1# COSET 2 3[](https://google.github.io/coset) 4[](https://github.com/google/coset/actions?query=workflow%3ACI) 5[](https://codecov.io/gh/google/coset) 6 7This crate holds a set of Rust types for working with CBOR Object Signing and Encryption (COSE) objects, as defined in 8[RFC 8152](https://tools.ietf.org/html/rfc8152). It builds on the core [CBOR](https://tools.ietf.org/html/rfc7049) 9parsing functionality from the [`ciborium` crate](https://docs.rs/ciborium). 10 11See [crate docs](https://google.github.io/coset/rust/coset/index.html), or the [signature 12example](examples/signature.rs) for documentation on how to use the code. 13 14**This repo is under construction** and so details of the API and the code may change without warning. 15 16## `no_std` Support 17 18This crate supports `no_std`, but uses the `alloc` crate. 19 20## Minimum Supported Rust Version 21 22MSRV is 1.56 (the main `ciborium` dependency is `edition="2021"`) 23 24## Integer Ranges 25 26CBOR supports integers in the range: 27 28```text 29[-18_446_744_073_709_551_616, -1] ∪ [0, 18_446_744_073_709_551_615] 30``` 31 32which is [-2<sup>64</sup>, -1] ∪ [0, 2<sup>64</sup> - 1]. 33 34This does not map onto a single Rust integer type, so different CBOR crates take different approaches. 35 36- The [`serde_cbor`](https://docs.rs/serde_cbor) crate uses a single `i128` integer type for all integer values, which 37 means that all CBOR integer values can be expressed, but there are also `i128` values that cannot be encoded in CBOR. 38 This also means that data size is larger. 39- The [`ciborium`](https://docs.rs/ciborium) also uses a single `i128` integer type internally, but wraps it in its own 40 [`Integer`](https://docs.rs/ciborium/latest/ciborium/value/struct.Integer.html) type and only implements `TryFrom` 41 (not `From`) for `i128` / `u128` conversions so that unrepresentable numbers can be rejected. 42- The [`sk-cbor`](https://docs.rs/sk-cbor) crate uses distinct types: 43 - positive numbers as u64, covering [0, 2<sup>64</sup> - 1] 44 - negative numbers as i64, covering [-2<sup>63</sup>, -1] (which means that some theoretically-valid large negative 45 values are not represented). 46 47This crate uses a single type to encompass both positive and negative values, but uses `i64` for that type to keep data 48sizes smaller. This means that: 49 50- positive numbers in `i64` cover [0, 2<sup>63</sup> - 1] 51- negative numbers in `i64` cover [-2<sup>63</sup>, -1] 52 53and so there are large values – both positive and negative – which are not supported by this crate. 54 55## Working on the Code 56 57Local coding conventions are enforced by the [continuous integration jobs](.github/workflows) and include: 58 59- Build cleanly and pass all tests. 60- Free of [Clippy](https://github.com/rust-lang/rust-clippy) warnings. 61- Formatted with `rustfmt` using the local [rustfmt.toml](.rustfmt.toml) settings. 62- Compliance with local conventions: 63 - All `TODO` markers should be of form `TODO(#99)` and refer to an open GitHub issue. 64 - Calls to functions that can panic (`panic!`, `unwrap`, `expect`) should have a comment on the same line in the 65 form `// safe: reason` (or `/* safe: reason */`) to document the reason why panicking is acceptable. 66 67## Disclaimer 68 69This is not an officially supported Google product. 70