Implement From<&PublicKey> for PublicKeyComponents (#698)

* Implement From<&PublicKey> for PublicKeyComponents

* Requires "ring-io" feature.

* Fix up

---------

Co-authored-by: Justin W Smith <[email protected]>
Co-authored-by: Justin Smith <[email protected]>

Author: djc

aws-lc-rs/src/rsa/key.rs

@@ -338,6 +338,11 @@ impl PublicKey {
     pub fn exponent(&self) -> io::Positive<'_> {
         io::Positive::new_non_empty_without_leading_zeros(Input::from(self.exponent.as_ref()))
     }
+
+    /// Returns the length in bytes of the public modulus.
+    pub fn modulus_len(&self) -> usize {
+        self.modulus.len()
+    }
 }
 
 /// Low-level API for RSA public keys.
@@ -430,6 +435,16 @@ where
     }
 }
 
+#[cfg(feature = "ring-io")]
+impl From<&PublicKey> for PublicKeyComponents<Vec<u8>> {
+    fn from(public_key: &PublicKey) -> Self {
+        PublicKeyComponents {
+            n: public_key.modulus.to_vec(),
+            e: public_key.exponent.to_vec(),
+        }
+    }
+}
+
 impl<B> TryInto<PublicEncryptingKey> for PublicKeyComponents<B>
 where
     B: AsRef<[u8]> + Debug,