This is the Zot! social communications protocol. Specification revision: 1 2 October 2011 Mike Macgirvin This specification is public domain. Zot is a framework for secure delivery of messages on the web based on webfinger and encapsulating salmon. First read the salmon and salmon magic envelope specifications. Zot also makes use of webfinger and ActivityStreams and several concepts from RFC822 (email). Zot encompasses the zot delivery framework and the zid remote access protocol. The current specification revision (1) is frozen until a reference implementation is available. After that, any protocol changes will require a change to the revision number. **************** * Zot delivery * **************** Format of a zot wrapper. This completely encapsulates a salmon magic envelope and provides privacy protection, while defining a delivery envelope - a concept familiar to email systems. All addresses in zot are webfinger resolvable addresses containing zot endpoints and salmon public keys (zot is a superset of salmon). ((key)) ((iv)) ((env_key)) ((env_iv)) ((envelope)) ((sender signature)) AES-256-CBC ((salmon)) zot:key ******* A suitable randomly generated encyption key of length 32 octets for encrypting the salmon packet. This is then encrypted with the sender's private key and base64url encoded. zot:iv ****** A suitable randomly generated initialisation vector of length 16 octets for encrypting the salmon packet. This is then encrypted with the sender's private key and base64url encoded. zot:env_key *********** A suitable randomly generated encyption key of length 32 octets for encrypting the envelope. This is then encrypted with the recipient's public key and base64url encoded. For bulk deliveries, it is encrypted with the site bulk delivery public key. zot:env_iv ********** A suitable randomly generated initialisation vector of length 16 octets for encrypting the envelope. This is then encrypted with the recipient's public key and base64url encoded. For bulk deliveries, it is encrypted with the site bulk delivery public key. zot:env ******* This consists of RFC822-style header fields representing the sender and recipient(s). Line lengths have no defined limit and RFC822 continuation lines are not supported. If an inbound server is not able to process an envelope or post due to size constraints, it SHOULD return a "413 Entity too large" HTTP response. Example: Z-From: zot:bob@example.com Z-Sender: zot:bob@example.com Z-To: zot:alice@example.com Both "Z-From:" and "Z-Sender:" MUST be provided, and represent a single webfinger address of the author and sender respectively. The webfinger address for the From address MUST contain a discoverable salmon public key which is needed to verify the enclosed salmon data. Sender is used to indicate the webfinger identity responsible for transmitting this message. From indicates the message author. In web-based social systems, a reply to a message SHOULD be conveyed to all of the original message participants. Only the author of the original message may know all the recipients (such as those contained in Bcc: elements). The author of a message always provides 'From'. They MUST duplicate this information as 'Sender' when posting a followup message. A reply to a given message MUST be sent to the From address of the original post, and MAY be sent to any additional addresses in the recipient list. The original post author MUST send the reply to all known recipients of the original message, with their webfinger identity as Sender, and the comment/reply author as From. Receiving agents SHOULD validate the From identity as the signer of the salmon magic envelope, and MAY reject it. They SHOULD also verify the Sender signature of the zot packet if it is different than the salmon signature. They MAY reject the message if the Sender is not allowed in their "friend list", or if they do not have a suitable relationship with the Sender, or if either signature fails to validate. Rejected messages for one of these reasons SHOULD be indicated with a "400 Bad Request" HTTP response. Z-To: * indicates a public message with no specifically enumerated recipients. The fields Z-To: and/or Z-Bcc: MAY be present. At least one recipient field MUST be present. Z-To: zot:bob@example.com, zot:alice@example.com, mailto:dave@example.com Z-Bcc: zot:https://example.com/profile/richard are valid entries. Addresses are comma separated and individual entries MUST NOT contain commas. There MAY be any number of ASCII space characters between entries for legibility. Header lines are terminated with a linefeed character (ASCII 0x0A). This specification provides the following protocol address prefixes for use in Z-To: or Z-Bcc: elements: zot: - normal zot delivery using webfinger or LRDD resolvable address dfrn: - legacy DFRN mode delivery using webfinger or LRDD resovable address ostatus: - normal OStatus delivery using webfinger or LRDD resovable address diaspora: - Diaspora network delivery using webfinger address facebook: - Facebook profile page URL twitter: - Twitter personal page URL without AJAX '#!' fragment mailto: - email RFC822/ESMTP address Examples: twitter:http://twitter.com/bjensen facebook:http://facebook.com/profile.php?id=000000001 Foreign protocol addresses which have not been defined in this specification or future revisions of this specification and which are unknown to the recipient delivery process MAY be ignored. In cases where an address may contain either a webfinger or LRDD address, the webfinger address SHOULD be used preferentially. Z-Bcc: ****** The Z-Bcc element may contain one or more addresses which are hidden from end user presentation. A zot receiving system MUST NOT store or allow for the display of the Bcc information. Implementations which require extreme privacy SHOULD send individual posts to each of the Bcc: recipients containing only a single address. They MAY send all Bcc: posts using bulk delivery, however this may have privacy implications as there is no guarantee a receiving system will not log, store, or otherwise reveal the contents of the Bcc recipient list. Z-To: addresses MAY be shown to an end user. Envelope encryption ******************* The entire envelope is encrypted using alg with env_key and env_iv and base64url encoded for transmission. The zot envelope MAY include remote addresses. A zot inbound delivery agent MUST parse the envelope and determine whether a delivery address to the current endpoint is valid. This may be the result of: 1. An address contains the public message wildcard '*' 2. The current endpoint is a personal endpoint and one of the recipients listed in the Z-To: or Z-Bcc: addresses matches the webfinger address of the "owner" of the endpoint. 3. The current endpoint is a bulk delivery endpoint. The bulk delivery endpoint is defined elsewhere in this document. The bulk delivery agent will deliver to all local addresses found in the address lists. zot:sig ******* The Sender of the message signs the underlying salmon data in the manner prescribed by salmon. If the Sender and From address are identical, the signature will be identical to the signature of the underlying salmon packet. If they are different, this signature is verified with the Sender's public key to verify the Sender. zot:alg ******* Currently the only valid choice for alg is "AES-256-CBC". zot:data ******** The data field is a salmon magic envelope. This is encrypted with alg using key and iv. The result is then base64url encoded for transmission. For the first release of this specification, the data format of the enclosed salmon SHOULD be 'application/atom+xml' representing an Atom formatted ActivityStream. Future revisions MAY allow other alternate data formats. All acceptable formats MUST be listed in an XRD property (described elsewhere in this document). Delivery ******** The zot message is then POSTed to the zot endpoint URL as application/text+xml and can be decoded/decrypted by the recipient using their private key. The normal salmon endpoint for a service MAY be used as an alternate delivery method for non-encrypted (e.g. public) messages. Discover of the zot endpoint is based on webfinger XRD: Bulk Delivery ************* A site MAY provide a bulk delivery endpoint, which MAY be used to avoid multiple encryptions of the same data for a single destination. This is discoverable by providing a zot endpoint with a corresponding salmon public key in the site's .well-known/host-meta file. A delivery to this endpoint will deliver to all local recipients provided within the zot envelope. Extensibility ************* This specification is subject to change. The current version which is in effect at a given site may be noted by XRD properties. The following properties MUST be present in the XRD providing the relevant endpoint: 1 application/atom+xml Version is specified in this document and indicates the current revision. Version is an increasing non-zero integer value. There are no minor versions. Implementations MAY provide compatibility to multiple incompatible versions by using this version indication. The "accept" indicates a range of document content types which may be enclosed in the underlying salmon magic envelope. We anticipate this specification will in the future allow for a close variant of "message/rfc822" and which may include MIME. This may also be used to embed alternate message formats and protocols such as "application/x-diaspora+xml". If a delivery agent is unable to provide any acceptable data format to the remote system, the delivery to that system MUST be terminated/cancelled. Foreign Messages **************** Messages MAY be imported from other networks and systems which have no knowledge of salmon signatures. The salmon signature in this case MUST be the exact string 'NOTSIGNED' to indicate that the author (From address) cannot be validated using salmon verification. This message MUST be relayed by a Sender who can provide a valid salmon signature of the message via zot:sig. Delivery systems MAY reject foreign messages. ******************************* * Zid (Zot-ID) authentication * ******************************* This section of the document is considered separate from the delivery specification precding it and represents a different protocol, which is currently incomplete. This will be split off into another document in the future, but is presented here as a synergistic component of the Zot network model. URLs may be present within a zot message which refer to private and/or protected resources. Zid uses OpenID to gain access to these protected resources. These could be private photos or profile information - or *any* web accessible resource. Using zid, these can have access controls which extends to any resolvable webfinger address. Zid authentication relies on the presence of an OpenID provider element in webfinger, and a URL template which is applied to protected resources within a zot message. The template is designated with the characters "{zid=}" within a URL of a zot message. When the page is rendered for viewing to an observer, this template is replaced with the webfinger address of the viewer (if known), or an empty string if the webfinger address of the viewer cannot be determined. For example in a message body: http://example.com/photos/bob/picture.jpg?{zid=} refers to a private photo which is only visible to alice@example.com. If Alice is viewing the page, the link is rendered with http://example.com/photos/bob/picture.jpg?zid=alice@example.com If the page viewer is unknown, it is rendered as http://example.com/photos/bob/picture.jpg?zid= When the link is visited, the web server at example.com notes the presence of the zid parameter and uses information from webfinger to locate the OpenID provider for the zid webfinger address. It then redirects to the OpenID server and requests authentication of the given person. If this is successful, access to the protected resource is granted. A browser cookie may be provided to avoid future authentication redirects and allow authenticated browsing to other resources on the website. Only authentication via OpenID is defined in this version of the specification. This can be used to provide access control of any web resource to any webfinger identity on the internet. ********* * Links * ********* Salmon Protocol http://www.salmon-protocol.org/salmon-protocol-summary Salmon Magic Envelope http://salmon-protocol.googlecode.com/svn/trunk/draft-panzer-magicsig-01.html Atom Activity Stream Draft http://activitystrea.ms/specs/atom/1.0/ Activity Stream Base Schema http://activitystrea.ms/head/activity-schema.html WebFinger Protocol http://code.google.com/p/webfinger/wiki/WebFingerProtocol