func (c *cipherSuiteTLS13) nextTrafficSecret(trafficSecret []byte) []byte {
	return c.expandLabel(trafficSecret, trafficUpdateLabel, nil, c.hash.Size())
}

// trafficKey generates traffic keys according to RFC 8446, Section 7.3.
func (c *cipherSuiteTLS13) trafficKey(trafficSecret []byte) (key, iv []byte) {
	key = c.expandLabel(trafficSecret, "key", nil, c.keyLen)
	iv = c.expandLabel(trafficSecret, "iv", nil, aeadNonceLength)
	return
}