// Copyright 2018 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package tls

import (
	
	
	
	
	
	

	
	
)

// This file contains the functions necessary to compute the TLS 1.3 key
// schedule. See RFC 8446, Section 7.

const (
	resumptionBinderLabel         = "res binder"
	clientEarlyTrafficLabel       = "c e traffic"
	clientHandshakeTrafficLabel   = "c hs traffic"
	serverHandshakeTrafficLabel   = "s hs traffic"
	clientApplicationTrafficLabel = "c ap traffic"
	serverApplicationTrafficLabel = "s ap traffic"
	exporterLabel                 = "exp master"
	resumptionLabel               = "res master"
	trafficUpdateLabel            = "traffic upd"
)

// expandLabel implements HKDF-Expand-Label from RFC 8446, Section 7.1.
func ( *cipherSuiteTLS13) ( []byte,  string,  []byte,  int) []byte {
	var  cryptobyte.Builder
	.AddUint16(uint16())
	.AddUint8LengthPrefixed(func( *cryptobyte.Builder) {
		.AddBytes([]byte("tls13 "))
		.AddBytes([]byte())
	})
	.AddUint8LengthPrefixed(func( *cryptobyte.Builder) {
		.AddBytes()
	})
	,  := .Bytes()
	if  != nil {
		// Rather than calling BytesOrPanic, we explicitly handle this error, in
		// order to provide a reasonable error message. It should be basically
		// impossible for this to panic, and routing errors back through the
		// tree rooted in this function is quite painful. The labels are fixed
		// size, and the context is either a fixed-length computed hash, or
		// parsed from a field which has the same length limitation. As such, an
		// error here is likely to only be caused during development.
		//
		// NOTE: another reasonable approach here might be to return a
		// randomized slice if we encounter an error, which would break the
		// connection, but avoid panicking. This would perhaps be safer but
		// significantly more confusing to users.
		panic(fmt.Errorf("failed to construct HKDF label: %s", ))
	}
	 := make([]byte, )
	,  := hkdf.Expand(.hash.New, , ).Read()
	if  != nil ||  !=  {
		panic("tls: HKDF-Expand-Label invocation failed unexpectedly")
	}
	return 
}

// deriveSecret implements Derive-Secret from RFC 8446, Section 7.1.
func ( *cipherSuiteTLS13) ( []byte,  string,  hash.Hash) []byte {
	if  == nil {
		 = .hash.New()
	}
	return .expandLabel(, , .Sum(nil), .hash.Size())
}

// extract implements HKDF-Extract with the cipher suite hash.
func ( *cipherSuiteTLS13) (,  []byte) []byte {
	if  == nil {
		 = make([]byte, .hash.Size())
	}
	return hkdf.Extract(.hash.New, , )
}

// nextTrafficSecret generates the next traffic secret, given the current one,
// according to RFC 8446, Section 7.2.
func ( *cipherSuiteTLS13) ( []byte) []byte {
	return .expandLabel(, trafficUpdateLabel, nil, .hash.Size())
}

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

// finishedHash generates the Finished verify_data or PskBinderEntry according
// to RFC 8446, Section 4.4.4. See sections 4.4 and 4.2.11.2 for the baseKey
// selection.
func ( *cipherSuiteTLS13) ( []byte,  hash.Hash) []byte {
	 := .expandLabel(, "finished", nil, .hash.Size())
	 := hmac.New(.hash.New, )
	.Write(.Sum(nil))
	return .Sum(nil)
}

// exportKeyingMaterial implements RFC5705 exporters for TLS 1.3 according to
// RFC 8446, Section 7.5.
func ( *cipherSuiteTLS13) ( []byte,  hash.Hash) func(string, []byte, int) ([]byte, error) {
	 := .deriveSecret(, exporterLabel, )
	return func( string,  []byte,  int) ([]byte, error) {
		 := .deriveSecret(, , nil)
		 := .hash.New()
		.Write()
		return .expandLabel(, "exporter", .Sum(nil), ), nil
	}
}

// generateECDHEKey returns a PrivateKey that implements Diffie-Hellman
// according to RFC 8446, Section 4.2.8.2.
func ( io.Reader,  CurveID) (*ecdh.PrivateKey, error) {
	,  := curveForCurveID()
	if ! {
		return nil, errors.New("tls: internal error: unsupported curve")
	}

	return .GenerateKey()
}

func ( CurveID) (ecdh.Curve, bool) {
	switch  {
	case X25519:
		return ecdh.X25519(), true
	case CurveP256:
		return ecdh.P256(), true
	case CurveP384:
		return ecdh.P384(), true
	case CurveP521:
		return ecdh.P521(), true
	default:
		return nil, false
	}
}

func ( ecdh.Curve) (CurveID, bool) {
	switch  {
	case ecdh.X25519():
		return X25519, true
	case ecdh.P256():
		return CurveP256, true
	case ecdh.P384():
		return CurveP384, true
	case ecdh.P521():
		return CurveP521, true
	default:
		return 0, false
	}
}