8

I wanted to know what steps are needed to get 100% on every category in ssllabs.com. I am aware that this could lead to problems in older systems, but I dont care.

My letsencrypt.org certificate uses 4096 bits. This is the best score I could get using the following config:

SSLCipherSuite AES256+EECDH:AES256+EDH:!aNULL
SSLHonorCipherOrder on
SSLProtocol all -TLSv1.1 -TLSv1 -SSLv3 -SSLv2

score before adding DHParameters

I read somewhere that the key exchange could be improved using a pregenerated dhparam file.

So I generated this file using openssl dhparam -out dhparam.pem 4096 (this took around a hour) and added it to my apache configuration using

SSLOpenSSLConfCmd DHParameters "/etc/ssl/certs/dhparam.pem"

but this results in the same score as before. So what am I missing here?

Full ssllabs.com result

  • 5
    Do not optimize for benchmarks. If you want to deploy the latest reasonably achievable security level, get an EC 384 bit certificate, roll out public key pinning and examine if SSLStrictSNIVHostCheck is useful to your setup. – anx Oct 10 '17 at 13:29
8

As of 2017-10, if you are using Diffie-Hellman, you ought to have both DH parameters and keys with equivalent 4096 bits RSA.

You are offering atleast one certificate for a 2048 bit key. You are also having unusual metadata in that certificate, check that (the default snake-oil certificate for saying "i dont serve non-sni clients" generally only has the host name in Common Name)

Edit: You will not be penalized in the SSL Labs rating for certificates that you exclusively offer no non-SNI clients. You will also not penalized for weak-keyed certificates you provide as part of your certificate chain to a known root.

You will find the full documentation on the rating on the ssllabs github account.

For suites that rely on DHE or ECDHE key exchange, the strength of DH parameters is taken into account when determining the strength of the handshake as a whole. Many servers that support DHE use DH parameters that provide 1024 bits of security. On such servers, the strength of the key exchange will never go above 1024 bits, even if the private key is stronger (usually 2048 bits).

The rating guide doesnt say, but i was able to confirm that you cannot get rating 100 if your server prefers secp256v1 (equivalent to 3k bits RSA) while offering ECDHE ciphers that could be using secp384v1 (equivalent to 7k bits RSA).

Chrome 57 / Win 7
R
RSA 4096 (SHA256)
TLS 1.2 > http/1.1
TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384   
ECDH secp256r1  FS

The Apache manual does list one option to force this (simply ordering the Curves parameter by strength appears to be insufficient)

Compatibility: Available in httpd 2.4.8 and later, if using OpenSSL 1.0.2 or later SSLOpenSSLConfCmd ECDHParameters brainpoolP256r1

https://httpd.apache.org/docs/2.4/mod/mod_ssl.html#sslopensslconfcmd

If you name a curve here that can be considered equivalent to RSA >=4096 bits, ssl labs will be using that for your ECDHE ciphers - listing you the clients that can no longer succeed a handshake with your server because they do not support that curve.

secp384r1 will grant 100%

Carefully investigate the list of browsers you wish to support, choosing a non-standard EC curve will make your site inaccessible by many older browsers!

| improve this answer | |
  • I am not sure why my apache keeps sending out my "localhost" certificate. I am using virtualhosts and if a domain is not found in the config, the first one is selected instead. So I made a "fallback" virtualhost first (this one has the localhost cert). – feedc0de Oct 11 '17 at 14:53
  • I just replaced the snakeoil one with a 16384bit long one. But still on change in points... – feedc0de Oct 11 '17 at 15:04

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