SOCKS

Group: ChallengerMember: Lichun Zhan

Agenda

Introduction SOCKS v4 SOCKS v5 Summary Conclusion References Questions

Introduction

SOCKS was originally developed by David and Michelle Koblas.

It is modified and extended by Ying-Da Lee -- SOCKS v4.

SOCKS v5 is defined in RFC 1928 by IETF.

Introduction – What is SOCKS

SOCKS is a generic, proxy protocol for TCP/IP based networking application.

It provides a flexible framework for developing secure communications by easily integrating other security technologies.

SOCKS consists of two parts: SOCKS server and SOCKS client.

Introduction – SOCKS Server and Client

SOCKS server is a program that is run on a host that can communicate directly with both the Internet and the internal computers on the network.

SOCKS client is a specially modified Internet client programs that contacts the SOCKS server instead of sending requests directly to the Internet.

According to the OSI model, the SOCKS server is implemented at the application layer.The SOCKS client is implemented between the application and transport layers.

Application

Transport

Physical

Application

Transport

Physical

Application

Transport

Physical

Client SOCKS

Server

Place In OSI Layer

Introduction – How does it work?

The client connects to a SOCKS proxy server.

The proxy server connects to the application server on behalf of the client.

The proxy server relays data between the client and the application server.

For the application server, the proxy server is the client.

Introduction – Connection Setup

UserSOCKS ProxyServer

Server

SOCKS Connection Setup

TCP Connect andSOCKS Request

SOCKS Reply

TCP Connect(SYN)

TCP ConnectACK

Introduction – Data Relay

UserSOCKS ProxyServer

Server

SOCKS Data Relay Phase

Packet

Packet Packet

Packet

SOCKS V4 – Three functions

CONNECT:makes connection requests.

BIND: sets up proxy circuits

Relays application data

V4 – CONNECT request & reply

Request(from client to SOCKS server): +------+-----+-------+-------+-------+--------+--------+---------+....+--------+

| VN | CD | DSTPORT | DSTIP | USERID |NULL| +------+-----+-------+-------+-------+--------+--------+---------+....+--------+ # of bytes: 1 1 2 4 variable 1

(if granted, SOCKS server makes connection to the destination server.) Reply(from SOCKS server to client) : +---- -+-----+-------+------- +-------+-------+

| VN | CD | DSTPORT | DSTIP | +----- +-----+-------+------ -+-------+-------+ # of bytes: 1 1 2 4

(SOCKS server closes the connection if reject, or ready relay data on both directions)

V4 – BIND request & reply

Request(from client to let SOCKS server prepare inbound connection):

+------+-----+-------+-------+-------+--------+--------+---------+....+--------+

| VN | CD | DSTPORT | DSTIP | USERID |NULL| +------+-----+-------+-------+-------+--------+--------+---------+....+--------+

# of bytes: 1 1 2 4 variable 1

Reply(from SOCKS server to client): +---- -+-----+-------+------- +-------+-------+

| VN | CD | DSTPORT | DSTIP | +----- +-----+-------+------ -+-------+-------+

# of bytes: 1 1 2 4

bind(), getsockname(), listen(), send IP and port to app., accept().

V4 Extension

It eliminates the requirement for SOCKSv4 clients to resolve internal and external domain names.

Appending the unresolved domain names to the SOCKSv4 client requests, SOCKSv4 servers can attempt to resolve domain names.

+-----+----+------+-----+-----+-----+-----+----+---+---+-------+----+-----+-----+-------+ | VN | CD | DSTPORT| DSTIP 0.0.0.x | USERID |NULL| HOSTNAME |NULL|

+-----+----+------+-----+-----+-----+-----+----+---+---+-------+----+-----+-----+-------+

# of bytes: 1 1 2 4 variable 1 variable 1

V4 – How it is plugged in (UNIX)

The SOCKS client replace calls to the socket functions such as connect(), getsocketname(), bind(), accept(), listen() and select() - with its own versions of these functions.

Makefile of the program used to compile the network client program is modified.

The resulting program is linked to the SOCKS library.

The SOCKS library intercepts the connection attempt and opens up a connection to the SOCKS server.

V4 Weakness

Lack of strong authentication. The requirement to recompile

applications with SOCKSv4 client library.

SOCKS v5 (rfc 1928) – New Functions

Authentication Encompass domain name and IPv6

address. Support UDP-based applications

V5 - Authentication Method Negotiation 1

The application client declares to the SOCKSv5 server the authentication methods it can support

The SOCKSv5 server sends a message to the client announcing the method the client should use

The SOCKSv5 server determines the authentication method based on the security policy defined in the SOCKSv5 server's configuration. If the client's declared methods fail to meet the security requirement, the SOCKSv5 server drops communication

V5 - Authentication Method Negotiation 2

+------+------------------+----------------+ +------+-------------+ | VER | NMETHODS | METHODS | |VER | METHOD| +------+------------------+----------------+ +------+-------------+| 1 | 1 | 1 to 255 | | 1 | 1

|+------+---------- --------+---------------+ +------+-------------+

The values currently defined for METHOD are:

X'00' NO AUTHENTICATION REQUIREDX'01' GSSAPI        X'02' USERNAME/PASSWORD        X'03' CHAP        X'04' to X'7F' IANA ASSIGNED        X'80' to X'FE' RESERVED FOR PRIVATE METHODS        X'FF' NO ACCEPTABLE METHODS

Username/Password Authentication for SOCKS v5.

Defined in RFC 1929 Consists of two simple messages

From the client to the SOCKS server stating the username and password to use

From the server to the client, stating whether the authentication succeeded or not.

GSS-API Authentication Method for SOCKS v5

Defined in RFC 1961. GSS-API: generic security service API. Establishing a GSS-API security context to

encapsulates negotiation protocol for mechanism selection and the agreement of security service options.

GSS-API per-message protection calls encapsulate TCP/UDP traffic between client and server.

V5 –Domain Name and IPv6 Address.

Request & Reply:

+------+------+-------+--------- +-----------------+---------------+ | VER | REP | RSV | ATYP | BND. ADDR | BND.PORT|+------+------+-------+--------- +-----------------+---------------+ | 1 | 1 |x’00’| 1 | variable | 2 |+------+------+-------+--------- +-----------------+---------------+

The values currently defined for ATYP are:

X'01' IP v4 addressX'03' DOMAINNAME      X'04' IP v6 address       

V5 – Support UDP Association

UDP association creates a virtual proxy circuit for traversing UDP-based application data.

The proxy circuit for UDP is a pair of addresses from the communication endpoints that send and receive datagrams

UDP headers encapsulate application data including the destination address of a datagram.

UDP request header:

+------+---------+---------+----------------+----------------+------------+ | RSV | FRAG | ATYP | DST.ADDR | DST.PORT | DATA | +------+---------+---------+----------------+----------------+------------+ | 2 | 1 | 1 | Variable | 2 | Variable |

+------+---------+---------+----------------+----------------+------------+

Control Flow of SOCKS (v4 & v5)

Summary 1

A single communication protocol authenticates users and establishes the

communication channel transfers user information from the SOCKS

client to the SOCKS server for user authentication

authenticates the user and the channel guarantees the integrity of TCP and UDP

channels

Summary 2

Application-Independent Proxy

It establishes communication channels, and manages and protects the channel for any application.

Can protect new applications without requiring additional development.

Summary 3

Flexible protection through a variety of access

control policies

SOCKS delivers TCP and UDP connections through a proxy mechanism at the TCP/UDP layer, therefore it works with any application, and virtually all IP layer technologies, such as firewalls, NAT, and private IP.

SOCKS adds the flexibility to manage the network through access control policies based on user, application, and time, in addition to source and destination addresses.

Summary 4

Bi-directional proxy support

SOCKS identifies communication targets through domain names, overcoming the private IP address restrictions.

SOCKS can also use domain names to establish communication between separate LANs with redundant IP addresses.

Conclusion – SOCKS is widely used…

As a network firewall As a generic application proxy In virtual private networks(VPN). For extranet applications.

References http://archive.socks.permeo.com/protocol/socks4.protocol http://socks.permeo.com/protocol/socks4a.protocol http://www.ietf.org/rfc/rfc1928.txt http://www.ietf.org/rfc/rfc1929.txt http://www.ietf.org/rfc/rfc1961.txt http://www.ietf.org/rfc/rfc3089.txt http://archive.socks.permeo.com/draft/draft-ietf-aft-socks-pro-

v5-04.txt http://www.answers.com/topic/socks http://www2.rad.com/networks/2005/anonym/page325.htm http://www.socks.permeo.com/AboutSOCKS/SOCKSOverview.asp http://www.unix.org.ua/orelly/networking/puis/ch22_04.htm http://www.clipcode.org/messaging/socks.html http://medialab.di.unipi.it/doc/JNetSec/jns_ch12.htm

Thank You !

Questions?