MirBSD manpage: bcrypt(3), bcrypt_gensalt(3), crypt(3), des_cipher(3), des_setkey(3), encrypt(3), md5crypt(3), setkey(3)

CRYPT(3)                   BSD Programmer's Manual                    CRYPT(3)


     crypt, setkey, encrypt, des_setkey, des_cipher - DES encryption


     #include <pwd.h>
     #include <unistd.h>

     char *
     crypt(const char *key, const char *setting);

     setkey(const char *key);

     encrypt(char *block, int flag);

     des_setkey(const char *key);

     des_cipher(const char *in, char *out, int32_t salt, int count);

     char *
     bcrypt_gensalt(u_int8_t log_rounds);

     char *
     bcrypt(const char *key, const char *salt);

     char *
     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 NUL-terminated string, typically a
     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 interpreting
     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

     The key is divided into groups of 8 characters (the last group is null-
     padded) and the low-order 7 bits of each character (56 bits per group)
     are used to form the DES key as follows: the first group of 56 bits be-
     comes the initial DES key. For each additional group, the XOR of the en-
     cryption of the current DES key with itself and the group bits becomes
     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". This allows 24
     bits for both count and salt.

MD5 crypt

     For MD5 crypt the version number, salt and the hashed password are
     separated by the '$' character. The maximum length of a password is lim-
     ited 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

     The Blowfish version of crypt has 128 bits of salt in order to make
     building dictionaries of common passwords space consuming. The initial
     state of the Blowfish cipher is expanded using the salt and the password
     repeating the process a variable number of rounds, which is encoded in
     the password string. The maximum password length is 72. The final Blowf-
     ish 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 con-
     catenation of salt and hashed password are separated by the '$' charac-
     ter. An encoded '8' would specify 256 rounds. A valid Blowfish password
     looks like this:


     The whole Blowfish password string is passed as setting for interpreta-

Traditional crypt

     The first 8 bytes of the key are null-padded, and the low-order 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

     The salt introduces disorder in the DES algorithm in one of 16777216 or
     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 iterations
     of DES. The value returned is a NUL-terminated string, 20 or 13 bytes
     (plus NUL) in length, consisting of the setting followed by the encoded
     64-bit encryption.

     The functions encrypt(), setkey(), des_setkey(), and des_cipher() provide
     access to the DES algorithm itself. setkey() is passed a 64-byte array 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 ig-
     nored by these functions.

     The block argument to encrypt() is also a 64-byte array of binary values.
     If the value of flag is 0, block is encrypted otherwise it is decrypted.
     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 function
     des_cipher() encrypts (or decrypts if count is negative) the 64-bits
     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 E-box output as
     described above.

     The function crypt() returns a pointer to the encrypted value on success,
     and NULL on failure. The functions setkey(), encrypt(), des_setkey(), and
     des_cipher() return 0 on success and 1 on failure.

     The crypt(), setkey(), and des_setkey() functions all manipulate the same
     key space.


     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 States of
     America as an unencumbered replacement for the U.S.-only libcrypt encryp-
     tion library. Programs linked against the crypt() interface may be ex-
     ported from the U.S.A. only if they use crypt() solely for authentication
     purposes and avoid use of the other programmer interfaces listed above.
     Special care has been taken in the library so that programs which only
     use the crypt() interface do not pull in the other components.


     David Burren <davidb@werj.com.au>


     The crypt() function returns a pointer to static data, and subsequent
     calls to crypt() will modify the same object.

MirBSD #10-current              March 9, 1994                                2

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