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encrypt(3) — Linux manual page

NAME \|LIBRARY \|SYNOPSIS \|DESCRIPTION \|RETURN VALUE \|ERRORS \|ATTRIBUTES \|STANDARDS \|HISTORY \|EXAMPLES \|SEE ALSO \|COLOPHON

encrypt(3)               Library Functions Manualencrypt(3)

NAME top

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

LIBRARY top

       Password hashing library (libcrypt,-lcrypt)

SYNOPSIS top

#define _XOPEN_SOURCE/* See feature_test_macros(7) */#include <unistd.h>[[deprecated]] void encrypt(charblock[64], intedflag);#define _XOPEN_SOURCE/* See feature_test_macros(7) */#include <stdlib.h>[[deprecated]] void setkey(const char *key);#define _GNU_SOURCE/* See feature_test_macros(7) */#include <crypt.h>[[deprecated]] void setkey_r(const char *key, struct crypt_data *data);[[deprecated]] void encrypt_r(char *block, intedflag,struct crypt_data *data);

DESCRIPTION top

       These functions encrypt and decrypt 64-bit messages.  Thesetkey()       function sets the key used byencrypt().  Thekey 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.       Theencrypt() function modifies the passed buffer, encoding ifedflag is 0, and decoding if 1 is being passed.  Like thekey       argument, alsoblock 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 functionssetkey_r() andencrypt_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 callingsetkey_r() setdata->initialized to zero.

RETURN VALUE top

       These functions do not return any value.

ERRORS top

       Seterrno to zero before calling the above functions.  On success,errno is unchanged.ENOSYSThe function is not provided.  (For example because of              former USA export restrictions.)

ATTRIBUTES top

       For an explanation of the terms used in this section, seeattributes(7).       ┌─────────────────────────┬───────────────┬──────────────────────┐       │Interface│Attribute│Value│       ├─────────────────────────┼───────────────┼──────────────────────┤       │encrypt(),setkey()     │ Thread safety │ MT-Unsafe race:crypt │       ├─────────────────────────┼───────────────┼──────────────────────┤       │encrypt_r(),setkey_r() │ Thread safety │ MT-Safe              │       └─────────────────────────┴───────────────┴──────────────────────┘

STANDARDS top

encrypt()setkey()              POSIX.1-2008.encrypt_r()setkey_r()              None.

HISTORY top

       Removed in glibc 2.28.       Because they employ the DES block cipher, which is no longer       considered secure, these functions were removed from glibc.       Applications should switch to a modern cryptography library, such       aslibgcrypt.encrypt()setkey()              POSIX.1-2001, SUS, SVr4.Availability in glibc       Seecrypt(3).Features in glibc       In glibc 2.2, these functions use the DES algorithm.

EXAMPLES top

       #define _XOPEN_SOURCE       #include <crypt.h>       #include <stdio.h>       #include <stdlib.h>       #include <unistd.h>       int       main(void)       {           char key[64];           char orig[9] = "eggplant";           char buf[64];           char txt[9];           for (size_t i = 0; i < 64; i++) {               key[i] = rand() & 1;           }           for (size_t i = 0; i < 8; i++) {               for (size_t 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 (size_t i = 0; i < 8; i++) {               for (size_t 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 (size_t i = 0; i < 8; i++) {               for (size_t 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);       }

COLOPHON top

       This page is part of theman-pages (Linux kernel and C library       user-space interface documentation) project.  Information about       the project can be found at        ⟨https://www.kernel.org/doc/man-pages/⟩.  If you have a bug report       for this manual page, see       ⟨https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩.       This page was obtained from the tarball man-pages-6.15.tar.gz       fetched from       ⟨https://mirrors.edge.kernel.org/pub/linux/docs/man-pages/⟩ on       2025-08-11.  If you discover any rendering problems in this HTML       version of the page, or you believe there is a better or more up-       to-date source for the page, or you have corrections or       improvements to the information in this COLOPHON (which isnot       part of the original manual page), send a mail to       man-pages@man7.orgLinux man-pages 6.15            2025-05-17encrypt(3)

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