Configuring SSL on Apache 2.4

Configuring a modern web server to employ strong encryption and forward secrecy doesn't have to be hard. There is excellent documentation from Mozilla and from the OWASP.

Obtaining an SSL certificate

One major stumbling block is where to obtain an SSL certificate. In the future, this should hopefully be easy with Let's Encrypt. Until that is actually functional, StartSSL offers free SSL certificates. The process takes a bit of patience, but it's not difficult. There's also a StartSSL HOWTO from h-online.com.

While I've used StartSSL in the past, I had some trouble with them because 10 years after I registered greek0.net, someone grabbed greekO.net and StartSSL was alleging I was trying to mislead users?! So that was the end of my business with them...

I've now switched to Comodo's Positive SSL Certificate, which I like for a couple of reasons:

  • it lasts for 3 years,
  • it's really uncomplicated, and
  • it's crazy cheap: 7.45$ per year.

The process of getting the cert from them was super easy, simpler than StartSSL. About 3 hours from going to their website to having the certificate installed on my server, with most of it waiting email verifications. Credit card payment was quick and easy. 10/10, would buy again :-)

Apache configuration

With the certificate acquisition out of the way, here are the juicy bits from my Apache config.

mod_ssl config:

# Enable only cyphers that support forward secrecy.
# See these two links for reference:
# https://stackoverflow.com/questions/17308690
# https://wiki.mozilla.org/Security/Server_Side_TLS#Non-Backward_Compatible_Ciphersuite
SSLCipherSuite ECDHE-RSA-AES128-GCM-SHA256:ECDHE-ECDSA-AES128-GCM-SHA256:ECDHE-RSA-AES256-GCM-SHA384:ECDHE-ECDSA-AES256-GCM-SHA384:DHE-RSA-AES128-GCM-SHA256:DHE-DSS-AES128-GCM-SHA256:kEDH+AESGCM:ECDHE-RSA-AES128-SHA256:ECDHE-ECDSA-AES128-SHA256:ECDHE-RSA-AES128-SHA:ECDHE-ECDSA-AES128-SHA:ECDHE-RSA-AES256-SHA384:ECDHE-ECDSA-AES256-SHA384:ECDHE-RSA-AES256-SHA:ECDHE-ECDSA-AES256-SHA:DHE-RSA-AES128-SHA256:DHE-RSA-AES128-SHA:DHE-DSS-AES128-SHA256:DHE-RSA-AES256-SHA256:DHE-DSS-AES256-SHA:DHE-RSA-AES256-SHA:!aNULL:!eNULL:!EXPORT:!DES:!RC4:!3DES:!MD5:!PSK

# Use server priorities for cipher algorithm choice.
SSLHonorCipherOrder on

# With Apache 2.4, SSLv2 is gone and only SSLv3 and TLSv* are supported.
# Disable SSLv3, all TLS protocols are OK.
SSLProtocol all -SSLv3

# Enable OCSP stapling
# With this, the client can verify that our certificate isn't revoked
# without having to query an external OCSP service.
SSLUseStapling On
SSLStaplingCache shmcb:${APACHE_RUN_DIR}/ssl_stapling(32768)

The per-site configuration:

SSLEngine On
SSLCertificateKeyFile   /path/to/serverkey.key    # The private server key.
SSLCertificateFile      /path/to/certificate.crt  # The certificate provided by CA.
SSLCertificateChainFile /path/to/cert-bundle      # A separate download from your CA.


# Use a customized prime group for DH key exchange (vs Logjam attack).
# Generate a DH group file with:
#    openssl dhparam -out dhparams.pem 2048
#
# Newer Apache versions support the following command to set the dhparams:
SSLOpenSSLConfCmd DHParameters "/path/to/dhparams.pem"

# If Apache reports an error for the above line, remove it and include
# the dhparams in the certificate:
#   cat <CERT>.crt dhparams.pem > cert-with-dhparams.crt
#   SSLCertificateFile cert-with-dhparams.crt


# HSTS: Force browsers to require SSL for this domain for the next year.
# Down-grade to HTTP will cause browsers to abort with a security error.
Header always set Strict-Transport-Security "max-age=31536000; includeSubDomains; preload"


# HPKP: Pin the current key for the next two months.
# Generate hash using:
#   openssl rsa -in <serverkey>.key -outform der -pubout | \
#   openssl dgst -sha256 -binary | openssl enc -base64
#
# You ideally want to generate a backup key and include that here as well,
# in case the primary key is lost or compromised.
# Also note the implications for key rollover.
# See: https://developer.mozilla.org/en-US/docs/Web/Security/Public_Key_Pinning
Header always set Public-Key-Pins "pin-sha256=\"<HASH>\"; max-age=5184000; includeSubDomains"


# Disable compression to avoid BREACH HTTPS/SSL attack.
<Location />
    SetEnv no-gzip
</Location>

That should cover the basics.

Testing

As for SSL connection testing, I found the Qualys SSL Labs Test helpful. It shows what browsers (browser versions) will get which encryption quality (forward secrecy or not) and highlights common problems such as certificate chain issues.

Hope this helps someone out there!