MicroID Specification, Version 0.3

Abstract

This specification defines the semantics of MicroID, a lightweight identity technology that enables the creation of a portable identity token from any two Uniform Resource Identifiers.

Table of Contents

1.  Introduction
2.  Terminology
3.  Architecture
4.  Format
5.  Generation
6.  Processing
7.  Using Technologies
    7.1.  HTML Class Attribute
    7.2.  HTML Meta Data
8.  Internationalization Considerations
9.  Security Considerations
10.  References
    10.1.  Normative References
    10.2.  Informative References
Appendix A.  Legacy Support
Appendix B.  Revision History
§  Authors' Addresses

1.  Introduction

MicroID is a lightweight identity technology that enables the creation of a portable identity token from any two Uniform Resource Identifiers ([URI] (Berners-Lee, T., Fielding, R., and L. Masinter, “Uniform Resource Identifier (URI): Generic Syntax,” January 2005.)).

Such identity tokens are desirable for several reasons:

• They enable individuals to assert ownership over information published and reputation earned on the Internet in a granular manner, even if that information or reputation is hosted at a third-party service.
• They enable service providers to "stamp" information and reputation based on a validated URI associated with an individual who uses the service.

Note: The preferred discussion forum for this specification is the MicroID mailing list; subscription information is located at <http://lists.ibiblio.org/mailman/listinfo/microid> and the mailing list archives are located at <http://lists.ibiblio.org/pipermail/microid/>.

2.  Terminology

In this specification, we use the following terms to describe the parties involved in the production and consumption of a MicroID:

• Consumer -- Any party that reads a MicroID issued by an Issuer (in other identity systems, a Consumer is sometimes called a Relying Party).
• Entity -- Either party identified by a URI or IRI that is used to construct a MicroID.
• Individual -- An Entity that generates information or earns reputation.
• Issuer -- The party that generates a MicroID. The Issuer can be a third party and need not be an Entity.
• Service Provider -- An Entity that is responsible for hosting information or reputation; a Service Provider may or may not be an Issuer.

The following keywords as used in this document are to be interpreted as described in [TERMS] (Bradner, S., “Key words for use in RFCs to Indicate Requirement Levels,” March 1997.): "MUST", "SHALL", "REQUIRED"; "MUST NOT", "SHALL NOT"; "SHOULD", "RECOMMENDED"; "SHOULD NOT", "NOT RECOMMENDED"; "MAY", "OPTIONAL".

3.  Architecture

In general we assume that MicroID technology will be used by service providers to stamp information or reputation that is hosted by the service provider on behalf of individuals. In this architecture, the Service Provider is both the Issuer and one of the Entities, where the other Entity is an Individual.

     +--------+
     | Entity |
     +--------+
         |
         | registration
         |
+-------------------+
| Service Provider  |
| (Entity + Issuer) |
+-------------------+
         |
         | issuance
         |
      MicroID

However, a MicroID can also be issued by a trusted third party with which both a Service Provider and Individual have registered. In this architecture, the Service Provider is merely one of the Entities.

+--------+    +------------------+
| Entity |    | Service Provider |
+--------+    +------------------+
    |                 |
    |                 |
    +-----------------+
           |
           | registration
           |
       +--------+
       | Issuer |
       +--------+
           |
           | issuance
           |
        MicroID

4.  Format

The syntax for a MicroID is defined below using the Augmented Backus-Naur Form as defined in [ABNF] (Crocker, D. and P. Overell, “Augmented BNF for Syntax Specifications: ABNF,” October 2005.).

microid = inputs ":" algo ":" hash
inputs  = scheme "+" scheme
scheme  = ALPHA *( ALPHA / DIGIT / "+" / "-" / "." )
          ; a URI scheme name (e.g., mailto)
algo    = ALPHA *( ALPHA / DIGIT )
          ; the short name of a hashing
          ; algorithm (e.g., sha256)
hash    = *( ALPHA / DIGIT )
          ; a hash of the URIs for both entities

Note: See the Legacy Support (Legacy Support) section of this document for information regarding the original MicroID format.

5.  Generation

A MicroID MUST be generated by an Issuer, not by an Individual. The Issuer MAY be the Service Provider that hosts the information about, content created by, or reputation earned by an Individual, or it MAY be a third party trusted by both the Individual and the Service Provider.

An Issuer MUST NOT generate a MicroID until it has verified that the Individual or Service Provider has control over a given EntityURI. Methods for such verification are out of scope for this specification and may vary according to local service policies and the URI scheme in question.

In general, the method for generating the hash is:

hash = algo(
            algo(EntityURI)
            +
            algo(EntityURI)
           )

The "algo" MAY be any recognized hashing algorithm, such as those defined in [SHA] (National Institute of Standards and Technology, “Secure Hash Standard,” August 2002.). Support for the SHA-1 and SHA-256 algorithms is REQUIRED for interoperability. The algorithm names are of the form "sha1", "sha256" (i.e., all lowercase with no hyphen). The output MUST be in hexadecimal (not base64) format. The same algorithm MUST be used for all hashing functions when generating a given MicroID.

The "EntityURI" MAY conform to any URI scheme, such as [HTTP] (Fielding, R., Gettys, J., Mogul, J., Frystyk, H., Masinter, L., Leach, P., and T. Berners-Lee, “Hypertext Transfer Protocol -- HTTP/1.1,” June 1999.), , [SIP] (Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A., Peterson, J., Sparks, R., Handley, M., and E. Schooler, “SIP: Session Initiation Protocol,” June 2002.), and [XMPP] (Saint-Andre, P., “Internationalized Resource Identifiers (IRIs) and Uniform Resource Identifiers (URIs) for the Extensible Messaging and Presence Protocol (XMPP),” August 2006.). The first EntityURI MUST be that of the Individual and the second EntityURI MUST be that of the Service Provider. Any given EntityURI MAY have meaning above and beyond that encapsulated in the relevant URI scheme; for example, the HTTP URI for an Individual could be hosted by an OpenID service (see <http://openid.net/>). However, MicroID places no restrictions on the semantics of a given EntityURI.

As an example, consider the following inputs, from which a MicroID is generated using the SHA-1 algorithm:

• The first Entity is an Individual identified by an XMPP URI of "xmpp:".
• The second Entity is a Service Provider identified by a HTTP URI of "https://www.xmpp.net/".

The hash is generated as follows:

sha1(
     sha1(xmpp:)
     +
     sha1(https://www.xmpp.net/)
    )

sha1(
     afa6353518f818af2f036da336c3097dedc00dee
     +
     3115de01ebfa34a34314060b5f30038b0fa359f8
    )

sha1(
afa6353518f818af2f036da336c3097dedc00dee3115de01ebfa34a34314060b5f30038b0fa359f8
    )

6196ea6709be2a4cbdf2bc0cfaeac491f2fb8921

Thus the issued MicroID is:

xmpp+https:sha1:6196ea6709be2a4cbdf2bc0cfaeac491f2fb8921

6.  Processing

A processing application MAY use only the hash portion of the MicroID for comparison purposes. An implementation SHOULD be liberal in accepting MicroIDs that conform to the legacy format (see the Legacy Support (Legacy Support) section of this document).

7.  Using Technologies

This specification does not limit the technologies that might make use of MicroIDs, and future versions of this specification might describe a wide range of such uses. Here we describe two such uses.

Note: The scope of information (e.g., markup) covered by a MicroID depends on the nature of the using technology and must be defined separately by each using technology.

7.1.  HTML Class Attribute

One possible use is to include a MicroID in the [HTML] (Jacobs, I., Raggett, D., and A. Hors, “HTML 4.01 Specification,” December 1999.) class attribute. The RECOMMENDED format is to prepend the MicroID itself with the string "microid-", as shown in the following example:

<p class='microid-xmpp+https:sha1:6196ea6709be2a4cbdf2bc0cfaeac491f2fb8921'>mycontent</p>

In this usage, the scope of the MicroID is all information contained within the element that possesses the class attribute, whether that information is represented as attributes, character data, or child elements. However, any given child element MAY itself possess a class attribute specifying a MicroID that overrides the content claim asserted by the parent element. In all cases, the relevant claim is always that of the nearest containing element in the hierarchy.

A MicroID can be used on its own to mark content as created by a certain Individual (e.g., a comment made on a web forum):

<div class='microid-xmpp+https:sha1:6196ea6709be2a4cbdf2bc0cfaeac491f2fb8921'>
  <p>This is a great idea!</p>
</div>

A MicroID can be also used in concert with other lightweight identity technologies such as the rel='me' value defined by XHTML Friends Network (XFN) as specified at <http://gmpg.org/xfn/11>:

<div class='microid-xmpp+https:sha1:6196ea6709be2a4cbdf2bc0cfaeac491f2fb8921'>
  <p>This is a great idea!</p>
  <p>--<a rel='me' href='http://2idi.com/contact/=stpeter'>stpeter</a></p>
</div>

7.2.  HTML Meta Data

Another possible use is in meta data about an [HTML] (Jacobs, I., Raggett, D., and A. Hors, “HTML 4.01 Specification,” December 1999.) file (e.g., to signify that a given web page is created by, owned by, or about a given Individual). This is done by including a <meta/> tag whose 'name' attribute is "microid" and whose 'content' attribute specifies the MicroID, as shown in the following example:

<meta name='microid' content='xmpp+https:sha1:6196ea6709be2a4cbdf2bc0cfaeac491f2fb8921'/>

In this usage, the scope of the MicroID is the page itself. However, the whole-page claim represented in the META tag can be overridden by claims represented in class attributes possessed by elements within the HTML body.

A file MAY contain multiple META tags with a name of "microid" (e.g., to claim ownership by multiple authors or to represent multiple identities associated with the same individual).

8.  Internationalization Considerations

A MicroID SHOULD be constructed using two Uniform Resource Identifiers ([URI] (Berners-Lee, T., Fielding, R., and L. Masinter, “Uniform Resource Identifier (URI): Generic Syntax,” January 2005.)) but one or both inputs MAY instead be an Internationalized Resource Identifier ([IRI] (Duerst, M. and M. Suignard, “Internationalized Resource Identifiers (IRIs),” January 2005.)).

9.  Security Considerations

MicroID is a technology for identifying the ownership or authorship of information on the Internet. It is not a mechanism for authentication, authorization, security, or encryption. Use of MicroID technology results only in weak verification of identities. MicroID may be susceptible to [DNS] (Mockapetris, P., “Domain names - implementation and specification,” November 1987.) poisoning attacks unless [DNSSEC] (Eastlake, D., “Domain Name System Security Extensions,” March 1999.) is used, since most URIs depend on DNS.

10.  References

10.1. Normative References

10.2. Informative References

Appendix A.  Legacy Support

MicroID originally assumed the use of SHA1 as the hashing algorithm and did not specify the schemes of the EntityURI inputs, resulting in the following format:

microid = hash
hash    = *( ALPHA / DIGIT )
          ; a hash of the URIs for both entities

For example, using the same inputs as shown in the body of this specification, the MicroID in legacy format would be:

6196ea6709be2a4cbdf2bc0cfaeac491f2fb8921

An implementation MUST generate MicroIDs in the format specified in the Format (Format) section of this document, but SHOULD process MicroIDs generated using the legacy format for the sake of backward compatibility.

Appendix B.  Revision History

Version 0.3 (2007-01-05) -- Specified that scope of applicability depends on the using technology, and defined scope with respect to HTML class attribute and meta tag.

Version 0.2 (2007-01-02) -- Clarified algorithm rules; began specification of MicroID processing; described legacy format; corrected several examples.

Version 0.1 (2007-01-01) -- Initial version.

Authors' Addresses