get digestValue

Good day,

I am writing a signature handler (like DocSign example) and I use PROP_PSENG_SignFormatPKCS1 to create the signature value; the digestValue is NULL and it says the dataBuffer is a handler to fetch the bytes to digest, but how?

And what's the difference between PROP_PSENG_SignFormatPKCS1Digest and PROP_PSENG_SignFormatPKCS1? The PubSecHFT.h says if using PROP_PSENG_SignFormatPKCS1Digest the handler need to do its own digesting and the PROP_PSENG_SignFormatPKCS1 don't. Then why the digestValue is null? For it's constant, when is it produced?

Please help me out. I'm really confused.

Regards,

freesnowxdy