1package xsecretbox
2
3import (
4	crypto_rand "crypto/rand"
5
6	"golang.org/x/crypto/chacha20"
7	"golang.org/x/crypto/curve25519"
8)
9
10// SharedKey computes a shared secret compatible with the one used by `crypto_box_xchacha20poly1305``
11func SharedKey(secretKey [32]byte, publicKey [32]byte) ([32]byte, error) {
12	dhKey, err := curve25519.X25519(secretKey[:], publicKey[:])
13	var subKey []byte
14	if err == nil {
15		var nonce [16]byte
16		subKey, err = chacha20.HChaCha20(dhKey[:], nonce[:])
17	}
18	var key [32]byte
19	if err != nil {
20		if _, err2 := crypto_rand.Read(key[:]); err != nil {
21			return key, err2
22		}
23		return key, err
24	}
25	copy(key[:], subKey)
26	return key, nil
27}
28