itsp/Security/ITSAppletPSE is a SAP Parameter attribute which is used to control enable ITS's own PSE for Applet Handshaking information. This is available within R/3 SAP systems depending on the version and release level.
Below is the standard documentation available and a few details of the attributes values .
The system PSE SAPSYS.PSE is normally used for the ITS applet
handshaking. However, if SAPSYS.PSE does not use a DSA algorithm that is
suitable for this purpose, you can create the ITS applet PSE
SAPSSF_ITSAPPLET.pse. To use this ITS applet PSE instead of the system
PSE, set this parameter to the value 1.
See SAP Parameter Documentation for full SAP documentation for this profile parameter.