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Definition
RC4 is a symmetric synchronous stream cipher. It is initialized by a variable length key, between 40 and 128 bits. The key is used to compute the initial value of the internal state of a pseudorandom generator, which produces a keystream. Encryption (respectively decryption) then consists in XOR-ing this keystream to the plaintext (respectively the ciphertext).
The internal state of the pseudorandom generator consists of a permutation S of all the 256 bytes, and two indices i and j. The secret key determines which permutation should be used as the initial state, before starting encryption/decryption. This step is called the key-scheduling. Then, the pseudorandom generator outputs as many bytes as needed to process encryption/decryption. The whole process is described in Fig. 1.
The pseudorandom number generator used in RC4
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Mantin I (2001) Analysis of the stream cipher RC4. Master’s thesis, Weizmann Institute of Science, Rehovot
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Fontaine, C. (2011). RC4. In: van Tilborg, H.C.A., Jajodia, S. (eds) Encyclopedia of Cryptography and Security. Springer, Boston, MA. https://doi.org/10.1007/978-1-4419-5906-5_365
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