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Introduction to Reverse Engineering

Introduction to Reverse Engineering. Information Security – Theory vs. Reality Tel Aviv University, 368-4474-01 , Winter 201 2 -2013 Lecture 7. Inbar Raz Malware Research Lab Manager. What is Reverse Engineering?.

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Introduction to Reverse Engineering

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  1. Introduction to Reverse Engineering Information Security – Theory vs. RealityTel Aviv University, 368-4474-01, Winter 2012-2013Lecture 7 Inbar RazMalware Research Lab Manager

  2. What is Reverse Engineering? Reverse engineering is the process of discovering the technological principles of a device, object, or system through analysis of its structure, function, and operation. aka: Reversing, RE, SRE

  3. Why do it? AcademicResearch(Yeah, right…) FindVulnerabilities Discover Trade Secrets Circumvent[Copy]Protection AnalyseProtocols Patch BinaryandAlter Behavior PureCuriosity

  4. Sounds awesome, right?

  5. So where’s the catch? • Low-level is, well, low level… 00401000 push ebp00401001 movebp, esp00401003 push ecx00401004 push ecx00401005 and dwordptr [ebp-4], 000401009 push esi0040100A movesi, [ebp+8]0040100D push edi0040100E push esi0040100F call ds:[00402008h]00401015 movedi, eax00401017 xoredx, edx00401019 test edi, edi0040101B jle 00401047h0040101D movsxecx, byte ptr [edx+esi]00401021 add [ebp-4], ecx00401024 mov [ebp-8], ecx00401027 roldwordptr [ebp-4], 10040102A moveax, ecx0040102C imuleax, [ebp-4]00401030 mov [ebp-4], eax00401033 moveax, [ebp-8]00401036 add [ebp-4], eax00401039 xor [ebp-4], ecx0040103C incedx0040103D cmpedx, edi0040103F jl 0040101Dh00401041 cmpdwordptr [ebp-4], 000401045 jnz 00401063h00401047 push 000401049 push 40230Ch0040104E push 4022CCh00401053 push ds:[004023ACh]00401059 call ds:[00402010h]0040105F xoreax, eax00401061 jmp 0040107Fh00401063 xordwordptr [ebp+0Ch], 01337C0DEh0040106A sub dwordptr [ebp+0Ch], 0BADC0DE5h00401071 moveax, [ebp-4]00401074 not dwordptr [ebp+0Ch]00401077 xoreax, [ebp+0Ch]0040107A negeax0040107C sbbeax, eax0040107E inceax0040107F pop edi00401080 pop esi00401081 leave00401082 retn for (Serial = 0, i = 0; i < strlen(UserName); i++) { CurChar = (int) UserName[i]; Serial += CurChar; Serial = (((Serial << 1) && 0xFFFFFFFE) || ((Serial >> 31) && 1)); Serial = (((Serial * CurChar) + CurChar) ^ CurChar); } UserSerial = ~((UserSerial ^ 0x1337C0DE) - 0xBADC0DE5);

  6. So where’s the catch? • Low-level is, well, low level… • Needle in a haystack • Average opcode size: 3 bytes • Average executable size: 500KB (on WinXP) • There are executables, libraries, drivers….

  7. So where’s the catch? • Low-level is, well, low level… • Needle in a haystack • Sometimes, the code resists • Packers and compressors • Obfuscators

  8. So where’s the catch? • Low-level is, well, low level… • Needle in a haystack • Sometimes, the code resists • Sometimes, the code fights back • Detect reversing tools • Detect VMs and emulators

  9. A Battle of Wits • Author writes code • Reverser reverses it • Author creates an anti-reversing technique • Reverser bypasses it • And so on…

  10. So what do you need in order to be a good reverser?

  11. We’ll come backto this…

  12. Tools of the Trade • Disassembler (Static code analysis) • Debugger (Dynamic code analysis) • Hex Editor • PE Analyzer • Resource Editor

  13. Disassemblers

  14. The old world: Sourcer

  15. The old world: Sourcer

  16. Old ages: Sourcer

  17. Old ages: Sourcer

  18. Welcome to Windows: W32DASM

  19. The Holy Grail: IDA-Pro • Started as an Interactive Dis-Assembler, enabling user interaction with the disassembler’s decisions. • Slowly evolved into an automatic RE tool: • Built-in full-control script language • Library recognition (including user-generated) • Function prototype information • Display • Propagate throughout the code • Support for plug-ins • Support for Python scripting • Multi-architecture, cross-platform support • Full incorporation with built-in and external debuggers

  20. Debuggers זין בדיבאג באג בדיזיין –

  21. First, there was DEBUG…

  22. GUI and much more: Turbo Debugger

  23. GUI and much more: Turbo Debugger

  24. GUI and much more: Turbo Debugger

  25. Next major step: Soft-ICE

  26. And finally: OllyDbg

  27. Other Tools

  28. Hex-Editor

  29. PE Analyzer

  30. Resource Editor

  31. Methodology

  32. How we do it? • Finding the interesting part • System calls (User mode and Kernel mode API) • Strings and constants • Dynamic loading of libraries • Provocation • Zoom-in and Zoom-out • Better and quicker (and how not to get stuck) • Iterative passes over the code • Leave no stone unturned • Macros/Scripts/Plugins • BinDiffing(manual and with tools)

  33. Let’s play with them tools…

  34. 60 seconds on x86 registers • General purpose registers:32bit/16bit/8bit • Index registers:32bit/16bit • Segment registers:16bit • Flags:32bit/16bit

  35. Exercise 1:Static Reversing

  36. Exercise 1: Static Reversing • Target: a 2004 “Crack-Me” • Tools: IDA-Pro

  37. Exercise 2:Dynamic Reversing

  38. Exercise 2: Dynamic Reversing • Target: a 2004 “Crack-Me” • Tools: OllyDbg, IDA-Pro

  39. Exercise 3:Simple Anti-Debugging

  40. Exercise 3: Simple Anti Debugging • Target: a 2006 “Crack-Me” • Tools: OllyDbg

  41. Reversing Malware • Malware is comprised of the following building blocks: • Infection Vector • Concealment • Operation • Communications • Check Point’s Anti-Malware Software Blade sits at the gateway • Therefore, communications interest us the most

  42. Introducing: Spy Eye • A CrimeWareToolKit, originating in Russia. • Used mostly for stealing financial information, but will settle for any other identity information and key logging… • Like any serious trojan, Spy Eye compresses its traffic and encrypts it • Compression is performed using a public library (LZO) • Encryption algorithm is proprietary

  43. Act 1:Encryption

  44. Act 2:Configuration Download

  45. Act 3:Another Encryption

  46. So what do you need in order to be a good reverser?

  47. What makes a good reverser? Qualities • Patient • Curious • Persistent • Outside-the-Box Thinking • Optional: Good lookin’ Knowledge • Assembly Language • Some High-Level programming • Best: origin of binary • Operating System Internals • API • Data Structures • File Structures • Good scripting skills • Anti-Debugging Tricks

  48. Outside-the-Box Thinking

  49. And remember, kids: Binary ReverseEngineer + =?

  50. Which means… F A I L

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