#include "lib2.h"
#include "lib.h"

/**
 * appends PKCS#7 padding to string. devide string in blocks of size blocksize
 * and append to last block so that it is also of blocksize length
 */

char *pkcs7_padding(char *string, int length_string, int blocksize)
{
	char *result = NULL;
	int i;
	int value = blocksize - (length_string % blocksize);

	result = malloc(length_string+value+1);
	memcpy(result, string, length_string);

	for(i=0;i<value;i++) {
		result[length_string+i] = (char) value;
	}
	result[length_string+i] = '\0';

	return result;
}

/**
 * unpadd a string
 * @param in string which should be unpadded
 * @param length_in length of paramter length_in
 * @param unpadded place where the unpadded text should be stored
 * @param blocksize size of the block to which should be padded
 */
int valid_pkcs7_padding(const char *in, int length_in, char *unpadded, int blocksize)
{
	int i, padding_length;
	// look how many equal bytes are at the end
	// ignore last byte \0
	for(i=length_in-1;i>0;i--) {
		if(in[i] != in[i-1])
			break;
	}
	
	padding_length = length_in - i;
	if ((length_in % padding_length) != 0)
		return 0;

	if(in[length_in-1] != padding_length)
		return 0;

	memcpy(unpadded, in, (length_in-padding_length));
	return 1;
}

/**
 * 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;

}