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// 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 crypto_provider::elliptic_curve::{EcdhProvider, EphemeralSecret};
use crypto_provider::p256::P256;
use openssl::bn::{BigNum, BigNumContext};
use openssl::derive::Deriver;
use openssl::ec::{EcGroup, EcKey, EcPoint, PointConversionForm};
use openssl::error::ErrorStack;
use openssl::nid::Nid;
use openssl::pkey::{PKey, Private, Public};
/// Public key type for P256 using OpenSSL's implementation.
#[derive(Debug)]
pub struct P256PublicKey(PKey<Public>);
impl PartialEq for P256PublicKey {
fn eq(&self, other: &Self) -> bool {
self.0.public_eq(&other.0)
}
}
/// Custom error type for OpenSSL operations.
#[derive(Debug)]
pub enum Error {
/// Error from the openssl crate.
OpenSslError(ErrorStack),
/// Unexpected size for the given input.
WrongSize,
}
impl From<ErrorStack> for Error {
fn from(value: ErrorStack) -> Self {
Self::OpenSslError(value)
}
}
/// The OpenSSL implementation of P256 public key.
impl crypto_provider::p256::P256PublicKey for P256PublicKey {
type Error = Error;
fn from_sec1_bytes(bytes: &[u8]) -> Result<Self, Self::Error> {
let ecgroup = EcGroup::from_curve_name(Nid::X9_62_PRIME256V1)?;
let mut bncontext = BigNumContext::new()?;
let ecpoint = EcPoint::from_bytes(&ecgroup, bytes, &mut bncontext)?;
let eckey = EcKey::from_public_key(&ecgroup, &ecpoint)?;
Ok(Self(eckey.try_into()?))
}
fn to_sec1_bytes(&self) -> Vec<u8> {
let ecgroup = EcGroup::from_curve_name(Nid::X9_62_PRIME256V1).unwrap();
let mut bncontext = BigNumContext::new().unwrap();
self.0
.ec_key()
.unwrap()
.public_key()
.to_bytes(&ecgroup, PointConversionForm::COMPRESSED, &mut bncontext)
.unwrap()
}
fn from_affine_coordinates(x: &[u8; 32], y: &[u8; 32]) -> Result<Self, Self::Error> {
let bn_x = BigNum::from_slice(x)?;
let bn_y = BigNum::from_slice(y)?;
let ecgroup = EcGroup::from_curve_name(Nid::X9_62_PRIME256V1)?;
let eckey = EcKey::from_public_key_affine_coordinates(&ecgroup, &bn_x, &bn_y)?;
Ok(Self(eckey.try_into()?))
}
fn to_affine_coordinates(&self) -> Result<([u8; 32], [u8; 32]), Self::Error> {
let mut bnctx = openssl::bn::BigNumContext::new()?;
let ecgroup = EcGroup::from_curve_name(Nid::X9_62_PRIME256V1)?;
let p256_key = self.0.ec_key()?;
let mut p256x = BigNum::new()?;
let mut p256y = BigNum::new()?;
p256_key
.public_key()
.affine_coordinates_gfp(&ecgroup, &mut p256x, &mut p256y, &mut bnctx)?;
Ok((
p256x.to_vec().try_into().map_err(|_| Error::WrongSize)?,
p256y.to_vec().try_into().map_err(|_| Error::WrongSize)?,
))
}
}
/// Private key type for P256 using OpenSSL's implementation.
pub struct P256EphemeralSecret(PKey<Private>);
impl EphemeralSecret<P256> for P256EphemeralSecret {
type Impl = P256Ecdh;
type Error = Error;
type Rng = ();
fn generate_random(_rng: &mut Self::Rng) -> Self {
let ecgroup = EcGroup::from_curve_name(Nid::X9_62_PRIME256V1).unwrap();
let eckey = EcKey::generate(&ecgroup).unwrap();
Self(eckey.try_into().unwrap())
}
fn public_key_bytes(&self) -> Vec<u8> {
let ecgroup = EcGroup::from_curve_name(Nid::X9_62_PRIME256V1).unwrap();
let mut bncontext = BigNumContext::new().unwrap();
self.0
.ec_key()
.unwrap()
.public_key()
.to_bytes(&ecgroup, PointConversionForm::COMPRESSED, &mut bncontext)
.unwrap()
}
fn diffie_hellman(
self,
other_pub: &<Self::Impl as EcdhProvider<P256>>::PublicKey,
) -> Result<<Self::Impl as EcdhProvider<P256>>::SharedSecret, Self::Error> {
let mut deriver = Deriver::new(&self.0)?;
deriver.set_peer(&other_pub.0)?;
let mut buf = [0_u8; 32];
let bytes_written = deriver.derive(&mut buf)?;
debug_assert_eq!(bytes_written, 32);
Ok(buf)
}
}
#[cfg(test)]
impl crypto_provider::elliptic_curve::EphemeralSecretForTesting<P256> for P256EphemeralSecret {
fn from_private_components(
private_bytes: &[u8; 32],
public_key: &P256PublicKey,
) -> Result<Self, Self::Error> {
let ecgroup = EcGroup::from_curve_name(Nid::X9_62_PRIME256V1).unwrap();
let private_key_bn = BigNum::from_slice(private_bytes)?;
let eckey = EcKey::from_private_components(
&ecgroup,
&private_key_bn,
public_key.0.ec_key()?.public_key(),
)?;
Ok(Self(eckey.try_into()?))
}
}
/// The OpenSSL implementation of P256 ECDH.
pub enum P256Ecdh {}
impl EcdhProvider<P256> for P256Ecdh {
type PublicKey = P256PublicKey;
type EphemeralSecret = P256EphemeralSecret;
type SharedSecret = [u8; 32];
}
#[cfg(test)]
mod tests {
use super::P256Ecdh;
use core::marker::PhantomData;
use crypto_provider::p256::testing::*;
#[apply(p256_test_cases)]
fn p256_tests(testcase: CryptoProviderTestCase<P256Ecdh>) {
testcase(PhantomData::<P256Ecdh>)
}
}
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