Kanal how does signature analysis work?

[ArC]

Is the best solution to rip the RC4 code and insert it into yor own app?

You can try to rip the RC4 code.....
But pay attention to the S-box and to the field K!
Don't forget to rip the init routine!

Once I isolated the code, is MASM the best tool for keygen creation?

When I code a keygen in ASM, I use MASM(32 v8).

I notice that Dede doesn't recognise win32 API calls and IDA doesn't recognise some custom Delphi library calls

That's why I usually use Olly and/or DeDe with IDA.
As sKAMER said: Olly and IDA --> deadly combo