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Internet Engineering Task Force                          P. Hallam-Baker
Internet-Draft                                         Comodo Group Inc.
Intended status: Standards Track                            R. Stradling
Expires: October 25, 2012                                 Comodo CA Ltd.
                                                              S. Farrell
                                                  Trinity College Dublin
                                                             D. Kutscher
                                                               B. Ohlman
                                                          April 23, 2012

        The Named Information (ni) URI Scheme: Optional Features


   This document specifies optional things that one can do with "ni"
   URIs and related names.  Those include an additional hash algorithm
   for handling dynamic content, some specific query-strong parameters
   for ni URIs and a mechanism for embedding ni URIs into QR codes.

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
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   This Internet-Draft will expire on October 25, 2012.

Copyright Notice

   Copyright (c) 2012 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of

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   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 3
   2.  Additional Algorithm  . . . . . . . . . . . . . . . . . . . . . 3
     2.1.  Hashed Dynamic Content  . . . . . . . . . . . . . . . . . . 3
   3.  Query String Paramaeters  . . . . . . . . . . . . . . . . . . . 4
     3.1.  Digest with Content Type  . . . . . . . . . . . . . . . . . 4
     3.2.  Additional Locators . . . . . . . . . . . . . . . . . . . . 5
     3.3.  Digest with Decryption Key  . . . . . . . . . . . . . . . . 6
     3.4.  Wrapped URL . . . . . . . . . . . . . . . . . . . . . . . . 7
   4.  QR Codes  . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
   5.  Security Considerations . . . . . . . . . . . . . . . . . . . . 7
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 7
     6.1.  Additional algorithm in RFCXXXX registry  . . . . . . . . . 7
     6.2.  Creation of ni parameter registry . . . . . . . . . . . . . 7
   7.  Normative References  . . . . . . . . . . . . . . . . . . . . . 8
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . . 8

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1.  Introduction

   The ni URI scheme [nischeme] supports extensibility in terms of the
   algorithm used to derive a value (normally, but not always a strong
   digest algorithm) and via support for a query-string thay can contain
   a list of key=value pairs.  This document defines some uses for both
   of these extensibility points and creates IANA registries that can be
   used to register additional algorithms and key strings for use in the
   query part of an ni name.  We [[will]] also define a way to embed ni
   names in QR codes.

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in RFC 2119 [RFC2119].

   [[Comments are included in double-square brackets, like this.]]

   [[Note that the features here are less mature than the specification
   in the [nischeme] document.  The intent is to develop these as
   required for the various use-cases as we go.  If something from here
   appears to be as widely useful as the core ni scheme, then the
   authors are willing to move features from this document to the core
   document.  We are also happy to incoroporate features to handle
   additional use-cases here if those arise.]]

2.  Additional Algorithm

   This section specifies an additional algorithm that MAY be used to
   handle hashes calculated over dynamically changing objects.

2.1.  Hashed Dynamic Content

   The ni scheme involves calculating digest values over content
   objects.  That works fine with static objects but is problematic for
   objects whose value is dynamically generated.  In this section we
   define an algorithm that supports the same core "name-data integrity"
   service for dynamic objects.  The basic idea is simply to include a
   hash of a public key in the ni name, and then for the dynamic object
   to be digitally signed with the corresponding private key.  With a
   little work to handle the various useful formats, this allows a
   client that is presented with the ni name and the signed object to
   verify the binding between the name and the object data.

   Note that the signature scheme used might or might not provide
   additional information, e.g. a name for the signer.  Applications
   might benefit from that, but it is not required in order to provide
   the core "name-data integrity" service for dynamically generated

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   Since there are a number of digital signing schemes that might be
   used, our approach is to define a new algorithm for the ni scheme
   that takes as input a specific public key encoded in a specific way,
   and runs that through a digest function.  That is, the ni algorithm
   fields will specify both a public key algorithm and a digest
   algorithm, just as is done with digital signature algorithm

   Since it is possible that an ni algorithm might also be defined where
   the value contains an actual digital signature we need to be careful
   to ensure there is no ambiguity.  However, since the lengths of
   signatures and hash outputs are (with current algorithms) always
   different, we could use that fact to disambigute between rsa-with-
   sha256 meaning the value is a sha256 hash of an rsa public key and
   the alternative meaning the the value is an rsa-with-sha256
   signature.  However, we prefer to use a new algorithm (see Section 6
   to disambiguate these.

   We define one such algorithm, "pk-rsa-with-sha256" that takes an RSA
   public key as input, with the input bits formatted as a
   SubjectPublicKeyInfo as defined by [nischeme] Note that this does not
   mean that one cannot use e.g.  PGP to sign the actual object.  It
   means that if you do use PGP then in order to verify the name-data
   integrity, the client needs to extract the signer's PGP public key,
   then reformat that as a SubjectPublicKeyInfo and then run that
   through the sha-256 algorithm and make the relevant comparison.

3.  Query String Paramaeters

   This section defines query string parameters that MAY be used to
   indicate the type of content hashed or to specify additional
   locations from which the named content can be retrieved.  We also
   define a way to specify how an encryption key MAY be included in an
   ni URI that allows for decryption of object content.

3.1.  Digest with Content Type

   The semantics of a digest being used to establish a secure reference
   from an authenticated source to an external source may be a function
   of associated meta data such as the content type.  This data MAY be
   specified by means of a parameter:


   The Content Type "ct" parameter specifies the MIME Content Type of

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   the associated data as defined in [RFC4288]

3.2.  Additional Locators

   In addition to the algorithm for mapping an ni URI to an HTTP(S) URL
   specified in the ni scheme definition [nischeme], an ni name MAY
   provide information about additional locations from which the
   referenced content might be available.  This is done via the
   inclusion of an "alt" or "alts" key in the query string that can
   supply more values for the authority field when constructing the HTTP
   or HTTPS URL.  For example:


   The corresponding content might then also be retrieved from the URL:


   A ni name MAY specify multiple locations from which the content MAY
   be obtained:


   The above example asserts that the content might be retrieved from
   either of the following URIs:



   The "alt" parameter means "use HTTP" and the "alts" parameter means
   use "HTTPS".

   The alt and alts parameters are used to specify a possible means of
   resolving the referenced content.  Multiple locator parameters MAY be
   used to specify alternative sources for accessing the content.

   The alt and alts parameters take a single argument, the authority to
   be used for resolution.  To permit the use of ni URIs in ASCII-only
   environments, the ASCII encoding (aka punycode) of the domain name

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   MUST be used.  [[Note sure if this is needed/correct.]]

3.3.  Digest with Decryption Key

   An ni name MAY provide a key for decrypting the referenced data.  The
   use-case here is where the referenced data has be distributed
   (somehow) in ciphertext form, probably with little or no access
   control required (since the data is strongly encrypted) and where a
   client wishing to decrypt that data subsequently acquires an ni name
   for that data that provides the required decryption key.

   Clearly, to be of any benefit, access to the ni name that includes
   the decryption key MUST be controlled so that only the appropriate
   clients get access to the ni name and of course this ni name MUST be
   strongly protected via some (probably mutual) authentication and
   confidentiality service such as can be provided by TLS.  [RFC5246]


   The "enc" specifier is used when the encrypted object consists of the
   ciphertext alone.  The "menc" spcifier is used when the encrypted
   object consists of a MIME header containing metadata followed by the
   binary object encoding.  [[Note: there may be more needed here.]]

   The encryption specifiers both take an agrument of the form:

   algorithm ":" base64url (key) [":" base64url (iv)]


   algorithm  Is the algorithm used to encrypt the associated content

   key  Is the value of the cryptographic key

   iv (optional)  Is the value of the cryptographic Initialization

      If the IV is not spcified for a block cipher mode that requires
      one, the IV MUST be prepended to the encrypted content.

      [[Note: Actually the IV does not provide any additional security
      for this application but explaining the reason might be more
      effort than it is worth and what we really care about is saving
      bytes in the identifier, not the resulting data package.]

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3.4.  Wrapped URL

   The "ni" URI form can usefully "wrap" an HTTP URL in order to provide
   a way for an HTTP client that has securely received an "ni" URI (e.g.
   embedded within some HTML received via a TLS session) to validate the
   referred-to content, at the same level of security as the embedding
   page.  A good use for this might be to provide data integrity for
   javascript or other files referred to by an HTML page.

   To achieve the above, we define the "url" parameter which allows for
   the inclusion of any URL within the query string.  The intent is that
   the content accessed via that URL match the hash in the ni name.

   [[TBD: say how to encode the URL]]

4.  QR Codes

   [[The idea of embedding ni names into QR codes has been floated.
   That seems like a fine thing to do, so we're likely to include text
   on that here in a future version.]]

5.  Security Considerations

   [[TBD for sure.]]

6.  IANA Considerations

6.1.  Additional algorithm in RFCXXXX registry

   We request IANA to add a new entry to the hash algorithm registry
   created in [nischeme], Section 9.3, as follows:

   ID: 7
   Hash string name: pk-rsa-with-sha256
   Value length: 256
   Reference: [RFC-THIS]

6.2.  Creation of ni parameter registry

   This specification creates a new IANA registry entitled "Named
   Information URI Parameter Definitions".

   The policy for future assignments to the registry is "RFC Required".

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   The initial contents of the registry are:

   Parameter    Meaning                                       Reference
   -----------  --------------------------------------------  ---------
   ct           Content Type                                  [RFC-THIS]
   alt          Additional HTTP Locator                       [RFC-THIS]
   alts         Additional HTTPS Locator                      [RFC-THIS]
   enc          Encryption Key                                [RFC-THIS]
   menc         Encryption Key                                [RFC-THIS]
   url          Wrapped URL                                   [RFC-THIS]

7.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC4288]  Freed, N. and J. Klensin, "Media Type Specifications and
              Registration Procedures", BCP 13, RFC 4288, December 2005.

   [RFC5246]  Dierks, T. and E. Rescorla, "The Transport Layer Security
              (TLS) Protocol Version 1.2", RFC 5246, August 2008.

              Farrell, S., Kutscher, D., Ohlman, B., Keranen, A., and P.
              Hallam-Baker, "Naming things with hashes",
              draft-farrell-decade-ni-04 (work in progress), April 2012.

Authors' Addresses

   Phillip Hallam-Baker
   Comodo Group Inc.

   Email: philliph@comodo.com

   Rob Stradling
   Comodo CA Ltd.

   Email: rob.stradling@comodo.com

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   Stephen Farrell
   Trinity College Dublin
   Dublin,   2

   Phone: +353-1-896-2354
   Email: stephen.farrell@cs.tcd.ie

   Dirk Kutscher
   Kurfuersten-Anlage 36

   Email: kutscher@neclab.eu

   Boerje Ohlman
   Stockholm  S-16480

   Email: Borje.Ohlman@ericsson.com

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