7035.rb

require 'bundler'
Bundler.setup
Bundler.require

key = OpenSSL::Digest::SHA256.new('password').digest
crypt = ActiveSupport::MessageEncryptor.new(key)
encrypted_data = crypt.encrypt_and_sign('my secret data')
# throws CipherError Illegal key size: possibly you need to install Java Cryptography Extension (JCE) Unlimited Strength Jurisdiction Policy Files for your JRE

Gemfile

source 'https://rubygems.org'

gem 'rails', '4.0.0.beta', github: 'rails/rails',
  :ref => '8a39d8331114c73805d5ce989a72763d23bc55b1'

with the jars installed

john@ubuntu:~/code/rails-8534$ ll ~/*.jar
-rw-rw-r-- 1 john john 2500 Jan 24 20:23 /home/john/local_policy.jar
-rw-rw-r-- 1 john john 2487 Jan 24 20:23 /home/john/US_export_policy.jar
john@ubuntu:~/code/rails-8534$ JAVA_HOME=$(readlink -f /usr/bin/java | sed "s:bin/java::")
john@ubuntu:~/code/rails-8534$ echo $JAVA_HOME 
/usr/lib/jvm/java-7-oracle/jre/
john@ubuntu:~/code/rails-8534$ ll $JAVA_HOME/lib/security 
total 132
drwxr-xr-x  2 root root  4096 Jan 24 19:55 ./
drwxr-xr-x 16 root root  4096 Jan 24 19:55 ../
-rw-r--r--  1 root root  2063 Jan 24 19:55 blacklist
-rw-r--r--  1 root root 83581 Jan 24 19:55 cacerts
-rw-r--r--  1 root root   158 Jan 24 19:55 javafx.policy
-rw-r--r--  1 root root  2254 Jan 24 19:55 java.policy
-rw-r--r--  1 root root 15203 Jan 24 19:55 java.security
-rw-r--r--  1 root root    98 Jan 24 19:55 javaws.policy
-rw-r--r--  1 root root  2971 Jan 24 19:55 local_policy.jar
-rw-r--r--  1 root root     0 Jan 24 19:55 trusted.libraries
-rw-r--r--  1 root root  2487 Jan 24 19:55 US_export_policy.jar
john@ubuntu:~/code/rails-8534$ sudo cp ~/*.jar $JAVA_HOME/lib/security/
[sudo] password for john: 
john@ubuntu:~/code/rails-8534$ ruby 7035.rb 
john@ubuntu:~/code/rails-8534$ 

without the jars installed

john@ubuntu:~/code/rails-8534$ ruby -v
jruby 1.7.3.dev (1.9.3p327) 2013-01-24 cc9acba on Java HotSpot(TM) 64-Bit Server VM 1.7.0_11-b21 +indy [linux-amd64]
john@ubuntu:~/code/rails-8534$ ruby 7035.rb 
OpenSSL::Cipher::CipherError: Illegal key size: possibly you need to install Java Cryptography Extension (JCE) Unlimited Strength Jurisdiction Policy Files for your JRE
            update at org/jruby/ext/openssl/Cipher.java:684
          _encrypt at /home/john/code/jruby/lib/ruby/gems/shared/bundler/gems/rails-8a39d8331114/activesupport/lib/active_support/message_encryptor.rb:75
  encrypt_and_sign at /home/john/code/jruby/lib/ruby/gems/shared/bundler/gems/rails-8a39d8331114/activesupport/lib/active_support/message_encryptor.rb:55
            (root) at 7035.rb:7