[Cryptography] Darpa wants a secure messaging app based on blockchains

[John Levine]

>As for classification ... this one looks to me like an engineering project more than a research product.  The basic techniques are all out there - it's
>a matter of putting them to use toward a particular end.  *Maybe* there's a need for something new for scalability; maybe not.  If they classify it,
>someone else can do the same work.

How do you do expiring messages without a central server?  I'd think
that once the data is in a blockchain, you're not going to make it go
away without unrealistic assumptions about the endpoint devices.

R's,
John