panic("tls: internal error: wrong nonce length")
	}
	aes, err := aes.NewCipher(key)
	if err != nil {
		panic(err)
	}
	var aead cipher.AEAD
	if boring.Enabled {
		aead, err = boring.NewGCMTLS(aes)
	} else {
		boring.Unreachable()
		aead, err = cipher.NewGCM(aes)
	}
	if err != nil {
		panic(err)
	}

	ret := &prefixNonceAEAD{aead: aead}
	copy(ret.nonce[:], noncePrefix)
	return ret