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