In computing, Internet Protocol Security (IPsec) is a secure network protocol suite that authenticates and encrypts the packets of data to provide secure encrypted communication between two computers over an Internet Protocol network. It is used in virtual private networks (VPNs).
IPsec includes protocols for establishing mutual authentication between agents at the beginning of a session and negotiation of cryptographic keys to use during the session. IPsec can protect data flows between a pair of hosts (host-to-host), between a pair of security gateways (network-to-network), or between a security gateway and a host (network-to-host). IPsec uses cryptographic security services to protect communications over Internet Protocol (IP) networks. It supports network-level peer authentication, data-origin authentication, data integrity, data confidentiality (encryption), and replay protection.
The initial IPv4 suite was developed with few security provisions. As a part of the IPv4 enhancement, IPsec is a layer 3 OSI model or internet layer end-to-end security scheme, while some other Internet security systems in widespread use operate above layer 3, such as Transport Layer Security (TLS) and Secure Shell (SSH), both of which operate at the Transport layer. IPsec can automatically secure applications at the IP layer.
Starting in the early 1970s, the Advanced Research Projects Agency sponsored a series of experimental ARPANET encryption devices, at first for native ARPANET packet encryption and subsequently for TCP/IP packet encryption; some of these were certified and fielded. From 1986 to 1991, the NSA sponsored the development of security protocols for the Internet under its Secure Data Network Systems (SDNS) program. This brought together various vendors including Motorola who produced a network encryption device in 1988. The work was openly published from about 1988 by NIST and, of these, Security Protocol at Layer 3 (SP3) would eventually morph into the ISO standard Network Layer Security Protocol (NLSP).
From 1992 to 1995, various research groups improved upon SDNS's SP3. In 1992, the US Naval Research Laboratory (NRL) began the SIPP project to research and implement IP encryption. In December 1993, the experimental Software IP Encryption Protocol (swIPe) was developed on SunOS at Columbia University and AT&T Bell Labs by John Ioannidis and others. Wei Xu at Trusted Information Systems (TIS) followed the swIPe research, enhanced the IP security protocols and developed the device driver of Data Encryption Standard. By December 1994, his team released the TIS Gauntlet Firewall product with the integrated 3DES hardware encryption and provided commercial IP Security at over T1 speeds, securing networks between the US East and West coasts.
During this period the Internet Engineering Task Force (IETF) IP Security Working Group formed to standardize these efforts as an open, freely available set of security extensions, called IPsec. In 1995, the working group published RFC-1825 through RFC-1827 with the NRL having the first working implementation.
The Security Authentication Header (AH) is derived partially from previous IETF standards work for authentication of the Simple Network Management Protocol (SNMP) version 2. Authentication Header (AH) is a member of the IPsec protocol suite. AH ensures connectionless integrity by using a hash function and a secret shared key in the AH algorithm. AH also guarantees the data origin by authenticating IP packets. Optionally a sequence number can protect the IPsec packet's contents against replay attacks, using the sliding window technique and discarding old packets.
|0||0||Next Header||Payload Len||Reserved|
|4||32||Security Parameters Index (SPI)|
|C||96||Integrity Check Value (ICV)|
The IP Encapsulating Security Payload (ESP) was researched at the Naval Research Laboratory starting in 1992 as part of a DARPA-sponsored research project, and was openly published by IETF SIPP Working Group drafted in December 1993 as a security extension for SIPP. This ESP was originally derived from the US Department of Defense SP3D protocol, rather than being derived from the ISO Network-Layer Security Protocol (NLSP). The SP3D protocol specification was published by NIST in the late 1980s, but designed by the Secure Data Network System project of the US Department of Defense. Encapsulating Security Payload (ESP) is a member of the IPsec protocol suite. It provides origin authenticity through source authentication, data integrity through hash functions and confidentiality through encryption protection for IP 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.
|0||0||Security Parameters Index (SPI)|
|...||...||Padding (0-255 octets)|
|...||...||Pad Length||Next Header|
|...||...||Integrity Check Value (ICV)|
The IPsec protocols use a security association, where the communicating parties establish shared security attributes such as algorithms and keys. As such IPsec provides a range of options once it has been determined whether AH or ESP is used. Before exchanging data the two hosts agree on which algorithm is used to encrypt the IP packet, for example DES or IDEA, and which hash function is used to ensure the integrity of the data, such as MD5 or SHA. These parameters are agreed for the particular session, for which a lifetime must be agreed and a session key.
The algorithm for authentication is also agreed before the data transfer takes place and IPsec supports a range of methods. Authentication is possible through pre-shared key, where a symmetric key is already in the possession of both hosts, and the hosts send each other hashes of the shared key to prove that they are in possession of the same key. IPsec also supports public key encryption, where each host has a public and a private key, they exchange their public keys and each host sends the other a nonce encrypted with the other host's public key. Alternatively if both hosts hold a public key certificate from a certificate authority, this can be used for IPsec authentication.
The security associations of IPsec are established using the Internet Security Association and Key Management Protocol (ISAKMP). 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 (SPI), an index to the security association database (SADB), along with the destination address in a packet header, which together uniquely identifies 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 IP 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.
The IPsec protocols AH and ESP can be implemented in a host-to-host transport mode, as well as in a network tunneling mode.
In transport mode, only the payload of the IP packet is usually encrypted 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 modified by network address translation, as this always invalidates the hash value. The transport and application layers are always secured by a hash, so they cannot be modified in any way, for example by translating the port numbers.
In tunnel mode, the entire IP packet is encrypted and 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 (e.g. between routers to link sites), host-to-network communications (e.g. remote user access) and host-to-host communications (e.g. private chat).
Tunnel mode supports NAT traversal.
Cryptographic algorithms defined for use with IPsec include:
Refer to [RFC 8221] for details.
The IPsec can be implemented in the IP stack of an operating system, which requires modification of the source code. This method of implementation is done for hosts and security gateways. Various IPsec capable IP stacks are available from companies, such as HP or IBM. An alternative is so called bump-in-the-stack (BITS) implementation, where the operating system source code does not have to be modified. Here IPsec is installed between the IP stack and the network drivers. This way operating systems can be retrofitted with IPsec. This method of implementation is also used for both hosts and gateways. However, when retrofitting IPsec the encapsulation of IP packets may cause problems for the automatic path MTU discovery, where the maximum transmission unit (MTU) size on the network path between two IP hosts is established. If a host or gateway has a separate cryptoprocessor, which is common in the military and can also be found in commercial systems, a so-called bump-in-the-wire (BITW) implementation of IPsec is possible.
When IPsec is implemented in the kernel the key management and ISAKMP/IKE negotiation is 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, Solaris or Linux, usually include PF_KEY version 2.
Embedded IPsec can be used to ensure the secure communication among applications running over constrained resource systems with a small overhead.
IPsec was developed in conjunction with IPv6 and was originally required to be supported by all standards-compliant implementations of IPv6 before RFC 6434 made it only a recommendation. IPsec is also optional for IPv4 implementations. 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 (IKE) 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 second version of the Internet Key Exchange standard IKEv2. These third-generation documents standardized the abbreviation of IPsec to uppercase "IP" and lowercase "sec". "ESP" generally refers to RFC 4303, which is the most recent version of the specification.
In 2013, as part of Snowden leaks, it was revealed that the US National Security Agency had been actively working to "Insert vulnerabilities into commercial encryption systems, IT systems, networks, and endpoint communications devices used by targets" as part of the Bullrun program. There are allegations that IPsec was a targeted encryption system.
The OpenBSD IPsec stack was the first implementation that was available under a permissive open-source license, and was therefore copied widely. In a letter which OpenBSD lead developer Theo de Raadt received on 11 Dec 2010 from Gregory Perry, it is alleged that Jason Wright and others, working for the FBI, inserted "a number of backdoors and side channel key leaking mechanisms" into the OpenBSD crypto code. In the forwarded email from 2010, Theo de Raadt did not at first express an official position on the validity of the claims, apart from the implicit endorsement from forwarding the email. Jason Wright's response to the allegations: "Every urban legend is made more real by the inclusion of real names, dates, and times. Gregory Perry's email falls into this category. ... I will state clearly that I did not add backdoors to the OpenBSD operating system or the OpenBSD crypto framework (OCF)." Some days later, de Raadt commented that "I believe that NETSEC was probably contracted to write backdoors as alleged. ... If those were written, I don't believe they made it into our tree." This was published before the Snowden leaks.
An alternative explanation put forward by the authors of the Logjam attack suggests that the NSA compromised IPsec VPNs by undermining the Diffie-Hellman algorithm used in the key exchange. In their paper they allege the NSA specially built a computing cluster to precompute multiplicative subgroups for specific primes and generators, such as for the second Oakley group defined in RFC 2409. As of May 2015, 90% of addressable IPsec VPNs supported the second Oakley group as part of IKE. If an organization were to precompute this group, they could derive the keys being exchanged and decrypt traffic without inserting any software backdoors.
A second alternative explanation that was put forward was that the Equation Group used zero-day exploits against several manufacturers' VPN equipment which were validated by Kaspersky Lab as being tied to the Equation Group and validated by those manufacturers as being real exploits, some of which were zero-day exploits at the time of their exposure. The Cisco PIX and ASA firewalls had vulnerabilities that were used for wiretapping by the NSA.
The spelling "IPsec" is preferred and used throughout this and all related IPsec standards. All other capitalizations of IPsec [...] are deprecated.