zipstrong.cpp

7z一个高压缩比的压缩程序源代码,重要的是里面的算法值得学习

// Crypto/ZipStrong.cpp

#include "StdAfx.h"

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

#include "../Common/StreamUtils.h"

#include "MyAES.h"
#include "Sha1.h"
#include "ZipStrong.h"

namespace NCrypto {
namespace NZipStrong {

static const UInt16 kAES128 = 0x660E;

// DeriveKey* function is similar to CryptDeriveKey() from Windows.
// But MSDN tells that we need such scheme only if
// "the required key length is longer than the hash value"
// but ZipStrong uses it always.

static void DeriveKey2(const Byte *digest, Byte c, Byte *dest)
{
  Byte buf[64];
  memset(buf, c, 64);
  for (unsigned i = 0; i < NSha1::kDigestSize; i++)
    buf[i] ^= digest[i];
  NSha1::CContext sha;
  sha.Init();
  sha.Update(buf, 64);
  sha.Final(dest);
}
 
static void DeriveKey(NSha1::CContext &sha, Byte *key)
{
  Byte digest[NSha1::kDigestSize];
  sha.Final(digest);
  Byte temp[NSha1::kDigestSize * 2];
  DeriveKey2(digest, 0x36, temp);
  DeriveKey2(digest, 0x5C, temp + NSha1::kDigestSize);
  memcpy(key, temp, 32);
}

void CKeyInfo::SetPassword(const Byte *data, UInt32 size)
{
  NSha1::CContext sha;
  sha.Init();
  sha.Update(data, size);
  DeriveKey(sha, MasterKey);
}

STDMETHODIMP CBaseCoder::CryptoSetPassword(const Byte *data, UInt32 size)
{
  _key.SetPassword(data, size);
  return S_OK;
}

STDMETHODIMP CBaseCoder::Init()
{
  return S_OK;
}

HRESULT CDecoder::ReadHeader(ISequentialInStream *inStream, UInt32 /* crc */, UInt64 /* unpackSize */)
{
  Byte temp[4];
  RINOK(ReadStream_FALSE(inStream, temp, 2));
  _ivSize = GetUi16(temp);
  if (_ivSize == 0)
  {
    return E_NOTIMPL;
    /*
    SetUi32(_iv, crc);
    for (int i = 0; i < 8; i++)
     _iv[4 + i] = (Byte)(unpackSize >> (8 * i));
    SetUi32(_iv + 12, 0);
    */
  }
  else if (_ivSize == 16)
  {
    RINOK(ReadStream_FALSE(inStream, _iv, _ivSize));
  }
  else
    return E_NOTIMPL;
  RINOK(ReadStream_FALSE(inStream, temp, 4));
  _remSize = GetUi32(temp);
  if (_remSize > _buf.GetCapacity())
  {
    _buf.Free();
    _buf.SetCapacity(_remSize);
  }
  return ReadStream_FALSE(inStream, _buf, _remSize);
}

HRESULT CDecoder::CheckPassword(bool &passwOK)
{
  passwOK = false;
  if (_remSize < 10)
    return E_NOTIMPL;
  Byte *p = _buf;
  UInt16 format = GetUi16(p);
  if (format != 3)
    return E_NOTIMPL;
  UInt16 algId  = GetUi16(p + 2);
  if (algId < kAES128)
    return E_NOTIMPL;
  algId -= kAES128;
  if (algId > 2)
    return E_NOTIMPL;
  UInt16 bitLen = GetUi16(p + 4);
  UInt16 flags  = GetUi16(p + 6);
  if (algId * 64 + 128 != bitLen)
    return E_NOTIMPL;
  _key.KeySize = 16 + algId * 8;
  if ((flags & 1) == 0)
    return E_NOTIMPL;
  UInt32 rdSize = GetUi16(p + 8);
  UInt32 pos = 10;
  Byte *rd = p + pos;
  pos += rdSize;
  if (pos + 4 > _remSize)
    return E_NOTIMPL;
  UInt32 reserved = GetUi32(p + pos);
  pos += 4;
  if (reserved != 0)
    return E_NOTIMPL;
  if (pos + 2 > _remSize)
    return E_NOTIMPL;
  UInt32 validSize = GetUi16(p + pos);
  pos += 2;
  Byte *validData = p + pos;
  if (pos + validSize != _remSize)
    return E_NOTIMPL;

  if (!_aesFilter)
    _aesFilter = new CAesCbcDecoder;

  CMyComPtr<ICryptoProperties> cp;
  RINOK(_aesFilter.QueryInterface(IID_ICryptoProperties, &cp));
  {
    RINOK(cp->SetKey(_key.MasterKey, _key.KeySize));
    RINOK(cp->SetInitVector(_iv, 16));
    _aesFilter->Init();
    if (_aesFilter->Filter(rd, rdSize) != rdSize)
      return E_NOTIMPL;
  }

  Byte fileKey[32];
  NSha1::CContext sha;
  sha.Init();
  sha.Update(_iv, 16);
  sha.Update(rd, rdSize - 16); // we don't use last 16 bytes (PAD bytes)
  DeriveKey(sha, fileKey);
  
  RINOK(cp->SetKey(fileKey, _key.KeySize));
  RINOK(cp->SetInitVector(_iv, 16));
  _aesFilter->Init();
  if (_aesFilter->Filter(validData, validSize) != validSize)
    return E_NOTIMPL;

  if (validSize < 4)
    return E_NOTIMPL;
  validSize -= 4;
  if (GetUi32(validData + validSize) != CrcCalc(validData, validSize))
    return S_OK;
  passwOK = true;
  _aesFilter->Init();
  return S_OK;
}

STDMETHODIMP_(UInt32) CDecoder::Filter(Byte *data, UInt32 size)
{
  return _aesFilter->Filter(data, size);
}

}}