This is a Java library for encryption and decryption of the Cisco "type 7" password which use a modified Vigenere algorithm.
Usage is simple as the class already includes the Cisco key - just call those methods yo!
If you are trying to provision certain passwords, such as an IS-IS lsp-password, to an IOS XR box over NETCONF/YANG you will notice that it requires an already encrypted key.
If you are using Cisco NSO (formerly Tail-F NCS) to do your provisioning you are likely writing Java code and if your input key is cleartext it means you have to encrypt it before you send it to the device. Thus requiring something like this library.