// Copyright (c) 2020 Tailscale Inc & AUTHORS All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

// Package key defines some types related to curve25519 keys.
package key

import (
	"encoding/base64"

	"golang.org/x/crypto/curve25519"
)

// Private represents a curve25519 private key.
type Private [32]byte

// Private reports whether p is the zero value.
func (p Private) IsZero() bool { return p == Private{} }

// B32 returns k as the *[32]byte type that's used by the
// golang.org/x/crypto packages. This allocates; it might
// not be appropriate for performance-sensitive paths.
func (k Private) B32() *[32]byte { return (*[32]byte)(&k) }

// Public represents a curve25519 public key.
type Public [32]byte

// Public reports whether p is the zero value.
func (p Public) IsZero() bool { return p == Public{} }

// ShortString returns the Tailscale conventional debug representation
// of a public key: the first five base64 digits of the key, in square
// brackets.
func (p Public) ShortString() string {
	return "[" + base64.StdEncoding.EncodeToString(p[:])[:5] + "]"
}

// B32 returns k as the *[32]byte type that's used by the
// golang.org/x/crypto packages. This allocates; it might
// not be appropriate for performance-sensitive paths.
func (k Public) B32() *[32]byte { return (*[32]byte)(&k) }

func (k Private) Public() Public {
	var pub [32]byte
	curve25519.ScalarBaseMult(&pub, (*[32]byte)(&k))
	return Public(pub)
}