CRYPT(3,L)                  AIX Technical Reference                  CRYPT(3,L)



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crypt, encrypt, setkey



PURPOSE

Encrypts user passwords.

LIBRARY

Standard C Library (libc.a)

SYNTAX


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

                void setkey (key)
                char *key;


DESCRIPTION

The crypt and encrypt subroutines encrypt user passwords.  They are based on a
hashing encryption algorithm with variations intended to frustrate the use of
hardware-implemented key searches.  These subroutines are provided for
compatibility with UNIX system implementations, 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 algorithm in one of 4096
different ways, after which the password is used as the key to repeatedly
encrypt a constant 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 other subroutines provide a somewhat primitive access to the actual hashing
algorithm.

The key parameter to setkey is a character array of length 64, containing only
the characters with numerical value 0 and 1.  If this string is divided into




Processed November 7, 1990        CRYPT(3,L)                                  1

CRYPT(3,L)                  AIX Technical Reference                  CRYPT(3,L)



groups of eight, the low-order bit in each group is ignored, leading to a
56-bit key which is set into the machine.

The block parameter to the encrypt subroutine is also 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 subjected to the hashing
algorithm using the key set by crypt or setkey.  If the edflag parameter is 0,
the argument is encrypted; if nonzero, it is decrypted.

Note:  Depending on license agreements, the setkey function and the decrypt
       capability of encrypt may be disabled.

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.

ERROR CONDITIONS

The crypt, encrypt, and setkey subroutines fail if the following is true:

ENOSYS    This functionality is not supported in this implementation.

RELATED INFORMATION

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

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
























Processed November 7, 1990        CRYPT(3,L)                                  2