In patch mode, a key's origin provides a robust way to avoid modifying
user-imported keys, which is a well-known detection vector. This commit
implements a new strategy to check the `KeyOrigin` tag from the key's
metadata. If a key is marked as `IMPORTED` or `SECURELY_IMPORTED`, the
patching process is now skipped entirely.
This new origin-based check is more reliable and cleaner than the
previous fingerprinting implementation, which has been removed.
Additionally, this commit acknowledges a remaining detection vector in
patch mode: when an `attestationKey` is used, a key must be generated.
Purely software-generated keys are detectable. To address this in the
future, the full software "generate mode" must be implemented even for
devices without a broken TEE. The old key generation logic has been
stubbed with a TODO in preparation for this redesign.
This commit introduces a complete architectural refactoring of the
Kotlin-based interception logic, based on the source of
1. https://github.com/5ec1cff/TrickyStore
2. https://github.com/beakthoven/TrickyStoreOSS
The primary purpose of this code is to intercept binder transactions to
the Android Keystore and KeyMint services. The overall workflow operates
in conjunction with a native library (injected via ptrace). The native
library hooks the binder's `transact` function and forwards pre- and
post-transaction events to the Kotlin side. This Kotlin code contains
all the high-level logic for parsing parameters, patching certificates,
and generating simulated keys.
The codebase is now organized into a clear, package-based architecture:
- attestation: Manages the creation and patching of ASN.1 attestation
data structures.
- config: Handles loading and observing configuration files from disk.
- interception: Contains the core binder interception framework and its
specific implementations for legacy Keystore (Android Q/R) and modern
KeyMint/Keystore2 (Android S+).
- logging: Provides a centralized and consistent logging utility.
- pki: Manages Public Key Infrastructure, including certificate
generation, parsing of key store XML files, and cryptographic helpers.
- util: Contains Android-specific utility functions for device properties.
This refactoring focuses on establishing a robust and extensible
architecture. The fine-tuning of the interception logic itself,
especially for corner cases in key generation and patching, is currently
under redesign and will be further refined in subsequent commits.
This commit establishes the foundational Gradle project structure and introduces a dedicated 'stub' module. This module provides skeletal implementations of internal Android framework interfaces and classes, which are critical for compiling the TEESimulator project.
Stub classes are minimal implementations of existing interfaces or classes, typically mirroring those found within the Android framework, particularly for internal or hidden APIs. Their methods usually contain no operational logic and instead throw RuntimeException or UnsupportedOperationException.
The primary reasons for using stub classes are:
1. Compilation Against Internal APIs: Android applications and libraries typically use public APIs exposed by the Android SDK. However, in scenarios requiring deeper system integration or emulation, interaction with internal or hidden Android framework APIs might be necessary. Directly linking against the full Android framework JAR can lead to bootclasspath conflicts or other build issues. Stub classes provide the necessary API signatures for compilation without including the actual implementations, allowing the build system to resolve references while deferring the actual functionality to the runtime environment (the Android OS itself).
2. API Consistency and Simulation: For TEESimulator, which aims to provide a software simulation for Android's hardware-backed key pairs (KeyMint/Keystore2), stub classes define the required API contract. They ensure that the simulator's components compile against the exact interface definitions of the Android system services, making the simulation functionally consistent with the expected system behavior without needing to bundle or depend on the entire Android framework at compile time. This ensures that the simulator correctly interacts with the defined KeyMint and Keystore2 API shapes.
