Assignment 5 - Software Security - Teil 1/crackme/Makefile

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+.phony: all
+all: crackme
+crackme:
+	gcc -o crackme -m32 -O0 -fno-pie -fno-stack-protector crackme.c

Assignment 5 - Software Security - Teil 1/crackme/crackme.c

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+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+// Define the length of the serial number
+#define SERIAL_LENGTH 5
+
+int verify_key(char *serial) {
+    // Allocate a buffer to store the derived key (5 capital letters + null byte)
+    char derived[SERIAL_LENGTH + 1] = {0};
+
+    // Derive the key from the serial by iterating over the serial
+    // and subtracting 2 times the current index from each character
+    for(int i = 0; i < SERIAL_LENGTH; i++) {
+        derived[i] = serial[i] - 2 * i;
+    }
+
+    // Compare the derived key with the expected key "MMNNQ"
+    if(strcmp(derived, "MMNNQ") == 0)
+        return 1; // Return 1 if the keys match
+
+    return 0; // Return 0 if the keys do not match
+}
+
+int main(int argc, char **argv) {
+    // Buffer to store the user input (5 capital letters + null byte)
+    char serial[SERIAL_LENGTH + 1] = {0};
+    
+    // Read the serial number from the user and store it in the serial buffer
+    printf("Enter serial (5 capital letters):\n");
+    scanf("%5s", serial);
+
+    // Verify the serial number   
+    if(verify_key(serial)) {
+        // Print this message if the serial is correct
+        printf("Key is valid! Whoop whoop :)\n");
+    } else {
+        // Print this message if the serial is not correct
+        printf("Key is not valid :(\n");
+    }
+
+    // End the program without errors
+    return 0;
+}

Assignment 5 - Software Security - Teil 1/crackme/key.txt

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+MORTY