From 27a1b8050d2170b40024fe82cb27088f3c676f26 Mon Sep 17 00:00:00 2001
From: Benedict <benedict@0xb8000.de>
Date: Mon, 21 Mar 2016 21:32:46 +0100
Subject: completed set2, challenge 10

---
 lib/lib.c  | 51 +++++++++++++++++++++++++++++++++++++++++++++++++++
 lib/lib.h  |  2 +-
 lib/lib2.c | 39 +++++++++++++++++++++++++++++++++++++++
 lib/lib2.h |  5 +++--
 4 files changed, 94 insertions(+), 3 deletions(-)

(limited to 'lib')

diff --git a/lib/lib.c b/lib/lib.c
index c2ee753..0eb5be8 100644
--- a/lib/lib.c
+++ b/lib/lib.c
@@ -471,3 +471,54 @@ char brute_force_single_byte_xor(char *string, int length, struct key_and_freq *
 
 	return key;
 }
+
+
+/**
+ * reads a base64 an decode it
+ * @param file path of the file
+ * @param out writes file in this buffer, allocated by this method
+ */
+int read_base64_file(const char *file, char **out)
+{
+	char ch;
+	FILE *fp;
+	int file_size = 60;
+	char *new_file_content;
+	int file_pos = 0;
+
+	fp = fopen(file, "r");
+
+	if (fp == NULL) {
+		printf("Error open file\n");
+		exit(1);
+	}
+	
+	*out = malloc(file_size);
+
+	if (*out == NULL) {
+		perror("out of memory");
+		exit(1);
+	}
+
+	// read data and decode it from base64
+	while ( (ch = fgetc(fp)) != EOF) {
+		// ignore new lines as this is part of base64
+		if (ch == '\n' || ch == '\r')
+			continue;
+
+		if (file_pos+1 >= file_size) {
+			new_file_content = realloc(*out, (file_size+60));
+			if (new_file_content != NULL) {
+				*out = new_file_content;
+				file_size += 60;
+			}
+			else {
+				printf("error allocating memory\n");
+				exit(1);
+			}
+		}
+		(*out)[file_pos++] = ch;
+	}
+	return file_pos;
+
+}
diff --git a/lib/lib.h b/lib/lib.h
index 3e2a309..cca5fb0 100644
--- a/lib/lib.h
+++ b/lib/lib.h
@@ -22,6 +22,6 @@ void print_base64_string(char *string);
 int hamming_distance_equal_length(char *string1, char *string2, int length);
 char brute_force_single_byte_xor(char *string, int length, struct key_and_freq *tmp);
 int isprintable(char *string, int length);
-
+int read_base64_file(const char *file, char **out);
 
 #endif /* __CYRPTO_LIB__ */
diff --git a/lib/lib2.c b/lib/lib2.c
index 86dd823..fe65bb8 100644
--- a/lib/lib2.c
+++ b/lib/lib2.c
@@ -1,4 +1,5 @@
 #include "lib2.h"
+#include "lib.h"
 
 /**
  * appends PKCS#7 padding to string. devide string in blocks of size blocksize
@@ -21,3 +22,41 @@ char *pkcs7_padding(char *string, int length_string, int blocksize)
 
 	return result;
 }
+
+/**
+ * decrypts content which is encrypted in AES CBC mode
+ * @param in input content
+ * @param length_in length of parametere in
+ * @param out place where the decrypted content should be written to
+ * @param string_key key with which the content in in has been decrypted
+ * @param iv initalization vector
+ */
+int aes_cbc(char *in, int length_in, char *out, unsigned char *string_key, char *init_vector)
+{
+	char iv[16];
+	AES_KEY key;
+	int number_blocks = length_in / 16;
+	int i, j;
+	unsigned char ciphertext[128+1];
+	unsigned char tmp_after_aes[128+1];
+	unsigned char cleartext[128+1];
+	// set the key and bits
+	AES_set_decrypt_key(string_key, 128, &key);
+
+	memcpy(init_vector, iv, 16);
+
+	// implement cbc mode
+	for(i=0;i<number_blocks;i++) {
+		//do aes decryption
+		AES_decrypt(&in[i*16], tmp_after_aes, &key);
+		// xor
+		xor_string(iv, tmp_after_aes, &out[i*16], 16, 16);
+		// this ciphertext block is the next iv
+		for(j=0;j<16;j++) {
+			iv[j] = in[i*16+j];
+		}
+	}
+
+	return 0;
+
+}
diff --git a/lib/lib2.h b/lib/lib2.h
index 818558d..fabca8a 100644
--- a/lib/lib2.h
+++ b/lib/lib2.h
@@ -1,11 +1,12 @@
 #ifndef __LIB2_H__
-#define __LIN2_H__
+#define __LIB2_H__
 
 #include <stdio.h>
 #include <string.h>
 #include <stdlib.h>
+#include <openssl/aes.h>
 
 char *pkcs7_padding(char *string, int length_string, int blocksize);
-
+int aes_cbc(char *in, int length_in, char *out, unsigned char *string_key, char *init_vector);
 
 #endif
-- 
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