As receiver:
cd example/handler
HBBP_KEYDIR=../keys strace ../../hbbpd

As sender:
HBBP_KEYDIR=example/keys/ ./hbbpc eth0 hello world

* packet structure
** no encryption, empty payload
   - task

   This packet type is not send by hbbpc, but accepted by hbbpd.
** no encryption
   - task
   - '\0'
   - payload (may be empty)
** encryption
   - task
   - '\0'
   - nonce
   - encrypted payload (may be empty)
* cryptography
  HBBP uses the elliptic curve based assymetric cryptography to
  - limit the sender
  - limit the receiver
  to those peers that have knowledge of the corresponding keys. There
  is no protection against replay attacks.

  The sender (hbbpc) needs the senders private key (send.priv) and the
  receivers public key (recv.pub). The receiver needs the senders
  public key (send.pub) and the receivers private key (recv.priv).

  These key files are searched in the directory $base/$task where
  $base is the value of the environment variable HBBP_KEYDIR or
  /etc/hbbp/keys (the former takes precedence). If a key is not found
  in this directory, it is searched in $base/default.

  Note that this search is executed for each individual key. This
  allows to selectively overwrite default keys with task specific
  keys. Keep in mind that for each task only one key-pair (2 private &
  two public keys!) must be used in the entire network: The receiver
  assumes a certain sender key only be looking at the packets task
  name.

  To create keys use the accompanied hbbp_keygen in the desired
  destination directory. It will not overwrite any existing keys.

** key deployment examples
*** peer to peer as default
*** priviledged sender with fully overwritten defaults
*** priviliedged receiver with partially overwritten defaults

* software security
  - at most one task handler running at any time (wait for child
    termination)
  - no heap allocations at all
  - bounded stack
  - all syscall return codes checked, abort program in case of
    unhandled condition
  - in case of doubt: terminate (use watchdog for availability!)
  - compiled with -Wall -Wextra without generating any warnings
  - small codebase