![]() ![]() At first glance it may appear that a PN key stream can provide the same security as the one-time pad, since the period of the sequence generated by a maximum-length linear shift register is 2 n - 1 bits, where n is the number of stages in the register. ![]() These techniques are popular because the encryption and decryption algorithms are readily implemented with feedback shift registers. However, the sequences, of course, are deterministic (see Section12.2). Pseudorandom sequences have statistical properties similar to the random flipping of a fair coin. Such stream encryption techniques use pseudorandom (PN) sequences, which derive their name from the fact that they appear random to the casual observer binary Great emphasis was placed on generating key streams that appeared to be random, yet could easily be implemented for decryption, because they could be generated by algorithms. The development of stream encryption schemes represents an attempt to emulate the one-time pad. Thus, perfect secrecy can be achieved for an infinite number of messages, since each message would be encrypted with a different portion of the random key stream. One can conceptualize a stream encryption implementation of a one-time pad using a truly random key stream (the key sequence never repeats). Digital Communications: Fundamentals and Applications, 3rd EditionĮarlier, we defined a one-time pad as an encryption system with a random key, used one time only, that exhibits unconditional security. ![]()
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