easy7zip/CPP/7zip/Crypto/Zip/ZipCrypto.cpp

// Crypto/ZipCrypto.cpp

#include "StdAfx.h"

#include "ZipCipher.h"
extern "C"
{
#include "../../../../C/7zCrc.h"
}

namespace NCrypto {
namespace NZip {

void CCipher::UpdateKeys(Byte b)
{
  Keys[0] = CRC_UPDATE_BYTE(Keys[0], b);
  Keys[1] += Keys[0] & 0xff;
  Keys[1] = Keys[1] * 134775813L + 1;
  Keys[2] = CRC_UPDATE_BYTE(Keys[2], (Byte)(Keys[1] >> 24));
}

void CCipher::SetPassword(const Byte *password, UInt32 passwordLength)
{
  Keys[0] = 305419896L;
  Keys[1] = 591751049L;
  Keys[2] = 878082192L;
  for (UInt32 i = 0; i < passwordLength; i++)
    UpdateKeys(password[i]);
}

Byte CCipher::DecryptByteSpec()
{
  UInt32 temp = Keys[2] | 2;
  return (Byte)((temp * (temp ^ 1)) >> 8);
}

Byte CCipher::DecryptByte(Byte encryptedByte)
{
  Byte c = (Byte)(encryptedByte ^ DecryptByteSpec());
  UpdateKeys(c);
  return c;
}

Byte CCipher::EncryptByte(Byte b)
{
  Byte c = (Byte)(b ^ DecryptByteSpec());
  UpdateKeys(b);
  return c;
}

void CCipher::DecryptHeader(Byte *buffer)
{
  for (int i = 0; i < 12; i++)
    buffer[i] = DecryptByte(buffer[i]);
}

void CCipher::EncryptHeader(Byte *buffer)
{
  for (int i = 0; i < 12; i++)
    buffer[i] = EncryptByte(buffer[i]);
}

}}