Decipher Chat is prompting me for a passwordNo ratings yet.
If Decipher Chat is asking you for a password, that means it's trying to read data from a backup made with iOS backup encryption turned on. In order to read the WhatsApp messages from this backup, you'll need to enter the backup you set up encryption with in iTunes.
The password is used briefly to read the WhatsApp data locally on your computer, and is not stored.
If you don't remember setting up backup encryption, or don't remember the password, this post about forgetting your iTunes backup password may be helpful!