321 lines
7.9 KiB
Go
321 lines
7.9 KiB
Go
package dns
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import (
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"crypto/hmac"
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"crypto/md5"
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"crypto/sha1"
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"crypto/sha256"
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"crypto/sha512"
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"encoding/hex"
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"hash"
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"io"
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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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HmacMD5 = "hmac-md5.sig-alg.reg.int."
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HmacSHA1 = "hmac-sha1."
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HmacSHA256 = "hmac-sha256."
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HmacSHA512 = "hmac-sha512."
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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"`
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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"`
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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"
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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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// 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"`
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}
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// If we have the MAC use this type to convert it to wiredata.
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// 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"`
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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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if m.IsTsig() == nil {
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panic("dns: TSIG not last RR in additional")
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}
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// If we barf here, the caller is to blame
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rawsecret, err := fromBase64([]byte(secret))
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if err != nil {
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return nil, "", err
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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 := tsigBuffer(mbuf, rr, requestMAC, timersOnly)
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t := new(TSIG)
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var h hash.Hash
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switch strings.ToLower(rr.Algorithm) {
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case HmacMD5:
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h = hmac.New(md5.New, []byte(rawsecret))
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case HmacSHA1:
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h = hmac.New(sha1.New, []byte(rawsecret))
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case HmacSHA256:
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h = hmac.New(sha256.New, []byte(rawsecret))
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case HmacSHA512:
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h = hmac.New(sha512.New, []byte(rawsecret))
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default:
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return nil, "", ErrKeyAlg
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}
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io.WriteString(h, string(buf))
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t.MAC = hex.EncodeToString(h.Sum(nil))
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t.MACSize = uint16(len(t.MAC) / 2) // Size is half!
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t.Hdr = RR_Header{Name: rr.Hdr.Name, Rrtype: TypeTSIG, Class: ClassANY, Ttl: 0}
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t.Fudge = rr.Fudge
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t.TimeSigned = rr.TimeSigned
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t.Algorithm = rr.Algorithm
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t.OrigId = m.Id
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tbuf := make([]byte, t.len())
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if off, err := PackRR(t, tbuf, 0, nil, false); err == nil {
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tbuf = tbuf[:off] // reset to actual size used
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} else {
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return nil, "", err
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}
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mbuf = append(mbuf, tbuf...)
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rawSetExtraLen(mbuf, 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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rawsecret, err := fromBase64([]byte(secret))
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if err != nil {
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return err
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}
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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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msgMAC, err := hex.DecodeString(tsig.MAC)
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if err != nil {
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return err
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}
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buf := tsigBuffer(stripped, tsig, requestMAC, timersOnly)
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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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now := uint64(time.Now().Unix())
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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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var h hash.Hash
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switch strings.ToLower(tsig.Algorithm) {
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case HmacMD5:
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h = hmac.New(md5.New, rawsecret)
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case HmacSHA1:
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h = hmac.New(sha1.New, rawsecret)
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case HmacSHA256:
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h = hmac.New(sha256.New, 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 ErrKeyAlg
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}
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h.Write(buf)
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if !hmac.Equal(h.Sum(nil), msgMAC) {
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return ErrSig
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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 {
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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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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, _ := PackStruct(m, buf, 0)
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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, _ := PackStruct(tsig, tsigvar, 0)
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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 = strings.ToLower(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 = strings.ToLower(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, _ := PackStruct(tsig, tsigvar, 0)
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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
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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()
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// Header.
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var dh Header
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var err error
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dns := new(Msg)
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rr := new(TSIG)
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off := 0
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tsigoff := 0
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if off, err = UnpackStruct(&dh, 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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// Arrays.
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dns.Question = make([]Question, dh.Qdcount)
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dns.Answer = make([]RR, dh.Ancount)
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dns.Ns = make([]RR, dh.Nscount)
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dns.Extra = make([]RR, dh.Arcount)
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for i := 0; i < len(dns.Question); i++ {
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off, err = UnpackStruct(&dns.Question[i], 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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for i := 0; i < len(dns.Answer); i++ {
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dns.Answer[i], 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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}
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for i := 0; i < len(dns.Ns); i++ {
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dns.Ns[i], 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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}
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for i := 0; i < len(dns.Extra); i++ {
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tsigoff = off
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dns.Extra[i], 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 dns.Extra[i].Header().Rrtype == TypeTSIG {
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rr = dns.Extra[i].(*TSIG)
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// Adjust Arcount.
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arcount, _ := unpackUint16(msg, 10)
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msg[10], msg[11] = packUint16(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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