repvir.cpp

使用CRC进行病毒检测的简单程序

# include "dos.h"
# include "dir.h"
# include "stdlib.h"
# include "iostream.h"
# include "fstream.h"
# include "conio.h"
# define OK 0
# define Cancel 255
unsigned int ChkCRC(char * filename,unsigned int FileCRC);
void main(void)
{
  ifstream Result("CRCSUM.DAT");
  char FileName[13];
  unsigned int FileCRC;
  unsigned int CRC;
  if(Result)//The file crcsum.dat exist.
  {
    Result>>FileName>>FileCRC;
    while(!Result.eof())
    {
      CRC=ChkCRC(FileName,FileCRC);
      switch(CRC)
      {
        case OK:
          cout<<FileName<<"  Ok!"<<endl;
          break;
        case Cancel:
          cout<<FileName<<"  Not Found!  Press any key to continue..."<<endl;
          getch();
          break;
        default:
          cout<<FileName<<"  CRC Error!  Press any key to continue..."<<endl;
          getch();
          break;
      }
      Result>>FileName>>FileCRC;
    }
  }
}
unsigned int ChkCRC(char * filename,unsigned int FileCRC)
{
  static unsigned long Gx=0x18005;//The IBM generate polynomial
  static unsigned long ChkSum=0;
  static unsigned int CRC=0xaa;
  static unsigned int TmpCRC;
  unsigned char tmp;
  struct ffblk Fblk;
  int i;
  ifstream ChkFile;
  Gx=0x18005;
  ChkSum=0;
  CRC=0;
  TmpCRC=FileCRC;
  if(!findfirst(filename,&Fblk,FA_ARCH|FA_RDONLY))
  {
    ChkFile.open(filename,ios::binary);
    if(Fblk.ff_fsize>=3)
    {
      tmp=ChkFile.get();
      ChkSum|=tmp;
      ChkSum<<=8;
      tmp=ChkFile.get();
      ChkSum|=tmp; //Read 2 byte for deviding soon
      tmp=ChkFile.get();
      do
      {
        for(i=0;i<8;i++)//move the next bits to value ChkSum
        {
          ChkSum<<=1;
          if(tmp&0x80)
            ChkSum|=1;
          tmp<<=1;
          if(ChkSum & 0x10000)
          {
            CRC=ChkSum^Gx;
            ChkSum=CRC;
          }
        }
        tmp=ChkFile.get();
      }while(!ChkFile.eof());
      TmpCRC>>=8;
      tmp=TmpCRC;//get the high 8 bits of FileCRC
      for(i=0;i<8;i++)//Calculate the CRC
      {
        ChkSum<<=1;
        if(tmp&0x80)
          ChkSum|=1;
        tmp<<=1;
        if(ChkSum & 0x10000)
        {
          CRC=ChkSum^Gx;
          ChkSum=CRC;
        }
      }
      TmpCRC=FileCRC;
      TmpCRC&=0xff;
      tmp=TmpCRC;//get the low 8 bits of FileCRC
      for(i=0;i<8;i++)//Calculate the CRC
      {
        ChkSum<<=1;
        if(tmp&0x80)
          ChkSum|=1;
        tmp<<=1;
        if(ChkSum & 0x10000)
        {
          CRC=ChkSum^Gx;
          ChkSum=CRC;
        }
      }
      CRC=ChkSum;
      return(CRC);
    }
    else //the length of file >=2
    {
      for(i=0;i<Fblk.ff_fsize;i++)
      {
        ChkSum<<=8*i;
        tmp=ChkFile.get();
        ChkSum|=tmp;
      }
      TmpCRC=FileCRC;
      TmpCRC>>=8;
      tmp=TmpCRC;//get the high 8 bits of FileCRC
      for(i=0;i<8;i++)//Calculate the CRC
      {
        ChkSum<<=1;
        if(tmp&0x80)
          ChkSum|=1;
        tmp<<=1;
        if(ChkSum & 0x10000)
        {
          CRC=ChkSum^Gx;
          ChkSum=CRC;
        }
      }
      TmpCRC=FileCRC;
      TmpCRC&=0xff;
      tmp=TmpCRC;//get the low 8 bits of FileCRC
      for(i=0;i<8;i++)//Calculate the CRC
      {
        ChkSum<<=1;
        if(tmp&0x80)
          ChkSum|=1;
        tmp<<=1;
        if(ChkSum & 0x10000)
        {
          CRC=ChkSum^Gx;
          ChkSum=CRC;
        }
      }
      CRC=ChkSum;
      return(CRC);
    }
  }
  else
    return(Cancel);
}