des(3) libdes des(3)
NAME
des_random_key, des_set_key, des_key_sched, des_set_key_checked,
des_set_key_unchecked, des_set_odd_parity, des_is_weak_key,
des_ecb_encrypt, des_ecb2_encrypt, des_ecb3_encrypt, des_ncbc_encrypt,
des_cfb_encrypt, des_ofb_encrypt, des_pcbc_encrypt, des_cfb64_encrypt,
des_ofb64_encrypt, des_xcbc_encrypt, des_ede2_cbc_encrypt,
des_ede2_cfb64_encrypt, des_ede2_ofb64_encrypt, des_ede3_cbc_encrypt,
des_ede3_cbcm_encrypt, des_ede3_cfb64_encrypt, des_ede3_ofb64_encrypt,
des_read_password, des_read_2passwords, des_read_pw_string,
des_cbc_cksum, des_quad_cksum, des_string_to_key, des_string_to_2keys,
des_fcrypt, des_crypt, des_enc_read, des_enc_write  DES encryption
SYNOPSIS
#include <openssl/des.h>
void des_random_key(des_cblock *ret);
int des_set_key(const_des_cblock *key, des_key_schedule schedule);
int des_key_sched(const_des_cblock *key, des_key_schedule schedule);
int des_set_key_checked(const_des_cblock *key,
des_key_schedule schedule);
void des_set_key_unchecked(const_des_cblock *key,
des_key_schedule schedule);
void des_set_odd_parity(des_cblock *key);
int des_is_weak_key(const_des_cblock *key);
void des_ecb_encrypt(const_des_cblock *input, des_cblock *output,
des_key_schedule ks, int enc);
void des_ecb2_encrypt(const_des_cblock *input, des_cblock *output,
des_key_schedule ks1, des_key_schedule ks2, int enc);
void des_ecb3_encrypt(const_des_cblock *input, des_cblock *output,
des_key_schedule ks1, des_key_schedule ks2,
des_key_schedule ks3, int enc);
void des_ncbc_encrypt(const unsigned char *input, unsigned char *output,
long length, des_key_schedule schedule, des_cblock *ivec,
int enc);
void des_cfb_encrypt(const unsigned char *in, unsigned char *out,
int numbits, long length, des_key_schedule schedule,
des_cblock *ivec, int enc);
void des_ofb_encrypt(const unsigned char *in, unsigned char *out,
int numbits, long length, des_key_schedule schedule,
des_cblock *ivec);
void des_pcbc_encrypt(const unsigned char *input, unsigned char *output,
long length, des_key_schedule schedule, des_cblock *ivec,
int enc);
void des_cfb64_encrypt(const unsigned char *in, unsigned char *out,
long length, des_key_schedule schedule, des_cblock *ivec,
int *num, int enc);
void des_ofb64_encrypt(const unsigned char *in, unsigned char *out,
long length, des_key_schedule schedule, des_cblock *ivec,
int *num);
void des_xcbc_encrypt(const unsigned char *input, unsigned char *output,
long length, des_key_schedule schedule, des_cblock *ivec,
const_des_cblock *inw, const_des_cblock *outw, int enc);
void des_ede2_cbc_encrypt(const unsigned char *input,
unsigned char *output, long length, des_key_schedule ks1,
des_key_schedule ks2, des_cblock *ivec, int enc);
void des_ede2_cfb64_encrypt(const unsigned char *in,
unsigned char *out, long length, des_key_schedule ks1,
des_key_schedule ks2, des_cblock *ivec, int *num, int enc);
void des_ede2_ofb64_encrypt(const unsigned char *in,
unsigned char *out, long length, des_key_schedule ks1,
des_key_schedule ks2, des_cblock *ivec, int *num);
void des_ede3_cbc_encrypt(const unsigned char *input,
unsigned char *output, long length, des_key_schedule ks1,
des_key_schedule ks2, des_key_schedule ks3, des_cblock *ivec,
int enc);
void des_ede3_cbcm_encrypt(const unsigned char *in, unsigned char *out,
long length, des_key_schedule ks1, des_key_schedule ks2,
des_key_schedule ks3, des_cblock *ivec1, des_cblock *ivec2,
int enc);
void des_ede3_cfb64_encrypt(const unsigned char *in, unsigned char *out,
long length, des_key_schedule ks1, des_key_schedule ks2,
des_key_schedule ks3, des_cblock *ivec, int *num, int enc);
void des_ede3_ofb64_encrypt(const unsigned char *in, unsigned char *out,
long length, des_key_schedule ks1,
des_key_schedule ks2, des_key_schedule ks3,
des_cblock *ivec, int *num);
int des_read_password(des_cblock *key, const char *prompt, int verify);
int des_read_2passwords(des_cblock *key1, des_cblock *key2,
const char *prompt, int verify);
int des_read_pw_string(char *buf, int length, const char *prompt,
int verify);
DES_LONG des_cbc_cksum(const unsigned char *input, des_cblock *output,
long length, des_key_schedule schedule,
const_des_cblock *ivec);
DES_LONG des_quad_cksum(const unsigned char *input, des_cblock output[],
long length, int out_count, des_cblock *seed);
void des_string_to_key(const char *str, des_cblock *key);
void des_string_to_2keys(const char *str, des_cblock *key1,
des_cblock *key2);
char *des_fcrypt(const char *buf, const char *salt, char *ret);
char *des_crypt(const char *buf, const char *salt);
char *crypt(const char *buf, const char *salt);
int des_enc_read(int fd, void *buf, int len, des_key_schedule sched,
des_cblock *iv);
int des_enc_write(int fd, const void *buf, int len,
des_key_schedule sched, des_cblock *iv);
DESCRIPTION
This library contains a fast implementation of the DES encryption
algorithm.
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 consists of
8 bytes with odd parity. The least significant bit in each byte is the
parity bit. The key schedule is an expanded form of the key; it is
used to speed the encryption process.
des_random_key() generates a random key. The PRNG must be seeded prior
to using this function (see rand(3); for backward compatibility the
function des_random_seed() is available as well). If the PRNG could
not generate a secure key, 0 is returned. In earlier versions of the
library, des_random_key() did not generate secure keys.
Before a DES key can be used, it must be converted into the
architecture dependent des_key_schedule via the des_set_key_checked()
or des_set_key_unchecked() function.
des_set_key_checked() will check that the key passed is of odd parity
and is not a week or semiweak 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.
des_set_key() (called des_key_sched() in the MIT library) works like
des_set_key_checked() if the des_check_key flag is nonzero, otherwise
like des_set_key_unchecked(). These functions are available for
compatibility; it is recommended to use a function that does not depend
on a global variable.
des_set_odd_parity() (called des_fixup_key_parity() in the MIT library)
sets the parity of the passed key to odd.
des_is_weak_key() returns 1 is the passed key is a weak key, 0 if it is
ok. The probability that a randomly generated key is weak is 1/2^52,
so it is not really worth checking for them.
The following routines mostly operate on an input and output stream of
des_cblocks.
des_ecb_encrypt() is the basic DES encryption routine that encrypts or
decrypts a single 8byte des_cblock in electronic code book (ECB) mode.
It always transforms the input data, pointed to by input, into the
output data, pointed to by the output argument. If the encrypt
argument is nonzero (DES_ENCRYPT), the input (cleartext) is encrypted
in to the output (ciphertext) using the key_schedule specified by the
schedule argument, previously set via des_set_key. If encrypt is zero
(DES_DECRYPT), the input (now ciphertext) is decrypted into the output
(now cleartext). Input and output may overlap. des_ecb_encrypt() does
not return a value.
des_ecb3_encrypt() encrypts/decrypts the input block by using threekey
TripleDES encryption in ECB mode. This involves encrypting the input
with ks1, decrypting with the key schedule ks2, and then encrypting
with ks3. This routine greatly reduces the chances of brute force
breaking of DES and has the advantage of if ks1, ks2 and ks3 are the
same, it is equivalent to just encryption using ECB mode and ks1 as the
key.
The macro des_ecb2_encrypt() is provided to perform twokey TripleDES
encryption by using ks1 for the final encryption.
des_ncbc_encrypt() encrypts/decrypts using the cipherblockchaining
(CBC) mode of DES. If the encrypt argument is nonzero, the routine
cipherblockchain encrypts the cleartext data pointed to by the input
argument into the ciphertext pointed to by the output argument, using
the key schedule provided by the schedule argument, and initialization
vector provided 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.
des_xcbc_encrypt() is RSA's DESX mode of DES. It uses inw and outw to
'whiten' the encryption. inw and outw are secret (unlike the iv) and
are as such, part of the key. So the key is sort of 24 bytes. This is
much better than CBC DES.
des_ede3_cbc_encrypt() implements outer triple CBC DES encryption with
three keys. This means that each DES operation inside the CBC mode is
really an "C=E(ks3,D(ks2,E(ks1,M)))". This mode is used by SSL.
The des_ede2_cbc_encrypt() macro implements twokey TripleDES by
reusing ks1 for the final encryption. "C=E(ks1,D(ks2,E(ks1,M)))".
This form of TripleDES is used by the RSAREF library.
des_pcbc_encrypt() encrypt/decrypts using the propagating cipher block
chaining mode used by Kerberos v4. Its parameters are the same as
des_ncbc_encrypt().
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.
des_cfb64_encrypt() implements CFB mode of DES with 64bit feedback.
Why is this useful you ask? Because this routine will allow you to
encrypt an arbitrary number of bytes, no 8 byte padding. Each call to
this routine will encrypt the input bytes to output and then update
ivec and num. num contains 'how far' we are though ivec. If this does
not make much sense, read more about cfb mode of DES :).
des_ede3_cfb64_encrypt() and des_ede2_cfb64_encrypt() is the same as
des_cfb64_encrypt() except that TripleDES is used.
des_ofb_encrypt() encrypts 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.
des_ofb64_encrypt() is the same as des_cfb64_encrypt() using Output
Feed Back mode.
des_ede3_ofb64_encrypt() and des_ede2_ofb64_encrypt() is the same as
des_ofb64_encrypt(), using TripleDES.
The following functions are included in the DES library for
compatibility with the MIT Kerberos library. des_read_pw_string() is
also available under the name EVP_read_pw_string().
des_read_pw_string() writes the string specified by prompt to standard
output, turns echo off and reads in input string from the terminal.
The string is returned in buf, which must have space for at least
length bytes. If verify is set, the user is asked for the password
twice and unless the two copies match, an error is returned. A return
code of 1 indicates a system error, 1 failure due to use interaction,
and 0 is success.
des_read_password() does the same and converts the password to a DES
key by calling des_string_to_key(); des_read_2password() operates in
the same way as des_read_password() except that it generates two keys
by using the des_string_to_2key() function. des_string_to_key() is
available for backward compatibility with the MIT library. New
applications should use a cryptographic hash function. The same
applies for des_string_to_2key().
des_cbc_cksum() produces an 8 byte checksum based on the input stream
(via CBC encryption). The last 4 bytes of the checksum are returned
and the complete 8 bytes are placed in output. This function is used by
Kerberos v4. Other applications should use EVP_DigestInit(3) etc.
instead.
des_quad_cksum() is a Kerberos v4 function. It returns a 4 byte
checksum from the input bytes. The algorithm can be iterated over the
input, depending on out_count, 1, 2, 3 or 4 times. If output is non
NULL, the 8 bytes generated by each pass are written into output.
The following are DESbased transformations:
des_fcrypt() is a fast version of the Unix crypt(3) function. This
version takes only a small amount of space relative to other fast
crypt() implementations. This is different to the normal crypt in that
the third parameter is the buffer that the return value is written
into. It needs to be at least 14 bytes long. This function is thread
safe, unlike the normal crypt.
des_crypt() is a faster replacement for the normal system crypt().
This function calls des_fcrypt() with a static array passed as the
third parameter. This emulates the normal nonthread safe semantics of
crypt(3).
des_enc_write() writes len bytes to file descriptor fd from buffer buf.
The data is encrypted via pcbc_encrypt (default) using sched for the
key and iv as a starting vector. The actual data send down 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.
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.
Warning: The data format used by des_enc_write() and des_enc_read() has
a cryptographic weakness: When asked to write more than MAXWRITE bytes,
des_enc_write() will split the data into several chunks that are all
encrypted using the same IV. So don't use these functions unless you
are sure you know what you do (in which case you might not want to use
them anyway). They cannot handle nonblocking sockets. des_enc_read()
uses an internal state and thus cannot be used on multiple files.
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.
NOTES
Singlekey DES is insecure due to its short key size. ECB mode is not
suitable for most applications; see des_modes(7).
The evp(3) library provides higherlevel encryption functions.
BUGS
des_3cbc_encrypt() is flawed and must not be used in applications.
des_cbc_encrypt() does not modify ivec; use des_ncbc_encrypt() instead.
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
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!
des_read_pw_string() is the most machine/OS dependent function and
normally generates the most problems when porting this code.
CONFORMING TO
ANSI X3.106
The des library was written to be source code compatible with the MIT
Kerberos library.
SEE ALSO
crypt(3), des_modes(7), evp(3), rand(3)
HISTORY
des_cbc_cksum(), des_cbc_encrypt(), des_ecb_encrypt(),
des_is_weak_key(), des_key_sched(), des_pcbc_encrypt(),
des_quad_cksum(), des_random_key(), des_read_password() and
des_string_to_key() are available in the MIT Kerberos library;
des_check_key_parity(), des_fixup_key_parity() and des_is_weak_key()
are available in newer versions of that library.
des_set_key_checked() and des_set_key_unchecked() were added in OpenSSL
0.9.5.
des_generate_random_block(), des_init_random_number_generator(),
des_new_random_key(), des_set_random_generator_seed() and
des_set_sequence_number() and des_rand_data() are used in newer
versions of Kerberos but are not implemented here.
des_random_key() generated cryptographically weak random data in SSLeay
and in OpenSSL prior version 0.9.5, as well as in the original MIT
library.
AUTHOR
Eric Young (eayATcryptsoft.com). Modified for the OpenSSL project
(http://www.openssl.org).
0.9.6j 20090720 des(3)
