What is a JKS File?

Taken from: https://en.wikipedia.org/wiki/Java_KeyStore

A Java KeyStore (JKS) is a repository of security certificates – either authorization certificates or public key certificates – plus corresponding private keys, used for instance in SSL encryption.

Basically, applications like Presto use JKS files to enable them to do Transport Layer Security (TLS).

How Do You Create One?

As an example, Presto, a common big-data query tool, uses JKS for both secure internal and external communication.  At this link https://prestosql.io/docs/current/security/internal-communication.html they show you how to create one.

Here is an excerpt.  Note that you must make sure you replace *.example.com with the domain you will host the service using the JKS file on or it will not work.  Certificates are domain specific.

keytool -genkeypair -alias example.com -keyalg RSA \
    -keystore keystore.jks
Enter keystore password:
Re-enter new password:
What is your first and last name?
  [Unknown]:  *.example.com
What is the name of your organizational unit?
  [Unknown]:
What is the name of your organization?
  [Unknown]:
What is the name of your City or Locality?
  [Unknown]:
What is the name of your State or Province?
  [Unknown]:
What is the two-letter country code for this unit?
  [Unknown]:
Is CN=*.example.com, OU=Unknown, O=Unknown, L=Unknown, ST=Unknown, C=Unknown correct?
  [no]:  yes

Enter key password for <presto>
        (RETURN if same as keystore password):

Pit Fall! – 90 Day Expiry Date – Change It?

Now… here’s a fun pitfall.  Certificates are made with an expiry date and have to be reissued periodically (for security reasons).  The default expiry date for JKS is 90 days.

https://docs.oracle.com/javase/tutorial/security/toolsign/step3.html

This certificate will be valid for 90 days, the default validity period if you don’t specify a –validity option.

This is fine on a big managed service with lots of attention.  But if you’re just TLS securing an internal app not many people see, you will probably forget to rotate it or neglect to set up appropriate automation.  Then, when it expires, things will break.

Now… for security reasons you generally shouldn’t set too high a value for certificate expiry time.  But for example purposes, here is how you would set it to 10 years.

keytool -genkeypair -alias example.com -keyalg RSA \
    -keystore keystore.jks -validity 3650

Determine Expiry Date

If you have a JKS file that you are using for your application and you are not sure when it expires, here’s a command that you can use:

keytool -list -v -keystore keystore.jks

This will output different things based on where your key store came from.  E.g. you will probably see more interesting output from a real SSL cert than you will from a self-signed one created like we did above.

In any case, you will clearly see a line in the large output from this command that says something like this:

Valid from: Fri Jul 12 01:27:21 UTC 2019 until: Thu Oct 10 01:27:21 UTC 2019

Note that in this case, it is just valid for 3 months.  Be careful when looking at this output because you may find multiple expiry dates in the output for different components of the JKS file.  You need to make sure you read the right one.  Though, chances are that the one on your domain will be the one that expires earliest anyway.