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des(3)
NAME
des, des_random_key, des_set_key, des_set_key_checked,
des_set_key_unchecked, des_set_odd_parity, 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_string_to_2keys, des_fcrypt, 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,
nsigned char *output,
u,
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 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.
The des_random_key() generates a random key. The PRNG must be seeded prior
to using this function (see rand_ssl(3); for backward compatibility the
des_random_seed() function 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() functions.
The des_set_key_checked() function will check that the key passed is of odd
parity and is not a weak 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.
The des_set_key() function (called des_key_sched() in the MIT library)
works like des_set_key_checked() if the des_check_key flag is non-zero;
otherwise, it works like des_set_key_unchecked(). These functions are
available for compatibility; we recommend you use a function that does not
depend on a global variable.
The des_set_odd_parity() function (called des_fixup_key_parity() in the MIT
library) sets the parity of the passed key to odd.
The des_is_weak_key() function 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.
The following routines mostly operate on an input and output stream of
des_cblock:
· The des_ecb_encrypt() function is the basic DES encryption routine
that encrypts or decrypts a single 8-byte 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 non-zero (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. The
des_ecb_encrypt() function does not return a value.
· The des_ecb3_encrypt() function encrypts and decrypts the input block
by using three-key Triple-DES 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 if ks1,
ks2 and ks3 are the same. It is equivalent to encryption using ECB
mode and ks1 as the key.
· The des_ecb2_encrypt() macro is provided to perform two-key Triple-DES
encryption by using ks1 for the final encryption.
· The des_ncbc_encrypt() function encrypts and decrypts using the
cipher-block-chaining (CBC) 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 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.
· The des_xcbc_encrypt() function is RSA's DESX mode of DES. It uses
inw and outw to whiten the encryption. The inw and outw are secret
(unlike the iv) and are part of the key. So the key is sort of 24
bytes. This is much better than CBC DES.
· The des_ede3_cbc_encrypt() function 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 two-key Triple-DES by
reusing ks1 for the final encryption. C=E(ks1,D(ks2,E(ks1,M))). This
form of Triple-DES is used by the RSAREF library.
· The des_pcbc_encrypt() function encrypts and decrypts using the
propagating cipher block chaining mode used by Kerberos v4. Its
parameters are the same as des_ncbc_encrypt().
· The des_cfb_encrypt() function encrypts and 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. 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.
· The des_cfb64_encrypt() function implements CFB mode of DES with
64-bit feedback. This is useful 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. The num shows where you are through ivec.
· The des_ede3_cfb64_encrypt() and des_ede2_cfb64_encrypt() functions
are the same as the des_cfb64_encrypt() function except that Triple-
DES is used.
· The des_ofb_encrypt() function 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. 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, we recommend using
this function only when sending small numbers of characters.
· The des_ofb64_encrypt() function is the same as the
des_cfb64_encrypt() function using Output Feed Back mode.
· The des_ede3_ofb64_encrypt() and des_ede2_ofb64_encrypt() functions
are the same as des_ofb64_encrypt() using Triple-DES.
The following functions are included in the DES library for compatibility
with the MIT Kerberos library. The des_read_pw_string() function is also
available under the name EVP_read_pw_string().
· The des_read_pw_string() function 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. 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.
· The des_read_password() function does the same and converts the
password to a DES key by calling des_string_to_key(); the
des_read_2password() function operates in the same way as
des_read_password() except that it generates two keys by using the
des_string_to_2key() function. The des_string_to_key() function is
available for backward compatibility with the MIT library. New
applications should use a cryptographic hash function. The same
applies for the des_string_to_2key() function.
· The des_cbc_cksum() function 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() etc. instead.
· The des_quad_cksum() function 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 DES-based transformations:
· The des_fcrypt() function is a fast version of the Unix crypt()
function. This version takes only a small amount of space relative to
other fast crypt() implementations. This is different from 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.
· The des_crypt() function 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 non-thread safe
semantics of crypt().
· The des_enc_write() function 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.
· The des_enc_read() function 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.
Note
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. We do not recommend using
these functions unless you are sure you know what you do. They
cannot handle non-blocking sockets. The des_enc_read() function uses
an internal state and cannot be used on multiple files.
· The des_rw_mode specifies the encryption mode to use with the
des_enc_read() and des_end_write() functions. If it is set to
DES_PCBC_MODE (the default), des_pcbc_encrypt is used. If it is set
to DES_CBC_MODE, des_cbc_encrypt is used.
NOTES
Single-key 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 higher-level encryption functions.
RESTRICTIONS
The des_3cbc_encrypt() function is flawed and must not be used in
applications.
The des_cbc_encrypt() function does not modify ivec; use the
des_ncbc_encrypt() function instead.
The des_cfb_encrypt() and des_ofb_encrypt() functions operate 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 first 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 fourth input
byte. The same holds for output. This function has been implemented this
way because most people will be using a multiple of 8.
The des_read_pw_string() function is the most machine/OS dependent function
and normally generates the most problems when porting this code.
The des library was written to be source code compatible with the MIT
Kerberos library. It conforms to ANSI X3.106.
HISTORY
The 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() functions
are available in the MIT Kerberos library; the des_check_key_parity(),
des_fixup_key_parity(), and des_is_weak_key() functions are available in
newer versions of that library.
The des_set_key_checked() and des_set_key_unchecked() functions were added
in OpenSSL 0.9.5.
The des_generate_random_block(), des_init_random_number_generator(),
des_new_random_key(), des_set_random_generator_seed(),
des_set_sequence_number(), and des_rand_data() functions are used in newer
versions of Kerberos but are not implemented here.
The des_random_key() function generated cryptographically weak random data
in SSLeay and in OpenSSL prior version 0.9.5, as well as in the original
MIT library.
Author is Eric Young (eay@cryptsoft.com). Modified for the OpenSSL project
(http://www.openssl.org).
SEE ALSO
Functions: crypt(3), des_crypt(3), evp(3), rand_ssl(3)
Files: des_modes(7)
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