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Reverse Code Engineering RCE CD +sandman 2000
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ReverseCodeEngineeringRceCdsandman2000.iso
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tc_crackme1.txt
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Text File
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2000-05-25
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3KB
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66 lines
CrackMe #1 By tC Surrealizm
---------------------------
Tools Used:
SoftIce
---
Protection:
Keyfile Prot
---
Ok, start the crackme, choose Try it and set a breakpoint on ReadFile, choose a file
and press Open, then step until you come here:
:00429DA3 E840A7FDFF CALL 004044E8 ; reads the file
:00429DA8 E86B88FDFF CALL 00402618
:00429DAD 33C0 XOR EAX,EAX ; eax = 0
:00429DAF 8A45FF MOV AL,[EBP-01] ; al = char from file
:00429DB2 03D8 ADD EBX,EAX ; ebx = ebx + al
:00429DB4 8D85B0FEFFFF LEA EAX,[EBP-0150]
:00429DBA E8D5A6FDFF CALL 00404494
:00429DBF E85488FDFF CALL 00402618
:00429DC4 84C0 TEST AL,AL
:00429DC6 74D2 JZ 00429E9A ; check if EOF, if not jump
:00429DC8 8D85B0FEFFFF LEA EAX,[EBP-0150]
:00429DCE E885A6FDFF CALL 00404458
:00429DD3 E84088FDFF CALL 00402618
:00429DD8 81FBA9200000 CMP EBX,000020A9 ; check if sum = 20A9h
:00429DDE 750E JNZ 00429DEE ; jump if not
:00429DE0 BA4C9E4200 MOV EDX,00429E4C ; edx = Status: Registered - Well Done
:00429DE5 8BC6 MOV EAX,ESI
:00429DE7 E85CEEFEFF CALL 00418C48
:00429DEC EB0C JMP 00429DFA
:00429DEE BA2C9E4200 MOV EDX,00429E2C ; edx = Status: Unregistered
so all the file should contain is chars of a value of 20A9h , and with some small
calculations that means 68 * z and 1 * A
so the file can look like this:
zzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzA
and to get the titlebar to say 'Status: Registered - Well Done' when starting, you need
to patch one byte.. disassemble the file in W32DASM, search for 'Status: Unregistered'
and you will come here:
* Possible StringData Ref from Code Obj ->"Status: Unregistered"
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:00429D44 BA2C9E4200 mov edx, 00429E2C <-- note that push adress
:00429D49 8BC6 mov eax, esi
now search for 'Status: Registered - Well Done' and you will land here:
* Possible StringData Ref from Code Obj ->"Status: Registered - Well done"
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:00429DE0 BA4C9E4200 mov edx, 00429E4C <-- note that push adress
:00429DE5 8BC6 mov eax, esi
:00429DE7 E85CEEFEFF call 00418C48
:00429DEC EB0C jmp 00429DFA
so all we have to do is to search for
BA2C9E4200
and change to BA4C9E4200
Now it will be fully cracked..
---
/Klefz - http://klefz.cjb.net