Editing Stream cipher (section)

==Loose inspiration from the one-time pad==
Stream ciphers can be viewed as approximating the action of a proven unbreakable cipher, the [[one-time pad]] (OTP). A one-time pad uses a [[keystream]] of completely [[random]] digits. The keystream is combined with the plaintext digits one at a time to form the ciphertext. This system was proven to be secure by [[Claude E. Shannon]] in 1949.<ref>{{cite book |last1 = Deane |first1 = Arthur |last2 = Kraus |first2 = Aaron |date = 2021 |title = The Official (ISC)2 CISSP CBK Reference |edition = 6th |publication-place = Hoboken, New Jersey |publisher = John Wiley & Sons, Inc. |chapter = Chapter 3: Domain 3: Security Architecture and Engineering |page = 232 |isbn = 978-1-119-78999-4}}</ref> However, the keystream must be generated completely at random with at least the same length as the plaintext and cannot be used more than once. This makes the system cumbersome to implement in many practical applications, and as a result the one-time pad has not been widely used, except for the most critical applications. Key generation, distribution and management are critical for those applications.

A stream cipher makes use of a much smaller and more convenient key such as 128 bits. Based on this key, it generates a pseudorandom keystream which can be combined with the plaintext digits in a similar fashion to the one-time pad. However, this comes at a cost. The keystream is now pseudorandom and so is not truly random. The proof of security associated with the one-time pad no longer holds. It is quite possible for a stream cipher to be completely insecure.{{citation needed|date=October 2021}}