.\" Copyright 2000 Nicolás Lichtmaier <nick@debian.org>
.\" Created 2000-07-22 00:52-0300
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.\" Modified 2002-07-23 19:21:35 CEST 2002 Walter Harms
.\" <walter.harms@informatik.uni-oldenburg.de>
.\"
.\" Modified 2003-04-04, aeb
.\"
.TH ENCRYPT 3 2017-09-15 "" "Linux Programmer's Manual"
.SH NAME
encrypt, setkey, encrypt_r, setkey_r \- encrypt 64-bit messages
.SH SYNOPSIS
.nf
.BR "#define _XOPEN_SOURCE" "       /* See feature_test_macros(7) */"
.B #include <unistd.h>
.PP
.BI "void encrypt(char " block "[64], int " edflag );

.BR "#define _XOPEN_SOURCE" "       /* See feature_test_macros(7) */"
.B #include <stdlib.h>
.PP
.BI "void setkey(const char *" key );

.BR "#define _GNU_SOURCE" "         /* See feature_test_macros(7) */"
.B "#include <crypt.h>"
.PP
.BI "void setkey_r(const char *" key ", struct crypt_data *" data );
.BI "void encrypt_r(char *" block ", int " edflag \
", struct crypt_data *" data );
.fi
.PP
Each of these requires linking with \fI\-lcrypt\fP.
.SH DESCRIPTION
These functions encrypt and decrypt 64-bit messages.
The
.BR setkey ()
function sets the key used by
.BR encrypt ().
The
.I key
argument used here is an array of 64 bytes, each of which has
numerical value 1 or 0.
The bytes key[n] where n=8*i-1 are ignored,
so that the effective key length is 56 bits.
.PP
The
.BR encrypt ()
function modifies the passed buffer, encoding if
.I edflag
is 0, and decoding if 1 is being passed.
Like the
.I key
argument, also
.I block
is a bit vector representation of the actual value that is encoded.
The result is returned in that same vector.
.PP
These two functions are not reentrant, that is, the key data is
kept in static storage.
The functions
.BR setkey_r ()
and
.BR encrypt_r ()
are the reentrant versions.
They use the following
structure to hold the key data:
.PP
.in +4n
.EX
struct crypt_data {
    char     keysched[16 * 8];
    char     sb0[32768];
    char     sb1[32768];
    char     sb2[32768];
    char     sb3[32768];
    char     crypt_3_buf[14];
    char     current_salt[2];
    long int current_saltbits;
    int      direction;
    int      initialized;
};
.EE
.in
.PP
Before calling
.BR setkey_r ()
set
.I data\->initialized
to zero.
.SH RETURN VALUE
These functions do not return any value.
.SH ERRORS
Set
.I errno
to zero before calling the above functions.
On success, it is unchanged.
.TP
.B ENOSYS
The function is not provided.
(For example because of former USA export restrictions.)
.SH ATTRIBUTES
For an explanation of the terms used in this section, see
.BR attributes (7).
.TS
allbox;
lbw23 lb lb
l l l.
Interface	Attribute	Value
T{
.BR encrypt (),
.BR setkey ()
T}	Thread safety	MT-Unsafe race:crypt
T{
.BR encrypt_r (),
.BR setkey_r ()
T}	Thread safety	MT-Safe
.TE
.SH CONFORMING TO
.BR encrypt (),
.BR setkey ():
POSIX.1-2001, POSIX.1-2008, SUS, SVr4.
.PP
The functions
.BR encrypt_r ()
and
.BR setkey_r ()
are GNU extensions.
.SH NOTES
In glibc 2.2, these functions use the DES algorithm.
.SH EXAMPLE
.EX
#define _XOPEN_SOURCE
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <crypt.h>

int
main(void)
{
    char key[64];
    char orig[9] = "eggplant";
    char buf[64];
    char txt[9];
    int i, j;

    for (i = 0; i < 64; i++) {
        key[i] = rand() & 1;
    }

    for (i = 0; i < 8; i++) {
        for (j = 0; j < 8; j++) {
            buf[i * 8 + j] = orig[i] >> j & 1;
        }
        setkey(key);
    }
    printf("Before encrypting: %s\\n", orig);

    encrypt(buf, 0);
    for (i = 0; i < 8; i++) {
        for (j = 0, txt[i] = \(aq\\0\(aq; j < 8; j++) {
            txt[i] |= buf[i * 8 + j] << j;
        }
        txt[8] = \(aq\\0\(aq;
    }
    printf("After encrypting:  %s\\n", txt);

    encrypt(buf, 1);
    for (i = 0; i < 8; i++) {
        for (j = 0, txt[i] = \(aq\\0\(aq; j < 8; j++) {
            txt[i] |= buf[i * 8 + j] << j;
        }
        txt[8] = \(aq\\0\(aq;
    }
    printf("After decrypting:  %s\\n", txt);
    exit(EXIT_SUCCESS);
}
.EE
.SH SEE ALSO
.BR cbc_crypt (3),
.BR crypt (3),
.BR ecb_crypt (3),
.\" .BR fcrypt (3)
.SH COLOPHON
This page is part of release 4.15 of the Linux
.I man-pages
project.
A description of the project,
information about reporting bugs,
and the latest version of this page,
can be found at
\%https://www.kernel.org/doc/man\-pages/.