cipher

type Cipher interface {
	Scheme() Scheme

	// Seal encrypts and authenticates plaintext and
	// appends the result to dst, returning the updated slice.
	// The nonce must be Scheme().NonceSize() bytes long.
	Seal(dst, nonce, plaintext []byte) []byte

	// Open decrypts and authenticates ciphertext and, if successful,
	// appends the resulting plaintext to dst, returning the updated slice.
	// The nonce must be Scheme().NonceSize() bytes long.
	Open(dst, nonce, ciphertext []byte) ([]byte, error)
}

type Scheme interface {
	KeySize() int
	NonceSize() int
	Overhead() int

	Unpack(key []byte) (Cipher, error)
}