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
}

	c := hs.c

	finished := &finishedMsg{
		verifyData: hs.suite.finishedHash(c.out.trafficSecret, hs.transcript),
	}

	if _, err := hs.c.writeHandshakeRecord(finished, hs.transcript); err != nil {
		return err
	}

	c.out.setTrafficSecret(hs.suite, QUICEncryptionLevelApplication, hs.trafficSecret)

	if !c.config.SessionTicketsDisabled && c.config.ClientSessionCache != nil {

		verifyData: hs.suite.finishedHash(c.out.trafficSecret, hs.transcript),
	}

	if _, err := hs.c.writeHandshakeRecord(finished, hs.transcript); err != nil {
		return err
	}

	// Derive secrets that take context through the server Finished.

	hs.masterSecret = hs.suite.extract(nil,
		hs.suite.deriveSecret(hs.handshakeSecret, "derived", nil))

	hs.trafficSecret = hs.suite.deriveSecret(hs.masterSecret,

				t.Errorf("cipherSuiteTLS13.deriveSecret() = % x, want % x", got, tt.want)
			}
		})
	}
}

func TestTrafficKey(t *testing.T) {
	trafficSecret := parseVector(
		`PRK (32 octets):  b6 7b 7d 69 0c c1 6c 4e 75 e5 42 13 cb 2d 37 b4
		e9 c9 12 bc de d9 10 5d 42 be fd 59 d3 91 ad 38`)
	wantKey := parseVector(

	nextCipher any       // next encryption state
	nextMac    hash.Hash // next MAC algorithm

	level         QUICEncryptionLevel // current QUIC encryption level
	trafficSecret []byte              // current TLS 1.3 traffic secret
}

type permanentError struct {
	err net.Error
}

func (e *permanentError) Error() string   { return e.err.Error() }