It looks like age with SSH keys uses a birationally equivalent keypair. https://github.com/FiloSottile/age/blob/176e245b3cb3ada322c21eef0bce166dc5a5e4c7/agessh

It looks like age with SSH keys uses a birationally equivalent keypair. https://github.com/FiloSottile/age/blob/176e245b3cb3ada322c21eef0bce166dc5a5e4c7/agessh/agessh.go#L157 https://github.com/FiloSottile/age/blob/176e245b3cb3ada322c2... If you're using, for example, libsodium, you'd want the Ed25519 to X25519 functions to convert the two. (Note that you need to operate over raw bytes to do this.) In practice, you shouldn't do this. Use different keys for different purposes!