HTTPS vs HTTP speed comparison

Asked 2009-09-23T21:37:12.417

Update 2013-04-25:

This is a popular question that is getting more attention than it probably should. In order to stop the spread of misinformation please read the following paragraphs and the accompanying article first:

Speed should not be a factor in deciding whether to use HTTPS or HTTP. If you need HTTPS for any part of your site (log-ins, registration, credit cards, etc), you absolutely need HTTPS for all of it, all the time.

Please read SSL is not about encryption by Troy Hunt for the reasons why.

I'm considered running my entire e-commerce website under https. I decided to run a crude benchmark to measure the download time of a 156KB image through https vs http because I had read that https is burdened with additional overhead from the encryption process.

Benchmark was performed using Firefox's Firebug simply by transcribing the "Waiting" and "Receiving" times (all other times are 0) to Excel from the Net panel when downloading the image from an empty cache.

My results were unexpected:

http: 11.233 seconds
Waiting     Receiving   Total 
1.56        0.88        2.44 
1.55        0.101       1.651 
1.53        0.9         2.43 
1.71        0.172       1.882 
1.9         0.93        2.83 

https: 9.936 seconds
Waiting     Receiving  Total
0.867       1.59       2.457
0.4         1.67       2.07
0.277       1.5        1.777
0.536       1.29       1.826
0.256       1.55       1.806

[Obvious] Observations from benchmark:

The server response is faster but the download time is slower for https than http.
https is faster overall by a significant amount (~10%).

Can anyone explain why this would happen?
Do you think a d

http ssl https benchmarking download-speed

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2 Answers

18

If you look at your times http has bigger waiting time and smaller receiving time. https on the other hand has smaller waiting time and bigger receiving time. I would interpret this as the http port on the shared hosting server is more busy, thus a request stays longer in the queue until is accepted by the server. Once accepted, the requests is transferred faster than https. On the https port there is less traffic on the server so the request is serviced faster but takes longer to transfer.

For any https vs. http comparison you'll have to take into account the bigger time to handshake each request for https compared with http. You should see worsening when doing many small requests.

answered 2009-09-23T21:50:20.753

2

https works as follows: First a 4-way handshake is performed (at least if i remember correctly it was 4way), here client and server agree on the symmetric encryption algorithm used later on and exchange certificates (containing public keys).

They exchange a session (key for the symmetric enc later) using publickey crypto.

Now they send messages encrypted with the session key and some encryption algorithm (3des, aes, rc4, rc5, etc). Since symmetric encryptions are not that expensive operations the differences in download time are not that big.

The fact that you have less waiting time is because you probably have less traffic on http port or less traffic at the time you did the https request compared to the http requests.

So to optimize performance you should use as few https connections as possible since the handshake is a relative expensive procedure.

answered 2009-09-23T21:59:45.180

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