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429 lines
11 KiB
429 lines
11 KiB
package dns
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import (
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"crypto/hmac"
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"crypto/sha1"
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"crypto/sha256"
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"crypto/sha512"
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"encoding/binary"
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"encoding/hex"
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"hash"
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"strconv"
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"strings"
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"time"
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)
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// HMAC hashing codes. These are transmitted as domain names.
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const (
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HmacSHA1 = "hmac-sha1."
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HmacSHA224 = "hmac-sha224."
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HmacSHA256 = "hmac-sha256."
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HmacSHA384 = "hmac-sha384."
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HmacSHA512 = "hmac-sha512."
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HmacMD5 = "hmac-md5.sig-alg.reg.int." // Deprecated: HmacMD5 is no longer supported.
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)
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// TsigProvider provides the API to plug-in a custom TSIG implementation.
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type TsigProvider interface {
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// Generate is passed the DNS message to be signed and the partial TSIG RR. It returns the signature and nil, otherwise an error.
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Generate(msg []byte, t *TSIG) ([]byte, error)
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// Verify is passed the DNS message to be verified and the TSIG RR. If the signature is valid it will return nil, otherwise an error.
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Verify(msg []byte, t *TSIG) error
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}
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type tsigHMACProvider string
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func (key tsigHMACProvider) Generate(msg []byte, t *TSIG) ([]byte, error) {
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// If we barf here, the caller is to blame
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rawsecret, err := fromBase64([]byte(key))
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if err != nil {
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return nil, err
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}
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var h hash.Hash
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switch CanonicalName(t.Algorithm) {
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case HmacSHA1:
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h = hmac.New(sha1.New, rawsecret)
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case HmacSHA224:
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h = hmac.New(sha256.New224, rawsecret)
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case HmacSHA256:
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h = hmac.New(sha256.New, rawsecret)
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case HmacSHA384:
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h = hmac.New(sha512.New384, rawsecret)
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case HmacSHA512:
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h = hmac.New(sha512.New, rawsecret)
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default:
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return nil, ErrKeyAlg
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}
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h.Write(msg)
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return h.Sum(nil), nil
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}
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func (key tsigHMACProvider) Verify(msg []byte, t *TSIG) error {
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b, err := key.Generate(msg, t)
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if err != nil {
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return err
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}
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mac, err := hex.DecodeString(t.MAC)
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if err != nil {
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return err
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}
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if !hmac.Equal(b, mac) {
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return ErrSig
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}
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return nil
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}
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// TSIG is the RR the holds the transaction signature of a message.
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// See RFC 2845 and RFC 4635.
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type TSIG struct {
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Hdr RR_Header
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Algorithm string `dns:"domain-name"`
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TimeSigned uint64 `dns:"uint48"`
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Fudge uint16
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MACSize uint16
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MAC string `dns:"size-hex:MACSize"`
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OrigId uint16
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Error uint16
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OtherLen uint16
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OtherData string `dns:"size-hex:OtherLen"`
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}
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// TSIG has no official presentation format, but this will suffice.
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func (rr *TSIG) String() string {
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s := "\n;; TSIG PSEUDOSECTION:\n; " // add another semi-colon to signify TSIG does not have a presentation format
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s += rr.Hdr.String() +
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" " + rr.Algorithm +
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" " + tsigTimeToString(rr.TimeSigned) +
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" " + strconv.Itoa(int(rr.Fudge)) +
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" " + strconv.Itoa(int(rr.MACSize)) +
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" " + strings.ToUpper(rr.MAC) +
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" " + strconv.Itoa(int(rr.OrigId)) +
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" " + strconv.Itoa(int(rr.Error)) + // BIND prints NOERROR
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" " + strconv.Itoa(int(rr.OtherLen)) +
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" " + rr.OtherData
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return s
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}
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func (*TSIG) parse(c *zlexer, origin string) *ParseError {
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return &ParseError{err: "TSIG records do not have a presentation format"}
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}
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// The following values must be put in wireformat, so that the MAC can be calculated.
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// RFC 2845, section 3.4.2. TSIG Variables.
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type tsigWireFmt struct {
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// From RR_Header
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Name string `dns:"domain-name"`
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Class uint16
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Ttl uint32
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// Rdata of the TSIG
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Algorithm string `dns:"domain-name"`
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TimeSigned uint64 `dns:"uint48"`
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Fudge uint16
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// MACSize, MAC and OrigId excluded
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Error uint16
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OtherLen uint16
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OtherData string `dns:"size-hex:OtherLen"`
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}
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// If we have the MAC use this type to convert it to wiredata. Section 3.4.3. Request MAC
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type macWireFmt struct {
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MACSize uint16
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MAC string `dns:"size-hex:MACSize"`
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}
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// 3.3. Time values used in TSIG calculations
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type timerWireFmt struct {
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TimeSigned uint64 `dns:"uint48"`
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Fudge uint16
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}
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// TsigGenerate fills out the TSIG record attached to the message.
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// The message should contain
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// a "stub" TSIG RR with the algorithm, key name (owner name of the RR),
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// time fudge (defaults to 300 seconds) and the current time
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// The TSIG MAC is saved in that Tsig RR.
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// When TsigGenerate is called for the first time requestMAC is set to the empty string and
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// timersOnly is false.
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// If something goes wrong an error is returned, otherwise it is nil.
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func TsigGenerate(m *Msg, secret, requestMAC string, timersOnly bool) ([]byte, string, error) {
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return tsigGenerateProvider(m, tsigHMACProvider(secret), requestMAC, timersOnly)
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}
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func tsigGenerateProvider(m *Msg, provider TsigProvider, requestMAC string, timersOnly bool) ([]byte, string, error) {
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if m.IsTsig() == nil {
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panic("dns: TSIG not last RR in additional")
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}
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rr := m.Extra[len(m.Extra)-1].(*TSIG)
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m.Extra = m.Extra[0 : len(m.Extra)-1] // kill the TSIG from the msg
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mbuf, err := m.Pack()
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if err != nil {
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return nil, "", err
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}
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buf, err := tsigBuffer(mbuf, rr, requestMAC, timersOnly)
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if err != nil {
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return nil, "", err
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}
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t := new(TSIG)
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// Copy all TSIG fields except MAC and its size, which are filled using the computed digest.
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*t = *rr
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mac, err := provider.Generate(buf, rr)
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if err != nil {
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return nil, "", err
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}
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t.MAC = hex.EncodeToString(mac)
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t.MACSize = uint16(len(t.MAC) / 2) // Size is half!
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tbuf := make([]byte, Len(t))
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off, err := PackRR(t, tbuf, 0, nil, false)
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if err != nil {
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return nil, "", err
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}
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mbuf = append(mbuf, tbuf[:off]...)
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// Update the ArCount directly in the buffer.
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binary.BigEndian.PutUint16(mbuf[10:], uint16(len(m.Extra)+1))
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return mbuf, t.MAC, nil
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}
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// TsigVerify verifies the TSIG on a message.
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// If the signature does not validate err contains the
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// error, otherwise it is nil.
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func TsigVerify(msg []byte, secret, requestMAC string, timersOnly bool) error {
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return tsigVerify(msg, tsigHMACProvider(secret), requestMAC, timersOnly, uint64(time.Now().Unix()))
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}
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func tsigVerifyProvider(msg []byte, provider TsigProvider, requestMAC string, timersOnly bool) error {
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return tsigVerify(msg, provider, requestMAC, timersOnly, uint64(time.Now().Unix()))
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}
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// actual implementation of TsigVerify, taking the current time ('now') as a parameter for the convenience of tests.
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func tsigVerify(msg []byte, provider TsigProvider, requestMAC string, timersOnly bool, now uint64) error {
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// Strip the TSIG from the incoming msg
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stripped, tsig, err := stripTsig(msg)
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if err != nil {
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return err
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}
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buf, err := tsigBuffer(stripped, tsig, requestMAC, timersOnly)
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if err != nil {
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return err
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}
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if err := provider.Verify(buf, tsig); err != nil {
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return err
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}
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// Fudge factor works both ways. A message can arrive before it was signed because
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// of clock skew.
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// We check this after verifying the signature, following draft-ietf-dnsop-rfc2845bis
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// instead of RFC2845, in order to prevent a security vulnerability as reported in CVE-2017-3142/3143.
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ti := now - tsig.TimeSigned
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if now < tsig.TimeSigned {
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ti = tsig.TimeSigned - now
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}
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if uint64(tsig.Fudge) < ti {
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return ErrTime
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}
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return nil
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}
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// Create a wiredata buffer for the MAC calculation.
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func tsigBuffer(msgbuf []byte, rr *TSIG, requestMAC string, timersOnly bool) ([]byte, error) {
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var buf []byte
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if rr.TimeSigned == 0 {
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rr.TimeSigned = uint64(time.Now().Unix())
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}
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if rr.Fudge == 0 {
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rr.Fudge = 300 // Standard (RFC) default.
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}
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// Replace message ID in header with original ID from TSIG
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binary.BigEndian.PutUint16(msgbuf[0:2], rr.OrigId)
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if requestMAC != "" {
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m := new(macWireFmt)
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m.MACSize = uint16(len(requestMAC) / 2)
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m.MAC = requestMAC
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buf = make([]byte, len(requestMAC)) // long enough
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n, err := packMacWire(m, buf)
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if err != nil {
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return nil, err
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}
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buf = buf[:n]
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}
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tsigvar := make([]byte, DefaultMsgSize)
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if timersOnly {
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tsig := new(timerWireFmt)
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tsig.TimeSigned = rr.TimeSigned
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tsig.Fudge = rr.Fudge
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n, err := packTimerWire(tsig, tsigvar)
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if err != nil {
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return nil, err
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}
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tsigvar = tsigvar[:n]
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} else {
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tsig := new(tsigWireFmt)
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tsig.Name = CanonicalName(rr.Hdr.Name)
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tsig.Class = ClassANY
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tsig.Ttl = rr.Hdr.Ttl
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tsig.Algorithm = CanonicalName(rr.Algorithm)
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tsig.TimeSigned = rr.TimeSigned
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tsig.Fudge = rr.Fudge
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tsig.Error = rr.Error
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tsig.OtherLen = rr.OtherLen
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tsig.OtherData = rr.OtherData
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n, err := packTsigWire(tsig, tsigvar)
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if err != nil {
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return nil, err
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}
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tsigvar = tsigvar[:n]
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}
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if requestMAC != "" {
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x := append(buf, msgbuf...)
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buf = append(x, tsigvar...)
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} else {
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buf = append(msgbuf, tsigvar...)
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}
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return buf, nil
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}
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// Strip the TSIG from the raw message.
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func stripTsig(msg []byte) ([]byte, *TSIG, error) {
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// Copied from msg.go's Unpack() Header, but modified.
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var (
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dh Header
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err error
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)
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off, tsigoff := 0, 0
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if dh, off, err = unpackMsgHdr(msg, off); err != nil {
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return nil, nil, err
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}
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if dh.Arcount == 0 {
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return nil, nil, ErrNoSig
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}
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// Rcode, see msg.go Unpack()
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if int(dh.Bits&0xF) == RcodeNotAuth {
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return nil, nil, ErrAuth
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}
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for i := 0; i < int(dh.Qdcount); i++ {
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_, off, err = unpackQuestion(msg, off)
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if err != nil {
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return nil, nil, err
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}
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}
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_, off, err = unpackRRslice(int(dh.Ancount), msg, off)
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if err != nil {
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return nil, nil, err
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}
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_, off, err = unpackRRslice(int(dh.Nscount), msg, off)
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if err != nil {
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return nil, nil, err
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}
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rr := new(TSIG)
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var extra RR
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for i := 0; i < int(dh.Arcount); i++ {
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tsigoff = off
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extra, off, err = UnpackRR(msg, off)
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if err != nil {
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return nil, nil, err
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}
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if extra.Header().Rrtype == TypeTSIG {
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rr = extra.(*TSIG)
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// Adjust Arcount.
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arcount := binary.BigEndian.Uint16(msg[10:])
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binary.BigEndian.PutUint16(msg[10:], arcount-1)
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break
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}
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}
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if rr == nil {
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return nil, nil, ErrNoSig
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}
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return msg[:tsigoff], rr, nil
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}
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// Translate the TSIG time signed into a date. There is no
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// need for RFC1982 calculations as this date is 48 bits.
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func tsigTimeToString(t uint64) string {
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ti := time.Unix(int64(t), 0).UTC()
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return ti.Format("20060102150405")
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}
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func packTsigWire(tw *tsigWireFmt, msg []byte) (int, error) {
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// copied from zmsg.go TSIG packing
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// RR_Header
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off, err := PackDomainName(tw.Name, msg, 0, nil, false)
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if err != nil {
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return off, err
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}
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off, err = packUint16(tw.Class, msg, off)
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if err != nil {
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return off, err
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}
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off, err = packUint32(tw.Ttl, msg, off)
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if err != nil {
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return off, err
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}
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off, err = PackDomainName(tw.Algorithm, msg, off, nil, false)
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if err != nil {
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return off, err
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}
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off, err = packUint48(tw.TimeSigned, msg, off)
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if err != nil {
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return off, err
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}
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off, err = packUint16(tw.Fudge, msg, off)
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if err != nil {
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return off, err
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}
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off, err = packUint16(tw.Error, msg, off)
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if err != nil {
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return off, err
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}
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off, err = packUint16(tw.OtherLen, msg, off)
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if err != nil {
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return off, err
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}
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off, err = packStringHex(tw.OtherData, msg, off)
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if err != nil {
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return off, err
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}
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return off, nil
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}
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func packMacWire(mw *macWireFmt, msg []byte) (int, error) {
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off, err := packUint16(mw.MACSize, msg, 0)
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if err != nil {
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return off, err
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}
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off, err = packStringHex(mw.MAC, msg, off)
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if err != nil {
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return off, err
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}
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return off, nil
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}
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func packTimerWire(tw *timerWireFmt, msg []byte) (int, error) {
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off, err := packUint48(tw.TimeSigned, msg, 0)
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if err != nil {
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return off, err
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}
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off, err = packUint16(tw.Fudge, msg, off)
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if err != nil {
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return off, err
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}
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return off, nil
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}
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