Why https is slow and what can I do?
I needed to look after how https works on my hobby project, I read through the technical specification (It’s in RFC2246) and here are my consequences.
I used an Amazon micro instance with an unmodified Ubuntu 12.10 installation for my test and time results.
In order to start a TLS connection, the browser after requested the DNS record for the domain, needs done the following steps before any data been received (it’s from RFC2246)
Client Server
ClientHello -------->
ServerHello
Certificate*
ServerKeyExchange*
CertificateRequest*
<-------- ServerHelloDone
Certificate*
ClientKeyExchange
CertificateVerify*
[ChangeCipherSpec]
Finished -------->
[ChangeCipherSpec]
<-------- Finished
Application Data <-------> Application Data
Fig. 1 - Message flow for a full handshake
The easiest demonstration can be made simply in an incognito window in Chrome and see the Network traffic when I load a small image from the server. First time I loaded it through http protocoll so I can compare the results:
The image was loaded in 384ms. We have an apache overhead, almost the half of the download time, but because Ubuntu is using KeepAlive directive for apache, this overhead is much smaller for the second request.
Go ahead to the https protocoll and see the results. Same file, same server, new incognito window for a fresh connection:
So here is it. 521ms just for the TLS handshake before any communication been made with the webserver. Then we have the apache overhead again (302ms) and we have received the file very quickly.
Let’s see it for the second time using the still active connection (KeepAlive directive in the Apache configuration):
Lovely. Because it does not connecting again to the server, it’s much faster. Note in Ubuntu, Keepalive is set to 60s by default, it’s far enough to download a whole frontpage with slow connections as well. Thus the benefits of the KeepAlive directive is much bigger than for http protocol. Most users will also use the same connection for the next click as they always navigating to the next page in the first 10 seconds.
How can I make it faster?
https is not just slow. In a high traffic website it eats a lot of CPU. Some SSL providers are faster, others have more security. You probably using only one provider on the same server. In a default Ubuntu installation, the openssl package supports every cryptographic algorithm. This means the library has a lot of precompiled algorithm in it and It’s loaded every time when a connection should be established. So it’s an evidence in a high traffic system to take care about it.
To list all the available cryptographic algorithms perform this command:
openssl ciphers -v 'ALL:RC4+RSA:+HIGH:+MEDIUM:+LOW:+SSLv2:+EXP'My result is the following:
ECDHE-RSA-AES256-GCM-SHA384 TLSv1.2 Kx=ECDH Au=RSA Enc=AESGCM(256) Mac=AEAD ECDHE-ECDSA-AES256-GCM-SHA384 TLSv1.2 Kx=ECDH Au=ECDSA Enc=AESGCM(256) Mac=AEAD ECDHE-RSA-AES256-SHA384 TLSv1.2 Kx=ECDH Au=RSA Enc=AES(256) Mac=SHA384 ECDHE-ECDSA-AES256-SHA384 TLSv1.2 Kx=ECDH Au=ECDSA Enc=AES(256) Mac=SHA384 ECDHE-RSA-AES256-SHA SSLv3 Kx=ECDH Au=RSA Enc=AES(256) Mac=SHA1 ECDHE-ECDSA-AES256-SHA SSLv3 Kx=ECDH Au=ECDSA Enc=AES(256) Mac=SHA1 SRP-DSS-AES-256-CBC-SHA SSLv3 Kx=SRP Au=DSS Enc=AES(256) Mac=SHA1 SRP-RSA-AES-256-CBC-SHA SSLv3 Kx=SRP Au=RSA Enc=AES(256) Mac=SHA1 DHE-DSS-AES256-GCM-SHA384 TLSv1.2 Kx=DH Au=DSS Enc=AESGCM(256) Mac=AEAD DHE-RSA-AES256-GCM-SHA384 TLSv1.2 Kx=DH Au=RSA Enc=AESGCM(256) Mac=AEAD DHE-RSA-AES256-SHA256 TLSv1.2 Kx=DH Au=RSA Enc=AES(256) Mac=SHA256 DHE-DSS-AES256-SHA256 TLSv1.2 Kx=DH Au=DSS Enc=AES(256) Mac=SHA256 DHE-RSA-AES256-SHA SSLv3 Kx=DH Au=RSA Enc=AES(256) Mac=SHA1 DHE-DSS-AES256-SHA SSLv3 Kx=DH Au=DSS Enc=AES(256) Mac=SHA1 DHE-RSA-CAMELLIA256-SHA SSLv3 Kx=DH Au=RSA Enc=Camellia(256) Mac=SHA1 DHE-DSS-CAMELLIA256-SHA SSLv3 Kx=DH Au=DSS Enc=Camellia(256) Mac=SHA1 AECDH-AES256-SHA SSLv3 Kx=ECDH Au=None Enc=AES(256) Mac=SHA1 SRP-AES-256-CBC-SHA SSLv3 Kx=SRP Au=None Enc=AES(256) Mac=SHA1 ADH-AES256-GCM-SHA384 TLSv1.2 Kx=DH Au=None Enc=AESGCM(256) Mac=AEAD ADH-AES256-SHA256 TLSv1.2 Kx=DH Au=None Enc=AES(256) Mac=SHA256 ADH-AES256-SHA SSLv3 Kx=DH Au=None Enc=AES(256) Mac=SHA1 ADH-CAMELLIA256-SHA SSLv3 Kx=DH Au=None Enc=Camellia(256) Mac=SHA1 ECDH-RSA-AES256-GCM-SHA384 TLSv1.2 Kx=ECDH/ECDSA Au=ECDH Enc=AESGCM(256) Mac=AEAD ECDH-ECDSA-AES256-GCM-SHA384 TLSv1.2 Kx=ECDH/ECDSA Au=ECDH Enc=AESGCM(256) Mac=AEAD ECDH-RSA-AES256-SHA384 TLSv1.2 Kx=ECDH/ECDSA Au=ECDH Enc=AES(256) Mac=SHA384 ECDH-ECDSA-AES256-SHA384 TLSv1.2 Kx=ECDH/ECDSA Au=ECDH Enc=AES(256) Mac=SHA384 ECDH-RSA-AES256-SHA SSLv3 Kx=ECDH/RSA Au=ECDH Enc=AES(256) Mac=SHA1 ECDH-ECDSA-AES256-SHA SSLv3 Kx=ECDH/ECDSA Au=ECDH Enc=AES(256) Mac=SHA1 AES256-GCM-SHA384 TLSv1.2 Kx=RSA Au=RSA Enc=AESGCM(256) Mac=AEAD AES256-SHA256 TLSv1.2 Kx=RSA Au=RSA Enc=AES(256) Mac=SHA256 AES256-SHA SSLv3 Kx=RSA Au=RSA Enc=AES(256) Mac=SHA1 CAMELLIA256-SHA SSLv3 Kx=RSA Au=RSA Enc=Camellia(256) Mac=SHA1 PSK-AES256-CBC-SHA SSLv3 Kx=PSK Au=PSK Enc=AES(256) Mac=SHA1 ECDHE-RSA-DES-CBC3-SHA SSLv3 Kx=ECDH Au=RSA Enc=3DES(168) Mac=SHA1 ECDHE-ECDSA-DES-CBC3-SHA SSLv3 Kx=ECDH Au=ECDSA Enc=3DES(168) Mac=SHA1 SRP-DSS-3DES-EDE-CBC-SHA SSLv3 Kx=SRP Au=DSS Enc=3DES(168) Mac=SHA1 SRP-RSA-3DES-EDE-CBC-SHA SSLv3 Kx=SRP Au=RSA Enc=3DES(168) Mac=SHA1 EDH-RSA-DES-CBC3-SHA SSLv3 Kx=DH Au=RSA Enc=3DES(168) Mac=SHA1 EDH-DSS-DES-CBC3-SHA SSLv3 Kx=DH Au=DSS Enc=3DES(168) Mac=SHA1 AECDH-DES-CBC3-SHA SSLv3 Kx=ECDH Au=None Enc=3DES(168) Mac=SHA1 SRP-3DES-EDE-CBC-SHA SSLv3 Kx=SRP Au=None Enc=3DES(168) Mac=SHA1 ADH-DES-CBC3-SHA SSLv3 Kx=DH Au=None Enc=3DES(168) Mac=SHA1 ECDH-RSA-DES-CBC3-SHA SSLv3 Kx=ECDH/RSA Au=ECDH Enc=3DES(168) Mac=SHA1 ECDH-ECDSA-DES-CBC3-SHA SSLv3 Kx=ECDH/ECDSA Au=ECDH Enc=3DES(168) Mac=SHA1 DES-CBC3-SHA SSLv3 Kx=RSA Au=RSA Enc=3DES(168) Mac=SHA1 PSK-3DES-EDE-CBC-SHA SSLv3 Kx=PSK Au=PSK Enc=3DES(168) Mac=SHA1 ECDHE-RSA-AES128-GCM-SHA256 TLSv1.2 Kx=ECDH Au=RSA Enc=AESGCM(128) Mac=AEAD ECDHE-ECDSA-AES128-GCM-SHA256 TLSv1.2 Kx=ECDH Au=ECDSA Enc=AESGCM(128) Mac=AEAD ECDHE-RSA-AES128-SHA256 TLSv1.2 Kx=ECDH Au=RSA Enc=AES(128) Mac=SHA256 ECDHE-ECDSA-AES128-SHA256 TLSv1.2 Kx=ECDH Au=ECDSA Enc=AES(128) Mac=SHA256 ECDHE-RSA-AES128-SHA SSLv3 Kx=ECDH Au=RSA Enc=AES(128) Mac=SHA1 ECDHE-ECDSA-AES128-SHA SSLv3 Kx=ECDH Au=ECDSA Enc=AES(128) Mac=SHA1 SRP-DSS-AES-128-CBC-SHA SSLv3 Kx=SRP Au=DSS Enc=AES(128) Mac=SHA1 SRP-RSA-AES-128-CBC-SHA SSLv3 Kx=SRP Au=RSA Enc=AES(128) Mac=SHA1 DHE-DSS-AES128-GCM-SHA256 TLSv1.2 Kx=DH Au=DSS Enc=AESGCM(128) Mac=AEAD DHE-RSA-AES128-GCM-SHA256 TLSv1.2 Kx=DH Au=RSA Enc=AESGCM(128) Mac=AEAD DHE-RSA-AES128-SHA256 TLSv1.2 Kx=DH Au=RSA Enc=AES(128) Mac=SHA256 DHE-DSS-AES128-SHA256 TLSv1.2 Kx=DH Au=DSS Enc=AES(128) Mac=SHA256 DHE-RSA-AES128-SHA SSLv3 Kx=DH Au=RSA Enc=AES(128) Mac=SHA1 DHE-DSS-AES128-SHA SSLv3 Kx=DH Au=DSS Enc=AES(128) Mac=SHA1 DHE-RSA-CAMELLIA128-SHA SSLv3 Kx=DH Au=RSA Enc=Camellia(128) Mac=SHA1 DHE-DSS-CAMELLIA128-SHA SSLv3 Kx=DH Au=DSS Enc=Camellia(128) Mac=SHA1 AECDH-AES128-SHA SSLv3 Kx=ECDH Au=None Enc=AES(128) Mac=SHA1 SRP-AES-128-CBC-SHA SSLv3 Kx=SRP Au=None Enc=AES(128) Mac=SHA1 ADH-AES128-GCM-SHA256 TLSv1.2 Kx=DH Au=None Enc=AESGCM(128) Mac=AEAD ADH-AES128-SHA256 TLSv1.2 Kx=DH Au=None Enc=AES(128) Mac=SHA256 ADH-AES128-SHA SSLv3 Kx=DH Au=None Enc=AES(128) Mac=SHA1 ADH-CAMELLIA128-SHA SSLv3 Kx=DH Au=None Enc=Camellia(128) Mac=SHA1 ECDH-RSA-AES128-GCM-SHA256 TLSv1.2 Kx=ECDH/ECDSA Au=ECDH Enc=AESGCM(128) Mac=AEAD ECDH-ECDSA-AES128-GCM-SHA256 TLSv1.2 Kx=ECDH/ECDSA Au=ECDH Enc=AESGCM(128) Mac=AEAD ECDH-RSA-AES128-SHA256 TLSv1.2 Kx=ECDH/ECDSA Au=ECDH Enc=AES(128) Mac=SHA256 ECDH-ECDSA-AES128-SHA256 TLSv1.2 Kx=ECDH/ECDSA Au=ECDH Enc=AES(128) Mac=SHA256 ECDH-RSA-AES128-SHA SSLv3 Kx=ECDH/RSA Au=ECDH Enc=AES(128) Mac=SHA1 ECDH-ECDSA-AES128-SHA SSLv3 Kx=ECDH/ECDSA Au=ECDH Enc=AES(128) Mac=SHA1 AES128-GCM-SHA256 TLSv1.2 Kx=RSA Au=RSA Enc=AESGCM(128) Mac=AEAD AES128-SHA256 TLSv1.2 Kx=RSA Au=RSA Enc=AES(128) Mac=SHA256 AES128-SHA SSLv3 Kx=RSA Au=RSA Enc=AES(128) Mac=SHA1 CAMELLIA128-SHA SSLv3 Kx=RSA Au=RSA Enc=Camellia(128) Mac=SHA1 PSK-AES128-CBC-SHA SSLv3 Kx=PSK Au=PSK Enc=AES(128) Mac=SHA1 DHE-RSA-SEED-SHA SSLv3 Kx=DH Au=RSA Enc=SEED(128) Mac=SHA1 DHE-DSS-SEED-SHA SSLv3 Kx=DH Au=DSS Enc=SEED(128) Mac=SHA1 ADH-SEED-SHA SSLv3 Kx=DH Au=None Enc=SEED(128) Mac=SHA1 SEED-SHA SSLv3 Kx=RSA Au=RSA Enc=SEED(128) Mac=SHA1 IDEA-CBC-SHA SSLv3 Kx=RSA Au=RSA Enc=IDEA(128) Mac=SHA1 ECDHE-RSA-RC4-SHA SSLv3 Kx=ECDH Au=RSA Enc=RC4(128) Mac=SHA1 ECDHE-ECDSA-RC4-SHA SSLv3 Kx=ECDH Au=ECDSA Enc=RC4(128) Mac=SHA1 AECDH-RC4-SHA SSLv3 Kx=ECDH Au=None Enc=RC4(128) Mac=SHA1 ADH-RC4-MD5 SSLv3 Kx=DH Au=None Enc=RC4(128) Mac=MD5 ECDH-RSA-RC4-SHA SSLv3 Kx=ECDH/RSA Au=ECDH Enc=RC4(128) Mac=SHA1 ECDH-ECDSA-RC4-SHA SSLv3 Kx=ECDH/ECDSA Au=ECDH Enc=RC4(128) Mac=SHA1 RC4-SHA SSLv3 Kx=RSA Au=RSA Enc=RC4(128) Mac=SHA1 RC4-MD5 SSLv3 Kx=RSA Au=RSA Enc=RC4(128) Mac=MD5 PSK-RC4-SHA SSLv3 Kx=PSK Au=PSK Enc=RC4(128) Mac=SHA1 EDH-RSA-DES-CBC-SHA SSLv3 Kx=DH Au=RSA Enc=DES(56) Mac=SHA1 EDH-DSS-DES-CBC-SHA SSLv3 Kx=DH Au=DSS Enc=DES(56) Mac=SHA1 ADH-DES-CBC-SHA SSLv3 Kx=DH Au=None Enc=DES(56) Mac=SHA1 DES-CBC-SHA SSLv3 Kx=RSA Au=RSA Enc=DES(56) Mac=SHA1 DES-CBC3-MD5 SSLv2 Kx=RSA Au=RSA Enc=3DES(168) Mac=MD5 IDEA-CBC-MD5 SSLv2 Kx=RSA Au=RSA Enc=IDEA(128) Mac=MD5 RC2-CBC-MD5 SSLv2 Kx=RSA Au=RSA Enc=RC2(128) Mac=MD5 RC4-MD5 SSLv2 Kx=RSA Au=RSA Enc=RC4(128) Mac=MD5 DES-CBC-MD5 SSLv2 Kx=RSA Au=RSA Enc=DES(56) Mac=MD5 EXP-EDH-RSA-DES-CBC-SHA SSLv3 Kx=DH(512) Au=RSA Enc=DES(40) Mac=SHA1 export EXP-EDH-DSS-DES-CBC-SHA SSLv3 Kx=DH(512) Au=DSS Enc=DES(40) Mac=SHA1 export EXP-ADH-DES-CBC-SHA SSLv3 Kx=DH(512) Au=None Enc=DES(40) Mac=SHA1 export EXP-DES-CBC-SHA SSLv3 Kx=RSA(512) Au=RSA Enc=DES(40) Mac=SHA1 export EXP-RC2-CBC-MD5 SSLv3 Kx=RSA(512) Au=RSA Enc=RC2(40) Mac=MD5 export EXP-ADH-RC4-MD5 SSLv3 Kx=DH(512) Au=None Enc=RC4(40) Mac=MD5 export EXP-RC4-MD5 SSLv3 Kx=RSA(512) Au=RSA Enc=RC4(40) Mac=MD5 export EXP-RC2-CBC-MD5 SSLv2 Kx=RSA(512) Au=RSA Enc=RC2(40) Mac=MD5 export EXP-RC4-MD5 SSLv2 Kx=RSA(512) Au=RSA Enc=RC4(40) Mac=MD5 export
That’s a lot. 9 of them are marked as ‘export’, that means it was used in the past for the US cryptographic algorithm exportation policy and was abandoned years ago because they are not safe. None of the modern SSL providers encrypting their SSL’s with them these days. Let’s see which ones are required and which ones can be removed.
Let’s do some benchmark on every protocol. Fortunately we have a nice command to do this, but it will take 20 minutes and causing high server load:
openssl speedIt’s a big task to remove all the non required ones, but here is a simple Apache directive only for the purpose to pass the ScanAlert scan (just found it on Google:
SSLCipherSuite ALL:!ADH:!NULL:!EXP:!SSLv2:!LOW:!MEDIUM:RC4+RSA:+HIGHThis code should be in ssl.conf in a default container labeled as <VirtualHost default:443>. Of course in order to work this directive in other virtualhosts using the non default IP address, should be repeated in the virtualhost file as well.
Always provide an intermediate certificate. It’s easy. When the intermediate is not available from your server the browser will block the connection until it is downloaded from the provider. But for example, Internet Explorer will not do this and it will display the connection as unsafe.
CDN’s with a lot of hostnames: If you have more than one CDN, it means ~400ms download time for every hostname. So if you need a CDN, it’s better to use only one.
Activate KeepAlive if it’s disabled. It has a lot of benefit especially for https.
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