Add X25519 bindings for bssl-crypto
Bug: 285222831
Change-Id: I35219ac312fd97e7a51af8156c73fa7eb38c17c2
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/60268
Commit-Queue: Bob Beck <bbe@google.com>
Reviewed-by: Bob Beck <bbe@google.com>
diff --git a/rust/bssl-crypto/src/lib.rs b/rust/bssl-crypto/src/lib.rs
index 0ad352d..cd40b81 100644
--- a/rust/bssl-crypto/src/lib.rs
+++ b/rust/bssl-crypto/src/lib.rs
@@ -50,6 +50,9 @@
/// Random number generation.
pub mod rand;
+/// X25519 elliptic curve operations.
+pub mod x25519;
+
/// Memory-manipulation operations.
pub mod mem;
diff --git a/rust/bssl-crypto/src/x25519.rs b/rust/bssl-crypto/src/x25519.rs
new file mode 100644
index 0000000..6e1a574
--- /dev/null
+++ b/rust/bssl-crypto/src/x25519.rs
@@ -0,0 +1,213 @@
+/* Copyright (c) 2023, Google Inc.
+ *
+ * Permission to use, copy, modify, and/or distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
+ * SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
+ * OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
+ * CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+
+//! X25519 is the Diffie-Hellman primitive built from curve25519. It is sometimes referred to as
+//! “curve25519”, but “X25519” is a more precise name. See http://cr.yp.to/ecdh.html and
+//! https://tools.ietf.org/html/rfc7748.
+
+/// Number of bytes in a private key in X25519
+pub const PRIVATE_KEY_LEN: usize = bssl_sys::X25519_PRIVATE_KEY_LEN as usize;
+/// Number of bytes in a public key in X25519
+pub const PUBLIC_KEY_LEN: usize = bssl_sys::X25519_PUBLIC_VALUE_LEN as usize;
+/// Number of bytes in a shared secret derived with X25519
+pub const SHARED_KEY_LEN: usize = bssl_sys::X25519_SHARED_KEY_LEN as usize;
+
+/// Error while performing a X25519 Diffie-Hellman key exchange.
+#[derive(Debug)]
+pub struct DiffieHellmanError;
+
+/// A struct containing a X25519 key pair.
+pub struct PrivateKey {
+ private_key: [u8; PRIVATE_KEY_LEN],
+ public_key: [u8; PUBLIC_KEY_LEN],
+}
+
+impl PrivateKey {
+ /// Derives a shared secrect from this private key and the given public key.
+ pub fn diffie_hellman(
+ &self,
+ other_public_key: &PublicKey,
+ ) -> Result<SharedSecret, DiffieHellmanError> {
+ let mut shared_key_uninit = core::mem::MaybeUninit::<[u8; SHARED_KEY_LEN]>::uninit();
+ // Safety:
+ // - private_key and other_public_key are Rust 32-byte arrays
+ // - shared_key_uninit is just initialized above to a 32 byte array
+ let result = unsafe {
+ bssl_sys::X25519(
+ shared_key_uninit.as_mut_ptr() as *mut u8,
+ self.private_key.as_ptr(),
+ other_public_key.0.as_ptr(),
+ )
+ };
+ if result == 1 {
+ // Safety:
+ // - `shared_key_uninit` is initialized by `X25519` above, and we checked that it
+ // succeeded
+ let shared_key = unsafe { shared_key_uninit.assume_init() };
+ Ok(crate::ecdh::SharedSecret(shared_key))
+ } else {
+ Err(DiffieHellmanError)
+ }
+ }
+
+ /// Generate a new key pair for use in a Diffie-Hellman key exchange.
+ pub fn generate() -> Self {
+ let mut public_key_uninit = core::mem::MaybeUninit::<[u8; PUBLIC_KEY_LEN]>::uninit();
+ let mut private_key_uninit = core::mem::MaybeUninit::<[u8; PRIVATE_KEY_LEN]>::uninit();
+ // Safety:
+ // - private_key_uninit and public_key_uninit are allocated to 32-bytes
+ let (public_key, private_key) = unsafe {
+ bssl_sys::X25519_keypair(
+ public_key_uninit.as_mut_ptr() as *mut u8,
+ private_key_uninit.as_mut_ptr() as *mut u8,
+ );
+ // Safety: Initialized by `X25519_keypair` above
+ (
+ public_key_uninit.assume_init(),
+ private_key_uninit.assume_init(),
+ )
+ };
+ Self {
+ private_key,
+ public_key,
+ }
+ }
+
+ /// Tries to convert the given bytes into a private key.
+ pub fn from_private_bytes(private_key_bytes: &[u8; PRIVATE_KEY_LEN]) -> Self {
+ let mut public_key_uninit = core::mem::MaybeUninit::<[u8; PUBLIC_KEY_LEN]>::uninit();
+ let private_key: [u8; PRIVATE_KEY_LEN] = private_key_bytes.to_owned();
+ // Safety:
+ // - private_key and public_key are Rust 32-byte arrays
+ let public_key = unsafe {
+ bssl_sys::X25519_public_from_private(
+ public_key_uninit.as_mut_ptr() as *mut _,
+ private_key.as_ptr(),
+ );
+ public_key_uninit.assume_init()
+ };
+ Self {
+ private_key,
+ public_key,
+ }
+ }
+}
+
+impl<'a> From<&'a PrivateKey> for PublicKey {
+ fn from(value: &'a PrivateKey) -> Self {
+ Self(value.public_key)
+ }
+}
+
+/// A public key for X25519 elliptic curve.
+#[derive(Debug, PartialEq, Eq)]
+pub struct PublicKey([u8; PUBLIC_KEY_LEN]);
+
+impl PublicKey {
+ /// Converts this public key to its byte representation.
+ pub fn to_bytes(&self) -> [u8; PUBLIC_KEY_LEN] {
+ self.0
+ }
+
+ /// Returns a reference to the byte representation of this public key.
+ pub fn as_bytes(&self) -> &[u8; PUBLIC_KEY_LEN] {
+ &self.0
+ }
+}
+
+impl From<&[u8; 32]> for PublicKey {
+ fn from(value: &[u8; 32]) -> Self {
+ Self(*value)
+ }
+}
+
+/// Shared secret derived from a Diffie-Hellman key exchange. Don't use the shared key directly,
+/// rather use a KDF and also include the two public values as inputs.
+type SharedSecret = crate::ecdh::SharedSecret<SHARED_KEY_LEN>;
+
+#[cfg(test)]
+#[allow(clippy::unwrap_used)]
+mod tests {
+ use crate::{
+ test_helpers::decode_hex,
+ x25519::{PrivateKey, PublicKey},
+ };
+
+ #[test]
+ fn x25519_test_diffie_hellman() {
+ // wycheproof/testvectors/x25519_test.json tcId 1
+ let public_key_bytes: [u8; 32] =
+ decode_hex("504a36999f489cd2fdbc08baff3d88fa00569ba986cba22548ffde80f9806829");
+ let private_key =
+ decode_hex("c8a9d5a91091ad851c668b0736c1c9a02936c0d3ad62670858088047ba057475");
+ let expected_shared_secret: [u8; 32] =
+ decode_hex("436a2c040cf45fea9b29a0cb81b1f41458f863d0d61b453d0a982720d6d61320");
+ let public_key = PublicKey::from(&public_key_bytes);
+ let private_key = PrivateKey::from_private_bytes(&private_key);
+
+ let shared_secret = private_key.diffie_hellman(&public_key).unwrap();
+ assert_eq!(expected_shared_secret, shared_secret.to_bytes());
+ }
+
+ #[test]
+ fn x25519_generate_diffie_hellman_matches() {
+ let private_key_1 = PrivateKey::generate();
+ let private_key_2 = PrivateKey::generate();
+ let public_key_1 = PublicKey::from(&private_key_1);
+ let public_key_2 = PublicKey::from(&private_key_2);
+
+ let diffie_hellman_1 = private_key_1.diffie_hellman(&public_key_2).unwrap();
+ let diffie_hellman_2 = private_key_2.diffie_hellman(&public_key_1).unwrap();
+
+ assert_eq!(diffie_hellman_1.to_bytes(), diffie_hellman_2.to_bytes());
+ }
+
+ #[test]
+ fn x25519_test_diffie_hellman_zero_public_key() {
+ // wycheproof/testvectors/x25519_test.json tcId 32
+ let public_key_bytes =
+ decode_hex("0000000000000000000000000000000000000000000000000000000000000000");
+ let private_key =
+ decode_hex("88227494038f2bb811d47805bcdf04a2ac585ada7f2f23389bfd4658f9ddd45e");
+ let public_key = PublicKey::from(&public_key_bytes);
+ let private_key = PrivateKey::from_private_bytes(&private_key);
+
+ let shared_secret = private_key.diffie_hellman(&public_key);
+ assert!(shared_secret.is_err());
+ }
+
+ #[test]
+ fn x25519_public_key_byte_conversion() {
+ let public_key_bytes =
+ decode_hex("504a36999f489cd2fdbc08baff3d88fa00569ba986cba22548ffde80f9806829");
+ let public_key = PublicKey::from(&public_key_bytes);
+ assert_eq!(public_key_bytes, public_key.to_bytes());
+ }
+
+ #[test]
+ fn x25519_test_public_key_from_private_key() {
+ // Taken from https://www.rfc-editor.org/rfc/rfc7748.html#section-6.1
+ let public_key_bytes =
+ decode_hex("8520f0098930a754748b7ddcb43ef75a0dbf3a0d26381af4eba4a98eaa9b4e6a");
+ let private_key_bytes =
+ decode_hex("77076d0a7318a57d3c16c17251b26645df4c2f87ebc0992ab177fba51db92c2a");
+ let private_key = PrivateKey::from_private_bytes(&private_key_bytes);
+
+ assert_eq!(
+ PublicKey::from(&public_key_bytes),
+ PublicKey::from(&private_key)
+ );
+ }
+}
