Preshared

Preshared refers to a pre-shared key or pre-shared secret, a secret value that is manually configured on all communicating endpoints before any secure session begins. It is a simple form of symmetric authentication and key establishment used to enable encrypted communication without a public key infrastructure.

The term is commonly encountered in wireless networking and virtual private networks. In wireless networks, WPA-PSK and WPA2-PSK use a preshared key to derive encryption keys for securing traffic between clients and the access point. In VPNs, IPsec and some OpenVPN configurations may rely on a preshared secret to authenticate the tunnel endpoints and derive session keys. Preshared keys are often chosen by an administrator and distributed to each authenticated device in a trusted manner.

Security considerations are central to the use of preshared keys. The distribution method must be secure, and the key should be strong, random, and of sufficient length to resist brute force or dictionary attacks. A compromised preshared key can allow an attacker to join the network or decrypt traffic on all devices using that key. PSKs generally do not support per-user or per-device authentication, making revocation and rotation more challenging in larger environments.

Compared with certificate-based or other public-key infrastructures, preshared keys offer simplicity and minimal setup but poorer scalability and weaker security guarantees in larger or more dynamic deployments. Best practices recommend using strong random keys, minimizing distribution exposure, rotating keys when compromise is suspected, and preferring certificate-based methods for enterprise networks or environments requiring finer-grained access control.