vigenere cipher

vigenere.c

@@ -0,0 +1,116 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+/*
+Vigenère cipher and decipher
+https://en.wikipedia.org/wiki/Vigen%C3%A8re_cipher
+
+Made after a friend told me she was making it an uni, decided to give it a shot ;P
+*/
+
+char *text = "IF YOU READ THIS YOU WILL PASS THE EXAM";
+char *worm = "CKQWC";
+
+char *cipher(char *, char *);
+char *decipher(char *, char *);
+char *replicateWorm(char*, int);
+int min(int, int);
+
+int main() {
+    printf("Original Text: %s\t|\tWorm: %s\n", text, worm);
+    char *ciphred = cipher(text, worm);
+    printf("Encrypted text: %s\n", ciphred);
+
+    printf("Encrypted Text: %s\t|\tWorm: %s\n", ciphred, worm);
+    char *deciphred = decipher(ciphred, worm);
+    printf("Decrypted text: %s\n", deciphred);
+}
+
+char *cipher(char *a_text, char *a_worm) {
+    //First: create result string by allocating as much memory as used for text
+    char *result = malloc(strlen(a_text) * sizeof(char));
+
+    if(strlen(a_text) != strlen(a_worm)) a_worm = replicateWorm(a_worm, strlen(a_text));
+
+    for (int i = 0; i < strlen(a_text); i++) {
+        char ascii_char_result = ' ';
+        if (a_text[i] != ' ') {
+            //Get the ASCII integer of the char in both text and it's corresponding worm and substract 64 to get the index in the alphabet
+            //Little reminder: A in ascii is 65, every other capital letter comes after in increasing order (B is 66, C is 67...)
+            //Just subtract 65 from the ascii integer to get the index  in the alphabeth -1 for the given char (So A is 9, B is 1...)
+            //Start counting from 0 is needed because of how the modulo operation works (%26 counts number from 0 up to 25)
+            int ascii_int_text = ((int)a_text[i]) - 65;
+            int ascii_int_worm = ((int)a_worm[i]) - 65;
+
+            //Compute encrypted char
+            int ascii_int_result = (ascii_int_text + ascii_int_worm) % 26;
+
+            //Now add 64 again to get the ascii integer from the alphabet index
+            ascii_char_result = (char)(ascii_int_result + 65);
+        }
+
+        //Insert the character in the string
+        result[i] = ascii_char_result;
+    }
+    return result;
+}
+
+char *decipher(char *a_text, char *a_worm) {
+    //First: create result string by allocating as much memory as used for text
+    char *result = malloc(strlen(a_text) * sizeof(char));
+
+    if(strlen(a_text) != strlen(a_worm)) a_worm = replicateWorm(a_worm, strlen(a_text));
+
+    for (int i = 0; i < strlen(a_text); i++) {
+        char ascii_char_result = ' ';
+        if (a_text[i] != ' ') {
+            //Get the ASCII integer of the char in both text and it's corresponding worm and substract 64 to get the index in the alphabet
+            //Little reminder: A in ascii is 65, every other capital letter comes after in increasing order (B is 66, C is 67...)
+            //Just subtract 65 from the ascii integer to get the index  in the alphabeth -1 for the given char (So A is 9, B is 1...)
+            //Start counting from 0 is needed because of how the modulo operation works (%26 counts number from 0 up to 25)
+            int ascii_int_text = ((int)a_text[i]) - 65;
+            int ascii_int_worm = ((int)a_worm[i]) - 65;
+
+            //Compute encrypted char
+            int ascii_int_result = (ascii_int_text - ascii_int_worm + 26) % 26;
+
+            //Now add 64 again to get the ascii integer from the alphabet index
+            ascii_char_result = (char)(ascii_int_result + 65);
+        }
+
+        //Insert the character in the string
+        result[i] = ascii_char_result;
+    }
+    return result;
+}
+
+//Replicate the worm until it gets up to the desired length
+char* replicateWorm(char* a_worm, int len){
+
+    char* result1 = malloc(strlen(a_worm) * sizeof(char) * len);
+
+    while(strlen(result1) < len){
+        //The strncat(dest, src, n) functions copy the first n characterc of ssrc into dest
+        //We simply copy the minimum between how many characters we still have left to copy (len - strlen(result1)) and the length of the worm
+        //This will copy the full worm until the number of remaining characters will be less than the length of the worm, when it will copy just the first len - strlen(result1) of the worm
+        result1 = strncat(result1, a_worm, min((len - strlen(result1)), strlen(a_worm)));
+        printf("%s", a_worm);
+    }
+
+    return result1;
+
+}
+
+//Returns minimum between a and b
+int min(int a, int b){
+    // This is just a nice short way of writing
+    // if(a <= b){
+    // return a;
+    // }else{
+    // return b;
+    // }
+    //Could probably to a macro for it but idc atm
+
+    return a <= b ? a : b;
+}