RC4(3)

💅 RC4(3) — RC4 encryption 💅

okay bestie, welcome to the Library Functions Manual page for RC4(3) — manual name folded in right up top, no boring header-line copy-paste energy. The stars are RC4_set_key and RC4, and honestly this whole page is giving “historic crypto with a giant warning sticker.” 🫶

🌸 NAME 🌸

RC4_set_key, RC4 — RC4 encryption.

✨ SYNOPSIS ✨

the synopsis says library “libcrypto” and tells you to include:

library “libcrypto”
#include <openssl/rc4.h>

then the function signatures, exactly:

void
RC4_set_key(RC4_KEY *key, int len, const unsigned char *data);

void
RC4(RC4_KEY *key, unsigned long len, const unsigned char *indata,
    unsigned char *outdata);

💖 DESCRIPTION 💖

so this library implements the alleged RC4 cipher — the one described, for example, in "Applied Cryptography". It's believed to be compatible with RC4[TM], which is a proprietary cipher of RSA Security Inc. 👑

RC4 is a stream cipher with a variable key length. Typically, 128-bit (16-byte) keys are used for strong encryption, but shorter insecure key sizes have been widely used due to export restrictions. 💀

RC4 has two phases: a key setup phase, and then the actual encryption or decryption phase. main character structure, honestly. 🎀

RC4_set_key() handles the setup: it sets up the RC4_KEY named key using the len bytes long key at data. 🗝️

RC4() encrypts or decrypts the len bytes of data at indata using key, and places the result at outdata. Repeated RC4() calls with the same key yield a continuous key stream — no cap. 🔥

Since RC4 is a stream cipher (the input is XOR'ed with a pseudo-random key stream to produce the output), decryption uses the same function calls as encryption. one function, both directions, iconic. 🦋

👀 SEE ALSO 👀

go read these when you're done, bestie:

• blowfish(3)
• EVP_EncryptInit(3)
• EVP_rc4(3)

🕰️ HISTORY 🕰️

RC4_set_key() and RC4() appeared in SSLeay 0.4 or earlier, and they've been available since OpenBSD 2.4. old-school but not old enough to escape the warning. 🫠

💀 BUGS 💀

🚨 This cipher is broken and should no longer be used. Periodt. Not a quirky legacy flex — broken. please don't use it. 😭

xoxo bestie — source/version: Debian; date: June 8, 2025. mwah 💋