How to use the command jarsigner (with examples)

The jarsigner command is a utility provided by Java to sign and verify Java archive (JAR) files. This command is commonly used in the process of digital signing, where a unique digital signature is added to a JAR file to confirm its authenticity and integrity.

Use case 1: Sign a JAR file

Code:

jarsigner path/to/file.jar keystore_alias

Motivation: The motivation for signing a JAR file is to provide a means of verifying the integrity and authenticity of the JAR file. By signing a JAR file with a digital signature, users can trust that the contents of the file have not been tampered with since it was signed.

Explanation:

• path/to/file.jar: This is the path to the JAR file that you want to sign.
• keystore_alias: This is the alias of the key in the keystore that will be used to sign the JAR file.

Example output:

Signing JAR: path/to/file.jar to keystore_alias ...

Use case 2: Sign a JAR file with a specific algorithm

Code:

jarsigner -sigalg algorithm path/to/file.jar keystore_alias

Motivation: In some cases, it may be necessary to use a specific signing algorithm. By using the -sigalg option, you can specify the algorithm to be used for signing the JAR file.

Explanation:

• -sigalg algorithm: This option is used to specify the signing algorithm to be used. Replace algorithm with the desired signing algorithm.
• path/to/file.jar: This is the path to the JAR file that you want to sign.
• keystore_alias: This is the alias of the key in the keystore that will be used to sign the JAR file.

Example output:

Signing JAR with algorithm: algorithm, file: path/to/file.jar, keystore alias: keystore_alias ...

Use case 3: Verify the signature of a JAR file

Code:

jarsigner -verify path/to/file.jar

Motivation: Verifying the signature of a JAR file is important to ensure that the file has not been tampered with since it was signed. By using the jarsigner command with the -verify option, you can easily verify the integrity and authenticity of a JAR file.

Explanation:

• -verify: This option is used to verify the signature of the JAR file.
• path/to/file.jar: This is the path to the JAR file that you want to verify.

Example output:

Verification successful. The signature of the JAR file is valid.

Conclusion:

In this article, we have explored three different use cases of the jarsigner command. We have learned how to sign a JAR file, sign it with a specific algorithm, and verify the signature of a JAR file. By using this command, you can ensure the integrity and authenticity of your Java archive (JAR) files.