type BoxKey [32]byte

type ControlCipher interface {
    // MACSize returns the number of bytes in the MAC.
    MACSize() int

    // Seal replaces the message with an authenticated and encrypted version.
    // The trailing MACSize bytes of the data are used for the MAC; they are
    // discarded and overwritten.
    Seal(data []byte) error

    // Open authenticates and decrypts a box produced by Seal.  The trailing
    // MACSize bytes are not changed.  Returns true on success.
    Open(data []byte) bool

    // Encrypt encrypts the data in place.  No MAC is added.
    Encrypt(data []byte)

    // Decrypt decrypts the data in place.  No MAC is verified.
    Decrypt(data []byte)

    // ChannelBinding Returns a byte slice that is unique for the the
    // particular cipher (and the parties between which it is operating).
    // Having both parties assert out of the band that they are indeed
    // participating in a connection with that channel binding value is
    // sufficient to authenticate the data received through the cipher.
    ChannelBinding() []byte
}

type NullControlCipher struct{}