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sdlj8051

金虫 (著名写手)

应助: 0 (幼儿园)
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金币: 1149.8
红花: 3
帖子: 2254
在线: 18.1小时
虫号: 71297
注册: 2005-05-30
专业: 电路与系统

[交流] [转贴]CRC32碰撞的实现

?????????????????????

??CRC32??????N??????Ч??,???Ч????0xFFFFFFFF,????N????????????????Ч???

?????????????????????4????????Ч????????????????????????

??:
???????????Ч????ABCD,?????Ч?????????abcd,Ч???????WXYZ,????4???????????mnop
(??????????????????)
???????????ABCD+WXYZ???abcd

????4??????F(x),G(x),H(x),I(x)???????x????????,???????DWORD????λ????λ??4?????

CRC32Ч??abcd???????????:

R0:A,B,C,D
R1:F(m),A^G(m),B^H(m),C^I(m)
R2:F(n),F(m)^G(n),A^G(m)^H(n),B^H(m)^I(n)
R3:F(o),F(n)^G(o),F(m)^G(n)^H(o),A^G(m)^H(n)^I(o)
R4:F(p),F(o)^G(p),F(n)^G(o)^H(p),F(m)^G(n)^H(o)^I(p)

??R4????????4???????Ч???WXYZ,?????????????:

-------------------------
<1>
W=F(p);
X=F(o)^G(p);
Y=F(n)^G(o)^H(p);
Z=F(m)^G(n)^H(o)^I(p);

<2>
m=d^D;
n=c^C^I(m);
o=b^B^H(m)^I(n);
p=a^A^G(m)^H(n)^I(o);
-------------------------

????????????????ABCD,abcd,WXYZ??????,??mnop???м????

????abcd????????,??F(x)???????RF(x),??:
-----------------------
~<1>
p=RF(W);
o=RF(X^G(p));
n=RF(Y^G(o)^H(p));
m=RF(Z^G(n)^H(o)^I(p));

~<2>
d=m^D;
c=n^C^I(m);
b=o^B^H(m)^I(n);
a=p^A^G(m)^H(n)^I(o);
-----------------------

???????????????????????е?????:d,c,b,a  (????????????С????)

???????????????????,??????????????????RF(x)??????,??????????????????y=F(x)????????:

void TestRF()
{
  BYTE i,j;
  DWORD flag;
  for(i=0;i<=0xFF;i++)
  {
flag=0;
for(j=0;j<=0xFF;j++)
{
   if(HIBYTE(HIWORD(CRC32_tab[j])) == i)
   {
      flag=1;
      printf("%X gets!\r\n",i);
      break;
   }
   if(j==0xFF)break;
}
if(!flag)printf("%X can't get RF\r\n",i);
if(i==0xFF)break;
  }
}

???????????е?0~255????RF(x)???????,?????RF(x)??????????,?????????????!

??????~<1> ~<2>????:

BYTE RF(BYTE x)
{
  BYTE j;
  for(j=0;j<=0xFF;j++)
  {
if(HIBYTE(HIWORD(CRC32_tab[j])) == x)break;
  }
  return j;
}

BYTE F(BYTE x)
{
  return HIBYTE(HIWORD(CRC32_tab[x]));
}
BYTE G(BYTE x)
{
  return LOBYTE(HIWORD(CRC32_tab[x]));
}
BYTE H(BYTE x)
{
  return HIBYTE(LOWORD(CRC32_tab[x]));
}
BYTE I(BYTE x)
{
  return LOBYTE(LOWORD(CRC32_tab[x]));
}

#define MakeLong(a,b) MAKELONG(b,a)
#define MakeWord(a,b) MAKEWORD(b,a)

DWORD rCRC32(DWORD WXYZ,DWORD ABCD)
{
  BYTE p,o,n,m,a,b,c,d,W,X,Y,Z,A,B,C,D;

  W=HIBYTE(HIWORD(WXYZ));
  X=LOBYTE(HIWORD(WXYZ));
  Y=HIBYTE(LOWORD(WXYZ));
  Z=LOBYTE(LOWORD(WXYZ));

  A=HIBYTE(HIWORD(ABCD));
  B=LOBYTE(HIWORD(ABCD));
  C=HIBYTE(LOWORD(ABCD));
  D=LOBYTE(LOWORD(ABCD));

  p=RF(W);
  o=RF(X^G(p));
  n=RF(Y^G(o)^H(p));
  m=RF(Z^G(n)^H(o)^I(p));

  d=m^D;
  c=n^C^I(m);
  b=o^B^H(m)^I(n);
  a=p^A^G(m)^H(n)^I(o);

  return MakeLong(MakeWord(a,b),MakeWord(c,d));
}

DWORD RCRC32(DWORD WXYZ,DWORD abcd)
{
  BYTE p,o,n,m,a,b,c,d,W,X,Y,Z,A,B,C,D;

  W=HIBYTE(HIWORD(WXYZ));
  X=LOBYTE(HIWORD(WXYZ));
  Y=HIBYTE(LOWORD(WXYZ));
  Z=LOBYTE(LOWORD(WXYZ));

  a=HIBYTE(HIWORD(abcd));
  b=LOBYTE(HIWORD(abcd));
  c=HIBYTE(LOWORD(abcd));
  d=LOBYTE(LOWORD(abcd));

  p=RF(W);
  o=RF(X^G(p));
  n=RF(Y^G(o)^H(p));
  m=RF(Z^G(n)^H(o)^I(p));

  D=m^d;
  C=n^c^I(m);
  B=o^b^H(m)^I(n);
  A=p^a^G(m)^H(n)^I(o);

  return MakeLong(MakeWord(A,B),MakeWord(C,D));
}

DWORD CRC32(DWORD ABCD,DWORD abcd)
{
  BYTE p,o,n,m,a,b,c,d,W,X,Y,Z,A,B,C,D;

  A=HIBYTE(HIWORD(ABCD));
  B=LOBYTE(HIWORD(ABCD));
  C=HIBYTE(LOWORD(ABCD));
  D=LOBYTE(LOWORD(ABCD));

  a=HIBYTE(HIWORD(abcd));
  b=LOBYTE(HIWORD(abcd));
  c=HIBYTE(LOWORD(abcd));
  d=LOBYTE(LOWORD(abcd));

  m=d^D;
  n=c^C^I(m);
  o=b^B^H(m)^I(n);
  p=a^A^G(m)^H(n)^I(o);

  W=F(p);
  X=F(o)^G(p);
  Y=F(n)^G(o)^H(p);
  Z=F(m)^G(n)^H(o)^I(p);

  return MakeLong(MakeWord(W,X),MakeWord(Y,Z));
}

??????????????÷????,??????????????????,??CRC32Ч??,???????ABCD
???????????<1><2>????abcd,??abcd?????????????????????????!

????,"DonQuixote[CCG][iPB]"??????????CRC32??0x8A0C90C9,??????δ??????????????????:

int main(int argc, char* argv[])
{

  DWORD x=rCRC32(~0x8A0C90C9,~CRC((BYTE*)"ipb",3));

  char str[5];
  memcpy(str,&x,4);
  str[4]=0;
  printf("x=%X\r\nstring=%s\r\n",x,str);

  return 0;
}

????????Щ???:

DonQuixote[CCG][iPB]
123?Dp0
ccg_G??
ipbkw??

?????????????CRC32Ч???=0x8A0C90C9
(????и???????????????,?????http://www.pediy.com/tools/Crypt ... N%20Hash%20Calculat

or%20.zip)

??????????????????????DWORD,????????????????м????λ???DWORD,????????????
??????WXYZ,abcd?????ABCD???????:
-------------------------
(mnop??????~<1>~<2>???)
~<2'>
D=m^d;
C=n^c^I(m);
B=o^b^H(m)^I(n);
A=p^a^G(m)^H(n)^I(o);
-------------------------
????????????????"Ч??"???,?????м????λ????????????

****************************************************************************************8

?????????Щ???:

??????????????????????anti-debug??,?????Ч?鶼???????????Ч???????
???????~<2'>??~<2>????????Ч?????????,?????????????:CRC(***A***)=A

????windows??????????CRC32Ч???,?????????д??????????????????????Ч?????????????
??????????????RootKit?????????,??????????????????

???TCP/IP??????????CRC32Ч??,??????????д?????????????????????????Ч??????

[ Last edited by sdlj8051 on 2006-10-6 at 12:34 ]

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1楼 2006-08-23 18:15:09

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sdlj8051

金虫 (著名写手)

应助: 0 (幼儿园)
贵宾: 0.1
金币: 1149.8
红花: 3
帖子: 2254
在线: 18.1小时
虫号: 71297
注册: 2005-05-30
专业: 电路与系统

利用反向效验写了一个anti-debug的例子，全部代码和数据一起效验，然后利用效验值解密，当然效验值是事先想好的，这个例子里效验值=0x123456789

加密前的代码：
.code

check_start:

start:
mov esi,check_start
call InitCRC32
mov ecx,check_end-check_start
mov eax,0FFFFFFFFh
call CRC32

mov ecx,(encrypt_end-encrypt_start)
shr ecx,2
mov esi,encrypt_start

decrypt:
push eax
push ecx

mov ecx,4
call CRC32
mov [esi-4],eax

pop ecx
pop eax

inc eax

loop decrypt

encrypt_start:

jmp msgout
msg db "this debugme cracked by none!",0,0,0,0,0,0,0,0,0
tmsg db "test CRC32 by DonQuixote[CCG][iPB]",0
msgout:
invoke MessageBox,NULL,offset msg,offset tmsg,MB_OK
invoke ExitProcess,NULL

encrypt_end:

InitCRC32:

mov ecx, 256

_nexttable:
lea eax, [ecx-1]
push ecx
mov ecx, 8

_nextbit:
shr eax,1
jnc _notcarry
xor eax, 0edb88320h
_notcarry:
dec ecx
jnz _nextbit

pop ecx
mov [dwcrc32table + ecx*4 - 4], eax
dec ecx
jnz _nexttable

ret

CRC32:
;esi=data
;ecx=len of data
;eax=init of checksum

or esi, esi
jz _done
or ecx, ecx
jz _done

_nextbyte:
mov dl, [esi]

xor dl, al
movzx edx, dl
shr eax, 8
xor eax, [dwcrc32table + edx*4]

inc esi
call antibp
loop _nextbyte
_done:
not eax

ret

antibp:
push seh
push fs:[0]
mov fs:[0],esp
db 0CCh
pop fs:[0]
add esp,4
ret

seh:
mov eax,dword ptr ss:[esp+4h]
mov ecx,dword ptr ss:[esp+0Ch]
inc dword ptr ds:[ecx+0B8h]
mov eax,dword ptr ds:[eax]
xor eax,80000003h
jnz start
;xor eax,eax
and dword ptr ds:[ecx+4h],eax
and dword ptr ds:[ecx+8h],eax
and dword ptr ds:[ecx+0Ch],eax
and dword ptr ds:[ecx+10h],eax
and dword ptr ds:[ecx+14h],0FFFF0FF0h
and dword ptr ds:[ecx+18h],0DC00h
ret

check_end:

end start

对硬件断点做了一点处理，加密算法仍然是CRC32
因为用CRC32效验一个DWORD时，知道效验数据效验初值效验值 3个中的2个就可以求另外一个
CRC32:是CRC32效验，eax指定效验初值(eax=0xFFFFFFFF就是标准CRC32)

加密时的算法：
#define LEN 0x141
BYTE data[LEN];
DWORD wantedcrc=0x12345678;
DWORD filebase=0x400;
int fixfile()
{
FILE*fh=fopen("E:\\Crack\\CRC32\\anti.exe","r+"

;
  fseek(fh,filebase,SEEK_SET);
  fread(data,1,LEN,fh);

  DWORD iendata=0x3A;
  for(int i=0;i<0x1A;i++)
  {
*(DWORD*)(data+iendata)=rCRC32(~*(DWORD*)(data+iendata),(wantedcrc+i));
iendata+=4;
  }

  DWORD b=~StdCRC(data,0x5D);
  DWORD a=RevCRC(~wantedcrc,(DWORD*)(data+0x61),(0x141-0x61)/4);
  *(DWORD*)(data+0x5D)=rCRC32(a,b);

  fseek(fh,filebase,SEEK_SET);
  fwrite(data,1,LEN,fh);
  fclose(fh);
  return 0;
}

wantedcrc=0x12345678是预先设定的效验值
for(int i=0;i<0x1A;i++)部分加密数据
RevCRC反向效验，然后在*(DWORD*)(data+0x5D)这里patch修补码，使效验值=wantedcrc

反向效验的代码：
//return init reg
DWORD RevCRC(DWORD reg,DWORD*pdata,int n)
{
  for(int i=n-1;i>=0;i--)reg=RCRC32(reg,pdata);
  return reg;
}
//根据数据和效验值求出效验初值

利用CRC32加密的变换也可以应用到序列号变换里，可以增加一点写KeyGen的难度：）

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2楼2006-08-23 18:15:28

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