W32Dasm8.93捉虫记

标题：W32DASM8.93捉虫记湖北 wuhuashang
时间：2000-7-21 9:01:47
链接：http://bbs.pediy.com

W32DASM8.93捉虫记湖北 wuhuashang
W32DASM是调试修改程序的强大工具，作为SOFTICE的辅助工具W32DASM为CRACKER必备。
当前许多软件采用注册方式，输入注册号,若正确显示"THANK YOU",否则显示"INCORRECT PASSWORD",用W32DASM反编译该软件,然后查找指定的错误信息如"INCORRECT PASSWORD"或其他因没有注册而显示的某些提示信息,假若被找到,对熟练的CRACKER而言,可能10分钟后便完成破解,而对于没有破解经验的计算机爱好者,只要他有一点汇编语言知识,再看一些别人用W32DASM破解的文章,用不了几天,他便可以破解INTERNET网上的许多共享软件;但是如果显示的信息并不是英文而是中文如"注册号不正确",您试着也找......,您发现只要是中文信息,W32DASM是没法对中文反编译的!
W32DASM不支持中文日文韩文的反编译,把它看作BUG应该可以被修改,磨刀不误砍柴工!.
我写此文章不是教人破解软件的加密信息,而是写出修改此软件的BUG的过程,假设反编译的中文软件DEMO.EXE,输入错误注册号后显示"无效的注册号".
1.您可以用HEXEDIT修改为"ERRORPASS"(若被未知的软件压缩加密呢?),修改后最好注销或重新启动计算机(内存有ERRORPASS字串)
2.启动W32DASM,打开DEMO.EXE,在32DASM反编译约1-3秒钟后CTRL+D切入SOFTICE
S DS:0 L FFFFFFFF "ERRORPA" (不要输入为ERRORPASS,就是不要完整啦)
若没有找到退出SOFTICE,重新打开DEMO.EXE,大约3秒钟后CTRL+D切入SOFTICE(依次类推),经过一翻斗争
在167:00610175处发现有"ERRORPASS"字串.
3.设置断点BPM 167:610175,退出SOFTICE,W32DASM继续编译,马上被SOFTICE拦截,分析:W32DASM能反编译的字符串的ASCII值在20H-7F之间,必然有CMP AX,20类似的比较,上下观察并没有该语句,退出SOFTICE,马上又被 SOFTICE拦截下来,停止在CS:417241处:

.0041721A: 8B8530FFFFFF mov eax,[ebp][0FFFFFF30]
.00417220: 85C0 test eax,eax
.00417222: 0F848B000000 je .0004172B3
.00417228: 8B93A5726000 mov edx,[ebx][0006072A5]
.0041722E: 8B8B081F6F00 mov ecx,[ebx][0006F1F08]
.00417234: 8D040A lea eax,[edx][ecx]
.00417237: 8B9530FFFFFF mov edx,[ebp][0FFFFFF30]
.0041723D: 0FBE0C10 movsx ecx,b,[eax][edx]

说明:D DS:EAX+EDX 好家伙!原来正在读入"ERRORPASS",可以猜想,W32DASM能识别的字符串的ASCII码为20-7D之间而中文的ASCII码>A0 (是负数),改CS:417244 75 CC ==>90 90 ,中文信息不就可以处理吗?哈哈,别高兴太早,会失败得惨!记录下CS:417241 83F9207C5C
.00417241: 83F920 cmp ecx,020 ;" "
.00417244: 7C5C jl .0004172A2 -------- (1)
.00417246: 8B83A5726000 mov eax,[ebx][0006072A5]
.0041724C: 8B93081F6F00 mov edx,[ebx][0006F1F08]
.00417252: 8D0C10 lea ecx,[eax][edx]
.00417255: 8B8530FFFFFF mov eax,[ebp][0FFFFFF30]
.0041725B: 0FBE1401 movsx edx,b,[ecx][eax]
.0041725F: 83FA7D cmp edx,07D ;"}"
.00417262: 7F3E jg .0004172A2

.00417264: 8B8BA5726000 mov ecx,[ebx][0006072A5]
.0041726A: 8B83081F6F00 mov eax,[ebx][0006F1F08]
.00417270: 8D1401 lea edx,[ecx][eax]
.00417273: 8B8D30FFFFFF mov ecx,[ebp][0FFFFFF30]
.00417279: 0FBE440AFF movsx eax,b,[edx][ecx][-0001]
.0041727E: 83F820 cmp eax,020 ;" "
说明:有敏感的比较,共有多少处要修改呢?您不是设置有断点吗?退出SOFTICE,必然又拦截下来,用笔记录拦截的CS:IP.
.00417281: 7C23 jl .0004172A6 -------- (2)
.00417283: 8B93A5726000 mov edx,[ebx][0006072A5]
.00417289: 8B8B081F6F00 mov ecx,[ebx][0006F1F08]
.0041728F: 8D040A lea eax,[edx][ecx]
.00417292: 8B9530FFFFFF mov edx,[ebp][0FFFFFF30]
.00417298: 0FBE4C10FF movsx ecx,b,[eax][edx][-0001]
.0041729D: 83F97D cmp ecx,07D ;"}"
.004172A0: 7F04 jg .0004172A6

.004172A2: 33C0 xor eax,eax
.004172A4: EB05 jmps .0004172AB
.004172A6: B801000000 mov eax,000000001 ;" "
.004172AB: 898574FFFFFF mov [ebp][0FFFFFF74],eax
.004172B1: EB4B jmps .0004172FE
.004172B3: 8B93A5726000 mov edx,[ebx][0006072A5]
.004172B9: 8B8B081F6F00 mov ecx,[ebx][0006F1F08]
.004172BF: 8D040A lea eax,[edx][ecx]
.004172C2: 8B9530FFFFFF mov edx,[ebp][0FFFFFF30]
.004172C8: 0FBE0C10 movsx ecx,b,[eax][edx]
.004172CC: 83F920 cmp ecx,020 ;" "
.004172CF: 7C1E jl .0004172EF -------- (3)
.004172D1: 8B83A5726000 mov eax,[ebx][0006072A5]
.004172D7: 8B93081F6F00 mov edx,[ebx][0006F1F08]
.004172DD: 8D0C10 lea ecx,[eax][edx]
......
00417392: 0FBE0431 movsx eax,b,[ecx][esi]
.00417396: 83F820 cmp eax,020 ;" "
.00417399: 7C25 jl .0004173C0 -------- (4)
.0041739B: 8B93A5726000 mov edx,[ebx][0006072A5]
.004173A1: 8B8B081F6F00 mov ecx,[ebx][0006F1F08]
.004173A7: 8D040A lea eax,[edx][ecx]
.004173AA: 8B9530FFFFFF mov edx,[ebp][0FFFFFF30]
.004173B0: 8D0C10 lea ecx,[eax][edx]
.004173B3: 0FBE0431 movsx eax,b,[ecx][esi]
.004173B7: 83F87D cmp eax,07D ;"}"
.004173BA: 0F8E68FFFFFF jle .000417328
.004173C0: 8B9530FFFFFF mov edx,[ebp][0FFFFFF30]
.004173C6: 85D2 test edx,edx
.004173C8: 0F8483000000 je .000417451
.004173CE: 8B8BA5726000 mov ecx,[ebx][0006072A5]
.004173D4: 8B83081F6F00 mov eax,[ebx][0006F1F08]
.004173DA: 8D1401 lea edx,[ecx][eax]
.004173DD: 8B8D30FFFFFF mov ecx,[ebp][0FFFFFF30]
.004173E3: 66833C0A20 cmp w,[edx][ecx],020 ;" "
此处的比较有点奇怪,为啥是CMP WORD PTR [EDX+ECX],20 而不是CMP BYTE PTR[EDX+ECX],20呢?而且有好几个地方.
.004173E8: 7256 jb .000417440 -------- (5)
.004173EA: 8B83A5726000 mov eax,[ebx][0006072A5]
.004173F0: 8B93081F6F00 mov edx,[ebx][0006F1F08]
.004173F6: 8D0C10 lea ecx,[eax][edx]

......
.004173F9: 8B8530FFFFFF mov eax,[ebp][0FFFFFF30]
.004173FF: 66833C017D cmp w,[ecx][eax],07D ;"}"
.00417404: 773A ja .000417440
.00417406: 8B93A5726000 mov edx,[ebx][0006072A5]
.0041740C: 8B8B081F6F00 mov ecx,[ebx][0006F1F08]
.00417412: 8D040A lea eax,[edx][ecx]
.00417415: 8B9530FFFFFF mov edx,[ebp][0FFFFFF30]
.0041741B: 66837C10FF20 cmp w,[eax][edx][-0001],020 ;" "
多好的比较方式,用此方法可以快速解决某些西文软件不能输入汉字的问题.不是吗?

.00417421: 7221 jb .000417444 -------- (6)
.00417423: 8B8BA5726000 mov ecx,[ebx][0006072A5]
.00417429: 8B83081F6F00 mov eax,[ebx][0006F1F08]
.0041742F: 8D1401 lea edx,[ecx][eax]
.00417432: 8B8D30FFFFFF mov ecx,[ebp][0FFFFFF30]
.00417438: 66837C0AFF7D cmp w,[edx][ecx][-0001],07D ;"}"
.0041743E: 7704 ja .000417444
.00417440: 33C0 xor eax,eax
.00417442: EB05 jmps .000417449
.00417444: B801000000 mov eax,000000001 ;" "
.00417449: 898570FFFFFF mov [ebp][0FFFFFF70],eax
.0041744F: EB47 jmps .000417498
.00417451: 8B93A5726000 mov edx,[ebx][0006072A5]
.00417457: 8B8B081F6F00 mov ecx,[ebx][0006F1F08]
.0041745D: 8D040A lea eax,[edx][ecx]

......
00460556: 8A0418 mov al,[eax][ebx]
.00460559: 3C20 cmp al,020 ;" "
.0046055B: 7204 jb .000460561 -------- (7)
.0046055D: 3C7D cmp al,07D ;"}"
.0046055F: 7613 jbe .000460574
.00460561: 68DE3D4C00 push 0004C3DDE ;" L=?
.00460566: 8D95C0FEFFFF lea edx,[ebp][0FFFFFEC0]
.0046056C: 52 push edx
.0046056D: E8E8E60400 call .0004AEC5A
.00460572: EB2D jmps .0004605A1
.00460574: 6A01 push 001
我试所有的类似 CMP xxxx,20
JB/JL xxxx (该行用90 90 替换)
经验证发现许多应该显示的字符串也没有显示,惨惨惨!问题出在比较的方式不一样.您可以用HEXEDIT打开一个EXE文件,所有被显示字符串末尾有一个字节00H,当读取字符串完毕后读入字符00H,此时JB/JL必然成立,必须正常跳转,不能被改成NOP,所以改思路:
CMP WORD PTR [XXXX],20
JB/JL XXXX ==>90 90
CMP BYTE PTR[XXXX],20 { 对照(3)(4) (7)处} ===>20改00
JB/JL XXXX ==>JB改JE
完整记录下要修改处的CS:IP或16进制字串,用UNASPACK脱掉W32DASM的外壳,再用HEXEDIT(必须记录被修改处的16进制字串)或HACKVIEW修改,最后您去测试,中文信息是不是全显示出来了?

版权所有，请不要修改原内容