A Complete Guide to VPN Encryption
Updated May 11, 2019
A Virtual Private Network (VPN) is a privacy and security tool that encrypts all data transmitted between a device and a VPN server.
The simplest way of understanding encryption is by thinking of a lock. With the right key, it’ll open. The lock, or encryption, is used to protect the data of your online activity, whether it’s making purchases or using personal log-ins. If someone doesn’t have the right key to open the lock and access the data, they may attempt to break it. One type of encryption varies from other types, in the same way, the lock securing a suitcase is not as strong as one securing a bank vault.
Length of Encryption Keys
Ciphers rely on highly complex algorithms that are extremely hard to crack. The complexity of the algorithm behind a cipher is the simplest way of measuring its strength.
You probably know that computers use binary digits (ones and zeros) to perform all calculations. A cipher’s complexity relies on its size in bits, i.e. the number of ones and zeros required to express the algorithm. A single bit comprises a one or a zero. As the size of a cipher increases, the number of possible combinations, and its impenetrability increases drastically.
Increasingly complex algorithms make a cipher difficult to crack by way of a “brute force” attack, a primitive method of cipher-cracking technically referred to as an exhaustive key search. It works by trying every possible number combination until the right key is discovered.
- 1-bit cipher: 2 possible combinations
- 2-bit cipher: 4 possible combinations
- 8-bit cipher: 256 possible combinations
- 16-bit cipher: 65,536 possible combinations
- 64-bit cipher: 1.8 x 10^19 possible combinations
- 128-bit cipher: 3.4 x 10^38 possible combinations
- 192-bit cipher: 6.2 x 10^57 possible combinations
- 256-bit cipher: 1.1 x 10^77 possible combinations
To fully appreciate this concept, consider the following:
- Fujitsu K, the fastest existing supercomputer in 2011, had a 10.51 petaflops peak speed. It would have taken the supercomputer 1.02 x 10^18 (one quintillion or one-billion billion) years to break into a 128-bit Advanced Encryption Standard (AES) key using a brute force attack. The universe, which is 13.75 billion years old, hasn’t even been around that long.
- The most powerful supercomputer in the world in 2017, with its 93.02 petaflops peak speed, would have taken 885 quadrillion years to crack the 128-bit AES key using a brute force attack.
- To crack a 256-bit cipher, the number of operations required by a supercomputer is 3.31 x 10^65, which is about the number of atoms in the universe.
VPN Encryption and VPN Protocols
A VPN protocol is a set of rules and instructions that two devices use to settle on a secure, encrypted connection. Commercial VPN services support a wide range of such VPN protocols, the most widely used being L2TP/IPSec, PPTP, SSTP, OpenVPN, and IKEv2. The industry standard VPN protocols for commercial VPN services is OpenVPN, but we’ll analyze each of the ones mentioned.
1. PPTP (Point-to-Point Tunneling Protocol)
- Easy to install
- Has a client built into almost all device platforms
- Not secure
- Easily blocked
- Has been compromised by the NSA
PPTP functions only as a VPN protocol, and it uses a range of authentication methods for security. For PPTP, commercial VPN providers typically use MS-CHAP v2 as the authentication method and Microsoft Point-to-Point Encryption (MPPE) as the encryption protocol.
Corporate VPN networks have since been using it as the standard protocol. Nearly all VPN-enabled devices and platforms support PPTP, which is easy to install, without having to set up additional software. For that reason, the protocol remains popular among commercial VPN services and business VPNs. Another plus for PPTP is that implementing it requires low computational overhead, meaning that it’s fast.
On the downside, however, PPTP offers absolutely no security. Even though it now uses only 128-bit encryption keys, experts have revealed its numerous security vulnerabilities since 1992 when it first came built into Windows 95 OSR2.
That the NSA cracks PPTP-encrypted communicated with ease comes as no surprise. Even more unsettling is the fact that the agency gathered massive amounts of older PPTP-encrypted data that was considered secure back then, and it would have no difficulty decrypting this legacy data too.
Avoid using the PPTP protocol unless it is necessitated by the need for compatibility.
2. L2TP/IPSec (Layer 2 Tunneling Protocol/IPSec)
- Easy to install
- Moderately secure
- Somewhat faster than OpenVPN
- Clients on all current device platforms
- Possibly weakened by the NSA (not proven)
- Might have been compromised by the NSA (not proven)
- Usually poorly implemented
- Some issues with restrictive firewalls
Nearly all VPN-capable devices and current operating systems have L2TP/IPSec built into it, meaning setting it up is just as quick and easy as PPTP. This protocol doesn’t encrypt and anonymize traffic, so it’s used in combination with IPSec authentication to create L2TP/IPSec. If a provider mentions L2TP or IPSec only, they are usually referring to L2TP/IPSec.
The protocol is compatible with AES and 3DES ciphers, but you’re not likely to come across 3DES nowadays because it’s vulnerable to Sweet32 and Meet-in-the-Middle attacks. The limit to the number of ports that L2TP/IPSec uses might present some problems, such as hitches when used under NAT firewalls and susceptibility to blocks.
L2TP/IPSec can be slow because it encapsulates data twice. However, it makes up for it by allowing multi-threading and encrypting/decrypting within the kernel, things that OpenVPN doesn’t do. That means that L2TP/IPSec is faster than OpenVPN, at least in theory.
Perhaps the most worrying issue with L2TP/IPSec is that VPN services tend to implement it poorly, using pre-shared keys (PSKs) which someone can easily download from their websites. Granted, AES encryption still secures your data even if the PSKs used for authentication are compromised.
The bottom line is that, provided pre-shared keys are not openly published, L2TP/IPSec is still considered adequately secure despite some issues which are by and large theoretical.
3. SSTP (Secure Socket Tunneling Protocol)
- Complete Windows integration
- Supported by Microsoft
- Highly secure
- Bypasses a majority of firewalls
- Microsoft-owned proprietary software
SSTP is like OpenVPN in that it uses SSL, meaning it gets around censorship using TCP port 443. It offers more stability than OpenVPN on Windows because it’s tightly integrated into the operating system.
The disadvantage of SSTP is that it is a Microsoft-owned proprietary standard, meaning the code cannot be scrutinized publicly. Furthermore, many people aren’t confident in the standard because Microsoft is known for cooperating with the NSA and there’s speculation that the company may have built possible backdoors into its platform.
First introduced in Windows Vista SP1, SSTP is now available for Mac OS X and Linux despite it being a platform tailored primarily for Windows.
Another concern is the vulnerability of SSL v.30 to “POODLE” attacks, which is why experts don’t recommend it. It’s not yet clear whether SSTP is affected by this, and that has further eroded confidence in the standard.
SSTP appears to be almost as good as OpenVPN on paper, but its credibility suffers because it’s a proprietary standard by Microsoft.
IKEv2 (Internet Key Exchange version 2)
- Stable, especially when reconnecting after a dropped connection or when switching a network
- Easy to install
- Secure (When used with AES)
- Also supported by Blackberry devices
- Can only be trusted with open source implementations
- Tricky to implement (potential development issues)
- Unsupported on several platforms
The development of IKEv2 was a joint effort by Cisco and Microsoft. In addition to Windows 7+ devices, IKEv2 is also supported by iOS and Blackberry devices.
Developers have built independent versions of IKEv2 for other operating systems, such as Linux, and a number of those versions are open source. As mentioned earlier, be wary of proprietary technology by Microsoft. However, you need not worry about the open source iterations of IKEv2.
Referred to as VPN Connect by Microsoft, this standard is highly effective at automatically reconnecting to a VPN in case of a temporary loss of the connection, such as when you enter and leave a train tunnel.
When it comes to changing networks, IKEv2 is highly resilient due to its support for the Mobility and Multihoming (MOBIKE) protocol. It is, therefore, the ideal standard for users who frequently migrate hotspots and often switch between mobile and home connections.
Lack of support on many platforms that are L2TP/IPSec means IKEv2 is not as common. Nonetheless, it is considered as good as, if not better than, L2TP/IPSec in terms of establishing/reestablishing a connection, speed/performance, and security.
In summary, this protocol is fast and secure. Thanks to its ability to easily reconnect to the Internet, IKEv2 is popular with mobile users. It’s the sole option available for Blackberry users. We recommend using the open source versions of the standard.
- Easy to configure
- Highly secure (When used with PFS)
- Bypasses firewalls
- Open source
- Requires third-party software
OpenVPN is an open source VPN protocol that uses TLS protocols and the OpenSSL library, among other technology, to provide a highly reliable and robust VPN solution. There are several reasons why it is the industry standard employed by commercial VPN providers.
The protocol can be used on any port, but it runs best on a UDP port. It’s also commonly run on TCP port 443, which is frequently employed for HTTPS traffic. OpenVPN is extremely difficult to block because it is hard to differentiate OpenVPN run over TCP port 443 with secure connections used by online retailers, email services, and banks.
This protocol is also advantageous because it uses the OpenSSL library, which supports a variety of ciphers. However, in practice, commercial VPN services use only AES and Blowfish ciphers. According to reports by Edward Snowden, it appears that provided it uses Perfect Forward Secrecy, OpenVPN has not been weakened or compromised by the NSA.
There are no known vulnerabilities that put users of OpenVPN at risk. Some vulnerabilities that made the protocol potential open to DDoS attacks were patched in OpenVPN 2.4.2.
Data security experts consider OpenVPN to be the most secure VPN protocol in the industry, which explains its wide support in the industry. It is, therefore, our most recommended protocol.