encrypt(3) -- Linux man page



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


#include <unistd.h>

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

#include <stdlib.h>

void setkey(const char *key);

#define _GNU_SOURCE
#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.  


These functions encrypt and decrypt 64-bit messages. The setkey() function sets the key used by encrypt(). The key parameter 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 parameter 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 int current_saltbits;
      int  direction, initialized;
Before calling setkey_r() set data->initialized to zero.  


These functions do not return any value.  


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


You need to link with libcrypt to compile this example with glibc2.2. To do useful work the key[] and txt[] array must be filled with a useful bit pattern. Note that the <crypt.h> header unconditionally gives the prototypes for setkey() and encrypt().

#include <crypt.h>

main() {
  char key[64];      /* bit pattern for key */
  char txt[64];      /* bit pattern for messages */
  encrypt(txt, 0);   /* encode */
  encrypt(txt, 1);   /* decode */


In glibc2.2 these functions use the DES algorithm.  


The functions encrypt() and setkey() conform to SVID, SUSv2, and POSIX 1003.1-2001. The functions encrypt_r() and setkey_r() are GNU extensions.  


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