if hc.cipher == nil {
		return append(record, payload...), nil
	}

	var explicitNonce []byte
	if explicitNonceLen := hc.explicitNonceLen(); explicitNonceLen > 0 {
		record, explicitNonce = sliceForAppend(record, explicitNonceLen)
		if _, isCBC := hc.cipher.(cbcMode); !isCBC && explicitNonceLen < 16 {
			// The AES-GCM construction in TLS has an explicit nonce so that the

func macSHA256(key []byte) hash.Hash {
	return hmac.New(sha256.New, key)
}

type aead interface {
	cipher.AEAD

	// explicitNonceLen returns the number of bytes of explicit nonce
	// included in each record. This is eight for older AEADs and
	// zero for modern ones.
	explicitNonceLen() int
}

const (
	aeadNonceLength   = 12
	noncePrefixLength = 4
)