Java Glossary : jarsigner

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JDK 1.2 tool for signing jars with DSA or RSA certificates. Replaces javakey. It is the analog of Netscape Signtool. It requires a special Java certificate. A Netscape or Authenticode certificate will not do. jarsigner can sign a JAR file using either:

DSA (Digital Signature Algorithm) with the SHA-1 digest algorithm.
RSA algorithm with the SHA-1 digest algorithm, or MD-5 in previous versions.

It embeds two files in the jar:

a signature file, with a .SF extension. These are the hashes of the elements of the jar encrypted with your private key. They can be verified by decrypting with your public key.
a signature block file, with a .DSA or .RSA extension. This is your binary public key and certificate.

In the simplest case all you need is this:

jarsigner.exe theapp.jar phony

where theapp.jar is the name of the previously created jar file with your app in it, and phony is the alias (short name) for the code signing cert you want to use.

Mitch Gallant has written an essay on the differences between signtool and jarsigner. In java 1,2+, you use jar.exe to create the jar and jarsigner.exe to sign it. You will need to use keytool.exe either to help purchase or fake a digital code-signing certificate before you can use jarsigner. Many of the parameters that jarsigner uses are the same as keytool, so you may find that my keytool docs are helpful.

Don't sign jars just for the heck of it. It slows down loading because all the hashes need to be computed, every time the classes in the jar are loaded, even if you are not using the security features.

jar.exe ¤ keytool.exe ¤ signtool.exe

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