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.\" ========================================================================
.\"
.IX Title "rc4 3"
.TH rc4 3 2019-12-20 1.0.2u OpenSSL
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.SH NAME
RC4_set_key, RC4 \- RC4 encryption
.SH SYNOPSIS
.IX Header "SYNOPSIS"
.Vb 1
\& #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);
.Ve
.SH DESCRIPTION
.IX Header "DESCRIPTION"
This library implements the Alleged RC4 cipher, which is described for
example in \fIApplied Cryptography\fR.  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
\&\fBRC4_set_key()\fR sets up the \fBRC4_KEY\fR \fBkey\fR using the \fBlen\fR bytes long
key at \fBdata\fR.
.PP
\&\fBRC4()\fR encrypts or decrypts the \fBlen\fR bytes of data at \fBindata\fR using
\&\fBkey\fR and places the result at \fBoutdata\fR.  Repeated \fBRC4()\fR calls with
the same \fBkey\fR yield a continuous key stream.
.PP
Since RC4 is a stream cipher (the input is XORed with a pseudo-random
key stream to produce the output), decryption uses the same function
calls as encryption.
.PP
Applications should use the higher level functions
\&\fBEVP_EncryptInit\fR\|(3)
etc. instead of calling the RC4 functions directly.
.SH "RETURN VALUES"
.IX Header "RETURN VALUES"
\&\fBRC4_set_key()\fR and \fBRC4()\fR do not return values.
.SH NOTE
.IX Header "NOTE"
Certain conditions have to be observed to securely use stream ciphers.
It is not permissible to perform multiple encryptions using the same
key stream.
.SH "SEE ALSO"
.IX Header "SEE ALSO"
\&\fBblowfish\fR\|(3), \fBdes\fR\|(3), \fBrc2\fR\|(3)
.SH HISTORY
.IX Header "HISTORY"
\&\fBRC4_set_key()\fR and \fBRC4()\fR are available in all versions of SSLeay and OpenSSL.