Adds a trait for crypto, porting EC first (#606)

* Adds a trait for crypto, porting EC first

* Moves crypto implementation next to its trait

* Renames constants and types

libraries/opensk/src/api/crypto/ecdsa.rs

@@ -0,0 +1,72 @@
+// Copyright 2023 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+use super::{EC_FIELD_SIZE, EC_SIGNATURE_SIZE};
+use alloc::vec::Vec;
+use rng256::Rng256;
+
+/// Container for all ECDSA cryptographic material.
+pub trait Ecdsa {
+    type SecretKey: SecretKey<PublicKey = Self::PublicKey, Signature = Self::Signature>;
+    type PublicKey: PublicKey<Signature = Self::Signature>;
+    type Signature: Signature;
+}
+
+/// ECDSA signing key.
+pub trait SecretKey: Sized {
+    type PublicKey: PublicKey;
+    type Signature: Signature;
+
+    /// Generates a new random secret key.
+    fn random(rng: &mut impl Rng256) -> Self;
+
+    /// Creates a signing key from its representation in bytes.
+    fn from_slice(bytes: &[u8; EC_FIELD_SIZE]) -> Option<Self>;
+
+    /// Computes the corresponding public key for this private key.
+    fn public_key(&self) -> Self::PublicKey;
+
+    /// Signs the message.
+    ///
+    /// For hashing, SHA256 is used implicitly.
+    fn sign(&self, message: &[u8]) -> Self::Signature;
+
+    /// Writes the signing key bytes into the passed in parameter.
+    fn to_slice(&self, bytes: &mut [u8; EC_FIELD_SIZE]);
+}
+
+/// ECDSA verifying key.
+pub trait PublicKey: Sized {
+    type Signature: Signature;
+
+    /// Creates a public key from its coordinates.
+    fn from_coordinates(x: &[u8; EC_FIELD_SIZE], y: &[u8; EC_FIELD_SIZE]) -> Option<Self>;
+
+    /// Verifies if the signature matches the message.
+    ///
+    /// For hashing, SHA256 is used implicitly.
+    fn verify(&self, message: &[u8], signature: &Self::Signature) -> bool;
+
+    /// Writes the public key coordinates into the passed in parameters.
+    fn to_coordinates(&self, x: &mut [u8; EC_FIELD_SIZE], y: &mut [u8; EC_FIELD_SIZE]);
+}
+
+/// ECDSA signature.
+pub trait Signature: Sized {
+    /// Creates a signature from its affine coordinates, represented as concatenated bytes.
+    fn from_slice(bytes: &[u8; EC_SIGNATURE_SIZE]) -> Option<Self>;
+
+    /// Encodes the signatures as ASN1 DER.
+    fn to_der(&self) -> Vec<u8>;
+}