Open-Source Effort to Hack GSM

“Each GSM phone has its own secret key, which is known by the
network. Every time a call is initiated, a new session key for that
particular call is derived from the secret key and used to encrypt
the call. Nohl aims to crack the session key.

“The engineer has designed an open-source software program that
participants in his A5/1 cracking project can install on their PCs
and use to share the task of computing the lookup tables that make
up the cryptography system. The final codebook with the computed
tables will be shared across a peer-to-peer network. Therefore, no
one computer contains all the files, making it difficult, if not
impossible, to remove the cracking tool entirely from the
Internet.”

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