CRYPT(S) UNIX System V CRYPT(S)
Name
crypt - password and file encryption functions
Syntax
cc [flag ...] file ... -lcrypt
char *crypt (key, salt)
char *key, *salt;
void setkey (key)
char *key;
void encrypt (block, flag)
char *block;
int flag;
char *des_crypt (key, salt)
char *key, *salt;
void des_setkey (key)
char *key;
void des_encrypt (block, flag)
char *block;
int flag;
int run_setkey (p, key)
int p[2];
char *key;
int run_crypt (offset, buffer, count, p)
long offset;
char *buffer;
unsigned int count;
int p[2];
int crypt_close(p)
int p[2];
Description
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; this gives a 56-bit key which
is set into the machine. This 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 edflag is zero, the argument is
encrypted; if non-zero, it is decrypted.
Note that decryption is not provided in the international
version of crypt(S). 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(C) and vi(C)) that must be compatible with the
crypt(C) user-level utility. run_setkey establishes a two-
way pipe connection with crypt(C), using key as the password
argument. run_crypt takes a block of characters and
transforms the cleartext or ciphertext using crypt(C).
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
crypt(C).
run_setkey returns -1 if a connection with crypt(C) cannot
be established. This will occur on international versions
of the UNIX system where crypt(C) 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.
See Also
crypt(S), getpass(S), passwd(F), crypt(C), login(M),
passwd(C)
Diagnostics
In the international version of crypt(S), a flag argument of
1 to des_encrypt is not accepted, and an error message is
printed.
Note
The return value in crypt points to static data that are
overwritten by each call.
Standards Conformance
crypt is conformant with:
AT&T SVID Issue 2, Select Code 307-127;
and The X/Open Portability Guide II of January 1987.
(printed 6/20/89)