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authorTomasz Kramkowski <tk@the-tk.com>2015-04-02 02:23:14 +0200
committerTomasz Kramkowski <tk@the-tk.com>2015-04-02 02:23:14 +0200
commita4a0b84f2765c19eae7d270e1627f4b00fa0a99a (patch)
tree3243b380663bec22ccdc7fc2a4bbf2deea627bb8
parente60bdf760f69760501e826957d6dac053bccede5 (diff)
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Simple implementation of vigenere cipher. (offset of 1 for desired results)
-rw-r--r--vigenere.c62
1 files changed, 62 insertions, 0 deletions
diff --git a/vigenere.c b/vigenere.c
new file mode 100644
index 0000000..8ed4a6c
--- /dev/null
+++ b/vigenere.c
@@ -0,0 +1,62 @@
+#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, *decodepos, *decodeneg;
+ long offset;
+ size_t keylength, textlength;
+
+ if (argc != 4) {
+ fprintf(stderr, "Usage: %s <key> <offset> <ciphertext>\n", argv[0]);
+ exit(EXIT_FAILURE);
+ }
+
+ key = argv[1];
+ offset = strtol(argv[2], NULL, 10);
+ ciphertext = argv[3];
+
+ preprocess(key);
+ preprocess(ciphertext);
+
+ keylength = strlen(key);
+ textlength = strlen(ciphertext);
+
+ decodepos = malloc(textlength + 1);
+ decodeneg = malloc(textlength + 1);
+
+ for (size_t i = 0; i < textlength; i++) {
+ decodepos[i] = ITOC((CTOI(ciphertext[i]) + offset + CTOI(key[i % keylength])) % 26);
+ decodeneg[i] = ITOC((CTOI(ciphertext[i]) + 52 - offset - CTOI(key[i % keylength])) % 26);
+ }
+
+ decodepos[textlength] = '\0';
+ decodeneg[textlength] = '\0';
+
+ printf("+ %s\n- %s\n", decodepos, decodeneg);
+
+ free(decodepos);
+ free(decodeneg);
+
+ return EXIT_SUCCESS;
+}
+
+void preprocess(char *str)
+{
+ char *src = str, *dest = str;
+
+ while (*src != '\0') {
+ if (isalpha(*src))
+ *(dest++) = toupper(*src);
+ src++;
+ }
+
+ *dest = '\0';
+}