A crypt12 to crypt conversion is related to a recovery of WhatsApp backup files. The only known way to convert latest WhatsApp archives (.crypt12) back to the original .crypt files is through app called Omni-Crypt, previously known as WhatsApp Tri-Crypt. This app can be used to easily downgrade their WhatsApp backup files, however this procedure often requires Root Access to the device, which may not be convenient way for some users, because doing this often causes warranty problems.
Nevertheless, nowadays most Android devices run Android 4.0 or above and Omni-Crypt no longer requires Root Access to convert crypt12 to crypt.Open CRYPT12 file Open CRYPT file
Online service for WhatsApp databases
Android app used to decrypt and convert CRYPT files