cc [ flag ... ] file ... –lcrypt [ library ... ] #include <crypt.h> char *crypt(const char *key, const char *salt);
void setkey(const char *key);
void encrypt(char *block, int flag);
char *des_crypt(const char *key, const char *salt);
void des_setkey(const char *key);
void des_encrypt(char *block, int flag);
int run_setkey(int *p, const char *key);
int run_crypt(long offset, char *buffer, unsigned int count, int *p);
int crypt_close(int *p);
des_crypt() is the password encryption function. It is based on a one-way hashing encryption algorithm with variations intended (among other things) to frustrate 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 hashing algorithm in one of 4096 different ways, after which the password is used as the key to encrypt repeatedly a constant string. The returned value points to the encrypted password. The first two characters are the salt itself.
The des_setkey() and des_encrypt() entries provide (rather primitive) access to the actual hashing algorithm. The argument of des_setkey() is a character array of length 64 containing only the characters with numerical value 0 and 1. If this string is divided into groups of 8, the low-order bit in each group is ignored, thereby creating a 56-bit key that is set into the machine. This key is the key that will be used with the hashing algorithm to encrypt the string block with the function des_encrypt ().
The argument to the des_encrypt() entry 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 des_setkey(). If flag is zero, the argument is encrypted; if non-zero, it is decrypted.
Note that decryption is not provided in the international version of crypt(). The international version is part of the C Development Set, and the domestic version is part of the Security Administration Utilities. If decryption is attempted with the international version of des_encrypt(), an error message is printed.
crypt(), setkey(), and encrypt() are front-end routines that invoke des_crypt(), des_setkey(), and des_encrypt() respectively.
The routines run_setkey() and run_crypt() are designed for use by applications that need cryptographic capabilities, such as ed(1) and vi(1). run_setkey() establishes a two-way pipe connection with the crypt utility, using key as the password argument. run_crypt() takes a block of characters and transforms the cleartext or ciphertext into their ciphertext or cleartext using the crypt utility. offset is the relative byte position from the beginning of the file that the block of text provided in block is coming from. count is the number of characters in block, and connection is an array containing indices to a table of input and output file streams. When encryption is finished, crypt_close() is used to terminate the connection with the crypt utility.
run_setkey() returns −1 if a connection with the crypt utility cannot be established. This result will occur in international versions of the UNIX system in which the crypt utility is not available. If a null key is passed to run_setkey(), 0 is returned. Otherwise, 1 is returned. run_crypt() returns −1 if it cannot write output or read input from the pipe attached to crypt(). Otherwise it returns 0.
The program must be linked with the object file access routine library libcrypt.a.
In the international version of crypt(), a flag argument of 1 to encrypt() or des_encrypt() is not accepted, and errno is set to ENOSYS to indicate that the functionality is not available.
See attributes(5) for descriptions of the following attributes:
The return value in crypt() points to static data that are overwritten by each call.