COSET

This crate holds a set of Rust types for working with CBOR Object Signing and Encryption (COSE) objects, as defined in RFC 8152. It builds on the core CBOR parsing functionality from the ciborium crate.

See crate docs, or the signature example for documentation on how to use the code.

This repo is under construction and so details of the API and the code may change without warning.

Features

The std feature of the crate enables an implementation of std::error::Error for CoseError.

no_std Support

This crate supports no_std (when the std feature is not set, which is the default), but uses the alloc crate.

Minimum Supported Rust Version

MSRV is 1.58.

Integer Ranges

CBOR supports integers in the range:

[-18_446_744_073_709_551_616, -1] ∪ [0, 18_446_744_073_709_551_615]

which is [-2⁶⁴, -1] ∪ [0, 2⁶⁴ - 1].

This does not map onto a single Rust integer type, so different CBOR crates take different approaches.

• The serde_cbor crate uses a single i128 integer type for all integer values, which means that all CBOR integer values can be expressed, but there are also i128 values that cannot be encoded in CBOR. This also means that data size is larger.
• The ciborium also uses a single i128 integer type internally, but wraps it in its own Integer type and only implements TryFrom (not From) for i128 / u128 conversions so that unrepresentable numbers can be rejected.
• The sk-cbor crate uses distinct types:
  • positive numbers as u64, covering [0, 2⁶⁴ - 1]
  • negative numbers as i64, covering [-2⁶³, -1] (which means that some theoretically-valid large negative values are not represented).

This crate uses a single type to encompass both positive and negative values, but uses i64 for that type to keep data sizes smaller. This means that:

• positive numbers in i64 cover [0, 2⁶³ - 1]
• negative numbers in i64 cover [-2⁶³, -1]

and so there are large values – both positive and negative – which are not supported by this crate.

Working on the Code

Local coding conventions are enforced by the continuous integration jobs and include:

• Build cleanly and pass all tests.
• Free of Clippy warnings.
• Formatted with rustfmt using the local rustfmt.toml settings.
• Compliance with local conventions:
  • All TODO markers should be of form TODO(#99) and refer to an open GitHub issue.
  • Calls to functions that can panic (panic!, unwrap, expect) should have a comment on the same line in the form // safe: reason (or /* safe: reason */) to document the reason why panicking is acceptable.

Disclaimer

This is not an officially supported Google product.