
des(3) OpenSSL 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_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);
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);
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)). If the PRNG could not generate a secure key, 0 is returned.
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() works like DES_set_key_checked() if the DES_check_key flag is nonzero, oth
erwise 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() 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 probabil
ity 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, previ
ously 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 encryp
tion 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 argu
ment, 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 pad
ding 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_cbc_cksum() produces an 8 byte checksum based on the input stream (via CBC encryp
tion). 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_Diges
tInit(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 ran
dom 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 inter
nal 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 peo
ple will be using a multiple of 8 and because once you get into pulling bytes input bytes
apart things get ugly!
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().
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
In OpenSSL 0.9.7, all des_ functions were renamed to DES_ to avoid clashes with older ver
sions of libdes. Compatibility des_ functions are provided for a short while, as well as
crypt(). Declarations for these are in <openssl/des_old.h>. There is no DES_ variant for
des_random_seed(). This will happen to other functions as well if they are deemed redun
dant (des_random_seed() just calls RAND_seed() and is present for backward compatibility
only), buggy or already scheduled for removal.
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() and des_string_to_key() are avail
able 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).
0.9.7a 20011025 des(3) 
