You can decrypt WhatsApp message backup file i.e. msgstore.db.crypt8. You can also decrypt the previous backup file with format crypt7, crypt5.
In order to decrypt the WhatsApp message we need three files.
These are:
Path: Device Storage/WhatsApp/Database
Edit: It is required to root your phone to find key otherwise you will get empty folder.
Key: Key file contains a decryption key which is essential to decrypt an encrypted file. Since WhatsApp saves this key in your system storage so you can find that file on following location. To open system folder you can use ES File Explorer. ES File Explorer File Manager - Android Apps on Google Play
Path: /data/data/com.whatsapp/f
WhatsApp viewer: It is a small Windows application. You can download it by this link. WhatsApp.viewer.zip
Now you have to copy all these three items in your computer and follow these steps.
1. Open WhatsApp.viewer.zip
2. You will see a File option in left-upper corner. Click on this.
3. Here Select Decrypt.crypt8
4. Select database i.e. msgstore.db.crypt8 and Key file.
5. Click on Ok. You will see a popup.
6. Now a new file would be created in your computer where you have saved database file. Name of file will be somewhat like msgstore.decrypted.db. Locate that file.
7. Now again open WhatsApp.viewer.zip
8. This time select File option and Click on Open.
9. You will get this popup. Select your newly created decrypted database file. Press Ok.
10. Select any number from left side bar.
11. And now mission accomplished.
You can also Export your chat in a text file or in a html page.
Edit: You may have to root your phone to access the key file. Comment, if you are facing any problem.
Python: http://bit.ly/2dep7id
See the full articl https://www.quora.com/How-do-I-decrypt-a-crypt8-file-of-WhatsApp-database