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crypt(3p) — Linux manual page

CRYPT(3P)               POSIX Programmer's ManualCRYPT(3P)

PROLOG        top

       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.

NAME        top

       crypt — string encoding function (CRYPT)

SYNOPSIS        top

       #include <unistd.h>       char *crypt(const char *key, const char *salt);

DESCRIPTION        top

       Thecrypt() function is a string encoding function. The algorithm       is implementation-defined.       Thekey argument points to a string to be encoded. Thesalt       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 ofcrypt() points to static data that is       overwritten by each call.       Thecrypt() function need not be thread-safe.

RETURN VALUE        top

       Upon successful completion,crypt() shall return a pointer to the       encoded string. The first two bytes of the returned value shall be       those of thesalt argument. Otherwise, it shall return a null       pointer and seterrno to indicate the error.

ERRORS        top

       Thecrypt() function shall fail if:ENOSYSThe functionality is not supported on this implementation.The following sections are informative.

EXAMPLES        top

Encoding Passwords       The following example finds a user database entry matching a       particular user name and changes the current password to a new       password. Thecrypt() function generates an encoded version of       each password. The first call tocrypt() 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 tocrypt() encodes the new password before it is stored.       Theputpwent() 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);           }

APPLICATION USAGE        top

       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 thesalt argument for specifying alternative       algorithms; while not portable, these extensions may offer better       security. The use ofcrypt() for anything other than password       hashing is not recommended.

RATIONALE        top

       None.

FUTURE DIRECTIONS        top

       None.

SEE ALSO        top

encrypt(3p),setkey(3p)       The Base Definitions volume of POSIX.1‐2017,unistd.h(0p)

COPYRIGHT        top

       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 athttp://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, seehttps://www.kernel.org/doc/man-pages/reporting_bugs.html .IEEE/The Open Group                2017CRYPT(3P)

Pages that refer to this page:unistd.h(0p), encrypt(3p), setkey(3p)

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