从磁盘而不是内存加密和解密文件？

Question

When I am trying to encrypt and decrypt a 250MB file using AES algorithm, I am getting the following error. When I am trying with datasets less than 250, I am able to get the output.

Answer 1

From the COMMENTS:

string cipher, encoded, recovered;
FileSource file("C:/Users/sai/desktop/RA/250.avi", true, new StringSink(plain));

This may or may not work depending on several factors. On a desktop or server you should have no problems because it will have a lot of RAM and a swap file.

On a mobile device it will probably die if the file is large. If it dies then the problem is probably because StringSink is an in-memory string but the device ran out of memory.

---

From the COMMENTS:

... Do I need to break the file into chunks and then encrypt and decrypt?

No, you should not need to break the file into chunks. The FileSource will do it for you. It will break the data into 4096 chunks, if I recall correctly. What you probably need to do is switch from a StringSink to a FileSink .

Also see Pumping Data | Encryption on the Crypto++ wiki. Here's the sample provided:

inline bool EndOfFile(const FileSource& file)
{
  std::istream* stream = const_cast<FileSource&>(file).GetStream();
  return stream->eof();
}

int main(int argc, char* argv[])
{
  try
  {
      byte key[AES::DEFAULT_KEYLENGTH]={}, iv[AES::BLOCKSIZE]={};
      CTR_Mode<AES>::Encryption encryptor;
      encryptor.SetKeyWithIV(key, sizeof(key), iv);

      MeterFilter meter;
      StreamTransformationFilter filter(encryptor);

      FileSource source("plain.bin", false);
      FileSink sink("cipher.bin");

      source.Attach(new Redirector(filter));
      filter.Attach(new Redirector(meter));
      meter.Attach(new Redirector(sink));

      const word64 BLOCK_SIZE = 4096;
      word64 processed = 0;

      while(!EndOfFile(source) && !source.SourceExhausted())
      {
        source.Pump(BLOCK_SIZE);
        filter.Flush(false);

        processed += BLOCK_SIZE;

        if (processed % (1024*1024*10) == 0)
          cout << "Processed: " << meter.GetTotalBytes() << endl;
      }

      // Signal there is no more data to process.
      // The dtor's will do this automatically.
      filter.MessageEnd();
  }
  catch(const Exception& ex)
  {
    cerr << ex.what() << endl;
  }

  return 0;
}

---

From the TITLE:

[How to] encrypt and decrypt a file from disk rather than memory?

Try something like the following. Your code is missing the encryption or decryption object, so be sure to include one in the real code.

FileSource file("C:/Users/sai/desktop/RA/250.avi", true, new FileSink("C:/Users/sai/desktop/RA/250.avi.enc"));

Or, you can use the code that shows you how to manually pump data.

---

From the COMMENTS:

int start_s = clock();

Also see Benchmarks | Sample Program on the Crypto++ wiki. Here's the sample provided:

const double runTimeInSeconds = 3.0;
const double cpuFreq = 2.7 * 1000 * 1000 * 1000;

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

    SecByteBlock key(16);
    prng.GenerateBlock(key, key.size());

    CTR<AES>::Encryption cipher;
    cipher.SetKeyWithIV(key, key.size(), key);

    const int BUF_SIZE = RoundUpToMultipleOf(2048U,
        dynamic_cast<StreamTransformation&>(cipher).OptimalBlockSize());

    AlignedSecByteBlock buf(BUF_SIZE);
    prng.GenerateBlock(buf, buf.size());

    double elapsedTimeInSeconds;
    unsigned long i=0, blocks=1;

    ThreadUserTimer timer;
    timer.StartTimer();

    do
    {
        blocks *= 2;
        for (; i<blocks; i++)
            cipher.ProcessString(buf, BUF_SIZE);
        elapsedTimeInSeconds = timer.ElapsedTimeAsDouble();
    }
    while (elapsedTimeInSeconds < runTimeInSeconds);

    const double bytes = static_cast<double>(BUF_SIZE) * blocks;
    const double ghz = cpuFreq / 1000 / 1000 / 1000;
    const double mbs = bytes / elapsedTimeInSeconds / 1024 / 1024;
    const double cpb = elapsedTimeInSeconds * cpuFreq / bytes;

    std::cout << cipher.AlgorithmName() << " benchmarks..." << std::endl;
    std::cout << "  " << ghz << " GHz cpu frequency"  << std::endl;
    std::cout << "  " << cpb << " cycles per byte (cpb)" << std::endl;
    std::cout << "  " << mbs << " MiB per second (MiB)" << std::endl;   

    return 0;
}