[Annotation] Each modification of LeafNode content MUST be reflected by a change in its signature.

[duesee]

Each modification of LeafNode content MUST be reflected by a change in its signature.

---

Annotation

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[duesee]

From my understanding, this translates to, "OpenMLS should make sure that any instance of LeafNode is guaranteed to have a correct signature."

This means that ...

• 1) LeafNodes can only be created with a correct signature.

  • Constructors (impls) can only create a LeafNode with a valid signature.
  • Due to From<OpenMlsLeafNode>, check OpenMlsLeafNode as well. OpenMlsLeafNode is a thin wrapper around LeafNode that (optionally) has the private_key and leaf_index .
    • OpenMlsLeafNode::add_capabilities may break the signature. (Allow to pass Capabilities and Extensions when creating an OpenMlsLeafNode. openmls#1192)
    • OpenMlsLeafNode::add_extension may break the signature. (Allow to pass Capabilities and Extensions when creating an OpenMlsLeafNode. openmls#1192)
    • OpenMlsLeafNode::update_encryption_key may break the signature. (Resign in place.)
    • OpenMlsLeafNode::rekey may break the signature. (Resign in place.)
    • OpenMlsLeafNode::update_parent_hash may break the signature. (Resign in place.)
    • OpenMlsLeafNode::set_public_key may break the signature. (Resign in place.)
  • Bad LeafNode can be constructed through SignedStruct::from_payload.
  • LeafNode implements TlsDeserialize (which is also used in KeyPackages deserialize implementation.).

• 2) LeafNodes can't be changed in a way that breaks the signature.

  • Currently, we only have the #[test]-gated capabilities_mut and set_credential methods that are &mut LeafNode to test for library erros, i.e., that a broken signature was used in LeafNode.