Capability - Revision history

Kosik: /* Examples */

2012-07-16T13:33:14Z

Examples

New page

== Definition ==

A ''capability'' is a token that identifies an [[subject, object, operation and permission|object]] and provides its holder with the [[subject, object, operation and permission|permission]] to operate on the object it identifies. Capabilities must either be totally unforgeable or infeasible to forge by being ''sparse''.

== Examples ==
Some examples of unforgeable capabilities:
* Designations of objects in the [[E language]]. Those who hold these capabilities have the permission to invoke any method supported by the designated object.
* Designations of functions and procedures in [[Emily]]. Those who hold these capabilities have the permission to call designated functions or procedures.
* Capabilities held by a process in [[capability operating system]]s.
* POSIX file descriptors.
Some examples of sparse capabilities (sometimes called password capabilities):
* Designations of remote objects in E, such as <code>captp://*orwqphzlugjwqj2wozz7tmg47ime466j@74.125.87.147:55189/oa6vn5whhapylswhzesdlqh5ppmjkcrq.</code> Those who hold these capabilities have the permission to invoke any method supported by the designated object.
* Private URLs where having the URL is necessary and sufficient to use the resource. Common examples are:
** "Confirm your e-mail address" links for website account registrations, mailing list subscriptions or opt-outs, e.g. <code><nowiki>http://drupal.cbreurope.sk/civicrm/mailing/optout?reset=1&jid=XX&qid=XXXXX&h=XXXXXXXXXXXXXXXX&confirm=1</nowiki></code>
** Shared private documents such as in Google Docs, Google Maps, [http://picasa.google.com Picasa] albums, [http://www.doodle.com Doodle] schedulers.
* Designation of file-system sub-trees in [[MinorFs]], such as <code>/mnt/minorfs/cap/3d5d3efbf73bb711e7a47f82a44f471fcf77c70e/</code>
* URL links to Bitcoin [http://blog.maschinenraum.tk/2012/07/15/bitcoin-vending-machine-exchange-euro-coins-for-bitcoin-wallets/btc-vending-machine-3 wallets].

An [[Unum]] can be also considered as a capability to a (replicated) object in a similar way as file descriptors of transparently replicated files by RAID are still regarded as file descriptors.

== URLs as capabilities ==

As noted above, URLs are often used as capabilities in practice, especially when sent over e-mail. Some explicitly capability-structured systems, such as [[Tahoe-LAFS]], use capability URLs.

A hazard to using capability URLs directly in a web browser is that many browser extensions or options may transmit URLs to a third-party server. In the worst case, this may make those URLs public. However, there is some mitigation:
* The fragment part of a URL reference (<code>#id</code>) is not transmitted. If the browser supports executing JavaScript, then the capability can be placed in the fragment and transmitted only under script control, not as part of a URL.
* The query string part (<code>?foo=bar</code>) is often not transmitted. (Citation needed on this one!)

== See also ==

See [http://www.eros-os.org/essays/capintro.html What is a Capability, Anyway?] for a partisan explanation of what capabilities actually are.

See also [http://www.erights.org/elib/capability/overview.html Overview: Capability Computation]

{{stub}}

Kevin Reid: Add some info on URLs as capabilities

2011-09-20T22:15:41Z

Add some info on URLs as capabilities

←Older revision		Revision as of 22:15, 20 September 2011
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	An [[Unum]] can be also considered as a capability to a (replicated) object in a similar way as file descriptors of transparently replicated files by RAID are still regarded as file descriptors.		An [[Unum]] can be also considered as a capability to a (replicated) object in a similar way as file descriptors of transparently replicated files by RAID are still regarded as file descriptors.
		+
		+	== URLs as capabilities ==
		+
		+	As noted above, URLs are often used as capabilities in practice, especially when sent over e-mail. Some explicitly capability-structured systems, such as [[Tahoe-LAFS]], use capability URLs.
		+
		+	A hazard to using capability URLs directly in a web browser is that many browser extensions or options may transmit URLs to a third-party server. In the worst case, this may make those URLs public. However, there is some mitigation:
		+	* The fragment part of a URL reference (<code>#<em>id</em></code>) is not transmitted. If the browser supports executing JavaScript, then the capability can be placed in the fragment and transmitted only under script control, not as part of a URL.
		+	* The query string part (<code>?<em>foo</em>=<em>bar</em></code>) is often not transmitted. (Citation needed on this one!)

	== See also ==		== See also ==

Kevin Reid: sample URLs shouldn't be buried in actual links

2011-09-16T11:52:36Z

sample URLs shouldn't be buried in actual links

←Older revision		Revision as of 11:52, 16 September 2011
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	* POSIX file descriptors.		* POSIX file descriptors.
	Some examples of sparse capabilities (sometimes called password capabilities):		Some examples of sparse capabilities (sometimes called password capabilities):
-	* Designations of remote objects in E, such as <tt>captp://*orwqphzlugjwqj2wozz7tmg47ime466j@74.125.87.147:55189/oa6vn5whhapylswhzesdlqh5ppmjkcrq.</tt> Those who hold these capabilities have the permission to invoke any method supported by the designated object.	+	* Designations of remote objects in E, such as <code>captp://*orwqphzlugjwqj2wozz7tmg47ime466j@74.125.87.147:55189/oa6vn5whhapylswhzesdlqh5ppmjkcrq.</code> Those who hold these capabilities have the permission to invoke any method supported by the designated object.
	* Private URLs where having the URL is necessary and sufficient to use the resource. Common examples are:		* Private URLs where having the URL is necessary and sufficient to use the resource. Common examples are:
-	** "Confirm your e-mail address" links for website account registrations, mailing list subscriptions or [http://drupal.cbreurope.sk/civicrm/mailing/optout?reset=1&jid=XX&qid=XXXXX&h=XXXXXXXXXXXXXXXX&confirm=1 ~~opt-outs] from newsletters.~~	+	** "Confirm your e-mail address" links for website account registrations, mailing list subscriptions or opt-outs, e.g. <code><nowiki>http://drupal.cbreurope.sk/civicrm/mailing/optout?reset=1&jid=XX&qid=XXXXX&h=XXXXXXXXXXXXXXXX&confirm=1</nowiki></code>
	** Shared private documents such as in Google Docs, Google Maps, [http://picasa.google.com Picasa] albums, [http://www.doodle.com Doodle] schedulers.		** Shared private documents such as in Google Docs, Google Maps, [http://picasa.google.com Picasa] albums, [http://www.doodle.com Doodle] schedulers.
-	* Designation of file-system sub-trees in [[MinorFs]], such as <tt> /mnt/minorfs/cap/3d5d3efbf73bb711e7a47f82a44f471fcf77c70e/</tt>	+	* Designation of file-system sub-trees in [[MinorFs]], such as <code>/mnt/minorfs/cap/3d5d3efbf73bb711e7a47f82a44f471fcf77c70e/</code>

-	[[Unum]] can be also considered as a capability to a (replicated) object in a similar way as file descriptors of transparently replicated files by RAID are still regarded as file descriptors.	+	An [[Unum]] can be also considered as a capability to a (replicated) object in a similar way as file descriptors of transparently replicated files by RAID are still regarded as file descriptors.

	== See also ==		== See also ==

Kosik: added another example of sparse capability (opt-outs from "newsletters")

2011-04-15T20:04:26Z

added another example of sparse capability (opt-outs from "newsletters")

←Older revision		Revision as of 20:04, 15 April 2011
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	* Designations of remote objects in E, such as <tt>captp://*orwqphzlugjwqj2wozz7tmg47ime466j@74.125.87.147:55189/oa6vn5whhapylswhzesdlqh5ppmjkcrq.</tt> Those who hold these capabilities have the permission to invoke any method supported by the designated object.		* Designations of remote objects in E, such as <tt>captp://*orwqphzlugjwqj2wozz7tmg47ime466j@74.125.87.147:55189/oa6vn5whhapylswhzesdlqh5ppmjkcrq.</tt> Those who hold these capabilities have the permission to invoke any method supported by the designated object.
	* Private URLs where having the URL is necessary and sufficient to use the resource. Common examples are:		* Private URLs where having the URL is necessary and sufficient to use the resource. Common examples are:
-	** "Confirm your e-mail address" links for website account registrations ~~and~~ mailing list subscriptions.	+	** "Confirm your e-mail address" links for website account registrations, mailing list subscriptions or [http://drupal.cbreurope.sk/civicrm/mailing/optout?reset=1&jid=XX&qid=XXXXX&h=XXXXXXXXXXXXXXXX&confirm=1 opt-outs] from newsletters.
	** Shared private documents such as in Google Docs, Google Maps, [http://picasa.google.com Picasa] albums, [http://www.doodle.com Doodle] schedulers.		** Shared private documents such as in Google Docs, Google Maps, [http://picasa.google.com Picasa] albums, [http://www.doodle.com Doodle] schedulers.
	* Designation of file-system sub-trees in [[MinorFs]], such as <tt> /mnt/minorfs/cap/3d5d3efbf73bb711e7a47f82a44f471fcf77c70e/</tt>		* Designation of file-system sub-trees in [[MinorFs]], such as <tt> /mnt/minorfs/cap/3d5d3efbf73bb711e7a47f82a44f471fcf77c70e/</tt>

Kosik: Added note concerning unums.

2011-04-15T15:22:51Z

Added note concerning unums.

←Older revision		Revision as of 15:22, 15 April 2011
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	* Designation of file-system sub-trees in [[MinorFs]], such as <tt> /mnt/minorfs/cap/3d5d3efbf73bb711e7a47f82a44f471fcf77c70e/</tt>		* Designation of file-system sub-trees in [[MinorFs]], such as <tt> /mnt/minorfs/cap/3d5d3efbf73bb711e7a47f82a44f471fcf77c70e/</tt>

-	[[Unum]]~~s are capabilities~~ to replicated ~~objects~~.	+	[[Unum]] can be also considered as a capability to a (replicated) object in a similar way as file descriptors of transparently replicated files by RAID are still regarded as file descriptors.

	== See also ==		== See also ==

Kosik at 15:16, 15 April 2011

2011-04-15T15:16:24Z

←Older revision		Revision as of 15:16, 15 April 2011
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	** Shared private documents such as in Google Docs, Google Maps, [http://picasa.google.com Picasa] albums, [http://www.doodle.com Doodle] schedulers.		** Shared private documents such as in Google Docs, Google Maps, [http://picasa.google.com Picasa] albums, [http://www.doodle.com Doodle] schedulers.
	* Designation of file-system sub-trees in [[MinorFs]], such as <tt> /mnt/minorfs/cap/3d5d3efbf73bb711e7a47f82a44f471fcf77c70e/</tt>		* Designation of file-system sub-trees in [[MinorFs]], such as <tt> /mnt/minorfs/cap/3d5d3efbf73bb711e7a47f82a44f471fcf77c70e/</tt>
		+
		+	[[Unum]]s are capabilities to replicated objects.

	== See also ==		== See also ==

Kosik: I have removed the "XXX improve this section". This is redundant note. The page is already marked as a stub.

2011-04-15T15:13:31Z

I have removed the "XXX improve this section". This is redundant note. The page is already marked as a stub.

←Older revision		Revision as of 15:13, 15 April 2011
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	== See also ==		== See also ==
-
-	~~{{XXX\|improve this section}}~~

	See [http://www.eros-os.org/essays/capintro.html What is a Capability, Anyway?] for a partisan explanation of what capabilities actually are.		See [http://www.eros-os.org/essays/capintro.html What is a Capability, Anyway?] for a partisan explanation of what capabilities actually are.

Kosik: Controversy concerning sparse vs. password capabilities is settled. These terms are synonyms. I have removed XXX question.

2011-04-15T15:12:19Z

Controversy concerning sparse vs. password capabilities is settled. These terms are synonyms. I have removed XXX question.

←Older revision		Revision as of 15:12, 15 April 2011
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	** Shared private documents such as in Google Docs, Google Maps, [http://picasa.google.com Picasa] albums, [http://www.doodle.com Doodle] schedulers.		** Shared private documents such as in Google Docs, Google Maps, [http://picasa.google.com Picasa] albums, [http://www.doodle.com Doodle] schedulers.
	* Designation of file-system sub-trees in [[MinorFs]], such as <tt> /mnt/minorfs/cap/3d5d3efbf73bb711e7a47f82a44f471fcf77c70e/</tt>		* Designation of file-system sub-trees in [[MinorFs]], such as <tt> /mnt/minorfs/cap/3d5d3efbf73bb711e7a47f82a44f471fcf77c70e/</tt>
-	~~{{XXX\|What exactly do we mean by password capabilities here, such that a captp URL is not one?}}~~

	== See also ==		== See also ==

92.70.45.2: /* Examples */

2011-04-14T10:04:03Z

Examples

←Older revision		Revision as of 10:04, 14 April 2011
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	** "Confirm your e-mail address" links for website account registrations and mailing list subscriptions.		** "Confirm your e-mail address" links for website account registrations and mailing list subscriptions.
	** Shared private documents such as in Google Docs, Google Maps, [http://picasa.google.com Picasa] albums, [http://www.doodle.com Doodle] schedulers.		** Shared private documents such as in Google Docs, Google Maps, [http://picasa.google.com Picasa] albums, [http://www.doodle.com Doodle] schedulers.
-	* Designation of file-system sub-trees in MinorFs, such as <tt> /mnt/minorfs/cap/3d5d3efbf73bb711e7a47f82a44f471fcf77c70e/</tt>	+	* Designation of file-system sub-trees in [[MinorFs]], such as <tt> /mnt/minorfs/cap/3d5d3efbf73bb711e7a47f82a44f471fcf77c70e/</tt>
	{{XXX\|What exactly do we mean by password capabilities here, such that a captp URL is not one?}}		{{XXX\|What exactly do we mean by password capabilities here, such that a captp URL is not one?}}

92.70.45.2 at 09:57, 14 April 2011

2011-04-14T09:57:06Z

←Older revision		Revision as of 09:57, 14 April 2011
Line 14:		Line 14:
	** "Confirm your e-mail address" links for website account registrations and mailing list subscriptions.		** "Confirm your e-mail address" links for website account registrations and mailing list subscriptions.
	** Shared private documents such as in Google Docs, Google Maps, [http://picasa.google.com Picasa] albums, [http://www.doodle.com Doodle] schedulers.		** Shared private documents such as in Google Docs, Google Maps, [http://picasa.google.com Picasa] albums, [http://www.doodle.com Doodle] schedulers.
-		+	* Designation of file-system sub-trees in MinorFs, such as <tt> /mnt/minorfs/cap/3d5d3efbf73bb711e7a47f82a44f471fcf77c70e/</tt>
	{{XXX\|What exactly do we mean by password capabilities here, such that a captp URL is not one?}}		{{XXX\|What exactly do we mean by password capabilities here, such that a captp URL is not one?}}