Agent skill for Android APK reverse engineering: dex patching, unpacking, repacking, ad and paywall removal, native .so analysis, and runtime instrumentation with Frida.
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<a href="#what-it-is-good-at">Capabilities</a> · <a href="#structure">Structure</a> · <a href="#install">Install</a> · <a href="#requirements">Requirements</a> · <a href="#read-this-first">Failure catalogue</a> · <a href="#scope">Scope</a> · <a href="#repository-maintenance">Maintenance</a> · <a href="#disclaimer">Disclaimer</a>
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# apk-reverse
An Agent Skill for Android APK reverse engineering, debloating, ad removal, surgical
dex patching, repacking, and runtime/server analysis.
It is a **skill**, not a tutorial: it is written to be loaded by an agent (Claude Code,
Codex, or any harness that supports the Agent Skills format) while it works, so it is
organized for progressive disclosure — a short decision-oriented `SKILL.md`, detailed
references loaded only when a step needs them, and parameterized scripts you can run
directly.
## How an agent is expected to consume this
`SKILL.md` is deliberately written as a **procedure with gates** rather than as advice, because the
observed failure mode is not ignorance — it is a model reading the whole thing, agreeing with it, and
then reasoning from first principles anyway.
So there are four things in the body that are meant to be *acted on*, not read:
- **Four override rules (R1–R4).** Where they conflict with the current plan, they win until evidence
overrides them.
- **A symptom index.** Each row is a failure that has already been paid for. **A matching row is a
stop signal**: load that file before running another command, rather than after a few more attempts.
Reasoning past a known symptom is how the same hours get spent twice.
- **Four gates (G1–G4),** each an action with a pass criterion. "I understand the idea" does not clear
a gate. They exist so that classification, environment truth and a control build happen *before*
the first patch, not after the third failure.
- **A two-strike rule and stop conditions.** Two failures of the same shape mean the model is wrong,
not the parameters. The third variant of a hypothesis that already failed twice is where rounds go
to die.
And one thing at the end that is meant to be *withheld*: **"done"** has a definition (six items). A
clean log is not one of them. Anything short of all six is a checkpoint, and should be reported as a
checkpoint with what remains.
If you are an agent reading this: the cheapest possible first command is
`python skills/apk-reverse/scripts/doctor.py`. It tells you which of these tools exist here, which
scripts can actually run, and whether something in the environment is already poisoning your
measurements.
## What it is good at
- Deciding **fast** whether a request is even achievable client-side, instead of
burning hours on a paywall that is enforced by a server.
- Deciding **what form the deliverable must take** before any work starts — an
unrooted, self-contained artifact is a different problem from "make it work on this
machine", and confusing the two is the most expensive drift in this domain.
- Choosing the **safest patch layer** for a given change, and avoiding the layers that
break the app.
- Catching the repack failure that looks like success: an app that installs, launches and
renders perfectly while **every signed request is rejected**, because the client derives its
request-signing key from its own signing certificate.
- Separating **your own mistakes from the app's or the server's problems** — a
feature-scoped failure (login, registration, payment) is often a TLS/certificate issue on
one code path, not a consequence of the patch you just built. Device state, a dead device
server and clock drift masquerade the same way.
- Establishing **which architecture and which library are actually executing**, rather
than trusting what the manifest ships or what the device claims.
- Working through **packed/hardened targets**: identifying the packer, unpacking, and turning a
memory dump back into a patched, installable APK.
- Handling a **hardened library that terminates the process on purpose** — including the
deliberate-crash shape (`fault addr 0x4`) that looks exactly like an ordinary null-dereference
bug, and the "neutralise it, but never by making it *not return*" rule that decides whether the
fix works or freezes the whole app in a way that looks nothing like the cause.
- Knowing **which tools to reach for and where each one lies** — including the ones that only
exist as a GUI, so you ask for a human instead of silently substituting a weaker method.
- Making a patched build **stay** patched: neutralising version checks, forced-upgrade dialogs and
self-update installers so the work cannot be switched off remotely — and recognising the
hot-update/remote-config channel that can quietly undo it without any version change.
- Separating a **client-side sign-in gate** (patchable) from an **account-scoped resource** (empty
because the server has nothing to answer with), and knowing that forging a session produces a state
worse than being signed out.
- Keeping a **long task honest**: a live record, graded conclusions, calibrated timeouts, and
bounded waits, so progress is not lost and the same mistake is not made twice.
- Avoiding the specific mistakes that produce an APK that builds perfectly and dies at
runtime.
- Deciding **what the deliverable should be when an APK is not an option** — a repack refused by
several independent checks is *blocked*, not expensive, and the fallback ladder is a system-level
module, a local RPC service, or an honest report with a stated boundary.
- Telling a **real memory dump from an extraction-shell skeleton**, and knowing which recovery route
applies — including the root-side dump for when `frida` itself is refused. What the measurement can
and cannot see is in `skills/apk-reverse/references/advanced-unpacking.md`.
- **Calling a routine instead of reversing it** when reversing costs more than invoking: emulated
execution on the host, or a live function service-ified over Frida RPC.
- Reading **instruction-level execution evidence** when a native function has been flattened into a
state machine by OLLVM — including the two ways Stalker was measured to bite back on a real device.
- Recognising when **userspace hooking cannot reach the check at all** (raw `svc` syscalls,
`init_array`-early detection), what the next layer up and down can actually do, and when escalating
is the wrong answer.
- Working **protocols that are not REST** — protobuf without a schema, gRPC, QUIC/HTTP3 — and
native-side certificate pinning that ignores the system trust store.
- Working **from the phone itself**: MT Manager's edit/repack/sign flow and its APK MCP surface,
LSPosed Manager, and on-device data inspection, alongside the PC toolchain rather than instead of it.
- Telling **Java2C apart from an extraction shell** before spending hours hunting a decrypted DEX that
does not exist at any point in the process lifetime — the code was compiled into a `.so`.
- Handling a build that arrives as a **split APK / App Bundle set**: reading the set off a device,
signing every member with one keystore for `pm install-multiple`, or merging code/native members
into a standalone APK when that is legal.
- Working a **real Dex VMP** with the known-plaintext differential — which links can be automated and
which cannot, what a compiled fixture can and cannot reach, and how to *prove* a derived
private-opcode table instead of asserting one.
- **Publishing what it learns without publishing the target** — a scanner that reports identity
shapes with their context, an explicit list of what must *not* be redacted (tools, libraries,
protocol fields, CVEs, hardening products, public crackmes) because redacting those destroys the
reusable part, and exit codes that gate a commit.
- Reading a **precedent** before repeating work this repository already converged on: the positive
half of the record, with the route including its dead ends, a grade on every assertion, and the
files the case says to write back to.
## Structure
`SKILL.md`, `references/` and `scripts/` are all inside the skill directory, `skills/apk-reverse/`.
Everything at the repository root is maintenance tooling shared across skills, not part of an
installed skill.
```
SKILL.md a procedure with gates, not background reading:
how-to-use -> four override rules (R1-R4)
symptom index (a matching row is a stop signal)
four gates (G1-G4, actions with pass criteria)
thirteen classification questions
the workflow, with a per-step skip condition and a two-strike rule
what "done" means -> stop conditions -> constraints -> indexes
references/ loaded on demand, one topic each
recon.md identify packer, SDKs, code location, tamper checks; unpacking
server-config-and-updates.md
the most common shape of "ad" and the one usually mis-diagnosed:
the server supplies UI the client renders (launch screen, popup,
announcement, tab set). The two-layer fetch that proves it, how to
find the config DTOs by the field names data classes keep, why you
patch the decision and not the data, deciding the scope of "remove",
and remote re-enable / cached config durability
byte-level-patching.md equal-length byte edits: why they beat method rebuilding (measured),
locating an instruction's exact offset without scraping listings,
the instruction width traps that desynchronise a decode, neutralise
a branch vs redirect it, dex header integrity field order, and the
verifier's move-result rule
packers.md hardened targets: rejection signals, measuring the validation
boundary with single-variable tests, choosing a native host
code-virtualization-and-custom-linkers.md
the layer between "packed" and "clean": whole classes turned into
`native` declarations, a private loader whose SONAME does not match
its filename, an embedded self-decrypting payload, a Java-layer
"signature killer" that logs success while a native check kills you.
The keep-it/drop-it deadlock, how to separate the *checker* from the
*implementation*, and the string-redirect technique that ends it
without neutralizing anything
framework-runtimes.md Flutter / React Native / Unity: which layer owns the UI, and how to
find logic when there are no symbols (string encoding traps)
dart-aot.md Dart AOT in depth: version pinning and building a matching decompiler,
the object pool and reference indexes, register/boolean conventions,
the three signatures that identify business logic, locating, patching.
Begins with the snapshot-decoding front end it depends on (aotopsy or
blutter) because the pool listing is an input, not something this skill
produces itself
native-and-so.md .so hosts, DT_NEEDED vs JNI_OnLoad, relocation limits,
relocation-free bootstrapping, replacing Java methods natively,
and which ABI/library is *actually loaded and executing*
native-tamper-and-suicide.md how a hardened library kills its own process: the visible
mechanisms, how to tell which one actually fires, how to find the
site, forged section headers, function boundaries from
PT_GNU_EH_FRAME, scanner traps, and neutralising safely
detection-and-anti-analysis.md when the app fights back or the tool cannot run here: telling
detection apart from a broken environment, deciding by cost instead
of escalating, recognising an environment where dynamic analysis
simply does not work, and keeping the "blocks my analysis" question
separate from "blocks the deliverable"
toolchain.md what to install, how to invoke it non-interactively, which tools
are GUI-only, version-alignment traps, working offline,
**"not on PATH" is not "not installed"**, and which signer to use
long-task-discipline.md live record, conclusion grading, drift control, timeout and
wait calibration, deliverable-form drift, captures-you-never-looked-at,
long-context decay, handover
ad-removal.md ad taxonomy, wrapper mapping, callback trap, global gates, verification
updates-and-forced-upgrade.md keeping a patched build alive: locating the version check, the
two-layer patch (no-op the routine, neutralise the comparison), what not
to touch (manifest version, installer permission, host blocking),
self-update and hot-update/remote-config channels, verifying that no
version request is issued at all
account-gates.md sign-in walls, forced phone binding, guest mode: telling a client-side
gate (patchable) apart from an account-scoped resource (not), why
fabricating a session is worse than staying signed out, and the
unavoidable session loss after a reinstall
signature-derived-keys.md when the app's own signing certificate is used as key material:
detection greps, why offline extraction is unreliable, the
hardcode-then-verify procedure
membership-and-limits.md server vs client authority; what is and is not patchable
server-api.md probe an app's API; prove who owns the gate
tls-and-cert.md feature-scoped network failures: expired certs, dual trust chains
third-party-builds.md auditing a "cracked"/"modded" APK before trusting it
dex-patching.md patch-layer table + dexlib2 technique in depth
patch-audit.md proving a patch *landed* and is *legal*: length-vs-bytes
comparison, the equal-length-replacement blind spot, verifier-level
legality (move-result adjacency) checked statically, text-matching
patch traps, and reporting a missing patch
repack-and-sign.md repack rules, unpack-and-repack, signing, post-install hazards
runtime-data.md DataStore / SharedPreferences / SQLite / protobuf; when the app
rewrites your edit, and decoding a value that looks encrypted
dynamic-frida.md Frida setup, version pinning, the four-layer probe, hook strategy
environment.md device/emulator setup, root, ADB, offline devices, log signals,
emulator console control and recovery, preflight, look-at-the-screen
verification.md the claim ladder; what "done" means
desensitization-and-leak-scans.md
publishing discipline: what must be desensitized and what must stay,
the do-not-anonymize list, the leak scanner and its exit states, and
the entry-point file as a prompt surface
precedents/ the positive case library: route including dead ends, a grade per
assertion, measured pit-falls, and the write-back checklist
routing.md the on-demand inventory: every reference with when to load it, every
script with what it does, and a mirror of the symptom index
rasc-and-droidsaw.md the Rust re-implementation of the ASC indexer: measured speedup and
identical class sets, the enum shape where it silently drops bodies,
and how to build and verify it
evidence-summary.md the condensation that ships with the skill: capability, one-line
conclusion, strength, and the evidence you can actually open in an
installed copy
../evals/ NOT a spec directory either, but the location the Agent
Skills guidance recommends: `evals.json` holds the
with-skill / without-skill cases this skill has **not** run,
with the method for running them written into the file
../evidence/ NOT a spec directory: the machine-readable companions to the evidence
summary reference above -- `capability-matrix.json` (the same rows with
more fields), `tested-tool-versions.json` (versions and the probe behind
each), `known-limitations.md` (the installer-facing limit list). Shipped
inside the skill so an installed copy can answer "was this verified, and
how strongly" without the repository
pitfalls.md the failure catalogue -- read before building
advanced-unpacking.md the dump landed but the bodies are empty: extraction-shell diagnosis by
trivial-body ratio, FART-style active invocation and why its classic hooks
died on Android 12-16, code_item splicing, the root-side dump for when
frida itself is refused, and the honest VMP boundary
lsposed-and-modules.md the repack is refused, so deliver a system-level hook module instead:
module anatomy, a gradle-free build chain, scope configuration and how to
verify injection, and the layer a Java module cannot reach
emulation-and-rpc.md call the routine instead of reading it: Unidbg/Unicorn emulation and its
environment-filling cost, versus service-ifying a live function over Frida RPC
native-dbi-and-deobfuscation.md
OLLVM shapes, Frida-Stalker traces, the trace-to-CFG route, the
Stalker/QBDI/emulation decision, and two measured boundaries (a follow that
delivers no events, and a crash from following a hot libc export)
protocol-reverse.md protobuf without a schema, schema recovery from decompiled code, gRPC frame
capture, the QUIC/HTTP3 limit, and native-side certificate pinning
kernel-and-environment-hardening.md
userspace hooking provably cannot reach the check: raw `svc`, init_array-early
detection, what each root scheme hides, the kernel-route map with its version
gate, and when to stop escalating
on-device-tooling.md working from the phone itself: MT Manager edit/repack/sign and its APK MCP,
LSPosed Manager, Termux+frida, on-device data inspection
java2c-and-jni-sinking.md Java2C and JNI sinking, the two hardening shapes most easily confused
with an extraction shell: the table that separates landing shell /
extraction shell / VMP / Java2C / JNI sinking, why the code is in the
`.so` and *never* in a dumped dex, and why a `Java_*` symbol search
comes back empty (dynamic registration, `-fvisibility=hidden`)
split-apk.md App Bundle / split APK sets: what the set is, pulling it off a device,
merging into one APK vs signing the set as a unit, the install refusals
and what each means, and making an installable fixture from a pulled set
vmp-differential-analysis.md
the known-plaintext differential for a real Dex VMP: which links can be
automated and which cannot (the upload is the bottleneck), the coverage a
compiled fixture can reach, how to *prove* a derived private-opcode
table, smali generation, and when the route is closed
coverage-and-limits.md the claim ladder applied to the skill itself: the evidence behind each
covered item, the dependencies this skill does not ship, and what was
never exercised
handoff-boundaries.md where this skill ends and another discipline begins: the JNI form
table, the packer-versus-loader split, and what "verified" means for
each of the four deliverable forms
scripts/ parameterized, path-agnostic
doctor.py run this first: capability report + per-script runnability, finds
tools installed off-PATH or as runnable jars, and surfaces the
environment facts that poison experiments (clock skew, leftover
adb forward / proxy, a device-side frida process already running)
dexutil.py dependency-free dex reader: structural walk + exact instruction
decode, dex header recompute/verify (correct checksum/signature
order), branch-target and operand helpers. Library shared by the
dex scripts, also runs standalone to dump one method with offsets
dex_find_insn.py locate an instruction by decoded semantics and print its exact byte
offset with context and both sides of any branch -- how you find a
patch site instead of guessing offsets
dex_patch_bytes.py equal-length byte patches from a JSON spec: semantic match, polarity
pin via expect_next, equal-length enforcement, verifier check, dex
header recompute, re-decode to prove it landed (--dry-run first)
dex_check_verifier.py tier-3 check: does any conditional branch target a move-result
(bypassing its producer)? Compares two builds and separates
pre-existing findings from regressions your patch introduced
coldstart.py cold-launch capture: timed screenshot burst + logcat signals +
installed-build facts + launch timing, and warns when the foreground
activity is not your app
so_constpatch.py same-length in-place rewrite of an isolated string constant, for
redirecting a library load instead of defeating a check
smtool.py baksmali/smali wrapper with a configurable classpath
dexpatch/ dexlib2 method-level rewriter (for changes that need new instructions)
patch_smali.py method-body replacement in a smali tree
dex_strpatch.py byte-level string patch with a string_ids ordering guard
dex_classdiff.py prove a dex edit was surgical
dex_strings.py strings/URLs/SDK markers without a decompiler
dart_pool_strings.py recover literals from a Dart AOT snapshot (framed entries, the
one-byte vs UTF-16 split, file offsets, run-length noise filter)
dart_pprefs.py build/query the object-pool -> code-site index for a Dart snapshot
dart_disasm.py annotated windowed disassembly of Dart AOT code + B/BL caller index
find_refs.py count callers of a method before patching it
repack.py rebuild APK, strip only signatures, keep META-INF/services/, write a
4-byte-aligned archive (resources.arsc STORED+aligned), sign, verify;
also split APK / App Bundle sets: inventory, sign every member with one
keystore, or merge code/native members into a standalone APK
devsh.py quoting-safe ADB shell helper
usb_net_proxy.py give an offline device network over USB
datastore_inject.py encode/inject AndroidX DataStore preferences safely
probe_api.py probe an HTTP API with the right headers
grab_crash.py recover stacks hidden by a crash-reporter SDK
install_test.py install + launch health check with logcat signal scan
frida_probe.js four-layer runtime probe (app net layer + OkHttp + java.net + exceptions)
run_probe.py inject the probe, stream it to a log file, stay resident
tls_check.py strict certificate check for one or more hosts
preflight.py environment check before every experiment block (device, root,
ABI/translation, clock skew, leftover proxy/forwards, dead server)
lib_map.py what is *actually mapped* into a live process: per-library path,
base, architecture, and whether it came from the APK or was
materialized at runtime
elf_plt.py resolve a PLT stub to its imported symbol (x86_64 + aarch64) from
the relocation table; list a symbol's callers; byte-diff two
libraries and name the symbol each changed stub belongs to
apk_diff.py entry-level diff of two builds: changed / added / removed, by
content hash so same-size replacements are caught
native_crash.py locate a native death from a log or tombstone: signal, fault
address, registers, frames split app vs system, the faulting
instruction, and a flag when the fault looks *arranged*
blob_decode.py search, don't guess, the framing of a stored value
(base64/hex x rotation x deflate); re-encode the edited payload
snap.py bounded burst screenshots + control-tree capture with a stall
detector, and a verdict on whether the tree is usable at all
sig_probe.py find the exact signatures[0].toCharsString() value — offline
candidates from an APK, or the authoritative read from a device
spawn_patch_detach.py spawn under a Frida probe, detach, then launch and capture: under
spawn mode the Activity stack often never comes up, and memory
writes survive detach while hooks do not
hook_patch_only.js the minimal probe for spawn_patch_detach.py — neutralise one native
death site by offset and report PATCHED
dex_dump_validate.py dedupe, validate and rank a directory of dumped dex images: sha256
grouping, header integrity, the trivial-body ratio that separates a real
dump from an extraction-shell skeleton, and a most-likely-original ranking
(--trim for page-aligned /proc/<pid>/mem captures)
dex_mem_scan.py search memory captures for embedded dex images and extract each at the
size its own header declares -- for a decrypted dex sitting in an
anonymous mapping no maps entry names
lsposed_scaffold.py generate a minimal LSPosed/Xposed module project (manifest with the
xposed meta-data, assets/xposed_init, hook class, gradle-free build notes)
frida_rpc_serve.py bridge a Frida script's rpc.exports to a local caller with reconnect
handling, so a live native function can be called rather than reversed
rpc_template.js the editable companion to frida_rpc_serve.py
stalker_trace.js instruction-level tracing with Frida Stalker: configurable targets,
trigger selection, the event stream, and output-size rules
stalker_report.py reduce a stalker_trace.js log to block histograms and call sequences,
with an explicit diagnostic for the measured zero-event case
mt_mcp_probe.py probe MT Manager's on-device APK MCP (Streamable HTTP, port 8787):
JSON-RPC handshake plus the grouped tool inventory
java2c_probe.py collect the evidence that separates Java2C from an extraction shell, a
VMP and ordinary JNI sinking: native density and stub ratio from the dex,
JNI_OnLoad / dynamic registration / toolchain strings from the `.so`,
each item labelled strong/medium/weak
protobuf_decode_raw.py schema-free protobuf decode: hex / file / stdin to a JSON tree, every
length-delimited field kept as a candidate set with ties labelled rather
than guessed, plus a byte-exact re-encode to check a round trip
vmp_diff_harness.py build a labelled opcode-coverage fixture, derive a candidate private-
opcode map from an original/hardened dex pair, verify the comparison in a
closed loop, and render a restored stream as a smali skeleton
kernelsu_syscall_mask.py generate a KernelSU/APatch syscall-masking scaffold: an installable
userspace module skeleton plus KPM/LKM/eBPF kernel-side templates, each
with its version gate and an explicit unverified label
rasc_build.py build and verify rasc, the Rust ASC re-implementation:
--check what is present, --build clone plus cargo, --verify an APK
against droidasc and fail on any class-set difference
scan_leaks.py scan a repository for target identity before publishing it: bundle ids
in manifest / `pm` / `ps` contexts, serial-shaped tokens, PATs, inline
appkey assignments, literal endpoints, host user paths. Exemptions for
everything that must stay (tools, libraries, CVEs, hardening products,
public crackmes, placeholders), findings carry their context,
`--show-exempt` prints why a hit was suppressed, exit 0/1/2
svc_scan.py name the syscall behind an inline `svc` and the segment it sits in,
which decides whether a libc-level hook can observe the call at all;
`--context` shows neighbours because a byte scan also matches data
anti_detect_probe.js observer-only Frida probe (patches nothing): path/loader/thread/kill
hooks with caller module + offset, an environment self-report
(`TracerPid`, frida-named mappings), and live streaming so a sub-second
self-destructing target still yields evidence
```
The repository also carries an **executable** test layer, which is a different thing from the
evidence record: `tests/` asserts what the scripts do (unit, CLI contract, no-device
integration) and `tests/benchmark.md` records what a route did on a real target. `tests/README.md`
states the split, and `.github/workflows/ci.yml` runs the gates plus the suite.
## Install
This repository is a **skills repository**: the skill lives at `skills/apk-reverse/`, which is the
layout the `skills` CLI resolves, and it is installed by name rather than by copying a directory:
```
npx skills add newliver666/apk-reverse # install every skill in the repo
npx skills add newliver666/apk-reverse --list # list what is here, install nothing
npx skills add newliver666/apk-reverse --skill apk-reverse -y
npx skills use newliver666/apk-reverse@apk-reverse # use it once, without installing
```
The CLI symlinks the skill into your agent's skills directory by default (`--copy` makes independent
copies instead), and `-g` installs for every project rather than the current one. With one skill in
the repository, `--skill apk-reverse` is redundant today; it is written out here because it is what
selects a single skill once a second one exists.
Once installed, the agent loads `SKILL.md` when a task matches its description, and pulls in
`references/*` only as needed. No global state, no machine-specific paths, and no build step.
## Requirements
Nothing is mandatory; each script checks what it needs. `skills/apk-reverse/scripts/doctor.py` reports
which of these are present here, which scripts can therefore run, and — usefully — which tools exist
somewhere other than PATH.
If your toolchain lives outside PATH (a project-local `tools/` directory, a versioned SDK folder, a
runnable `.jar` instead of a command), set `APKREV_TOOLS` to one or more directories and `doctor.py`
will find them:
```
set APKREV_TOOLS=<dir>;<dir> # Windows, e.g. an SDK or project-local tools dir
export APKREV_TOOLS=<dir>:<dir> # POSIX
```
The scripts themselves are plain `python3` and are intended to work identically on Windows, macOS and
Linux; where a snippet is POSIX-only it is labelled. Nothing here assumes a Unix shell.
| Tool | Used for |
|---|---|
| Python 3.9+ | all scripts |
| **`droidasc`** (ASC) (**optional but strongly recommended — install this first**) | whole-APK cross-reference index: `findrefs` / `listclass` / `getclass` / `getmanifest`. One `pip install droidasc`, no JVM, no SDK, no index build. Turns "which of N thousand classes mentions this string" into a sub-second query, and it is the only route to a class whose name R8 mangled. **This is the tool an agent should reach for before any full decompile** — see `skills/apk-reverse/references/toolchain.md` §droidasc (ASC) — ask an APK "who references this?", in one query |
| `ddc` (optional but strongly recommended) | single-binary dex→Java decompiler with query subcommands (`info`, `findrefs`, `strings --with-locations`, per-class decompile). No JVM. **Reads** what ASC **locates**; also reports package identity reliably — see `skills/apk-reverse/references/toolchain.md` §ddc — dex-to-Java with query subcommands (worth adopting) |
| `baksmali` / `smali` + `dexlib2` jars | disassembly, assembly, surgical patching |
| JDK (`javac`, `java`) | building/running the dexlib2 patcher; also provides `keytool`/`jarsigner` |
| Android SDK build-tools (`aapt`, `zipalign`, `apksigner`) | manifest info, alignment, signing. **`apksigner` is the signer to use** — `jarsigner` rewrites the archive and breaks the alignment Android R+ requires |
| `uber-apk-signer` (optional) | one-step align + sign |
| ADB | device work |
| Frida (host package + matching on-device server) | dynamic analysis |
| a rooted device or emulator | anything beyond static analysis |
None of these need to be on `PATH`: every script accepts an explicit path for the
tools it shells out to, and `skills/apk-reverse/references/toolchain.md` covers finding
an install that `PATH` does not know about (the common case for `apksigner` and
`keytool`).
## Read this first
**This project is published for learning, research and authorized security testing only.** It ships
no exploit payloads, no target data and no third-party binaries — it is a method, a set of scripts
and an evidence record. You are responsible for having the right to analyze whatever you point it at;
see **Disclaimer** at the end of this file.
`skills/apk-reverse/references/pitfalls.md`. It is the most valuable file here — every entry is a
failure that produced a broken artifact while looking completely healthy.
The four that hurt most:
1. Stripping the whole `META-INF/` during a repack deletes ServiceLoader registrations
and the app dies at startup with an error that names an unrelated library.
2. Patching a byte-level string without preserving `string_ids` ordering gets the whole
dex rejected, while checksums and signatures verify perfectly.
3. Rebuilding a dex with a whole-tree smali round-trip damages R8 output invisibly —
class tables compare clean, and it only blows up at runtime.
4. Neutralising a native terminate path by making it **not return**. A spinning stub does not
suppress the check; it freezes the caller and every thread behind it. The app hangs with *no
crash record at all*, and the eventual death gets blamed on whatever killed the frozen process.
## Scope
Built for working on your own applications, on samples you are authorized to analyze,
and in CTF/competition sandboxes. It contains no vendored third-party binaries and no
target-specific data.
What it covers, and what it deliberately does not, is stated at the top of `SKILL.md`
under **Coverage**. The short version: Android only (no iOS), and deep on the layers
that have been worked through for real — dex patching, repacking, packers and custom
loaders, native tamper response, and Flutter/Dart AOT. An extension pass added a second
tier of documented routes: **module-side delivery** when a repack is blocked,
**extraction-shell recovery** and its VMP boundary, **emulation and live RPC** for
calling rather than reading, **instruction-level tracing** against OLLVM, **protocol
reversing** beyond REST, the **kernel-side route** map for when userspace hooking is
provably out of reach, and **on-device tooling**. A **benchmark pass** then put public
targets under those routes (`tests/benchmark.md`): it added **Java2C discrimination** (the
misdiagnosis that sends an agent hunting a decrypted DEX that never exists), **split APK /
App Bundle handling**, **schema-free protobuf decoding**, a **Dex-VMP differential** harness,
and **kernel-module templates with their version gates** — and it corrected two earlier claims
whose measurements disagreed with them. Unity/IL2CPP logic recovery,
React Native/Hermes bytecode internals, and defeating a server-side authority are **not**
covered, and the skill is written to say so and stop rather than apply the nearest
documented procedure to a target it was not written for.
Four qualifications that the Coverage section states in full and that belong here too:
- **Flutter/Dart AOT analysis has a dependency.** The workflow begins at a pool listing
(`pp.txt`-class output). Producing that needs a snapshot-decoding decompiler — aotopsy (a static
binary, no toolchain) or blutter (built from source, ~80 s) — and this repository does not contain
one. It is named as a prerequisite rather than left implicit.
- **Not every claim in this repository has a run behind it.** `docs/tool-verification/` records
what was actually measured, on which target, and with which independent cross-check; anything not
covered there is documented from experience and should be read as *inferred*, per this skill's own
claim ladder.
- **The extension pass is recorded separately and is mostly *inferred*.** Its evidence lives in
`docs/tool-verification/EXTENSION-*.md`, one file per topic, with its own strength note. The
common shape there is *the tool was measured, the route was not* — so read those files before
treating any of the newer documents as a verified path.
- **The benchmark pass is recorded per row, with that row's own strength.** `tests/benchmark.md`
names each public target, the scripts the row exercises, what actually happened (including the
rows that failed and the rows nobody ran), and how strong the evidence is. Rows marked
`unverified` are statements about the evidence in this repository, not about the mechanism.
## Repository maintenance
Four tools live at the root and are not part of the installed skill:
```
check_repo.py every skill discovered, frontmatter valid, scripts runnable,
documented paths resolve, README paths explicit and existing,
and -- on the tracked surface only -- no target identity
(delegates the rules to skills/apk-reverse/scripts/scan_leaks.py
so there is one place to argue with the exemption list)
check_refs.py every cross-reference that names a section of another
document reaches a real heading in that document
check_routing.py the on-demand inventory still matches the entry point: the
symptom mirror agrees with SKILL.md, every reference file is
named in skills/apk-reverse/references/routing.md, and every
script is too
check_commands.py every command a document tells you to run is checked against
the script's own argparse table -- a documented flag that does
not exist is a drift the anchor checks cannot see
check_budget.py keep the always-loaded part from creeping: SKILL.md's whole
body (index lines included, because they load too) measured in
lines and tokens, index-row length, long files with no
navigable head, and hedged rules reported as a trend
build_scripts.py audit for machine-specific leftovers (absolute paths, credentials)
```
Consistency has a natural counter-pressure -- a broken path fails loudly, and someone fixes it.
Bloat has none, which is why the third tool exists: every pass adds a reference, an index row and
a coverage claim, and without a measurement nothing in the repository notices.
`tests/benchmark.md` holds the **regression matrix**: dimension -> public target -> the scripts the
row exercises -> measured result -> strength label. It is the checklist to re-run before trusting
any claim under `docs/tool-verification/`. Samples are downloaded into `tools/_work/` and are never
committed, so each row names its public source and records the hash it was run against.
`docs/tool-verification/` is not part of the installed skill either. It is the evidence record
for one measurement pass against a real target: what each script actually did, which independent
method confirmed it, which defects were found, and which scenarios the target could not exercise.
It exists so the **Coverage** claims in `SKILL.md` can be checked against runs instead of trusted,
and so the gaps are written down where the next person will find them.
---
Proudly supported by the [LINUX DO](https://linux.do) community.
## Disclaimer
**For learning, research and authorized security testing only.** Every script, reference and
recorded result in this repository exists to explain *how* Android application analysis works, so
that practitioners can reason about the tools they already own. Nothing here is a service, a
product, or an endorsement of any particular use.
- **Authorized targets only.** Use this on applications you own or have been explicitly permitted to
analyze, on public CTF/challenge material, or in a sandbox you control. Analyzing software you have
no right to analyze may be unlawful where you live, and that determination is yours to make, not
this repository's.
- **No warranty, no fitness for any purpose.** The material is provided *as is*, without warranty of
any kind. Results are recorded as they were measured on one machine at one time; nothing here
promises that a route will work on your target, your device, your toolchain or today's app version.
- **Verify before you trust; back up before you act.** Several scripts modify artifacts (dex, APK,
`.so`, stored app data) and some operate on a rooted device. Keep your own copies, work on
duplicates, and read `SKILL.md`'s gates before running anything against something you care about.
- **Your use is your responsibility.** The authors and contributors accept no liability for any loss,
damage, legal consequence or service interruption arising from the use or misuse of this
repository, and are not affiliated with, endorsed by, or acting on behalf of any application,
vendor or platform it may be used to examine.
- **Test data is not distributed here.** Samples, dumps and device artifacts are deliberately absent
from the tree (`.gitignore` excludes them) and live only in a local, ignored workspace. Anything you
obtain to follow along is yours to keep safe and to delete when you are done with it — follow your
local rules and the terms that came with the sample. What this repository *does* publish is the
method and the evidence, with all target identity removed.
- **No affiliation.** Names of tools, libraries, hardening products and public challenge targets
appear only to make the material reusable; they belong to their respective owners and this project
is not connected to them.