Decrypt encrypted Android Phone (MIUI 4.2)

I've encrypted my Phone because of my organization's policy. Unfortunately the device is a bit slower and moreover I am not able to update ROMs anymore. I do have root access and my device is running fine, but I'd like to undo the encryption of my Android-device. I've searched for several solutions on line, but it appears as if no one really has THE solution. Could anyone help me solving this issue? Some extra information that I've used so far: - https://android.stackexchange.com/questions/52046/ways-to-remove-android-device-encryption - http://forum.xda-developers.com/showthread.php?t=1187741 - Factory reset/data wipe (results in errors, because of encryption) - reflashed ROM, didn't work either: /data remained untouched - forum . xda-developers.com/showpost.php?p=25635462&postcount=54 - 0xfeedface . org/blog/lattera/2012-06-04/installing-cm9-encrypted-android-tablet MY Phone is: Xioami Hongmi with MIUI 3.8.11 (Android 4.2)