Use OpenSSL to encrypt file contents in c++ - c++

Question

I am creating an application which encrypts some text and then it writes it to a file.
The problem I am seeing is that when I run the encryption more than once, I am only able to decrypt the text I added firstly.
This is the code:
encrypt and decrypt functions:
std::vector<char> CryptCTR::encrypt(const char* textToEncrypt)
{
size_t sizeToEncrypt = strlen(textToEncrypt);
std::vector< char > encryptedText ( sizeToEncrypt );
unsigned long long lengthProcessed = 0;
do {
auto maxCipherLen = sizeToEncrypt > std::numeric_limits<int>::max() ? std::numeric_limits<int>::max() : sizeToEncrypt;
encryptCTR(textToEncrypt,
&encryptedText[lengthProcessed],
maxCipherLen);
lengthProcessed += maxCipherLen;
sizeToEncrypt -= maxCipherLen;
} while (sizeToEncrypt > 0);
return encryptedText;
}
std::vector<char> CryptCTR::decrypt(const char* textToDecrypt/*, SecurityKey& key*/)
{
size_t sizeToDecrypt = strlen(textToDecrypt);
unsigned long long lengthProcessed = 0;
std::vector< char > recoveredText ( sizeToDecrypt );
do
{
int maxPlainLen = sizeToDecrypt > std::numeric_limits<int>::max() ? std::numeric_limits<int>::max() : sizeToDecrypt;
decryptCTR(textToDecrypt,
&recoveredText[lengthProcessed],
sizeToDecrypt/*, &key*/);
lengthProcessed += maxPlainLen;
sizeToDecrypt -= maxPlainLen;
} while(sizeToDecrypt > 0);
return recoveredText;
}
void CryptCTR::encryptCTR ( const char* pvBufferIn, char* pvBufferOut, unsigned long dwLength )
{
CRYPTO_ctr128_encrypt(
(const unsigned char*)pvBufferIn,
(unsigned char*)pvBufferOut,
dwLength,
(AES_KEY*)&m_aesSecurityKey.getKey().front(),
state.ivec,
state.ecount,
&state.num,
(block128_f)AES_encrypt);
}
void CryptCTR::decryptCTR ( const char* pvBufferIn, char* pvBufferOut, unsigned long dwLength)
{
CRYPTO_ctr128_encrypt((const unsigned char*)pvBufferIn,
(unsigned char*)pvBufferOut,
dwLength,
(AES_KEY*)&m_aesSecurityKey.getKey().front(),
state.ivec,
state.ecount,
&state.num,
(block128_f)AES_encrypt);
}
If I encrypt decrypt and then decrypt once it works. But the problem starts when I try to do this:
// ENCODING //
{
for (int i=0;i<kStrVector.size();++i)
{
CryptCTR cryptCtr;
//SecurityKey aesExampleKey ( std::vector< char > (1) );
cryptCtr.initializeAesKey(/*&aesExampleKey*/);
const char* textToEncrypt = kStrVector.at(i).c_str();
auto output = cryptCtr.encrypt(textToEncrypt/*, aesExampleKey*/);
std::ofstream out("encoded-append.dat", std::ios::app);
for (const auto &e : output)
out << e;
out.close();
}
}
// DECODING //
{
CryptCTR cryptCtr;
std::ifstream t("encoded-append.dat");
std::stringstream buffer;
buffer << t.rdbuf();
std::string ss = buffer.str();
//SecurityKey aesExampleKey2 ( std::vector< char > (1) );
cryptCtr.initializeAesKey(/*&aesExampleKey2*/);
//initializeAesKey ( (const unsigned char*)CRYPT_AES_KEY, sizeof(CRYPT_AES_KEY) * 8, &aesExmapleKey2 );
auto output = cryptCtr.decrypt(buffer.str().c_str()/*, aesExampleKey2*/);
std::string s2(output.begin(), output.end());
std::ofstream out("decoded-append.dat");
out << s2;
out.close();
}
Then the program is able to decrypt only the text written in the first iteration.
Could you please tell me what I have wrong in my code?
Thanks in advance and regards

Answer 1

Shot in the dark guess, but encryption is typically binary. As such your encrypted output will have null char bytes inside it. So if you treat the encrypted data as a null terminated string, you risk losing data. Hence, your decrypt function should taking in a vector instead of a null terminated string.
Also, don't forget to pass ios_base::binary into the constructor of your ifstream and ofstream constructors for reading/writing to your .dat file. This will be important if you want your code to run reliably on Windows.