Source: messages.go in package golang.org/x/crypto/ssh


package ssh

import (
	"bytes"
	"encoding/binary"
	"errors"
	"fmt"
	"io"
	"math/big"
	"reflect"
	"strconv"
	"strings"
)

These are SSH message type numbers. They are scattered around several documents but many were taken from [SSH-PARAMETERS].

const (
	msgIgnore        = 2
	msgUnimplemented = 3
	msgDebug         = 4
	msgNewKeys       = 21
)

SSH messages: These structures mirror the wire format of the corresponding SSH messages. They are marshaled using reflection with the marshal and unmarshal functions in this file. The only wrinkle is that a final member of type []byte with a ssh tag of "rest" receives the remainder of a packet when unmarshaling.

See RFC 4253, section 11.1.

const msgDisconnect = 1

disconnectMsg is the message that signals a disconnect. It is also the error type returned from mux.Wait()

type disconnectMsg struct {
	Reason   uint32 `sshtype:"1"`
	Message  string
	Language string
}

func (d *disconnectMsg) Error() string {
	return fmt.Sprintf("ssh: disconnect, reason %d: %s", d.Reason, d.Message)
}

See RFC 4253, section 7.1.

const msgKexInit = 20

type kexInitMsg struct {
	Cookie                  [16]byte `sshtype:"20"`
	KexAlgos                []string
	ServerHostKeyAlgos      []string
	CiphersClientServer     []string
	CiphersServerClient     []string
	MACsClientServer        []string
	MACsServerClient        []string
	CompressionClientServer []string
	CompressionServerClient []string
	LanguagesClientServer   []string
	LanguagesServerClient   []string
	FirstKexFollows         bool
	Reserved                uint32
}

See RFC 4253, section 8.

Diffie-Helman

const msgKexDHInit = 30

type kexDHInitMsg struct {
	X *big.Int `sshtype:"30"`
}

const msgKexECDHInit = 30

type kexECDHInitMsg struct {
	ClientPubKey []byte `sshtype:"30"`
}

const msgKexECDHReply = 31

type kexECDHReplyMsg struct {
	HostKey         []byte `sshtype:"31"`
	EphemeralPubKey []byte
	Signature       []byte
}

const msgKexDHReply = 31

type kexDHReplyMsg struct {
	HostKey   []byte `sshtype:"31"`
	Y         *big.Int
	Signature []byte
}

See RFC 4419, section 5.

const msgKexDHGexGroup = 31

type kexDHGexGroupMsg struct {
	P *big.Int `sshtype:"31"`
	G *big.Int
}

const msgKexDHGexInit = 32

type kexDHGexInitMsg struct {
	X *big.Int `sshtype:"32"`
}

const msgKexDHGexReply = 33

type kexDHGexReplyMsg struct {
	HostKey   []byte `sshtype:"33"`
	Y         *big.Int
	Signature []byte
}

const msgKexDHGexRequest = 34

type kexDHGexRequestMsg struct {
	MinBits      uint32 `sshtype:"34"`
	PreferedBits uint32
	MaxBits      uint32
}

See RFC 4253, section 10.

const msgServiceRequest = 5

type serviceRequestMsg struct {
	Service string `sshtype:"5"`
}

See RFC 4253, section 10.

const msgServiceAccept = 6

type serviceAcceptMsg struct {
	Service string `sshtype:"6"`
}

See RFC 4252, section 5.

const msgUserAuthRequest = 50

type userAuthRequestMsg struct {
	User    string `sshtype:"50"`
	Service string
	Method  string
	Payload []byte `ssh:"rest"`
}

Used for debug printouts of packets.

type userAuthSuccessMsg struct {
}

See RFC 4252, section 5.1

const msgUserAuthFailure = 51

type userAuthFailureMsg struct {
	Methods        []string `sshtype:"51"`
	PartialSuccess bool
}

See RFC 4252, section 5.1

const msgUserAuthSuccess = 52

See RFC 4252, section 5.4

const msgUserAuthBanner = 53

type userAuthBannerMsg struct {

unused, but required to allow message parsing

	Language string
}

See RFC 4256, section 3.2

const msgUserAuthInfoRequest = 60
const msgUserAuthInfoResponse = 61

type userAuthInfoRequestMsg struct {
	User               string `sshtype:"60"`
	Instruction        string
	DeprecatedLanguage string
	NumPrompts         uint32
	Prompts            []byte `ssh:"rest"`
}

See RFC 4254, section 5.1.

const msgChannelOpen = 90

type channelOpenMsg struct {
	ChanType         string `sshtype:"90"`
	PeersID          uint32
	PeersWindow      uint32
	MaxPacketSize    uint32
	TypeSpecificData []byte `ssh:"rest"`
}

const msgChannelExtendedData = 95
const msgChannelData = 94

Used for debug print outs of packets.

type channelDataMsg struct {
	PeersID uint32 `sshtype:"94"`
	Length  uint32
	Rest    []byte `ssh:"rest"`
}

See RFC 4254, section 5.1.

const msgChannelOpenConfirm = 91

type channelOpenConfirmMsg struct {
	PeersID          uint32 `sshtype:"91"`
	MyID             uint32
	MyWindow         uint32
	MaxPacketSize    uint32
	TypeSpecificData []byte `ssh:"rest"`
}

See RFC 4254, section 5.1.

const msgChannelOpenFailure = 92

type channelOpenFailureMsg struct {
	PeersID  uint32 `sshtype:"92"`
	Reason   RejectionReason
	Message  string
	Language string
}

const msgChannelRequest = 98

type channelRequestMsg struct {
	PeersID             uint32 `sshtype:"98"`
	Request             string
	WantReply           bool
	RequestSpecificData []byte `ssh:"rest"`
}

See RFC 4254, section 5.4.

const msgChannelSuccess = 99

type channelRequestSuccessMsg struct {
	PeersID uint32 `sshtype:"99"`
}

See RFC 4254, section 5.4.

const msgChannelFailure = 100

type channelRequestFailureMsg struct {
	PeersID uint32 `sshtype:"100"`
}

See RFC 4254, section 5.3

const msgChannelClose = 97

type channelCloseMsg struct {
	PeersID uint32 `sshtype:"97"`
}

See RFC 4254, section 5.3

const msgChannelEOF = 96

type channelEOFMsg struct {
	PeersID uint32 `sshtype:"96"`
}

See RFC 4254, section 4

const msgGlobalRequest = 80

type globalRequestMsg struct {
	Type      string `sshtype:"80"`
	WantReply bool
	Data      []byte `ssh:"rest"`
}

See RFC 4254, section 4

const msgRequestSuccess = 81

type globalRequestSuccessMsg struct {
	Data []byte `ssh:"rest" sshtype:"81"`
}

See RFC 4254, section 4

const msgRequestFailure = 82

type globalRequestFailureMsg struct {
	Data []byte `ssh:"rest" sshtype:"82"`
}

See RFC 4254, section 5.2

const msgChannelWindowAdjust = 93

type windowAdjustMsg struct {
	PeersID         uint32 `sshtype:"93"`
	AdditionalBytes uint32
}

See RFC 4252, section 7

const msgUserAuthPubKeyOk = 60

type userAuthPubKeyOkMsg struct {
	Algo   string `sshtype:"60"`
	PubKey []byte
}

See RFC 4462, section 3

const msgUserAuthGSSAPIResponse = 60

type userAuthGSSAPIResponse struct {
	SupportMech []byte `sshtype:"60"`
}

const msgUserAuthGSSAPIToken = 61

type userAuthGSSAPIToken struct {
	Token []byte `sshtype:"61"`
}

const msgUserAuthGSSAPIMIC = 66

type userAuthGSSAPIMIC struct {
	MIC []byte `sshtype:"66"`
}

See RFC 4462, section 3.9

const msgUserAuthGSSAPIErrTok = 64

type userAuthGSSAPIErrTok struct {
	ErrorToken []byte `sshtype:"64"`
}

See RFC 4462, section 3.8

const msgUserAuthGSSAPIError = 65

type userAuthGSSAPIError struct {
	MajorStatus uint32 `sshtype:"65"`
	MinorStatus uint32
	Message     string
	LanguageTag string
}

typeTags returns the possible type bytes for the given reflect.Type, which should be a struct. The possible values are separated by a '|' character.

func typeTags(structType reflect.Type) (tags []byte) {
	tagStr := structType.Field(0).Tag.Get("sshtype")

	for _, tag := range strings.Split(tagStr, "|") {
		i, err := strconv.Atoi(tag)
		if err == nil {
			tags = append(tags, byte(i))
		}
	}

	return tags
}

func fieldError(t reflect.Type, field int, problem string) error {
	if problem != "" {
		problem = ": " + problem
	}
	return fmt.Errorf("ssh: unmarshal error for field %s of type %s%s", t.Field(field).Name, t.Name(), problem)
}

var errShortRead = errors.New("ssh: short read")

Unmarshal parses data in SSH wire format into a structure. The out argument should be a pointer to struct. If the first member of the struct has the "sshtype" tag set to a '|'-separated set of numbers in decimal, the packet must start with one of those numbers. In case of error, Unmarshal returns a ParseError or UnexpectedMessageError.

func Unmarshal(data []byte, out interface{}) error {
	v := reflect.ValueOf(out).Elem()
	structType := v.Type()
	expectedTypes := typeTags(structType)

	var expectedType byte
	if len(expectedTypes) > 0 {
		expectedType = expectedTypes[0]
	}

	if len(data) == 0 {
		return parseError(expectedType)
	}

	if len(expectedTypes) > 0 {
		goodType := false
		for _, e := range expectedTypes {
			if e > 0 && data[0] == e {
				goodType = true
				break
			}
		}
		if !goodType {
			return fmt.Errorf("ssh: unexpected message type %d (expected one of %v)", data[0], expectedTypes)
		}
		data = data[1:]
	}

	var ok bool
	for i := 0; i < v.NumField(); i++ {
		field := v.Field(i)
		t := field.Type()
		switch t.Kind() {
		case reflect.Bool:
			if len(data) < 1 {
				return errShortRead
			}
			field.SetBool(data[0] != 0)
			data = data[1:]
		case reflect.Array:
			if t.Elem().Kind() != reflect.Uint8 {
				return fieldError(structType, i, "array of unsupported type")
			}
			if len(data) < t.Len() {
				return errShortRead
			}
			for j, n := 0, t.Len(); j < n; j++ {
				field.Index(j).Set(reflect.ValueOf(data[j]))
			}
			data = data[t.Len():]
		case reflect.Uint64:
			var u64 uint64
			if u64, data, ok = parseUint64(data); !ok {
				return errShortRead
			}
			field.SetUint(u64)
		case reflect.Uint32:
			var u32 uint32
			if u32, data, ok = parseUint32(data); !ok {
				return errShortRead
			}
			field.SetUint(uint64(u32))
		case reflect.Uint8:
			if len(data) < 1 {
				return errShortRead
			}
			field.SetUint(uint64(data[0]))
			data = data[1:]
		case reflect.String:
			var s []byte
			if s, data, ok = parseString(data); !ok {
				return fieldError(structType, i, "")
			}
			field.SetString(string(s))
		case reflect.Slice:
			switch t.Elem().Kind() {
			case reflect.Uint8:
				if structType.Field(i).Tag.Get("ssh") == "rest" {
					field.Set(reflect.ValueOf(data))
					data = nil
				} else {
					var s []byte
					if s, data, ok = parseString(data); !ok {
						return errShortRead
					}
					field.Set(reflect.ValueOf(s))
				}
			case reflect.String:
				var nl []string
				if nl, data, ok = parseNameList(data); !ok {
					return errShortRead
				}
				field.Set(reflect.ValueOf(nl))
			default:
				return fieldError(structType, i, "slice of unsupported type")
			}
		case reflect.Ptr:
			if t == bigIntType {
				var n *big.Int
				if n, data, ok = parseInt(data); !ok {
					return errShortRead
				}
				field.Set(reflect.ValueOf(n))
			} else {
				return fieldError(structType, i, "pointer to unsupported type")
			}
		default:
			return fieldError(structType, i, fmt.Sprintf("unsupported type: %v", t))
		}
	}

	if len(data) != 0 {
		return parseError(expectedType)
	}

	return nil
}

Marshal serializes the message in msg to SSH wire format. The msg argument should be a struct or pointer to struct. If the first member has the "sshtype" tag set to a number in decimal, that number is prepended to the result. If the last of member has the "ssh" tag set to "rest", its contents are appended to the output.

func Marshal(msg interface{}) []byte {
	out := make([]byte, 0, 64)
	return marshalStruct(out, msg)
}

func marshalStruct(out []byte, msg interface{}) []byte {
	v := reflect.Indirect(reflect.ValueOf(msg))
	msgTypes := typeTags(v.Type())
	if len(msgTypes) > 0 {
		out = append(out, msgTypes[0])
	}

	for i, n := 0, v.NumField(); i < n; i++ {
		field := v.Field(i)
		switch t := field.Type(); t.Kind() {
		case reflect.Bool:
			var v uint8
			if field.Bool() {
				v = 1
			}
			out = append(out, v)
		case reflect.Array:
			if t.Elem().Kind() != reflect.Uint8 {
				panic(fmt.Sprintf("array of non-uint8 in field %d: %T", i, field.Interface()))
			}
			for j, l := 0, t.Len(); j < l; j++ {
				out = append(out, uint8(field.Index(j).Uint()))
			}
		case reflect.Uint32:
			out = appendU32(out, uint32(field.Uint()))
		case reflect.Uint64:
			out = appendU64(out, uint64(field.Uint()))
		case reflect.Uint8:
			out = append(out, uint8(field.Uint()))
		case reflect.String:
			s := field.String()
			out = appendInt(out, len(s))
			out = append(out, s...)
		case reflect.Slice:
			switch t.Elem().Kind() {
			case reflect.Uint8:
				if v.Type().Field(i).Tag.Get("ssh") != "rest" {
					out = appendInt(out, field.Len())
				}
				out = append(out, field.Bytes()...)
			case reflect.String:
				offset := len(out)
				out = appendU32(out, 0)
				if n := field.Len(); n > 0 {
					for j := 0; j < n; j++ {
						f := field.Index(j)
						if j != 0 {
							out = append(out, ',')
						}
						out = append(out, f.String()...)

overwrite length value

					binary.BigEndian.PutUint32(out[offset:], uint32(len(out)-offset-4))
				}
			default:
				panic(fmt.Sprintf("slice of unknown type in field %d: %T", i, field.Interface()))
			}
		case reflect.Ptr:
			if t == bigIntType {
				var n *big.Int
				nValue := reflect.ValueOf(&n)
				nValue.Elem().Set(field)
				needed := intLength(n)
				oldLength := len(out)

				if cap(out)-len(out) < needed {
					newOut := make([]byte, len(out), 2*(len(out)+needed))
					copy(newOut, out)
					out = newOut
				}
				out = out[:oldLength+needed]
				marshalInt(out[oldLength:], n)
			} else {
				panic(fmt.Sprintf("pointer to unknown type in field %d: %T", i, field.Interface()))
			}
		}
	}

	return out
}

var bigOne = big.NewInt(1)

func parseString(in []byte) (out, rest []byte, ok bool) {
	if len(in) < 4 {
		return
	}
	length := binary.BigEndian.Uint32(in)
	in = in[4:]
	if uint32(len(in)) < length {
		return
	}
	out = in[:length]
	rest = in[length:]
	ok = true
	return
}

var (
	comma         = []byte{','}
	emptyNameList = []string{}
)

func parseNameList(in []byte) (out []string, rest []byte, ok bool) {
	contents, rest, ok := parseString(in)
	if !ok {
		return
	}
	if len(contents) == 0 {
		out = emptyNameList
		return
	}
	parts := bytes.Split(contents, comma)
	out = make([]string, len(parts))
	for i, part := range parts {
		out[i] = string(part)
	}
	return
}

func parseInt(in []byte) (out *big.Int, rest []byte, ok bool) {
	contents, rest, ok := parseString(in)
	if !ok {
		return
	}
	out = new(big.Int)

This is a negative number

		notBytes := make([]byte, len(contents))
		for i := range notBytes {
			notBytes[i] = ^contents[i]
		}
		out.SetBytes(notBytes)
		out.Add(out, bigOne)
		out.Neg(out)

Positive number

		out.SetBytes(contents)
	}
	ok = true
	return
}

func parseUint32(in []byte) (uint32, []byte, bool) {
	if len(in) < 4 {
		return 0, nil, false
	}
	return binary.BigEndian.Uint32(in), in[4:], true
}

func parseUint64(in []byte) (uint64, []byte, bool) {
	if len(in) < 8 {
		return 0, nil, false
	}
	return binary.BigEndian.Uint64(in), in[8:], true
}

func intLength(n *big.Int) int {
	length := 4 /* length bytes */
	if n.Sign() < 0 {
		nMinus1 := new(big.Int).Neg(n)
		nMinus1.Sub(nMinus1, bigOne)
		bitLen := nMinus1.BitLen()

The number will need 0xff padding

			length++
		}
		length += (bitLen + 7) / 8

A zero is the zero length string

	} else {
		bitLen := n.BitLen()

The number will need 0x00 padding

			length++
		}
		length += (bitLen + 7) / 8
	}

	return length
}

func marshalUint32(to []byte, n uint32) []byte {
	binary.BigEndian.PutUint32(to, n)
	return to[4:]
}

func marshalUint64(to []byte, n uint64) []byte {
	binary.BigEndian.PutUint64(to, n)
	return to[8:]
}

func marshalInt(to []byte, n *big.Int) []byte {
	lengthBytes := to
	to = to[4:]
	length := 0

A negative number has to be converted to two's-complement form. So we'll subtract 1 and invert. If the most-significant-bit isn't set then we'll need to pad the beginning with 0xff in order to keep the number negative.

		nMinus1 := new(big.Int).Neg(n)
		nMinus1.Sub(nMinus1, bigOne)
		bytes := nMinus1.Bytes()
		for i := range bytes {
			bytes[i] ^= 0xff
		}
		if len(bytes) == 0 || bytes[0]&0x80 == 0 {
			to[0] = 0xff
			to = to[1:]
			length++
		}
		nBytes := copy(to, bytes)
		to = to[nBytes:]
		length += nBytes

A zero is the zero length string

	} else {
		bytes := n.Bytes()

We'll have to pad this with a 0x00 in order to stop it looking like a negative number.

			to[0] = 0
			to = to[1:]
			length++
		}
		nBytes := copy(to, bytes)
		to = to[nBytes:]
		length += nBytes
	}

	lengthBytes[0] = byte(length >> 24)
	lengthBytes[1] = byte(length >> 16)
	lengthBytes[2] = byte(length >> 8)
	lengthBytes[3] = byte(length)
	return to
}

func writeInt(w io.Writer, n *big.Int) {
	length := intLength(n)
	buf := make([]byte, length)
	marshalInt(buf, n)
	w.Write(buf)
}

func writeString(w io.Writer, s []byte) {
	var lengthBytes [4]byte
	lengthBytes[0] = byte(len(s) >> 24)
	lengthBytes[1] = byte(len(s) >> 16)
	lengthBytes[2] = byte(len(s) >> 8)
	lengthBytes[3] = byte(len(s))
	w.Write(lengthBytes[:])
	w.Write(s)
}

func stringLength(n int) int {
	return 4 + n
}

func marshalString(to []byte, s []byte) []byte {
	to[0] = byte(len(s) >> 24)
	to[1] = byte(len(s) >> 16)
	to[2] = byte(len(s) >> 8)
	to[3] = byte(len(s))
	to = to[4:]
	copy(to, s)
	return to[len(s):]
}

var bigIntType = reflect.TypeOf((*big.Int)(nil))

Decode a packet into its corresponding message.

func decode(packet []byte) (interface{}, error) {
	var msg interface{}
	switch packet[0] {
	case msgDisconnect:
		msg = new(disconnectMsg)
	case msgServiceRequest:
		msg = new(serviceRequestMsg)
	case msgServiceAccept:
		msg = new(serviceAcceptMsg)
	case msgKexInit:
		msg = new(kexInitMsg)
	case msgKexDHInit:
		msg = new(kexDHInitMsg)
	case msgKexDHReply:
		msg = new(kexDHReplyMsg)
	case msgUserAuthRequest:
		msg = new(userAuthRequestMsg)
	case msgUserAuthSuccess:
		return new(userAuthSuccessMsg), nil
	case msgUserAuthFailure:
		msg = new(userAuthFailureMsg)
	case msgUserAuthPubKeyOk:
		msg = new(userAuthPubKeyOkMsg)
	case msgGlobalRequest:
		msg = new(globalRequestMsg)
	case msgRequestSuccess:
		msg = new(globalRequestSuccessMsg)
	case msgRequestFailure:
		msg = new(globalRequestFailureMsg)
	case msgChannelOpen:
		msg = new(channelOpenMsg)
	case msgChannelData:
		msg = new(channelDataMsg)
	case msgChannelOpenConfirm:
		msg = new(channelOpenConfirmMsg)
	case msgChannelOpenFailure:
		msg = new(channelOpenFailureMsg)
	case msgChannelWindowAdjust:
		msg = new(windowAdjustMsg)
	case msgChannelEOF:
		msg = new(channelEOFMsg)
	case msgChannelClose:
		msg = new(channelCloseMsg)
	case msgChannelRequest:
		msg = new(channelRequestMsg)
	case msgChannelSuccess:
		msg = new(channelRequestSuccessMsg)
	case msgChannelFailure:
		msg = new(channelRequestFailureMsg)
	case msgUserAuthGSSAPIToken:
		msg = new(userAuthGSSAPIToken)
	case msgUserAuthGSSAPIMIC:
		msg = new(userAuthGSSAPIMIC)
	case msgUserAuthGSSAPIErrTok:
		msg = new(userAuthGSSAPIErrTok)
	case msgUserAuthGSSAPIError:
		msg = new(userAuthGSSAPIError)
	default:
		return nil, unexpectedMessageError(0, packet[0])
	}
	if err := Unmarshal(packet, msg); err != nil {
		return nil, err
	}
	return msg, nil
}

var packetTypeNames = map[byte]string{
	msgDisconnect:          "disconnectMsg",
	msgServiceRequest:      "serviceRequestMsg",
	msgServiceAccept:       "serviceAcceptMsg",
	msgKexInit:             "kexInitMsg",
	msgKexDHInit:           "kexDHInitMsg",
	msgKexDHReply:          "kexDHReplyMsg",
	msgUserAuthRequest:     "userAuthRequestMsg",
	msgUserAuthSuccess:     "userAuthSuccessMsg",
	msgUserAuthFailure:     "userAuthFailureMsg",
	msgUserAuthPubKeyOk:    "userAuthPubKeyOkMsg",
	msgGlobalRequest:       "globalRequestMsg",
	msgRequestSuccess:      "globalRequestSuccessMsg",
	msgRequestFailure:      "globalRequestFailureMsg",
	msgChannelOpen:         "channelOpenMsg",
	msgChannelData:         "channelDataMsg",
	msgChannelOpenConfirm:  "channelOpenConfirmMsg",
	msgChannelOpenFailure:  "channelOpenFailureMsg",
	msgChannelWindowAdjust: "windowAdjustMsg",
	msgChannelEOF:          "channelEOFMsg",
	msgChannelClose:        "channelCloseMsg",
	msgChannelRequest:      "channelRequestMsg",
	msgChannelSuccess:      "channelRequestSuccessMsg",
	msgChannelFailure:      "channelRequestFailureMsg",