dhbitty is a small public key encryption program written in C.  It
uses elliptic curve Diffie-Hellman in the form of Curve25519 to
establish a shared secret between two users, and uses that secret to
symmetrically encrypt and authenticate messages.

There are no private key files; only passphrases.  Never lose that
pesky thing again.

Both the sender and the receiver can decrypt a message.  In fact,
there is no distinction between sender and receiver.  Both passphrases
must be strong.

There is no signing.  A similarly useful form of authentication occurs
using only DH.  dhbitty attempts to be as simple as possible.  It is
not optimized, but achieves a comfortable speed for most uses.  It
does not use floating point numbers, or integers longer than 32 bits.
It does not contain more algorithms than are needed.
