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Understanding Digital Certificates and Pre-Shared Keys

 

 

A Pre-Shared Key (PSK) is a key both peers use to identify themselves to each other. If one pre-shared key is different from the other, then the authentication will not be successful. In a real world scenario you would specify this on a VPN Gateway at one site, such as a VPN device and then specify the exact same key on the other site’s VPN device. It is a way for a device to prove it is authorised by providing a Pre-Shared Key identical to the opposite peer in negotiation.

Within a VPN tunnel you would typically use either a Pre-Shared Key or use digital certificates to provide authenticity of each VPN device. Pre shared keys are easier to configure than digital certificates, and are typically used for small to medium sized businesses that require a VPN connection. You would usually create a PSK, which is made up of random characters, and this is usually agreed upon via the phone, using text messages, emails, or even in person when it's a high profile company that requires maximum security, so that it is not captured by anyone sniffing any of the technology mediums just mentioned.

The PSK would then be configured within VPN configuration, on both sides of the VPN tunnel. It is best practice that a VPN gateway uses long Pre-shared keys to eliminate chances of being hacked \ compromised, 10 plus characters is recommended. For large networks though, digital certificates should be implemented over Pre-Shared Keys as digital certificates are scalable and provide better security.

Also see PKI

Further Reading

Wikipedia's guide to Pre-shared Key