openpgp: Either derive both Eq and Hash, or impl both.

  - crypto::mpi::SecretKeyMaterial is the sole exception to this rule,
    because we are trying to compare them in constant time.  Add a
    hint for clippy that this is okay.

  - KeyHandle no longer implements Eq, so there is no point in
    implementing Hash.  Simply remove it.

  - Implement Hash for SubpacketLength by hashing the serialized
    form.  Manually implement Eq for consistency.

  - Fixes #567.

3 files changed, 19 insertions, 2 deletions

diff --git a/openpgp/src/crypto/mpi.rs b/openpgp/src/crypto/mpi.rs
index 5088e9f3..1c6757b2 100644
--- a/openpgp/src/crypto/mpi.rs
+++ b/openpgp/src/crypto/mpi.rs
@@ -613,6 +613,7 @@ impl Arbitrary for PublicKey {
 /// extensions.
 // Deriving Hash here is okay: PartialEq is manually implemented to
 // ensure that secrets are compared in constant-time.
+#[allow(clippy::derive_hash_xor_eq)]
 #[derive(Clone, Hash)]
 pub enum SecretKeyMaterial {
     /// RSA secret key.
diff --git a/openpgp/src/keyhandle.rs b/openpgp/src/keyhandle.rs
index c9b613c1..e92efd05 100644
--- a/openpgp/src/keyhandle.rs
+++ b/openpgp/src/keyhandle.rs
@@ -13,7 +13,7 @@ use crate::{
 /// Identifies certificates and keys.
 ///
 /// A `KeyHandle` is either a `Fingerprint` or a `KeyID`.
-#[derive(Debug, Clone, Hash)]
+#[derive(Debug, Clone)]
 pub enum KeyHandle {
     /// A Fingerprint.
     Fingerprint(Fingerprint),
diff --git a/openpgp/src/packet/signature/subpacket.rs b/openpgp/src/packet/signature/subpacket.rs
index cbcb2df2..62494df9 100644
--- a/openpgp/src/packet/signature/subpacket.rs
+++ b/openpgp/src/packet/signature/subpacket.rs
@@ -1674,7 +1674,7 @@ impl Subpacket {
     }
 }
 
-#[derive(Clone, Debug, Hash, Eq)]
+#[derive(Clone, Debug)]
 pub(crate) struct SubpacketLength {
     /// The length.
     pub(crate) len: u32,
@@ -1715,6 +1715,22 @@ impl PartialEq for SubpacketLength {
     }
 }
 
+impl Eq for SubpacketLength {}
+
+impl Hash for SubpacketLength {
+    fn hash<H: Hasher>(&self, state: &mut H) {
+        match &self.raw {
+            Some(raw) => raw.hash(state),
+            None => {
+                let l = self.serialized_len();
+                let mut raw = [0; 5];
+                self.serialize_into(&mut raw[..l]).unwrap();
+                raw[..l].hash(state);
+            },
+        }
+    }
+}
+
 impl SubpacketLength {
     pub(crate) fn new(len: u32, raw: Option<Vec<u8>>) -> Self {
         Self { len, raw }