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PROLOG | NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | EXAMPLES | APPLICATION USAGE | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT |
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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.
Several implementations offer extensions via characters outside
of the set specified for the salt argument for specifying
alternative algorithms; while not portable, these extensions may
offer better security. The use of crypt() for anything other than
password hashing is not recommended.
None.
None.
encrypt(3p), setkey(3p)
The Base Definitions volume of POSIX.1‐2017, unistd.h(0p)
Portions of this text are reprinted and reproduced in electronic
form from IEEE Std 1003.1-2017, Standard for Information
Technology -- Portable Operating System Interface (POSIX), The
Open Group Base Specifications Issue 7, 2018 Edition, Copyright
(C) 2018 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 .
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 2017 CRYPT(3P)
Pages that refer to this page: unistd.h(0p), encrypt(3p), setkey(3p)
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HTML rendering created 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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