OpenVPN is a virtual private network (VPN) package for creating point-to-point encrypted tunnels between host computers. It was written by James Yonan.
It allows peers to authenticate to each other using a preshared private key, certificates, or username/password. It makes extensive use of the OpenSSL encryption library, and uses the SSLv3/TLSv1 protocol. It is available on Linux, xBSD, Mac OS X, and Windows 2000/XP. It offers a wealth of security and control features. It is not a "web-based" VPN, and is not compatible with IPsec or any other VPN package. The entire package consists of one binary for both client and server connections, an optional configuration file, and one or more key files depending on the authentication method used.
OpenVPN uses the OpenSSL library to provide encryption of both the data and control channels. It lets OpenSSL do all the encryption and authentication work, allowing OpenVPN to use all the ciphers available in the OpenSSL package. It can also use the HMAC packet authentication feature to add an additional layer of security to the connection (referred to as an "HMAC Firewall" by the creator). It can also use hardware acceleration to get better encryption performance.
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