114 lines
3.1 KiB
C
114 lines
3.1 KiB
C
#include <stdio.h>
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#include <stdlib.h>
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#include <string.h>
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#include <stdbool.h>
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#include <ctype.h>
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#include <getopt.h>
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#define NUMLETTERS 26
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#define BUFSIZE 4096
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char *get_input(void);
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int main(int argc, char *argv[])
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{
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char const usage[] = "Usage: vinigere [-d] key";
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char sign = 1;
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char const plainmsg[] = "Plain text: ";
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char const cryptmsg[] = "Cipher text: ";
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bool encrypt = true;
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int opt;
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while ((opt = getopt(argc, argv, "d")) != -1) {
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switch (opt) {
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case 'd':
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sign = -1;
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encrypt = false;
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break;
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default:
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fprintf(stderr, "Unrecogized command line argument:'-%i'\n", opt);
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fprintf(stderr, "\n%s\n", usage);
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return 1;
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}
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}
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if (argc - optind != 1) {
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fprintf(stderr, "%s requires one argument and one only\n", argv[0]);
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fprintf(stderr, "\n%s\n", usage);
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return 1;
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}
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// Convert argument into array of shifts
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char const *const restrict key = argv[optind];
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size_t const keylen = strlen(key);
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char shifts[keylen];
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char const *restrict plaintext = NULL;
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for (size_t i = 0; i < keylen; i++) {
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if (!(isalpha(key[i]))) {
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fprintf(stderr, "Invalid key\n");
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return 2;
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}
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char const charcase = (isupper(key[i])) ? 'A' : 'a';
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// If decrypting, shifts will be negative.
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// This line would turn "bacon" into {1, 0, 2, 14, 13}
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shifts[i] = (key[i] - charcase) * sign;
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}
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do {
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fflush(stdout);
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// Print "Plain text: " if encrypting and "Cipher text: " if
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// decrypting
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printf("%s", (encrypt) ? plainmsg : cryptmsg);
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plaintext = get_input();
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if (plaintext == NULL) {
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fprintf(stderr, "Error getting input\n");
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return 4;
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}
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} while (strcmp(plaintext, "") == 0); // Reprompt if entry is empty
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size_t const plainlen = strlen(plaintext);
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char* const restrict ciphertext = calloc(plainlen + 1, sizeof *ciphertext);
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if (ciphertext == NULL) {
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fprintf(stderr, "Memory error\n");
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return 5;
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}
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for (size_t i = 0, j = 0; i < plainlen; i++) {
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// Skip non-alphabetical characters
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if (!(isalpha(plaintext[i]))) {
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ciphertext[i] = plaintext[i];
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continue;
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}
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// Check case
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char const charcase = (isupper(plaintext[i])) ? 'A' : 'a';
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// Wrapping conversion algorithm
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ciphertext[i] = ((plaintext[i] + shifts[j] - charcase + NUMLETTERS) % NUMLETTERS) + charcase;
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j = (j+1) % keylen;
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}
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ciphertext[plainlen] = '\0';
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printf("%s%s\n", (encrypt) ? cryptmsg : plainmsg, ciphertext);
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free(ciphertext);
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// Silence warnings about const not being maintained in cast to void*
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free((char*) plaintext);
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return 0;
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}
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char *get_input(void) {
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char *const restrict buf = malloc(BUFSIZE * sizeof (char));
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if (buf == NULL) {
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return NULL;
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}
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fgets(buf, BUFSIZE, stdin);
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// Get rid of newline
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size_t const len = strlen(buf);
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if (buf[len - 1] == '\n') buf[len - 1] = '\0';
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return buf;
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}
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