How much overhead does SSL impose?

joelneely_3525 0
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I know there's no single hard-and-fast answer, but is there a generic order-of-magnitude estimate approximation for the encryption overhead of SSL versus unencrypted socket communication? I'm talking only about the comm processing and wire time, not counting application-level processing.

Update

There is a question about HTTPS versus HTTP, but I'm interested in looking lower in the stack.

(I replaced the phrase "order of magnitude" to avoid confusion; I was using it as informal jargon rather than in the formal CompSci sense. Of course if I had meant it formally, as a true geek I would have been thinking binary rather than decimal! ;-)

Update

Per request in comment, assume we're talking about good-sized messages (range of 1k-10k) over persistent connections. So connection set-up and packet overhead are not significant issues.

overhead sockets ssl performance
3 Answers

Order of magnitude: zero.

In other words, you won't see your throughput cut in half, or anything like it, when you add TLS. Answers to the "duplicate" question focus heavily on application performance, and how that compares to SSL overhead. This question specifically excludes application processing, and seeks to compare non-SSL to SSL only. While it makes sense to take a global view of performance when optimizing, that is not what this question is asking.

The main overhead of SSL is the handshake. That's where the expensive asymmetric cryptography happens. After negotiation, relatively efficient symmetric ciphers are used. That's why it can be very helpful to enable SSL sessions for your HTTPS service, where many connections are made. For a long-lived connection, this "end-effect" isn't as significant, and sessions aren't as useful.

Here's an interesting anecdote. When Google switched Gmail to use HTTPS, no additional resources were required; no network hardware, no new hosts. It only increased CPU load by about 1%.

erickson_34740

I second @erickson: The pure data-transfer speed penalty is negligible. Modern CPUs reach a crypto/AES throughput of several hundred MBit/s. So unless you are on resource constrained system (mobile phone) TLS/SSL is fast enough for slinging data around.

But keep in mind that encryption makes caching and load balancing much harder. This might result in a huge performance penalty.

But connection setup is really a show stopper for many application. On low bandwidth, high packet loss, high latency connections (mobile device in the countryside) the additional roundtrips required by TLS might render something slow into something unusable.

For example we had to drop the encryption requirement for access to some of our internal web apps - they where next to unusable if used from china.

user_494070
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