The DMCA Anti-circumvention clause explicitly makes an exception for "security testing" and "encryption research", amongst others. Search for those terms on this page:
I am no law scholar, but I get the impression that, in general, reverse engineering and research are exempt from most forms of IP protection (which is what the DMCA is).
As far as the text of the DMCA goes, the only restrictions on sharing what you learned are if that sharing could facilitate copyright infringement rather than advance knowledge or security. I can see how that could be a bit hazy in some cases, but certainly should not apply to cases like this one.
http://www.law.cornell.edu/uscode/text/17/1201
I am no law scholar, but I get the impression that, in general, reverse engineering and research are exempt from most forms of IP protection (which is what the DMCA is).