.\"	$OpenBSD: RC4.3,v 1.8 2020/03/29 17:05:02 schwarze Exp $
.\"	OpenSSL 99d63d46 Oct 26 13:56:48 2016 -0400
.\"
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.Dd $Mdocdate: March 29 2020 $
.Dt RC4 3
.Os
.Sh NAME
.Nm RC4_set_key ,
.Nm RC4
.Nd RC4 encryption
.Sh SYNOPSIS
.In openssl/rc4.h
.Ft void
.Fo RC4_set_key
.Fa "RC4_KEY *key"
.Fa "int len"
.Fa "const unsigned char *data"
.Fc
.Ft void
.Fo RC4
.Fa "RC4_KEY *key"
.Fa "unsigned long len"
.Fa "const unsigned char *indata"
.Fa "unsigned char *outdata"
.Fc
.Sh DESCRIPTION
This library implements the alleged RC4 cipher, which is described for
example in
.Qq Applied Cryptography .
It is believed to be compatible with RC4[TM], a proprietary cipher of
RSA Security Inc.
.Pp
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.
.Pp
RC4 consists of a key setup phase and the actual encryption or
decryption phase.
.Pp
.Fn RC4_set_key
sets up the
.Vt RC4_KEY
.Fa key
using the
.Fa len
bytes long key at
.Fa data .
.Pp
.Fn RC4
encrypts or decrypts the
.Fa len
bytes of data at
.Fa indata
using
.Fa key
and places the result at
.Fa outdata .
Repeated
.Fn RC4
calls with the same
.Fa key
yield a continuous key stream.
.Pp
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.
.Sh SEE ALSO
.Xr blowfish 3 ,
.Xr EVP_EncryptInit 3 ,
.Xr EVP_rc4 3
.Sh HISTORY
.Fn RC4_set_key
and
.Fn RC4
appeared in SSLeay 0.4 or earlier and have been available since
.Ox 2.4 .
.Sh BUGS
This cipher is broken and should no longer be used.