用C++写一个简单的保密通讯系统

以下是一个简单的基于AES算法和Diffie-Hellman密钥交换算法的保密通讯系统的C++实现，其中使用了Crypto++库来实现AES加密和Diffie-Hellman密钥交换算法：

#include <iostream>
#include <string>
#include <cryptopp/aes.h>
#include <cryptopp/filters.h>
#include <cryptopp/modes.h>
#include <cryptopp/osrng.h>
#include <cryptopp/hex.h>
#include <cryptopp/dh.h>
#include <cryptopp/dh2.h>
#include <cryptopp/secblock.h>

using namespace CryptoPP;

void generateKeys(DH& dh, AutoSeededRandomPool& rnd, SecByteBlock& privKey, SecByteBlock& pubKey)
{
    dh.GenerateKeyPair(rnd, privKey, pubKey);
}

void computeSharedSecret(const SecByteBlock& privKey, const SecByteBlock& pubKey, SecByteBlock& sharedSecret)
{
    size_t len = std::min(privKey.size(), pubKey.size());
    for (size_t i = 0; i < len; i++) {
        sharedSecret[i] = privKey[i] ^ pubKey[i];
    }
}

std::string aesEncrypt(const std::string& plainText, const SecByteBlock& key)
{
    byte iv[AES::BLOCKSIZE];
    prng.GenerateBlock(iv, sizeof(iv));

    std::string cipherText;
    CBC_Mode<AES>::Encryption encryption(key, sizeof(key), iv);
    StringSource(plainText, true,
        new StreamTransformationFilter(encryption,
            new StringSink(cipherText)
        )
    );

    std::string encodedCipherText;
    StringSource(cipherText, true,
        new HexEncoder(
            new StringSink(encodedCipherText)
        )
    );

    std::string encodedIV;
    StringSource(iv, sizeof(iv), true,
        new HexEncoder(
            new StringSink(encodedIV)
        )
    );

    return encodedIV + encodedCipherText;
}

std::string aesDecrypt(const std::string& cipherText, const SecByteBlock& key)
{
    std::string decodedCipherText;
    StringSource(cipherText, true,
        new HexDecoder(
            new StringSink(decodedCipherText)
        )
    );

    byte iv[AES::BLOCKSIZE];
    StringSource(decodedCipherText.substr(0, AES::BLOCKSIZE), true,
        new HexDecoder(
            new ArraySink(iv, sizeof(iv))
        )
    );

    std::string recoveredText;
    CBC_Mode<AES>::Decryption decryption(key, sizeof(key), iv);
    StringSource(decodedCipherText.substr(AES::BLOCKSIZE), true,
        new StreamTransformationFilter(decryption,
            new StringSink(recoveredText)
        )
    );

    return recoveredText;
}

int main()
{
    AutoSeededRandomPool prng;

    // Diffie-Hellman密钥交换
    DH dh;
    dh.AccessGroupParameters().Initialize(CryptoPP::ASN1::secp256r1());
    SecByteBlock privKey(dh.PrivateKeyLength());
    SecByteBlock pubKey(dh.PublicKeyLength());
    generateKeys(dh, prng, privKey, pubKey);
    std::cout << "私钥：" << std::endl;
    StringSource(privKey, privKey.size(), true,
        new HexEncoder(
            new FileSink(std::cout)
        )
    );
    std::cout << "公钥：" << std::endl;
    StringSource(pubKey, pubKey.size(), true,
        new HexEncoder(
            new FileSink(std::cout)
        )
    );

    // 协商密钥
    SecByteBlock sharedSecret(dh.AgreedValueLength());
    computeSharedSecret(privKey, pubKey, sharedSecret);

    // 加密和解密
    std::string plainText = "Hello, World!";
    std::string cipherText = aesEncrypt(plainText, sharedSecret);
    std::cout << "密文：" << cipherText << std::endl;
    std::string recoveredText = aesDecrypt(cipherText, sharedSecret);
    std::cout << "明文：" << recoveredText << std::endl;

    return 0;
}

该程序使用了Crypto++库中的DH类和DH2类来实现Diffie-Hellman密钥交换算法，使用了AES类和CBC_Mode类来实现AES加密算法。在程序中，首先生成Diffie-Hellman密钥对，然后使用协商的密钥对明文进行加密和解密。需要注意的是，在实际应用中需要确保密钥的安全性，比如使用SSL/TLS协议来保证通讯的安全性。