The One Time Pad Paradigm

The One Time Pad (OTP) is the paradigm for Perfect Secrecy.

Although based in a very simple encoding scheme, the only secure way to implement an OTP is to have an infinitely long source of perfectly random bits, shared by the sender and the recipient. Of course it is a lot easier to theorize about that, than to achieve it by computational or physical means.

The December 2006 issue of Computer reports a demonstration by Spanish researcher Claudio Mirasso’s group of hardware that can be used for the purpose of generating a stream of random bits on both ends of an optic link. It consists of a solid state laser which has a splitter and mirrors that inject part of its output in the cavity. Under this setup, the laser generates a signal with erratic fluctuations in amplitude.

The initial signal used to create the chaotic output is sent to the receiveing laser, which has similar characteristics to the sender laser. It has to be cut from the same wafer and must have identical characteristics within a 5% tolerance with the sender.

The chaotic signal from the sender is modulated with the information to be encoded and the result is sent to the receiving laser through optic fiber. The receiving laser can filter the information from the modulated signal using its own chaotic output that is the same as the sender laser. The only way to break the “encryption” process is to make a laser with the same characteristic and feed the transmitted signal into it.

Dr. Mirasso publication page can be found at here.

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