// onetimepad.cpp
//
// Copyright (C) 2006-2020 MicroNeil Research Corporation.
//
// This software is released under the MIT license. See LICENSE.TXT.

#include "onetimepad.hpp"
#include "timing.hpp"

/*
class OneTimePad {                                                              // One Time Pad generator.
  private:
    MANGLER PagGenerator;                                                       // MANGLER as a PRNG.
    PadBuffer Entropy(int Length = 1024);                                       // System entropy source.

  public:
**    OneTimePad();                                                               // Constructor initializes w/ Entropy.
**    PadBuffer Pad(int Length);                                                  // Get a pad of Length.
**    void addEntropy();                                                          // Add entropy from the system source.
**    void addEntropy(PadBuffer Entropy);                                         // Add entropy from this source.

};
*/

////////////////////////////////////////////////////////////////////////////////
// Platform specific strong entropy sourcing.

#ifdef WIN32

//// WIN32 Strong Entropy Source == CryptGenRandom() ///////////////////////////

#include <windows.h>
#include <wincrypt.h>

namespace codedweller {

PadBuffer OneTimePad::Entropy(int Length) {                                     // Get a PadBuffer full of randomness.
    PadBuffer Buffer(Length, 0);                                                // Start by initializing the buffer.
    HCRYPTPROV provider = 0;                                                    // We will need a handle for the source.

	if(                                                                         // Try a two different sources.
	  !CryptAcquireContext(                                                     // If we can get a hardware source
	    &provider, NULL, NULL, PROV_INTEL_SEC, CRYPT_VERIFYCONTEXT)) {          // from an intel CPU then use that first.

		if(                                                                     // If we can't use get that
		  !CryptAcquireContext(                                                 // entropy source for some reason then
		    &provider, NULL, NULL, PROV_RSA_FULL, CRYPT_VERIFYCONTEXT)) {       // try to use the RSA source. That should
                                                                                // always work, but if it doesn't we need
			  provider = 0;                                                     // to know about it so we'll have a zero
		}                                                                       // handle.
	}

    if(0 != provider) {                                                         // If we did get a good source then
        CryptGenRandom (provider, Length, (BYTE*)&Buffer[0]);                   // grab the random bit required and
        CryptReleaseContext(provider,0);                                        // then let the provider go.
        StrongEntropyFlag = true;                                               // We DID get strong entropy.
    }
    else {                                                                      // If we did not get a good source
        StrongEntropyFlag = false;                                              // then we are not strong.
    }

    return Buffer;                                                              // Return the data we got.
}

} // End namespace codddweller

#else

//// *NIX Strong Entropy Source == /dev/urandom ////////////////////////////////

#include <fstream>

namespace codedweller {

PadBuffer OneTimePad::Entropy(int Length) {                                     // Get Length bytes of strong entropy.
    PadBuffer Buffer(Length, 0);                                                // Initialize a buffer to hold them.
    try {                                                                       // Handle this in a try block.
        std::ifstream Source("/dev/urandom", std::ios::binary);                 // Open /dev/urandom if possible.
        Source.read(reinterpret_cast<char*>(&Buffer[0]), Length);               // Read data into the buffer.
        if(!Source.bad() && Source.gcount() == Length) {                        // If we got what we came for then
            StrongEntropyFlag = true;                                           // we have strong cryptography.
        } else {                                                                // If we didn't then we are not
            StrongEntropyFlag = false;                                          // strong, and don't have things
        }                                                                       // to make us go.
        Source.close();                                                         // We're done, so close the stream.
    }

    catch(...) {                                                                // If we had an exception then we
        StrongEntropyFlag = false;                                              // did not get strong entropy.
    }
    return Buffer;                                                              // Return the buffer.
}

} // End namespace codedweller

#endif

// End Platform Specific Bits
////////////////////////////////////////////////////////////////////////////////

namespace codedweller {

// Lightweight entropy is built from a combination of the time in ms UTC that
// the application was started, the number of milliseconds since that time in
// milliseconds, the number and times of calls to addLightweightEntropy(), and
// the state of the MANGLER engine at each call -- that state is effected by
// the combined previous use of the MANGLER and any other entropy that was
// added including the timing of those events (since they all trigger the
// addLightweightEntropy() function.

Timer OneTimePadRunTimer;                                                       // Millisecond entropy source.
msclock LightweightEntropyBuffer;                                               // Lightweight entropy bucket.

void OneTimePad::addLightweightEntropy() {                                      // Add entropy based on the
    msclock StartFill = OneTimePadRunTimer.getStartClock();                     // initial start time of the app
    msclock ElapsedFill = OneTimePadRunTimer.getElapsedTime();                  // and the number of millisecs since.
    msclock CombinedFill = StartFill ^ ElapsedFill;                             // XOR the two together to combine.
    CombinedFill = CombinedFill ^ LightweightEntropyBuffer;                     // Pick up some previous state entropy.
    unsigned char* PrimerBuffer = (unsigned char*) &CombinedFill;               // Treat the value as a bunch of bytes.
    unsigned char* EntropyBuffer = (unsigned char*) &LightweightEntropyBuffer;  // Likewise with the entropy buffer.
    for(size_t i = 0; i < sizeof(msclock); i++) {                               // Fold bytes into the mangler one
        EntropyBuffer[i] +=                                                     // byte at a time, capturing the
          PadGenerator.Encrypt(                                                 // the results and using one extra
            PadGenerator.Encrypt(PrimerBuffer[i]));                             // round per byte to increase the
    }                                                                           // amount of guessing an attacker
}                                                                               // needs to do.

void OneTimePad::addEntropy() {                                                 // Add strong entropy if available.
    PadBuffer Fill = Entropy();                                                 // Grab the entropy bits to add.
    for(size_t i = 0; i < Fill.size(); i++) {                                   // Pump them in one byte at a
        PadGenerator.Encrypt(                                                   // time and then run an extra
          PadGenerator.Encrypt(Fill.at(i)));                                    // round per byte to increase the
    }                                                                           // amount of guessing an attacker
}                                                                               // needs to do.

void OneTimePad::addEntropy(PadBuffer Entropy) {                                // Add entropy from a given source.
    addLightweightEntropy();                                                    // Start with some lightweight entropy.
    for(size_t i = 0; i < Entropy.size(); i++) {                                // Then loop through the provided
        PadGenerator.Encrypt(                                                   // entropy and mix it in with one
          PadGenerator.Encrypt(Entropy.at(i)));                                 // extra round per byte to increase
    }                                                                           // the amount of guessing an attacker
}                                                                               // needs to do.

PadBuffer OneTimePad::Pad(int Length) {                                         // Grab a pad of a specific length.
    addLightweightEntropy();                                                    // Add some lightweight entropy.
    PadBuffer Output; Output.reserve(Length);                                   // Create a buffer the right size.
    unsigned char x;                                                            // Starting with an uninitialized
    for(int i = 0; i < Length; i++)                                             // char, fill the buffer with
      Output.push_back(x = PadGenerator.Encrypt(x));                            // random bytes from the mangler.
    return Output;                                                              // Return the new pad.
}

void* OneTimePad::fill(void* Object, int Size) {                                // Fill *Object with random bytes.
    PadBuffer FillData = Pad(Size);                                             // Get a Pad of the correct size.
    unsigned char* Ptr = reinterpret_cast<unsigned char*>(Object);              // Reinterpret the pointer type.
    for(int i = 0; i < Size; i++) Ptr[i] = FillData.at(i);                      // Fill the object with the Pad.
    return Object;                                                              // Return the object.
}

bool OneTimePad::isStrong() { return StrongEntropyFlag; }                       // Tell them if I'm strong!

OneTimePad::OneTimePad() {                                                      // Initialize the one time pad.
    addLightweightEntropy();                                                    // Add lightweight entropy.
    addEntropy();                                                               // Add cryptographic entropy.
    unsigned char x;                                                            // Starting with an uninitialized
    for(int i = 0; i < 1024; i++) {                                             // character, run 1024 rounds to
        x = PadGenerator.Encrypt(x);                                            // reduce the predictability of the
    }                                                                           // initial Mangler state.
}                                                                               // The OneTimePad object is ready.

} // End namespace codedweller