How to Override Java Security Configuration per JVM Instance

 Lately I encountered a configuration tweak I was not aware of, the problem: I had a single Java installation on a Linux machine from which I had to start two JVM instances - each using a different set of JCE providers. A reminder: the JVM loads its security configuration, including the JCE providers list, from a master security properties file within the JRE folder (JRE_HOME/lib/security/java.security), the location of that file is fixed in the JVM and cannot be modified. Going over the documentation (not too much helpful, I must admit) and the code (more helpful, look for Security.java, for example here) reveled the secret.

security.overridePropertiesFile

It all starts within the default java.security file provided with the JVM, looking at it we will find the following (somewhere around the middle of the file)

#
# Determines whether this properties file can be appended to
# or overridden on the command line via -Djava.security.properties
#
security.overridePropertiesFile=true

If the overridePropertiesFile doesn’t equal to true we can stop here - the rest of this article is irrelevant (unless we have the option to change it – but I didn’t have that). Lucky to me by default it does equal to true.

java.security.properties

Next step, the interesting one, is to override or append configuration to the default java.security file per JVM execution. This is done by setting the 'java.security.properties' system property to point to a properties file as part of the JVM invocation; it is important to notice that referencing to the file can be done in one of two flavors:

1. Overriding the entire file provided by the JVM - if the first character in the java.security.properties' value is the equals sign the default configuration file will be entirely ignored, only the values in the file we are pointing to will be affective
2. Appending and overriding values of the default file - any other first character in the property's value (that is the first character in the alternate configuration file path) means that the alternate file will be loaded and appended to the default one. If the alternate file contains properties which are already in the default configuration file the alternate file will override those properties.

Here are two examples

#
# Completely override the default java.security file content
# (notice the *two* equal signs) 
#
java -Djava.security.properties==/etc/sysconfig/jvm1.java.security

#
# Append or override parts of the default java.security file
# (notice the *single* equal sign)
#
java -Djava.security.properties=/etc/sysconfig/jvm.java.security

Be Carefull

As an important configuration option as it is we must not forget its security implications. We should always make sure that no one can tamper the value of the property and that no one can tamper the alternate file content if he shouldn't be allowed to.