NAME

       encrypt, setkey, encrypt_r, setkey_r - encrypt 64-bit messages

SYNOPSIS

       #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  reentrant  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 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, errno is unchanged.

       ENOSYS The  function  is  not  provided.   (For  example  because  of  former  USA  export
              restrictions.)

VERSIONS

       Because  they  employ the DES block cipher, which is no longer considered secure, crypt(),
       crypt_r(), setkey(), and setkey_r() were  removed  in  glibc  2.28.   Applications  should
       switch to a modern cryptography library, such as libgcrypt.

ATTRIBUTES

       For an explanation of the terms used in this section, see attributes(7).

       ┌──────────────────────────────────────────────────┬───────────────┬──────────────────────┐
       │Interface                                         │ Attribute     │ Value                │
       ├──────────────────────────────────────────────────┼───────────────┼──────────────────────┤
       │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

   Availability in glibc
       See crypt(3).

   Features in glibc
       In glibc 2.2, these functions use the DES algorithm.

EXAMPLES

       #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];

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

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

SEE ALSO

       cbc_crypt(3), crypt(3), ecb_crypt(3),

COLOPHON

       This  page  is  part of release 5.13 of the Linux man-pages project.  A description of the
       project, information about reporting bugs, and the latest version of  this  page,  can  be
       found at https://www.kernel.org/doc/man-pages/.

                                            2021-03-22                                 ENCRYPT(3)