OpenIPSec: Introduction (Part 1)

This is the first part of a series of articles in which I will explain how I will develop an open source IPSec Framework (Ndis Driver, Crypto API and Command Line Tools) for Windows OS.
This Framework will be available under GPLv3 license and all the source code will be available for download.

This first part is an introduction to IPSec and a kick overview of OpenIPSec project.

1. IPSec

IPSec stands for Internet Protocol Security and has been specified by the Internet Engineering Task Force (IETF).
IPSec operates at at the Network Layer (OSI Layer 3). This imply that it can protect all upper protocols such as UDP, TCP or ICMP.
IPSec is a successor of the ISO standard Network Layer Security Protocol (NLSP). NLSP was based on the SP3 protocol that was published by the NIST but designed by the Secure Data Network System project of the National Security Administration (NSA). Because it operates at OSI layer 3 it must be integrated at the Kernel/OS Layer. On Windows OS all Network APIs (e.g. Windows Sockets 2 or Layered Service Provider) operate at the upper layers (user/application Layer).
An example of security protocols working at user/application layer are Secure Sockets Layer (SSL), Transport Layer Security (TLS) or Secure Shell (SSH).

1.1 Protocols

IPSec have three main protocols: AH, ESP and IKE. AH and ESP are commonly called Security Protocols.

=>AH: Stands for Authentication Header and has been defined in RFC4302. It is used to provide connectionless integrity and data origin authentication for IP datagrams and to provide protection against replays.


=>ESP: Stands for Encapsulating Security Payload and has been defined in RFC4303. It is used to provide confidentiality, data origin authentication, connectionless integrity, an anti-replay service (a form of partial sequence integrity), and (limited) traffic flow confidentiality. It may be applied alone or in combination with AH.

=>IKEv1/IKEv2: Stands for Internet Key Exchange and have been defined in RFC4109 and RFC4306 respectively. Both are used for mutual authentication between two parties and establishes an IKE security association (SA) that includes shared secret information that can be used to efficiently establish SAs for Encapsulating Security Payload (ESP) and/or Authentication Header (AH) and a set of cryptographic algorithms to be used by the SAs to protect the traffic that they carry.

1.2 Security Association (SA)

IPSec Security Association (SA) is a virtual unidirectional association between two or more peers/entities (IP:port) . This mean that you should create two SAs for bidirectional communications. Each SA has its own ID called SAID stored in the Security Association Database (SAD) as per RFC4301. The SA defines:

• A unique security parameter index (SPI)
• Shared security Keys
• Lifetime
• Encryption algorithm to use : DES, 3DES or AES (all supported by OpenSec)
• Authentication algorithm to use: HMAC-MD5-96, AES-XCBC-MAC-96 or HMAC-SHA-1-96 (all supported by OpenSec)
• Which Protocol to use: ESP or AH

1.3 Key Management

Key Management mechanism is used to exchange mandatory security keys to setup SAs. Can be manual or automated using IKE.
For Example, 3GPP IMS use SIP to exchange security information and manually setup SAs (e.g. using ipsec command line tools).

1.4 Mode of operation (transport and tunnel)

Both ESP and AH may be applied individually or in combination with each other to provide IPv4 and IPv6 security services. Both supports two modes of use: transport mode and tunnel mode. In transport mode, AH and ESP provide protection primarily for next layer protocols; in tunnel mode, AH and ESP are applied to tunneled IP packets.

==>Transport: only the payload (without IP header) of the IP packet is encrypted (ESP) and/or authenticated (ESP or AH) before (re)transmission. This is the default mode in 3GPP IMS context (Both UE and P-CSCF).

=>Tunnel: both the IP header and the payload are encrypted (ESP) and/or authenticated (ESP or AH) before (re)transmission. It is used to create Virtual Private Networks (VPN).

2. OpenIPSec Framework

OpenIPSec is an open source IPSec Framework for Windows XP/Vista/Blackcomb/CE. The Framework will include an API for software development, command line tools, open source code (GPLv3) and documentation.
Development is done from scratch and all dependent projects are my own projects (To ease bug fix; release a soft 100% free and open source). This project depends on OpenSec and libonid. The first, contains IPSec algorithms implementation and the second allows monitoring Network cards. These two projects are under development (OpenSec: 90% done - libonid: 40% done) and the source code is freely available for download. To ease adoption, command line tools (setkey, spdadd, add ...) will have same name and options than those provided on Linux.

2.1 Standards

* RFC1825 - Security Architecture for the Internet Protocol (Obsoleted by: 2401)
* RFC2401 - Security Architecture for the Internet Protocol (Obsoletes: 1825 and Obsoleted by: 4301 and Updated by: 3168)
* RFC2402 - IP Authentication Header (Obsoleted by: 4302, 4305 and Obsoletes: 1826)
* RFC2410 - The NULL Encryption Algorithm and Its Use With IPsec
* RFC2405 - The ESP DES-CBC Cipher Algorithm With Explicit IV
* RFC2406 - IP Encapsulating Security Payload (ESP) (Obsoleted by: 4303, 4305 and Obsoletes: 1827)
* RFC2407 - The Internet IP Security Domain of Interpretation for ISAKMP (Obsoleted by: 4306)
* RFC2408 - Internet Security Association and Key Management Protocol (ISAKMP) (Obsoleted by: 4306)
* RFC2409 - The Internet Key Exchange (IKE) (Obsoleted by: 4306 and Updated by: 4109)
* RFC2481 - A Proposal to add Explicit Congestion Notification (ECN) to IP (Obsoleted by: 3168)
* RFC3168 - The Addition of Explicit Congestion Notification (ECN) to IP (Updates: 2474, 2401, 793 and Obsoletes: 2481)
* RFC3602 - The AES-CBC Cipher Algorithm and Its Use with IPsec
* RFC4109 - Algorithms for Internet Key Exchange version 1 (IKEv1) (Updates: 2409)
* RFC4301 - Security Architecture for the Internet Protocol
* RFC4302 - IP Authentication Header
* RFC4303 - IP Encapsulating Security Payload (ESP) (Obsoletes: 2406)
* RFC4305 - Cryptographic Algorithm Implementation Requirements for Encapsulating Security Payload (ESP) and Authentication Header (AH) (Obsoleted by: 4835 and Obsoletes: 2404, 2406 )
* RFC4306 - Internet Key Exchange (IKEv2) Protocol
* RFC4307 - Cryptographic Algorithms for Use in the Internet Key Exchange Version 2 (IKEv2)
* RFC4835 - Cryptographic Algorithm Implementation Requirements for Encapsulating Security Payload (ESP) and Authentication Header (AH) (Obsoletes: 4305)

/!\ OpenSec is now available for download at http://code.google.com/p/opensec/

References:
http://en.wikipedia.org/wiki/IPsec