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Posted 14 Jun 2006

Build your own cryptographically safe server/client protocol

, 21 Jun 2006
This article presents all you need to implement your own secure protocol using variable keysize RSA encryption/decryption, digital signing, multi precision library, Diffie-Hellman key exchange, Rijndael, and more. Everything is converged into a secure IOCP client/server chat server.

#ifndef __RIJNDAEL_H__
#define __RIJNDAEL_H__
#include "stdafx.h"

// If you are using .net. 
//using namespace std;
#include <exception>
//#include <cstring>

//Rijndael (pronounced Reindaal) is a block cipher, designed by Joan Daemen and Vincent Rijmen as a candidate algorithm for the AES.
//The cipher has a variable block length and key length. The authors currently specify how to use keys with a length
//of 128, 192, or 256 bits to encrypt blocks with al length of 128, 192 or 256 bits (all nine combinations of
//key length and block length are possible). Both block length and key length can be extended very easily to
// multiples of 32 bits.
//Rijndael can be implemented very efficiently on a wide range of processors and in hardware. 
//This implementation is based on the Java Implementation used with the Cryptix toolkit found at:
//Java code authors: Raif S. Naffah, Paulo S. L. M. Barreto
//This Implementation was tested against KAT test published by the authors of the method and the
//results were identical.

		char szHex[33];
		//One block testing
		CRijndael oRijndael;
		oRijndael.MakeKey("abcdefghabcdefgh", "\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0", 16, 16);
		char szDataIn[] = "aaaaaaabbbbbbbb";
		char szDataOut[17] = "\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0";
		oRijndael.EncryptBlock(szDataIn, szDataOut);
		CharStr2HexStr((unsigned char*)szDataIn, szHex, 16);
		cout << szHex << endl;
		cout << szDataIn << endl;
		CharStr2HexStr((unsigned char*)szDataOut, szHex, 16);
		cout << szHex << endl;
		cout << szDataOut << endl;
		memset(szDataIn, 0, 16);
		oRijndael.DecryptBlock(szDataOut, szDataIn);
		CharStr2HexStr((unsigned char*)szDataIn, szHex, 16);
		cout << szHex << endl;
		cout << szDataIn << endl;
		int i=0;
		cin >> i;
	catch(exception& roException)
		cout << roException.what() << endl;

class CRijndael
	//Operation Modes
	//The Electronic Code Book (ECB), Cipher Block Chaining (CBC) and Cipher Feedback Block (CFB) modes
	//are implemented.
	//In ECB mode if the same block is encrypted twice with the same key, the resulting
	//ciphertext blocks are the same.
	//In CBC Mode a ciphertext block is obtained by first xoring the
	//plaintext block with the previous ciphertext block, and encrypting the resulting value.
	//In CFB mode a ciphertext block is obtained by encrypting the previous ciphertext block
	//and xoring the resulting value with the plaintext.
	enum { ECB=0, CBC=1, CFB=2 };

	enum { DEFAULT_BLOCK_SIZE=16 };
	enum { MAX_BLOCK_SIZE=32, MAX_ROUNDS=14, MAX_KC=8, MAX_BC=8 };

	//Auxiliary Functions
	//Multiply two elements of GF(2^m)
	static int Mul(int a, int b)
		return (a != 0 && b != 0) ? sm_alog[(sm_log[a & 0xFF] + sm_log[b & 0xFF]) % 255] : 0;

	//Convenience method used in generating Transposition Boxes
	static int Mul4(int a, char b[])
		if(a == 0)
			return 0;
		a = sm_log[a & 0xFF];
		int a0 = (b[0] != 0) ? sm_alog[(a + sm_log[b[0] & 0xFF]) % 255] & 0xFF : 0;
		int a1 = (b[1] != 0) ? sm_alog[(a + sm_log[b[1] & 0xFF]) % 255] & 0xFF : 0;
		int a2 = (b[2] != 0) ? sm_alog[(a + sm_log[b[2] & 0xFF]) % 255] & 0xFF : 0;
		int a3 = (b[3] != 0) ? sm_alog[(a + sm_log[b[3] & 0xFF]) % 255] & 0xFF : 0;
		return a0 << 24 | a1 << 16 | a2 << 8 | a3;


	virtual ~CRijndael();

	//Expand a user-supplied key material into a session key.
	// key        - The 128/192/256-bit user-key to use.
	// chain      - initial chain block for CBC and CFB modes.
	// keylength  - 16, 24 or 32 bytes
	// blockSize  - The block size in bytes of this Rijndael (16, 24 or 32 bytes).
	void MakeKey(char const* key, char const* chain, int keylength=DEFAULT_BLOCK_SIZE, int blockSize=DEFAULT_BLOCK_SIZE);

	// Functions used to create a CRC16 checksum 
	// Is usefull to determine if the decryptionn went ok or not. 
	void crc16_final(unsigned short *uCrc16);
	void crc16_update(unsigned short *uCrc16, unsigned char *pBuffer, unsigned long uBufSize);
	void crc16_init(unsigned short *uCrc16);
	//Auxiliary Function
	inline void Xor(char* buff, char const* chain)
			throw exception(sm_szErrorMsg1);
		for(int i=0; i<m_blockSize; i++)
			*(buff++) ^= *(chain++);	

	//Convenience method to encrypt exactly one block of plaintext, assuming
	//Rijndael's default block size (128-bit).
	// in         - The plaintext
	// result     - The ciphertext generated from a plaintext using the key
	void DefEncryptBlock(char const* in, char* result);

	//Convenience method to decrypt exactly one block of plaintext, assuming
	//Rijndael's default block size (128-bit).
	// in         - The ciphertext.
	// result     - The plaintext generated from a ciphertext using the session key.
	void DefDecryptBlock(char const* in, char* result);

	//Encrypt exactly one block of plaintext.
	// in           - The plaintext.
    // result       - The ciphertext generated from a plaintext using the key.
    void EncryptBlock(char const* in, char* result);
	//Decrypt exactly one block of ciphertext.
	// in         - The ciphertext.
	// result     - The plaintext generated from a ciphertext using the session key.
	void DecryptBlock(char const* in, char* result);

	void Encrypt(char const* in, char* result, size_t n, int iMode=ECB);
	void Decrypt(char const* in, char* result, size_t n, int iMode=ECB);

	//Get Key Length
	int GetKeyLength()
			throw exception(sm_szErrorMsg1);
		return m_keylength;

	//Block Size
	int	GetBlockSize()
			throw exception(sm_szErrorMsg1);
		return m_blockSize;
	//Number of Rounds
	int GetRounds()
			throw exception(sm_szErrorMsg1);
		return m_iROUNDS;

	void ResetChain()
		memcpy(m_chain, m_chain0, m_blockSize);

	//Null chain
	static char const* sm_chain0;

	static const unsigned short crc16tab[256];
	static const int sm_alog[256];
	static const int sm_log[256];
	static const char sm_S[256];
    static const char sm_Si[256];
    static const int sm_T1[256];
    static const int sm_T2[256];
    static const int sm_T3[256];
    static const int sm_T4[256];
    static const int sm_T5[256];
    static const int sm_T6[256];
    static const int sm_T7[256];
    static const int sm_T8[256];
    static const int sm_U1[256];
    static const int sm_U2[256];
    static const int sm_U3[256];
    static const int sm_U4[256];
    static const char sm_rcon[30];
    static const int sm_shifts[3][4][2];
	//Error Messages
	static char const* sm_szErrorMsg1;
	static char const* sm_szErrorMsg2;
	//Key Initialization Flag
	bool m_bKeyInit;
	//Encryption (m_Ke) round key
	int m_Ke[MAX_ROUNDS+1][MAX_BC];
	//Decryption (m_Kd) round key
    int m_Kd[MAX_ROUNDS+1][MAX_BC];
	//Key Length
	int m_keylength;
	//Block Size
	int	m_blockSize;
	//Number of Rounds
	int m_iROUNDS;
	//Chain Block
	char m_chain0[MAX_BLOCK_SIZE];
	char m_chain[MAX_BLOCK_SIZE];
	//Auxiliary private use buffers
	int tk[MAX_KC];
	int a[MAX_BC];
	int t[MAX_BC];

#endif // __RIJNDAEL_H__

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About the Author

Program Manager
Sweden Sweden
Amin Gholiha.
- Master of Science in Information Technology.
- Degree of Master of Education.
Knowledge/interest: programming (.NET,Visual, C#/C++), neural network, mathematical modeling, signal processing, sequence analysis, pattern recognition,robot technology, system design, security and business management systems. For business proposal email, all other emails will be ignored.
Current Work:
Project Manager (the best free e-signature tool)

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