How does rc4 stream cipher work

RC4 is a stream cipher, symmetric key algorithm. The same algorithm is used for both encryption and decryption as the data stream is simply XORed with the generated key sequence. The key stream is completely independent of the plaintext used. What is a stream cipher with examples? Stream ciphers can encrypt plaintext messages of variable length. The one-time pad can be thought of as an example — each message uses a portion of the key with length equal to the length of the plaintext message.

Then that portion of the key is never re-eused. Is rc5 a stream cipher? RC4 -- a variable key-size stream cipher with byte-oriented operations. The algorithm is based on the use of a random permutation. RC5 -- a parameterized algorithm with a variable block size, a variable key size, and a variable number of rounds. Is rc4 encryption secure?

AES is considered more secure than RC4. RC4 is an old stream cipher which is considered broken. That is: it is possible to obtain information about the key stream and therefore plaintext. If the length of the key k is bytes, then k is assigned to T. Otherwise, for a key with length k-len bytes, the first k-len elements of T as copied from K, and then K is repeated as many times as necessary to fill T. The idea is illustrated as follow:. In this step, for each S[i] algorithm swap it with another byte in S according to a scheme dictated by the current configuration of S.

This video gives a clear example of RC4 algorithm. Skip to content. Change Language. Related Articles. Computer Network Fundamentals. Physical layer. Because of that issue, it is possible to obtain some information about the secret key based on the first bytes of keystream. It is recommended to simply discard a number of first bytes of the keystream. This improvement is known as RC4-dropN , where N is usually a multiple of RC4 does not take a separate nonce alongside the key for every encryption.

Therefore, the cryptosystem must take care of unique values of keystream and specify how to combine the nonce with the original secret key. The best idea would be to hash the nonce and the key together to generate the base for creating the RC4 keystream.

Unfortunately, many applications simply concatenate key and nonce, which make them vulnerable to so called related key attacks. During initialisation of the T table byte long used for generating keystream, the value of temporary variable is updated for every element in the table.

The updated temporary variable is then used for modifying other numbers in the table. After the operations above, the current value in the T table is swapped with the value at the position determined by the temporary variable. All positions in the table are numbered from 0. Initialisation a T table, used for generation of keystream bytes. For keystream bytes generation, the loop below is executed as long as new bytes are needed. Variants of the RC4 cipher.

There are 4 variants to the regular RC4 cipher: Spritz — Spritz is used to create cryptographic hash functions and deterministic random bit generator. RC4A was found to have not truly random numbers used in its cipher. Advantages and Disadvantages. RC4 boasts a number of advantages compared to other stream ciphers: RC4 is extremely simple to use, thus making the implementation simple as well.

RC4 is fast, due to its simplicity, which makes it a better performing cipher. RC4 also works with large streams of data swiftly and easily. Though it has advantages, RC4 has many disadvantages as well: The vulnerabilities found in RC4 means RC4 is extremely insecure, so very few applications use it now.

RC4 cannot be used on smaller streams of data, so its usage is more niche than other stream ciphers. RC4 also does not provide authentication, so a Man in the Middle attack could occur, and the RC4 cipher user would be none the wiser.

Please submit your Contact information for a custom quote. Please submit your Contact information for more details.