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libdes manpage.

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This may still contain a few errors from the old documentation,
but most of it should make sense.
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Ulf Möller 2000-03-19 02:09:37 +00:00
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crypto/des/des_crypt.pod
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=pod
=head1 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_ecb3_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
=head1 SYNOPSIS
#include <des.h>
int des_read_password(des_cblock *key, char *prompt, int verify);
int des_read_2password(des_cblock *key1, des_cblock *key2, char *prompt,
int verify);
int des_string_to_key(char *str, des_cblock *key);
int des_string_to_2keys(char *str, des_cblock *key1, des_cblock *key2);
int des_read_pw_string(char *buf, int length, char *prompt, int verify);
int des_random_key(des_cblock *key);
int des_set_key(des_cblock *key, des_key_schedule schedule);
int des_key_sched(des_cblock *key, des_key_schedule schedule);
int des_ecb_encrypt(des_cblock *input, des_cblock *output,
des_key_schedule schedule, int encrypt);
int des_ecb3_encrypt(des_cblock *input, des_cblock *output,
des_key_schedule ks1, des_key_schedule ks2, int encrypt);
int des_cbc_encrypt(des_cblock *input, des_cblock *output,
long length, des_key_schedule schedule, des_cblock *ivec,
int encrypt);
int des_3cbc_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);
int des_pcbc_encrypt(des_cblock *input, des_cblock *output,
long length, des_key_schedule schedule, des_cblock *ivec,
int encrypt);
int des_cfb_encrypt(unsigned char *input, unsigned char *output,
int numbits, long length, des_key_schedule schedule,
des_cblock *ivec, int encrypt);
int des_ofb_encrypt(unsigned char *input, unsigned char *output,
int numbits, long length, des_key_schedule schedule,
des_cblock *ivec);
unsigned long des_cbc_cksum(des_cblock *input, des_cblock *output,
long length, des_key_schedule schedule, des_cblock *ivec);
unsigned long des_quad_cksum(des_cblock *input, des_cblock *output,
long length, int out_count, des_cblock *seed);
int des_check_key;
int des_enc_read(int fd, char *buf, int len, des_key_schedule sched,
des_cblock *iv);
int des_enc_write(int fd, char *buf, int len, des_key_schedule sched,
des_cblock *iv);
extern int des_rw_mode;
void des_set_odd_parity(des_cblock *key);
int des_is_weak_key(des_cblock *key);
char *crypt(char *passwd, char *salt);
=head1 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 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.
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.
I<des_read_2password> operates in the same way as I<des_read_password>
except that it generates two keys by using the I<des_string_to_2key>
function.
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.
I<des_string_to_key> converts a string into a valid des key.
I<des_string_to_2key> converts a string into two valid des keys. This
routine is best suited for used to generate keys for use with
I<des_ecb3_encrypt>.
I<des_random_key> returns a random key that is made of a combination
of process id, time and an increasing counter.
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.
I<des_key_sched> is another name for the I<des_set_key> function.
The following routines mostly operate on an input and output stream of
I<des_cblock>'s.
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.
I<des_ecb3_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.
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 initialization 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.
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. Two initialization vectors are
required, I<ivec1> and I<ivec2>. Unlike I<des_cbc_encrypt>, these
initialization 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.
I<des_pcbc_encrypt> encrypt/decrypts using a modified block chaining
mode. It provides better error propagation characteristics than cbc
encryption.
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.
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.
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>.
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>.
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.
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.
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.
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.
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.
I<crypt> is a replacement for the normal system crypt. It is much
faster than the system crypt.
=head1 BUGS
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!
I<des_read_pw_string> is the most machine/OS dependent function and
normally generates the most problems when porting this code.
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.
=head1 AUTHOR
Eric Young (eay@cryptsoft.com)
=cut

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=pod
=head1 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
=head1 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);
=head1 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 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
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 L<rand(3)|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 dependant I<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 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.
des_set_key() (called des_key_sched() in the MIT library) works like
des_set_key_checked() if the I<des_check_key> flag is non-zero,
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 I<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
I<des_cblock>s.
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>
(ECB) 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. des_ecb_encrypt() does not return a value.
des_ecb3_encrypt() encrypts/decrypts the I<input> block by using
three-key Triple-DES encryption in ECB mode. This involves encrypting
the input with I<ks1>, decrypting with the key schedule I<ks2>, and
then encrypting with I<ks3>. This routine greatly reduces the chances
of brute force breaking of DES and has the advantage of if I<ks1>,
I<ks2> and I<ks3> are the same, it is equivalent to just encryption
using ECB mode and I<ks1> as the key.
The macro des_ecb2_encrypt() is provided to perform two-key Triple-DES
encryption by using I<ks1> for the final encryption.
des_ncbc_encrypt() encrypts/decrypts using the I<cipher-block-chaining>
(CBC) 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 initialization 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.
des_xcbc_encrypt() is RSA's DESX mode of DES. It uses I<inw> and
I<outw> to 'whiten' the encryption. I<inw> and I<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<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 I<ks1> for the final encryption. C<C=E(ks1,D(ks2,E(ks1,M)))>.
This form of Triple-DES is used by the RSAREF library.
des_pcbc_encrypt() encrypt/decrypts using the propagating cipher block
chaing 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 I<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 I<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 Triple-DES 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 I<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 Triple-DES.
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 I<prompt> to
standarf output, turns echo off and reads in input string from the
terminal. The string is returned in I<buf>, which must have space for
at least I<length> bytes. If I<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 I<output>. This function is
used by Kerberos v4. Other applications should use
L<EVP_DigestInit(3)|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 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>.
The following are DES-based tranformations:
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 non-thread safe semantics
of crypt(3).
des_enc_write() writes 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.
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 des_enc_write() and is decrypted using I<sched> for
the key schedule and I<iv> for the initial vector.
B<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 non-blocking sockets.
des_enc_read() uses an internal state and thus cannot be used on
multiple files.
I<des_rw_mode> is used to specify the encryption mode to use with
des_enc_read() and 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.
=head1 NOTES
Single-key DES is insecure due to its short key size. ECB mode is
not suitable for most applications; see L<des_modes(7)|des_modes(7)>.
The L<evp(3)|evp(3)> library provides higher-level encryption functions.
=head1 BUGS
des_3cbc_encrypt() is flawed and must not be used in applications.
des_cbc_encrypt() does not modify B<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.
=head1 CONFORMING TO
ANSI X3.106
The B<des> library was written to be source code compatible with
the MIT Kerberos library.
=head1 SEE ALSO
crypt(3), L<des_modes(3)|des_modes(3)>, L<evp(3)|evp(3)>, L<rand(3)|rand(3)>
=head1 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.
=head1 AUTHOR
Eric Young (eay@cryptsoft.com). Modified for the OpenSSL project
(http://www.openssl.org).
=cut