From 9dcc7348ad53cab8fd9396699de0177bac6729d5 Mon Sep 17 00:00:00 2001
From: Benedict <benedict@0xb8000.de>
Date: Tue, 31 Jan 2017 22:45:22 +0100
Subject: set7: task52: completed

---
 set7/task52.c | 248 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 248 insertions(+)
 create mode 100644 set7/task52.c

(limited to 'set7')

diff --git a/set7/task52.c b/set7/task52.c
new file mode 100644
index 0000000..aba8445
--- /dev/null
+++ b/set7/task52.c
@@ -0,0 +1,248 @@
+#include "../lib/lib.h"
+#include "../lib/lib2.h"
+#include "../lib/lib3.h"
+#include "../lib/lib4.h"
+#include "../lib/lib5.h"
+#include "../lib/lib7.h"
+
+/**
+  * MD-Hash implementation with AES-128. Outputs only 2^16 bits of the hash
+  **/ 
+void  md_hash_aes_128(char *input, int input_len, char *state, char *hash, int bytes, int print)
+{
+	int blocksize = 16;
+	int i;
+	int pad_len;
+	char h[blocksize];
+	char key[blocksize];
+	char h_hex[32];
+	char *input_padded = __pkcs7_padding(input, input_len, 16, &pad_len);
+
+	// set the intial state
+	memset(h, 0, blocksize);
+	memcpy(h, state, bytes);
+	if(print == 1)
+		printf("input len is: %i, in blocks: %i\n", input_len, input_len/blocksize);
+
+	for(i=0;i<input_len/blocksize;i++) {
+		// only use the first bytes of the hash as state
+		// zero the others out
+		memset(key, 0, 16);
+		memcpy(key, h, bytes);
+		if(print == 1) {
+			hex_binary_to_string(h, h_hex, 16);
+			printf("%i: key is: 5s\n", i, h_hex);
+			memset(key, 0, 16);
+			memcpy(key, h, bytes);
+		}
+		aes_ecb(&input[i*blocksize], 16, h, key, blocksize, 1);
+	}
+	
+	// output only bytes bytes
+	memcpy(hash, h, bytes);
+	free(input_padded);
+}
+
+
+void cascaded_md_hash_functions(char *input, int input_len, char *hash)
+{
+	// F: cheap one: 2 bytes
+	// G: expensive: 16 bytes
+	char state[16];
+	memset(state, 0, 16);
+	md_hash_aes_128(input, input_len, state, hash, 2, 0);
+	md_hash_aes_128(input, input_len, state, &hash[2], 4, 0);
+}
+
+void add_one(unsigned char *s, int s_len)
+{
+	if(s[s_len-1] == 255) {
+		s[s_len-1] = 0x00;
+		add_one(s, s_len-1);
+	}
+	else {
+		s[s_len-1] += 1;
+	}
+}
+
+int char_array_is_max(unsigned char *s, int s_len)
+{
+	int i;
+
+	for(i=0;i<s_len;i++)
+		if(s[i] != 255)
+			return 0;
+
+	return 1;
+}
+
+int _2_collision_finding_machine(char *state, char *in1, char *in2, int bytes)
+{
+	// find a collsion for the given state
+	char hash1[16];
+	char hash2[16];
+	char op_state[16];
+
+	memset(in1, 0, 16);
+	memset(in2, 0, 16);
+
+	do {
+		if(char_array_is_max(in2, 16) == 1) {
+			add_one(in1, 16);
+			memset(in2, 0, 16);
+		}
+		add_one(in2, 16);
+		memcpy(op_state, state, 16);
+		md_hash_aes_128(in1, 16, state, hash1, bytes, 0);
+		memcpy(op_state, state, 16);
+		md_hash_aes_128(in2, 16, state, hash2, bytes, 0);
+	} while(memcmp(hash1, hash2, bytes) != 0 && (memcmp(in1, in2, 16) != 0));
+	memcpy(state, hash1, bytes);
+}
+
+
+char **collisions = NULL;
+unsigned int coll_numbers = 0;
+
+void generate_collsions(char *prefix, int pref_len, char *coll1, char *coll2, int length)
+{
+	if(length == 0) {
+		collisions[coll_numbers++] = prefix;
+		return;
+	}
+		
+	char *print = malloc(pref_len+16);
+	memcpy(print, prefix, pref_len);
+	memcpy(&print[pref_len], coll1, 16);
+	generate_collsions(print, pref_len+16, &coll1[16], &coll2[16], length-1);
+	char *print2 = malloc(pref_len+16);
+	memcpy(print2, prefix, pref_len);
+	memcpy(&print2[pref_len], coll2, 16);
+	generate_collsions(print2, pref_len+16, &coll1[16], &coll2[16], length-1);
+	//free(print);
+}
+
+/**
+  * This functions computes 2^n collision for a MD-Hash function given
+  * an 2 collision finding machine
+  **/
+int f(int n, int bytes)
+{
+	int i;
+	char state[16];
+	char *block1 = malloc(n*16);
+	char *block2 = malloc(n*16);
+	char *hex_block = malloc(n*32);
+	memset(state, 0, 16);
+
+	printf("find collision blocks..\n");
+	for(i=0;i<n;i++) {
+		_2_collision_finding_machine(state, &block1[i*16], &block2[i*16], bytes);
+	}
+	printf("generating collsions out of the blocks\n");
+	generate_collsions("", 0, block1, block2, n);
+	free(block1);
+	free(block2);
+}
+
+void print_collisions(int coll_len, int bytes)
+{
+	int i;
+        char *coll_hex = malloc(coll_len*2);
+        char hex_hash[32];
+        char hash[16];
+        char state[16];
+
+	for(i=0;i<coll_numbers;i++) { 
+		printf("processing collision at %p\n", collisions[i]);
+		memset(state,0,16);
+		md_hash_aes_128(collisions[i], coll_len, state, hash, bytes, 0);
+		hex_binary_to_string(collisions[i], coll_hex, coll_len);
+		hex_binary_to_string(hash, hex_hash, bytes);
+		printf("data: %s:\t hash: %s\n", coll_hex, hex_hash);
+	}
+//	free(coll_hex);
+}
+
+/**
+  * find a collsion under both of the cascaded hash function
+  *
+  **/
+void f_cascaded()
+{
+	// generate 2^b/2 collsions with the cheap one
+	int i,j;
+	char state[16];
+	int found_collisions_expensive = 0;
+	int bytes_f = 2;
+	int bytes_g = 3;
+	int __collisions = 1;
+	int coll_controller = 12;
+	for(i=0;i<coll_controller;i++)
+		__collisions *= 2;
+
+	collisions = malloc(sizeof(char *)*__collisions);
+	printf("generate %i collisions\n", __collisions);
+	f(coll_controller, bytes_f);
+	char **hashes = malloc(sizeof(char *)*__collisions);
+	// check if one also collide in the not so cheap one
+	printf("check for collisions with the expensive hash function...\n");
+	for(i=0;i<coll_numbers;i++) {
+		hashes[i] = malloc(bytes_g);
+		memset(state, 0, 16);
+		md_hash_aes_128(collisions[i], coll_controller*16, state, hashes[i], bytes_g, 0);
+
+		for(j=0;j<i;j++) {
+			if(i != j && memcmp(hashes[j], hashes[i], bytes_g) == 0) {
+				char hex_hash[32];
+				char *coll_hex = malloc(coll_controller*32);
+				printf("collision in expensive hash function found: %i, %i ", i, j);
+				hex_binary_to_string(hashes[i], hex_hash, bytes_g);
+				printf("with hash: %s\n", hex_hash);
+
+				hex_binary_to_string(collisions[i], coll_hex, coll_controller*16);
+				printf("data %i: %s\n", i, coll_hex);
+				hex_binary_to_string(collisions[j], coll_hex, coll_controller*16);
+				printf("data %i: %s\n", j, coll_hex);
+				found_collisions_expensive++;
+			}
+		}
+	}
+	printf("found %i collisions in the expensive one out of %i collision candiate\n", found_collisions_expensive, coll_numbers);
+}
+
+
+int part1()
+{
+	int i;
+	int n = 3;
+	int  bytes = 2;
+	int __coll_numbers = 2;
+	for(i=1;i<n;i++)
+		__coll_numbers = __coll_numbers * 2;
+	printf("2^n is: %i\n", __coll_numbers);
+	collisions = malloc(sizeof(char *)*__coll_numbers);
+
+	f(n, bytes);
+	printf("found collision: %i\n", coll_numbers);
+	print_collisions(n*16, bytes);
+
+}
+
+
+int part2()
+{
+	if(collisions != NULL)
+		free(collisions);
+	coll_numbers = 0;
+	f_cascaded();
+}
+
+int main()
+{
+	srand(time(NULL));
+
+	part1();
+	printf("\n\npart2:\n\n");
+	part2();
+}
-- 
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