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Author: brendan-rius

main.c

@@ -7,31 +7,43 @@
 #include <time.h>
 #include "base64.h"
 
-
-char *g_header_b64 = NULL;
-char *g_payload_b64 = NULL;
-char *g_signature_b64 = NULL;
-unsigned char *g_to_encrypt = NULL;
-unsigned char *g_signature = NULL;
-
+char *g_header_b64 = NULL; // Holds the Base64 header of the original JWT
+char *g_payload_b64 = NULL; // Holds the Base64 payload of the original JWT
+char *g_signature_b64 = NULL; // Holds the Base64 signature of the original JWT
+unsigned char *g_to_encrypt = NULL; // Holds the part of the JWT that needs to be hashed
+unsigned char *g_signature = NULL; // Holds the Base64 *decoded* signature of the original JWT
+
+// Some lengths of buffers. Useful to avoid computing it multiple times.
+// Also, not all strings used finish with a '\0' for optimization purposes.
+// In that case, we need to have the length
 size_t g_header_b64_len = 0;
 size_t g_payload_b64_len = 0;
 size_t g_signature_b64_len = 0;
 size_t g_signature_len = 0;
 size_t g_to_encrypt_len = 0;
 
+// The alphabet to use when brute-forcing
 char *g_alphabet = NULL;
 size_t g_alphabet_len = 0;
 
-unsigned char* g_result = NULL;
+// Holds the computed signature at each iteration to compare it with the original
+// signature
+unsigned char *g_result = NULL;
 unsigned int g_result_len = 0;
 
 char *g_buffer = NULL;
 
+// The hash function to apply the HMAC to
 EVP_MD *g_evp_md = NULL;
 
+/**
+ * Check if the signature produced with "secret
+ * of size "secrent_len" (without the '\0') matches the original
+ * signature.
+ * Return true if it matches, false otherwise
+ */
 bool check(const char *secret, size_t secret_len) {
-	// Hash to_encrypt using HMAC-SHA256 into result
+	// Hash to_encrypt using HMAC into result
 	HMAC(
 		g_evp_md,
 		(const unsigned char *) secret, secret_len,
@@ -66,7 +78,7 @@ char *bruteSequential(int start, int maxLen)
     for (int i = start; i <= maxLen; ++i)
     {
       	if (bruteImpl(g_buffer, 0, i))
-					return strdup(g_buffer);
+            return strdup(g_buffer);
     }
 
 		return NULL;
@@ -97,11 +109,10 @@ int main(int argc, char **argv) {
 
 	g_alphabet_len = strlen(g_alphabet);
 
-	// Split it into header, payload and signature
+	// Split the JWT into header, payload and signature
 	g_header_b64 = strtok(jwt, ".");
 	g_payload_b64 = strtok(NULL, ".");
 	g_signature_b64 = strtok(NULL, ".");
-
 	g_header_b64_len = strlen(g_header_b64);
 	g_payload_b64_len = strlen(g_payload_b64);
 	g_signature_b64_len = strlen(g_signature_b64);
@@ -120,8 +131,11 @@ int main(int argc, char **argv) {
 	// is returned by this function
 	g_signature_len = Base64decode((char *) g_signature, (const char *) g_signature_b64);
 
+    // Allocate the buffer used to hold the calculated signature
 	g_result = malloc(EVP_MAX_MD_SIZE);
 	g_buffer = malloc(max_len + 1);
+
+    // The chosen hash function is SHA-256
 	g_evp_md = (EVP_MD *) EVP_sha256();
 
 	clock_t start = clock(), diff;