For Mac OS/X: Please install Java 11 [1] and follow the instructions [2] to run the downloaded app.
For Windows and Linux: This release bundles Java in the OpenJDK JRE version 11. It is not required anymore to have Java installed to run JCrypTool.
Instructions for OS/X
[1]
Download and install OpenJDK 11 for Mac OS/X.
[2]
Open a terminal window and complete, then execute the following commands:
cd <insert-location-where-JCrypTool-was-extracted>
sudo xattr -r -d com.apple.quarantine ./jcryptool.app