Automating JAR Signing with the Eclipse JAR Signer PluginCode signing is a critical step in Java application delivery: it ensures integrity, authenticity, and trust for JAR files distributed to users or deployed in environments that enforce signed artifacts. Manual signing of JARs is tedious and error-prone, especially in teams and CI/CD pipelines. The Eclipse JAR Signer Plugin automates and streamlines this process inside Eclipse-based builds and can be integrated into automated pipelines to produce reproducible, secure, and auditable signed JAR artifacts.
This article explains why you should automate JAR signing, what the Eclipse JAR Signer Plugin provides, how to set it up and configure it, examples of automation workflows (including Eclipse headless builds and CI/CD integration), best practices for key management and security, troubleshooting tips, and a sample end-to-end configuration you can adapt.
Why automate JAR signing?
- Security: Signed JARs prove the publisher and show that the content hasn’t been tampered with.
- Consistency: Automation reduces human error and ensures every build artifact receives the same signing treatment.
- CI/CD integration: Automated signing fits naturally into continuous delivery pipelines, enabling signed releases with minimal manual steps.
- Auditability: Automated processes can log and record signing operations for compliance.
What the Eclipse JAR Signer Plugin provides
The Eclipse JAR Signer Plugin is an Eclipse-based tool that wraps the standard Java jarsigner functionality into Eclipse build tooling. Its main features typically include:
- Integration with Eclipse project builds and export wizards.
- Configurable signing options (keystore location, alias, store password, key password, timestamping).
- Headless operation for automated builds (depends on plugin and environment).
- Support for signing multiple JARs in a workspace or build output folder.
- Options to preserve or update manifest entries related to signing.
Note: The plugin’s exact features and names may vary by version and distribution — consult the plugin documentation for specifics.
Prerequisites
- Java JDK (with jarsigner available).
- Eclipse IDE with plugin installed, or a headless Eclipse installation for automated builds.
- A keystore containing the signing key (JKS, PKCS12) and the corresponding credentials.
- Optional: a timestamping service (RFC 3161/TSA) URL for long-term validation.
Installing the Eclipse JAR Signer Plugin
- In Eclipse, go to Help → Install New Software.
- Add the plugin update site URL (from the plugin’s documentation).
- Select the JAR Signer Plugin features and follow the prompts to install.
- Restart Eclipse when prompted.
- Verify installation via Window → Preferences → (plugin name) or by checking project export options.
For headless or scripted environments, install the plugin into an Eclipse headless instance used by your build server or include it in an Eclipse installation image.
Configuring signing options in Eclipse
Most Eclipse JAR signer plugin configurations let you specify:
- Keystore path (absolute or workspace-relative).
- Keystore type (JKS or PKCS12).
- Keystore password (avoid storing plaintext; prefer external credentials management).
- Key alias (the alias of the key used to sign).
- Key password (if different from keystore password).
- Timestamping (TSA URL, optional) — strongly recommended for long-term signature validity.
- Target JARs or output directories to sign.
- Whether to overwrite existing signatures.
Example: Create a signing profile named “release-sign” that points to /opt/keys/release.p12, type PKCS12, alias release-key, with TSA URL https://tsa.example.com.
Automating within Eclipse headless builds
If your organization uses Eclipse headless builds (PDE build or Tycho for Maven), you can incorporate signing in different ways:
- Use the plugin’s headless commands (if provided) to sign JARs after build output. Invoke via eclipse -application
with appropriate parameters. - For Tycho builds, prefer using Maven plugins such as the maven-jarsigner-plugin or custom post-processing scripts, but you can call an external jarsigner or the Eclipse plugin’s headless application as a post-build step.
- As a generic approach, add a build step that runs a script to call jarsigner (comes with the JDK) using the same keystore and options configured in Eclipse. This keeps build definitions independent of IDE plugins.
Example headless invocation pattern (pseudo-command):
eclipse -nosplash -application com.example.jarsigner.headless -keystore /opt/keys/release.p12 -storetype PKCS12 -storepass-file /run/secrets/ks_pass -alias release-key -tsa https://tsa.example.com -input-dir build/output -recursive
CI/CD integration patterns
CI/CD systems (Jenkins, GitHub Actions, GitLab CI, Azure Pipelines, etc.) typically run builds on agents that shouldn’t store secrets in plaintext. Use one of these strategies:
-
Use the JDK jarsigner directly in a pipeline step (recommended for simplicity). Store the keystore and passwords in the CI secret store and inject them at runtime. Example steps:
- Checkout code and build JARs.
- Download or mount keystore from secure storage.
- Run jarsigner with environment-provided passwords or password files.
- Optionally run jarsigner –verify to confirm signatures.
- Archive signed artifacts.
-
Use the Eclipse JAR Signer Plugin headless app on the build agent if you need Eclipse-specific signing features. Provide plugin via a custom agent image.
-
Use a dedicated signing service or signing worker that holds the private keys in an HSM or cloud KMS. Pipeline sends artifacts to sign and receives signed artifacts back. This avoids exposing keys to many build agents.
Example GitHub Actions snippet using jarsigner:
- name: Sign JAR env: KEYSTORE_PASS: ${{ secrets.KEYSTORE_PASS }} KEY_PASS: ${{ secrets.KEY_PASS }} run: | echo "$KEYSTORE_PASS" > keystore.pass jarsigner -keystore release.p12 -storetype PKCS12 -storepass:file keystore.pass -tsa https://tsa.example.com build/libs/myapp.jar release-key jarsigner -verify -certs -verbose build/libs/myapp.jar
Key management and security best practices
- Use PKCS#11/HSM or cloud KMS (AWS KMS, Azure Key Vault, Google Cloud KMS) where possible to avoid storing private keys on disk.
- If storing a keystore file, limit access, use strong filesystem permissions, and keep it outside source control.
- Prefer password injection from secure secrets stores; do not hardcode passwords in build scripts or repository.
- Use timestamping (TSA) so signatures remain valid after certificate expiration.
- Rotate keys periodically and plan for key compromise by having a signing and revocation policy.
- Log signing operations securely for auditability.
Troubleshooting common issues
- “jarsigner: cannot open keystore” — check path, file permissions, and keystore format.
- Incorrect passwords — verify using keytool -list -keystore
-storetype . - Signature verification fails — ensure the same signing algorithm and that the manifest/entries weren’t modified after signing. Run jarsigner -verify -verbose.
- Headless plugin not found — confirm plugin is installed in the headless Eclipse instance and the correct application ID is used.
- CI agent cannot access keystore — ensure secrets are mounted or downloaded correctly and file permissions allow the agent to read.
Sample end-to-end setup (Eclipse + GitHub Actions)
-
Generate or obtain signing certificate and keystore:
- Prefer PKCS12: keytool -genkeypair -alias release-key -keystore release.p12 -storetype PKCS12 -keyalg RSA -keysize 4096 -validity 3650
-
Store release.p12 and the keystore password in your CI secrets or an artifact store (encrypt at rest).
-
Configure Eclipse plugin locally for developer builds (optional). Team members who produce release builds can use the plugin in Eclipse pointing to a local secure keystore.
-
GitHub Actions workflow (build + sign): “`yaml name: Build and Sign
on: [push]
jobs: build:
runs-on: ubuntu-latest steps: - uses: actions/checkout@v4 - name: Set up JDK uses: actions/setup-java@v4 with: distribution: temurin java-version: 17 - name: Build run: mvn -B package -DskipTests - name: Retrieve keystore run: | echo "${{ secrets.RELEASE_P12 }}" | base64 --decode > release.p12 echo "${{ secrets.KEYSTORE_PASS }}" > ks.pass - name: Sign JAR env: KEY_PASS: ${{ secrets.KEY_PASS }} run: | jarsigner -keystore release.p12 -storetype PKCS12 -storepass:file ks.pass -tsa https://tsa.example.com target/myapp.jar release-key jarsigner -verify -certs -verbose target/myapp.jar - name: Upload signed artifact uses: actions/upload-artifact@v4 with: name: myapp-signed path: target/myapp.jar
”`
When to prefer the Eclipse plugin vs jarsigner directly
Use case | Prefer Eclipse JAR Signer Plugin | Prefer jarsigner (JDK) |
---|---|---|
Developer IDE integration | Yes | No |
Headless CI on standard agents | Maybe (if plugin available) | Yes |
Complex Eclipse-specific exports | Yes | Maybe |
Minimal external dependencies | No | Yes |
Use of HSM/KMS via PKCS#11 | Depends on plugin support | Yes, via Java provider |
Final notes
Automating JAR signing improves security, consistency, and reproducibility of Java releases. The Eclipse JAR Signer Plugin offers convenient IDE integration and potential headless operation, but for CI/CD pipelines many teams find calling the JDK’s jarsigner or using a dedicated signing service/HSM preferable for simplicity and stronger key protection. Whichever approach you choose, enforce secure key handling, use timestamping, and verify signatures as part of the release pipeline.