Issues reimplementing some C# encryption stuff in C++ using cryptopp - c++

Question

So I have this piece of C# code:
void Decrypt(Stream input, Stream output, string password, int bufferSize) {
using (var algorithm = Aes.Create()) {
var IV = new byte[16];
input.Read(IV, 0, 16);
algorithm.IV = IV;
var key = new Rfc2898DeriveBytes(password, algorithm.IV, 100);
algorithm.Key = key.GetBytes(16);
using(var decryptor = algorithm.CreateDecryptor())
using(var cryptoStream = new CryptoStream(input, decryptor, CryptoStreamMode.Read)) {
CopyStream(cryptoStream, output, bufferSize);
}
}
}
and I am trying to translate this into C++ with CryptoPP.
So this is what I have written:
void decrypt(std::ifstream& in_file, std::ofstream& out_file, std::string_view password, size_t bufSize) {
using namespace CryptoPP;
// Get IV
byte iv[16];
in_file.read(reinterpret_cast<char*>(iv), sizeof(iv));
// Read cypher
std::string cypher;
while (in_file && cypher.size() != bufSize) {
char c;
in_file.read(&c, 1);
cypher.push_back(c);
}
// Get key
byte key[16];
PKCS5_PBKDF2_HMAC<SHA1> pbkdf2;
pbkdf2.DeriveKey(key, sizeof(key), 0, reinterpret_cast<const byte*>(password.data()), password.size(), iv, sizeof(iv), 100);
// Decrypt
CTR_Mode<AES>::Decryption decrypt(key, sizeof(key), iv);
std::string output;
StringSource(cypher, true, new StreamTransformationFilter(decrypt, new StringSink(output)));
// Write output to file
out_file.write(output.data(), output.size());
}
However, from this function, I am only getting back trash data. What could I be doing wrong?
Thanks
Tuxifan!

Answer 1

So I found the solution! First of all, as #mbd mentioned, C# uses CBC by default. Additionally, I need to cut away the rest of the data like this:
while ((cipher.size() % 16) != 0) {
cipher.pop_back();
}