This is the Zot! social communications protocol. Specification revision: 1 02 September 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). Example: From: bob@example.com Sender: bob@example.com To: alice@example.com Both "From:" and "Sender:" MUST be provided, and represent a webfinger address of the author and sender respectively. The webfinger address for the From address MUST contain a discoverable salmon public key that 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'. A reply to a given message MUST be sent to the original From address, and MAY be sent to any additional addresses in the recipient list. The original 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. To: * indicates a public message with no specifically enumerated recipients. The fields To:, Cc:, and/or Bcc: MAY be present. At least one recipient field MUST be present. These fields may use the entire syntax specified by RFC822, for example: To: "Bob Smith" , "Alice Jones" is a valid entry. A zot envelope is UTF-8 encoded, which differs from RFC822. The host component MUST be US-ASCII, with punycode translation of internationalised domain names applied. The entire envelope is then encrypted using alg with env_key and env_iv and base64url encoded for transmission. The zot envelope MAY include remote addresses. A zot delivery agent MUST parse all addresses 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 To:, Cc:, or 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: Version is specified in this document and indicates the current revision. 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, the delivery 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 authentication * ********************** 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/ Activty Stream Base Schema http://activitystrea.ms/head/activity-schema.html WebFinger Protocol http://code.google.com/p/webfinger/wiki/WebFingerProtocol