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package dns
import (
"crypto"
"crypto/dsa"
"crypto/ecdsa"
"crypto/rsa"
"encoding/binary"
"math/big"
"strings"
"time"
)
// Sign signs a dns.Msg. It fills the signature with the appropriate data.
// The SIG record should have the SignerName, KeyTag, Algorithm, Inception
// and Expiration set.
func (rr *SIG) Sign(k crypto.Signer, m *Msg) ([]byte, error) {
if k == nil {
return nil, ErrPrivKey
}
if rr.KeyTag == 0 || len(rr.SignerName) == 0 || rr.Algorithm == 0 {
return nil, ErrKey
}
rr.Hdr = RR_Header{Name: ".", Rrtype: TypeSIG, Class: ClassANY, Ttl: 0}
rr.OrigTtl, rr.TypeCovered, rr.Labels = 0, 0, 0
buf := make([]byte, m.Len()+Len(rr))
mbuf, err := m.PackBuffer(buf)
if err != nil {
return nil, err
}
if &buf[0] != &mbuf[0] {
return nil, ErrBuf
}
off, err := PackRR(rr, buf, len(mbuf), nil, false)
if err != nil {
return nil, err
}
buf = buf[:off:cap(buf)]
hash, ok := AlgorithmToHash[rr.Algorithm]
if !ok {
return nil, ErrAlg
}
hasher := hash.New()
// Write SIG rdata
hasher.Write(buf[len(mbuf)+1+2+2+4+2:])
// Write message
hasher.Write(buf[:len(mbuf)])
signature, err := sign(k, hasher.Sum(nil), hash, rr.Algorithm)
if err != nil {
return nil, err
}
rr.Signature = toBase64(signature)
buf = append(buf, signature...)
if len(buf) > int(^uint16(0)) {
return nil, ErrBuf
}
// Adjust sig data length
rdoff := len(mbuf) + 1 + 2 + 2 + 4
rdlen := binary.BigEndian.Uint16(buf[rdoff:])
rdlen += uint16(len(signature))
binary.BigEndian.PutUint16(buf[rdoff:], rdlen)
// Adjust additional count
adc := binary.BigEndian.Uint16(buf[10:])
adc++
binary.BigEndian.PutUint16(buf[10:], adc)
return buf, nil
}
// Verify validates the message buf using the key k.
// It's assumed that buf is a valid message from which rr was unpacked.
func (rr *SIG) Verify(k *KEY, buf []byte) error {
if k == nil {
return ErrKey
}
if rr.KeyTag == 0 || len(rr.SignerName) == 0 || rr.Algorithm == 0 {
return ErrKey
}
var hash crypto.Hash
switch rr.Algorithm {
case DSA, RSASHA1:
hash = crypto.SHA1
case RSASHA256, ECDSAP256SHA256:
hash = crypto.SHA256
case ECDSAP384SHA384:
hash = crypto.SHA384
case RSASHA512:
hash = crypto.SHA512
default:
return ErrAlg
}
hasher := hash.New()
buflen := len(buf)
qdc := binary.BigEndian.Uint16(buf[4:])
anc := binary.BigEndian.Uint16(buf[6:])
auc := binary.BigEndian.Uint16(buf[8:])
adc := binary.BigEndian.Uint16(buf[10:])
offset := headerSize
var err error
for i := uint16(0); i < qdc && offset < buflen; i++ {
_, offset, err = UnpackDomainName(buf, offset)
if err != nil {
return err
}
// Skip past Type and Class
offset += 2 + 2
}
for i := uint16(1); i < anc+auc+adc && offset < buflen; i++ {
_, offset, err = UnpackDomainName(buf, offset)
if err != nil {
return err
}
// Skip past Type, Class and TTL
offset += 2 + 2 + 4
if offset+1 >= buflen {
continue
}
rdlen := binary.BigEndian.Uint16(buf[offset:])
offset += 2
offset += int(rdlen)
}
if offset >= buflen {
return &Error{err: "overflowing unpacking signed message"}
}
// offset should be just prior to SIG
bodyend := offset
// owner name SHOULD be root
_, offset, err = UnpackDomainName(buf, offset)
if err != nil {
return err
}
// Skip Type, Class, TTL, RDLen
offset += 2 + 2 + 4 + 2
sigstart := offset
// Skip Type Covered, Algorithm, Labels, Original TTL
offset += 2 + 1 + 1 + 4
if offset+4+4 >= buflen {
return &Error{err: "overflow unpacking signed message"}
}
expire := binary.BigEndian.Uint32(buf[offset:])
offset += 4
incept := binary.BigEndian.Uint32(buf[offset:])
offset += 4
now := uint32(time.Now().Unix())
if now < incept || now > expire {
return ErrTime
}
// Skip key tag
offset += 2
var signername string
signername, offset, err = UnpackDomainName(buf, offset)
if err != nil {
return err
}
// If key has come from the DNS name compression might
// have mangled the case of the name
if !strings.EqualFold(signername, k.Header().Name) {
return &Error{err: "signer name doesn't match key name"}
}
sigend := offset
hasher.Write(buf[sigstart:sigend])
hasher.Write(buf[:10])
hasher.Write([]byte{
byte((adc - 1) << 8),
byte(adc - 1),
})
hasher.Write(buf[12:bodyend])
hashed := hasher.Sum(nil)
sig := buf[sigend:]
switch k.Algorithm {
case DSA:
pk := k.publicKeyDSA()
sig = sig[1:]
r := new(big.Int).SetBytes(sig[:len(sig)/2])
s := new(big.Int).SetBytes(sig[len(sig)/2:])
if pk != nil {
if dsa.Verify(pk, hashed, r, s) {
return nil
}
return ErrSig
}
case RSASHA1, RSASHA256, RSASHA512:
pk := k.publicKeyRSA()
if pk != nil {
return rsa.VerifyPKCS1v15(pk, hash, hashed, sig)
}
case ECDSAP256SHA256, ECDSAP384SHA384:
pk := k.publicKeyECDSA()
r := new(big.Int).SetBytes(sig[:len(sig)/2])
s := new(big.Int).SetBytes(sig[len(sig)/2:])
if pk != nil {
if ecdsa.Verify(pk, hashed, r, s) {
return nil
}
return ErrSig
}
}
return ErrKeyAlg
}
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