The most computationally expensive part of an SSL session is the stage where the SSL server (usually an SSL webserver) software is required to decrypt the SSL session key (an asymmetric key) that has been sent to it from the SSL client (usually a web browser), this is known as the SSL handshake. Typically a hardware SSL accelerator will offload processing of the SSL handshake while leaving the server software to process the less intense symmetric cryptography of the actual SSL data exchange, but some accelerators act as a proxy handling all SSL operations and leaving the server seeing only plaintext connections