254 lines
6.5 KiB
Go
254 lines
6.5 KiB
Go
package dns
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import (
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"io"
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"os"
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"time"
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"strings"
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"crypto/hmac"
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"encoding/hex"
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)
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// The structure Tsig is used in Read/Write functions to
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// add or remove a TSIG on a dns message. See RFC 2845
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// and RFC 4635.
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// Basic use pattern of Tsig:
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//
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// tsig := new(dns.Tsig)
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// tsig.Name = "axfr." // The name of the key.
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// tsig.Algorithm = dns.HmacMD5 // The HMAC to use.
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// tsig.Fudge = 300 // RFC recommends 300 here.
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// tsig.TimeSigned = uint64(time.Seconds())
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// tsig.Secret = "so6ZGir4GPAqINNh9U5c3A==" // Secret encoded in base64.
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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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)
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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 "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 "domain-name"
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TimeSigned uint64
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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 "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 "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
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Fudge uint16
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}
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// Add a Tsig to an message. // Must return the mac
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func TsigGenerate(m *Msg, secret string, timersOnly bool) (*Msg, os.Error) {
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if !m.IsTsig() {
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panic("TSIG not last RR in additional")
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}
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rawsecret, err := packBase64([]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].(*RR_TSIG)
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m.Extra = m.Extra[0:len(m.Extra)-1] // kill the TSIG from the msg
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buf, err := tsigBuffer(m, rr, 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(RR_TSIG)
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h := hmac.NewMD5([]byte(rawsecret))
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io.WriteString(h, string(buf))
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t.MAC = hex.EncodeToString(h.Sum()) // 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 = t.Fudge
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t.TimeSigned = t.TimeSigned
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t.Algorithm = t.Algorithm
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t.OrigId = m.MsgHdr.Id
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t.MAC = t.MAC
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t.MACSize = uint16(len(t.MAC) / 2)
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m.Extra = append(m.Extra, t)
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return m, nil
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}
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/*
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// Verify a TSIG on a message.
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// If the signature does not validate err contains the
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// error. If the it validates err is nil
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func (t *Tsig) Verify(msg []byte) (bool, os.Error) {
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rawsecret, err := packBase64([]byte(t.Secret))
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if err != nil {
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return false, err
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}
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// Stipped the TSIG from the incoming msg
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stripped, err := t.stripTsig(msg)
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if err != nil {
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return false, err
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}
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buf, err := t.Buffer(stripped)
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if err != nil {
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return false, err
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}
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// Time needs to be checked
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h := hmac.NewMD5([]byte(rawsecret))
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io.WriteString(h, string(buf))
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return strings.ToUpper(hex.EncodeToString(h.Sum())) == strings.ToUpper(t.MAC), nil
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}
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*/
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// Create a wiredata buffer for the MAC calculation.
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func tsigBuffer(msg *Msg, rr *RR_TSIG, timersOnly bool) ([]byte, os.Error) {
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var (
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macbuf []byte
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buf []byte
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)
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if rr.TimeSigned == 0 {
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rr.TimeSigned = uint64(time.Seconds())
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}
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if rr.Fudge == 0 {
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rr.Fudge = 300
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}
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if rr.MAC != "" {
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m := new(macWireFmt)
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m.MACSize = uint16(len(rr.MAC) / 2)
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m.MAC = rr.MAC
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macbuf = make([]byte, len(rr.MAC)) // reqmac should be twice as long
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n, ok := packStruct(m, macbuf, 0)
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if !ok {
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return nil, ErrSigGen
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}
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macbuf = macbuf[: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, ok1 := packStruct(tsig, tsigvar, 0)
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if !ok1 {
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return nil, ErrSigGen
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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 = strings.ToLower(rr.Hdr.Name)
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tsig.Class = ClassANY
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tsig.Ttl = 0
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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 = 0
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tsig.OtherLen = 0
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tsig.OtherData = ""
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n, ok1 := packStruct(tsig, tsigvar, 0)
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if !ok1 {
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return nil, ErrSigGen
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}
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tsigvar = tsigvar[:n]
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}
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if rr.MAC != "" {
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msgbuf, _ := msg.Pack()
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x := append(macbuf, msgbuf...)
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buf = append(x, tsigvar...)
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} else {
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msgbuf, _ := msg.Pack()
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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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/*
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// Strip the TSIG from the pkt.
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func (t *Tsig) stripTsig(orig []byte) ([]byte, os.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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dns := new(Msg)
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msg := make([]byte, len(orig))
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copy(msg, orig) // fhhh.. another copy TODO(mg)?
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off := 0
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tsigoff := 0
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var ok bool
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if off, ok = unpackStruct(&dh, msg, off); !ok {
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return nil, ErrUnpack
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}
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if dh.Arcount == 0 {
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return 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, 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, ok = unpackStruct(&dns.Question[i], msg, off)
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}
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for i := 0; i < len(dns.Answer); i++ {
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dns.Answer[i], off, ok = unpackRR(msg, off)
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}
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for i := 0; i < len(dns.Ns); i++ {
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dns.Ns[i], off, ok = unpackRR(msg, off)
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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, ok = unpackRR(msg, off)
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if dns.Extra[i].Header().Rrtype == TypeTSIG {
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if t.Name != "" {
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if t.Name != dns.Extra[i].Header().Name {
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return nil, ErrKey
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}
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}
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if t.Algorithm != "" {
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if t.Algorithm != dns.Extra[i].(*RR_TSIG).Algorithm {
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return nil, ErrAlg
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}
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}
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ti := uint64(time.Seconds()) - dns.Extra[i].(*RR_TSIG).TimeSigned
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if uint64(dns.Extra[i].(*RR_TSIG).Fudge) < ti {
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return nil, ErrTime
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}
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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 !ok {
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return nil, ErrUnpack
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}
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return msg[:tsigoff], nil
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}
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*/
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