PaperclipOrg
Claude Agent Skill · by Wshobson

Anti Reversing Techniques

This is a solid reference for anyone doing malware analysis, CTF challenges, or reverse engineering work where you hit anti-debugging roadblocks. It covers the

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Terminal · npx
$npx skills add https://github.com/wshobson/agents --skill anti-reversing-techniques
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How Anti Reversing Techniques fits into a Paperclip company.

Anti Reversing Techniques drops into any Paperclip agent that handles this kind of work. Assign it to a specialist inside a pre-configured PaperclipOrg company and the skill becomes available on every heartbeat — no prompt engineering, no tool wiring.

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---name: anti-reversing-techniquesdescription: Understand anti-reversing, obfuscation, and protection techniques encountered during software analysis. Use this skill when analyzing malware evasion techniques, when implementing anti-debugging protections for CTF challenges, when reverse engineering packed binaries, or when building security research tools that need to detect virtualized environments.--- > **AUTHORIZED USE ONLY**: This skill contains dual-use security techniques. Before proceeding with any bypass or analysis:>> 1. **Verify authorization**: Confirm you have explicit written permission from the software owner, or are operating within a legitimate security context (CTF, authorized pentest, malware analysis, security research)> 2. **Document scope**: Ensure your activities fall within the defined scope of your authorization> 3. **Legal compliance**: Understand that unauthorized bypassing of software protection may violate laws (CFAA, DMCA anti-circumvention, etc.)>> **Legitimate use cases**: Malware analysis, authorized penetration testing, CTF competitions, academic security research, analyzing software you own/have rights to # Anti-Reversing Techniques Understanding protection mechanisms encountered during authorized software analysis, security research, and malware analysis. This knowledge helps analysts bypass protections to complete legitimate analysis tasks. For advanced techniques, see [references/advanced-techniques.md](references/advanced-techniques.md) --- ## Input / Output **What you provide:** - **Binary path or sample**: the executable, DLL, or firmware image under analysis- **Platform**: Windows x86/x64, Linux, macOS, ARM — affects which checks apply- **Goal**: bypass for dynamic analysis, identify protection type, build detection code, implement for CTF **What this skill produces:** - **Protection identification**: named technique (e.g., RDTSC timing check, PEB BeingDebugged) with location in binary- **Bypass strategy**: specific patch addresses, hook points, or tool commands to neutralize each check- **Analysis report**: structured findings listing each protection layer, severity, and recommended bypass- **Code artifacts**: Python/IDAPython scripts, GDB command sequences, or C stubs for bypassing or implementing checks --- ## Anti-Debugging Techniques ### Windows Anti-Debugging #### API-Based Detection ```c// IsDebuggerPresentif (IsDebuggerPresent()) {    exit(1);} // CheckRemoteDebuggerPresentBOOL debugged = FALSE;CheckRemoteDebuggerPresent(GetCurrentProcess(), &debugged);if (debugged) exit(1); // NtQueryInformationProcesstypedef NTSTATUS (NTAPI *pNtQueryInformationProcess)(    HANDLE, PROCESSINFOCLASS, PVOID, ULONG, PULONG); DWORD debugPort = 0;NtQueryInformationProcess(    GetCurrentProcess(),    ProcessDebugPort,        // 7    &debugPort,    sizeof(debugPort),    NULL);if (debugPort != 0) exit(1); // Debug flagsDWORD debugFlags = 0;NtQueryInformationProcess(    GetCurrentProcess(),    ProcessDebugFlags,       // 0x1F    &debugFlags,    sizeof(debugFlags),    NULL);if (debugFlags == 0) exit(1);  // 0 means being debugged``` **Bypass:** Use ScyllaHide plugin in x64dbg (patches all common checks automatically). Manually: force `IsDebuggerPresent` return to 0, patch `PEB.BeingDebugged` to 0, hook `NtQueryInformationProcess`. In IDA: `ida_bytes.patch_byte(check_addr, 0x90)`. #### PEB-Based Detection ```c// Direct PEB access#ifdef _WIN64    PPEB peb = (PPEB)__readgsqword(0x60);#else    PPEB peb = (PPEB)__readfsdword(0x30);#endif // BeingDebugged flagif (peb->BeingDebugged) exit(1); // NtGlobalFlag// Debugged: 0x70 (FLG_HEAP_ENABLE_TAIL_CHECK |//                 FLG_HEAP_ENABLE_FREE_CHECK |//                 FLG_HEAP_VALIDATE_PARAMETERS)if (peb->NtGlobalFlag & 0x70) exit(1); // Heap flagsPDWORD heapFlags = (PDWORD)((PBYTE)peb->ProcessHeap + 0x70);if (*heapFlags & 0x50000062) exit(1);``` **Bypass:** In x64dbg, follow `gs:[60]` (x64) or `fs:[30]` (x86) in dump. Set `BeingDebugged` (offset +2) to 0; clear `NtGlobalFlag` (offset +0xBC on x64). #### Timing-Based Detection ```c// RDTSC timinguint64_t start = __rdtsc();// ... some code ...uint64_t end = __rdtsc();if ((end - start) > THRESHOLD) exit(1); // QueryPerformanceCounterLARGE_INTEGER start, end, freq;QueryPerformanceFrequency(&freq);QueryPerformanceCounter(&start);// ... code ...QueryPerformanceCounter(&end);double elapsed = (double)(end.QuadPart - start.QuadPart) / freq.QuadPart;if (elapsed > 0.1) exit(1);  // Too slow = debugger // GetTickCountDWORD start = GetTickCount();// ... code ...if (GetTickCount() - start > 1000) exit(1);``` **Python script — timing-based anti-debug detection scanner:** ```python#!/usr/bin/env python3"""Scan a binary for common timing-based anti-debug patterns."""import reimport sys PATTERNS = {    "RDTSC":              rb"\x0f\x31",                    # RDTSC opcode    "RDTSCP":             rb"\x0f\x01\xf9",                # RDTSCP opcode    "GetTickCount":       rb"GetTickCount\x00",    "QueryPerfCounter":   rb"QueryPerformanceCounter\x00",    "NtQuerySysInfo":     rb"NtQuerySystemInformation\x00",} def scan(path: str) -> None:    data = open(path, "rb").read()    print(f"Scanning: {path} ({len(data)} bytes)\n")    for name, pattern in PATTERNS.items():        hits = [m.start() for m in re.finditer(re.escape(pattern), data)]        if hits:            offsets = ", ".join(hex(h) for h in hits[:5])            print(f"  [{name}] found at: {offsets}")    print("\nDone. Cross-reference offsets in IDA/Ghidra to find check logic.") if __name__ == "__main__":    scan(sys.argv[1])``` **Bypass:** Use hardware breakpoints (no INT3 overhead), NOP the comparison + conditional jump, freeze RDTSC via hypervisor, or hook timing APIs to return consistent values. #### Exception-Based Detection ```c// SEH: if debugger is attached it consumes the INT3 exception// and execution falls through to exit(1) instead of the __except handler__try { __asm { int 3 } }__except(EXCEPTION_EXECUTE_HANDLER) { return; }  // Clean: exception handled hereexit(1);  // Dirty: debugger swallowed the exception // VEH: register handler that self-handles INT3 (increments RIP past INT3)// Debugger intercepts first, handler never runs → detectedLONG CALLBACK VectoredHandler(PEXCEPTION_POINTERS ep) {    if (ep->ExceptionRecord->ExceptionCode == EXCEPTION_BREAKPOINT) {        ep->ContextRecord->Rip++;        return EXCEPTION_CONTINUE_EXECUTION;    }    return EXCEPTION_CONTINUE_SEARCH;}``` **Bypass**: In x64dbg, set "Pass exception to program" for EXCEPTION_BREAKPOINT (Options → Exceptions → add 0x80000003). ### Linux Anti-Debugging ```c// ptrace self-traceif (ptrace(PTRACE_TRACEME, 0, NULL, NULL) == -1) {    // Already being traced    exit(1);} // /proc/self/statusFILE *f = fopen("/proc/self/status", "r");char line[256];while (fgets(line, sizeof(line), f)) {    if (strncmp(line, "TracerPid:", 10) == 0) {        int tracer_pid = atoi(line + 10);        if (tracer_pid != 0) exit(1);    }} // Parent process checkif (getppid() != 1 && strcmp(get_process_name(getppid()), "bash") != 0) {    // Unusual parent (might be debugger)}``` **Bypass (LD_PRELOAD hook):** ```bash# hook.c: long ptrace(int request, ...) { return 0; }# gcc -shared -fPIC -o hook.so hook.cLD_PRELOAD=./hook.so ./target``` **GDB bypass command sequence:** ```gdb# 1. Make ptrace(PTRACE_TRACEME) always return 0 (success)catch syscall ptracecommands  silent  set $rax = 0  continueend # 2. Bypass check after ptrace call: find "cmp rax, 0xffffffff; je <exit>"#    Clear ZF so the conditional jump is not taken:#    set $eflags = $eflags & ~0x40 # 3. Bypass /proc/self/status TracerPid check at the open() levelcatch syscall openatcommands  silent  # If arg contains "status", patch the fd result to /dev/null equivalent  continueend # 4. Bypass parent process name checkset follow-fork-mode childset detach-on-fork off``` --- ## Anti-VM Detection ### Hardware Fingerprinting ```c// CPUID-based detectionint cpuid_info[4];__cpuid(cpuid_info, 1);// Check hypervisor bit (bit 31 of ECX)if (cpuid_info[2] & (1 << 31)) {    // Running in hypervisor} // CPUID brand string__cpuid(cpuid_info, 0x40000000);char vendor[13] = {0};memcpy(vendor, &cpuid_info[1], 12);// "VMwareVMware", "Microsoft Hv", "KVMKVMKVM", "VBoxVBoxVBox" // MAC address prefix// VMware: 00:0C:29, 00:50:56// VirtualBox: 08:00:27// Hyper-V: 00:15:5D``` ### Registry/File Detection ```c// Windows registry keys// HKLM\SOFTWARE\VMware, Inc.\VMware Tools// HKLM\SOFTWARE\Oracle\VirtualBox Guest Additions// HKLM\HARDWARE\ACPI\DSDT\VBOX__ // Files// C:\Windows\System32\drivers\vmmouse.sys// C:\Windows\System32\drivers\vmhgfs.sys// C:\Windows\System32\drivers\VBoxMouse.sys // Processes// vmtoolsd.exe, vmwaretray.exe// VBoxService.exe, VBoxTray.exe``` ### Timing-Based VM Detection ```c// VM exits cause timing anomaliesuint64_t start = __rdtsc();__cpuid(cpuid_info, 0);  // Causes VM exituint64_t end = __rdtsc();if ((end - start) > 500) {    // Likely in VM (CPUID takes longer)}``` **Bypass:** Use bare-metal environment, harden VM (remove guest tools, randomize MAC, delete artifact files), patch detection branches in the binary, or use FLARE-VM/REMnux with hardened settings. For advanced VM detection (RDTSC delta calibration, VMware backdoor port, hypervisor leaf enumeration, guest driver artifact checks), see [references/advanced-techniques.md](references/advanced-techniques.md). --- ## Code Obfuscation ### Control Flow Obfuscation #### Control Flow Flattening ```c// Originalif (cond) {    func_a();} else {    func_b();}func_c(); // Flattenedint state = 0;while (1) {    switch (state) {        case 0:            state = cond ? 1 : 2;            break;        case 1:            func_a();            state = 3;            break;        case 2:            func_b();            state = 3;            break;        case 3:            func_c();            return;    }}``` **Analysis Approach:** - Identify state variable- Map state transitions- Reconstruct original flow- Tools: D-810 (IDA), SATURN #### Opaque Predicates ```cint x = rand();if ((x * x) >= 0) { real_code(); }   // Always true  → junk_code() is deadif ((x*(x+1)) % 2 == 1) { junk(); }  // Always false → consecutive product is even``` **Analysis Approach:** Identify invariant expressions via symbolic execution (angr, Triton), or pattern-match known opaque forms and prune them. ### Data Obfuscation #### String Encryption ```c// XOR encryptionchar decrypt_string(char *enc, int len, char key) {    char *dec = malloc(len + 1);    for (int i = 0; i < len; i++) {        dec[i] = enc[i] ^ key;    }    dec[len] = 0;    return dec;} // Stack stringschar url[20];url[0] = 'h'; url[1] = 't'; url[2] = 't'; url[3] = 'p';url[4] = ':'; url[5] = '/'; url[6] = '/';// ...``` **Analysis Approach:** ```python# FLOSS for automatic string deobfuscationfloss malware.exe # IDAPython string decryptiondef decrypt_xor(ea, length, key):    result = ""    for i in range(length):        byte = ida_bytes.get_byte(ea + i)        result += chr(byte ^ key)    return result``` #### API Obfuscation ```c// Dynamic API resolutiontypedef HANDLE (WINAPI *pCreateFileW)(LPCWSTR, DWORD, DWORD,    LPSECURITY_ATTRIBUTES, DWORD, DWORD, HANDLE); HMODULE kernel32 = LoadLibraryA("kernel32.dll");pCreateFileW myCreateFile = (pCreateFileW)GetProcAddress(    kernel32, "CreateFileW"); // API hashingDWORD hash_api(char *name) {    DWORD hash = 0;    while (*name) {        hash = ((hash >> 13) | (hash << 19)) + *name++;    }    return hash;}// Resolve by hash comparison instead of string``` **Analysis Approach:** Identify the hash algorithm, build a database of known API name hashes, use HashDB plugin for IDA, or run under a debugger to let the binary resolve calls at runtime. ### Instruction-Level Obfuscation ```asm; Dead code insertion — semantically inert but pollutes disassemblypush ebx / mov eax, 1 / pop ebx / xor ecx, ecx / add ecx, ecx ; Instruction substitution — same semantics, different encodingxor eax, eax  →  sub eax, eax  |  mov eax, 0  |  and eax, 0mov eax, 1    →  xor eax, eax; inc eax  |  push 1; pop eax``` For advanced anti-disassembly tricks (overlapping instructions, junk byte insertion, self-modifying code, ROP as obfuscation), see [references/advanced-techniques.md](references/advanced-techniques.md). --- ## Bypass Strategies Summary ### General Principles 1. **Understand the protection**: Identify what technique is used2. **Find the check**: Locate protection code in binary3. **Patch or hook**: Modify check to always pass4. **Use appropriate tools**: ScyllaHide, x64dbg plugins5. **Document findings**: Keep notes on bypassed protections ### Tool Recommendations ```Anti-debug bypass:    ScyllaHide, TitanHideUnpacking:           x64dbg + Scylla, OllyDumpExDeobfuscation:       D-810, SATURN, miasmVM analysis:         VMAttack, NoVmp, manual tracingString decryption:   FLOSS, custom scriptsSymbolic execution:  angr, Triton``` ### Ethical Considerations This knowledge should only be used for: - Authorized security research- Malware analysis (defensive)- CTF competitions- Understanding protections for legitimate purposes- Educational purposes Never use to bypass protections for: software piracy, unauthorized access, or malicious purposes. --- ## Troubleshooting **Detection technique works on x86 but not ARM** RDTSC and CPUID are x86-only. On ARM, use `MRS x0, PMCCNTR_EL0` (requires kernel PMU access) or `clock_gettime(CLOCK_MONOTONIC)`. PEB/TEB do not exist on ARM — replace with `/proc/self/status` (Linux) or `task_info` (macOS). Rebuild detection logic with platform-specific APIs. **False positive on legitimate debugger or analysis tool** Timing checks fire when Process Monitor or AV hooks inflate syscall latency. Calibrate the threshold at startup: measure the guarded path 3 times and use `mean + 3*stddev`. For ptrace checks, verify the TracerPid comm name via `/proc/<pid>/comm` before exiting — it may be an unrelated monitoring tool, not a debugger. **Bypass patch causes crash instead of continuing execution** Before NOPing a conditional jump, trace the "detected" branch fully. If it initializes or frees heap state needed later, patching the jump skips that setup and corrupts state. Instead, patch the comparison operand to the expected "clean" value, or use x64dbg's "Set condition to always false" on the breakpoint rather than modifying bytes. --- ## Related Skills - `binary-analysis-patterns` — static and dynamic analysis workflows for ELF/PE/Mach-O- `memory-forensics` — process memory acquisition, artifact extraction, and live analysis- `protocol-reverse-engineering` — decoding custom binary protocols and encrypted network traffic