encrypt(3) — Linux manual page


ENCRYPT(3)              Linux Programmer's Manual             ENCRYPT(3)

NAME         top

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

SYNOPSIS         top

       #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         top

       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

       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         top

       These functions do not return any value.

ERRORS         top

       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         top

       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         top

       For an explanation of the terms used in this section, see

       │Interface                Attribute     Value                │
       │encrypt(), setkey()      │ Thread safety │ MT-Unsafe race:crypt │
       │encrypt_r(), setkey_r()  │ Thread safety │ MT-Safe              │

CONFORMING TO         top

       encrypt(), setkey(): POSIX.1-2001, POSIX.1-2008, SUS, SVr4.

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

NOTES         top

   Availability in glibc
       See crypt(3).

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

EXAMPLES         top

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

           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;
           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);

SEE ALSO         top

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

COLOPHON         top

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                               2021-03-22                     ENCRYPT(3)

Pages that refer to this page: crypt(3)