This one time pad encryption program I have written (basically just an XOR "encryption" program) seems to be working fine, compiling nicely (gcc -o ./OTP.c), and doing what it's supposed to. However I would like to improve it as much as possible which is why I am posting this.
I am particularly insecure about the memory allocation. Any suggestions regarding improvements are more than welcome!
The code in its entirety is found below and can also be found on Github: PrivacyProject/OTP-Encryption.
#include <stdio.h>
#include <stdlib.h>
#include <sys/stat.h>
#include <sys/mman.h>
int main(int argc, char **argv)
{
struct stat statbuf;
struct stat keybuf;
char buffer [20];
int key;
int data;
int output;
int count;
char ans;
int * buf;
FILE * keyfile;
FILE * sourcefile;
FILE * destfile;
if(geteuid() !=0)
{
printf("Root access is required to run this program\n\n");
exit(0);
}
if(argc<4)
{
printf("\n");
printf(" OTP 1.0 \n\n");
printf(" This program encrypts a file using a random key\n");
printf(" and generates an output file with the resulting\n");
printf(" cipher. Decryption is achieved by running the\n");
printf(" output file as source file with the same key.\n\n");
printf(" WARNING: The security of the encryption provided\n");
printf(" by this program is entirely dependent on the key\n");
printf(" file. The keyfile should meet the requirements\n");
printf(" below:\n");
printf(" - Be of the same size or larger than the\n");
printf(" source file.\n");
printf(" - Be completely random, preferably generated by \n");
printf(" a Hardware Random Number Generator.\n");
printf(" - NEVER be reused!\n\n");
printf(" The author takes no responsibility for use of\n");
printf(" this program. Available under GNU General Public\n");
printf(" Licence v.2\n\n");
printf(" USAGE: OTP <source file> <output file> <keyfile>\n\n");
return (0);
}
/* Check number of arguments. */
if(argc>4)
{
printf("Too many arguments.\n");
printf("USAGE: OTP <source file> <output file> <keyfile>\n");
exit(1);
}
/* Allocate memory required by processes */
buf = (int*) malloc (sizeof(int));
if (buf == NULL)
{
perror("Error");
exit(1);
}
/* Lock down pages mapped to processes */
printf("Locking down processes...\n\n");
if(mlockall (MCL_CURRENT | MCL_FUTURE) < 0)
{
perror("mlockall");
exit (1);
}
/* Check if sourcefile can be opened. */
if((sourcefile = fopen(argv[1], "rb"))== NULL)
{
printf("Can't open source file\n");
perror("Error");
printf("USAGE: OTP <source file> <output file> <keyfile>\n");
exit (1);
}
/* Get size of sourcefile */
fstat(fileno(sourcefile), &statbuf);
/* Check if keyfile can be opened. */
if((keyfile = fopen(argv[3], "rb"))== NULL)
{
printf("Can't open keyfile.\n");
perror("Error");
printf("USAGE: OTP <source file> <output file> <keyfile>\n");
exit(1);
}
/* Get size of keyfile */
fstat(fileno(keyfile), &keybuf);
/* Check if keyfile is the same size as, or bigger than the sourcefile */
if((keybuf.st_size) < (statbuf.st_size))
{
printf("Source file is larger than keyfile.\n");
printf("This significantly reduces cryptographic strength.\n");
printf("Do you wish to continue? (Y/N)\n");
fgets(buffer, 20, stdin);
sscanf(buffer, "%c", &ans);
if(ans == 'n' || ans == 'N')
{
exit (1);
}
if(ans == 'y' || ans == 'Y')
{
printf("Proceeding with Encryption/Decryption.\n");
}
else
{
printf("No option selected. Exiting...\n");
exit (1);
}
}
/* Check if destfile can be opened. */
if((destfile = fopen(argv[2], "wb"))== NULL)
{
printf("Can't open output file.\n");
perror("Error");
exit(1);
}
/* Encrypt/Decrypt and write to output file. */
while(count < (statbuf.st_size))
{
key=fgetc(keyfile);
data=fgetc(sourcefile);
output=(key^data);
fputc(output,destfile);
count++;
}
/* Close files. */
fclose(keyfile);
fclose(sourcefile);
fclose(destfile);
printf("Encryption/Decryption Complete.\n\n");
/* delete Source file option. */
printf("Do you wish to delete the source file? (Y/N)\n");
fgets(buffer, 20, stdin);
sscanf(buffer, "%c", &ans);
if(ans == 'y' || ans == 'Y')
{
if ( remove(argv[1]) == 0)
{
printf("File deleted successfully.\n");
}
else
{
printf("Unable to delete the file.\n");
perror("Error");
exit(1);
}
}
/* delete keyfile option. */
printf("Do you wish to delete the keyfile? (Y/N)\n");
fgets(buffer, 20, stdin);
sscanf(buffer, "%c", &ans);
if(ans == 'y' || ans == 'Y')
{
if ( remove(argv[3]) == 0)
{
printf("File deleted successfully.\n");
}
else
{
printf("Unable to delete the file.\n");
perror("Error");
exit(1);
}
}
/* cleanup */
printf("Releasing memory.\n");
free (buf);
return(0);
}
