`crypt.3p` ( 3 )

функция кодирования строк (CRYPT) (string encoding function (CRYPT))

Пролог (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.

Имя (Name)

crypt — string encoding function (CRYPT)

Синопсис (Synopsis)

#include <unistd.h>

char *crypt(const char *key, const char *salt);

Описание (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 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.

Возвращаемое значение (Return value)

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.

Ошибки (Error)

The crypt() function shall fail if:

ENOSYS The functionality is not supported on this implementation.

The following sections are informative.

Примеры (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 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);
           }

Использование в приложениях (Application usage)

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.

Обоснование (Rationale)

None.

Будущие направления (Future directions)