Skip to content
Fetching contributors…
Cannot retrieve contributors at this time
367 lines (338 sloc) 9.89 KB
// TRANSACTION SIGNATURE (TSIG)
//
// An TSIG or transaction signature adds a HMAC TSIG record to each message sent.
// The supported algorithms include: HmacMD5, HmacSHA1 and HmacSHA256.
//
// Basic use pattern when querying with a TSIG name "axfr." (note that these key names
// must be fully qualified) and the base64 secret "so6ZGir4GPAqINNh9U5c3A==":
//
// c := new(dns.Client)
// c.TsigSecret = map[string]string{"axfr.": "so6ZGir4GPAqINNh9U5c3A=="}
// m := new(dns.Msg)
// m.SetQuestion("miek.nl.", dns.TypeMX)
// m.SetTsig("axfr.", dns.HmacMD5, 300, time.Now().Unix())
// ...
// // When sending the TSIG RR is calculated and filled in before sending
//
// When requesting an AXFR (almost all TSIG usage is when requesting zone transfers), with
// TSIG, this is the basic use pattern. In this example we request an AXFR for
// miek.nl. with TSIG key named "axfr." and secret "so6ZGir4GPAqINNh9U5c3A=="
// and using the server 85.223.71.124
//
// c := new(dns.Client)
// c.TsigSecret = map[string]string{"axfr.": "so6ZGir4GPAqINNh9U5c3A=="}
// m := new(dns.Msg)
// m.SetAxfr("miek.nl.")
// m.SetTsig("axfr.", dns.HmacMD5, 300, time.Now().Unix())
// t, err := c.XfrReceive(m, "85.223.71.124:53")
// for r := range t { /* ... */ }
//
// You can now read the records from the AXFR as they come in. Each envelope is checked with TSIG.
// If something is not correct an error is returned.
//
// Basic use pattern validating and replying to a message that has TSIG set.
//
// server := &dns.Server{Addr: ":53", Net: "udp"}
// server.TsigSecret = map[string]string{"axfr.": "so6ZGir4GPAqINNh9U5c3A=="}
// go server.ListenAndServe()
// dns.HandleFunc(".", handleRequest)
//
// func handleRequest(w dns.ResponseWriter, r *dns.Msg) {
// m := new(Msg)
// m.SetReply(r)
// if r.IsTsig() {
// if w.TsigStatus() == nil {
// // *Msg r has an TSIG record and it was validated
// m.SetTsig("axfr.", dns.HmacMD5, 300, time.Now().Unix())
// } else {
// // *Msg r has an TSIG records and it was not valided
// }
// }
// w.Write(m)
// }
package dns
import (
"crypto/hmac"
"crypto/md5"
"crypto/sha1"
"crypto/sha256"
"encoding/hex"
"hash"
"io"
"strconv"
"strings"
"time"
)
// HMAC hashing codes. These are transmitted as domain names.
const (
HmacMD5 = "hmac-md5.sig-alg.reg.int."
HmacSHA1 = "hmac-sha1."
HmacSHA256 = "hmac-sha256."
)
type RR_TSIG struct {
Hdr RR_Header
Algorithm string `dns:"domain-name"`
TimeSigned uint64
Fudge uint16
MACSize uint16
MAC string `dns:"size-hex"`
OrigId uint16
Error uint16
OtherLen uint16
OtherData string `dns:"size-hex"`
}
func (rr *RR_TSIG) Header() *RR_Header {
return &rr.Hdr
}
// TSIG has no official presentation format, but this will suffice.
func (rr *RR_TSIG) String() string {
s := "\n;; TSIG PSEUDOSECTION:\n"
s += rr.Hdr.String() +
" " + rr.Algorithm +
" " + tsigTimeToString(rr.TimeSigned) +
" " + strconv.Itoa(int(rr.Fudge)) +
" " + strconv.Itoa(int(rr.MACSize)) +
" " + strings.ToUpper(rr.MAC) +
" " + strconv.Itoa(int(rr.OrigId)) +
" " + strconv.Itoa(int(rr.Error)) + // BIND prints NOERROR
" " + strconv.Itoa(int(rr.OtherLen)) +
" " + rr.OtherData
return s
}
func (rr *RR_TSIG) Len() int {
return rr.Hdr.Len() + len(rr.Algorithm) + 1 + 6 +
4 + len(rr.MAC)/2 + 1 + 6 + len(rr.OtherData)/2 + 1
}
func (rr *RR_TSIG) Copy() RR {
return &RR_TSIG{*rr.Hdr.CopyHeader(), rr.Algorithm, rr.TimeSigned, rr.Fudge, rr.MACSize, rr.MAC, rr.OrigId, rr.Error, rr.OtherLen, rr.OtherData}
}
// The following values must be put in wireformat, so that the MAC can be calculated.
// RFC 2845, section 3.4.2. TSIG Variables.
type tsigWireFmt struct {
// From RR_Header
Name string `dns:"domain-name"`
Class uint16
Ttl uint32
// Rdata of the TSIG
Algorithm string `dns:"domain-name"`
TimeSigned uint64
Fudge uint16
// MACSize, MAC and OrigId excluded
Error uint16
OtherLen uint16
OtherData string `dns:"size-hex"`
}
// If we have the MAC use this type to convert it to wiredata.
// Section 3.4.3. Request MAC
type macWireFmt struct {
MACSize uint16
MAC string `dns:"size-hex"`
}
// 3.3. Time values used in TSIG calculations
type timerWireFmt struct {
TimeSigned uint64
Fudge uint16
}
// TsigGenerate fills out the TSIG record attached to the message.
// The message should contain
// a "stub" TSIG RR with the algorithm, key name (owner name of the RR),
// time fudge (defaults to 300 seconds) and the current time
// The TSIG MAC is saved in that Tsig RR.
// When TsigGenerate is called for the first time requestMAC is set to the empty string and
// timersOnly is false.
// If something goes wrong an error is returned, otherwise it is nil.
func TsigGenerate(m *Msg, secret, requestMAC string, timersOnly bool) ([]byte, string, error) {
if m.IsTsig() == nil {
panic("dns: TSIG not last RR in additional")
}
// If we barf here, the caller is to blame
rawsecret, err := packBase64([]byte(secret))
if err != nil {
return nil, "", err
}
rr := m.Extra[len(m.Extra)-1].(*RR_TSIG)
m.Extra = m.Extra[0 : len(m.Extra)-1] // kill the TSIG from the msg
mbuf, err := m.Pack()
if err != nil {
return nil, "", err
}
buf := tsigBuffer(mbuf, rr, requestMAC, timersOnly)
t := new(RR_TSIG)
var h hash.Hash
switch rr.Algorithm {
case HmacMD5:
h = hmac.New(md5.New, []byte(rawsecret))
case HmacSHA1:
h = hmac.New(sha1.New, []byte(rawsecret))
case HmacSHA256:
h = hmac.New(sha256.New, []byte(rawsecret))
default:
return nil, "", ErrKeyAlg
}
io.WriteString(h, string(buf))
t.MAC = hex.EncodeToString(h.Sum(nil))
t.MACSize = uint16(len(t.MAC) / 2) // Size is half!
t.Hdr = RR_Header{Name: rr.Hdr.Name, Rrtype: TypeTSIG, Class: ClassANY, Ttl: 0}
t.Fudge = rr.Fudge
t.TimeSigned = rr.TimeSigned
t.Algorithm = rr.Algorithm
t.OrigId = m.Id
tbuf := make([]byte, t.Len())
if off, err := PackRR(t, tbuf, 0, nil, false); err == nil {
tbuf = tbuf[:off] // reset to actual size used
} else {
return nil, "", err
}
mbuf = append(mbuf, tbuf...)
rawSetExtraLen(mbuf, uint16(len(m.Extra)+1))
return mbuf, t.MAC, nil
}
// TsigVerify verifies the TSIG on a message.
// If the signature does not validate err contains the
// error, otherwise it is nil.
func TsigVerify(msg []byte, secret, requestMAC string, timersOnly bool) error {
rawsecret, err := packBase64([]byte(secret))
if err != nil {
return err
}
// Srtip the TSIG from the incoming msg
stripped, tsig, err := stripTsig(msg)
if err != nil {
return err
}
buf := tsigBuffer(stripped, tsig, requestMAC, timersOnly)
ti := uint64(time.Now().Unix()) - tsig.TimeSigned
if uint64(tsig.Fudge) < ti {
return ErrTime
}
var h hash.Hash
switch tsig.Algorithm {
case HmacMD5:
h = hmac.New(md5.New, []byte(rawsecret))
case HmacSHA1:
h = hmac.New(sha1.New, []byte(rawsecret))
case HmacSHA256:
h = hmac.New(sha256.New, []byte(rawsecret))
default:
return ErrKeyAlg
}
io.WriteString(h, string(buf))
if strings.ToUpper(hex.EncodeToString(h.Sum(nil))) != strings.ToUpper(tsig.MAC) {
return ErrSig
}
return nil
}
// Create a wiredata buffer for the MAC calculation.
func tsigBuffer(msgbuf []byte, rr *RR_TSIG, requestMAC string, timersOnly bool) []byte {
var buf []byte
if rr.TimeSigned == 0 {
rr.TimeSigned = uint64(time.Now().Unix())
}
if rr.Fudge == 0 {
rr.Fudge = 300 // Standard (RFC) default.
}
if requestMAC != "" {
m := new(macWireFmt)
m.MACSize = uint16(len(requestMAC) / 2)
m.MAC = requestMAC
buf = make([]byte, len(requestMAC)) // long enough
n, _ := PackStruct(m, buf, 0)
buf = buf[:n]
}
tsigvar := make([]byte, DefaultMsgSize)
if timersOnly {
tsig := new(timerWireFmt)
tsig.TimeSigned = rr.TimeSigned
tsig.Fudge = rr.Fudge
n, _ := PackStruct(tsig, tsigvar, 0)
tsigvar = tsigvar[:n]
} else {
tsig := new(tsigWireFmt)
tsig.Name = strings.ToLower(rr.Hdr.Name)
tsig.Class = ClassANY
tsig.Ttl = rr.Hdr.Ttl
tsig.Algorithm = strings.ToLower(rr.Algorithm)
tsig.TimeSigned = rr.TimeSigned
tsig.Fudge = rr.Fudge
tsig.Error = rr.Error
tsig.OtherLen = rr.OtherLen
tsig.OtherData = rr.OtherData
n, _ := PackStruct(tsig, tsigvar, 0)
tsigvar = tsigvar[:n]
}
if requestMAC != "" {
x := append(buf, msgbuf...)
buf = append(x, tsigvar...)
} else {
buf = append(msgbuf, tsigvar...)
}
return buf
}
// Strip the TSIG from the raw message
func stripTsig(msg []byte) ([]byte, *RR_TSIG, error) {
// Copied from msg.go's Unpack()
// Header.
var dh Header
var err error
dns := new(Msg)
rr := new(RR_TSIG)
off := 0
tsigoff := 0
if off, err = UnpackStruct(&dh, msg, off); err !=nil {
return nil, nil, err
}
if dh.Arcount == 0 {
return nil, nil, ErrNoSig
}
// Rcode, see msg.go Unpack()
if int(dh.Bits&0xF) == RcodeNotAuth {
return nil, nil, ErrAuth
}
// Arrays.
dns.Question = make([]Question, dh.Qdcount)
dns.Answer = make([]RR, dh.Ancount)
dns.Ns = make([]RR, dh.Nscount)
dns.Extra = make([]RR, dh.Arcount)
for i := 0; i < len(dns.Question); i++ {
off, err = UnpackStruct(&dns.Question[i], msg, off)
if err != nil {
return nil, nil, err
}
}
for i := 0; i < len(dns.Answer); i++ {
dns.Answer[i], off, err = UnpackRR(msg, off)
if err != nil {
return nil, nil, err
}
}
for i := 0; i < len(dns.Ns); i++ {
dns.Ns[i], off, err = UnpackRR(msg, off)
if err != nil {
return nil, nil, err
}
}
for i := 0; i < len(dns.Extra); i++ {
tsigoff = off
dns.Extra[i], off, err = UnpackRR(msg, off)
if err != nil {
return nil, nil, err
}
if dns.Extra[i].Header().Rrtype == TypeTSIG {
rr = dns.Extra[i].(*RR_TSIG)
// Adjust Arcount.
arcount, _ := unpackUint16(msg, 10)
msg[10], msg[11] = packUint16(arcount - 1)
break
}
}
if rr == nil {
return nil, nil, ErrNoSig
}
return msg[:tsigoff], rr, nil
}
// Translate the TSIG time signed into a date. There is no
// need for RFC1982 calculations as this date is 48 bits.
func tsigTimeToString(t uint64) string {
ti := time.Unix(int64(t), 0).UTC()
return ti.Format("20060102150405")
}
Something went wrong with that request. Please try again.