Configuration

Signing is configured using the <signature> element:

<configuration>
  <signature>
    <keyId>12345678</keyId> <!-- the ID of the key -->
    <keyringFile>${user.home}/.gnupg/secring.gpg</keyringFile> <!-- path to the keyring file -->
    <passphrase>secret</passphrase> <!-- passphrase to unlock the key -->
    
    <hashAlgorithm>SHA1</hashAlgorithm>  <!-- optional : defaults to SHA1 -->
    <skip>false</skip> <!-- optional : defaults to "false", skip signature --> 
  </signature>
  
  <skipSigning>false</skipSigning> <!-- optional, defaults to "false" -->
</configuration>

The keyring file is a standard GPG keyring file. The key ID is the short ID of the key to use for signing.

The hash algorithm can be either SHA1, SHA256 or SHA512.

The <skip> element can be set to true in order to skip signing the package with this signature.

Hiding credentials

The passphrase should not be store in any pom.xml which is possibly checked in to some sort of source control system. It is possible to use properties and provide this information either from the command line or the global Maven settings file .m2/settings.xml.

<signature>
    …
    <phassphrase>${my.passphrase}</passphrase>
</signature>

The following command will then provide the passphrase using the command line:

mvn package -Dmy.passphrase=secret

Conditional signing

Sometime is may be useful to deactivate signing since the private key is not available. This may be case when packages are signed in a central server which has the private key available, or a privileged user who has access to the keyfile, but most other users don't.

This can be achieved using various different ways using the <skip> element of the <signature> element or the global <skipSigning> element. Either in combination with Maven profiles or external properties.

By default if the <signature> element is present in the configuration, the information provided has to be correct. So a missing/unset passphrase or key id will not disable the signing process, but cause the build to fail.

Remarks

There are a bunch of different ways to sign an RPM file, the RPM builder plugin currently only supports PGP header signatures using SHA1 or SHA512.

Although RPM does support multiple signatures for one RPM file, the RPM builder can currently only create one.