IPsec
IPsec is an end-to-end security scheme operating in the Internet Layer of the Internet Protocol Suite, while some other Internet security systems in widespread use, such as Secure Sockets Layer, Transport Layer Security (TLS) and Secure Shell (SSH), operate in the upper layers of the TCP/IP model. Hence, IPsec protects any application traffic across an IP network. Applications don't need to be specifically designed to use IPsec. The use of TLS/SSL had to be designed into an application to protect the application protocols.
In December 1993, the Software IP Encryption protocol swIPe was developed at Columbia University and AT&T Bell Labs by John Ioannidis and others.
In July 1994, Wei Xu at Trusted Information Systems continued this research which was completed successfully on the BSDI platform after a few months. Wei quickly extended his development on to Sun OS, HP UX, and other UNIX systems. One of the challenges was slow performance of DES and Triple DES. The software encryption was unable to support a T1 speed under the Intel 80386 architecture. By exploring the Crypto cards from Germany, Wei Xu further developed an automated device driver, known as plug-and-play today. By achieving the throughput for more than a T1s, this work made the commercial product practically feasible, that was released as a part of the well-known Gauntlet firewall. In December 1994, it was the 1st time in production for securing some remote sites between east and west coastal states of the United States.
The IETF IP Security Protocol was developed starting in 1992 at the Naval Research Laboratory as part of a DARPA-sponsored research project, with openly published drafts by 1993. ESP was originally derived from the US Department of Defense SP3D protocol, rather than being derived from the ISO Network-Layer Security Protocol. The SP3D protocol specification was published by NIST, but designed by the Secure Data Network System project of the US Department of Defense. AH is derived in part from previous IETF standards work for authentication of the Simple Network Management Protocol (SNMP) version 2.
IPsec is officially standardised by the Internet Engineering Task Force in a series of Request for Comments documents addressing various components and extensions. It specifies the spelling of the protocol name to be IPsec.
Authentication Header is a member of the IPsec protocol suite. AH guarantees connectionless integrity and data origin authentication of IP packets. Further, it can optionally protect against replay attacks by using the sliding window technique and discarding old packets (see below).
AH operates directly on top of IP, using IP protocol number 51.
Encapsulating Security Payload is a member of the IPsec protocol suite. In IPsec it provides origin authenticity, integrity and confidentiality protection of packets. ESP also supports encryption-only and authentication-only configurations, but using encryption without authentication is strongly discouraged because it is insecure. Unlike Authentication Header (AH), ESP in transport mode does not provide integrity and authentication for the entire IP packet. However, in Tunnel Mode, where the entire original IP packet is encapsulated with a new packet header added, ESP protection is afforded to the whole inner IP packet (including the inner header) while the outer header (including any outer IPv4 options or IPv6 extension headers) remains unprotected. ESP operates directly on top of IP, using IP protocol number 50.
The IP security architecture uses the concept of a security association as the basis for building security functions into IP. A security association is simply the bundle of algorithms and parameters that is being used to encrypt and authenticate a particular flow in one direction. Therefore, in normal bi-directional traffic, the flows are secured by a pair of security associations.
Security associations are established using the Internet Security Association and Key Management Protocol. ISAKMP is implemented by manual configuration with pre-shared secrets, Internet Key Exchange (IKE and IKEv2), Kerberized Internet Negotiation of Keys (KINK), and the use of IPSECKEY DNS records. RFC 5386 defines Better-Than-Nothing Security (BTNS) as an unauthenticated mode of IPsec using an extended IKE protocol.
In order to decide what protection is to be provided for an outgoing packet, IPsec uses the Security Parameter Index, an index to the security association database (SADB), along with the destination address in a packet header, which together uniquely identify a security association for that packet. A similar procedure is performed for an incoming packet, where IPsec gathers decryption and verification keys from the security association database.
For multicast, a security association is provided for the group, and is duplicated across all authorized receivers of the group. There may be more than one security association for a group, using different SPIs, thereby allowing multiple levels and sets of security within a group. Indeed, each sender can have multiple security associations, allowing authentication, since a receiver can only know that someone knowing the keys sent the data. Note that the relevant standard does not describe how the association is chosen and duplicated across the group; it is assumed that a responsible party will have made the choice.
IPsec can be implemented in a host-to-host transport mode, as well as in a network tunnel mode.
In transport mode, only the payload of the IP packet is usually encrypted and/or authenticated. The routing is intact, since the IP header is neither modified nor encrypted; however, when the authentication header is used, the IP addresses cannot be translated, as this will invalidate the hash value. The transport and application layers are always secured by hash, so they cannot be modified in any way.
A means to encapsulate IPsec messages for NAT traversal has been defined by RFC documents describing the NAT-T mechanism.
In tunnel mode, the entire IP packet is encrypted and/or authenticated. It is then encapsulated into a new IP packet with a new IP header. Tunnel mode is used to create virtual private networks for network-to-network communications, host-to-network communications (e.g. remote user access) and host-to-host communications (e.g. private chat).
Tunnel mode supports NAT traversal.
Refer to RFC 4835 for details.
IPsec support is usually implemented in the kernel with key management and ISAKMP/IKE negotiation carried out from user-space. The openly specified 'PF KEY Key Management API, Version 2' is often used to enable the application-space key management application to update the IPsec Security Associations stored within the kernel-space IPsec implementation.
Existing IPsec implementations usually include ESP, AH, and IKE version 2. Existing IPsec implementations on UNIX-like operating systems, for example Sun Solaris or Linux, usually include PF KEY version 2.
IPsec was developed in conjunction with IPv6 and was originally required in all standards-compliant implementations of IPv6 before RFC 6434 made it only a recommendation. IPsec is also optional for IPv4 implementations but due to the slow deployment of IPv6, IPsec is most commonly used to secure IPv4 traffic.
IPsec protocols were originally defined in RFC 1825 through RFC 1829, which were published in 1995. In 1998, these documents were superseded by RFC 2401 and RFC 2412 with a few incompatible engineering details, although they were conceptually identical. In addition, a mutual authentication and key exchange protocol Internet Key Exchange was defined to create and manage security associations. In December 2005, new standards were defined in RFC 4301 and RFC 4309 which are largely a superset of the previous editions with a 2nd version of the Internet Key Exchange standard IKEv2. These third-generation documents standardized the abbreviation of IPsec to uppercase “IP†and lowercase “secâ€. “ESP†generally refers to RFC 4303, which is the most recent version of the specification.
Since mid-2008, an IPsec Maintenance and Extensions working group is active at the IETF.
Related Sites for IPsec
- IPsec Tools Homepage read IPsec
- IP SEC - Packet Life read IPsec
- IPSec read IPsec
- RFC 4301 read IPsec
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