Google have recently announced that they are going to start reporting that SSL certificates that are signed with a SHA-1 Hash will be treated as having a lower security than those signed with newer, higher strength hashes such as SHA-256 or SHA-512.
Google’s announcement can be found here at http://googleonlinesecurity.blogspot.co.uk/2014/09/gradually-sunsetting-sha-1.html
Technically at the moment there isn’t anything really wrong with the SHA-1 hash function, but it is now quite old and is starting to show potential cracks. Hence the reason that the security industry is advising to move to something better. In this case SHA-256.
1. Generate a SSL Key File
Firstly you will need to generate a key file. The example below will generate a 2048 bit key file with a SHA-256 signature.
openssl genrsa -out key_name.key 2048
If you want extra security you could increase the bit lengths.
openssl genrsa -out key_name.key 4096
** Please note that both these examples will not add a password to the key file. To do that you will need to add -aes256 to the command.
2. Create a Certificate Signing Request (CSR)
This step will create the actually request file that you will submit to the Certificate Authority (CA) of your choice.
openssl req -out CSR.csr -key key_name.key -new -sha256
You can check that your Certificate Signing Request (CSR) has the correct signature by running the following.
openssl req -in CSR.csr -noout -text
It should display the following if the signature is correct.
Signature Algorithm: sha256WithRSAEncryption
3. Install the Certificate (CRT)
This step is very dependant of the software you use and I won’t really cover. All I will say is that these certificates are supported by a multitude of software, including Apache HTTPD and NGINX.
4. Test your installed Certificate
This step is extremely important and will show you any security problems with your SSL configuration.
Qualys have a free hosted service that tests the SSL configuration of Internet facing web servers for SSL issues. The sites tested are rated from A to F, and a report is generated. This report is really useful for tuning your SSL configuration.
The SSL Labs tests are regularly updated when new issues are discovered. This means that if your server is rated as A today, next week it maybe rated as C.