From 4e0e29f48f797206a21aa5ba7855ffde72e85cf9 Mon Sep 17 00:00:00 2001
From: Benedict <benedict@0xb8000.de>
Date: Thu, 4 Aug 2016 19:24:17 +0200
Subject: completed set3, challenge 20

---
 set3/Makefile |  8 ++++++--
 set3/task20.c | 64 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 70 insertions(+), 2 deletions(-)
 create mode 100644 set3/task20.c

(limited to 'set3')

diff --git a/set3/Makefile b/set3/Makefile
index d3b3f03..a6ed5fc 100644
--- a/set3/Makefile
+++ b/set3/Makefile
@@ -3,12 +3,16 @@ CC=gcc
 CFLAGS := -g $(CFLAGS) 
 CLIBS=`pkg-config --cflags --libs libcrypto`
 
-all: task17 task18
+all: task17 task18 task19 task20
 
 task17:
 	$(CC) $(CFLAGS) task17.c $(LIB) $(CLIBS) -o task17
 
 task18:
 	$(CC) $(CFLAGS) task18.c $(LIB) $(CLIBS) -o task18
+task19:
+	$(CC) $(CFLAGS) task19.c $(LIB) $(CLIBS) -o task19
+task20:
+	$(CC) $(CFLAGS) task20.c $(LIB) $(CLIBS) -o task20
 clean:
-	rm task17 task18
+	rm task17 task18 task19 task20
diff --git a/set3/task20.c b/set3/task20.c
new file mode 100644
index 0000000..7ab24de
--- /dev/null
+++ b/set3/task20.c
@@ -0,0 +1,64 @@
+#include "../lib/lib.h"
+#include "../lib/lib2.h"
+#include "../lib/lib3.h"
+#include <time.h>
+
+#define CHALLENGE20_FILE_NR 60
+int main()
+{
+	int i;
+	char **file = malloc(sizeof(char *)*CHALLENGE20_FILE_NR);
+	int length_file[CHALLENGE20_FILE_NR];
+	int length[CHALLENGE20_FILE_NR];
+	char **plaintext= malloc(sizeof(char *)*CHALLENGE20_FILE_NR);
+	char **ciphertext= malloc(sizeof(char *)*CHALLENGE20_FILE_NR);
+	char filename[] = "./task20_data/task20_00";
+
+	char nonce[16];
+	int min_length = 9999999;
+	generate_random_bytes(key, 16);
+	generate_random_bytes(nonce, 16);
+
+	for(i=0;i<CHALLENGE20_FILE_NR;i++) {
+		filename[strlen(filename)-1] = ((i % 10)+ '0');
+		filename[strlen(filename)-2] = ((i / 10) + '0');
+		length_file[i] = read_base64_file(filename, &file[i]);
+		plaintext[i] = malloc(length_file[i]);
+		length[i] = decode_base64(file[i], plaintext[i]);
+		if(length[i] < min_length)
+			min_length = length[i];
+		ciphertext[i] = malloc(length[i]);
+		aes_ctr(plaintext[i], length[i], ciphertext[i], key, nonce);
+	}
+
+	printf("smallest string : %i\n", min_length);
+	// let the cracking begin
+
+	// merge all the chunks and then do the vingere chiffre break
+	// so we have 60 blocks and the key length is min_length
+	// no need 
+	char *merged = malloc(min_length*CHALLENGE20_FILE_NR);
+	for(i=0;i<CHALLENGE20_FILE_NR;i++) {
+		memcpy(&merged[i*min_length], ciphertext[i], min_length);
+	}
+
+	char **blocks = transpose_blocks(merged, min_length,
+			(min_length*CHALLENGE20_FILE_NR));
+
+	// run the normal ceasr chiffre attack
+	char restored_keystream[min_length];
+	struct key_and_freq tmp_NOT_USED_HERE;
+	for(i=0;i<min_length;i++) {
+		restored_keystream[i] = brute_force_single_byte_xor(
+				blocks[i], min_length, &tmp_NOT_USED_HERE);
+	}
+
+	// xor ciphertext against keystream
+	char *restored_plaintext = malloc(min_length);
+	for(i=0;i<CHALLENGE20_FILE_NR;i++) {
+		xor_string(ciphertext[i], restored_keystream, restored_plaintext,
+				min_length, min_length);
+		printf("%s\n", plaintext[i]);
+		printf("%s\n", restored_plaintext);
+	}
+}
-- 
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