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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 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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