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CRYPT(3P) POSIX Programmer's Manual CRYPT(3P)
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.
crypt — string encoding function (CRYPT)
#include <unistd.h>
char *crypt(const char *key, const char *salt);
The crypt() function is a string encoding function. The algorithm is
implementation-defined.
The key argument points to a string to be encoded. The salt argument
shall be a string of at least two bytes in length not including the
null character chosen from the set:
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 . /
The first two bytes of this string may be used to perturb the
encoding algorithm.
The return value of crypt() points to static data that is overwritten
by each call.
The crypt() function need not be thread-safe.
Upon successful completion, crypt() shall return a pointer to the
encoded string. The first two bytes of the returned value shall be
those of the salt argument. Otherwise, it shall return a null pointer
and set errno to indicate the error.
The crypt() function shall fail if:
ENOSYS The functionality is not supported on this implementation.
The following sections are informative.
Encoding Passwords
The following example finds a user database entry matching a
particular user name and changes the current password to a new
password. The crypt() function generates an encoded version of each
password. The first call to crypt() 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 crypt()
encodes the new password before it is stored.
The putpwent() function, used in the following example, is not part
of POSIX.1‐2008.
#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);
}
The values returned by this function need not be portable among XSI-
conformant systems.
None.
None.
encrypt(3p), setkey(3p)
The Base Definitions volume of POSIX.1‐2008, unistd.h(0p)
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 .
IEEE/The Open Group 2013 CRYPT(3P)
Pages that refer to this page: unistd.h(0p), encrypt(3p), setkey(3p)