Unlock WM5 on HTC devices to install your own root CA certificate
I found the solution. Unfortunately it is much harder than I anticipated.
In fact you have to hack the security policy of WM5 in order to be able to install you own certificate. To accomplish this task you need two programs:
RegeditSTG.exe the trusted version of regedit from HTC.
SDA_ApplicationUnlock.zip a program to application unlock the SDA and alike smartphones.
Now use the following procedure:
Copy Regedit.zip to an internal folder of the phone and unpack Regedit.exe. It does not seem to work when it is copied to SD.
Start Regedit.exe and change the following registry keys:
HKLM\Security\Policies\Policies\00001001 = 2 => 1 (RAPI)HKLM\Security\Policies\Policies\00001005 = 16 => 40 (Cert)HKLM\Security\Policies\Policies\00001017 = 128 => 144 (?)
Now start SDA_ApplicationUnlock.exe on the PC with the phone attached to the USB port and click Unlock in the application.
Restart the phone
Now you can install your own root CA certificates by double clicking the .cer file.