[Cryptography] Cycles overhead for TLS

[Bill Cox]

On Wed, Sep 23, 2015 at 2:59 PM, Ryan Carboni <ryacko at gmail.com> wrote:

> I'm not sure so these are rough guesses, but:
>
> 5 cycles per byte for TCP overhead.
> 100,000 cycles for ECC key exchange.
> Several thousand cycles for PRF key generation.
> 10 to 1 cycles per byte for symmetric crypto
> Average webpage size is 1 megabyte, so maybe average TLS connection
> eventually transfers 15 megabytes.
>
> I think any performance improvements in asymmetric and symmetric
> cryptography would be minor compared to TCP overhead.
>
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Not a bad WAG.  It's probably a fairly minor point, but you did not include
the extra round-trips for the TLS handshake, which likely dwarfs the
overhead for key agreement.  QUIC, a new protocol with 0 round trips for
most handshakes, improves the network efficiency overall something like 3%,
just for the improved handshake.  The extra round-trip is the overhead we
need to kill in TLS.  They're working on it for TLS 1.3, I think.

BIll
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