des_set_key_schedule, des_key_sched, des_ecb_encrypt, des_3ecb_encrypt,
des_cbc_encrypt, des_3cbc_encrypt, des_pcbc_encrypt, des_cfb_encrypt,
des_ofb_encrypt, des_cbc_cksum, des_quad_cksum, des_enc_read,
des_enc_write, des_set_odd_parity, des_is_weak_key, crypt - (non USA)
DES encryption
SYNOPSIS
#include <des.h>
int des_read_password(key,prompt,verify)
des_cblock *key;
char *prompt;
int verify;
int des_read_2password(key1,key2,prompt,verify)
des_cblock *key1,*key2;
char *prompt;
int verify;
int des_string_to_key(str,key)
char *str;
des_cblock *key;
int des_string_to_2keys(str,key1,key2)
char *str;
des_cblock *key1,*key2;
int des_read_pw_string(buf,length,prompt,verify)
char *buf;
int length;
char *prompt;
int verify;
int des_random_key(key)
des_cblock *key;
int des_set_key_schedule(key,schedule)
des_cblock *key;
des_key_schedule schedule;
int des_key_sched(key,schedule)
des_cblock *key;
des_key_schedule schedule;
int des_ecb_encrypt(input,output,schedule,encrypt)
des_cblock *input;
des_cblock *output;
des_key_schedule schedule;
int encrypt;
int des_3ecb_encrypt(input,output,ks1,ks2,encrypt)
des_cblock *input;
des_cblock *output;
long length;
des_key_schedule sk1;
des_key_schedule sk2;
des_cblock *ivec1;
des_cblock *ivec2;
int encrypt;
int des_pcbc_encrypt(input,output,length,schedule,ivec,encrypt)
des_cblock *input;
des_cblock *output;
long length;
des_key_schedule schedule;
des_cblock *ivec;
int encrypt;
int des_cfb_encrypt(input,output,numbits,length,schedule,ivec,encrypt)
unsigned char *input;
unsigned char *output;
int numbits;
long length;
des_key_schedule schedule;
des_cblock *ivec;
int encrypt;
int des_ofb_encrypt(input,output,numbits,length,schedule,ivec)
unsigned char *input,*output;
int numbits;
long length;
des_key_schedule schedule;
des_cblock *ivec;
unsigned long des_cbc_cksum(input,output,length,schedule,ivec)
des_cblock *input;
des_cblock *output;
long length;
des_key_schedule schedule;
des_cblock *ivec;
unsigned long des_quad_cksum(input,output,length,out_count,seed)
des_cblock *input;
des_cblock *output;
long length;
int out_count;
des_cblock *seed;
int des_check_key;
int des_enc_read(fd,buf,len,sched,iv)
int fd;
char *buf;
int len;
int des_is_weak_key(key)
des_cblock *key;
char *crypt(passwd,salt)
char *passwd;
char *salt;
DESCRIPTION
This library contains a fast implementation of the DES encryption algo-
rithm.
There are two phases to the use of DES encryption. The first is the
generation of a des_key_schedule from a key, the second is the actual
encryption. A des key is of type des_cblock. This type is made from 8
characters with odd parity. The least significant bit in the character
is the parity bit. The key schedule is an expanded form of the key; it
is used to speed the encryption process.
des_read_password writes the string specified by prompt to the standard
output, turns off echo and reads an input string from standard input
until terminated with a newline. If verify is non-zero, it prompts and
reads the input again and verifies that both entered passwords are the
same. The entered string is converted into a des key by using the
des_string_to_key routine. The new key is placed in the des_cblock
that was passed (by reference) to the routine. If there were no
errors, des_read_password returns 0, -1 is returned if there was a ter-
minal error and 1 is returned for any other error.
des_read_2password operates in the same way as des_read_password except
that it generates 2 keys by using the des_string_to_2key function.
des_read_pw_string is called by des_read_password to read and verify a
string from a terminal device. The string is returned in buf. The
size of buf is passed to the routine via the length parameter.
des_string_to_key converts a string into a valid des key.
des_string_to_2key converts a string into 2 valid des keys. This rou-
tine is best suited for used to generate keys for use with
des_3ecb_encrypt.
des_random_key returns a random key that is made of a combination of
process id, time and an increasing counter.
Before a des key can be used it is converted into a des_key_schedule
via the des_set_key_schedule routine. If the des_check_key flag is
non-zero, des_set_key_schedule will check that the key passed is of odd
parity and is not a week or semi-weak key. If the parity is wrong,
then -1 is returned. If the key is a weak key, then -2 is returned.
If an error is returned, the key schedule is not generated.
(now cleartext). Input and output may overlap. No meaningful value is
returned.
des_3ecb_encrypt encrypts/decrypts the input block by using triple ecb
DES encryption. This involves encrypting the input with ks1, decryp-
tion with the key schedule ks2, and then encryption with the first
again. This routine greatly reduces the chances of brute force break-
ing of DES and has the advantage of if ks1 and ks2 are the same, it is
equivalent to just encryption using ecb mode and ks1 as the key.
des_cbc_encrypt encrypts/decrypts using the cipher-block-chaining mode
of DES. If the encrypt argument is non-zero, the routine cipher-block-
chain encrypts the cleartext data pointed to by the input argument into
the ciphertext pointed to by the output argument, using the key sched-
ule provided by the schedule argument, and initialisation vector pro-
vided by the ivec argument. If the length argument is not an integral
multiple of eight bytes, the last block is copied to a temporary area
and zero filled. The output is always an integral multiple of eight
bytes. To make multiple cbc encrypt calls on a large amount of data
appear to be one des_cbc_encrypt call, the ivec of subsequent calls
should be the last 8 bytes of the output.
des_3cbc_encrypt encrypts/decrypts the input block by using triple cbc
DES encryption. This involves encrypting the input with key schedule
ks1, decryption with the key schedule ks2, and then encryption with the
first again. 2 initialisation vectors are required, ivec1 and ivec2.
Unlike des_cbc_encrypt, these initialisation vectors are modified by
the subroutine. This routine greatly reduces the chances of brute
force breaking of DES and has the advantage of if ks1 and ks2 are the
same, it is equivalent to just encryption using cbc mode and ks1 as the
key.
des_pcbc_encrypt encrypt/decrypts using a modified block chaining mode.
It provides better error propagation characteristics than cbc encryp-
tion.
des_cfb_encrypt encrypt/decrypts using cipher feedback mode. This
method takes an array of characters as input and outputs and array of
characters. It does not require any padding to 8 character groups.
Note: the ivec variable is changed and the new changed value needs to
be passed to the next call to this function. Since this function runs
a complete DES ecb encryption per numbits, this function is only sug-
gested for use when sending small numbers of characters.
des_ofb_encrypt encrypt using output feedback mode. This method takes
an array of characters as input and outputs and array of characters.
It does not require any padding to 8 character groups. Note: the ivec
variable is changed and the new changed value needs to be passed to the
next call to this function. Since this function runs a complete DES
ecb encryption per numbits, this function is only suggested for use
when sending small numbers of characters.
lows, padded with random data out to a multiple of 8 bytes.
des_enc_read is used to read len bytes from file descriptor fd into
buffer buf. The data being read from fd is assumed to have come from
des_enc_write and is decrypted using sched for the key schedule and iv
for the initial vector. The des_enc_read/des_enc_write pair can be
used to read/write to files, pipes and sockets. I have used them in
implementing a version of rlogin in which all data is encrypted.
des_rw_mode is used to specify the encryption mode to use with
des_enc_read and des_end_write. If set to DES_PCBC_MODE (the default),
des_pcbc_encrypt is used. If set to DES_CBC_MODE des_cbc_encrypt is
used. These two routines and the variable are not part of the normal
MIT library.
des_set_odd_parity sets the parity of the passed key to odd. This rou-
tine is not part of the standard MIT library.
des_is_weak_key returns 1 is the passed key is a weak key (pick again
:-), 0 if it is ok. This routine is not part of the standard MIT
library.
crypt is a replacement for the normal system crypt. It is much faster
than the system crypt.
FILES
/usr/include/des.h
/usr/lib/libdes.a
The encryption routines have been tested on 16bit, 32bit and 64bit
machines of various endian and even works under VMS.
BUGS
If you think this manual is sparse, read the des_crypt(3) manual from
the MIT kerberos (or bones outside of the USA) distribution.
des_cfb_encrypt and des_ofb_encrypt operates on input of 8 bits. What
this means is that if you set numbits to 12, and length to 2, the first
12 bits will come from the 1st input byte and the low half of the sec-
ond input byte. The second 12 bits will have the low 8 bits taken from
the 3rd input byte and the top 4 bits taken from the 4th input byte.
The same holds for output. This function has been implemented this way
because most people will be using a multiple of 8 and because once you
get into pulling bytes input bytes apart things get ugly!
des_read_pw_string is the most machine/OS dependent function and nor-
mally generates the most problems when porting this code.
des_string_to_key is probably different from the MIT version since
there are lots of fun ways to implement one-way encryption of a text
Eric Young (eay@mincom.oz.au or eay@psych.psy.uq.oz.au)
DES_CRYPT(3)
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