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/crypto/src/ecdsa.rs

@@ -276,7 +276,6 @@ impl PubKey {
         ExponentP256::modn(u.to_int()) == *sign.r.as_exponent()
     }
 
-    #[cfg(feature = "std")]
     pub fn verify_vartime<H>(&self, msg: &[u8], sign: &Signature) -> bool
     where
         H: Hash256,

libraries/opensk/Cargo.toml

@@ -22,6 +22,8 @@ subtle = { version = "2.2", default-features = false, features = ["nightly"] }
 arbitrary = { version = "0.4.7", features = ["derive"], optional = true }
 rand = { version = "0.8.4", optional = true }
 ed25519-compact = { version = "1", default-features = false, optional = true }
+p256 = { version = "0.13.0", features = ["ecdh"], optional = true }
+rand_core = { version = "0.6.4", optional = true }
 
 [features]
 debug_ctap = []
@@ -30,6 +32,7 @@ with_ctap1 = ["crypto/with_ctap1"]
 vendor_hid = []
 fuzz = ["arbitrary", "std"]
 ed25519 = ["ed25519-compact"]
+rust_crypto = ["p256", "rand_core"]
 
 [dev-dependencies]
 enum-iterator = "0.6.0"

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

@@ -0,0 +1,53 @@
+// 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;
+use rng256::Rng256;
+
+/// Container for all ECDH cryptographic material.
+pub trait Ecdh {
+    type SecretKey: SecretKey<PublicKey = Self::PublicKey, SharedSecret = Self::SharedSecret>;
+    type PublicKey: PublicKey;
+    type SharedSecret: SharedSecret;
+}
+
+/// ECDH ephemeral key.
+pub trait SecretKey {
+    type PublicKey: PublicKey;
+    type SharedSecret: SharedSecret;
+
+    /// Generates a new random secret key.
+    fn random(rng: &mut impl Rng256) -> Self;
+
+    /// Computes the corresponding public key for this private key.
+    fn public_key(&self) -> Self::PublicKey;
+
+    /// Computes the shared secret when using Elliptic-curve Diffie–Hellman.
+    fn diffie_hellman(&self, public_key: &Self::PublicKey) -> Self::SharedSecret;
+}
+
+/// ECDH public key.
+pub trait PublicKey: Sized {
+    /// Creates a public key from its coordinates.
+    fn from_coordinates(x: &[u8; EC_FIELD_SIZE], y: &[u8; EC_FIELD_SIZE]) -> Option<Self>;
+
+    /// 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]);
+}
+
+/// ECDH shared secret.
+pub trait SharedSecret {
+    /// Exports the x component of the point computed by Diffie–Hellman.
+    fn raw_secret_bytes(&self) -> [u8; EC_FIELD_SIZE];
+}

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>;
+}

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

@@ -0,0 +1,37 @@
+// 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.
+
+pub mod ecdh;
+pub mod ecdsa;
+#[cfg(feature = "rust_crypto")]
+pub mod rust_crypto;
+#[cfg(not(feature = "rust_crypto"))]
+pub mod software_crypto;
+#[cfg(feature = "rust_crypto")]
+pub use rust_crypto as software_crypto;
+
+use self::ecdh::Ecdh;
+use self::ecdsa::Ecdsa;
+
+/// The size of field elements in the elliptic curve P256.
+pub const EC_FIELD_SIZE: usize = 32;
+
+/// The size of a serialized ECDSA signature.
+pub const EC_SIGNATURE_SIZE: usize = 2 * EC_FIELD_SIZE;
+
+/// Necessary cryptographic primitives for CTAP.
+pub trait Crypto {
+    type Ecdh: Ecdh;
+    type Ecdsa: Ecdsa;
+}