We have found one software suitable in our database for this conversion.
CRYPT archives from WhatsApp can be re-crypted to CRYPT8 files with Android app called WhatsApp Tri-Crypt. When launched, it can be used to recrypt older CRYPT archives for use in the latest WhatsApp messenger.
However, latest version of Whatsapp uses CRYPT9 files and you cannot simply convert older archives to it.
An application for Google Android operating system, which is used to monitor and convert WhatsApp .crypt5, .crypt6, .crypt7 and .crypt8, .crypt9, .crypt10, .crypt11, .crypt12 backup files to .crypt legacy encryption and to .crypt5, .crypt6, .crypt7 and .crypt8, .crypt9, .crypt10, .crypt11, .crypt12 decryption / encryption. It is available in free and pro paid version.