3des kryptering

Jeg har brug for at kryptere en string, til det formål har jeg fundet et eksempel på hvordan man laver en 3des kryptering. Men jeg kan ikke få det til at spille helt, på grund af min manglende c++ erfaring. Jeg poster lige den main.cpp fil, af det eksempel jeg har fundet. Hvordan får jeg den main metode, over i mit eget projekt, så det virker???

#define DEBUG 1
/* Encrypt/decrypt with triple DES */
#include <stdio.h>
#include "des.h"
#include "md5.h"

void gethex(char *result,char *cp,int cnt);
void memxor(char *,char *,int);
int doencrypt(DES3_KS,int cbc,char iv[8],FILE *in,FILE *out);
int dodecrypt(DES3_KS,int cbc,char iv[8],FILE *in,FILE *out);

main(int argc,char *argv[])
{
    int c,cnt,encrypt,decrypt,hexflag,tripflag,md5flag,keylen,cbc;
    register int i;
    char key[24],tkey1[256],tkey2[256],iv[8],*akey,*getpass();
    MD5_CTX mdcontext;
    DES3_KS ks;
    extern char *optarg;

    keylen = 8;
    tripflag = hexflag = encrypt = decrypt = md5flag = 0;
    cbc = 1;
    akey = NULL;
    while((c = getopt(argc,argv,"53hedk:b")) != EOF){
        switch(c){
        case 'e':
            encrypt++;
            break;
        case 'd':
            decrypt++;
            break;
        case 'k':
            akey = optarg;
            break;
        case 'b':
            cbc = 0;
            break;
        }
    }
    if(encrypt == 0 && decrypt == 0){
        fprintf(stderr,"Usage: des -e|-d [-b] [-k key]\n");
        exit(2);
    }
    if(akey == NULL){
        /* No key on command line, prompt for it */
        memset(tkey1,0,sizeof(tkey1));
        memset(tkey2,0,sizeof(tkey2));
        for(;;){
            akey = getpass("Enter key: ");
            strncpy(tkey1,akey,sizeof(tkey1));
            akey = getpass("Enter key again: ");
            strncpy(tkey2,akey,sizeof(tkey2));
            if(strncmp(tkey1,tkey2,sizeof(tkey1)) != 0){
                fprintf(stderr,"Key mistyped, try again\n");
            } else
                break;
        }
        akey = tkey1;
    }
    MD5Init(&mdcontext);
    MD5Update(&mdcontext,akey,strlen(akey));
    MD5Final(&mdcontext);
    memcpy(key,mdcontext.digest,16);
    memcpy(key+16,mdcontext.digest,8);

    /* Blot out original key */
    memset(akey,0,strlen(akey));

    des3key(ks,key,!encrypt);

    /* Initialize IV to all zeros */
    memset(iv,0,8);

    return ( encrypt ? doencrypt(ks,cbc,iv,stdin,stdout)
    : dodecrypt(ks,cbc,iv,stdin,stdout) );
}
/* Encrypt standard input to standard output */
int
doencrypt(DES3_KS ks,int cbc,char iv[8],FILE *in,FILE *out)
{
    char work[8];
    int cnt,i;

    for(;;){
        if((cnt = fread(work,1,8,in)) != 8){
            /* Put residual byte count in the last block.
            * Note that garbage is left in the other bytes,
            * if any; this is a feature, not a bug, since it'll
            * be stripped out at decrypt time.
            */
            work[7] = cnt;
        }
        if(cbc){
            /* CBC mode; chain in last cipher word */
            memxor(work,iv,8);
        }
        des3(ks,work);    /* Encrypt block */
        if(cbc){    /* Save outgoing ciphertext for chain */
            memcpy(iv,work,8);
        }
        fwrite(work,1,8,out);
        if(cnt != 8)
            break;
    }
    return 0;
}
int
dodecrypt(DES3_KS ks,int cbc,char iv[8],FILE *in,FILE *out)
{
    char work[8],nwork[8],ivtmp[8];
    int cnt,i;

    cnt = fread(work,1,8,in);    /* Prime the pump */
    for(;;){
        if(cbc){    /* Save incoming ciphertext for chain */
            memcpy(ivtmp,work,8);
        }
        des3(ks,work);
        if(cbc){    /* Unchain block, save ciphertext for next */
            memxor(work,iv,8);
            memcpy(iv,ivtmp,8);
        }
        /* Save buffer pending next read */
        memcpy(nwork,work,8);
        /* Try to read next block */
        cnt = fread(work,1,8,stdin);
        if(cnt != 8){    /* Can "only" be 0 if not 8 */
            /* Prev block was last one, write appropriate number
            * of bytes
            */
            cnt = nwork[7];
            if(cnt < 0 || cnt > 7){
                fprintf(stderr,"Corrupted file or wrong key\n");
            } else if(cnt != 0)
                fwrite(nwork,1,cnt,stdout);
            exit(0);
        } else {
            /* Now okay to write previous buffer */
            fwrite(nwork,1,8,out);
        }
    }
    return 0;
}
/* Convert hex/ascii nybble to binary */
int
htoa(char c)
{
    if(c >= '0' && c <= '9')
        return c - '0';
    if(c >= 'a' && c <= 'f')
        return 10 + c - 'a';
    if(c >= 'A' && c <= 'F')
        return 10 + c - 'A';
    return -1;
}
/* Convert bytes from hex/ascii to binary */
void
gethex(char *result,char *cp,int cnt)
{
    while(cnt-- != 0){
        *result = htoa(*cp++) << 4;
        *result++ |= htoa(*cp++);
    }
}
void
memxor(char *dest,char *src,int cnt)
{
    int i;

    for(i=0;i<cnt;i++)
        dest[i] ^= src[i];
}

#ifdef    DEBUG
put24(cp)
register char *cp;
{
    int i;

    for(i=0;i<24;i++){
        fprintf(stderr,"%02x ",*cp++ & 0xff);
    }
}
#endif


Jeg ved ikke helt hvordan jeg kalder den doencrypt metode rigtigt. Jeg har brug for at sende en char eller string til metoden, og få noget ulæseligt igen. Og så selvfølgelig få det dekrypteret igen. Nogen der kan hjælpe?