cc [flag . . . ] file . . . -lcrypt [library] . . .
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 connection, const char key);
int run_crypt(long offset, char buffer, unsigned int count, int connection);
int crypt_close(int connection);
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 access to the 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.
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)] that must be compatible with the crypt(1) user-level utility. 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 buffer is coming from. count is the number of characters in buffer, 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. crypt_close returns -1 if it fails to terminate the connection with the crypt utility, or a 0 if termination is successful.
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.