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/*
* Copyright (C) 2015 Tomasz Kramkowski <tk@the-tk.com>
*
* This program is free software. It is licensed under version 3 of the
* GNU General Public License.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see [http://www.gnu.org/licenses/].
*/
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>
#define CTOI(c) ((c) - 'A')
#define ITOC(c) ((c) + 'A')
void preprocess(char *str);
int main(int argc, char **argv)
{
char *key, *ciphertext, *decoded;
size_t keylength, textlength;
if (argc != 3) {
fprintf(stderr, "Usage: %s <ciphertext> <key>\n", argv[0]);
exit(EXIT_FAILURE);
}
ciphertext = argv[1];
key = argv[2];
preprocess(key);
preprocess(ciphertext);
keylength = strlen(key);
textlength = strlen(ciphertext);
decoded = malloc(textlength + 1);
for (size_t i = 0; i < textlength; i++)
decoded[i] = (CTOI(ciphertext[i]) + CTOI(key[i % keylength])) % 26;
for (unsigned offset = 0; offset < 26; offset++) {
printf("%.2u : ", offset);
for (unsigned i = 0; i < textlength; i++)
putchar(ITOC((decoded[i] + offset) % 26));
putchar('\n');
}
free(decoded);
return EXIT_SUCCESS;
}
void preprocess(char *str)
{
char *src = str, *dest = str;
while (*src != '\0') {
if (isalpha(*src))
*(dest++) = toupper(*src);
src++;
}
*dest = '\0';
}
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