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Versions: 00 01 02 03 04 05 06 07 08 09 10 RFC 6920

Internet Engineering Task Force                               S. Farrell
Internet-Draft                                    Trinity College Dublin
Intended status: Standards Track                             D. Kutscher
Expires: December 2, 2012                                            NEC
                                                            C. Dannewitz
                                                 University of Paderborn
                                                               B. Ohlman
                                                              A. Keranen
                                                                Ericsson
                                                         P. Hallam-Baker
                                                       Comodo Group Inc.
                                                            May 31, 2012


                       Naming Things with Hashes
                       draft-farrell-decade-ni-07

Abstract

   This document defines a set of ways to identify a thing using the
   output from a hash function, specifying URI, URL, binary and human
   "speakable" formats for these names.  The various formats are
   designed to support, but not require, a strong link to the referenced
   object such that the referenced object may be authenticated to the
   same degree as the reference to it.

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
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on December 2, 2012.

Copyright Notice

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




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   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
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Hashes are what Count  . . . . . . . . . . . . . . . . . . . .  4
   3.  Named Information (ni) URI Format  . . . . . . . . . . . . . .  5
   4.  .well-known URL Format . . . . . . . . . . . . . . . . . . . .  7
   5.  URL Segment Format . . . . . . . . . . . . . . . . . . . . . .  8
   6.  Binary Format  . . . . . . . . . . . . . . . . . . . . . . . .  9
   7.  Human-readable Format  . . . . . . . . . . . . . . . . . . . .  9
   8.  Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
   9.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 12
     9.1.  Assignment of Named Information (ni) URI Scheme  . . . . . 12
     9.2.  Assignment of Named Information for Humans (nih) URI
           Scheme . . . . . . . . . . . . . . . . . . . . . . . . . . 13
     9.3.  Assignment of Well Known URI prefix ni . . . . . . . . . . 13
     9.4.  Hash Name Algorithm Registry . . . . . . . . . . . . . . . 14
   10. Security Considerations  . . . . . . . . . . . . . . . . . . . 15
   11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 16
   12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 17
     12.1. Normative References . . . . . . . . . . . . . . . . . . . 17
     12.2. Informative References . . . . . . . . . . . . . . . . . . 18
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 19





















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1.  Introduction

   Names or identifiers are used in various protocols for identifying
   resources.  In many scenarios those names or identifiers contain
   values that are hash function outputs.  However, different
   deployments have chosen various different ways to include hash
   function outputs in such names or identifiers.  This document
   specifies standard ways to do that to aid interoperability.

   Hash function outputs can be used to ensure uniqueness in terms of
   mapping URIs [RFC3986] to a specific resource, or to make URIs hard
   to guess for security reasons.  Since, there is no standard way to
   interpret those strings, today in general only the creator of the URI
   knows how to use the hash function output.  Other protocols, such as
   application layer protocols for accessing "smart objects" in
   constrained environments also require more compact (e.g., binary)
   forms of such identifiers, while in other situations people may have
   to input such values or talk about them, e.g., in a voice call.

   As another example, protocols for accessing in-network storage
   servers need a way to identify stored resources uniquely and in a
   location-independent way so that replicas on different servers can be
   accessed by the same name.  Also, such applications may require
   verifying that a resource representation that has been obtained
   actually corresponds to the name that was used to request the
   resource, i.e., verifying the integrity of the name-data binding.

   Similarly, in the context of information-centric networking
   [ref.netinf-design] [ref.ccn] and elsewhere there is value in being
   able to compare a presented resource against the URI that was
   dereferenced in order to access that resource.  If a
   cryptographically-strong comparison function can be used then this
   allows for many forms of in-network storage, without requiring as
   much trust in the infrastructure used to present the resource.  The
   outputs of hash functions can be used in this manner, if presented in
   a standard way.

   Additional applications might include creating references from web
   pages delivered over HTTP/TLS; DNS resource records signed using
   DNSSEC or data values embedded in certificates, Certificate
   Revocation Lists (CRLs), or other signed data objects.

   The "ni" URI scheme defined here is very similar to the "magnet link"
   informally defined in various other protocols. [magnet]

   Media content-type, alternative locations for retrieval and other
   additional information about a resource named using this scheme can
   be provided using a query-string.  A companion specification



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   [I-D.hallambaker-decade-ni-params] describes specific values that can
   be used in such query strings for these various purposes and other
   extensions to this basic format specification.

   In addition, we also define a ".well-known" URL equivalent, and a way
   to include a hash as a segment of an HTTP URL, as well as a binary
   format for use in protocols that require more compact names and a
   human-speakable text form that could be used, e.g. for reading out
   (parts of) the name over a voice connection.

   Not all uses of these names require use of the full hash output -
   truncated hashes can be safely used in some environments.  For this
   reason, we define a new IANA registry for hash functions to be used
   with this specification so as not to mix strong and weak (truncated)
   hash algorithms in other protocol registries.

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].

   Syntax definitions in this memo are specified according to ABNF
   [RFC5234].


2.  Hashes are what Count

   This section contains basic considerations related to how we use hash
   function outputs that are common to all formats.

   When verifying whether two names refer to same object, an
   implementation MUST only consider the digest algorithm and the digest
   value, i.e., it MUST NOT consider other fields defined below (such as
   an authority field from a URI or any parameters).  Implementations
   MUST consider two hashes identical, regardless of encoding, if the
   decoded hashes are based on the same algorithm and have the same
   length and the same binary value.  In that case, the two names can be
   treated as referring to the same thing.

   The sha-256 algorithm as specified in [RFC4055] is mandatory to
   implement, that is, implementations MUST be able to generate/send and
   to accept/process names based on a sha-256 hash.  However
   implementations MAY support additional hash algorithms and MAY use
   those for specific names, for example in a constrained environment
   where sha-256 is non-optimal or where truncated names are needed to
   fit into corresponding protocols (when a higher collision probability
   can be tolerated).

   Truncated hashes MAY be supported if needed.  When a hash value is



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   truncated the name MUST indicate this.  Therefore we use different
   hash algorithm strings for these, such as sha-256-32 for a 32-bit
   truncation of a sha-256 output.  (Note that a 32-bit truncated hash
   is essentially useless for security but might be useful for naming.)

   When a hash value is truncated to N bits the left-most or most
   significant in network byte order N bits from the binary
   representation of the hash value MUST be used as the truncated value.
   An example of a 128-bit hash output truncated to 32 bits is shown in
   Figure 1.


              128-bit hash: 0x265357902fe1b7e2a04b897c6025d7a2
     32-bit truncated hash: 0x26535790

                    Figure 1: Example of Truncated Hash

   When the input to the hash algorithm is a public key value, as may be
   used by various security protocols, the hash SHOULD be calculated
   over the public key in an X.509 SubjectPublicKeyInfo structure
   (Section 4.1 of [RFC5280]).  This input has been chosen primarily for
   compatibility with DANE [I-D.ietf-dane-protocol], but also includes
   any relevant public key parameters in the hash input, which is
   sometimes necessary for security reasons.  Note also that this does
   not force use of X.509 or full compliance with [RFC5280] since
   formatting any public key as a SubjectPublicKeyInfo is relatively
   straightforward and well supported by libraries.

   Any of the formats defined below can be used to represent the
   resulting name for a public key.

   Other than in the above special case where public keys are used, we
   do not specify the hash function input here.  Other specifications
   are expected to define this.


3.  Named Information (ni) URI Format

   A Named Information (ni) URI consists of the following components:

   Scheme Name [Required]  The scheme name is 'ni'.

   Colon and Slashes [Required]  The literal "://"

   Authority [Optional]  The optional authority component may assist
      applications in accessing the object named by an ni URI.  Note
      that while the ni names with and without an authority differ
      syntactically, both names refer to the same object if the digest



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      algorithm and value are the same.

   One slash [Required]  The literal "/"

   Digest Algorithm [Required]  The name of the digest algorithm, as
      specified in the IANA registry defined in Section 9.4 below.

   Separator [Required]  The literal ";"

   Digest Value [Required]  The digest value MUST be encoded using the
      base64url [RFC4648] encoding.

   Query Parameter separator [Optional] '?'  The query parameter
      separator acts a separator between the digest value and the query
      parameters (if specified).

   Query Parameters [Optional]  A tag=value list of optional query
      parameters as are used with HTTP URLs [RFC2616] with a separator
      character '&' between each.  For example, "foo=bar&baz=bat"

   It is OPTIONAL for implementations to check the integrity of the URI/
   resource mapping when sending, receiving or processing "ni" URIs.

   The query segment of a URI is NOT hierarchical.  Thus escape encoding
   of slash '/' characters is NOT required.  Since application code
   often attempts to enforce such encoding, decoders MUST recognize the
   use of URI escape encoding (e.g., '%2f' or '%2F' for the slash
   character).  Section 3.4 of [RFC3986] states that "The characters
   slash ("/") and question mark ("?") may represent data within the
   query component."  All of this is as per RFC 3986, and should
   anything here conflict with that, RFC 3986 rules apply.

   Consequently no special escaping mechanism is required for the query
   parameter portion of ni URIs.  URI escaping is however frequently
   imposed automatically by scripting environments.  Thus to ensure
   interoperability, implementations SHOULD NOT generate URIs that
   employ URI character escaping, and implementations MUST NOT reject
   any URIs that employ URI character escaping.

   The Named Information URI adapts the URI definition from the URI
   Generic Syntax [RFC3986].  We start with the base URI production:


             URI = scheme ":" hier-part [ "?" query ] [ "#" fragment ]
                      ; from RFC 3986

                           Figure 2: URI syntax




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   Adapting that for the Named Information URI:

            NI-URI   = ni-scheme ":" ni-hier-part [ "?" ni-query ]
                           ; adapted from "URI" in RFC 3986
            ni-scheme   = "ni"

            ni-hier-part   = "//" authority path-algval
                             / path-algval
                             ; adapted from "hier-part" in RFC 3986

            path-algval = "/" alg ";" val
            alg = 1*unreserved
            val = 1*unreserved

            ni-query    =  attr "=" value  [*( "&" attr "=" value )]
            attr           = query-token
            value        = query-token

            query-token = 1*( unreserved / pct-encoded )

            unreserved  = ALPHA / DIGIT / "-" / "." / "_" / "~"
                ;  directly from RFC 3986, section 2.3
                ; "authority" and "pct-encoded" are also from RFC 3986


                         Figure 3: ni Name syntax

   The "val" field MUST contain the output of base64url encoding the
   result of applying the hash function ("alg") to its defined input,
   which defaults to the object bytes that are expected to be returned
   when the URI is dereferenced.


4.  .well-known URL Format

   We define a mapping between URIs following the ni URI scheme and HTTP
   [RFC2616] or HTTPS [RFC2617] URLs that makes use of the .well-known
   URI [RFC5785] by defining an "ni" suffix (see Section 9).

   The HTTP(S) mapping MAY be used in any context where clients without
   support for ni URIs are needed without loss of interoperability or
   functionality.

   Note that since the .well-known name-space is not intended for
   general information retrieval, if an application de-references a
   .well-known/ni URL via HTTP(S), then it SHOULD expect to receive a
   30x HTTP re-direction response and it MUST be able to handle this.
   Put another way, a server SHOULD return a 30x response when a .well-



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   known/ni URL is de-referenced.

   For an ni name of the form "ni://n-authority/alg;val?query-string"
   the corresponding HTTP(S) URL produced by this mapping is
   "http://h-authority/.well-known/ni/alg/val?query-string", where
   "h-authority" is derived as follows: If the ni name has a specified
   authority (i.e., the n-authority is non-empty) then the h-authority
   MUST have the same value.  If the ni name has no authority specified
   (i.e. the n-authority string is empty), a h-authority value MAY be
   derived from the application context.  For example, if the mapping is
   being done in the context of a web page then the origin [RFC6454] for
   that web site can be used.  Of course, there are in general no
   guarantees that the object named by the ni URI will be available at
   the corresponding HTTP(S) URL.  But in the case that any data is
   returned, the retriever can determine whether or not it is content
   that matches the ni URI.

   If an application is presented with a HTTP(S) URL with "/.well-
   known/ni/" as the start of its pathname component, then the reverse
   mapping to an ni URI either including or excluding the authority
   might produce an ni URI that is meaningful, but there is no guarantee
   that this will be the case.

   When mapping from an ni URI to a .well-known URL, an implementation
   will have to decide between choosing an "http" or "https" URL.  If
   the object referenced does in fact match the hash in the URL, then
   there is arguably no need for additional data integrity, if the ni
   URI or .well-known URL was received "securely."  However TLS also
   provides confidentiality, so there may still be reasons to use the
   "https" URL scheme even in this case.  Additionally, web server
   policy such as [I-D.ietf-websec-strict-transport-sec] may dictate
   that data might only be available over "https".  In general however,
   whether to use "http" or "https" is something that needs to be
   decided by the application.


5.  URL Segment Format

   Some applications may benefit from using hashes in existing HTTP URLs
   or other URLs.  To do this one simply uses the "alg;val" production
   from the ni name scheme ABNF which may be included in the pathname
   component of HTTP URLs [RFC2616].  In such cases there is nothing
   present in the URL that ensures that a client can depend on
   compliance with this specification, so clients MUST NOT assume that
   any URL with a pathname component that matches the "alg;val"
   production was in fact produced as a result of this specification.
   That URL might or might not be related to this specification, only
   the context will tell.



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6.  Binary Format

   If a more space-efficient version of the name is needed, the
   following binary format can be used.  The binary format name consists
   of two fields: a header and the hash value.  The header field defines
   how the identifier has been created and the hash value contains a
   (possibly truncated) result of a one-way hash over whatever is being
   identified by the hash value.  The format of the binary
   representation of a name is shown in Figure 4.


        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |Res| Suite ID  |              Hash Value                       /
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       /                             ...                               /
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       /      ...      |
       +-+-+-+-+-+-+-+-+

                       Figure 4: Binary Name Format

   The Res field is a reserved 2-bit field for future use and MUST be
   set to zero for this specification.

   The hash algorithm and truncation length are specified by the Suite
   ID.  For maintaining efficient encoding for the binary presentation,
   only a few hash algorithms and truncation lengths are supported.  See
   Section 9.4 for details.

   Note that a hash value that is truncated to 120 bits will result in
   the overall name being a 128-bit value which may be useful with
   certain use-cases.


7.  Human-readable Format

   Sometimes the name may need to be used in a format that is easy for
   humans to read and possibly communicate, for example, over the phone.
   For this purpose, the following more verbose but less ambiguous (when
   spoken) URI format is defined with scheme name "nih", standing for
   "Named Information for Humans."  (Or possibly "Not Invented Here,"
   which is clearly false, and therefore worth including :-)

   Fields in nih URIs are separated by a semi-colon (;) character.  The
   first field is a hash algorithm string, as in the ni URI format.  The
   hash value is represented using lower-case ASCII hex characters, for



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   example an octet with the decimal value 58 (0x3A) is encoded as '3a'.
   This is the same as base16 encoding as defined in RFC 4648 [RFC4648]
   except using lower-case letters.

   The hash value is OPTIONALLY followed by a semi-colon ';' then a
   checkdigit.  The checkdigit MUST be calculated using Luhn's mod N
   algorithm (with N=16) as defined in [ISOIEC7812], (see also
   http://en.wikipedia.org/wiki/Luhn_mod_N_algorithm).  The input to the
   calculation is the ASCII-HEX encoded hash value (i.e. "val" in the
   ABNF production below).  This maps the ASCII-HEX so that
   '0'=0,...'9'=9,'a'=10,...'f'=15.  None of the other fields are input
   when calculating the checkdigit.

         humanname = "nih:" algval [ ";" checkdigit ]
         algval = alg ";" val
         alg = 1*unreserved
         val = 1*unreserved
         checkdigit = unreserved

                      Figure 5: Human-readable syntax

   For algorithms that have a Suite ID reserved (see Figure 8), the alg
   field MAY contain the ID value as a UTF-8 encoded decimal number
   instead of the hash name string (for example, "3" instead of "sha-
   256-120").  Implementations MUST be able to match the decimal ID
   values for the algorithms and hash lengths that they support even if
   they do not support the binary presentation.


8.  Examples

   The following ni URI references the text "Hello World!" (without the
   quotes, being 12 characters), using the sha-256 algorithm shown with
   and without an authority field:

   ni:///sha-256;f4OxZX_x_FO5LcGBSKHWXfwtSx-j1ncoSt3SABJtkGk

   ni://example.com/sha-256;f4OxZX_x_FO5LcGBSKHWXfwtSx-j1ncoSt3SABJtkGk

   The following HTTP URL represents a mapping from the previous ni name
   based on the algorithm outlined above.

   http://example.com/.well-known/ni/sha-256/
   f4OxZX_x_FO5LcGBSKHWXfwtSx-j1ncoSt3SABJtkGk

   Given the SubjectPublicKeyInfo in Figure 6 we derive the names shown
   in Figure 7 for this value.




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   0000000 30 82 01 22 30 0d 06 09 2a 86 48 86 f7 0d 01 01
   0000020 01 05 00 03 82 01 0f 00 30 82 01 0a 02 82 01 01
   0000040 00 a2 5f 83 da 9b d9 f1 7a 3a 36 67 ba fd 5a 94
   0000060 0e cf 16 d5 5a 55 3a 5e d4 03 b1 65 8e 6d cf a3
   0000100 b7 db a4 e7 cc 0f 52 c6 7d 35 1d c4 68 c2 bd 7b
   0000120 9d db e4 0a d7 10 cd f9 53 20 ee 0d d7 56 6e 5b
   0000140 7a ae 2c 5f 83 0a 19 3c 72 58 96 d6 86 e8 0e e6
   0000160 94 eb 5c f2 90 3e f3 a8 8a 88 56 b6 cd 36 38 76
   0000200 22 97 b1 6b 3c 9c 07 f3 4f 97 08 a1 bc 29 38 9b
   0000220 81 06 2b 74 60 38 7a 93 2f 39 be 12 34 09 6e 0b
   0000240 57 10 b7 a3 7b f2 c6 ee d6 c1 e5 ec ae c5 9c 83
   0000260 14 f4 6b 58 e2 de f2 ff c9 77 07 e3 f3 4c 97 cf
   0000300 1a 28 9e 38 a1 b3 93 41 75 a1 a4 76 3f 4d 78 d7
   0000320 44 d6 1a e3 ce e2 5d c5 78 4c b5 31 22 2e c7 4b
   0000340 8c 6f 56 78 5c a1 c4 c0 1d ca e5 b9 44 d7 e9 90
   0000360 9c bc ee b0 a2 b1 dc da 6d a0 0f f6 ad 1e 2c 12
   0000400 a2 a7 66 60 3e 36 d4 91 41 c2 f2 e7 69 39 2c 9d
   0000420 d2 df b5 a3 44 95 48 7c 87 64 89 dd bf 05 01 ee
   0000440 dd 02 03 01 00 01

   0000000 53 26 90 57 e1 2f e2 b7 4b a0 7c 89 25 60 a2 d7
   0000020 53 87 7e b6 2f f4 4d 5a 19 00 25 30 ed 97 ff e4


     Figure 6: A SubjectPublicKeyInfo used in examples and its sha-256
                                   hash

























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   +-------------------------------------------------------------------+
   | URI:                                                              |
   | ni:///sha-256;UyaQV-Ev4rdLoHyJJWCi11OHfrYv9E1aGQAlMO2X_-Q         |
   +-------------------------------------------------------------------+
   | .well-known URL (split over 2 lines):                             |
   | http://example.com/.well-known/ni/sha256/                         |
   | UyaQV-Ev4rdLoHyJJWCi11OHfrYv9E1aGQAlMO2X_-Q                       |
   +-------------------------------------------------------------------+
   | URL Segment:                                                      |
   | sha-256;UyaQV-Ev4rdLoHyJJWCi11OHfrYv9E1aGQAlMO2X_-Q               |
   +-------------------------------------------------------------------+
   | Binary name (ASCII hex encoded) with 120-bit truncated hash value |
   | which is Suite ID 0x03:                                           |
   | 0353 2690 57e1 2fe2 b74b a07c 8925 60a2                           |
   +-------------------------------------------------------------------+
   | Human-readable form of a name for this key (truncated to 120 bits |
   | in length) with checkdigit:                                       |
   | nih:sha-256-120;53269057e12fe2b74ba07c892560a2;f                  |
   +-------------------------------------------------------------------+
   | Human-readable form of a name for this key (truncated to 32 bits  |
   | in length) with checkdigit:                                       |
   | nih:sha-256-32;53269057;b                                         |
   +-------------------------------------------------------------------+
   | Human-readable form using decimal presentation of the             |
   | algorithm ID (sha-256-120) with checkdigit:                       |
   | nih:3;53269057e12fe2b74ba07c892560a2;f                            |
   +-------------------------------------------------------------------+

                          Figure 7: Example Names


9.  IANA Considerations

9.1.  Assignment of Named Information (ni) URI Scheme

   The procedures for registration of a URI scheme are specified in RFC
   4395 [RFC4395].  The following is the proposed assignment template.

   URI scheme name: ni

   Status: Permanent

   URI scheme syntax.  See Section 3

   URI scheme semantics.  See Section 3

   Encoding considerations.  See Section 3




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   Applications/protocols that use this URI scheme name: General
   applicability with initial use cases provided by CoAP and DECADE

   Interoperability considerations: Defined here.

   Security considerations: See Section 10

   Contact: stephen.farrell@cs.tcd.ie

   Author/Change controller: IETF

   References: As specified in this document

9.2.  Assignment of Named Information for Humans (nih) URI Scheme

   The procedures for registration of a URI scheme are specified in RFC
   4395 [RFC4395].  The following is the proposed assignment template.

   URI scheme name: nih

   Status: Permanent

   URI scheme syntax.  See Section 7

   URI scheme semantics.  See Section 7

   Encoding considerations.  See Section 7

   Applications/protocols that use this URI scheme name: General
   applicability with initial use cases provided by CoAP and DECADE

   Interoperability considerations: Defined here.

   Security considerations: See Section 10

   Contact: stephen.farrell@cs.tcd.ie

   Author/Change controller: IETF

   References: As specified in this document

9.3.  Assignment of Well Known URI prefix ni

   The procedures for registration of a Well Known URI entry are
   specified in RFC 5785 [RFC5785].  The following is the proposed
   assignment template.

   URI suffix: ni



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   Change controller: IETF

   Specification document(s): This document

   Related information: None

9.4.  Hash Name Algorithm Registry

   IANA is requested to create a new registry for hash algorithms as
   used in the name formats specified here.  Future assignments are to
   be made through expert review [RFC5226].  This registry has five
   fields, the binary suite ID, the hash algorithm name string, the
   truncation length, the underlying algorithm reference and a status
   field that indicates if algorithm is deprecated and should no longer
   be used.  The status field can be empty or have the value
   "deprecated".  Other values are reserved for possible future
   definition.

   Note that if the status is not "deprecated" (it is empty), then that
   does not necessarily mean that the algorithm is "good" for any
   particular purpose, since the cryptographic strength requirements
   will be set by other applications or protocols.  The expert SHOULD
   seek IETF review before approving a request to mark an entry as
   "deprecated."  Such requests may simply take the form of a mail to
   the designated expert (an RFC is not required).  IETF review can be
   achieved if the designated expert sends a mail to the IETF discussion
   list.  At least two weeks for comments MUST be allowed thereafter
   before the request is approved and actioned.

   Initial values are specified below.  The expert SHOULD generally
   approve additions that reference hash algorithms that are widely used
   in other IETF protocols.  In addition, the expert SHOULD NOT accept
   additions where the underlying hash function (with no truncation) is
   considered weak for collisions.  Part of the reasoning behind this
   last point is that inclusion of code for weak hash functions, e.g.
   the MD5 algorithm, can trigger costly false-positives if code is
   audited for inclusion of obsolete ciphers.

   The binary suite ID field ("ID") can be empty, or can have values
   between 0 and 63, inclusive.  Because there are only 64 possible
   values, this field is OPTIONAL (leaving it empty if omitted).  Where
   the binary format is not expected to be used for a given hash
   algorithm, this field SHOULD be omitted.  If an entry is registered
   without a suite ID, the expert may allow for later allocation of a
   suite ID, if that appears warranted.  The expert MAY request IETF
   review before allocating a suite ID.





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        ID  Hash name string     Value length     Reference   Status
        0   Reserved
        1   sha-256              256 bits         [RFC4055]   -
        2   sha-256-128          128 bits         [RFC4055]   -
        3   sha-256-120          120 bits         [RFC4055]   -
        4   sha-256-96           96 bits          [RFC4055]   -
        5   sha-256-64           64 bits          [RFC4055]   -
        6   sha-256-32           32 bits          [RFC4055]   -
        32  Reserved

                        Figure 8: Suite Identifiers

   The Suite ID value 32 is reserved for compatibility with ORCHIDs
   [RFC4843].

   The referenced hash algorithm matching to the Suite ID, truncated to
   the length indicated, according to the description given in
   Section 2, is used for generating the hash.  The designated expert is
   responsible for ensuring that the document referenced for the hash
   algorithm is such that it would be acceptable were the "specification
   required" rule applied.


10.  Security Considerations

   No secret information is required to generate or verify a name of the
   form described here.  Therefore a name like this can only provide
   evidence for the integrity for the referenced object and the proof of
   integrity provided is only as good as the proof of integrity for the
   name from which we started.  In other words, the hash value can
   provide a name-data integrity binding between the name and the bytes
   returned when the name is de-referenced using some protocol.

   Disclosure of a name value does not necessarily entail disclosure of
   the referenced object but may enable an attacker to determine the
   contents of the referenced object by reference to a search engine or
   other data repository or, for a highly formatted object with little
   variation, by simply guessing the value and checking if the digest
   value matches.  So the fact that these names contain hashes does not
   protect the confidentiality of the object that was input to the hash.

   The integrity of the referenced content would be compromised if a
   weak hash function were used.  SHA-256 is currently our preferred
   hash algorithm which is why we've only added SHA-256 based suites to
   the initial IANA registry.

   If a truncated hash value is used, certain security properties will
   be affected.  In general a hash algorithm is designed to produce



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   sufficient bits to prevent a 'birthday attack' collision occurring.
   To ensure that the difficulty of discovering two pieces of content
   that result in the same digest with a work factor O(2^x) by brute
   force requires a digest length of 2x.  Many security applications
   only require protection against a 2nd pre-image attack which only
   requires a digest length of x to achieve the same work factor.
   Basically, the shorter the hash value used, the less security benefit
   you can possibly get.

   An important thing to keep in mind is not to make the mistake of
   thinking two names are the same when they aren't.  For example, a
   name with a 32 bit truncated sha-256 hash is not the same as a name
   with the full 256 bits of hash output, even if the hash value for one
   is a prefix of that for the other.

   The reason for this is that if an application treats those as the
   same name then that might open up a number of attacks.  For example,
   if I publish an object with the full hash, then I probably (in
   general) don't want some other application to treat a name with just
   the first 32 bits of that as referring to the same thing, since the
   32 bit name will have lots of colliding objects.  If ni or nih URIs
   become widely used, there will be many cases where names will occur
   more than once in application protocols, and it'll be unpredictable
   which instance of the name would be used for name-data integrity
   checking, leading to threats.  For this reason, we require that the
   algorithm, length and value all match before we consider two names to
   be the same.

   Note that fact that an ni URI includes a domain name in the authority
   field by itself implies nothing about the relationship between the
   owner of the domain name and any content referenced by that URI.
   While a name-data integrity service can be provided using ni URIs,
   that does not in any sense validate the authority part of the name,
   for example, there is nothing to stop anyone creating an ni URI
   containing a hash of someone else's content so application developers
   MUST NOT assume any relationship between the owner of a domain name
   that is part of an ni URI and some matching content just because the
   ni URI matches that content.


11.  Acknowledgements

   This work has been supported by the EU FP7 project SAIL.  The authors
   would like to thank SAIL participants to our naming discussions,
   especially Jean-Francois Peltier, for their input.

   The authors would also like to thank Bob Moskowitz, Tero Kivinen,
   Zach Shelby, Carsten Bormann, David McGrew, Eric Rescorla, Tobias



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   Heer, Martin Thomas, Alexey Melnikov, Barry Leiba and, in particular,
   James Manger for their comments and input to the document.


12.  References

12.1.  Normative References

   [ISOIEC7812]
              ISO, ""ISO/IEC 7812-1:2006 Identification cards --
              Identification of issuers -- Part 1: Numbering system",",
              October 2006, <http://www.iso.org/iso/iso_catalogue/
              catalogue_tc/catalogue_detail.htm?csnumber=39698>.

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

   [RFC2616]  Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
              Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext
              Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.

   [RFC2617]  Franks, J., Hallam-Baker, P., Hostetler, J., Lawrence, S.,
              Leach, P., Luotonen, A., and L. Stewart, "HTTP
              Authentication: Basic and Digest Access Authentication",
              RFC 2617, June 1999.

   [RFC3986]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
              Resource Identifier (URI): Generic Syntax", STD 66,
              RFC 3986, January 2005.

   [RFC4055]  Schaad, J., Kaliski, B., and R. Housley, "Additional
              Algorithms and Identifiers for RSA Cryptography for use in
              the Internet X.509 Public Key Infrastructure Certificate
              and Certificate Revocation List (CRL) Profile", RFC 4055,
              June 2005.

   [RFC4395]  Hansen, T., Hardie, T., and L. Masinter, "Guidelines and
              Registration Procedures for New URI Schemes", BCP 35,
              RFC 4395, February 2006.

   [RFC4648]  Josefsson, S., "The Base16, Base32, and Base64 Data
              Encodings", RFC 4648, October 2006.

   [RFC5234]  Crocker, D. and P. Overell, "Augmented BNF for Syntax
              Specifications: ABNF", STD 68, RFC 5234, January 2008.

   [RFC5280]  Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
              Housley, R., and W. Polk, "Internet X.509 Public Key



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              Infrastructure Certificate and Certificate Revocation List
              (CRL) Profile", RFC 5280, May 2008.

   [RFC5785]  Nottingham, M. and E. Hammer-Lahav, "Defining Well-Known
              Uniform Resource Identifiers (URIs)", RFC 5785,
              April 2010.

12.2.  Informative References

   [I-D.hallambaker-decade-ni-params]
              Hallam-Baker, P., Stradling, R., Farrell, S., Kutscher,
              D., and B. Ohlman, "The Named Information (ni) URI Scheme:
              Optional Features", draft-hallambaker-decade-ni-params-02
              (work in progress), April 2012.

   [I-D.ietf-dane-protocol]
              Hoffman, P. and J. Schlyter, "The DNS-Based Authentication
              of Named Entities (DANE) Transport Layer Security (TLS)
              Protocol: TLSA", draft-ietf-dane-protocol-21 (work in
              progress), May 2012.

   [I-D.ietf-websec-strict-transport-sec]
              Hodges, J., Jackson, C., and A. Barth, "HTTP Strict
              Transport Security (HSTS)",
              draft-ietf-websec-strict-transport-sec-08 (work in
              progress), May 2012.

   [RFC4843]  Nikander, P., Laganier, J., and F. Dupont, "An IPv6 Prefix
              for Overlay Routable Cryptographic Hash Identifiers
              (ORCHID)", RFC 4843, April 2007.

   [RFC5226]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in RFCs", BCP 26, RFC 5226,
              May 2008.

   [RFC6454]  Barth, A., "The Web Origin Concept", RFC 6454,
              December 2011.

   [magnet]   Wikipedia article, "Magnet URI Scheme", April 2012,
              <http://en.wikipedia.org/wiki/Magnet_link>.

   [ref.ccn]  Jacobson at al., "Networking Named Content", CoNEXT 2009 ,
              December 2009.

   [ref.netinf-design]
              Ahlgren, D'Ambrosio, Dannewitz, Marchisio, Marsh, Ohlman,
              Pentikousis, Rembarz, Strandberg, and Vercellone, "Design
              Considerations for a Network of Information", Re-Arch 2008



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              Workshop , December 2008.


Authors' Addresses

   Stephen Farrell
   Trinity College Dublin
   Dublin,   2
   Ireland

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


   Dirk Kutscher
   NEC
   Kurfuersten-Anlage 36
   Heidelberg,
   Germany

   Phone:
   Email: kutscher@neclab.eu


   Christian Dannewitz
   University of Paderborn
   Paderborn
   Germany

   Email: cdannewitz@upb.de


   Borje Ohlman
   Ericsson
   Stockholm  S-16480
   Sweden

   Email: Borje.Ohlman@ericsson.com


   Ari Keranen
   Ericsson
   Jorvas  02420
   Finland

   Email: ari.keranen@ericsson.com





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   Phillip Hallam-Baker
   Comodo Group Inc.

   Email: philliph@comodo.com















































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