p256

ssh-transport/Cargo.toml

@@ -7,6 +7,7 @@ edition = "2021"
 chacha20 = "0.9.1"
 ed25519-dalek = { version = "2.1.1" }
 eyre = "0.6.12"
+p256 = { version = "0.13.2", features = ["ecdh"] }
 poly1305 = "0.8.0"
 rand = "0.8.5"
 rand_core = "0.6.4"

ssh-transport/src/keys.rs

@@ -45,6 +45,29 @@ pub const KEX_CURVE_25519_SHA256: KexAlgorithm = KexAlgorithm {
         })
     },
 };
+/// <https://datatracker.ietf.org/doc/html/rfc5656>
+pub const KEX_ECDH_SHA2_NISTP256: KexAlgorithm = KexAlgorithm {
+    name: "ecdh-sha2-nistp256",
+    exchange: |client_public_key, rng| {
+        let secret = p256::ecdh::EphemeralSecret::random(&mut crate::SshRngRandAdapter(rng));
+        let server_public_key = p256::EncodedPoint::from(secret.public_key()); // Q_S
+
+        let client_public_key =
+            p256::PublicKey::from_sec1_bytes(client_public_key).map_err(|_| {
+                crate::client_error!(
+                    "invalid p256 public key length: {}",
+                    client_public_key.len()
+                )
+            })?; // Q_C
+
+        let shared_secret = secret.diffie_hellman(&client_public_key); // K
+
+        Ok(KexAlgorithmOutput {
+            server_public_key: server_public_key.as_bytes().to_vec(),
+            shared_secret: shared_secret.raw_secret_bytes().to_vec(),
+        })
+    },
+};
 
 pub struct AlgorithmNegotiation<T> {
     pub supported: Vec<(&'static str, T)>,

ssh-transport/src/lib.rs

@@ -175,11 +175,13 @@ impl ServerConnection {
                         }
                     };
 
-                    // TODO: support ecdh-sha2-nistp256
                     let kex_algorithms = AlgorithmNegotiation {
                         supported: vec![(
                             keys::KEX_CURVE_25519_SHA256.name,
                             keys::KEX_CURVE_25519_SHA256,
+                        ), (
+                            keys::KEX_ECDH_SHA2_NISTP256.name,
+                            keys::KEX_ECDH_SHA2_NISTP256,
                         )],
                     };
                     let kex_algorithm = kex_algorithms.find(kex.kex_algorithms.0)?;