I can't remember where, but during the holidays I remember reading that chestnuts should be used fairly quickly. I don't think yours would still be good, especially if they have something white on the outside of the shell. I was disappointed in the chestnuts I got over the holidays. I used them within a few days of buying them, but about half had mold growing on the chestnuts inside of the shells! Ick!
"If I had a minute for every hour that I've wasted I'd be rich in time." Jack Johnson, "Broken"