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CRYPT
!!!CRYPT
NAME
SYNOPSIS
DESCRIPTION
RETURN VALUE
ERRORS
CONFORMING TO
SEE ALSO
----
!!NAME


crypt - password and data encryption
!!SYNOPSIS


__#include __


__char *crypt(const char *__''key''__, const char
*__''salt''__);__
!!DESCRIPTION


__crypt__ provides acess to two algorithms for password
encryption. One it's based on the Data Encryption Standard
algorithm with variations intended (among other things) to
discourage use of hardware implementations of a key
search.


''key'' is a user's typed password.


''salt'' is a two-character string chosen from the set
[[__a__-__zA__-__Z0__-__9./__]. This string is
used to perturb the algorithm in one of 4096 different
ways.


By taking the lowest 7 bit of each character of the
''key'', a 56-bit key is obtained. This 56-bit key is
used to encrypt repeatedly a constant string (usually a
string consisting of all zeros). The returned value points
to the encrypted password, a series of 13 printable ASCII
characters (the first two characters represent the salt
itself). The return value points to static data whose
content is overwritten by each call.


Warning: The key space consists of 2 56 equal
7.2e16 possible values. Exhaustive searches of this key
space are possible using massively parallel computers.
Software, such as crack(1), is available which will
search the portion of this key space that is generally used
by humans for passwords. Hence, password selection should,
at minimum, avoid common words and names. The use of a
passwd(1) program that checks for crackable passwords
during the selection process is recommended.


The DES algorithm itself has a few quirks which make the use
of the crypt(3) interface a very poor choice for
anything other than password authentication. If you are
planning on using the crypt(3) interface for a
cryptography project, don't do it: get a good book on
encryption and one of the widely available DES
libraries.
!!RETURN VALUE


A pointer to the encrypted password is returned. On error,
NULL is returned.
!!ERRORS


__ENOSYS__


The __crypt__ function was not implemented, probably
because of U.S.A. export restrictions.


If the salt starts with ''$1$'' an MD5 based password
hashing algorithm is applied. The salt should consist off
''$1$'' followed with eight characters.


Programs using this function must be linked with
-lcrypt.
!!CONFORMING TO


SVID, X/OPEN, BSD 4.3
!!SEE ALSO


login(1), passwd(1), encrypt(3),
getpass(3), passwd(5)
----

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Last edited on Tuesday, June 4, 2002 12:24:15 am by "perry"

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