CRYPT(3) Library functions CRYPT(3)
NAME
crypt - password and data encryption
SYNOPSIS
#include <unistd.h>
char *crypt(const char *key, const char *salt);
DESCRIPTION
crypt is the password encryption function. It is 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. Soft-
ware, 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 crack-able passwords during the selection process is recommended.
The DES algorithm itself has a few quirks which make the use of the crypt(3) inter-
face 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.
CONFORMING TO
SVID, X/OPEN, BSD 4.3
SEE ALSO
login(1), passwd(1), encrypt(3), getpass(3), passwd(5)
September 3, 1994 1
The above manual page mentions that crypt function is based on the DES algorithm. DES is the government regulated Data Encryption Standard. In July 1998, the Electronic Frontier Foundation announced that it had succeeded in breaking the DES standard in 56 hours using a modified PC computer. The total cost of the modified machine was approximately $200,000.00. Previous successful attempts to break the DES standard took 5 months using a nationwide network of computers and 39 days, again, using a nationwide network of computers. This development means that it is now necessary to improve standard encryption algorithms.