@node Use cases @unnumbered Use cases @menu * Occasional connection to mail server: UsecaseMail. * Unreliable/expensive communication link: UsecaseUnreliable. * Slow/expensive link for high-volume data, bad QoS: UsecaseQoS. * Extreme terrestrial environments, no link: UsecaseNoLink. * Private, isolated MitM-resistant networks: UsecaseF2F. * Highly secure isolated air-gap computers: UsecaseAirgap. * Network censorship bypassing: UsecaseCensor. * Reconnaissance, spying, intelligence, covert agents: UsecaseSpy. @end menu @node UsecaseMail @section Occasional connection to mail server Assume that you have got your own @url{http://www.postfix.org/, Postfix} SMTP server connected to the Internet. But you read and write emails on your notebook, that is connected to it just from time to time. How can you flush buffered mail queues when your notebook is connected? One possibility is to log in and run something like @command{postqueue -f}, but by default you have got only several days so and sender will receive notification emails that his messages still are not delivered yet. Also you must have secure link (SSH, VPN, etc). Another possibility is to use POP3/IMAP4 servers, but this is too overcomplicated and bloated for the simple task. Not an option. KISS! @anchor{Postfix} Just tell both of your Postfixes (on the server and notebook) to drop email as a mail via NNCP to specified node. This is done similarly as with UUCP and as written in Postfix @url{http://www.postfix.org/UUCP_README.html, documentation}. Search for @code{uucp} related strings in @code{master.cf} and replace command to NNCP ones: @verbatim nncp unix - n n - - pipe flags=Fqhu user=nncp argv=nncp-mail -quiet $nexthop $recipient @end verbatim then add transport map, telling that mail for example.com domain can be reached through NNCP transport to node @code{bob}: @verbatim example.com nncp:bob @end verbatim Now, all mail will be stored in NNCP spool, that after exchanging and tossing will call local @code{sendmail} command to deliver them just that was happened on the same machine. @node UsecaseUnreliable @section Unreliable/expensive communication link Assume that you have got slow modem/radio/cellular link that frequently disconnects and causes TCP timeouts. Not all HTTP servers support file download continuation. SMTP does not support resuming at all and heavy messages is a problem to retrieve. Moreover, each disconnect leads to the same data retransmission again, that can be expensive to afford. Just send your mail and files through NNCP. You can use either offline delivery methods -- read about them below, or you can use included NNCP TCP daemon. The command below: @verbatim % nncp-file file_i_want_to_send bob: % nncp-file another_file bob:movie.avi @end verbatim will queue two files for sending to @code{bob} node. Fire and forget! Now this is daemon's job (or offline transfer) to send this file part by part to remote system when it is available. @node UsecaseQoS @section Slow/expensive link for high-volume data, bad QoS Assume that you can give your relatively cheap 2 TiB removable hard drive to someone each day at the morning (and take it back at the evening). This equals to 185 Mbps good quality (without any speed degradation) link in single direction. What about more and bigger hard drives? This type of data exchange is called @url{https://en.wikipedia.org/wiki/Sneakernet, sneakernet}/floppynet. NNCP allows traffic prioritizing: each packet has niceness level, that will guarantee that it will be processed earlier or later than the other ones. Nearly all commands has corresponding option: @verbatim % nncp-file -nice 32 myfile node:dst % nncp-xfer -nice 192 /mnt/shared % nncp-call -nice 224 bob [...] @end verbatim @node UsecaseNoLink @section Extreme terrestrial environments, no link This is some kind of too slow link. Offline delivery methods is the only choice. Just send files as shown above, but use removable media for transferring packets to other nodes. Assume that you send two files to @code{bob} node. Insert USB storage device, mount it and run: @verbatim % nncp-xfer -node bob /media/usbstick @end verbatim to copy all outbound packets related to @code{bob}'s node. Use @code{-force} option to forcefully create related directory on USB storage if they are missing (for example when running for the first time). If you use single storage device to transfer data both to @code{bob} and @code{alice}, then just omit @code{-node} option to copy all existing outgoing packets to that storage device. @verbatim % nncp-xfer /media/usbstick @end verbatim Unmount it and transfer somehow to Bob and Alice. When they will insert it in their computers, they will use exactly the same command: @verbatim % nncp-xfer /media/usbstick @end verbatim to find all packets related to their node and copy them locally for further processing. @code{nncp-xfer} is the only command used with removable devices. @node UsecaseF2F @section Private, isolated MitM-resistant networks All Internet connections can be eavesdropped and forged. You @strong{have to} to use encryption and authentication for securing them. But it is very hard to secure metadata, that leaks during each online session. When you start your shiny new software server be sure that there could be huge quantity of bogus peers trying to perform @url{https://en.wikipedia.org/wiki/Sybil_attack, Sybil attack}. Opennet peer-to-peer networking is dangerous thing to do. The most popular cryptographic protocol in Internet is @url{https://en.wikipedia.org/wiki/Transport_Layer_Security, TLS} that is very hard to implement right and hard to configure for mutual participants authentication. Not all TLS configurations and related protocols provide @url{https://en.wikipedia.org/wiki/Forward_secrecy, forward secrecy} property -- all previously intercepted packets could be read if private keys are compromised. Friend-to-friend networks, darknets can mitigate risks related to fake and forged nodes. However they are harder to support require more time to be done right. NNCP's TCP daemon uses @url{http://noiseprotocol.org/, Noise-IK} protocol to mutually authenticate peers and provide effective (both participants send payload in the very first packet) secure transport with forward secrecy property. @verbatim % nncp-daemon -bind [::]:5400 @end verbatim will start TCP daemon listening on all interfaces for incoming connections. @verbatim % nncp-call bob @end verbatim will try to connect to @code{bob}'s node known TCP addresses (taken from configuration file) and send all related outbound packets and retrieve those the Bob has. All interrupted transfers will be automatically resumed. @node UsecaseAirgap @section Highly secure isolated air-gap computers If you worry much about security, then air-gapped computer could be the only choice you can afford. Computer without any modems, wired and wireless networks. Obviously the only possibility to exchange mail and files is to use physically removable storage devices like CD-ROM, hard drive, tape and USB flash drives (worst choice, due to those devices complexity). Presumably you have got another own hop before that computer: another intermediate node which performs basic verification of retrieved storage devices, possibly by rewriting the data from USB/hard drives to CD-RWs. NNCP supports packets relying (transitioning) out-of-box. @verbatim neigh: bob: [...] addrs: lan: [fe80::5400%igb0]:5400 bob-airgap: [...] via: [bob] @end verbatim That configuration file tells that we have got two known neighbours (nodes, peers): @code{bob} and @code{bob-airgap}. @code{bob} can be reached via online connection using @code{lan} address. @code{bob-airgap} can be reached by sending intermediate relay packet through the @code{bob}. Any command like @code{nncp-file myfile bob-airgap:} will automatically create two packets: one for the destination endpoint, other for intermediate relaying node. Pay attention that relaying node knows nothing about the packet inside, but just its size and priority. Transition packets are encrypted too. @code{bob} can not read @code{bob-airgap}'s packets. @node UsecaseCensor @section Network censorship bypassing This is some kind of bad link too. Some governments tend to forbid @strong{any} kind of private communication between people, allowing only entertainment content delivering and popular social networks access (that are already bloated with advertisements, local proprietary JavaScript code execution (for spying on user activities, collect data on them), shamelessly exploiting of very basic interhuman need of communication). This is their natural right and wish. Nobody forces you to obey huge corporations like Apple, Google or Microsoft. It is your choice to create isolated friend-to-friend network with piles of harmless content and private messaging. Only predators silently watch for their victims in mammals world -- it harms your health being watched and feeling that you are the victim that has already done something wrong. @node UsecaseSpy @section Reconnaissance, spying, intelligence, covert agents Those guys know how Internet is a dangerous place incompatible with privacy. They require quick, fast dropping and picking of data. No possibility of many round-trips -- just drop the data, fire-and-forget. It could be either removable media again, or @url{https://en.wikipedia.org/wiki/USB_dead_drop, USB dead drops}, or @url{https://en.wikipedia.org/wiki/PirateBox, PirateBox}es, or @url{https://en.wikipedia.org/wiki/Short-range_agent_communications, SRAC}. Short lived short range networks like Bluetooth and WiFi can also be pretty fast, allowing to quickly fire chunks of queued packets. Very important property is that compromising of those dead drops and storages must not be fatal and even dangerous. Packets sent through the network and exchanged via those devices are end-to-end encrypted (but unfortunately lacking forward secrecy). No filenames, mail recipients are seen. All communications are done with so-called spool area: directory containing only those unprocessed encrypted packets. After packet transfer you still can not read any mail of get files: you have to run another stage: tossing. Only that stage involves your private cryptographic keys. So even if your loose your computer, storage devices and so on -- it is not so bad, because you are not carrying private keys with it, you do not "toss" those packets immediately on the same device. Tossing (reading those encrypted packets and extracting transferred files and mail messages) could and should be done on a separate computer.