Zeroize RSA private key data on drop (#275)

russh-keys/Cargo.toml

@@ -71,6 +71,7 @@ thiserror = "1.0"
 tokio = { version = "1.17.0", features = ["io-util", "rt-multi-thread", "time", "net"] }
 tokio-stream = { version = "0.1", features = ["net"] }
 typenum = "1.17"
+zeroize = "1.7"
 
 [features]
 vendored-openssl = ["openssl", "openssl/vendored"]

russh-keys/src/key.rs

@@ -462,6 +462,13 @@ pub struct RsaCrtExtra<'a> {
     pub dq: Cow<'a, [u8]>,
 }
 
+impl Drop for RsaCrtExtra<'_> {
+    fn drop(&mut self) {
+        zeroize_cow(&mut self.dp);
+        zeroize_cow(&mut self.dq);
+    }
+}
+
 fn ec_signature(key: &ec::PrivateKey, b: &[u8]) -> Result<Vec<u8>, Error> {
     let (r, s) = key.try_sign(b)?;
     let mut buf = Vec::new();
@@ -513,3 +520,16 @@ pub fn parse_public_key(p: &[u8], prefer_hash: Option<SignatureHash>) -> Result<
 pub fn safe_rng() -> impl rand::CryptoRng + rand::RngCore {
     rand::thread_rng()
 }
+
+/// Zeroize `Cow` if value is owned.
+pub(crate) fn zeroize_cow<T>(v: &mut Cow<T>)
+where
+    T: ToOwned + ?Sized,
+    <T as ToOwned>::Owned: zeroize::Zeroize,
+{
+    use zeroize::Zeroize;
+    match v {
+        Cow::Owned(v) => v.zeroize(),
+        Cow::Borrowed(_) => (),
+    }
+}

russh-keys/src/protocol.rs

@@ -1,6 +1,8 @@
-use crate::encoding::{Encoding, Position, SshRead, SshWrite};
 use std::borrow::Cow;
 
+use crate::encoding::{Encoding, Position, SshRead, SshWrite};
+use crate::key::zeroize_cow;
+
 type Result<T> = std::result::Result<T, crate::Error>;
 
 /// SSH RSA public key.
@@ -72,3 +74,14 @@ impl SshWrite for RsaPrivateKey<'_> {
         encoder.extend_ssh_string(&self.comment);
     }
 }
+
+impl Drop for RsaPrivateKey<'_> {
+    fn drop(&mut self) {
+        // Private parts only.
+        zeroize_cow(&mut self.private_exponent);
+        zeroize_cow(&mut self.coefficient);
+        zeroize_cow(&mut self.prime1);
+        zeroize_cow(&mut self.prime2);
+        zeroize_cow(&mut self.comment);
+    }
+}