--- /dev/null
+
+ GNU Free Documentation License
+ Version 1.3, 3 November 2008
+
+
+ Copyright (C) 2000, 2001, 2002, 2007, 2008 Free Software Foundation, Inc.
+ <http://fsf.org/>
+ Everyone is permitted to copy and distribute verbatim copies
+ of this license document, but changing it is not allowed.
+
+0. PREAMBLE
+
+The purpose of this License is to make a manual, textbook, or other
+functional and useful document "free" in the sense of freedom: to
+assure everyone the effective freedom to copy and redistribute it,
+with or without modifying it, either commercially or noncommercially.
+Secondarily, this License preserves for the author and publisher a way
+to get credit for their work, while not being considered responsible
+for modifications made by others.
+
+This License is a kind of "copyleft", which means that derivative
+works of the document must themselves be free in the same sense. It
+complements the GNU General Public License, which is a copyleft
+license designed for free software.
+
+We have designed this License in order to use it for manuals for free
+software, because free software needs free documentation: a free
+program should come with manuals providing the same freedoms that the
+software does. But this License is not limited to software manuals;
+it can be used for any textual work, regardless of subject matter or
+whether it is published as a printed book. We recommend this License
+principally for works whose purpose is instruction or reference.
+
+
+1. APPLICABILITY AND DEFINITIONS
+
+This License applies to any manual or other work, in any medium, that
+contains a notice placed by the copyright holder saying it can be
+distributed under the terms of this License. Such a notice grants a
+world-wide, royalty-free license, unlimited in duration, to use that
+work under the conditions stated herein. The "Document", below,
+refers to any such manual or work. Any member of the public is a
+licensee, and is addressed as "you". You accept the license if you
+copy, modify or distribute the work in a way requiring permission
+under copyright law.
+
+A "Modified Version" of the Document means any work containing the
+Document or a portion of it, either copied verbatim, or with
+modifications and/or translated into another language.
+
+A "Secondary Section" is a named appendix or a front-matter section of
+the Document that deals exclusively with the relationship of the
+publishers or authors of the Document to the Document's overall
+subject (or to related matters) and contains nothing that could fall
+directly within that overall subject. (Thus, if the Document is in
+part a textbook of mathematics, a Secondary Section may not explain
+any mathematics.) The relationship could be a matter of historical
+connection with the subject or with related matters, or of legal,
+commercial, philosophical, ethical or political position regarding
+them.
+
+The "Invariant Sections" are certain Secondary Sections whose titles
+are designated, as being those of Invariant Sections, in the notice
+that says that the Document is released under this License. If a
+section does not fit the above definition of Secondary then it is not
+allowed to be designated as Invariant. The Document may contain zero
+Invariant Sections. If the Document does not identify any Invariant
+Sections then there are none.
+
+The "Cover Texts" are certain short passages of text that are listed,
+as Front-Cover Texts or Back-Cover Texts, in the notice that says that
+the Document is released under this License. A Front-Cover Text may
+be at most 5 words, and a Back-Cover Text may be at most 25 words.
+
+A "Transparent" copy of the Document means a machine-readable copy,
+represented in a format whose specification is available to the
+general public, that is suitable for revising the document
+straightforwardly with generic text editors or (for images composed of
+pixels) generic paint programs or (for drawings) some widely available
+drawing editor, and that is suitable for input to text formatters or
+for automatic translation to a variety of formats suitable for input
+to text formatters. A copy made in an otherwise Transparent file
+format whose markup, or absence of markup, has been arranged to thwart
+or discourage subsequent modification by readers is not Transparent.
+An image format is not Transparent if used for any substantial amount
+of text. A copy that is not "Transparent" is called "Opaque".
+
+Examples of suitable formats for Transparent copies include plain
+ASCII without markup, Texinfo input format, LaTeX input format, SGML
+or XML using a publicly available DTD, and standard-conforming simple
+HTML, PostScript or PDF designed for human modification. Examples of
+transparent image formats include PNG, XCF and JPG. Opaque formats
+include proprietary formats that can be read and edited only by
+proprietary word processors, SGML or XML for which the DTD and/or
+processing tools are not generally available, and the
+machine-generated HTML, PostScript or PDF produced by some word
+processors for output purposes only.
+
+The "Title Page" means, for a printed book, the title page itself,
+plus such following pages as are needed to hold, legibly, the material
+this License requires to appear in the title page. For works in
+formats which do not have any title page as such, "Title Page" means
+the text near the most prominent appearance of the work's title,
+preceding the beginning of the body of the text.
+
+The "publisher" means any person or entity that distributes copies of
+the Document to the public.
+
+A section "Entitled XYZ" means a named subunit of the Document whose
+title either is precisely XYZ or contains XYZ in parentheses following
+text that translates XYZ in another language. (Here XYZ stands for a
+specific section name mentioned below, such as "Acknowledgements",
+"Dedications", "Endorsements", or "History".) To "Preserve the Title"
+of such a section when you modify the Document means that it remains a
+section "Entitled XYZ" according to this definition.
+
+The Document may include Warranty Disclaimers next to the notice which
+states that this License applies to the Document. These Warranty
+Disclaimers are considered to be included by reference in this
+License, but only as regards disclaiming warranties: any other
+implication that these Warranty Disclaimers may have is void and has
+no effect on the meaning of this License.
+
+2. VERBATIM COPYING
+
+You may copy and distribute the Document in any medium, either
+commercially or noncommercially, provided that this License, the
+copyright notices, and the license notice saying this License applies
+to the Document are reproduced in all copies, and that you add no
+other conditions whatsoever to those of this License. You may not use
+technical measures to obstruct or control the reading or further
+copying of the copies you make or distribute. However, you may accept
+compensation in exchange for copies. If you distribute a large enough
+number of copies you must also follow the conditions in section 3.
+
+You may also lend copies, under the same conditions stated above, and
+you may publicly display copies.
+
+
+3. COPYING IN QUANTITY
+
+If you publish printed copies (or copies in media that commonly have
+printed covers) of the Document, numbering more than 100, and the
+Document's license notice requires Cover Texts, you must enclose the
+copies in covers that carry, clearly and legibly, all these Cover
+Texts: Front-Cover Texts on the front cover, and Back-Cover Texts on
+the back cover. Both covers must also clearly and legibly identify
+you as the publisher of these copies. The front cover must present
+the full title with all words of the title equally prominent and
+visible. You may add other material on the covers in addition.
+Copying with changes limited to the covers, as long as they preserve
+the title of the Document and satisfy these conditions, can be treated
+as verbatim copying in other respects.
+
+If the required texts for either cover are too voluminous to fit
+legibly, you should put the first ones listed (as many as fit
+reasonably) on the actual cover, and continue the rest onto adjacent
+pages.
+
+If you publish or distribute Opaque copies of the Document numbering
+more than 100, you must either include a machine-readable Transparent
+copy along with each Opaque copy, or state in or with each Opaque copy
+a computer-network location from which the general network-using
+public has access to download using public-standard network protocols
+a complete Transparent copy of the Document, free of added material.
+If you use the latter option, you must take reasonably prudent steps,
+when you begin distribution of Opaque copies in quantity, to ensure
+that this Transparent copy will remain thus accessible at the stated
+location until at least one year after the last time you distribute an
+Opaque copy (directly or through your agents or retailers) of that
+edition to the public.
+
+It is requested, but not required, that you contact the authors of the
+Document well before redistributing any large number of copies, to
+give them a chance to provide you with an updated version of the
+Document.
+
+
+4. MODIFICATIONS
+
+You may copy and distribute a Modified Version of the Document under
+the conditions of sections 2 and 3 above, provided that you release
+the Modified Version under precisely this License, with the Modified
+Version filling the role of the Document, thus licensing distribution
+and modification of the Modified Version to whoever possesses a copy
+of it. In addition, you must do these things in the Modified Version:
+
+A. Use in the Title Page (and on the covers, if any) a title distinct
+ from that of the Document, and from those of previous versions
+ (which should, if there were any, be listed in the History section
+ of the Document). You may use the same title as a previous version
+ if the original publisher of that version gives permission.
+B. List on the Title Page, as authors, one or more persons or entities
+ responsible for authorship of the modifications in the Modified
+ Version, together with at least five of the principal authors of the
+ Document (all of its principal authors, if it has fewer than five),
+ unless they release you from this requirement.
+C. State on the Title page the name of the publisher of the
+ Modified Version, as the publisher.
+D. Preserve all the copyright notices of the Document.
+E. Add an appropriate copyright notice for your modifications
+ adjacent to the other copyright notices.
+F. Include, immediately after the copyright notices, a license notice
+ giving the public permission to use the Modified Version under the
+ terms of this License, in the form shown in the Addendum below.
+G. Preserve in that license notice the full lists of Invariant Sections
+ and required Cover Texts given in the Document's license notice.
+H. Include an unaltered copy of this License.
+I. Preserve the section Entitled "History", Preserve its Title, and add
+ to it an item stating at least the title, year, new authors, and
+ publisher of the Modified Version as given on the Title Page. If
+ there is no section Entitled "History" in the Document, create one
+ stating the title, year, authors, and publisher of the Document as
+ given on its Title Page, then add an item describing the Modified
+ Version as stated in the previous sentence.
+J. Preserve the network location, if any, given in the Document for
+ public access to a Transparent copy of the Document, and likewise
+ the network locations given in the Document for previous versions
+ it was based on. These may be placed in the "History" section.
+ You may omit a network location for a work that was published at
+ least four years before the Document itself, or if the original
+ publisher of the version it refers to gives permission.
+K. For any section Entitled "Acknowledgements" or "Dedications",
+ Preserve the Title of the section, and preserve in the section all
+ the substance and tone of each of the contributor acknowledgements
+ and/or dedications given therein.
+L. Preserve all the Invariant Sections of the Document,
+ unaltered in their text and in their titles. Section numbers
+ or the equivalent are not considered part of the section titles.
+M. Delete any section Entitled "Endorsements". Such a section
+ may not be included in the Modified Version.
+N. Do not retitle any existing section to be Entitled "Endorsements"
+ or to conflict in title with any Invariant Section.
+O. Preserve any Warranty Disclaimers.
+
+If the Modified Version includes new front-matter sections or
+appendices that qualify as Secondary Sections and contain no material
+copied from the Document, you may at your option designate some or all
+of these sections as invariant. To do this, add their titles to the
+list of Invariant Sections in the Modified Version's license notice.
+These titles must be distinct from any other section titles.
+
+You may add a section Entitled "Endorsements", provided it contains
+nothing but endorsements of your Modified Version by various
+parties--for example, statements of peer review or that the text has
+been approved by an organization as the authoritative definition of a
+standard.
+
+You may add a passage of up to five words as a Front-Cover Text, and a
+passage of up to 25 words as a Back-Cover Text, to the end of the list
+of Cover Texts in the Modified Version. Only one passage of
+Front-Cover Text and one of Back-Cover Text may be added by (or
+through arrangements made by) any one entity. If the Document already
+includes a cover text for the same cover, previously added by you or
+by arrangement made by the same entity you are acting on behalf of,
+you may not add another; but you may replace the old one, on explicit
+permission from the previous publisher that added the old one.
+
+The author(s) and publisher(s) of the Document do not by this License
+give permission to use their names for publicity for or to assert or
+imply endorsement of any Modified Version.
+
+
+5. COMBINING DOCUMENTS
+
+You may combine the Document with other documents released under this
+License, under the terms defined in section 4 above for modified
+versions, provided that you include in the combination all of the
+Invariant Sections of all of the original documents, unmodified, and
+list them all as Invariant Sections of your combined work in its
+license notice, and that you preserve all their Warranty Disclaimers.
+
+The combined work need only contain one copy of this License, and
+multiple identical Invariant Sections may be replaced with a single
+copy. If there are multiple Invariant Sections with the same name but
+different contents, make the title of each such section unique by
+adding at the end of it, in parentheses, the name of the original
+author or publisher of that section if known, or else a unique number.
+Make the same adjustment to the section titles in the list of
+Invariant Sections in the license notice of the combined work.
+
+In the combination, you must combine any sections Entitled "History"
+in the various original documents, forming one section Entitled
+"History"; likewise combine any sections Entitled "Acknowledgements",
+and any sections Entitled "Dedications". You must delete all sections
+Entitled "Endorsements".
+
+
+6. COLLECTIONS OF DOCUMENTS
+
+You may make a collection consisting of the Document and other
+documents released under this License, and replace the individual
+copies of this License in the various documents with a single copy
+that is included in the collection, provided that you follow the rules
+of this License for verbatim copying of each of the documents in all
+other respects.
+
+You may extract a single document from such a collection, and
+distribute it individually under this License, provided you insert a
+copy of this License into the extracted document, and follow this
+License in all other respects regarding verbatim copying of that
+document.
+
+
+7. AGGREGATION WITH INDEPENDENT WORKS
+
+A compilation of the Document or its derivatives with other separate
+and independent documents or works, in or on a volume of a storage or
+distribution medium, is called an "aggregate" if the copyright
+resulting from the compilation is not used to limit the legal rights
+of the compilation's users beyond what the individual works permit.
+When the Document is included in an aggregate, this License does not
+apply to the other works in the aggregate which are not themselves
+derivative works of the Document.
+
+If the Cover Text requirement of section 3 is applicable to these
+copies of the Document, then if the Document is less than one half of
+the entire aggregate, the Document's Cover Texts may be placed on
+covers that bracket the Document within the aggregate, or the
+electronic equivalent of covers if the Document is in electronic form.
+Otherwise they must appear on printed covers that bracket the whole
+aggregate.
+
+
+8. TRANSLATION
+
+Translation is considered a kind of modification, so you may
+distribute translations of the Document under the terms of section 4.
+Replacing Invariant Sections with translations requires special
+permission from their copyright holders, but you may include
+translations of some or all Invariant Sections in addition to the
+original versions of these Invariant Sections. You may include a
+translation of this License, and all the license notices in the
+Document, and any Warranty Disclaimers, provided that you also include
+the original English version of this License and the original versions
+of those notices and disclaimers. In case of a disagreement between
+the translation and the original version of this License or a notice
+or disclaimer, the original version will prevail.
+
+If a section in the Document is Entitled "Acknowledgements",
+"Dedications", or "History", the requirement (section 4) to Preserve
+its Title (section 1) will typically require changing the actual
+title.
+
+
+9. TERMINATION
+
+You may not copy, modify, sublicense, or distribute the Document
+except as expressly provided under this License. Any attempt
+otherwise to copy, modify, sublicense, or distribute it is void, and
+will automatically terminate your rights under this License.
+
+However, if you cease all violation of this License, then your license
+from a particular copyright holder is reinstated (a) provisionally,
+unless and until the copyright holder explicitly and finally
+terminates your license, and (b) permanently, if the copyright holder
+fails to notify you of the violation by some reasonable means prior to
+60 days after the cessation.
+
+Moreover, your license from a particular copyright holder is
+reinstated permanently if the copyright holder notifies you of the
+violation by some reasonable means, this is the first time you have
+received notice of violation of this License (for any work) from that
+copyright holder, and you cure the violation prior to 30 days after
+your receipt of the notice.
+
+Termination of your rights under this section does not terminate the
+licenses of parties who have received copies or rights from you under
+this License. If your rights have been terminated and not permanently
+reinstated, receipt of a copy of some or all of the same material does
+not give you any rights to use it.
+
+
+10. FUTURE REVISIONS OF THIS LICENSE
+
+The Free Software Foundation may publish new, revised versions of the
+GNU Free Documentation License from time to time. Such new versions
+will be similar in spirit to the present version, but may differ in
+detail to address new problems or concerns. See
+http://www.gnu.org/copyleft/.
+
+Each version of the License is given a distinguishing version number.
+If the Document specifies that a particular numbered version of this
+License "or any later version" applies to it, you have the option of
+following the terms and conditions either of that specified version or
+of any later version that has been published (not as a draft) by the
+Free Software Foundation. If the Document does not specify a version
+number of this License, you may choose any version ever published (not
+as a draft) by the Free Software Foundation. If the Document
+specifies that a proxy can decide which future versions of this
+License can be used, that proxy's public statement of acceptance of a
+version permanently authorizes you to choose that version for the
+Document.
+
+11. RELICENSING
+
+"Massive Multiauthor Collaboration Site" (or "MMC Site") means any
+World Wide Web server that publishes copyrightable works and also
+provides prominent facilities for anybody to edit those works. A
+public wiki that anybody can edit is an example of such a server. A
+"Massive Multiauthor Collaboration" (or "MMC") contained in the site
+means any set of copyrightable works thus published on the MMC site.
+
+"CC-BY-SA" means the Creative Commons Attribution-Share Alike 3.0
+license published by Creative Commons Corporation, a not-for-profit
+corporation with a principal place of business in San Francisco,
+California, as well as future copyleft versions of that license
+published by that same organization.
+
+"Incorporate" means to publish or republish a Document, in whole or in
+part, as part of another Document.
+
+An MMC is "eligible for relicensing" if it is licensed under this
+License, and if all works that were first published under this License
+somewhere other than this MMC, and subsequently incorporated in whole or
+in part into the MMC, (1) had no cover texts or invariant sections, and
+(2) were thus incorporated prior to November 1, 2008.
+
+The operator of an MMC Site may republish an MMC contained in the site
+under CC-BY-SA on the same site at any time before August 1, 2009,
+provided the MMC is eligible for relicensing.
+
+
+ADDENDUM: How to use this License for your documents
+
+To use this License in a document you have written, include a copy of
+the License in the document and put the following copyright and
+license notices just after the title page:
+
+ Copyright (c) YEAR YOUR NAME.
+ Permission is granted to copy, distribute and/or modify this document
+ under the terms of the GNU Free Documentation License, Version 1.3
+ or any later version published by the Free Software Foundation;
+ with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts.
+ A copy of the license is included in the section entitled "GNU
+ Free Documentation License".
+
+If you have Invariant Sections, Front-Cover Texts and Back-Cover Texts,
+replace the "with...Texts." line with this:
+
+ with the Invariant Sections being LIST THEIR TITLES, with the
+ Front-Cover Texts being LIST, and with the Back-Cover Texts being LIST.
+
+If you have Invariant Sections without Cover Texts, or some other
+combination of the three, merge those two alternatives to suit the
+situation.
+
+If your document contains nontrivial examples of program code, we
+recommend releasing these examples in parallel under your choice of
+free software license, such as the GNU General Public License,
+to permit their use in free software.
--- /dev/null
+@node Use cases
+@unnumbered Use cases
+
+@table @strong
+
+@item 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.
+
+Just tell both of your Postfixes (on the server and notebook) to drop
+email as a mail via NNCP to specified node. 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
+
+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.
+
+@item 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.
+
+@item Slow/expensive link for high-volume data
+
+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 transferring is called
+@url{https://en.wikipedia.org/wiki/Sneakernet, sneakernet}/floppynet.
+
+@item 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.
+
+@item 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.
+
+@item 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.
+
+@item 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 without forward secrecy property). 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.
+
+@end table