NAME
crypt — string
encoding function (CRYPT)
SYNOPSIS
char *crypt(const char *key, const char *salt);
DESCRIPTION
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 is a string 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 characters 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
reentrant. A function that is not required to be reentrant is not required
to be thread-safe.
RETURN VALUE
Upon successful completion, crypt () shall
return a pointer to the encoded string. The first two characters 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.
ERRORS
The crypt () function shall fail if:
- [ENOSYS]
- The functionality is not supported on this implementation.
EXAMPLES
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 IEEE Std 1003.1-2001 (“POSIX.1”).
#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);
}
APPLICATION USAGE
The values returned by this function need not be portable among XSI-conformant systems.
RATIONALE
None.
FUTURE DIRECTIONS
None.
SEE ALSO
encrypt(3), setkey(3), the Base Definitions volume of IEEE Std 1003.1-2001 (“POSIX.1”), <unistd.h>
CHANGE HISTORY
First released in Issue 1. Derived from Issue 1 of the SVID.
Issue 5
Normative text previously in the APPLICATION USAGE section is moved to the DESCRIPTION.
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