128 lines
2.9 KiB
Go
128 lines
2.9 KiB
Go
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package crypto
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import (
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"crypto/aes"
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"crypto/cipher"
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"crypto/rand"
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"crypto/sha256"
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"crypto/subtle"
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"encoding/binary"
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"errors"
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"fmt"
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"io"
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"time"
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"github.com/lucas-clemente/quic-go/protocol"
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"golang.org/x/crypto/hkdf"
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)
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// StkSource is used to create and verify source address tokens
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type StkSource interface {
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// NewToken creates a new token for a given IP address
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NewToken(sourceAddress []byte) ([]byte, error)
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// VerifyToken verifies if a token matches a given IP address and is not outdated
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VerifyToken(sourceAddress []byte, data []byte) error
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}
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type sourceAddressToken struct {
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sourceAddr []byte
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// unix timestamp in seconds
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timestamp uint64
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}
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func (t *sourceAddressToken) serialize() []byte {
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res := make([]byte, 8+len(t.sourceAddr))
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binary.LittleEndian.PutUint64(res, t.timestamp)
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copy(res[8:], t.sourceAddr)
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return res
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}
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func parseToken(data []byte) (*sourceAddressToken, error) {
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if len(data) != 8+4 && len(data) != 8+16 {
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return nil, fmt.Errorf("invalid STK length: %d", len(data))
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}
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return &sourceAddressToken{
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sourceAddr: data[8:],
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timestamp: binary.LittleEndian.Uint64(data),
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}, nil
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}
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type stkSource struct {
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aead cipher.AEAD
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}
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const stkKeySize = 16
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// Chrome currently sets this to 12, but discusses changing it to 16. We start
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// at 16 :)
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const stkNonceSize = 16
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// NewStkSource creates a source for source address tokens
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func NewStkSource(secret []byte) (StkSource, error) {
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key, err := deriveKey(secret)
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if err != nil {
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return nil, err
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}
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c, err := aes.NewCipher(key)
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if err != nil {
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return nil, err
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}
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aead, err := cipher.NewGCMWithNonceSize(c, stkNonceSize)
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if err != nil {
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return nil, err
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}
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return &stkSource{aead: aead}, nil
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}
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func (s *stkSource) NewToken(sourceAddr []byte) ([]byte, error) {
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return encryptToken(s.aead, &sourceAddressToken{
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sourceAddr: sourceAddr,
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timestamp: uint64(time.Now().Unix()),
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})
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}
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func (s *stkSource) VerifyToken(sourceAddr []byte, data []byte) error {
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if len(data) < stkNonceSize {
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return errors.New("STK too short")
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}
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nonce := data[:stkNonceSize]
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res, err := s.aead.Open(nil, nonce, data[stkNonceSize:], nil)
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if err != nil {
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return err
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}
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token, err := parseToken(res)
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if err != nil {
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return err
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}
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if subtle.ConstantTimeCompare(token.sourceAddr, sourceAddr) != 1 {
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return errors.New("invalid source address in STK")
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}
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if time.Now().Unix() > int64(token.timestamp)+protocol.STKExpiryTimeSec {
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return errors.New("STK expired")
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}
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return nil
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}
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func deriveKey(secret []byte) ([]byte, error) {
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r := hkdf.New(sha256.New, secret, nil, []byte("QUIC source address token key"))
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key := make([]byte, stkKeySize)
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if _, err := io.ReadFull(r, key); err != nil {
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return nil, err
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}
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return key, nil
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}
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func encryptToken(aead cipher.AEAD, token *sourceAddressToken) ([]byte, error) {
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nonce := make([]byte, stkNonceSize)
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if _, err := rand.Read(nonce); err != nil {
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return nil, err
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}
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return aead.Seal(nonce, nonce, token.serialize(), nil), nil
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}
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