package tor import ( "crypto/rand" "encoding/hex" "fmt" "net" "strconv" "github.com/btcsuite/btcd/connmgr" "github.com/miekg/dns" "golang.org/x/net/proxy" ) var ( // dnsCodes maps the DNS response codes to a friendly description. This // does not include the BADVERS code because of duplicate keys and the // underlying DNS (miekg/dns) package not using it. For more info, see // https://www.iana.org/assignments/dns-parameters/dns-parameters.xhtml. dnsCodes = map[int]string{ 0: "no error", 1: "format error", 2: "server failure", 3: "non-existent domain", 4: "not implemented", 5: "query refused", 6: "name exists when it should not", 7: "RR set exists when it should not", 8: "RR set that should exist does not", 9: "server not authoritative for zone", 10: "name not contained in zone", 16: "TSIG signature failure", 17: "key not recognized", 18: "signature out of time window", 19: "bad TKEY mode", 20: "duplicate key name", 21: "algorithm not supported", 22: "bad truncation", 23: "bad/missing server cookie", } ) // proxyConn is a wrapper around net.Conn that allows us to expose the actual // remote address we're dialing, rather than the proxy's address. type proxyConn struct { net.Conn remoteAddr net.Addr } func (c *proxyConn) RemoteAddr() net.Addr { return c.remoteAddr } // Dial is a wrapper over the non-exported dial function that returns a wrapper // around net.Conn in order to expose the actual remote address we're dialing, // rather than the proxy's address. func Dial(address, socksAddr string, streamIsolation bool) (net.Conn, error) { conn, err := dial(address, socksAddr, streamIsolation) if err != nil { return nil, err } // Now that the connection is established, we'll create our internal // proxyConn that will serve in populating the correct remote address // of the connection, rather than using the proxy's address. remoteAddr, err := ParseAddr(address, socksAddr) if err != nil { return nil, err } return &proxyConn{ Conn: conn, remoteAddr: remoteAddr, }, nil } // dial establishes a connection to the address via Tor's SOCKS proxy. Only TCP // is supported over Tor. The final argument determines if we should force // stream isolation for this new connection. If we do, then this means this new // connection will use a fresh circuit, rather than possibly re-using an // existing circuit. func dial(address, socksAddr string, streamIsolation bool) (net.Conn, error) { // If we were requested to force stream isolation for this connection, // we'll populate the authentication credentials with random data as // Tor will create a new circuit for each set of credentials. var auth *proxy.Auth if streamIsolation { var b [16]byte if _, err := rand.Read(b[:]); err != nil { return nil, err } auth = &proxy.Auth{ User: hex.EncodeToString(b[:8]), Password: hex.EncodeToString(b[8:]), } } // Establish the connection through Tor's SOCKS proxy. dialer, err := proxy.SOCKS5("tcp", socksAddr, auth, proxy.Direct) if err != nil { return nil, err } return dialer.Dial("tcp", address) } // LookupHost performs DNS resolution on a given host via Tor's native resolver. // Only IPv4 addresses are returned. func LookupHost(host, socksAddr string) ([]string, error) { ip, err := connmgr.TorLookupIP(host, socksAddr) if err != nil { return nil, err } // Only one IPv4 address is returned by the TorLookupIP function. return []string{ip[0].String()}, nil } // LookupSRV uses Tor's SOCKS proxy to route DNS SRV queries. Tor does not // natively support SRV queries so we must route all SRV queries through the // proxy by connecting directly to a DNS server and querying it. The DNS server // must have TCP resolution enabled for the given port. func LookupSRV(service, proto, name, socksAddr, dnsServer string, streamIsolation bool) (string, []*net.SRV, error) { // Connect to the DNS server we'll be using to query SRV records. conn, err := dial(dnsServer, socksAddr, streamIsolation) if err != nil { return "", nil, err } dnsConn := &dns.Conn{Conn: conn} defer dnsConn.Close() // Once connected, we'll construct the SRV request for the host // following the format _service._proto.name. as described in RFC #2782. host := fmt.Sprintf("_%s._%s.%s.", service, proto, name) msg := new(dns.Msg).SetQuestion(host, dns.TypeSRV) // Send the request to the DNS server and read its response. if err := dnsConn.WriteMsg(msg); err != nil { return "", nil, err } resp, err := dnsConn.ReadMsg() if err != nil { return "", nil, err } // We'll fail if we were unable to query the DNS server for our record. if resp.Rcode != dns.RcodeSuccess { return "", nil, fmt.Errorf("unable to query for SRV records: "+ "%s", dnsCodes[resp.Rcode]) } // Retrieve the RR(s) of the Answer section. var rrs []*net.SRV for _, rr := range resp.Answer { srv := rr.(*dns.SRV) rrs = append(rrs, &net.SRV{ Target: srv.Target, Port: srv.Port, Priority: srv.Priority, Weight: srv.Weight, }) } return "", rrs, nil } // ResolveTCPAddr uses Tor's proxy to resolve TCP addresses instead of the // standard system resolver provided in the `net` package. func ResolveTCPAddr(address, socksAddr string) (*net.TCPAddr, error) { // Split host:port since the lookup function does not take a port. host, port, err := net.SplitHostPort(address) if err != nil { return nil, err } ip, err := LookupHost(host, socksAddr) if err != nil { return nil, err } p, err := strconv.Atoi(port) if err != nil { return nil, err } return &net.TCPAddr{ IP: net.ParseIP(ip[0]), Port: p, }, nil } // ParseAddr parses an address from its string format to a net.Addr. func ParseAddr(address, socksAddr string) (net.Addr, error) { host, portStr, err := net.SplitHostPort(address) if err != nil { return nil, err } port, err := strconv.Atoi(portStr) if err != nil { return nil, err } if IsOnionHost(host) { return &OnionAddr{OnionService: host, Port: port}, nil } return ResolveTCPAddr(address, socksAddr) } // IsOnionHost determines whether a host is part of an onion address. func IsOnionHost(host string) bool { // Note the starting index of the onion suffix in the host depending // on its length. var suffixIndex int switch len(host) { case V2Len: suffixIndex = V2Len - OnionSuffixLen case V3Len: suffixIndex = V3Len - OnionSuffixLen default: return false } // Make sure the host ends with the ".onion" suffix. if host[suffixIndex:] != OnionSuffix { return false } // We'll now attempt to decode the host without its suffix, as the // suffix includes invalid characters. This will tell us if the host is // actually valid if succesful. host = host[:suffixIndex] if _, err := Base32Encoding.DecodeString(host); err != nil { return false } return true }