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#include <crypt.h>
char *crypt(const char *key, const char *salt);
void setkey(const char *key);
void encrypt(char *block, int edflag);
Safe
key is the input string to encrypt, for instance, a user’s typed password. Only the first eight characters are used; the rest are ignored. salt is a two-character string chosen from the set [a-zA-Z0-9./]; this string is used to perturb the hashing algorithm in one of 4096 different ways, after which the input string is used as the key to repeatedly encrypt a constant string. The returned value points to the encrypted input string. The first two characters of the return value are the salt itself.
The setkey() and encrypt() functions provide (rather primitive) access to the actual hashing algorithm. The argument of setkey() is a character array of length 64 containing only the characters with numerical value 0 and 1. This string is divided into groups of 8, the low-order bit in each group is ignored; this gives a 56-bit key that is set into the machine. This is the key that will be used with the hashing algorithm to encrypt the string block with the encrypt() function.
The block argument of encrypt() is a character array of length 64 containing only the characters with numerical value 0 and 1. The argument array is modified in place to a similar array representing the bits of the argument after having been subjected to the hashing algorithm using the key set by setkey(). The argument edflag, indicating decryption rather than encryption, is ignored; use encrypt() in libcrypt() (see crypt(3X) ) for decryption.