/system on topic? on Meta. – Paŭlo Ebermann Aug 26 '11 at 19:20

In cellular phone IMEI not used for authentication. authentication key is a key naming Ki. Google is helpful.Refer to these links: 16 in 1 super SIM

For GSM security see GSM Security and this other document on GSM security.


Usually the mechanism is matching IMEI with the phone number. However GSM networks, which use a SIM card embedded with the phone number, don't have such a matching mechanism. So you can use the SIM card on different phones, thus phone numbers are not fixed on devices.

Here's a Wikipedia article to explain that. But, this subject is not relevant to cryptography.

Authentication itself is, of course, achieved by a simple cryptographic function using an authentication key. This article explains it a bit.

  • This is not quite right. The question asks what prevents cloning. In digital cellphones, the answer is cryptographic authentication, using a key that is kept secret by the phone (and the carrier). GSM uses the A3A8 authentication algorithm together with the secret key Ki. US cellphone standards (e.g., TDMA, CMDA) use their own algorithm (e.g., CAVE) together with the secret key A-key. I'm leaving out many details, and some of these mechanisms have been updated over the past decade, but hopefully this gives you a basic idea. In particular, IMEI-matching is not the main defense against cloning. – D.W. Aug 5 '11 at 1:50
  • The question was based on the assumption that phone numbers were matched to mobile devices. I was merely correcting that assumption and pointing towards the authentication point of view with that last link. Sorry if I wasn't clear enough. – uygar.raf Aug 18 '11 at 15:39

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