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package xsecretbox
import (
crypto_rand "crypto/rand"
"golang.org/x/crypto/chacha20"
"golang.org/x/crypto/curve25519"
)
// SharedKey computes a shared secret compatible with the one used by `crypto_box_xchacha20poly1305`
func SharedKey(secretKey [32]byte, publicKey [32]byte) ([32]byte, error) {
dhKey, err := curve25519.X25519(secretKey[:], publicKey[:])
var subKey []byte
if err == nil {
var nonce [16]byte
subKey, err = chacha20.HChaCha20(dhKey[:], nonce[:])
}
var key [32]byte
if err != nil {
if _, err2 := crypto_rand.Read(key[:]); err != nil {
return key, err2
}
return key, err
}
copy(key[:], subKey)
return key, nil
}
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