encrypt()

Encrypt or decrypt a string

Synopsis:

#include <unistd.h>

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

Arguments:

block

A 64-character array of binary values to encrypt. The function stores the encrypted value in the same array.

flag

0 if you want to encrypt block, nonzero to decrypt it.

Library:

libc

Use the -l c option to qcc to link against this library. This library is usually included automatically.

---

This function is in libc.a, but not in libc.so (in order to save space).

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Description:

The encrypt() function uses the NBS Data Encryption Standard (DES) algorithm and the key you specify by calling setkey() to encrypt (if flags is zero) or decrypt (if flags is nonzero) the given block of data.

---

For more secure encryption, use OpenSSL instead.

---

Examples:

/* Run the program with argument -rw */
/* Run a different binary variant with -r */

#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <sys/types.h>

#define ENCRYPT_DATA 0  /* 0 to encrypt block */
#define DECRYPT_DATA 1  /* nonzero to decrypt block */
#define MYFILE "/tmp/myfile"

/* Note: You must use a key, or else a new, random key will be selected
   every day, thus making correct file decryption highly unlikely. */

const char ElsterKey[64] =                      
      { 0,0,1,0, 0,1,0,1, 0,1,0,1, 0,1,0,0,         
        0,0,1,1, 0,0,1,1, 0,0,1,1, 0,1,0,0,
        0,0,1,0, 0,1,0,1, 0,0,1,1, 0,0,1,0,
        0,0,1,0, 0,1,0,1, 0,1,0,1, 0,1,0,0  };

/*
 * in == 8-byte string (expanded version of the 56-bit key)
 * out == 64-byte string where each byte is either 1 or 0
 * Note that the low-order "bit" is always ignored by by setkey()
 */
static void Expand(u_char *in, u_char *out)
{
        int j, c;
        int i;

        for (i = 0; i < 64; in++){
                c = *in;
                for (j = 7; j >= 0; j--)
                        *out++ = (c >> j) & 01;
                i += 8;
        }
}

/* The inverse of Expand */
static void Collapse(u_char *in, u_char *out)
{
        int j;
        int i;
        unsigned int c;

        for (i = 0; i < 64; i += 8, out++) {
            c = 0;
            for (j = 7; j >= 0; j--, in++)
                c |= *in << j;
            *out = c & 0xff;
        }
}


int main(int argc, char *argv[])
{
        char crypt_file[64];
     /* char orig[]={1,1,0,1,0,1,0,1,1,1,1,0,1,0,1,0,1,1,0,1,0,1,0,1,0,1,0,1, *
      *              0,0,0,0,0,0,1,1,0,1,0,1,0,1,0,1,0,1,0,1,0};              */
        char orig[]={"Welcome"};
        char orig_bin[64], buf[8];
        int opt, write_mode=0, read_mode=0, i;
        FILE *fp;

        while((opt = getopt(argc, argv, "wr")) != -1)
                        switch(opt)
                        {
                                case 'w':
                                        write_mode = 1;
                                        break;
                                case 'r':
                                        read_mode = 1;
                                        break;
                                default: ;
                        }
        if ( write_mode )
                printf( "Write mode\n" );
        if ( read_mode )
                printf( "Read mode\n" );

        if (!read_mode && !write_mode){
                printf( "Use arg -w or/and -r\n" );
                exit(1);
        }

        setkey(ElsterKey);
        if (write_mode)
        {
                printf("Original string: %s\n", orig);
                Expand(orig, orig_bin);
                encrypt(orig_bin, ENCRYPT_DATA);

                unlink(MYFILE);
           fp = fopen( MYFILE, "w" );
                if( fp != NULL ) {
                i = fwrite( orig_bin, sizeof( orig_bin ), 1, fp );
                printf( "Successfully wrote %d records to %s\n", i, MYFILE );
                fclose( fp );
                }

                encrypt(orig_bin, DECRYPT_DATA);
                Collapse(orig_bin, buf);
                printf("decypted %s\n", buf);

                if (strcmp(orig, buf) == 0)
                        printf( "Strings are equal\n" );
                else
                        printf( "Strings are NOT equal\n" );
        }

        if (read_mode)
        {
            fp = fopen( MYFILE, "r" );
                if( fp != NULL ) {
                i = fread( crypt_file, sizeof( crypt_file ), 1, fp );
                fclose( fp );
                encrypt(crypt_file, DECRYPT_DATA);
                          Collapse(crypt_file, buf);
                printf("decypted from file: %s\n", buf);
                
                        if (strcmp(orig, buf) == 0)
                                printf( "Strings (file/mem) are equal\n" );
                        else
                                printf( "Strings (file/mem) are NOT equal\n" );

                } else
                        printf( "No file %s\n", MYFILE );

        }

        return EXIT_SUCCESS;
}

Classification:

POSIX 1003.1 XSI

See also:

crypt(), setkey()