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DES_ofb_encrypt(3)




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);

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des(3)                       OpenSSL                       des(3)

      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);

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des(3)                       OpenSSL                       des(3)

      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 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.

     DES_set_key() works like DES_set_key_checked() if the
     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() sets the parity of the passed key to
     odd.

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des(3)                       OpenSSL                       des(3)

     DES_is_weak_key() returns 1 if the passed key is a weak key,
     0 if it is ok.

     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 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.
     DES_ecb_encrypt() does not return a value.

     DES_ecb3_encrypt() encrypts/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 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 two-key
     Triple-DES encryption by using ks1 for the final encryption.

     DES_ncbc_encrypt() encrypts/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.

     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 an

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des(3)                       OpenSSL                       des(3)

     "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.

     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 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 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_cbc_cksum() produces an 8 byte checksum based on the
     input stream (via CBC encryption).  The last 4 bytes of the

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des(3)                       OpenSSL                       des(3)

     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 DES-based 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 non-thread 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 non-blocking
     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

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des(3)                       OpenSSL                       des(3)

     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.


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_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 versions 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
     redundant (des_random_seed() just calls RAND_seed() and is
     present for backward compatibility only), buggy or already
     scheduled for removal.

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des(3)                       OpenSSL                       des(3)

     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 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).

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