In computer security, a key server is a computer -- typically running special software -- which provides keys to users or other programs. The users / programs can be working in that or another networked computer.

The keys provided are nearly always provided as a part of a cryptographically protected identity certificate containing not only a key but also 'entity' information about the owner of that key. The certificate is usually in a standard format, for instance X.509 or PKCS. Further, the key is almost always a public key for use with an asymmetric key encryption algorithm.

The most important universally accessible key servers are those computers, located around the world, which store and provide PGP (or GPG) keys over the Internet for users of that crypto system. In this instance, the computers can be, and are, mostly run by individuals as a pro bono service, facilitating the web of trust model PGP uses. There are also multiple proprietary PKI systems which maintain key servers for their users; only their users are likely to be aware of them at all.