.\" Portions Copyright © 2005-2006 Nokia. All rights reserved.
.\" FreeSec: libcrypt for NetBSD
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.\" Copyright (c) 1994 David Burren
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.\" $FreeBSD: src/lib/libcrypt/crypt.3,v 1.31 2005/02/09 18:03:14 ru Exp $
.\"
.Dd January 19, 1997
.Dt ENCRYPT 3
.Os
.Sh NAME
.Nm encrypt, setkey
.Nd encrypt 64-bit messages
.Sh LIBRARY
.Lb libcrypt
.Sh SYNOPSIS
.In unistd.h
.Ft void
.Fn encrypt "char block[64]" "int edflag"
.In stdlib.h
.Ft void
.Fn setkey "const char *key"
.Sh RETURN VALUES
The
.Fn encrypt 
and 
.Fn setkey
functions do not return any value.
.Sh DESCRIPTION
.Fn encrypt()
function encrypts and decrypts 64-bit messages. The algorithm used to perform 
encryption/decryption is Data Encryption Standard (DES).
.Pp
.Fn setkey()
is invoked to set the key for the DES machine.
.Fn setkey()'
s
.Fn key
parameter is an array of 64 bytes, and the numerical value of each byte in this
array is either 0 or 1. The 56-bit key for the DES algorithm is computed from the
.Fn key
parameter.
.Pp
.Fn encrypt
function either encrypts or decrypts the data block. The exact operation depends 
on the value of 
.Fn edflag
parameter. 
.Fn block
is encrypted if 
.Fn edflag
parameter is 0, and decrypted if 1 is being passed as the value of 
.Fn edflag 
parameter. 
.Fn block
is an array of 64 bytes, wherein the numerical value of each byte is either 0 or 1.
Like the 
.Fn setkey'
s
.Fn key 
parameter, 
.Fn block 
is a bit vector representation of the actual value that is encoded. It is modified in place
to return the result.
.Pp
.Fn encrypt
and
.Fn setkey
are not reentrant as the key is stored statically.

.Sh ERRORS
.Fn errno
should be set to zero prior to calling any of the above functions. The behavior of
.Fn encrypt
will be undefined if size of
.Fn block
argument is not 64.
.Sh EXAMPLE
.Bd -literal -offset indent
#include <stdlib.h>
#include <unistd.h>

void encrypt_user()
{
	/* bit vector containing the key */
	char key[64] = 
	{
			0, 0, 0, 0, 0, 0, 0, 1,
			0, 0, 1, 1, 0, 0, 0, 1,
			1, 1, 0, 1, 1, 0, 0, 1,
			0, 1, 1, 0, 0, 0, 0, 1,
			1, 0, 0, 1, 1, 1, 0, 1,
			1, 1, 0, 0, 0, 0, 0, 1,
			0, 0, 1, 1, 0, 1, 1, 1,
			0, 1, 1, 0, 1, 1, 1, 0
	};

	/* bit vector containing the data block to be encrypted */
	char block[64] = 
	{
		0, 1, 0, 1, 1, 1, 0, 0,
		1, 1, 0, 1, 0, 1, 0, 1,
		0, 1, 0, 0, 1, 1, 0, 0,
		1, 0, 1, 0, 1, 0, 0, 0,
		0, 0, 1, 1, 1, 1, 0, 1,
		1, 1, 1, 0, 1, 1, 1, 1,
		0, 1, 0, 1, 0, 1, 1, 1,
		1, 1, 0, 1, 1, 0, 1, 0
	};

	setkey(key);		/* Set the key for DES encryption */
	
	/* Perform encryption/decryption of the message block */
	encrypt(block, 0);	/* Encryption. The input block is modified in place
					 * to return the output to the user
					 */

	encrypt(block, 1);	/* Decryption. The input block is modified in place
					 * to return the result of the decryption operation
					 */
}
.Ed
.Sh SEE ALSO
.Sh HISTORY
.Sh BUGS
If 
.Fn encrypt
is called without priorly invoking 
.Fn setkey
the implementation assumes a bit vector consisting of all zeroes as the key
for the DES algorithm. In this scenaro the outcome of 
.Fn encrypt
function is different from that of Linux's.