Seite 5: Listing 1

Inhaltsverzeichnis

Listing 1: miniCrypt.c – einfaches Programm zur Verschlüsselung von Dateien

#include <stdio.h>
#include <malloc.h>
#include <errno.h>

#define    BUFLEN    1024*1024

int main(int argc, char *argv[]) {
    int argcnt=1;
    char    *passwd=NULL, *argstr, fileName[280];
    unsigned char *buffer;

    if (argc < 3) {
        fprintf(stderr,"usage: %s password file ...\n", argv[0]);
        exit(1);
    }
    if ((buffer=malloc(BUFLEN))==NULL) {
        fprintf(stderr,"unable to allocate buffer: malloc() 
            failed with %d: %s\n", errno, strerror(errno));
        exit(errno);
    }
    while (--argc) {
        FILE    *ifp, *ofp;
        int        i, rb;
        long    seed=0;

        argstr=argv[argcnt++];
        if (!passwd) {
            passwd=argstr;
            continue;
        }
        strcpy(fileName, argstr);
        for (i=0;i<strlen(passwd);i++) {
            seed <<=5; seed |= passwd[i];
        }
        srand(seed);
        if ((ifp=fopen(fileName,"rb"))==NULL) {
            fprintf(stderr,"cannot open \"%s\": fopen() returned %d:
               %s\n", fileName, errno, strerror(errno));
            exit(errno);
        }
        strcat(fileName,".crypt");
        if ((ofp=fopen(fileName,"wb"))==NULL) {
            fprintf(stderr,"cannot open \"%s\": fopen() returned %d: 
               %s\n", fileName, errno, strerror(errno));
            exit(errno);
        }
        while ((rb=fread(buffer, 1, BUFLEN, ifp))>0) {
            for (i=0;i<rb;i++) {
                buffer[i] = buffer[i] ^ ~rand();
            }
            fwrite(buffer, 1, rb, ofp);
        }
        fclose(ifp);
        fclose(ofp);
    }
}