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, it 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

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                                                   2020-11-01                                         ENCRYPT(3)