In fact, over the last 20 years, several bytes like that have been found. It is possible to find keystream byte values that are slightly more likely to occur than other combinations. The cipher was created quite long time ago and it has some weaknesses which have been improved in modern stream ciphers. Unlike many other stream ciphers, it doesn't use LFSR registers, which can be implemented optimally in hardware solutions but they are not so fast in applications. The RC4 algorithm is designed especially to be used in software solutions because it only manipulates single bytes. If more keystream bytes are needed, all the steps from the point II onwards should be repeated.The value in the array at the position p 3 is a new keystream byte.Then, the result is modulo divided by 256 and assigned to the new helper variable p 3. The value in the array at the position p 1 is added to the value in the array at the position p 2.The value in the array at the position p 1 is swapped with the value in the array at the position p 2.Then, the result is divided modulo by 256. The variable p 2 is increased by the value in the array T at the position determined by the temporary variable p 1 ( T).The variable p 1 is increased by 1 and the result is modulo divided by 256.Two helper variables p 1 and p 2 are created and set to 0.The keystream bytes are produced based on the T table. The number in the array at the current position is swapped with the number in the array at the position determined by the temporary variable.ĭuring encryption and decryption the keystream bytes are constantly generated.The value of temporary variable is updated (see Mathematical functions tab).For each element in the array the two following operations are performed (note, that the values are from 0 to 255):.A new temporary helper variable is created and set to 0.The positions of the table are numbered from 0 to 255. Every cell in the table is filled with a number equal to its position.The following operations must be performed in order to create the table: It is created as a first step of both encryption and decryption. The T table is 256-byte long, and is created based on the secret key. The keystream is received from a 1-d table called the T table. The whole RC4 algorithm is based on creating keystream bytes. RC4 encrypts data by adding it XOR byte by byte, one after the other, to keystream bytes. It operates by creating long keystream sequences and adding them to data bytes. It is widely used in popular protocols, for example to protect Internet traffic - TLS (Transport Layer Security) or to protect wireless networks - WEP (Wired Equivalent Privacy). The cipher is officially named after "Rivest Cipher 4" but the acronym RC is alternatively understood to stand for "Ron's Code". RC4 is often referred to as ARCFOUR or ARC4 to avoid problems with RC4 trademarked name. Implementation of RC4 cipher wasn't known until September 1994 when it was anonymously posted to the Cypherpunks mailing list. Usageĭesigned by Ron Rivest of RSA Security in 1987. RC4 is a symmetric stream cipher, known and praised for its speed and simplicity. RC4 Stream cipher with symmetric secret key
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