FYI, NBitcoin is "other soft" which he was asking not to use. Not to mention that it is a wrapper around C# implementation of Bouncy Castle which is a wrapper around the main project which is Bouncy Castle and it is written in Java.

P.S. If you want fast EC calculations then you have to have the Gs pre-calculated and use that for the scalar multiplication. Otherwise if you are using the usual "Double-and-add" method, it will be time consuming. Of course 10 second is not because of that. It is because of all the overhead that these libraries have! Otherwise if you re-write the same functions and use that, your timing will be reduced to <3 second per 100 iteration (checked with debug mode, it will be faster in compiled).