RSA: implement EncodePublicKey for VerifyingKeys (#207)

Implement key -> der conversion for public keys.

Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>

src/pkcs1v15.rs

@@ -4,7 +4,7 @@ use core::fmt::{Debug, Display, Formatter, LowerHex, UpperHex};
 use core::marker::PhantomData;
 use core::ops::Deref;
 use digest::Digest;
-use pkcs8::AssociatedOid;
+use pkcs8::{AssociatedOid, Document, EncodePublicKey};
 use rand_core::{CryptoRng, RngCore};
 #[cfg(feature = "hazmat")]
 use signature::hazmat::{PrehashSigner, PrehashVerifier};
@@ -574,6 +574,15 @@ where
     }
 }
 
+impl<D> EncodePublicKey for VerifyingKey<D>
+where
+    D: Digest,
+{
+    fn to_public_key_der(&self) -> pkcs8::spki::Result<Document> {
+        self.inner.to_public_key_der()
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;

src/pss.rs

@@ -5,6 +5,7 @@ use core::fmt::{Debug, Display, Formatter, LowerHex, UpperHex};
 use core::marker::PhantomData;
 use core::ops::Deref;
 use digest::{Digest, DynDigest, FixedOutputReset};
+use pkcs8::{Document, EncodePublicKey};
 use rand_core::{CryptoRng, RngCore};
 #[cfg(feature = "hazmat")]
 use signature::hazmat::{PrehashVerifier, RandomizedPrehashSigner};
@@ -874,6 +875,15 @@ where
     }
 }
 
+impl<D> EncodePublicKey for VerifyingKey<D>
+where
+    D: Digest,
+{
+    fn to_public_key_der(&self) -> pkcs8::spki::Result<Document> {
+        self.inner.to_public_key_der()
+    }
+}
+
 #[cfg(test)]
 mod test {
     use crate::pss::{BlindedSigningKey, SigningKey, VerifyingKey};