Well, just done a quick search and from what I've read you don't want to be carrying anything with a blade over 3" even if it's concealed. If you are carrying something with intent to use in an unlawful manner you will will charged with a felony and be punishable with 5 years in the state prison or a $2500 fine. I'm not sure how up to date all of this is so you might want to look it up on a official .gov site or something of the sort.
Have a good time in Boston,
Gabriel.