crypt, encrypt

Purpose

     Encrypts user passwords.

Library

     Standard C Library (libc.a)

Syntax

     char *crypt (key, salt)                   void encrypt (block)
     char *key, *salt;                         char *block;
     Description

     The crypt and encrypt subroutines encrypt user passwords.
     They are based on  a one-way hashing encryption algorithm
     with  variations   intended  to  frustrate  the   use  of
     hardware-implemented key searches.  These subroutines are
     provided for  compatibility with UNIX  system implementa-
     tions, and no assertion is made about the strength of the
     algorithm.

     The key parameter  is a user's typed  password.  The salt
     parameter is  a two-character string chosen  from the set
     ["a-zA-Z0-9./"].

     The salt parameter  is used to perturb  the hashing algo-
     rithm  in one  of 4096  different ways,  after which  the
     password is used as the  key to repeatedly encrypt a con-
     stant string.   The return value points  to the encrypted
     password.  The  first two characters of  the return value
     are the string entered in the salt parameter.

     The crypt subroutine uses a  character array of length 64
     containing  only the  values  "(char) 0" and  "(char) 1".
     This string  is divided  into groups of  eight characters
     each, and  the low-order  bit in  each group  is ignored.
     This provides a 56-bit key, which is set into the machine
     by crypt.

     The encrypt subroutine provides somewhat primitive access
     to the actual hashing  algorithm.  The block parameter is
     a   64-character  array   containing   only  the   values
     "(char) 0" and  "(char) 1".  encrypt modifies  this array
     in place,  producing a similar  array that has  been sub-
     jected  to the  hashing algorithm  using the  key set  by
     crypt.

     Return Value

     The crypt  subroutine returns a pointer  to the encrypted
     password.  The first two characters of it are the same as
     the salt parameter.

     Note:  The  return value  points to  static data  that is
     overwritten by subsequent calls.

     Related Information

     In this book:  "getpass" and "passwd."

     The  login and  passwd commands  in AIX  Operating System
     Commands Reference.