encrypt

       #define _XOPEN_SOURCE       /* See feature_test_macros(7) */
       #include <unistd.h>

       void encrypt(char block[64], int edflag);

       #define _XOPEN_SOURCE       /* See feature_test_macros(7) */
       #include <stdlib.h>

       void setkey(const char *key);

       #define _GNU_SOURCE         /* See feature_test_macros(7) */
       #include <crypt.h>

       void setkey_r(const char *key, struct crypt_data *data);
       void encrypt_r(char *block, int edflag, struct crypt_data *data);

       Each of these requires linking with -lcrypt.

DESCRIPTION
       These  functions  encrypt  and  decrypt  64-bit messages.  The setkey()
       function sets the key used by encrypt().  The key argument used here is
       an  array  of  64 bytes, each of which has numerical value 1 or 0.  The
       bytes key[n] where n=8*i-1 are  ignored,  so  that  the  effective  key
       length is 56 bits.

       The  encrypt()  function modifies the passed buffer, encoding if edflag
       is 0, and decoding if 1 is being passed.  Like the key  argument,  also
       block  is  a  bit  vector  representation  of  the actual value that is
       encoded.  The result is returned in that same vector.

       These two functions are not reentrant, that is, the key data is kept in
       static storage.  The functions setkey_r() and encrypt_r() are the reen-
       trant versions.  They use the following structure to hold the key data:

           struct crypt_data {
               char     keysched[16 * 8];
               char     sb0[32768];
               char     sb1[32768];
               char     sb2[32768];
               char     sb3[32768];
               char     crypt_3_buf[14];
               char     current_salt[2];
               long int current_saltbits;
               int      direction;
               int      initialized;
           };

       Before calling setkey_r() set data->initialized to zero.

RETURN VALUE
       These functions do not return any value.

ERRORS
       Set errno to zero before calling the above functions.  On  success,  it
       |encrypt(), setkey()     | Thread safety | MT-Unsafe race:crypt |
       +------------------------+---------------+----------------------+
       |encrypt_r(), setkey_r() | Thread safety | MT-Safe              |
       +------------------------+---------------+----------------------+
CONFORMING TO
       encrypt(), setkey(): POSIX.1-2001, POSIX.1-2008, SUS, SVr4.

       The functions encrypt_r() and setkey_r() are GNU extensions.

NOTES
       In glibc 2.2, these functions use the DES algorithm.

EXAMPLE
       #define _XOPEN_SOURCE
       #include <stdio.h>
       #include <stdlib.h>
       #include <unistd.h>
       #include <crypt.h>

       int
       main(void)
       {
           char key[64];
           char orig[9] = "eggplant";
           char buf[64];
           char txt[9];
           int i, j;

           for (i = 0; i < 64; i++) {
               key[i] = rand() & 1;
           }

           for (i = 0; i < 8; i++) {
               for (j = 0; j < 8; j++) {
                   buf[i * 8 + j] = orig[i] >> j & 1;
               }
               setkey(key);
           }
           printf("Before encrypting: %s\n", orig);

           encrypt(buf, 0);
           for (i = 0; i < 8; i++) {
               for (j = 0, txt[i] = '\0'; j < 8; j++) {
                   txt[i] |= buf[i * 8 + j] << j;
               }
               txt[8] = '\0';
           }
           printf("After encrypting:  %s\n", txt);

           encrypt(buf, 1);
           for (i = 0; i < 8; i++) {
               for (j = 0, txt[i] = '\0'; j < 8; j++) {
                   txt[i] |= buf[i * 8 + j] << j;
               }

       latest     version     of     this    page,    can    be    found    at
       http://www.kernel.org/doc/man-pages/.

                                  2015-08-08                        ENCRYPT(3)
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