Expand description
§RustCrypto: Digital Signature Algorithms
This crate contains traits which provide generic, object-safe APIs for generating and verifying digital signatures.
Used by the dsa
, ecdsa
, ed25519
, and rsa
crates maintained by
the RustCrypto organization, as well as ed25519-dalek
.
§Minimum Supported Rust Version
Rust 1.60 or higher.
Minimum supported Rust version can be changed in the future, but it will be done with a minor version bump.
§SemVer Policy
- All on-by-default features of this library are covered by SemVer
- MSRV is considered exempt from SemVer as noted above
- The
derive
feature is stable and covered by SemVer - The off-by-default features
digest
andrand_core
are unstable features which are also considered exempt from SemVer as they correspond to pre-1.0 crates which are still subject to changes. Breaking changes to these features will, like MSRV, be done with a minor version bump.
§License
Licensed under either of
at your option.
§Contribution
Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in the work by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.
§Design
This crate provides a common set of traits for signing and verifying digital signatures intended to be implemented by libraries which produce or contain implementations of digital signature algorithms, and used by libraries which want to produce or verify digital signatures while generically supporting any compatible backend.
§Goals
The traits provided by this crate were designed with the following goals in mind:
- Provide an easy-to-use, misuse resistant API optimized for consumers (as opposed to implementers) of its traits.
- Support common type-safe wrappers around “bag-of-bytes” representations which can be directly parsed from or written to the “wire”.
- Expose a trait/object-safe API where signers/verifiers spanning multiple homogeneous provider implementations can be seamlessly leveraged together in the same logical “keyring” so long as they operate on the same underlying signature type.
- Allow one provider type to potentially implement support (including being generic over) several signature types.
- Keep signature algorithm customizations / “knobs” out-of-band from the signing/verification APIs, ideally pushing such concerns into the type system so that algorithm mismatches are caught as type errors.
- Opaque error type which minimizes information leaked from cryptographic failures, as “rich” error types in these scenarios are often a source of sidechannel information for attackers (e.g. BB’06)
§Implementation
To accomplish the above goals, the Signer
and Verifier
traits
provided by this are generic over a signature value, and use generic
parameters rather than associated types. Notably, they use such a parameter
for the return value, allowing it to be inferred by the type checker based
on the desired signature type.
§Alternatives considered
This crate is based on many years of exploration of how to encapsulate digital signature systems in the most flexible, developer-friendly way. During that time many design alternatives were explored, tradeoffs compared, and ultimately the provided API was selected.
The tradeoffs made in this API have all been to improve simplicity, ergonomics, type safety, and flexibility for consumers of the traits. At times, this has come at a cost to implementers. Below are some concerns we are cognizant of which were considered in the design of the API:
- “Bag-of-bytes” serialization precludes signature providers from using their own internal representation of a signature, which can be helpful for many reasons (e.g. advanced signature system features like batch verification).
- Associated types, rather than generic parameters of traits, could allow more customization of the types used by a particular signature system, e.g. using custom error types.
It may still make sense to continue to explore the above tradeoffs, but
with a new set of traits which are intended to be implementor-friendly,
rather than consumer friendly. The existing Signer
and Verifier
traits could have blanket impls for the “provider-friendly” traits.
However, as noted above this is a design space easily explored after
stabilizing the consumer-oriented traits, and thus we consider these
more important.
That said, below are some caveats of trying to design such traits, and why we haven’t actively pursued them:
- Generics in the return position are already used to select which trait impl to use, i.e. for a particular signature algorithm/system. Avoiding a unified, concrete signature type adds another dimension to complexity and compiler errors, and in our experience makes them unsuitable for this sort of API. We believe such an API is the natural one for signature systems, reflecting the natural way they are written absent a trait.
- Associated types preclude multiple implementations of the same trait. These parameters are common in signature systems, notably ones which support different serializations of a signature (e.g. raw vs ASN.1).
- Digital signatures are almost always larger than the present 32-entry
trait impl limitation on array types, which complicates bounds
for these types (particularly things like
From
orBorrow
bounds).
§Unstable features
Despite being post-1.0, this crate includes off-by-default unstable optional features, each of which depends on a pre-1.0 crate.
These features are considered exempt from SemVer. See the SemVer policy above for more information.
The following unstable features are presently supported:
digest
: enables theDigestSigner
andDigestVerifier
traits which are based on theDigest
trait from thedigest
crate. These traits are used for representing signature systems based on the Fiat-Shamir heuristic which compute a random challenge value to sign by computing a cryptographically secure digest of the input message.rand_core
: enables the [RandomizedSigner
] trait for signature systems which rely on a cryptographically secure random number generator for security.
NOTE: the async-signature
crate contains experimental async
support
for Signer
and DigestSigner
.
Re-exports§
pub use digest;
Modules§
- Hazardous Materials: low-level APIs which can be insecure if misused.
Structs§
- Signature errors.
Traits§
- Sign the given prehashed message
Digest
usingSelf
. - Verify the provided signature for the given prehashed message
Digest
is authentic. - Signing keypair with an associated verifying key.
- Signing keypair with an associated verifying key.
- Marker trait for
Signature
types computable as𝐒(𝐇(𝒎))
i.e. ones which prehash a message to be signed as𝐇(𝒎)
- Support for decoding/encoding signatures as bytes.
- Sign the provided message bytestring using
Self
(e.g. a cryptographic key or connection to an HSM), returning a digital signature. - Sign the provided message bytestring using
&mut Self
(e.g. an evolving cryptographic key such as a stateful hash-based signature), returning a digital signature. - Verify the provided message bytestring using
Self
(e.g. a public key)
Type Aliases§
- Result type.