104 lines
3.2 KiB
C
104 lines
3.2 KiB
C
#include <stdio.h>
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#include <stdlib.h>
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#include <string.h>
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#include <time.h>
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#define KEY_LENGTH 4096
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void genkey(int length, char *key) {
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srand(time(NULL));
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for (int i = 0; i < length; ++i) {
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key[i] = rand() % 256;
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}
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}
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void vernam(char *s, char *t, int length, char *result) {
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for (int i = 0; i < length; ++i) {
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result[i] = s[i] ^ t[i];
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}
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}
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void writeKeyToFile(char *key, int key_count) {
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char filename[9]; // 4 digits only
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for (int i = 0; i < key_count; ++i) {
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sprintf(filename, "key-%d", i + 1);
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FILE *key_file = fopen(filename, "wb"); // b means binary
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if (key_file == NULL) {
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fprintf(stderr, "ERROR: Cannot open key file.\n");
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exit(EXIT_FAILURE);
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}
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// writes KEY_LENGTH items of data, each 1 byte long, to the
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// stream key_file pointed to by stream, obtaining them from the
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// location given by pointer key.
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fwrite(key, 1, KEY_LENGTH, key_file);
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fclose(key_file);
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}
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}
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void vernam_files(char *input_file, char* key_file, char *output_file) {
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FILE *input = fopen(input_file, "rb");
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FILE *key = fopen(key_file, "rb");
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if (input == NULL || key == NULL) {
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fprintf(stderr, "ERROR: Cannot open input or key file.\n");
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exit(EXIT_FAILURE);
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}
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// Get the length of the input file
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fseek(input, 0, SEEK_END);
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int length = ftell(input);
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rewind(input);
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char *message = malloc(length);
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char *keybuf = malloc(length);
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fread(message, 1, length, input);
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fread(keybuf, 1, length, key);
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fclose(input);
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fclose(key);
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char encrypted[length];
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vernam(message, keybuf, length, encrypted);
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FILE *out = fopen(output_file, "wb");
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if (out == NULL) {
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fprintf(stderr, "ERROR: Cannot open output file.\n");
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exit(EXIT_FAILURE);
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}
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fwrite(encrypted, 1, length, out);
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fclose(out);
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free(message);
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free(keybuf);
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}
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int main(int argc, char *argv[]) {
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char *usage = "Usage: %s -i <input_file> -k <key_file> -o <output_file> | -g <keys_count> | -h\n";
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if (argc < 2) {
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fprintf(stderr, usage, argv[0]);
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exit(EXIT_FAILURE);
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}
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if (strncmp(argv[1], "-i", 2) == 0 && argc == 7 && strncmp(argv[3], "-k", 2) == 0 && strncmp(argv[5], "-o", 2) == 0) {
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vernam_files(argv[2], argv[4], argv[6]);
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} else if (strncmp(argv[1], "-g", 2) == 0 && argc == 3) {
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int key_count = atoi(argv[2]);
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if (key_count <= 0 || key_count > 9999) {
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fprintf(stderr, "vernam: Key count must be more than 0 and less than 9999.\n");
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exit(EXIT_FAILURE);
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}
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char key[KEY_LENGTH];
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genkey(KEY_LENGTH, key);
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writeKeyToFile(key, key_count);
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} else if (strncmp(argv[1], "-h", 2) == 0 && argc == 2) {
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printf("Vernam Cipher Tool\n");
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printf(usage, "vernam");
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printf("Example: vernam -i message_to_tom -k key-1 -o encrypted_to_tom\n");
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printf("To acquire a truly random and secure key, use\nvernam -g <keys_count>\n\n");
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printf("Made with <3 by night0721. Licensed under GPL v3.\n");
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} else {
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fprintf(stderr, usage, argv[0]);
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exit(EXIT_FAILURE);
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}
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return 0;
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}
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