CRYPT(3)

NAME
crypt - one-way password encryption function

SYNOPSIS
#define _MINIX_SOURCE 1
#include <unistd.h>
char *crypt(const char *key, const char *salt)

DESCRIPTION
The first use of crypt() is to encrypt a password. Its second use is to authenticate a shadow password. In both cases crypt() calls pwdauth(8) to do the real work.

Crypt() encrypts a password if called with a user typed key, and a salt whose first two characters are in the set [./0-9A-Za-z]. The result is a character string in the [./0-9A-Za-z] alphabet of which the first two characters are equal to the salt, and the rest is the result of encrypting the key and the salt.

If crypt() is called with a salt that has the form ##user then the key is encrypted and compared to the encrypted password of user in the shadow password file. If they are equal then crypt() returns the ##user argument, if not then some other string is returned. This trick assures that the normal way to authenticate a password still works:

    if (strcmp(pw->pw_passwd, crypt(key, pw->pw_passwd))) ...

If key is a null string, and the shadow password is a null string or the salt is a null string then the result equals salt. (This is because the caller can't tell if a password field is empty in the shadow password file.)

The key and salt are limited to 1024 bytes total including the null bytes.

FILES

/usr/lib/pwdauth
    The password authentication program

SEE ALSO
getpass(3), getpwent(3), passwd(5), pwdauth(8).

NOTES
The result of an encryption is returned in a static array that is overwritten by each call. The return value should not be modified.

AUTHOR
Kees J. Bot (kjb@cs.vu.nl)