.\" Copyright (c) 2001-2003 The Open Group, All Rights Reserved 
.TH "CRYPT" 3P 2003 "IEEE/The Open Group" "POSIX Programmer's Manual"
.\" crypt 
.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 \- string encoding function (\fBCRYPT\fP)
.SH SYNOPSIS
.LP
\fB#include <unistd.h>
.br
.sp
char *crypt(const char *\fP\fIkey\fP\fB, const char *\fP\fIsalt\fP\fB);
\fP
\fB
.br
\fP
.SH DESCRIPTION
.LP
The \fIcrypt\fP() function is a string encoding function. The algorithm
is implementation-defined.
.LP
The \fIkey\fP argument points to a string to be encoded. The \fIsalt\fP
argument is a string chosen from the set:
.sp
.RS
.nf

\fBa 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 . /
\fP
.fi
.RE
.LP
The first two characters of this string may be used to perturb the
encoding algorithm.
.LP
The return value of \fIcrypt\fP() points to static data that is overwritten
by each call.
.LP
The \fIcrypt\fP() function need not be reentrant. A function that
is not required to be reentrant is not required to be
thread-safe.
.SH RETURN VALUE
.LP
Upon successful completion, \fIcrypt\fP() shall return a pointer to
the encoded string. The first two characters of the
returned value shall be those of the \fIsalt\fP argument. Otherwise,
it shall return a null pointer and set \fIerrno\fP to
indicate the error.
.SH ERRORS
.LP
The \fIcrypt\fP() function shall fail if:
.TP 7
.B ENOSYS
The functionality is not supported on this implementation.
.sp
.LP
\fIThe following sections are informative.\fP
.SH EXAMPLES
.SS Encoding Passwords
.LP
The following example finds a user database entry matching a particular
user name and changes the current password to a new
password. The \fIcrypt\fP() function generates an encoded version
of each password. The first call to \fIcrypt\fP() 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\fP() encodes the new password before it is stored.
.LP
The \fIputpwent\fP() function, used in the following example, is not
part of IEEE\ Std\ 1003.1-2001.
.sp
.RS
.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\\n");
        }
    }
    /* Put passwd entry into ptmp. */
    putpwent(p, fpfd);
}
\fP
.fi
.RE
.SH APPLICATION USAGE
.LP
The values returned by this function need not be portable among XSI-conformant
systems.
.SH RATIONALE
.LP
None.
.SH FUTURE DIRECTIONS
.LP
None.
.SH SEE ALSO
.LP
\fIencrypt\fP(), \fIsetkey\fP(), the Base Definitions volume of
IEEE\ Std\ 1003.1-2001, \fI<unistd.h>\fP
.SH COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group. 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.opengroup.org/unix/online.html .
