
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 nonNULL, 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 (eay@cryptsoft.com). Modified for the OpenSSL project (http://www.openssl.org).
0.9.6j 20090720 des(3) 
