SSL acceleration

SSL acceleration is a method of offloading the processor-intensive public key encryption algorithms involved in SSL transactions to a hardware accelerator.

Typically this means having a separate card that plugs into a PCI slot in a computer that contains one or more co-processors able to handle much of the SSL processing.

SSL accelerators may use off the shelf CPUs, but most use custom ASICs and RISC chips to do most of the difficult computational work.

How it works

The most computationally expensive part of an SSL session is the SSL handshake, where the SSL server (usually an SSL webserver) and the SSL client (usually a web browser) agree on a number of parameters that establish the security of the connection.

Part of the role of the SSL handshake is to agree on session keys (symmetric keys, used for the duration of a given session), but the encryption and signature of the SSL handshake messages itself is done using asymmetric keys (contained in the certificates), which requires more computational power than the symmetric cryptography used for the encryption/decryption of the session data.

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 unencrypted connections.

Because TLS is essentially an updated form of SSL, TLS session...
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