In this video, Limor and Philip from Citizen Engineer, demonstrate how to clone SIM cards and hack payphones to do interesting things. The SIM card section starts with a primer on how the authentication works in the GSM world – challenge / response where the SIM contains the encryption key which is used to encrypt the challenge sent by the base station. Now the problem seems to be that there is no way to retrieve the encryption key directly from the SIM cards and the only way (which also only works for older cards) is to use a chosen plain text attack. This attack is carried out by connecting the SIM to a computer and bombarding it with encryption requests for known plain texts. After enough samples go through, the encryption key can be cracked. Once the encryption key is known it is trivial to clone the card using a writer. The video demonstrates the whole hardware hack on how to build your own reader, however, if you do not have the patience or the necessary skills / equipment then you can purchase one from them directly. In the later part of the video, Limor demonstrates how to modify Western Electric payphones so that they can be used as a home telephone, for VoIP (Skype) and to make it accept quarters. The whole video is more of a “hardware hacking” session than much of software. Its very well made and is definitely a recommended watch.