RC4s

RC4s is a term that appears in some sources but does not denote a single, standardized cipher. In most cryptographic literature, RC4s is used informally to refer to variants or implementations of the RC4 stream cipher rather than to a formally defined algorithm. Because RC4 itself is a family of related stream-cipher configurations, the label RC4s can be applied differently depending on the author or vendor, leading to ambiguity about what specific techniques or modifications are involved.

RC4 is a symmetric-key stream cipher designed by Ron Rivest. It uses a variable-length key to initialize a 256-byte state array S with a key-scheduling algorithm, then generates a keystream via a pseudo-random generation algorithm. The keystream is XORed with the plaintext to produce ciphertext. Many practical uses of RC4 in protocols or software have given rise to variants or tweaks intended to improve certain properties or to adapt RC4 for particular environments. Examples that are sometimes encountered under the broader RC4 umbrella include approaches that drop initial keystream bytes to reduce bias, or configurations integrated into larger protocols.

Security considerations for RC4 and its variants are significant. RC4, including many of its common offshoots, exhibits biases in the early keystream bytes and has known weaknesses that can be exploited under certain conditions. As a result, modern cryptographic guidance discourages the use of RC4 or RC4-based variants in new designs, and several protocols have phased RC4 out entirely. When encountering the term RC4s, it is important to consult the specific documentation to determine the exact variant and its security implications.