--- /dev/null
+package dns
+
+import (
+ "crypto/hmac"
+ "crypto/md5"
+ "crypto/sha1"
+ "crypto/sha256"
+ "crypto/sha512"
+ "encoding/binary"
+ "encoding/hex"
+ "hash"
+ "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."
+ HmacSHA512 = "hmac-sha512."
+)
+
+// TSIG is the RR the holds the transaction signature of a message.
+// See RFC 2845 and RFC 4635.
+type TSIG struct {
+ Hdr RR_Header
+ Algorithm string `dns:"domain-name"`
+ TimeSigned uint64 `dns:"uint48"`
+ Fudge uint16
+ MACSize uint16
+ MAC string `dns:"size-hex:MACSize"`
+ OrigId uint16
+ Error uint16
+ OtherLen uint16
+ OtherData string `dns:"size-hex:OtherLen"`
+}
+
+// TSIG has no official presentation format, but this will suffice.
+
+func (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 *TSIG) parse(c *zlexer, origin, file string) *ParseError {
+ panic("dns: internal error: parse should never be called on TSIG")
+}
+
+// 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 `dns:"uint48"`
+ Fudge uint16
+ // MACSize, MAC and OrigId excluded
+ Error uint16
+ OtherLen uint16
+ OtherData string `dns:"size-hex:OtherLen"`
+}
+
+// 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:MACSize"`
+}
+
+// 3.3. Time values used in TSIG calculations
+type timerWireFmt struct {
+ TimeSigned uint64 `dns:"uint48"`
+ 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 := fromBase64([]byte(secret))
+ if err != nil {
+ return nil, "", err
+ }
+
+ rr := m.Extra[len(m.Extra)-1].(*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(TSIG)
+ var h hash.Hash
+ switch strings.ToLower(rr.Algorithm) {
+ case HmacMD5:
+ h = hmac.New(md5.New, rawsecret)
+ case HmacSHA1:
+ h = hmac.New(sha1.New, rawsecret)
+ case HmacSHA256:
+ h = hmac.New(sha256.New, rawsecret)
+ case HmacSHA512:
+ h = hmac.New(sha512.New, rawsecret)
+ default:
+ return nil, "", ErrKeyAlg
+ }
+ h.Write(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, Len(t))
+ off, err := PackRR(t, tbuf, 0, nil, false)
+ if err != nil {
+ return nil, "", err
+ }
+ mbuf = append(mbuf, tbuf[:off]...)
+ // Update the ArCount directly in the buffer.
+ binary.BigEndian.PutUint16(mbuf[10:], 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 := fromBase64([]byte(secret))
+ if err != nil {
+ return err
+ }
+ // Strip the TSIG from the incoming msg
+ stripped, tsig, err := stripTsig(msg)
+ if err != nil {
+ return err
+ }
+
+ msgMAC, err := hex.DecodeString(tsig.MAC)
+ if err != nil {
+ return err
+ }
+
+ buf := tsigBuffer(stripped, tsig, requestMAC, timersOnly)
+
+ // Fudge factor works both ways. A message can arrive before it was signed because
+ // of clock skew.
+ now := uint64(time.Now().Unix())
+ ti := now - tsig.TimeSigned
+ if now < tsig.TimeSigned {
+ ti = tsig.TimeSigned - now
+ }
+ if uint64(tsig.Fudge) < ti {
+ return ErrTime
+ }
+
+ var h hash.Hash
+ switch strings.ToLower(tsig.Algorithm) {
+ case HmacMD5:
+ h = hmac.New(md5.New, rawsecret)
+ case HmacSHA1:
+ h = hmac.New(sha1.New, rawsecret)
+ case HmacSHA256:
+ h = hmac.New(sha256.New, rawsecret)
+ case HmacSHA512:
+ h = hmac.New(sha512.New, rawsecret)
+ default:
+ return ErrKeyAlg
+ }
+ h.Write(buf)
+ if !hmac.Equal(h.Sum(nil), msgMAC) {
+ return ErrSig
+ }
+ return nil
+}
+
+// Create a wiredata buffer for the MAC calculation.
+func tsigBuffer(msgbuf []byte, 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.
+ }
+
+ // Replace message ID in header with original ID from TSIG
+ binary.BigEndian.PutUint16(msgbuf[0:2], rr.OrigId)
+
+ if requestMAC != "" {
+ m := new(macWireFmt)
+ m.MACSize = uint16(len(requestMAC) / 2)
+ m.MAC = requestMAC
+ buf = make([]byte, len(requestMAC)) // long enough
+ n, _ := packMacWire(m, buf)
+ buf = buf[:n]
+ }
+
+ tsigvar := make([]byte, DefaultMsgSize)
+ if timersOnly {
+ tsig := new(timerWireFmt)
+ tsig.TimeSigned = rr.TimeSigned
+ tsig.Fudge = rr.Fudge
+ n, _ := packTimerWire(tsig, tsigvar)
+ 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, _ := packTsigWire(tsig, tsigvar)
+ 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, *TSIG, error) {
+ // Copied from msg.go's Unpack() Header, but modified.
+ var (
+ dh Header
+ err error
+ )
+ off, tsigoff := 0, 0
+
+ if dh, off, err = unpackMsgHdr(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
+ }
+
+ for i := 0; i < int(dh.Qdcount); i++ {
+ _, off, err = unpackQuestion(msg, off)
+ if err != nil {
+ return nil, nil, err
+ }
+ }
+
+ _, off, err = unpackRRslice(int(dh.Ancount), msg, off)
+ if err != nil {
+ return nil, nil, err
+ }
+ _, off, err = unpackRRslice(int(dh.Nscount), msg, off)
+ if err != nil {
+ return nil, nil, err
+ }
+
+ rr := new(TSIG)
+ var extra RR
+ for i := 0; i < int(dh.Arcount); i++ {
+ tsigoff = off
+ extra, off, err = UnpackRR(msg, off)
+ if err != nil {
+ return nil, nil, err
+ }
+ if extra.Header().Rrtype == TypeTSIG {
+ rr = extra.(*TSIG)
+ // Adjust Arcount.
+ arcount := binary.BigEndian.Uint16(msg[10:])
+ binary.BigEndian.PutUint16(msg[10:], 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")
+}
+
+func packTsigWire(tw *tsigWireFmt, msg []byte) (int, error) {
+ // copied from zmsg.go TSIG packing
+ // RR_Header
+ off, err := PackDomainName(tw.Name, msg, 0, nil, false)
+ if err != nil {
+ return off, err
+ }
+ off, err = packUint16(tw.Class, msg, off)
+ if err != nil {
+ return off, err
+ }
+ off, err = packUint32(tw.Ttl, msg, off)
+ if err != nil {
+ return off, err
+ }
+
+ off, err = PackDomainName(tw.Algorithm, msg, off, nil, false)
+ if err != nil {
+ return off, err
+ }
+ off, err = packUint48(tw.TimeSigned, msg, off)
+ if err != nil {
+ return off, err
+ }
+ off, err = packUint16(tw.Fudge, msg, off)
+ if err != nil {
+ return off, err
+ }
+
+ off, err = packUint16(tw.Error, msg, off)
+ if err != nil {
+ return off, err
+ }
+ off, err = packUint16(tw.OtherLen, msg, off)
+ if err != nil {
+ return off, err
+ }
+ off, err = packStringHex(tw.OtherData, msg, off)
+ if err != nil {
+ return off, err
+ }
+ return off, nil
+}
+
+func packMacWire(mw *macWireFmt, msg []byte) (int, error) {
+ off, err := packUint16(mw.MACSize, msg, 0)
+ if err != nil {
+ return off, err
+ }
+ off, err = packStringHex(mw.MAC, msg, off)
+ if err != nil {
+ return off, err
+ }
+ return off, nil
+}
+
+func packTimerWire(tw *timerWireFmt, msg []byte) (int, error) {
+ off, err := packUint48(tw.TimeSigned, msg, 0)
+ if err != nil {
+ return off, err
+ }
+ off, err = packUint16(tw.Fudge, msg, off)
+ if err != nil {
+ return off, err
+ }
+ return off, nil
+}
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