package client import ( "encoding/binary" "github.com/cbeuw/Cloak/internal/common" log "github.com/sirupsen/logrus" "net" ) const appDataMaxLength = 16401 type clientHelloFields struct { random []byte sessionId []byte x25519KeyShare []byte sni []byte } type browser interface { composeClientHello(clientHelloFields) []byte } func makeServerName(serverName string) []byte { serverNameListLength := make([]byte, 2) binary.BigEndian.PutUint16(serverNameListLength, uint16(len(serverName)+3)) serverNameType := []byte{0x00} // host_name serverNameLength := make([]byte, 2) binary.BigEndian.PutUint16(serverNameLength, uint16(len(serverName))) ret := make([]byte, 2+1+2+len(serverName)) copy(ret[0:2], serverNameListLength) copy(ret[2:3], serverNameType) copy(ret[3:5], serverNameLength) copy(ret[5:], serverName) return ret } // addExtensionRecord, add type, length to extension data func addExtRec(typ []byte, data []byte) []byte { length := make([]byte, 2) binary.BigEndian.PutUint16(length, uint16(len(data))) ret := make([]byte, 2+2+len(data)) copy(ret[0:2], typ) copy(ret[2:4], length) copy(ret[4:], data) return ret } func genStegClientHello(ai authenticationPayload, serverName string) (ret clientHelloFields) { // random is marshalled ephemeral pub key 32 bytes // The authentication ciphertext and its tag are then distributed among SessionId and X25519KeyShare ret.random = ai.randPubKey[:] ret.sessionId = ai.ciphertextWithTag[0:32] ret.x25519KeyShare = ai.ciphertextWithTag[32:64] ret.sni = makeServerName(serverName) return } type DirectTLS struct { *common.TLSConn browser browser } // NewClientTransport handles the TLS handshake for a given conn and returns the sessionKey // if the server proceed with Cloak authentication func (tls *DirectTLS) Handshake(rawConn net.Conn, authInfo AuthInfo) (sessionKey [32]byte, err error) { payload, sharedSecret := makeAuthenticationPayload(authInfo) chOnly := tls.browser.composeClientHello(genStegClientHello(payload, authInfo.MockDomain)) chWithRecordLayer := common.AddRecordLayer(chOnly, common.Handshake, common.VersionTLS11) _, err = rawConn.Write(chWithRecordLayer) if err != nil { return } log.Trace("client hello sent successfully") tls.TLSConn = &common.TLSConn{Conn: rawConn} buf := make([]byte, 1024) log.Trace("waiting for ServerHello") _, err = tls.Read(buf) if err != nil { return } encrypted := append(buf[6:38], buf[84:116]...) nonce := encrypted[0:12] ciphertextWithTag := encrypted[12:60] sessionKeySlice, err := common.AESGCMDecrypt(nonce, sharedSecret[:], ciphertextWithTag) if err != nil { return } copy(sessionKey[:], sessionKeySlice) for i := 0; i < 2; i++ { // ChangeCipherSpec and EncryptedCert (in the format of application data) _, err = tls.Read(buf) if err != nil { return } } return sessionKey, nil }