c++ - 使用 Crypto++ 解密时原始文本末尾的车库冗余字符

Question

我正在使用 Crypto++，CTR 模式，在 C++ 中加密和解密文本。一切似乎都有效 99%。加密成功，解密也返回原始文本，但我在解密文本的末尾给出了一些额外的随机垃圾冗余文本，如“ð”。这个额外的部分是每次我运行代码时随机生成的。我的代码有问题吗？

将字符串加密为字符串

string  encryptString(string plain, byte key[], int sizeKey, byte iv[], int sizeIV){
    string cipher;
    try{
        CTR_Mode< AES >::Encryption e;
        e.SetKeyWithIV(key, sizeKey, iv, sizeIV);

        // The StreamTransformationFilter removes
        //  padding as required.
        StringSource s(plain, true,
            new StreamTransformationFilter(e,
                new StringSink(cipher)
                ) 
            ); 

#if 0
        StreamTransformationFilter filter(e);
        filter.Put((const byte*)plain.data(), plain.size());
        filter.MessageEnd();

        const size_t ret = filter.MaxRetrievable();
        cipher.resize(ret);
        filter.Get((byte*)cipher.data(), cipher.size());
#endif
        return cipher;
    }
    catch (const CryptoPP::Exception& e)
    {
        cerr << e.what() << endl;
        return NULL;
    }
}

将加密后的字符串解密为字符串

string  decryptString(string cipher, byte key[], int sizeKey, byte iv[], int sizeIV){
    string reco ="";
    try{
        CTR_Mode< AES >::Decryption d;
        d.SetKeyWithIV(key, sizeKey, iv, sizeIV);

        StringSource s(cipher, true,
            new StreamTransformationFilter(d,
                new StringSink(reco)
                ) 
            ); 

    }
    catch (const CryptoPP::Exception& e)
    {
        cerr << e.what() << endl;
    }
    return reco;

}

包装上面的 encryptString 函数。

char* encrypt(char * plainText, byte key[], int sizeKey, byte iv[], int sizeIV, long &len){
    string cipher = encryptString(plainText, key, sizeKey, iv, sizeIV);
    len = cipher.size() + 1;
    char * writable = new  char[len];
    std::copy(cipher.begin(), cipher.end(), writable);
    writable[len] = '\0'; // don't forget the terminating 0
    return writable;
 }

包装上面的 decryptString 函数。

char* decrypt(char * cipher,  byte key[], int sizeKey, byte iv[], int sizeIV, long len){
    string ss(cipher, len);
    long lengSS = ss.length();
    string recovered = decryptString(ss, key, sizeKey, iv, sizeIV);
    char * writable = new char[recovered.size() + 1];
    std::copy(recovered.begin(), recovered.end(), writable);
    writable[recovered.size()] = '\0'; // don't forget the terminating 0
    return writable;
}

我的测试脚本很简单。读取some.txt内容(“我爱你”)，写入s1.txt，检查读取是否正确。加密、解密，然后将恢复的文本写入另一个文件 (d1.txt)。

int main(int argc, char* argv[])
{
    AutoSeededRandomPool prng;

    byte key[AES::DEFAULT_KEYLENGTH] = { '1', '2', '3', '4', '5', '6', '7', '8', '1', '2', '3', '4', '5', '6', '7', '8' };
    //prng.GenerateBlock(key, sizeof(key));

    byte iv[AES::BLOCKSIZE] = { '8', '7', '6', '5', '4', '3', '2', '1', '8', '7', '6', '5', '4', '3', '2', '1' };
    prng.GenerateBlock(iv, sizeof(iv));
    long size = 0;
    char * s1 = FileUtil::readAllByte("some.txt");
    //Result: s1.txt content is "I love you"

    long len = 0;
    char* result1 = encrypt(s1, key, sizeof(key), iv, sizeof(iv), len);
    //Result: result1 is a bunch of ciphered characters

    cout << "desc" << endl;
    char* recovered1 = decrypt(result1, key, sizeof(key), iv, sizeof(iv), len);
    //Result: recovered1="I love youð". Generally, it has form of "I love youX"
    //X can be any garbage chatacter, and each time I run the code, X is one different
    //character.
}

根据接受的答案，解决方案是:像这样更新我的 encrypt():

char* encrypt(char * plainText, byte key[], int sizeKey, byte iv[], int sizeIV, long &len){
    string cipher = encryptString(plainText, key, sizeKey, iv, sizeIV);
    FileUtil::writeFile("ss1.txt", cipher, cipher.length());
    len = cipher.size() ;
     char * writable = new  char[len];
    std::copy(cipher.begin(), cipher.end(), writable);
    writable[len] = '\0'; // don't forget the terminating 0
    FileUtil::writeFile("w1.txt",writable, len);

    return writable;
}

只需分配可写的长度 = 密码的长度。将终止符设置为 writeble[len]

Answer 1

当您遇到缓冲区溢出和未终止的字符串时，往往会发生这种情况。如果我们查看您的 encrypt 函数，我们会看到缓冲区溢出:

len = cipher.size() + 1;
char * writable = new  char[len];
std::copy(cipher.begin(), cipher.end(), writable);
writable[len] = '\0';

看到这里你分配了 len 个字节，其中 len 比 cipher 大一个。但是，当您终止字符串时，您正在使用 len 来索引越界。

您应该使用 len-1 或 cipher.size() 作为终止符索引。