Software Architect at Chariot Solutions focusing on integration using Java and Open Source technologies. Rod has posted 6 posts at DZone. View Full User Profile

PGP Encryption with Mule ESB

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Recently I encounter an encryption problem in Mule ESB that surprised me...I could not figure out how to encrypt a message?!?!  I wasn't able to find an example on how PGP "encryption" should be configured even after numerous google and mule forum searches.  I was getting a little concerned that the PGP support in mule may be for decryption only.  The PGP Security documentation shows how to setup a security filter to decrypt messages but no example for encrypting (that may change soon...more on that later).  I finally posted a question on the mule forum and got some help from the community.

First of all, I should of been looking at the transformers in mule to perform encryption...duh!  I was so focused on trying to get the security filter to encrypt messages that I forgot about transformers...I know it's hard to image :)  I found out the there is an <encrypt-transformer> and was a little embarrassed that I didn't find it before.  So, I configured the <encrypt-transformer> to use the <pgp:keybased-encryption-strategy> just like I did for the security filter per the PGP Security documentation.  I thought "wow, that was easy", ran my configuration and got a NullPointerException. :(

I could see in the stacktrace that the problem was in the KeyBasedEncryptionStrategy, which was surprising because I was referencing the same <pgp:keybased-encryption-strategy> configuration in the security filter and that was working fine.  Then after taking a closer look at the security filter configuration I noticed that I was missing a reference to the credentialsAccessor.  The problem I was faced with is how to configured the <encrypt-transformer> to use the credentialsAccessor I was using?  Spring to the rescue!  The solution is quite simple.  Basically, all I had to do was inject the credentialsAccessor into the KeyBasedEncryptionStrategy.  To do that I had to configure a new spring bean (id="keyBEStrategy" below) and inject my keyManager and credentialsAccessor.  The nice thing about this solution is that the <encrypt-transformer> can still be used as is with just referencing the newly created strategy (i.e., strategy-ref="keyBEStrategy").  Here's an example configuration:

<?xml version="1.0"?>
<mule xmlns=""

<file:connector name="fileConnector" pollingFrequency="10000" streaming="false" autoDelete="true">

<spring:bean id="pgpKeyManager" class="org.mule.module.pgp.PGPKeyRingImpl" init-method="initialise">
<spring:property name="publicKeyRingFileName" value="<path to public keyring>/pubring.gpg"/>
<spring:property name="secretKeyRingFileName" value="<path to private keyring>/secring.gpg"/>
<!-- secretAliasId is the public key -->
<spring:property name="secretAliasId" value="<public key id"/>
<spring:property name="secretPassphrase" value="<password>"/>

<spring:bean id="keyBEStrategy" class="org.mule.module.pgp.KeyBasedEncryptionStrategy"
<spring:property name="keyManager" ref="pgpKeyManager"/>
<spring:property name="credentialsAccessor" ref="credentialAccessor"/>

<pgp:security-provider name="pgpSecurityProvider" keyManager-ref="pgpKeyManager"/>
<pgp:keybased-encryption-strategy name="keyBasedEncryptionStrategy"

<spring:bean id="credentialAccessor" class="org.mule.module.pgp.FakeCredentialAccessor"/>

<model name="fileInboundModel">
<service name="fileInboundService">
<file:inbound-endpoint connector-ref="fileConnector"

<pgp:security-filter strategyName="keyBasedEncryptionStrategy"

<file:outbound-endpoint connector-ref="fileConnector" path="./encrypted"
<encrypt-transformer name="pgpEncrypt" strategy-ref="keyBEStrategy"/>

This workaround is pretty clean.  MuleSoft is going to review the solution and possibly update their documentation accordingly.



Published at DZone with permission of its author, Rod Biresch.

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