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/lib2.c | 39 +++++++++++++++++++++++++++++++++++++++
 1 file changed, 39 insertions(+)

(limited to 'lib/lib2.c')

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;
+
+}
-- 
cgit v1.2.3-70-g09d2