| madsovenielsen |
06-14-2010 11:54 AM |
C xor encryption strength
Hey.
i have found this xor encryption program
Code:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define MAX_SIZE 256
void strip_newline(char* to_strip);
void encrypt_data(FILE* input_file, FILE* output_file, char *key);
int main(int argc, char* argv[])
{
//Check for valid number of arguments
if (argc != 3)
{
printf("Invalid number of arguments. %d arguments were supplied.\n", argc);
printf("Usage: %s inputfile outputfile\n", argv[0]); //Usage: ./xortest inputfile outputfile
exit(0);
}
FILE* input;
FILE* output;
//Open input and output files
input = fopen(argv[1], "r");
output = fopen(argv[2], "w");
//Check input file
if (input == NULL)
{
printf("Input file cannot be read.\n");
exit(0);
}
//Check output file
if (output == NULL)
{
printf("Output file cannot be written to.\n");
exit(0);
}
//Key strings
char *key = malloc(MAX_SIZE);
//Prompt for key
printf("Passphrase: ");
//Read in key
fgets(key, MAX_SIZE, stdin);
printf("Encrypting %s\n", argv[1]);
//strip newlines
strip_newline(key);
//XOR data and write it to file
encrypt_data(input, output, key);
printf("Encrypted data written to %s\n", argv[2]);
//Release memory
free(key);
//Close files
fclose(input);
fclose(output);
return 0;
}
void encrypt_data(FILE* input_file, FILE* output_file, char* key)
{
int key_count = 0; //Used to restart key if strlen(key) < strlen(encrypt)
int encrypt_byte;
while( (encrypt_byte = fgetc(input_file)) != EOF) //Loop through each byte of file until EOF
{
//XOR the data and write it to a file
fputc(encrypt_byte ^ key[key_count], output_file);
//Increment key_count and start over if necessary
key_count++;
if(key_count == strlen(key))
key_count = 0;
}
}
void strip_newline(char* to_strip)
{
//remove newlines
if (to_strip[strlen(to_strip) - 1] == '\n')
{
to_strip[strlen(to_strip) - 1] = '\0';
}
Its working fine, it can encrypt and decrypt. but how strong is it ? is it all depending on the specified key ?
How do i measure the strength of this encryption in bits ?
/mads |
