We were pressured to weaken the mobile security in the 80’s

They wanted a key length of 48 bit. We were very surprised. The West Germans protested because they wanted a stronger encryption to prevent spying from East Germany. The compromise was a key length of 64 bit – where the ten last bits were set to zero. The result was an effective key length of 54 bit.

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One other thing that was put in the GSM specification, after demands from some countries, was that the encryption could be turned off, without the cell phone user knowing.

When the encryption is turned off, it is also quite easy for private citizens with the right equipment to eavesdrop on cell phone calls.