It has been awhile that I read the IS-95 spec. but the randomization aspect and the 'seed' used to start the whole process keeps everyone "guessing" long enough to prevent decryption. That is, even if the general method is known, there are no computers fast enough to decrypt the information. To make things more difficult, the seed can be provided by the base station, the electronic id of the phone, or a combination of the both. If both the EID and the randomized base station numbers are used, one can quickly see how the whole system would be difficult to decrypt. Oh yeah, don't forget that the information is randomly spread throughout the wide band frequency. Though a feature used primarily to prevent jamming, spread spectrum does a number on those trying to determine which bit to put first and which to put last. Essentially, yet another barrier to decryption.
NB: public-key encryption is a publicly known method of encryption but the length of the keys keep the information private. Unlike systems of past, the key is what keeps things private and not the method of jumbling the information up. CDMA is like this since the method used in IS-95 must be well known but the length and variation of the keys keeps people guessing.
Also, it is interesting to note that the functions used in public-key encryption are one-way or not reversible. Once you encrypt data using a public key, you can not reverse the steps to decrypt. Instead, you must perform another process with a person's private key. Of course, since the private key is truly unknown, only the recepient of the data can decrypt. |
