#include <stdio.h>
#include <unistd.h>
#include <string.h>
#include <openssl/des.h>


char *
Encrypt( char *Key, char *Msg, int size)
{

        static char*    Res;
        int             n=0;
        DES_cblock      Key2;
        DES_key_schedule schedule;

        Res = ( char * ) malloc( size );

        /* Prepare the key for use with DES_cfb64_encrypt */
        memcpy( Key2, Key,8);
        DES_set_odd_parity( &Key2 );
        DES_set_key_checked( &Key2, &schedule );

        /* Encryption occurs here */
        DES_cfb64_encrypt( ( unsigned char * ) Msg, ( unsigned char * ) Res,
                           size, &schedule, &Key2, &n, DES_ENCRYPT );

         return (Res);
}


char *
Decrypt( char *Key, char *Msg, int size)
{

        static char*    Res;
        int             n=0;

        DES_cblock      Key2;
        DES_key_schedule schedule;

        Res = ( char * ) malloc( size );

        /* Prepare the key for use with DES_cfb64_encrypt */
        memcpy( Key2, Key,8);
        DES_set_odd_parity( &Key2 );
        DES_set_key_checked( &Key2, &schedule );

        /* Decryption occurs here */
        DES_cfb64_encrypt( ( unsigned char * ) Msg, ( unsigned char * ) Res,
                           size, &schedule, &Key2, &n, DES_DECRYPT );

        return (Res);

}

int main() {

char key[]="password";
char clear[]="This is a secret message";
char *decrypted;
char *encrypted;

encrypted=malloc(sizeof(clear));
decrypted=malloc(sizeof(clear));

printf("Clear text\t : %s \n",clear);
memcpy(encrypted,Encrypt(key,clear,sizeof(clear)), sizeof(clear));
printf("Encrypted text\t : %s \n",encrypted);
memcpy(decrypted,Decrypt(key,encrypted,sizeof(clear)), sizeof(clear));
printf("Decrypted text\t : %s \n",decrypted);



return (0);
}
				
				

编译运行

$ gcc des.c -o des -lssl -lcrypto
$ ./des