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104 lines
2.7 KiB
Go
104 lines
2.7 KiB
Go
package server
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import (
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"crypto"
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"errors"
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"fmt"
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"io"
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"math/rand"
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"net"
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"github.com/cbeuw/Cloak/internal/common"
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"github.com/cbeuw/Cloak/internal/ecdh"
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log "github.com/sirupsen/logrus"
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)
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const appDataMaxLength = 16401
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type TLS struct{}
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var ErrBadClientHello = errors.New("non (or malformed) ClientHello")
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func (TLS) String() string { return "TLS" }
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func (TLS) processFirstPacket(clientHello []byte, privateKey crypto.PrivateKey) (fragments authFragments, respond Responder, err error) {
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ch, err := parseClientHello(clientHello)
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if err != nil {
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log.Debug(err)
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err = ErrBadClientHello
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return
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}
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fragments, err = TLS{}.unmarshalClientHello(ch, privateKey)
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if err != nil {
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err = fmt.Errorf("failed to unmarshal ClientHello into authFragments: %v", err)
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return
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}
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respond = TLS{}.makeResponder(ch.sessionId, fragments.sharedSecret)
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return
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}
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func (TLS) makeResponder(clientHelloSessionId []byte, sharedSecret [32]byte) Responder {
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respond := func(originalConn net.Conn, sessionKey [32]byte, randSource io.Reader) (preparedConn net.Conn, err error) {
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// the cert length needs to be the same for all handshakes belonging to the same session
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// we can use sessionKey as a seed here to ensure consistency
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possibleCertLengths := []int{42, 27, 68, 59, 36, 44, 46}
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rand.Seed(int64(sessionKey[0]))
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cert := make([]byte, possibleCertLengths[rand.Intn(len(possibleCertLengths))])
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common.RandRead(randSource, cert)
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var nonce [12]byte
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common.RandRead(randSource, nonce[:])
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encryptedSessionKey, err := common.AESGCMEncrypt(nonce[:], sharedSecret[:], sessionKey[:])
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if err != nil {
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return
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}
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var encryptedSessionKeyArr [48]byte
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copy(encryptedSessionKeyArr[:], encryptedSessionKey)
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reply := composeReply(clientHelloSessionId, nonce, encryptedSessionKeyArr, cert)
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_, err = originalConn.Write(reply)
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if err != nil {
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err = fmt.Errorf("failed to write TLS reply: %v", err)
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originalConn.Close()
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return
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}
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preparedConn = common.NewTLSConn(originalConn)
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return
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}
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return respond
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}
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func (TLS) unmarshalClientHello(ch *ClientHello, staticPv crypto.PrivateKey) (fragments authFragments, err error) {
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copy(fragments.randPubKey[:], ch.random)
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ephPub, ok := ecdh.Unmarshal(fragments.randPubKey[:])
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if !ok {
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err = ErrInvalidPubKey
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return
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}
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var sharedSecret []byte
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sharedSecret, err = ecdh.GenerateSharedSecret(staticPv, ephPub)
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if err != nil {
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return
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}
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copy(fragments.sharedSecret[:], sharedSecret)
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var keyShare []byte
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keyShare, err = parseKeyShare(ch.extensions[[2]byte{0x00, 0x33}])
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if err != nil {
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return
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}
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ctxTag := append(ch.sessionId, keyShare...)
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if len(ctxTag) != 64 {
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err = fmt.Errorf("%v: %v", ErrCiphertextLength, len(ctxTag))
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return
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}
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copy(fragments.ciphertextWithTag[:], ctxTag)
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return
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}
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