signature/
signer.rs

Help
1//! Traits for generating digital signatures
2
3use crate::error::Error;
4
5#[cfg(feature = "digest")]
6use crate::digest::Digest;
7
8#[cfg(feature = "rand_core")]
9use crate::rand_core::CryptoRngCore;
10
11/// Sign the provided message bytestring using `Self` (e.g. a cryptographic key
12/// or connection to an HSM), returning a digital signature.
13pub trait Signer<S> {
14    /// Sign the given message and return a digital signature
15    fn sign(&self, msg: &[u8]) -> S {
16        self.try_sign(msg).expect("signature operation failed")
17    }
18
19    /// Attempt to sign the given message, returning a digital signature on
20    /// success, or an error if something went wrong.
21    ///
22    /// The main intended use case for signing errors is when communicating
23    /// with external signers, e.g. cloud KMS, HSMs, or other hardware tokens.
24    fn try_sign(&self, msg: &[u8]) -> Result<S, Error>;
25}
26
27/// Sign the provided message bytestring using `&mut Self` (e.g. an evolving
28/// cryptographic key such as a stateful hash-based signature), returning a
29/// digital signature.
30pub trait SignerMut<S> {
31    /// Sign the given message, update the state, and return a digital signature.
32    fn sign(&mut self, msg: &[u8]) -> S {
33        self.try_sign(msg).expect("signature operation failed")
34    }
35
36    /// Attempt to sign the given message, updating the state, and returning a
37    /// digital signature on success, or an error if something went wrong.
38    ///
39    /// Signing can fail, e.g., if the number of time periods allowed by the
40    /// current key is exceeded.
41    fn try_sign(&mut self, msg: &[u8]) -> Result<S, Error>;
42}
43
44/// Blanket impl of [`SignerMut`] for all [`Signer`] types.
45impl<S, T: Signer<S>> SignerMut<S> for T {
46    fn try_sign(&mut self, msg: &[u8]) -> Result<S, Error> {
47        T::try_sign(self, msg)
48    }
49}
50
51/// Sign the given prehashed message [`Digest`] using `Self`.
52///
53/// ## Notes
54///
55/// This trait is primarily intended for signature algorithms based on the
56/// [Fiat-Shamir heuristic], a method for converting an interactive
57/// challenge/response-based proof-of-knowledge protocol into an offline
58/// digital signature through the use of a random oracle, i.e. a digest
59/// function.
60///
61/// The security of such protocols critically rests upon the inability of
62/// an attacker to solve for the output of the random oracle, as generally
63/// otherwise such signature algorithms are a system of linear equations and
64/// therefore doing so would allow the attacker to trivially forge signatures.
65///
66/// To prevent misuse which would potentially allow this to be possible, this
67/// API accepts a [`Digest`] instance, rather than a raw digest value.
68///
69/// [Fiat-Shamir heuristic]: https://en.wikipedia.org/wiki/Fiat%E2%80%93Shamir_heuristic
70#[cfg(feature = "digest")]
71pub trait DigestSigner<D: Digest, S> {
72    /// Sign the given prehashed message [`Digest`], returning a signature.
73    ///
74    /// Panics in the event of a signing error.
75    fn sign_digest(&self, digest: D) -> S {
76        self.try_sign_digest(digest)
77            .expect("signature operation failed")
78    }
79
80    /// Attempt to sign the given prehashed message [`Digest`], returning a
81    /// digital signature on success, or an error if something went wrong.
82    fn try_sign_digest(&self, digest: D) -> Result<S, Error>;
83}
84
85/// Sign the given message using the provided external randomness source.
86#[cfg(feature = "rand_core")]
87pub trait RandomizedSigner<S> {
88    /// Sign the given message and return a digital signature
89    fn sign_with_rng(&self, rng: &mut impl CryptoRngCore, msg: &[u8]) -> S {
90        self.try_sign_with_rng(rng, msg)
91            .expect("signature operation failed")
92    }
93
94    /// Attempt to sign the given message, returning a digital signature on
95    /// success, or an error if something went wrong.
96    ///
97    /// The main intended use case for signing errors is when communicating
98    /// with external signers, e.g. cloud KMS, HSMs, or other hardware tokens.
99    fn try_sign_with_rng(&self, rng: &mut impl CryptoRngCore, msg: &[u8]) -> Result<S, Error>;
100}
101
102/// Combination of [`DigestSigner`] and [`RandomizedSigner`] with support for
103/// computing a signature over a digest which requires entropy from an RNG.
104#[cfg(all(feature = "digest", feature = "rand_core"))]
105pub trait RandomizedDigestSigner<D: Digest, S> {
106    /// Sign the given prehashed message `Digest`, returning a signature.
107    ///
108    /// Panics in the event of a signing error.
109    fn sign_digest_with_rng(&self, rng: &mut impl CryptoRngCore, digest: D) -> S {
110        self.try_sign_digest_with_rng(rng, digest)
111            .expect("signature operation failed")
112    }
113
114    /// Attempt to sign the given prehashed message `Digest`, returning a
115    /// digital signature on success, or an error if something went wrong.
116    fn try_sign_digest_with_rng(&self, rng: &mut impl CryptoRngCore, digest: D)
117        -> Result<S, Error>;
118}
signature/signer.rs

signature/
signer.rs
