docs: add docs for starknet-signers (#638)

starknet-signers/src/key_pair.rs

@@ -6,23 +6,29 @@ use starknet_core::{
 };
 use starknet_crypto::get_public_key;
 
+/// A ECDSA signing (private) key on the STARK curve.
 #[derive(Debug, Clone)]
 pub struct SigningKey {
     secret_scalar: Felt,
 }
 
+/// A ECDSA verifying (public) key on the STARK curve.
 #[derive(Debug, Clone)]
 pub struct VerifyingKey {
     scalar: Felt,
 }
 
+/// Errors using an encrypted JSON keystore.
 #[cfg(not(target_arch = "wasm32"))]
 #[derive(Debug, thiserror::Error)]
 pub enum KeystoreError {
+    /// The file path is invalid.
     #[error("invalid path")]
     InvalidPath,
+    /// The decrypted secret scalar is not a valid private key.
     #[error("invalid decrypted secret scalar")]
     InvalidScalar,
+    /// Upstream `eth-keystore` error propagated.
     #[error(transparent)]
     Inner(eth_keystore::KeystoreError),
 }
@@ -47,6 +53,7 @@ impl SigningKey {
         Self { secret_scalar }
     }
 
+    /// Constructs [`SigningKey`] directly from a secret scalar.
     pub const fn from_secret_scalar(secret_scalar: Felt) -> Self {
         Self { secret_scalar }
     }
@@ -92,28 +99,35 @@ impl SigningKey {
         Ok(())
     }
 
+    /// Gets the secret scalar in the signing key.
     pub const fn secret_scalar(&self) -> Felt {
         self.secret_scalar
     }
 
+    /// Derives the verifying (public) key that corresponds to the signing key.
     pub fn verifying_key(&self) -> VerifyingKey {
         VerifyingKey::from_scalar(get_public_key(&self.secret_scalar))
     }
 
+    /// Signs a raw hash using ECDSA for a signature.
     pub fn sign(&self, hash: &Felt) -> Result<Signature, EcdsaSignError> {
         ecdsa_sign(&self.secret_scalar, hash).map(|sig| sig.into())
     }
 }
 
 impl VerifyingKey {
+    /// Constructs [`VerifyingKey`] directly from a scalar.
     pub const fn from_scalar(scalar: Felt) -> Self {
         Self { scalar }
     }
 
+    /// Gets the scalar in the verifying key.
     pub const fn scalar(&self) -> Felt {
         self.scalar
     }
 
+    /// Verifies that an ECDSA signature is valid for the verifying key against a certain message
+    /// hash.
     pub fn verify(&self, hash: &Felt, signature: &Signature) -> Result<bool, EcdsaVerifyError> {
         ecdsa_verify(&self.scalar, hash, signature)
     }

starknet-signers/src/ledger.rs

@@ -37,18 +37,29 @@ pub struct LedgerStarknetApp {
     transport: Ledger,
 }
 
+/// Errors using the Ledger hardware wallet.
 #[derive(Debug, thiserror::Error)]
 pub enum LedgerError {
+    /// The HD wallet derivation path is malformed or does not conform to EIP-2645.
     #[error("derivation path is empty, not prefixed with m/2645', or is not 6-level long")]
     InvalidDerivationPath,
+    /// Error communicating with the Ledger hardware device.
     #[error(transparent)]
     TransportError(coins_ledger::LedgerError),
+    /// An unknown response code is returned from the device.
     #[error("unknown response code from Ledger: {0}")]
     UnknownResponseCode(u16),
+    /// The response code returned from the device does not indicate success.
     #[error("failed Ledger request: {0}")]
     UnsuccessfulRequest(APDUResponseCodes),
+    /// The response has an unexpected size.
     #[error("unexpected response length - expected: {expected}; actual: {actual}")]
-    UnexpectedResponseLength { expected: usize, actual: usize },
+    UnexpectedResponseLength {
+        /// The expected response size.
+        expected: usize,
+        /// The actual response size.
+        actual: usize,
+    },
 }
 
 /// The `GetPubKey` Ledger command.

starknet-signers/src/lib.rs

@@ -1,3 +1,7 @@
+//! Starknet signer interface and common implementations.
+
+#![deny(missing_docs)]
+
 mod key_pair;
 pub use key_pair::{SigningKey, VerifyingKey};
 
@@ -7,13 +11,17 @@ pub use key_pair::KeystoreError;
 mod signer;
 pub use signer::Signer;
 
+/// Module containing types related to the use of a simple in-memory signer.
 pub mod local_wallet;
 pub use local_wallet::LocalWallet;
 
+/// Module containing types related to the Ledger hardware wallet.
 #[cfg(feature = "ledger")]
 pub mod ledger;
 #[cfg(feature = "ledger")]
 pub use ledger::{DerivationPath, LedgerError, LedgerSigner};
 
+/// An error type that indicates an error cannot possibly occur. Used as placeholder where
+/// [`Result`] is expected.
 #[derive(Debug, thiserror::Error)]
 pub enum Infallible {}

starknet-signers/src/local_wallet.rs

@@ -6,18 +6,23 @@ use starknet_core::{
     types::Felt,
 };
 
+/// A signer that simply holds the signing (private) key in memory for performing cryptographic
+/// operations. It's recommended to use hardware-based signers for use cases involving real value.
 #[derive(Debug, Clone)]
 pub struct LocalWallet {
     private_key: SigningKey,
 }
 
+/// Errors using [`LocalWallet`].
 #[derive(Debug, thiserror::Error)]
 pub enum SignError {
+    /// ECDSA signature error.
     #[error(transparent)]
     EcdsaSignError(EcdsaSignError),
 }
 
 impl LocalWallet {
+    /// Constructs [`LocalWallet`] from a [`SigningKey`].
     pub fn from_signing_key(key: SigningKey) -> Self {
         key.into()
     }

starknet-signers/src/signer.rs

@@ -5,15 +5,29 @@ use auto_impl::auto_impl;
 use starknet_core::{crypto::Signature, types::Felt};
 use std::error::Error;
 
+/// Any signer that can provide a public key as [`Felt`], and sign a raw hash for a signature
+/// encoded as [`Vec<Felt>`].
 #[cfg_attr(not(target_arch = "wasm32"), async_trait)]
 #[cfg_attr(target_arch = "wasm32", async_trait(?Send))]
 #[auto_impl(&, Box, Arc)]
 pub trait Signer {
+    /// Possible errors for calling [`get_public_key`](fn.get_public_key).
     type GetPublicKeyError: Error + Send + Sync;
+    /// Possible errors for calling [`sign`](fn.sign).
     type SignError: Error + Send + Sync;
 
+    /// Retrieves the verifying (public) key from the signer.
     async fn get_public_key(&self) -> Result<VerifyingKey, Self::GetPublicKeyError>;
 
+    /// Requests an ECDSA signature for a message hash.
+    ///
+    /// Signing a raw hash is known as "blind signing". For interactive signers (e.g. hardware
+    /// wallets) that can theoretically provide better security properties via "clear signing",
+    /// using blind signing is bad practice.
+    ///
+    /// However, as of this writing, no actual interactive signer implementation offers clear
+    /// signing. When this changes in the future, this trait shall be altered to allow such clear
+    /// signing capabilities.
     async fn sign_hash(&self, hash: &Felt) -> Result<Signature, Self::SignError>;
 
     /// Whether the underlying signer implementation is interactive, such as a hardware wallet.