docs: add some proxies docs

docs/user/index.rst

@@ -1,3 +1,41 @@
 Introduction
 ============
 
+Censorship is the suppression of speech, public communication, or other information.
+This may be done on the basis that such material is considered objectionable, harmful, sensitive, or "inconvenient".
+Regardless of the reasons for censorship, the technical measures taken to implement it often look the same.
+The *Bypass Censorship* portal provides a toolkit for circumventing censorship of Internet resources.
+The circumvention methods available will often exploit either collateral freedom, traffic obfuscation, or both in order
+to counter the measures put in place by the censor.
+
+Collateral Freedom
+------------------
+
+*Used by:* :doc:`Web Proxies <proxies>`, :doc:`Tor Bridges <bridges>`
+
+"Collateral freedom" is an anti-censorship strategy that attempts to make it economically prohibitive for censors to
+block an Internet resource.
+The way in which a censor restricts access to resources will require knowing which content to block and which to allow.
+It's incredibly difficult to achieve accuracy with filtering as the Internet is comprised of untagged free-form content
+that must be categorised at speed.
+This results in either over-blocking or under-blocking, and neither of these are desirable properties for the censor.
+
+This can be exploited by circumvention systems by deploying solutions at places that are "too big to block", like cloud
+providers.
+Either encryption or constantly rotating identifiers are then used to prevent censors from identifying requests for
+censored information that is hosted among other content.
+This forces censors to either allow access to the censored information or take down entire services.
+
+Traffic Obfuscation
+-------------------
+
+*Used by:* :doc:`Tor Bridges <bridges>`
+
+"Traffic Obfuscation" is an anti-censorship strategy that attempts to make it difficult to fingerprint traffic.
+This is more commonly used for general censorship circumvention solutions rather than means of accessing specific
+resources.
+There is a long tail of types of traffic on the Internet, including critical infrastructure communications like
+industrial control systems, point-of-sale systems and security systems.
+This can be exploited by circumvention systems by making their traffic look like one of these unclassified systems.
+Not being able to accurately identify the traffic means that the cost of blocking access is unknown, and so it is more
+difficult for a censor to justify the block.

docs/user/lists.rst

@@ -1,2 +1,2 @@
-Mirror Lists
-============
+Distribution Lists
+==================

docs/user/proxies.rst

@@ -1,2 +1,29 @@
 Web Proxies
-===========
+===========
+
+Web proxies provide alternate URLs to access censored resources.
+These can be accessed through a normal web browser.
+They use frequently changing URLs to evade censorship.
+Some functionality on more complex websites may not work fully.
+The URLs will have a limited lifetime as, once discovered, they can be blocked by censors.
+
+This assumption of a limited lifetime is built-in to the system, allowing for automated block detection to trigger the
+deployment of new URLs, and for the :doc:`distribution lists <lists>` to allow applications and end-users to discover
+new URLs.
+
+Web Origins
+-----------
+
+Static Origins
+--------------
+
+These have not yet been implemented.
+
+Simple Proxies
+--------------
+
+Smart Proxies
+-------------
+
+Where a simple proxy leads to a broken user experience, it may be necessary to use a smart proxy to mitigate the
+brokenness.