openpgp: seal Aead trait.

- Seal the Aead trait so it cannot be implemented outside the openpgp
  crate.

- This way we can extend the trait without breaking the API
  compatibility.

- See #538.

1 files changed, 2 insertions, 0 deletions

diff --git a/openpgp/src/crypto/backend/nettle/aead.rs b/openpgp/src/crypto/backend/nettle/aead.rs
index 1614a20a..797dd040 100644
--- a/openpgp/src/crypto/backend/nettle/aead.rs
+++ b/openpgp/src/crypto/backend/nettle/aead.rs
@@ -4,8 +4,10 @@ use nettle::{aead, cipher};
 use crate::{Error, Result};
 
 use crate::crypto::aead::Aead;
+use crate::seal;
 use crate::types::{AEADAlgorithm, SymmetricAlgorithm};
 
+impl<T: nettle::aead::Aead> seal::Sealed for T {}
 impl<T: nettle::aead::Aead> Aead for T {
     fn update(&mut self, ad: &[u8]) {
         self.update(ad)