path: root/lib/libdes/des_crypt.3

.\" Copyright (C) 1995-1998 Eric Young (eay@cryptsoft.com)
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.TH DES_CRYPT 3 
.SH NAME
des_read_password, des_read_2password,
des_string_to_key, des_string_to_2key, des_read_pw_string,
des_random_key, des_set_key,
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
.SH SYNOPSIS
.nf
.nj
.ft B
#include <des.h>
.PP
.B int des_read_password(key,prompt,verify)
des_cblock *key;
char *prompt;
int verify;
.PP
.B int des_read_2password(key1,key2,prompt,verify)
des_cblock *key1,*key2;
char *prompt;
int verify;
.PP
.B int des_string_to_key(str,key)
char *str;
des_cblock *key;
.PP
.B int des_string_to_2keys(str,key1,key2)
char *str;
des_cblock *key1,*key2;
.PP
.B int des_read_pw_string(buf,length,prompt,verify)
char *buf;
int length;
char *prompt;
int verify;
.PP
.B int des_random_key(key)
des_cblock *key;
.PP
.B int des_set_key(key,schedule)
des_cblock *key;
des_key_schedule schedule;
.PP
.B int des_key_sched(key,schedule)
des_cblock *key;
des_key_schedule schedule;
.PP
.B int des_ecb_encrypt(input,output,schedule,encrypt)
des_cblock *input;
des_cblock *output;
des_key_schedule schedule;
int encrypt;
.PP
.B int des_3ecb_encrypt(input,output,ks1,ks2,encrypt)
des_cblock *input;
des_cblock *output;
des_key_schedule ks1,ks2;
int encrypt;
.PP
.B int des_cbc_encrypt(input,output,length,schedule,ivec,encrypt)
des_cblock *input;
des_cblock *output;
long length;
des_key_schedule schedule;
des_cblock *ivec;
int encrypt;
.PP
.B int des_3cbc_encrypt(input,output,length,sk1,sk2,ivec1,ivec2,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;
.PP
.B 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;
.PP
.B 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;
.PP
.B 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;
.PP
.B 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;
.PP
.B 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;
.PP
.B int des_check_key;
.PP
.B int des_enc_read(fd,buf,len,sched,iv)
int fd;
char *buf;
int len;
des_key_schedule sched;
des_cblock *iv;
.PP
.B int des_enc_write(fd,buf,len,sched,iv)
int fd;
char *buf;
int len;
des_key_schedule sched;
des_cblock *iv;
.PP
.B extern int des_rw_mode;
.PP
.B void des_set_odd_parity(key)
des_cblock *key;
.PP
.B int des_is_weak_key(key)
des_cblock *key;
.PP
.B char *crypt(passwd,salt)
char *passwd;
char *salt;
.PP
.fi
.SH DESCRIPTION
This library contains a fast implementation of the DES encryption
algorithm.
.PP
There are two phases to the use of DES encryption.
The first is the generation of a
.I des_key_schedule
from a key,
the second is the actual encryption.
A des key is of type
.I 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.
.PP
.I 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
.I des_string_to_key
routine.
The new key is placed in the
.I des_cblock
that was passed (by reference) to the routine.
If there were no errors,
.I des_read_password
returns 0,
-1 is returned if there was a terminal error and 1 is returned for
any other error.
.PP
.I des_read_2password
operates in the same way as
.I des_read_password
except that it generates 2 keys by using the
.I des_string_to_2key
function.
.PP
.I des_read_pw_string
is called by
.I des_read_password
to read and verify a string from a terminal device.
The string is returned in
.I buf.
The size of
.I buf
is passed to the routine via the
.I length
parameter.
.PP
.I des_string_to_key
converts a string into a valid des key.
.PP
.I des_string_to_2key
converts a string into 2 valid des keys.
This routine is best suited for used to generate keys for use with
.I des_3ecb_encrypt.
.PP
.I des_random_key
returns a random key that is made of a combination of process id,
time and an increasing counter.
.PP
Before a des key can be used it is converted into a
.I des_key_schedule
via the
.I des_set_key
routine.
If the
.I des_check_key
flag is non-zero,
.I des_set_key
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.
.PP
.I des_key_sched
is another name for the
.I des_set_key
function.
.PP
The following routines mostly operate on an input and output stream of
.I des_cblock's.
.PP
.I des_ecb_encrypt
is the basic DES encryption routine that encrypts or decrypts a single 8-byte
.I des_cblock
in
.I electronic code book
mode.
It always transforms the input data, pointed to by
.I input,
into the output data,
pointed to by the
.I output
argument.
If the
.I encrypt
argument is non-zero (DES_ENCRYPT),
the
.I input
(cleartext) is encrypted in to the
.I output
(ciphertext) using the key_schedule specified by the
.I schedule
argument,
previously set via
.I des_set_key.
If
.I encrypt
is zero (DES_DECRYPT),
the
.I input
(now ciphertext)
is decrypted into the
.I output
(now cleartext).
Input and output may overlap.
No meaningful value is returned.
.PP
.I des_3ecb_encrypt
encrypts/decrypts the
.I input
block by using triple ecb DES encryption.
This involves encrypting the input with 
.I ks1,
decryption with the key schedule
.I ks2,
and then encryption with the first again.
This routine greatly reduces the chances of brute force breaking of
DES and has the advantage of if
.I ks1
and
.I ks2
are the same, it is equivalent to just encryption using ecb mode and
.I ks1
as the key.
.PP
.I des_cbc_encrypt
encrypts/decrypts using the
.I cipher-block-chaining
mode of DES.
If the
.I encrypt
argument is non-zero,
the routine cipher-block-chain encrypts the cleartext data pointed to by the
.I input
argument into the ciphertext pointed to by the
.I output
argument,
using the key schedule provided by the
.I schedule
argument,
and initialisation vector provided by the
.I ivec
argument.
If the
.I 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 
.I des_cbc_encrypt
call, the
.I ivec
of subsequent calls should be the last 8 bytes of the output.
.PP
.I des_3cbc_encrypt
encrypts/decrypts the
.I input
block by using triple cbc DES encryption.
This involves encrypting the input with key schedule
.I ks1,
decryption with the key schedule
.I ks2,
and then encryption with the first again.
2 initialisation vectors are required,
.I ivec1
and
.I ivec2.
Unlike
.I 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
.I ks1
and
.I ks2
are the same, it is equivalent to just encryption using cbc mode and
.I ks1
as the key.
.PP
.I des_pcbc_encrypt
encrypt/decrypts using a modified block chaining mode.
It provides better error propagation characteristics than cbc
encryption.
.PP
.I 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 suggested for
use when sending small numbers of characters.
.PP
.I 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.
.PP
.I des_cbc_cksum
produces an 8 byte checksum based on the input stream (via cbc encryption).
The last 4 bytes of the checksum is returned and the complete 8 bytes is
placed in
.I output.
.PP
.I des_quad_cksum
returns a 4 byte checksum from the input bytes.
The algorithm can be iterated over the input,
depending on
.I out_count,
1, 2, 3 or 4 times.
If
.I output
is non-NULL,
the 8 bytes generated by each pass are written into
.I output.
.PP
.I des_enc_write
is used to write
.I len
bytes
to file descriptor
.I fd
from buffer
.I buf.
The data is encrypted via
.I pcbc_encrypt
(default) using
.I sched
for the key and
.I iv
as a starting vector.
The actual data send down
.I fd
consists of 4 bytes (in network byte order) containing the length of the
following encrypted data.  The encrypted data then follows, padded with random
data out to a multiple of 8 bytes.
.PP
.I des_enc_read
is used to read
.I len
bytes
from file descriptor
.I fd
into buffer
.I buf.
The data being read from
.I fd
is assumed to have come from
.I des_enc_write
and is decrypted using
.I sched
for the key schedule and
.I iv
for the initial vector.
The
.I 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.
.PP
.I des_rw_mode
is used to specify the encryption mode to use with 
.I des_enc_read
and 
.I des_end_write.
If set to
.I DES_PCBC_MODE
(the default), des_pcbc_encrypt is used.
If set to
.I DES_CBC_MODE
des_cbc_encrypt is used.
These two routines and the variable are not part of the normal MIT library.
.PP
.I des_set_odd_parity
sets the parity of the passed
.I key
to odd.  This routine is not part of the standard MIT library.
.PP
.I 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.
.PP
.I crypt
is a replacement for the normal system crypt.
It is much faster than the system crypt.
.PP
.SH FILES
/usr/include/des.h
.br
/usr/lib/libdes.a
.PP
The encryption routines have been tested on 16bit, 32bit and 64bit
machines of various endian and even works under VMS.
.PP
.SH BUGS
.PP
If you think this manual is sparse,
read the des_crypt(3) manual from the MIT kerberos (or bones outside
of the USA) distribution.
.PP
.I des_cfb_encrypt
and
.I 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 second 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!
.PP
.I des_read_pw_string
is the most machine/OS dependent function and normally generates the
most problems when porting this code.
.PP
.I 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 string.
.PP
The routines are optimised for 32 bit machines and so are not efficient
on IBM PCs.
.PP
NOTE: extensive work has been done on this library since this document
was originally written.  Please try to read des.doc from the libdes
distribution since it is far more up to date and documents more of the
functions.  Libdes is now also being shipped as part of SSLeay, a
general cryptographic library that amonst other things implements
netscapes SSL protocol.  The most recent version can be found in
SSLeay distributions.
.SH AUTHOR
Eric Young (eay@mincom.oz.au or eay@psych.psy.uq.oz.au)