# asnfuzzgen - ASN.1 Structure-Aware Fuzzing Compiler

_asnfuzzgen_ is an ASN.1 compiler capable of producing structure-aware fuzzing modules for arbitrary ASN.1 specifications.
It currently supports Packed Encoding Rules (PER), and it generates a Rust module that can be exported into a linked C-ABI library for cross-compatibility with other languages.

This project is divided into three crates, described below.

1. `asnfuzzgen`: This crate provides the actual ASN.1 Compiler. Typically a utility (`asnfuzzgen`) will generate Rust structures starting with ASN.1 Specifications. Basic working features required to work with the 3GPP specifications is provided by the compiler, this includes Parameterized Types, Information Object Classes and Type Constraints.

2. `asnfuzzgen-codecs`: Support for different encodings supported by individual ASN.1 specifications is provided in this crate. As of the current release, APER/UPER Codecs are supported. Every Codec is supported as a `trait` implementing respective 'encode' and 'decode' functions. Support for different 'encoding rules' will be implemented in this crate and then the derive macros will utilize this code to actually generate the encoding support for Rust Structures generated by the compiler above.

3. `asnfuzzgen-codecs-derive`: This crate provides the `derive` macros for the codecs in `asn-codecs`. The code generated using `asnfuzzgen` can be directed to `derive` appropriate codecs by passing the flags during compilation.

## Acknowledgements

This project makes use of source code from the [Hampi Rust ASN.1 Toolkit](https://github.com/gabhijit/hampi), which is likewise licensed under the MIT License. Special thanks goes to Abhijit Gadgil for authoring the Rust ASN.1 Toolkit that has contributed significantly to this project.

## Supported Codecs

- APER
- UPER

## Getting Started

### `build.rs` Support

Typically the compiler can be invoked also using `build.rs` mechanism. An example `build.rs` is provided in the `examples/` sub project. And the code generated through this `build.rs` can be integrated into your project. Examples of that is provided in `examples/tests/` directory.

### Using CLI tool

A tool `asnfuzzgen` can be installed using `cargo install asnfuzzgen` and then following the CLI usage.
```shell
cargo install asnfuzzgen
asnfuzzgen --help
```

### Running Test Cases

1. Test cases can be run through `cargo test`.

### Generating ASN.1 spec files

Currently there are two ways of generating the 'ASN.1' spec files from the '.docx' specifications (This mainly applies to 3GPP specifications).

1. Using the script inside `examples/specs/parse_specs.py`. This is recommended way. (note: this requires installation of `docx` or `python-docx` in the case of Python3).
2. Using the rust binary `extract-asn-spec`. Note: this is not the recommended way and your mileage may vary. Eventual goal is to make this the default way - so as to also have a `build.rs` integration. But this is for now a work in progress. This is not available by default and is enabled only with a feature flag `rs-specs-gen`.

## License & Attribution

The source code of this project is licensed under the MIT License.