This change will cause a problem when a private key is written by an older version and read by a newer version (or vice-versa). These private keys aren't usually transmitted in a secure protocol, but they may be written to storage (encrypted) and then read later. But this scenario is unlikely for these keys because: 1) The X25519/X448 implementation is relatively new, so it is probably not widely used yet. 2) Storing key agreement keys and reusing them is much less common than generating new ephemeral keys when needed. 3) There is no way to use keytool to produce a keystore containing one of these keys. Storing an X25519/X448 private key requires custom code that extracts the encoded key and then stores it.