IPsec

Incomputing,Internet Protocol Security(IPsec) is a secure networkprotocol suitethatauthenticatesandencryptspacketsof data to provide secure encrypted communication between two computers over anInternet Protocolnetwork. It is used invirtual private networks(VPNs).

IPsec

Internet Protocol Security
Year started	1996
Organization	Internet Engineering Task Force
Base standards	Various, see IETF documentation chapter

IPsec includes protocols for establishingmutual authenticationbetween agents at the beginning of asessionand negotiation ofcryptographic keysto 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 overInternet Protocol(IP) networks. It supports network-level peer authentication,data origin authentication,data integrity,data confidentiality (encryption), and protection fromreplay attacks.

History

Starting in the early 1970s, theAdvanced Research Projects Agencysponsored a series of experimentalARPANET encryption devices,at first for nativeARPANETpacket encryption and subsequently forTCP/IPpacket encryption; some of these were certified and fielded. From 1986 to 1991, theNSAsponsored the development of security protocols for the Internet under its Secure Data Network Systems (SDNS) program.This brought together various vendors includingMotorolawho produced a network encryption device in 1988. The work was openly published from about 1988 byNISTand, of these,Security Protocol at Layer 3(SP3) would eventually morph into the ISO standard Network Layer Security Protocol (NLSP).

In 1992, the USNaval Research Laboratory(NRL) was funded by DARPA CSTO to implement IPv6 and to research and implement IP encryption in 4.4BSD,supporting both SPARC and x86 CPU architectures. DARPA made its implementation freely available via MIT. Under NRL'sDARPA-funded research effort, NRL developed theIETFstandards-track specifications (RFC 1825 through RFC 1827) for IPsec.NRL's IPsec implementation was described in their paper in the 1996USENIX ConferenceProceedings.NRL's open-source IPsec implementation was made available online byMITand became the basis for most initial commercial implementations.

TheInternet Engineering Task Force(IETF) formed the IP Security Working Group in 1992to standardize openly specified security extensions to IP, calledIPsec.The NRL developed standards were published by the IETF as RFC 1825 through RFC 1827.

Security architecture

The initialIPv4suite was developed with few security provisions. As a part of the IPv4 enhancement, IPsec is alayer 3OSI modelorinternet layerend-to-end security scheme. In contrast, while some other Internet security systems in widespread use operate above thenetwork layer,such asTransport Layer Security(TLS) that operates above thetransport layerandSecure Shell(SSH) that operates at theapplication layer,IPsec can automatically secure applications at theinternet layer.

IPsec is anopen standardas a part of the IPv4 suite and uses the followingprotocolsto perform various functions:

• Authentication Header (AH)provides connectionlessdata integrityanddata origin authenticationfor IPdatagramsand provides protection against IP header modification attacks andreplay attacks.
• Encapsulating Security Payload (ESP)providesconfidentiality,connectionless data integrity, data originauthentication,an anti-replay service (a form of partial sequence integrity), and limited traffic-flow confidentiality.

• Internet Security Association and Key Management Protocol(ISAKMP) provides a framework for authentication and key exchange,with actual authenticated keying material provided either by manual configuration withpre-shared keys,Internet Key Exchange(IKE and IKEv2),Kerberized Internet Negotiation of Keys(KINK), or IPSECKEYDNS records.The purpose is to generate thesecurity associations (SA)with the bundle of algorithms and parameters necessary for AH and/or ESP operations.

Authentication Header

Usage of IPsec Authentication Header format in Tunnel and Transport modes

The Security Authentication Header (AH) was developed at theUS Naval Research Laboratoryin the early 1990s and is derived in part from previous IETF standards' work for authentication of theSimple Network Management Protocol(SNMP) version 2. Authentication Header (AH) is a member of the IPsec protocol suite. AH ensures connectionlessintegrityby using ahash functionand a secret shared key in the AH algorithm. AH also guarantees the data origin byauthenticatingIPpackets.Optionally a sequence number can protect the IPsec packet's contents againstreplay attacks,using thesliding windowtechnique and discarding old packets.

• InIPv4,AH prevents option-insertion attacks. InIPv6,AH protects both against header insertion attacks and option insertion attacks.
• InIPv4,the AH protects the IP payload and all header fields of anIP datagramexcept for mutable fields (i.e. those that might be altered in transit), and also IP options such as the IP Security Option.Mutable (and therefore unauthenticated) IPv4 header fields areDSCP/ToS,ECN,Flags,FragmentOffset,TTLandHeader Checksum.
• InIPv6,the AH protects most of the IPv6 base header, AH itself, non-mutable extension headers after the AH, and the IP payload. Protection for the IPv6 header excludes the mutable fields:DSCP,ECN,Flow Label, and Hop Limit.

AH operates directly on top of IP, usingIP protocol number51.

The following AH packet diagram shows how an AH packet is constructed and interpreted:

Authentication Header format

Offset	Octet	0								1								2								3
Octet	Bit	0	1	2	3	4	5	6	7	8	9	10	11	12	13	14	15	16	17	18	19	20	21	22	23	24	25	26	27	28	29	30	31
0	0	Next Header								Payload Len								Reserved
4	32	Security Parameters Index
8	64	Sequence Number
12	96	Integrity Check Value
⋮	⋮

Next Header: 8 bits

Type of the next header, indicating what upper-layer protocol was protected. The value is taken from thelist of IP protocol numbers.

Payload Len: 8 bits

The length of thisAuthentication Headerin 4-octet units, minus 2. For example, an AH value of 4 equals 3×(32-bit fixed-length AH fields) + 3×(32-bit ICV fields) − 2 and thus an AH value of 4 means 24 octets. Although the size is measured in 4-octet units, the length of this header needs to be a multiple of 8 octets if carried in an IPv6 packet. This restriction does not apply to anAuthentication Headercarried in an IPv4 packet.

Reserved: 16 bits

Reserved for future use (all zeroes until then).

Security Parameters Index: 32 bits

Arbitrary value which is used (together with the destination IP address) to identify thesecurity associationof the receiving party.

Sequence Number:32 bits

Amonotonicstrictly increasing sequence number (incremented by 1 for every packet sent) to preventreplay attacks.When replay detection is enabled, sequence numbers are never reused, because a new security association must be renegotiated before an attempt to increment the sequence number beyond its maximum value.

Integrity Check Value: multiple of 32 bits

Variable length check value. It may contain padding to align the field to an 8-octet boundary forIPv6,or a 4-octet boundary forIPv4.

Encapsulating Security Payload

Usage of IPsec Encapsulating Security Payload (ESP) in Tunnel and Transport modes

The IP Encapsulating Security Payload (ESP)was developed at theNaval Research Laboratorystarting in 1992 as part of aDARPA-sponsored research project, and was openly published byIETFSIPPWorking Group drafted in December 1993 as a security extension for SIPP. ThisESPwas originally derived from the US Department of DefenseSP3Dprotocol, rather than being derived from the ISO Network-Layer Security Protocol (NLSP). The SP3D protocol specification was published byNISTin the late 1980s, but designed by the Secure Data Network System project of theUS Department of Defense. Encapsulating Security Payload (ESP) is a member of the IPsec protocol suite. It provides originauthenticitythrough sourceauthentication,data integritythrough hash functions andconfidentialitythroughencryptionprotection for IPpackets.ESP also supportsencryption-only andauthentication-only configurations, but using encryption without authentication is strongly discouraged because it is insecure.

UnlikeAuthentication Header (AH),ESP in transport mode does not provide integrity and authentication for the entireIP packet.However, intunnel mode,where the entire original IP packet isencapsulatedwith 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 following ESP packet diagram shows how an ESP packet is constructed and interpreted:

Encapsulating Security Payload format

Offset	Octet	0								1								2								3
Octet	Bit	0	1	2	3	4	5	6	7	8	9	10	11	12	13	14	15	16	17	18	19	20	21	22	23	24	25	26	27	28	29	30	31
0	0	Security Parameters Index
4	32	Sequence Number
8	64	Payload Data
⋮	⋮
⋮	⋮
⋮	⋮	(Padding)
⋮	⋮																	Pad Length								Next Header
⋮	⋮	Integrity Check Value ⋮
⋮	⋮

Security Parameters Index(SPI): 32 bits

Arbitrary value used (together with the destination IP address) to identify thesecurity associationof the receiving party.

Sequence Number: 32 bits

Amonotonicallyincreasing sequence number (incremented by 1 for every packet sent) to protect againstreplay attacks.There is a separate counter kept for every security association.

Payload Data: variable

The protected contents of the original IP packet, including any data used to protect the contents (e.g. an Initialisation Vector for the cryptographic algorithm). The type of content that was protected is indicated by theNext Headerfield.

Padding: 0-255 octets

Optional. Padding for encryption, to extend the payload data to a size that fits the encryption'scipherblock size,and to align the next field.

Pad Length: 8 bits

Size of the padding (in octets).

Next Header: 8 bits

Indicates theprotocol typeof thePayload Data,like the value6forTCP.As ESP is an encapsulation protocol, a value of4is also possible, indicatingIP in IP.A value of41indicatesIPv6encapsulated inIPv4,e.g.6to4.The value59(meaning:No Next Header) is used for dummy packets, which may be inserted in the stream, and which contents should be discarded.

Integrity Check Value(ICV): variable

Variable length check value. It may contain padding to align the field to an 8-octet boundary forIPv6,or a 4-octet boundary forIPv4.

Security association

Main article:Security association

The IPsec protocols use asecurity association,where the communicating parties establish shared security attributes such asalgorithmsand 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 whichsymmetric encryption algorithmis used to encrypt the IP packet, for exampleAESorChaCha20,and which hash function is used to ensure the integrity of the data, such asBLAKE2orSHA256.These parameters are agreed for the particular session, for which a lifetime must be agreed and asession key.

The algorithm for authentication is also agreed before the data transfer takes place and IPsec supports a range of methods. Authentication is possible throughpre-shared key,where asymmetric keyis 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 supportspublic key encryption,where each host has a public and a private key, they exchange their public keys and each host sends the other anonceencrypted with the other host's public key. Alternatively if both hosts hold apublic key certificatefrom acertificate authority,this can be used for IPsec authentication.

The security associations of IPsec are established using theInternet 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 IPSECKEYDNS records.RFC 5386 defines Better-Than-Nothing Security (BTNS) as an unauthenticated mode of IPsec using an extended IKE protocol. C. Meadows, C. Cremers, and others have usedformal methodsto identify various anomalies which exist in IKEv1 and also in IKEv2.

In order to decide what protection is to be provided for an outgoing packet, IPsec uses theSecurity 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.

ForIP multicasta 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.

Keepalives

To ensure that the connection between two endpoints has not been interrupted, endpoints exchangekeepalivemessages at regular intervals, which can also be used to automatically reestablish a tunnel lost due to connection interruption.

Dead Peer Detection (DPD) is a method of detecting a deadInternet Key Exchange(IKE) peer. The method uses IPsec traffic patterns to minimize the number of messages required to confirm the availability of a peer. DPD is used to reclaim the lost resources in case a peer is found dead and it is also used to perform IKE peer failover.

UDP keepalive is an alternative to DPD.

Modes of operation

The IPsec protocols AH and ESP can be implemented in a host-to-host transport mode, as well as in a network tunneling mode.

IPsec Modes

Transport mode

In transport mode, only the payload of the IP packet is usuallyencryptedor authenticated. The routing is intact, since the IP header is neither modified nor encrypted; however, when theauthentication headeris used, the IP addresses cannot be modified bynetwork address translation,as this always invalidates thehash value.Thetransportandapplicationlayers are always secured by a hash, so they cannot be modified in any way, for example bytranslatingtheportnumbers.

A means to encapsulate IPsec messages forNAT traversal{NAT-T} has been defined byRFCdocuments describing the NAT-T mechanism.

Tunnel mode

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 createvirtual private networksfor 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.

Algorithms

Symmetric encryption algorithms

Cryptographic algorithms defined for use with IPsec include:

• HMAC-SHA1/SHA2for integrity protection and authenticity.
• TripleDES-CBCfor confidentiality
• AES-CBCandAES-CTRfor confidentiality.
• AES-GCMandChaCha20-Poly1305providing confidentiality and authentication together efficiently.

Refer to RFC 8221 for details.

Key exchange algorithms

• Diffie–Hellman(RFC 3526)
• ECDH(RFC 4753)

Authentication algorithms

• RSA
• ECDSA(RFC 4754)
• PSK(RFC 6617)
• EdDSA(RFC 8420)

Implementations

The IPsec can be implemented in the IP stack of anoperating system.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 calledbump-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 networkdrivers.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 automaticpath MTU discovery,where themaximum transmission unit(MTU) size on the network path between two IP hosts is established. If a host or gateway has a separatecryptoprocessor,which is common in the military and can also be found in commercial systems, a so-calledbump-in-the-wire(BITW) implementation of IPsec is possible.

When IPsec is implemented in thekernel,the key management andISAKMP/IKEnegotiation is carried out from user space. The NRL-developed and 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 onUnix-like operating systems,for example,SolarisorLinux,usually include PF_KEY version 2.

EmbeddedIPsec can be used to ensure the secure communication among applications running over constrained resource systems with a small overhead.

Standards status

IPsec was developed in conjunction withIPv6and was originally required to be supported by all standards-compliant implementations ofIPv6before RFC 6434 made it only a recommendation.IPsec is also optional forIPv4implementations. 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 protocolInternet 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 standardIKEv2.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.

Since mid-2008, an IPsec Maintenance and Extensions (ipsecme) working group is active at the IETF.

Alleged NSA interference

In 2013, as part ofSnowden leaks,it was revealed that the USNational Security Agencyhad been actively working to "Insert vulnerabilities into commercial encryption systems, IT systems, networks, and endpoint communications devices used by targets" as part of theBullrunprogram.There are allegations that IPsec was a targeted encryption system.

The OpenBSD IPsec stack came later on and also was widely copied. In a letter whichOpenBSDlead developerTheo de Raadtreceived on 11 Dec 2010 from Gregory Perry, it is alleged that Jason Wright and others, working for the FBI, inserted "a number ofbackdoorsandside channelkey 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 theOpenBSD Cryptographic 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 theLogjam attacksuggests that the NSA compromised IPsec VPNs by undermining theDiffie-Hellmanalgorithm 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 theEquation Groupusedzero-day exploitsagainst several manufacturers' VPN equipment which were validated byKaspersky Labas being tied to the Equation Groupand validated by those manufacturers as being real exploits, some of which were zero-day exploits at the time of their exposure.TheCisco PIX and ASAfirewalls had vulnerabilities that were used for wiretapping by the NSA.

Furthermore, IPsec VPNs using "Aggressive Mode" settings send a hash of the PSK in the clear. This can be and apparently is targeted by the NSA using offlinedictionary attacks.

See also

• Dynamic Multipoint Virtual Private Network
• Information security
• NAT traversal
• Opportunistic encryption
• tcpcrypt
• Tunneling protocol

Further reading

Standards track

• RFC1829:The ESP DES-CBC Transform
• RFC2403:The Use of HMAC-MD5-96 within ESP and AH
• RFC2404:The Use of HMAC-SHA-1-96 within ESP and AH
• RFC2405:The ESP DES-CBC Cipher Algorithm With Explicit IV
• RFC2410:The NULL Encryption Algorithm and Its Use With IPsec
• RFC2451:The ESP CBC-Mode Cipher Algorithms
• RFC2857:The Use of HMAC-RIPEMD-160-96 within ESP and AH
• RFC3526:More Modular Exponential (MODP)Diffie-Hellmangroups for Internet Key Exchange (IKE)
• RFC3602:TheAES-CBCCipher Algorithm and Its Use with IPsec
• RFC3686:Using Advanced Encryption Standard (AES) Counter Mode With IPsec Encapsulating Security Payload (ESP)
• RFC3947:Negotiation of NAT-Traversal in the IKE
• RFC3948:UDP Encapsulation of IPsec ESP Packets
• RFC4106:The Use of Galois/Counter Mode (GCM) in IPsec Encapsulating Security Payload (ESP)
• RFC4301:Security Architecture for the Internet Protocol
• RFC4302:IP Authentication Header
• RFC4303:IP Encapsulating Security Payload
• RFC4304:Extended Sequence Number (ESN) Addendum to IPsec Domain of Interpretation (DOI) for Internet Security Association and Key Management Protocol (ISAKMP)
• RFC4307:Cryptographic Algorithms for Use in the Internet Key Exchange Version 2 (IKEv2)
• RFC4308:Cryptographic Suites for IPsec
• RFC4309:UsingAdvanced Encryption Standard(AES)CCM modewith IPsec Encapsulating Security Payload (ESP)
• RFC4543:The Use ofGalois Message Authentication Code(GMAC) in IPsec ESP and AH
• RFC4555:IKEv2 Mobility and Multihoming Protocol (MOBIKE)
• RFC4806:Online Certificate Status Protocol (OCSP) Extensions to IKEv2
• RFC4868:UsingHMAC-SHA-256,HMAC-SHA-384, and HMAC-SHA-512 with IPsec
• RFC4945:The Internet IP Security PKI Profile of IKEv1/ISAKMP, IKEv2, and PKIX
• RFC5280:Internet X.509 Public Key Infrastructure Certificate and Certificate Revocation List (CRL) Profile
• RFC5282:Using Authenticated Encryption Algorithms with the Encrypted Payload of the Internet Key Exchange version 2 (IKEv2) Protocol
• RFC5386:Better-Than-Nothing Security: An Unauthenticated Mode of IPsec
• RFC5529:Modes of Operation forCamelliafor Use with IPsec
• RFC5685:Redirect Mechanism for the Internet Key Exchange Protocol Version 2 (IKEv2)
• RFC5723:Internet Key Exchange Protocol Version 2 (IKEv2) Session Resumption
• RFC5857:IKEv2 Extensions to Support Robust Header Compression over IPsec
• RFC5858:IPsec Extensions to Support Robust Header Compression over IPsec
• RFC7296:Internet Key Exchange Protocol Version 2 (IKEv2)
• RFC7321:Cryptographic Algorithm Implementation Requirements and Usage Guidance for Encapsulating Security Payload (ESP) and Authentication Header (AH)
• RFC7383:Internet Key Exchange Protocol Version 2 (IKEv2) Message Fragmentation
• RFC7427:Signature Authentication in the Internet Key Exchange Version 2 (IKEv2)
• RFC7634:ChaCha20, Poly1305, and Their Use in the Internet Key Exchange Protocol (IKE) and IPsec

Experimental RFCs

• RFC4478:Repeated Authentication in Internet Key Exchange (IKEv2) Protocol

Informational RFCs

• RFC2367:PF_KEY Interface
• RFC2412:The OAKLEY Key Determination Protocol
• RFC3706:A Traffic-Based Method of Detecting Dead Internet Key Exchange (IKE) Peers
• RFC3715:IPsec-Network Address Translation (NAT) Compatibility Requirements
• RFC4621:Design of the IKEv2 Mobility and Multihoming (MOBIKE) Protocol
• RFC4809:Requirements for an IPsec Certificate Management Profile
• RFC5387:Problem and Applicability Statement for Better-Than-Nothing Security (BTNS)
• RFC5856:Integration of Robust Header Compression over IPsec Security Associations
• RFC5930:Using Advanced Encryption Standard Counter Mode (AES-CTR) with the Internet Key Exchange version 02 (IKEv2) Protocol
• RFC6027:IPsec Cluster Problem Statement
• RFC6071:IPsec and IKE Document Roadmap
• RFC6379:Suite BCryptographic Suites for IPsec
• RFC6380:Suite B Profile for Internet Protocol Security (IPsec)
• RFC6467:Secure Password Framework for Internet Key Exchange Version 2 (IKEv2)

Best current practice RFCs

• RFC5406:Guidelines for Specifying the Use of IPsec Version 2

Obsolete/historic RFCs

• RFC1825:Security Architecture for the Internet Protocol (obsoleted by RFC 2401)
• RFC1826:IP Authentication Header (obsoleted by RFC 2402)
• RFC1827:IP Encapsulating Security Payload (ESP) (obsoleted by RFC 2406)
• RFC1828:IP Authentication using KeyedMD5(historic)
• RFC2401:Security Architecture for the Internet Protocol (IPsec overview) (obsoleted by RFC 4301)
• RFC2406:IP Encapsulating Security Payload (ESP) (obsoleted by RFC 4303 and RFC 4305)
• RFC2407:The Internet IP Security Domain of Interpretation for ISAKMP (obsoleted by RFC 4306)
• RFC2409:The Internet Key Exchange (obsoleted by RFC 4306)
• RFC4305:Cryptographic Algorithm Implementation Requirements for Encapsulating Security Payload (ESP) and Authentication Header (AH) (obsoleted by RFC 4835)
• RFC4306:Internet Key Exchange (IKEv2) Protocol (obsoleted by RFC 5996)
• RFC4718:IKEv2 Clarifications and Implementation Guidelines (obsoleted by RFC 7296)
• RFC4835:Cryptographic Algorithm Implementation Requirements for Encapsulating Security Payload (ESP) and Authentication Header (AH) (obsoleted by RFC 7321)
• RFC5996:Internet Key Exchange Protocol Version 2 (IKEv2) (obsoleted by RFC 7296)

External links

• All IETF active security WGs
  • IETF ipsecme WG( "IP Security Maintenance and Extensions" Working Group)
  • IETF btns WG( "Better-Than-Nothing Security" Working Group) (chartered to work on unauthenticated IPsec, IPsec APIs, connection latching)]
• Securing Data in Transit with IPsecArchived2008-10-13 at theWayback MachineWindowsSecurity.com article by Deb Shinder
• IPsecon Microsoft TechNet
  • Microsoft IPsec Diagnostic Toolon Microsoft Download Center
• An Illustrated Guide to IPsecby Steve Friedl
• Security Architecture for IP (IPsec)Data Communication Lectures by Manfred Lindner Part IPsec
• Creating VPNs with IPsec and SSL/TLSLinux Journal article by Rami Rosen