type AEADPrivateKey struct {
	PublicKey AEADPublicKey
	HashSeed  [32]byte
	Key       []byte
}

type AEADPublicKey struct {
	Cipher      algorithm.CipherFunction
	BindingHash [32]byte
	Key         []byte
}

type HMACPrivateKey struct {
	PublicKey HMACPublicKey
	HashSeed  [32]byte
	Key       []byte
}

type HMACPublicKey struct {
	Hash        algorithm.Hash
	BindingHash [32]byte
	// While this is a "public" key, the symmetric key needs to be present here.
	// Symmetric cryptographic operations use the same key material for
	// signing and verifying, and go-crypto assumes that a public key type will
	// be used for verification. Thus, this `Key` field must never be exported
	// publicly.
	Key []byte
}