crypt, setkey, encrypt, des_setkey, des_cipher - DES encryption
crypt(const char *key, const char *setting);
encrypt(char *block, int flag);
des_setkey(const char *key);
des_cipher(const char *in, char *out, int32_t salt, int
bcrypt(const char *key, const char *salt);
md5crypt(const char *key, const char *salt);
The crypt() function performs password encryption based on
the NBS Data
Encryption Standard (DES). Additional code has been added
to deter key
search attempts and to use stronger hashing algorithms.
The first argument to crypt() is a null-terminated string,
user's typed password. The second is in one of three forms:
if it begins
with an underscore (`_') then an extended format is used in
both the key and the setting, as outlined below. If it begins with a
string character (`$') and a number then a different algorithm is used
depending on the number. At the moment a `$1' chooses MD5
hashing and a
`$2' chooses Blowfish hashing; see below for more information.
Extended crypt [Toc] [Back]
The key is divided into groups of 8 characters (the last
group is nullpadded)
and the low-order 7 bits of each character (56 bits
are used to form the DES key as follows: the first group of
56 bits becomes
the initial DES key. For each additional group, the
XOR of the encryption
of the current DES key with itself and the group
the next DES key.
The setting is a 9-character array consisting of an underscore followed
by 4 bytes of iteration count and 4 bytes of salt. These
are encoded as
printable characters, 6 bits per character, least significant character
first. The values 0 to 63 are encoded as ``./0-9A-Za-z''.
24 bits for both count and salt.
MD5 crypt [Toc] [Back]
For MD5 crypt the version number, salt and the hashed password are separated
by the `$' character. The maximum length of a password is limited
by the length counter of the MD5 context, which is about
2**64. A valid
MD5 password entry looks like this:
The whole MD5 password string is passed as setting for interpretation.
Blowfish crypt [Toc] [Back]
The Blowfish version of crypt has 128 bits of salt in order
building dictionaries of common passwords space consuming.
state of the Blowfish cipher is expanded using the salt and
repeating the process a variable number of rounds, which is
the password string. The maximum password length is 72.
The final Blowfish
password entry is created by encrypting the string
with the Blowfish state 64 times.
The version number, the logarithm of the number of rounds
and the concatenation
of salt and hashed password are separated by the
An encoded `8' would specify 256 rounds. A valid
looks like this:
The whole Blowfish password string is passed as setting for
Traditional crypt [Toc] [Back]
The first 8 bytes of the key are null-padded, and the loworder 7 bits of
each character is used to form the 56-bit DES key.
The setting is a 2-character array of the ASCII-encoded
salt. Thus only
12 bits of salt are used. count is set to 25.
DES Algorithm [Toc] [Back]
The salt introduces disorder in the DES algorithm in one of
4096 possible ways (i.e., with 24 or 12 bits: if bit i of
the salt is
set, then bits i and i+24 are swapped in the DES E-box output).
The DES key is used to encrypt a 64-bit constant using count
of DES. The value returned is a null-terminated string, 20
or 13 bytes
(plus null) in length, consisting of the setting followed by
The functions encrypt(), setkey(), des_setkey(), and
access to the DES algorithm itself. setkey() is passed a
of binary values (numeric 0 or 1). A 56-bit key is extracted from this
array by dividing the array into groups of 8, and ignoring
the last bit
in each group. That bit is reserved for a byte parity check
by DES, but
is ignored by these functions.
The block argument to encrypt() is also a 64-byte array of
If the value of flag is 0, block is encrypted otherwise it
The result is returned in the original array block after using the key
specified by setkey() to process it.
The argument to des_setkey() is a character array of length
8. The least
significant bit (the parity bit) in each character is ignored, and the
remaining bits are concatenated to form a 56-bit key. The
des_cipher() encrypts (or decrypts if count is negative) the
stored in the 8 characters at in using abs(3) of count iterations of DES
and stores the 64-bit result in the 8 characters at out
(which may be the
same as in). The salt specifies perturbations to the DES Ebox output as
The function crypt() returns a pointer to the encrypted value on success,
and NULL on failure. The functions setkey(), encrypt(),
and des_cipher() return 0 on success and 1 on failure.
The crypt(), setkey(), and des_setkey() functions all manipulate the same
login(1), passwd(1), blowfish(3), getpass(3), md5(3), passwd(5)
A rotor-based crypt() function appeared in Version 3 AT&T
UNIX. The current
style crypt() first appeared in Version 7 AT&T UNIX.
This library (FreeSec 1.0) was developed outside the United
America as an unencumbered replacement for the U.S.-only
library. Programs linked against the crypt() interface
may be exported
from the U.S.A. only if they use crypt() solely for
purposes and avoid use of the other programmer interfaces
Special care has been taken in the library so that programs
use the crypt() interface do not pull in the other components.
David Burren <email@example.com>
The crypt() function returns a pointer to static data, and
calls to crypt() will modify the same object.
OpenBSD 3.6 March 9, 1994
[ Back ]