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RC4(3) Library Functions Manual RC4(3)

RC4_set_key, RC4
RC4 encryption

#include <openssl/rc4.h>
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);

This library implements the alleged RC4 cipher, which is described for example in “Applied Cryptography”. It is believed to be compatible with RC4[TM], a proprietary cipher of RSA Security Inc.
RC4 is a stream cipher with 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 consists of a key setup phase and the actual encryption or decryption phase.
RC4_set_key() sets up the RC4_KEY 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.
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.

RC4_set_key() and RC4() do not return values.

blowfish(3), EVP_EncryptInit(3)

RC4_set_key() and RC4() appeared in SSLeay 0.4 or earlier and have been available since OpenBSD 2.4.

This cipher is broken and should no longer be used.
March 27, 2018 OpenBSD-current