From 3940ee3a21d1cdf289cafdeb1c92dd35cd10e097 Mon Sep 17 00:00:00 2001
From: Thomas Florian <thomas.florian@tum.de>
Date: Wed, 29 Jun 2022 15:53:46 +0200
Subject: [PATCH] feat: implement step 2: checksum

---
 Implementierung/src/md2.c | 40 ++++++++++++++++++++++++++++++++++++---
 1 file changed, 37 insertions(+), 3 deletions(-)

diff --git a/Implementierung/src/md2.c b/Implementierung/src/md2.c
index 1bcc23a..1b3e0a3 100644
--- a/Implementierung/src/md2.c
+++ b/Implementierung/src/md2.c
@@ -3,6 +3,27 @@
 // The file "testfile" should lead to this hash:
 // fc982e558db259f298b43cd4c1241c66
 
+// Source: https://datatracker.ietf.org/doc/html/rfc1319
+static unsigned char PI_SUBST[256] = {
+    41, 46, 67, 201, 162, 216, 124, 1, 61, 54, 84, 161, 236, 240, 6,
+    19, 98, 167, 5, 243, 192, 199, 115, 140, 152, 147, 43, 217, 188,
+    76, 130, 202, 30, 155, 87, 60, 253, 212, 224, 22, 103, 66, 111, 24,
+    138, 23, 229, 18, 190, 78, 196, 214, 218, 158, 222, 73, 160, 251,
+    245, 142, 187, 47, 238, 122, 169, 104, 121, 145, 21, 178, 7, 63,
+    148, 194, 16, 137, 11, 34, 95, 33, 128, 127, 93, 154, 90, 144, 50,
+    39, 53, 62, 204, 231, 191, 247, 151, 3, 255, 25, 48, 179, 72, 165,
+    181, 209, 215, 94, 146, 42, 172, 86, 170, 198, 79, 184, 56, 210,
+    150, 164, 125, 182, 118, 252, 107, 226, 156, 116, 4, 241, 69, 157,
+    112, 89, 100, 113, 135, 32, 134, 91, 207, 101, 230, 45, 168, 2, 27,
+    96, 37, 173, 174, 176, 185, 246, 28, 70, 97, 105, 52, 64, 126, 15,
+    85, 71, 163, 35, 221, 81, 175, 58, 195, 92, 249, 206, 186, 197,
+    234, 38, 44, 83, 13, 110, 133, 40, 132, 9, 211, 223, 205, 244, 65,
+    129, 77, 82, 106, 220, 55, 200, 108, 193, 171, 250, 36, 225, 123,
+    8, 12, 189, 177, 74, 120, 136, 149, 139, 227, 99, 232, 109, 233,
+    203, 213, 254, 59, 0, 29, 57, 242, 239, 183, 14, 102, 88, 208, 228,
+    166, 119, 114, 248, 235, 117, 75, 10, 49, 68, 80, 180, 143, 237,
+    31, 26, 219, 153, 141, 51, 159, 17, 131, 20};
+
 void printBuf(size_t len, uint8_t buf[len]) {
   for (int i = 0; i < len; i++) {
     printf("'%lx',", buf[i]);
@@ -10,7 +31,17 @@ void printBuf(size_t len, uint8_t buf[len]) {
   printf("\n");
 }
 
-void md2_checksum(size_t len, uint8_t* buf) {}
+void md2_checksum(size_t len, uint8_t* buf) {
+  uint8_t l = 0;
+
+  for (int i = 0; i < len / 16; i++) {
+    for (int j = 0; j < 16; j++) {
+      u_int8_t c = buf[i * 16 + j];
+      buf[len + j] = PI_SUBST[c ^ l];
+      l = buf[len + j];
+    }
+  }
+}
 
 void md2_hash(size_t len, const uint8_t buf[len], uint8_t out[16]) {
   // add padding
@@ -20,7 +51,7 @@ void md2_hash(size_t len, const uint8_t buf[len], uint8_t out[16]) {
 
   printf("len: %d\n", len);
 
-  uint8_t* newBuf = malloc(len);
+  uint8_t* newBuf = malloc(len + 16);  // 16 = Checksum
   memcpy(newBuf, buf, len - paddingNeeded);
   newBuf[4] = 'f';
 
@@ -28,8 +59,11 @@ void md2_hash(size_t len, const uint8_t buf[len], uint8_t out[16]) {
     newBuf[len - paddingNeeded] = originalPadding;
     paddingNeeded--;
   }
-
   printBuf(len, newBuf);
 
+  md2_checksum(len, newBuf);
+
+  printBuf(len + 16, newBuf);
+
   free(newBuf);
 }
\ No newline at end of file