From b89f95500660607f6f4f24b8adff0ad37c012146 Mon Sep 17 00:00:00 2001
From: EstebanKubata <Esteban.Kubata@gmail.com>
Date: Wed, 22 Apr 2015 17:29:34 +0200
Subject: [PATCH] Create modified_md5.c

---
 modified_md5.c | 119 +++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 119 insertions(+)
 create mode 100644 modified_md5.c

diff --git a/modified_md5.c b/modified_md5.c
new file mode 100644
index 0000000..3758a33
--- /dev/null
+++ b/modified_md5.c
@@ -0,0 +1,119 @@
+#include <stdint.h>
+#include <math.h>
+#include <stdlib.h>
+#include <stdio.h>
+#include <assert.h>
+#include <string.h>
+#define printf(...) (void)0;
+
+int shift[] = {7, 12, 17, 22, 7, 12, 17, 22, 7, 12, 17, 22, 7, 12, 17, 22,
+               5,  9, 14, 20, 5,  9, 14, 20, 5,  9, 14, 20, 5,  9, 14, 20,
+               4, 11, 16, 23, 4, 11, 16, 23, 4, 11, 16, 23, 4, 11, 16, 23,
+               6, 10, 15, 21, 6, 10, 15, 21, 6, 10, 15, 21, 6, 10, 15, 21};
+
+uint32_t F(uint32_t B, uint32_t C, uint32_t D)
+{
+   return (B & C) | (~B & D);
+}
+
+uint32_t G(uint32_t B, uint32_t C, uint32_t D)
+{
+   return (B & D) | (C & ~D);
+}
+
+uint32_t H(uint32_t B, uint32_t C, uint32_t D)
+{
+   return B ^ C ^ D;
+}
+
+uint32_t I(uint32_t B, uint32_t C, uint32_t D)
+{
+   return C ^ (B | ~D);
+}
+
+
+uint32_t rol(uint32_t input, int count)
+{
+   return ((input << count) & 0xffffffff) | (input & 0xffffffff) >> (32-count);
+}
+
+void swap(uint32_t* a, uint32_t* b)
+{
+   printf("%08x <-> %08x\n", *a, *b);
+   uint32_t c = *a;
+   *a = *b;
+   *b = c;
+}
+
+void modified_md5(unsigned char* originalblockIn, unsigned char* keyIn, unsigned char* keyOut)
+{
+   unsigned char blockIn[64];
+   uint32_t* block_words = (uint32_t*)blockIn;
+   uint32_t* key_words = (uint32_t*)keyIn;
+   uint32_t* out_words = (uint32_t*)keyOut;
+   uint32_t A, B, C, D, Z, tmp;
+   int i;
+   
+   memcpy(blockIn, originalblockIn, 64);
+
+   // Each cycle does something like this:
+   A = key_words[0];
+   B = key_words[1];
+   C = key_words[2];
+   D = key_words[3];
+   for (i = 0; i < 64; i++)
+   {
+      uint32_t input;
+      int j;
+      if (i < 16)
+         j = i;
+      else if (i < 32)
+         j = (5*i + 1) % 16;
+      else if (i < 48)
+         j = (3*i + 5) % 16;
+      else if (i < 64)
+         j = 7*i % 16;
+
+      input = blockIn[4*j] << 24 | blockIn[4*j+1] << 16 | blockIn[4*j+2] << 8 | blockIn[4*j+3];
+      printf("Key = %08x\n", A);
+      Z = A + input + (int)(long long)((1LL << 32) * fabs(sin(i + 1)));
+      if (i < 16)
+         Z = rol(Z + F(B,C,D), shift[i]);
+      else if (i < 32)
+         Z = rol(Z + G(B,C,D), shift[i]);
+      else if (i < 48)
+         Z = rol(Z + H(B,C,D), shift[i]);
+      else if (i < 64)
+         Z = rol(Z + I(B,C,D), shift[i]);
+      if (i == 63)
+         printf("Ror is %08x\n", Z);
+      printf("Output of round %d: %08X + %08X = %08X (shift %d, constant %08X)\n", i, Z, B, Z+B, shift[i], (int)(long long)((1LL << 32) * fabs(sin(i + 1))));
+      Z = Z + B;
+      tmp = D;
+      D = C;
+      C = B;
+      B = Z;
+      A = tmp;
+      if (i == 31)
+      {
+         // swapsies
+         swap(&block_words[A & 15], &block_words[B & 15]);
+         swap(&block_words[C & 15], &block_words[D & 15]);
+         swap(&block_words[(A & (15<<4))>>4], &block_words[(B & (15<<4))>>4]);
+         swap(&block_words[(A & (15<<8))>>8], &block_words[(B & (15<<8))>>8]);
+         swap(&block_words[(A & (15<<12))>>12], &block_words[(B & (15<<12))>>12]);
+      }
+   }
+   printf("%08X %08X %08X %08X\n", A, B, C, D);
+   // Now we can actually compute the output
+   printf("Out:\n");
+   printf("%08x + %08x = %08x\n", key_words[0], A, key_words[0] + A);
+   printf("%08x + %08x = %08x\n", key_words[1], B, key_words[1] + B);
+   printf("%08x + %08x = %08x\n", key_words[2], C, key_words[2] + C);
+   printf("%08x + %08x = %08x\n", key_words[3], D, key_words[3] + D);
+   out_words[0] = key_words[0] + A;
+   out_words[1] = key_words[1] + B;
+   out_words[2] = key_words[2] + C;
+   out_words[3] = key_words[3] + D;
+   
+}