The propeller head version:
Voice privacy of IS-95 CDMA is provided by means of the long code mask.The long code mask is not transmitted through any channel, it is constructed by the base station and the mobile station. To recover the long code sequence,the eavesdropper may exhaustively search the 42-bit long code mask, with a time complexity of O(2 42 ). This attack is viable but is hard to implement in real time. Alternatively, it can be shown that the long code sequence can also be recovered if the eavesdropper can obtain 42 bits of plaintext-ciphertext pairs.As there are many mobile stations transmitting simultaneously on the trac channel and each mobile station only transmits approximately 3 minutes on the average, it is rather di cult to obtain 42 bits of the plaintext message.