I don't understand the Inkan comparison. The Inkan just looks like a unique seal so that someone knows a document is legitimate. That seems more comparable to something like signing with your private key. Care to explain?
I can go to the bank teller, offer them my driver's license, citizenship card and can recite the PIN code to them but they won't believe I'm me and let me access my money.
Show them my plastic stamp and I'm magically me! I could give it to another individual and he could withdraw money from my account, no questions asked.
Possession is simply not security.