304 lines
11 KiB
Text
304 lines
11 KiB
Text
This is the Zot! social communications protocol.
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Specification revision: 1
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02 September 2011
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Mike Macgirvin
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This specification is public domain.
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Zot is a framework for secure delivery of messages on the web based on
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webfinger and encapsulating salmon.
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First read the salmon and salmon magic envelope specifications. Zot also
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makes use of webfinger and ActivityStreams and several concepts from RFC822
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(email). Zot encompasses the zot delivery framework and the zid remote
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access protocol.
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The current specification revision (1) is frozen until a reference
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implementation is available. After that, any protocol changes will require a
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change to the revision number.
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****************
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* Zot delivery *
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****************
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Format of a zot wrapper. This completely encapsulates a salmon magic envelope
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and provides privacy protection, while defining a delivery envelope - a
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concept familiar to email systems. All addresses in zot are webfinger
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resolvable addresses containing zot endpoints and salmon public keys (zot
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is a superset of salmon).
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<?xml version='1.0' encoding='UTF-8'?>
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<zot:msg xmlns:zot='http://purl.org/zot/1.0'>
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<zot:key>((key))</zot:key>
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<zot:iv>((iv))</zot:iv>
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<zot:env_key>((env_key))</zot:env_key>
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<zot:env_iv>((env_iv))</zot:env_iv>
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<zot:env>((envelope))</zot:env>
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<zot:sig key_id="xxx">((sender signature))</zot:sig>
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<zot:alg>AES-256-CBC</zot:alg>
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<zot:data type='application/magic-envelope+xml'>((salmon))</zot:data>
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</zot:msg>
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zot:key
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*******
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A suitable randomly generated encyption key of length 32 octets for encrypting
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the salmon packet. This is then encrypted with the sender's private key and
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base64url encoded.
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zot:iv
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******
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A suitable randomly generated initialisation vector of length 16 octets for
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encrypting the salmon packet. This is then encrypted with the sender's private
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key and base64url encoded.
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zot:env_key
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***********
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A suitable randomly generated encyption key of length 32 octets for encrypting
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the envelope. This is then encrypted with the recipient's public key and
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base64url encoded. For bulk deliveries, it is encrypted with the site bulk
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delivery public key.
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zot:env_iv
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**********
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A suitable randomly generated initialisation vector of length 16 octets for
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encrypting the envelope. This is then encrypted with the recipient's public
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key and base64url encoded. For bulk deliveries, it is encrypted with the site
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bulk delivery public key.
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zot:env
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*******
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This consists of RFC822-style header fields representing the sender and
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recipient(s). Example:
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From: bob@example.com
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Sender: bob@example.com
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To: alice@example.com
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Both "From:" and "Sender:" MUST be provided, and represent a webfinger
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address of the author and sender respectively. The webfinger address for
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the From address MUST contain a discoverable salmon public key that
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is needed to verify the enclosed salmon data. Sender is used to indicate
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the webfinger identity responsible for transmitting this message. From
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indicates the message author.
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In web-based social systems, a reply to a message SHOULD be conveyed to all of
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the original message participants. Only the author of the original message
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may know all the recipients (such as those contained in Bcc: elements). The
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author of a message always provides 'From'. They MUST duplicate this
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information as 'Sender'.
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A reply to a given message MUST be sent to the original From address, and MAY
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be sent to any additional addresses in the recipient list. The original author
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MUST send the reply to all known recipients of the original message, with
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their webfinger identity as Sender, and the comment/reply author as From.
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Receiving agents SHOULD validate the From identity as the signer of the salmon
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magic envelope, and MAY reject it. They SHOULD also verify the Sender signature
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of the zot packet if it is different than the salmon signature. They MAY
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reject the message if the Sender is not allowed in their "friend list", or if
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they do not have a suitable relationship with the Sender, or if either
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signature fails to validate.
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To: *
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indicates a public message with no specifically enumerated recipients.
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The fields To:, Cc:, and/or Bcc: MAY be present. At least one recipient field
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MUST be present. These fields may use the entire syntax specified by RFC822,
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for example:
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To: "Bob Smith" <bob@example.com>, "Alice Jones" <alice@example.com>
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is a valid entry. A zot envelope is UTF-8 encoded, which differs from RFC822.
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The host component MUST be US-ASCII, with punycode translation of
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internationalised domain names applied.
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The entire envelope is then encrypted using alg with env_key and env_iv and
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base64url encoded for transmission.
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The zot envelope MAY include remote addresses. A zot delivery agent MUST parse
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all addresses and determine whether a delivery address to the current endpoint
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is valid. This may be the result of:
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1. An address contains the public message wildcard '*'
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2. The current endpoint is a personal endpoint and one of the recipients
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listed in the To:, Cc:, or Bcc: addresses matches the webfinger address of
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the "owner" of the endpoint.
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3. The current endpoint is a bulk delivery endpoint. The bulk delivery
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endpoint is defined elsewhere in this document. The bulk delivery agent
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will deliver to all local addresses found in the address lists.
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zot:sig
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*******
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The Sender of the message signs the underlying salmon data in the manner
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prescribed by salmon. If the Sender and From address are identical, the
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signature will be identical to the signature of the underlying salmon packet.
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If they are different, this signature is verified with the Sender's public
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key to verify the Sender.
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zot:alg
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*******
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Currently the only valid choice for alg is "AES-256-CBC".
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zot:data
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********
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The data field is a salmon magic envelope. This is encrypted with alg using
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key and iv. The result is then base64url encoded for transmission.
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For the first release of this specification, the data format of the enclosed
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salmon SHOULD be 'application/atom+xml' representing an Atom formatted
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ActivityStream. Future revisions MAY allow other alternate data formats.
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All acceptable formats MUST be listed in an XRD property (described elsewhere
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in this document).
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Delivery
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********
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The zot message is then POSTed to the zot endpoint URL as
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application/text+xml and can be decoded/decrypted by the recipient using
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their private key.
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The normal salmon endpoint for a service MAY be used as an alternate
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delivery method for non-encrypted (e.g. public) messages.
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Discover of the zot endpoint is based on webfinger XRD:
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<link rel="http://purl.org/zot/1.0/post"
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href="http://example/org/zot-endpoint" />
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Bulk Delivery
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*************
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A site MAY provide a bulk delivery endpoint, which MAY be used to avoid
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multiple encryptions of the same data for a single destination.
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This is discoverable by providing a zot endpoint with a corresponding
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salmon public key in the site's .well-known/host-meta file.
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A delivery to this endpoint will deliver to all local recipients provided
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within the zot envelope.
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Extensibility
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*************
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This specification is subject to change. The current version which is in
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effect at a given site may be noted by XRD properties. The following
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properties MUST be present in the XRD providing the relevant endpoint:
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<Property xmlns:zot="http://purl.og/zot/1.0"
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type="http://purl.org/zot/1.0/version"
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zot:version="1" />
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<Property xmlns:zot="http://purl.og/zot/1.0"
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type="http://purl.org/zot/1.0/accept"
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zot:accept="application/atom+xml" />
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Version is specified in this document and indicates the current revision.
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Implementations MAY provide compatibility to multiple incompatible versions
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by using this version indication. The "accept" indicates a range of document
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content types which may be enclosed in the underlying salmon magic envelope.
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We anticipate this specification will in the future allow for a close variant
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of "message/rfc822" and which may include MIME. This may also be used to
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embed alternate message formats and protocols such as
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"application/x-diaspora+xml". If a delivery agent is unable to provide any
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acceptable data format, the delivery MUST be terminated/cancelled.
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Foreign Messages
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****************
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Messages MAY be imported from other networks and systems which have no
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knowledge of salmon signatures. The salmon signature in this case MUST be the
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exact string 'NOTSIGNED' to indicate that the author (From address) cannot be
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validated using salmon verification. This message MUST be relayed by a Sender
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who can provide a valid salmon signature of the message via zot:sig. Delivery
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systems MAY reject foreign messages.
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**********************
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* Zid authentication *
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**********************
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URLs may be present within a zot message which refer to private and/or
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protected resources. Zid uses OpenID to gain access to these protected
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resources. These could be private photos or profile information - or *any*
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web accessible resource. Using zid, these can have access controls which
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extends to any resolvable webfinger address.
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Zid authentication relies on the presence of an OpenID provider element in
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webfinger, and a URL template which is applied to protected resources within
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a zot message.
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The template is designated with the characters "{zid=}" within a URL of a zot
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message. When the page is rendered for viewing to an observer, this template
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is replaced with the webfinger address of the viewer (if known), or an empty
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string if the webfinger address of the viewer cannot be determined.
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For example in a message body:
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http://example.com/photos/bob/picture.jpg?{zid=}
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refers to a private photo which is only visible to alice@example.com.
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If Alice is viewing the page, the link is rendered with
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http://example.com/photos/bob/picture.jpg?zid=alice@example.com
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If the page viewer is unknown, it is rendered as
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http://example.com/photos/bob/picture.jpg?zid=
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When the link is visited, the web server at example.com notes the presence of
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the zid parameter and uses information from webfinger to locate the OpenID
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provider for the zid webfinger address. It then redirects to the OpenID
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server and requests authentication of the given person. If this is successful,
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access to the protected resource is granted.
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A browser cookie may be provided to avoid future authentication redirects
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and allow authenticated browsing to other resources on the website.
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Only authentication via OpenID is defined in this version of the specification.
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This can be used to provide access control of any web resource to any
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webfinger identity on the internet.
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*********
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* Links *
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*********
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Salmon Protocol
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http://www.salmon-protocol.org/salmon-protocol-summary
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Salmon Magic Envelope
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http://salmon-protocol.googlecode.com/svn/trunk/draft-panzer-magicsig-01.html
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Atom Activity Stream Draft
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http://activitystrea.ms/specs/atom/1.0/
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Activty Stream Base Schema
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http://activitystrea.ms/head/activity-schema.html
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WebFinger Protocol
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http://code.google.com/p/webfinger/wiki/WebFingerProtocol
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