'\" et

.TH CRYPT "3P" 2013 "IEEE/The Open Group" "POSIX Programmer's Manual"

.SH PROLOG

This manual page is part of the POSIX Programmer's Manual.

The Linux implementation of this interface may differ (consult

the corresponding Linux manual page for details of Linux behavior),

or the interface may not be implemented on Linux.

.SH NAME

crypt

\(em string encoding function

(\fBCRYPT\fP)

.SH SYNOPSIS

.LP

.nf

#include <unistd.h>

.P

char *crypt(const char *\fIkey\fP, const char *\fIsalt\fP);

.fi

.SH DESCRIPTION

The

\fIcrypt\fR()

function is a string encoding function. The algorithm is

implementation-defined.

.P

The

.IR key

argument points to a string to be encoded. The

.IR salt

argument shall be a string of at least two bytes in length not

including the null character chosen from the set:

.sp

.RS 4

.nf

\fB

a b c d e f g h i j k l m n o p q r s t u v w x y z

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

0 1 2 3 4 5 6 7 8 9 . /

.fi \fR

.P

.RE

.P

The first two bytes of this string may be used to perturb the

encoding algorithm.

.P

The return value of

\fIcrypt\fR()

points to static data that is overwritten by each call.

.P

The

\fIcrypt\fR()

function need not be thread-safe.

.SH "RETURN VALUE"

Upon successful completion,

\fIcrypt\fR()

shall return a pointer to the encoded string. The first two bytes

of the returned value shall be those of the

.IR salt

argument. Otherwise, it shall return a null pointer and set

.IR errno

to indicate the error.

.SH ERRORS

The

\fIcrypt\fR()

function shall fail if:

.TP

.BR ENOSYS

The functionality is not supported on this implementation.

.LP

.IR "The following sections are informative."

.SH EXAMPLES

.SS "Encoding Passwords"

.P

The following example finds a user database entry matching a particular

user name and changes the current password to a new password. The

\fIcrypt\fR()

function generates an encoded version of each password. The

first call to

\fIcrypt\fR()

produces an encoded version of the old password; that encoded password

is then compared to the password stored in the user database. The

second call to

\fIcrypt\fR()

encodes the new password before it is stored.

.P

The

\fIputpwent\fR()

function, used in the following example, is not part of POSIX.1\(hy2008.

.sp

.RS 4

.nf

\fB

#include <unistd.h>

#include <pwd.h>

#include <string.h>

#include <stdio.h>

\&...

int valid_change;

int pfd;  /* Integer for file descriptor returned by open(). */

FILE *fpfd;  /* File pointer for use in putpwent(). */

struct passwd *p;

char user[100];

char oldpasswd[100];

char newpasswd[100];

char savepasswd[100];

\&...

valid_change = 0;

while ((p = getpwent()) != NULL) {

    /* Change entry if found. */

    if (strcmp(p->pw_name, user) == 0) {

        if (strcmp(p->pw_passwd, crypt(oldpasswd, p->pw_passwd)) == 0) {

            strcpy(savepasswd, crypt(newpasswd, user));

            p->pw_passwd = savepasswd;

            valid_change = 1;

        }

        else {

            fprintf(stderr, "Old password is not valid\en");

        }

    }

    /* Put passwd entry into ptmp. */

    putpwent(p, fpfd);

}

.fi \fR

.P

.RE

.SH "APPLICATION USAGE"

The values returned by this function need not be portable among

XSI-conformant systems.

.SH RATIONALE

None.

.SH "FUTURE DIRECTIONS"

None.

.SH "SEE ALSO"

.IR "\fIencrypt\fR\^(\|)",

.IR "\fIsetkey\fR\^(\|)"

.P

The Base Definitions volume of POSIX.1\(hy2008,

.IR "\fB<unistd.h>\fP"

.SH COPYRIGHT

Portions of this text are reprinted and reproduced in electronic form

from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology

-- Portable Operating System Interface (POSIX), The Open Group Base

Specifications Issue 7, Copyright (C) 2013 by the Institute of

Electrical and Electronics Engineers, Inc and The Open Group.

(This is POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) In the

event of any discrepancy between this version and the original IEEE and

The Open Group Standard, the original IEEE and The Open Group Standard

is the referee document. The original Standard can be obtained online at

http://www.unix.org/online.html .

Any typographical or formatting errors that appear

in this page are most likely

to have been introduced during the conversion of the source files to

man page format. To report such errors, see

https://www.kernel.org/doc/man-pages/reporting_bugs.html .