IPsec

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

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).^[1] IPsec uses cryptographic security services to protect communications over

data origin authentication, data integrity, data confidentiality (encryption), and replay protection (protection from replay attacks

History

Starting in the early 1970s, the

NSA sponsored the development of security protocols for the Internet under its Secure Data Network Systems (SDNS) program.^[2] 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).^[3]

In 1992, the US

MIT and became the basis for most initial commercial implementations.^[4]

The Internet Engineering Task Force (IETF) formed the IP Security Working Group in 1992^[6] to standardize openly specified security extensions to IP, called IPsec.^[7] The NRL developed standards were published by the IETF as RFC-1825 through RFC-1827.^[8]

Security architecture

The initial

layer 3 OSI model or internet layer end-to-end security scheme. In contrast, while some other Internet security systems in widespread use operate above the network layer, such as Transport Layer Security (TLS) that operates above the transport layer and Secure Shell (SSH) that operates at the application layer, IPsec can automatically secure applications at the internet layer

IPsec is an

protocols to perform various functions:^[9]^[10]

datagrams and provides protection against IP header modification attacks and replay attacks.^[11]^[12]

Encapsulating Security Payload (ESP) provides confidentiality, connectionless data integrity, data origin authentication, an anti-replay service (a form of partial sequence integrity), and limited traffic-flow confidentiality.^[1]
Internet Security Association and Key Management Protocol (ISAKMP) provides a framework for authentication and key exchange,^[13] with actual authenticated keying material provided either by manual configuration with pre-shared keys, Internet Key Exchange (IKE and IKEv2), Kerberized Internet Negotiation of Keys (KINK), or IPSECKEY DNS records.^[14]^[15]^[16]^[17] The purpose is to generate the security associations (SA) with the bundle of algorithms and parameters necessary for AH and/or ESP operations.

Authentication Header

The Security Authentication Header (AH) was developed at the

sliding window

technique and discarding old packets.

In IPv4, AH prevents option-insertion attacks. In IPv6, AH protects both against header insertion attacks and option insertion attacks.
In
Header Checksum.^[12]

In
DSCP, ECN, Flow Label, and Hop Limit.^[12]

AH operates directly on top of IP, using IP protocol number 51.^[20]

The following AH packet diagram shows how an AH packet is constructed and interpreted:^[11]^[12]

*Authentication Header* format
Offsets	Octet₁₆	0								1								2								3
Octet₁₆	Bit₁₀	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 (SPI)
8	64	Sequence Number
C	96	Integrity Check Value (ICV) ...
...	...	Integrity Check Value (ICV) ...

Next Header (8 bits): Type of the next header, indicating what upper-layer protocol was protected. The value is taken from the list of IP protocol numbers.
Payload Len (8 bits): The length of this Authentication Header in 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 an Authentication Header carried 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 the security association of the receiving party.
Sequence Number (32 bits): A
monotonic strictly increasing sequence number (incremented by 1 for every packet sent) to prevent replay 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.^[12]
Integrity Check Value (multiple of 32 bits): Variable length check value. It may contain padding to align the field to an 8-octet boundary for IPv6, or a 4-octet boundary for IPv4.

Encapsulating Security Payload

The IP Encapsulating Security Payload (ESP)

US Department of Defense

. Encapsulating Security Payload (ESP) is a member of the IPsec protocol suite. It provides origin

packets. ESP also supports encryption-only and authentication-only configurations, but using encryption without authentication is strongly discouraged because it is insecure.^[23]^[24]^[25]

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.[20]

The following ESP packet diagram shows how an ESP packet is constructed and interpreted:^[1]^[26]

*Encapsulating Security Payload* format
Offsets	Octet₁₆	0								1								2								3
Octet₁₆	Bit₁₀	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 (SPI)
4	32	Sequence Number
8	64	Payload data
...	...	Payload data
...	...
...	...									Padding (0-255 octets)
...	...																	Pad Length								Next Header
...	...	Integrity Check Value (ICV) ...
...	...	Integrity Check Value (ICV) ...

Security Parameters Index (32 bits): Arbitrary value used (together with the destination IP address) to identify the security association of the receiving party.
Sequence Number (32 bits): A
monotonically increasing sequence number (incremented by 1 for every packet sent) to protect against replay 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 the Next Header field.
Padding (0-255 octets): Padding for encryption, to extend the payload data to a size that fits the encryption's cipher block size, and to align the next field.
Pad Length (8 bits): Size of the padding (in octets).
Next Header (8 bits): Type of the next header. The value is taken from the list of IP protocol numbers.
Integrity Check Value (multiple of 32 bits): Variable length check value. It may contain padding to align the field to an 8-octet boundary for IPv6, or a 4-octet boundary for IPv4.

Security association

The IPsec protocols use a

BLAKE2 or SHA256. These parameters are agreed for the particular session, for which a lifetime must be agreed and a session key.^[27]

The algorithm for authentication is also agreed before the data transfer takes place and IPsec supports a range of methods. Authentication is possible through

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.^[28]

The security associations of IPsec are established using the

formal methods to identify various anomalies which exist in IKEv1 and also in IKEv2.^[31]

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.

Keepalives

To ensure that the connection between two endpoints has not been interrupted, endpoints exchange keepalive messages 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 dead Internet 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.

Transport mode

In transport mode, only the payload of the IP packet is usually

port

numbers.

A means to encapsulate IPsec messages for NAT traversal {NAT-T} has been defined by RFC documents 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 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).^[32]

Tunnel mode supports NAT traversal.

Algorithms

Symmetric encryption algorithms

Cryptographic algorithms defined for use with IPsec include:

SHA2
for integrity protection and authenticity.
CBC
for confidentiality
AES-
AES-CTR
for confidentiality.
AES-GCM and ChaCha20-Poly1305 providing 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 an

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.^[34]

When IPsec is implemented in the

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.^[36]

Standards status

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.^[37] IPsec is also optional for IPv4 implementations. IPsec is most commonly used to secure IPv4 traffic.^{[citation needed]}

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

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.

Since mid-2008, an IPsec Maintenance and Extensions (ipsecme) working group is active at the IETF.^[38]^[39]

Alleged NSA interference

In 2013, as part of

Bullrun program.^[40] There are allegations that IPsec was a targeted encryption system.^[41]

The OpenBSD IPsec stack came later on and also was widely copied. In a letter which

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.^[42] 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 Cryptographic Framework (OCF)."^[43] 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."^[44]

This was published before the Snowden leaks.

An alternative explanation put forward by the authors of the

Diffie-Hellman algorithm used in the key exchange. In their paper,^[45]

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

zero-day exploits against several manufacturers' VPN equipment which were validated by Kaspersky Lab as being tied to the Equation Group^[46] and validated by those manufacturers as being real exploits, some of which were zero-day exploits at the time of their exposure.^[47]^[48]^[49] The Cisco PIX and ASA firewalls had vulnerabilities that were used for wiretapping by the NSA^{[citation needed}

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 offline dictionary attacks.^[45]^[50]^[51]

IETF documentation

Standards track

RFC 1829: The ESP DES-CBC Transform
RFC 2403: The Use of HMAC-MD5-96 within ESP and AH
RFC 2404: The Use of HMAC-SHA-1-96 within ESP and AH
RFC 2405: The ESP DES-CBC Cipher Algorithm With Explicit IV
RFC 2410: The NULL Encryption Algorithm and Its Use With IPsec
RFC 2451: The ESP CBC-Mode Cipher Algorithms
RFC 2857: The Use of HMAC-RIPEMD-160-96 within ESP and AH
RFC 3526: More Modular Exponential (MODP) Diffie-Hellman groups for Internet Key Exchange (IKE)
RFC 3602: The
AES-CBC
Cipher Algorithm and Its Use with IPsec
RFC 3686: Using Advanced Encryption Standard (AES) Counter Mode With IPsec Encapsulating Security Payload (ESP)
RFC 3947: Negotiation of NAT-Traversal in the IKE
RFC 3948: UDP Encapsulation of IPsec ESP Packets
RFC 4106: The Use of Galois/Counter Mode (GCM) in IPsec Encapsulating Security Payload (ESP)
RFC 4301: Security Architecture for the Internet Protocol
RFC 4302: IP Authentication Header
RFC 4303: IP Encapsulating Security Payload
RFC 4304: Extended Sequence Number (ESN) Addendum to IPsec Domain of Interpretation (DOI) for Internet Security Association and Key Management Protocol (ISAKMP)
RFC 4307: Cryptographic Algorithms for Use in the Internet Key Exchange Version 2 (
IKEv2
)
RFC 4308: Cryptographic Suites for IPsec
RFC 4309: Using Advanced Encryption Standard (AES) CCM mode with IPsec Encapsulating Security Payload (ESP)
RFC 4543: The Use of
Galois Message Authentication Code
(GMAC) in IPsec ESP and AH
RFC 4555: IKEv2 Mobility and Multihoming Protocol (MOBIKE)
RFC 4806: Online Certificate Status Protocol (OCSP) Extensions to IKEv2
RFC 4868: Using
HMAC-SHA-256
, HMAC-SHA-384, and HMAC-SHA-512 with IPsec
RFC 4945: The Internet IP Security PKI Profile of IKEv1/ISAKMP, IKEv2, and PKIX
RFC 5280: Internet X.509 Public Key Infrastructure Certificate and Certificate Revocation List (CRL) Profile
RFC 5282: Using Authenticated Encryption Algorithms with the Encrypted Payload of the Internet Key Exchange version 2 (IKEv2) Protocol
RFC 5386: Better-Than-Nothing Security: An Unauthenticated Mode of IPsec
RFC 5529: Modes of Operation for Camellia for Use with IPsec
RFC 5685: Redirect Mechanism for the Internet Key Exchange Protocol Version 2 (IKEv2)
RFC 5723: Internet Key Exchange Protocol Version 2 (IKEv2) Session Resumption
RFC 5857: IKEv2 Extensions to Support Robust Header Compression over IPsec
RFC 5858: IPsec Extensions to Support Robust Header Compression over IPsec
RFC 7296: Internet Key Exchange Protocol Version 2 (IKEv2)
RFC 7321: Cryptographic Algorithm Implementation Requirements and Usage Guidance for Encapsulating Security Payload (ESP) and Authentication Header (AH)
RFC 7383: Internet Key Exchange Protocol Version 2 (IKEv2) Message Fragmentation
RFC 7427: Signature Authentication in the Internet Key Exchange Version 2 (IKEv2)
RFC 7634: ChaCha20, Poly1305, and Their Use in the Internet Key Exchange Protocol (IKE) and IPsec

Experimental RFCs

RFC 4478: Repeated Authentication in Internet Key Exchange (IKEv2) Protocol

Informational RFCs

RFC 2367: PF_KEY Interface
RFC 2412: The OAKLEY Key Determination Protocol
RFC 3706: A Traffic-Based Method of Detecting Dead Internet Key Exchange (IKE) Peers
RFC 3715: IPsec-Network Address Translation (NAT) Compatibility Requirements
RFC 4621: Design of the IKEv2 Mobility and Multihoming (MOBIKE) Protocol
RFC 4809: Requirements for an IPsec Certificate Management Profile
RFC 5387: Problem and Applicability Statement for Better-Than-Nothing Security (BTNS)
RFC 5856: Integration of Robust Header Compression over IPsec Security Associations
RFC 5930: Using Advanced Encryption Standard Counter Mode (AES-CTR) with the Internet Key Exchange version 02 (IKEv2) Protocol
RFC 6027: IPsec Cluster Problem Statement
RFC 6071: IPsec and IKE Document Roadmap
RFC 6379:
Suite B
Cryptographic Suites for IPsec
RFC 6380: Suite B Profile for Internet Protocol Security (IPsec)
RFC 6467: Secure Password Framework for Internet Key Exchange Version 2 (IKEv2)

Best current practice RFCs

RFC 5406: Guidelines for Specifying the Use of IPsec Version 2

Obsolete/historic RFCs

RFC 1825: Security Architecture for the Internet Protocol (obsoleted by RFC 2401)
RFC 1826: IP Authentication Header (obsoleted by RFC 2402)
RFC 1827: IP Encapsulating Security Payload (ESP) (obsoleted by RFC 2406)
RFC 1828: IP Authentication using Keyed MD5 (historic)
RFC 2401: Security Architecture for the Internet Protocol (IPsec overview) (obsoleted by RFC 4301)
RFC 2406: IP Encapsulating Security Payload (ESP) (obsoleted by RFC 4303 and RFC 4305)
RFC 2407: The Internet IP Security Domain of Interpretation for ISAKMP (obsoleted by RFC 4306)
RFC 2409: The Internet Key Exchange (obsoleted by RFC 4306)
RFC 4305: Cryptographic Algorithm Implementation Requirements for Encapsulating Security Payload (ESP) and Authentication Header (AH) (obsoleted by RFC 4835)
RFC 4306: Internet Key Exchange (IKEv2) Protocol (obsoleted by RFC 5996)
RFC 4718: IKEv2 Clarifications and Implementation Guidelines (obsoleted by RFC 7296)
RFC 4835: Cryptographic Algorithm Implementation Requirements for Encapsulating Security Payload (ESP) and Authentication Header (AH) (obsoleted by RFC 7321)
RFC 5996: Internet Key Exchange Protocol Version 2 (IKEv2) (obsoleted by RFC 7296)

References

^
doi:10.17487/RFC2406. RFC 2406
.

S2CID 16526652
.

^ Gilmore, John. "Network Encryption – history and patents". Archived from the original on 2014-09-03. Retrieved 2014-02-18.

^ ^a ^b "IPv6 + IPSEC + ISAKMP Distribution Page". web.mit.edu.

^ "USENIX 1996 ANNUAL TECHNICAL CONFERENCE". www.usenix.org.

^ "IP Security Protocol (ipsec) -". datatracker.ietf.org.

doi:10.17487/RFC4301. RFC 4301
. The spelling "IPsec" is preferred and used throughout this and all related IPsec standards. All other capitalizations of IPsec [...] are deprecated.

^ "NRL ITD Accomplishments - IPSec and IPv6" (PDF). US Naval Research Laboratories. Archived (PDF) from the original on 2015-09-15.

doi:10.17487/RFC2411. RFC 2411
.

doi:10.17487/RFC4308. RFC 4308
.

^
doi:10.17487/RFC2402. RFC 2402
.

^
doi:10.17487/RFC4302. RFC 4302
.

^ The Internet Key Exchange (IKE), RFC 2409, §1 Abstract

doi:10.17487/RFC2409. RFC 2409
.

doi:10.17487/RFC4306. RFC 4306
.

doi:10.17487/RFC4430. RFC 4430
.

^
doi:10.17487/RFC4025. RFC 4025
.

ISBN 9780852969823
.

doi:10.17487/RFC4949. RFC 4949
. Informational.

^ ^a ^b "Protocol Numbers". IANA. 2010-05-27. Archived from the original on 2010-05-29.

^ "SIPP Encapsulating Security Payload". IETF SIPP Working Group. 1993. Archived from the original on 2016-09-09. Retrieved 2013-08-07.

^ Deering, Steve E. (1993). "Draft SIPP Specification". IETF. p. 21.

^ Bellovin, Steven M. (1996). "Problem Areas for the IP Security Protocols" (PostScript). Proceedings of the Sixth Usenix Unix Security Symposium. San Jose, CA. pp. 1–16. Retrieved 2007-07-09.

^ Paterson, Kenneth G.; Yau, Arnold K.L. (2006-04-24). "Cryptography in theory and practice: The case of encryption in IPsec" (PDF). Eurocrypt 2006, Lecture Notes in Computer Science Vol. 4004. Berlin. pp. 12–29. Retrieved 2007-08-13.

^ Degabriele, Jean Paul; Paterson, Kenneth G. (2007-08-09). "Attacking the IPsec Standards in Encryption-only Configurations" (PDF). IEEE Symposium on Security and Privacy, IEEE Computer Society. Oakland, CA. pp. 335–349. Retrieved 2007-08-13.

doi:10.17487/RFC4303. RFC 4303
.

ISBN 9780852969823
.

ISBN 9780852969823
.

^ RFC 2406, §1, page 2

doi:10.17487/RFC3129. RFC 3129
.

S2CID 18222662
.

^ William, S., & Stallings, W. (2006). Cryptography and Network Security, 4/E. Pearson Education India. p. 492-493

ISBN 9780852969823
.

ISBN 9780852969823
.

^ RFC 2367, PF_KEYv2 Key Management API, Dan McDonald, Bao Phan, & Craig Metz (July 1998)

S2CID 16935000
.

^ RFC 6434, "IPv6 Node Requirements", E. Jankiewicz, J. Loughney, T. Narten (December 2011)

^ "ipsecme charter". Retrieved 2015-10-26.

^ "ipsecme status". Retrieved 2015-10-26.

^ "Secret Documents Reveal N.S.A. Campaign Against Encryption". New York Times.

^ John Gilmore. "Re: [Cryptography] Opening Discussion: Speculation on "BULLRUN"".

^ Theo de Raadt. "Allegations regarding OpenBSD IPSEC".

^ Jason Wright. "Allegations regarding OpenBSD IPSEC".

^ Theo de Raadt. "Update on the OpenBSD IPSEC backdoor allegation".

^
S2CID 347988
.

^ Goodin, Dan (August 16, 2016). "Confirmed: hacking tool leak came from "omnipotent" NSA-tied group". Ars Technica. Retrieved August 19, 2016.

^ Thomson, Iain (August 17, 2016). "Cisco confirms two of the Shadow Brokers' 'NSA' vulns are real". The Register. Retrieved September 16, 2016.

^ Pauli, Darren (August 24, 2016). "Equation Group exploit hits newer Cisco ASA, Juniper Netscreen". The Register. Retrieved September 16, 2016.

^ Chirgwin, Richard (August 18, 2016). "Fortinet follows Cisco in confirming Shadow Broker vuln". The Register. Retrieved September 16, 2016.

^ "key exchange - What are the problems of IKEv1 aggressive mode (compared to IKEv1 main mode or IKEv2)?". Cryptography Stack Exchange.

^ "Don't stop using IPsec just yet". No Hats. December 29, 2014.

External links

Computer Security at
Curlie

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 IPsec WindowsSecurity.com article by Deb Shinder

IPsec on Microsoft TechNet
Microsoft IPsec Diagnostic Tool on Microsoft Download Center

An Illustrated Guide to IPsec by Steve Friedl

Security Architecture for IP (IPsec) Data Communication Lectures by Manfred Lindner Part IPsec

Creating VPNs with IPsec and SSL/TLS Linux Journal article by Rami Rosen

v
t
e
Virtual private networking
Communication protocols

DTLS

DirectAccess

EVPN

IPsec

L2F

L2TP

L2TPv3

PPTP

SSTP

Split tunneling

SSL/TLS

(Opportunistic: tcpcrypt)

Connection applications

FreeLAN

FreeS/WAN

Libreswan

n2n

OpenConnect

OpenIKED

Openswan

OpenVPN

Social VPN

SoftEther VPN

strongSwan

tcpcrypt

tinc

VTun

WireGuard

Shadowsocks

Enterprise software

Avast SecureLine VPN

Check Point VPN-1

LogMeIn Hamachi

Risk vectors

Content-control software

Deep content inspection

Deep packet inspection

IP address blocking

Network enumeration

Stateful firewall

TCP reset attack

VPN blocking

VPN Services
Avast

HMA

SecureLine

Kape Technologies

CyberGhost

ExpressVPN

Private Internet Access

Zenmate

McAfee

TunnelBear

Tesonet

NordVPN

NordLayer

Surfshark

Ziff Davis

IPVanish

StrongVPN

Hola

IVPN

Mozilla VPN

Mullvad

PrivadoVPN

Proton VPN

PureVPN

SaferVPN

Windscribe

Authority control databases: National

Germany

Israel

United States

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