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// Copyright 2018 The GoPacket Authors. All rights reserved.
//
// Use of this source code is governed by a BSD-style license
// that can be found in the LICENSE file in the root of the source
// tree.
package layers
import (
"encoding/binary"
"errors"
"github.com/google/gopacket"
)
// TLSType defines the type of data after the TLS Record
type TLSType uint8
// TLSType known values.
const (
TLSChangeCipherSpec TLSType = 20
TLSAlert TLSType = 21
TLSHandshake TLSType = 22
TLSApplicationData TLSType = 23
TLSUnknown TLSType = 255
)
// String shows the register type nicely formatted
func (tt TLSType) String() string {
switch tt {
default:
return "Unknown"
case TLSChangeCipherSpec:
return "Change Cipher Spec"
case TLSAlert:
return "Alert"
case TLSHandshake:
return "Handshake"
case TLSApplicationData:
return "Application Data"
}
}
// TLSVersion represents the TLS version in numeric format
type TLSVersion uint16
// Strings shows the TLS version nicely formatted
func (tv TLSVersion) String() string {
switch tv {
default:
return "Unknown"
case 0x0200:
return "SSL 2.0"
case 0x0300:
return "SSL 3.0"
case 0x0301:
return "TLS 1.0"
case 0x0302:
return "TLS 1.1"
case 0x0303:
return "TLS 1.2"
case 0x0304:
return "TLS 1.3"
}
}
// TLS is specified in RFC 5246
//
// TLS Record Protocol
// 0 1 2 3 4 5 6 7 8
// +--+--+--+--+--+--+--+--+
// | Content Type |
// +--+--+--+--+--+--+--+--+
// | Version (major) |
// +--+--+--+--+--+--+--+--+
// | Version (minor) |
// +--+--+--+--+--+--+--+--+
// | Length |
// +--+--+--+--+--+--+--+--+
// | Length |
// +--+--+--+--+--+--+--+--+
// TLS is actually a slide of TLSrecord structures
type TLS struct {
BaseLayer
// TLS Records
ChangeCipherSpec []TLSChangeCipherSpecRecord
Handshake []TLSHandshakeRecord
AppData []TLSAppDataRecord
Alert []TLSAlertRecord
}
// TLSRecordHeader contains all the information that each TLS Record types should have
type TLSRecordHeader struct {
ContentType TLSType
Version TLSVersion
Length uint16
}
// LayerType returns gopacket.LayerTypeTLS.
func (t *TLS) LayerType() gopacket.LayerType { return LayerTypeTLS }
// decodeTLS decodes the byte slice into a TLS type. It also
// setups the application Layer in PacketBuilder.
func decodeTLS(data []byte, p gopacket.PacketBuilder) error {
t := &TLS{}
err := t.DecodeFromBytes(data, p)
if err != nil {
return err
}
p.AddLayer(t)
p.SetApplicationLayer(t)
return nil
}
// DecodeFromBytes decodes the slice into the TLS struct.
func (t *TLS) DecodeFromBytes(data []byte, df gopacket.DecodeFeedback) error {
t.BaseLayer.Contents = data
t.BaseLayer.Payload = nil
t.ChangeCipherSpec = t.ChangeCipherSpec[:0]
t.Handshake = t.Handshake[:0]
t.AppData = t.AppData[:0]
t.Alert = t.Alert[:0]
return t.decodeTLSRecords(data, df)
}
func (t *TLS) decodeTLSRecords(data []byte, df gopacket.DecodeFeedback) error {
if len(data) < 5 {
df.SetTruncated()
return errors.New("TLS record too short")
}
// since there are no further layers, the baselayer's content is
// pointing to this layer
t.BaseLayer = BaseLayer{Contents: data[:len(data)]}
var h TLSRecordHeader
h.ContentType = TLSType(data[0])
h.Version = TLSVersion(binary.BigEndian.Uint16(data[1:3]))
h.Length = binary.BigEndian.Uint16(data[3:5])
if h.ContentType.String() == "Unknown" {
return errors.New("Unknown TLS record type")
}
hl := 5 // header length
tl := hl + int(h.Length)
if len(data) < tl {
df.SetTruncated()
return errors.New("TLS packet length mismatch")
}
switch h.ContentType {
default:
return errors.New("Unknown TLS record type")
case TLSChangeCipherSpec:
var r TLSChangeCipherSpecRecord
e := r.decodeFromBytes(h, data[hl:tl], df)
if e != nil {
return e
}
t.ChangeCipherSpec = append(t.ChangeCipherSpec, r)
case TLSAlert:
var r TLSAlertRecord
e := r.decodeFromBytes(h, data[hl:tl], df)
if e != nil {
return e
}
t.Alert = append(t.Alert, r)
case TLSHandshake:
var r TLSHandshakeRecord
e := r.decodeFromBytes(h, data[hl:tl], df)
if e != nil {
return e
}
t.Handshake = append(t.Handshake, r)
case TLSApplicationData:
var r TLSAppDataRecord
e := r.decodeFromBytes(h, data[hl:tl], df)
if e != nil {
return e
}
t.AppData = append(t.AppData, r)
}
if len(data) == tl {
return nil
}
return t.decodeTLSRecords(data[tl:len(data)], df)
}
// CanDecode implements gopacket.DecodingLayer.
func (t *TLS) CanDecode() gopacket.LayerClass {
return LayerTypeTLS
}
// NextLayerType implements gopacket.DecodingLayer.
func (t *TLS) NextLayerType() gopacket.LayerType {
return gopacket.LayerTypeZero
}
// Payload returns nil, since TLS encrypted payload is inside TLSAppDataRecord
func (t *TLS) Payload() []byte {
return nil
}
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