One document matched: draft-farrell-decade-ni-05.xml
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<rfc category="std" ipr="trust200902" submissionType="independent" docName="draft-farrell-decade-ni-05">
<front>
<title abbrev="Naming Things with Hashes">Naming Things with Hashes</title>
<author fullname="Stephen Farrell" initials="S."
surname="Farrell">
<organization>Trinity College Dublin</organization>
<address>
<postal>
<street></street>
<!-- Reorder these if your country does things differently -->
<city>Dublin</city>
<region></region>
<code>2</code>
<country>Ireland</country>
</postal>
<phone>+353-1-896-2354</phone>
<email>stephen.farrell@cs.tcd.ie</email>
<!-- uri and facsimile elements may also be added -->
</address>
</author>
<author fullname="Dirk Kutscher" initials="D."
surname="Kutscher">
<organization>NEC</organization>
<address>
<postal>
<street>Kurfuersten-Anlage 36</street>
<!-- Reorder these if your country does things differently -->
<city>Heidelberg</city>
<region></region>
<code></code>
<country>Germany</country>
</postal>
<phone></phone>
<email>kutscher@neclab.eu</email>
<!-- uri and facsimile elements may also be added -->
</address>
</author>
<author fullname="Christian Dannewitz" initials="C" surname="Dannewitz">
<organization>University of Paderborn</organization>
<address>
<postal>
<street></street>
<city>Paderborn</city>
<!--code> 12345</code-->
<country>Germany</country>
</postal>
<email>cdannewitz@upb.de</email>
</address>
</author>
<author fullname="Borje Ohlman" initials="B" surname="Ohlman">
<organization>Ericsson</organization>
<address>
<postal>
<street></street>
<code> S-16480</code>
<city>Stockholm</city>
<country>Sweden</country>
</postal>
<email>Borje.Ohlman@ericsson.com</email>
</address>
</author>
<author initials="A." surname="Keranen" fullname="Ari Keranen">
<organization>Ericsson</organization>
<address>
<postal>
<street/>
<city>Jorvas</city> <code>02420</code>
<country>Finland</country>
</postal>
<email>ari.keranen@ericsson.com</email>
</address>
</author>
<author fullname="Phillip Hallam-Baker" initials="P. M." surname="Hallam-Baker">
<organization>Comodo Group Inc.</organization>
<address>
<email>philliph@comodo.com</email>
</address>
</author>
<date />
<area>General</area>
<workgroup>Internet Engineering Task Force</workgroup>
<keyword>Cryptography</keyword>
<keyword>URI</keyword>
<keyword>Information Centric Networking</keyword>
<abstract>
<t>
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.
</t>
</abstract>
</front>
<middle>
<section title="Introduction">
<t>
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.
</t>
<t>
Hash function outputs can be used to ensure uniqueness in terms
of mapping URIs <xref target="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.
</t>
<t>
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.
</t>
<t>
Similarly, in the context of information-centric networking
<xref target="ref.netinf-design"/> <xref target="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.
</t>
<t>
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.
</t>
<!--
<t>
Accordingly, a standard form of name using a hash outout allows for checking of the
integrity of the name-data mapping, but it is OPTIONAL for
implementations to do so when sending, receiving or processing
these name forms.
</t>
-->
<t>
The new URI scheme defined here allows for the use of a
query-string, similar to how query-strings are used in HTTP
URLs. A companion specification <xref target="I-D.hallambaker-decade-ni-params"/>
describes specific values that can be used in such query
strings for various purposes and other extensions to this
basic format specification.
</t>
<t>The "ni" URI scheme defined here is very similar to the "magnet
link" informally defined in various other protocols. <xref target="magnet"/>
</t>
<t>
In addition to the URI form 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.
</t>
<t>
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.
</t>
<t>
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 <xref target="RFC2119">RFC 2119</xref>.
</t>
<t>
Syntax definitions in this memo are specified according to
ABNF <xref target="RFC5234"/>.
</t>
<!--
<t>[[Comments are included in double-square brackets, like this.]]</t>
-->
</section>
<section anchor="basics" title="Basics">
<t>This section contains basic considerations common to all
formats.</t>
<t>
When verifying whether two names refer to same object, an implementation MUST
only consider the digest algorithm identifier and the digest value, i.e., it
MUST NOT consider the authority field from a URI or any parameters and MUST
consider two hashes identical, regardless of encoding, if the decoded hashes
are the same length and have the same binary value.
</t>
<t>
The sha-256 algorithm as specified in <xref target="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).
</t>
<t>Truncated hashes MAY be supported if needed. When a hash value is
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.)</t>
<t>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 <xref target="fig-trunc"/>. </t>
<figure anchor="fig-trunc" title="Example of Truncated Hash">
<artwork>
<![CDATA[
128-bit hash: 0x265357902fe1b7e2a04b897c6025d7a2
32-bit truncated hash: 0x26535790
]]></artwork></figure>
<t> 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 <xref
target="RFC5280"/>). This input has been chosen primarily for
compatibility with DANE <xref target="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 <xref target="RFC5280"/>
since formatting any public key as a SubjectPublicKeyInfo is
relatively straightforward and well supported by libraries. </t>
<t>Any of the formats defined below can be used to represent the
resulting name for a public key.</t>
<t>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.</t>
</section>
<section anchor="syntax" title="Named Information (ni) URI Format">
<t>
A Named Information (ni) URI consists of the following components:
</t>
<t>
<list style="hanging">
<t hangText="Scheme Name [Required]">The scheme name is 'ni'.
</t>
<t hangText="Colon and Slashes [Required]">The literal "://" </t>
<t hangText="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 algorithm and value are the
same.
</t>
<t hangText="One slash [Required]">The literal "/" </t>
<t hangText="Digest Algorithm [Required]">
The name of the digest algorithm, as specified in the IANA registry
defined in <xref target="IANAbin"/> below.
</t>
<t hangText="Separator [Required]">The literal ";" </t>
<t hangText="Digest Value [Required]">
The digest value encoded in the specified encoding.
</t>
<t hangText="Query Parameter separator [Optional] '?'">
The query parameter separator acts a
separator between the digest value
and the query parameters (if specified).
</t>
<t hangText="Query Parameters [Optional]">
A tag=value list of optional query parameters as are used with HTTP URLs
<xref target="RFC2616"/>
with a separator character '&' between each. For example, "foo=bar&baz=bat"
</t>
</list>
</t>
<t>
It is OPTIONAL for implementations to check the integrity of the
URI/resource mapping when sending, receiving or processing "ni"
URIs.
</t>
<t>
The digest value MUST be encoded using base64url
<xref target="RFC4648"/> encoding.
</t>
<t>
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 <xref
target="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.
</t>
<t>
Note that when mapped to HTTP or HTTPS URLs, '/' and '?' characters in a query
string will have to be percent encoded.
</t>
<!--
<t>[[The above is maybe ambiguous, 'cause we're not sure of what's right.
Is it better to say "decoders MUST treat %2f as /" or that they MUST NOT
do that, or that the world's a nasty place so you just need to know when
to do which?]]</t>
-->
<t>
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.
</t>
<!--
<t>Old way:</t>
<t>
The Named Information URI has the following syntax:
</t>
<figure title="ni Name syntax" anchor="fig_abnfo">
<artwork type="abnf">
niname ="ni://" [ authority ] "/" algval [ "?" query ]
algval = alg ";" val
alg = 1*unreserved
val = 1*unreserved
unreserved = ALPHA / DIGIT / "-" / "." / "_" / "~"
</artwork>
</figure>
-->
<t>
The Named Information URI adapts the URI definition from the URI
Generic Syntax <xref target="RFC3986"/>. We start with the base URI production:
</t>
<figure title="URI syntax" anchor="fig_uri">
<artwork type="abnf">
URI = scheme ":" hier-part [ "?" query ] [ "#" fragment ]
; from RFC 3986
</artwork>
</figure>
<t>
Adapting that for the Named Information URI:
</t>
<figure title="ni Name syntax" anchor="fig_niabnf">
<artwork type="abnf">
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 = *( unreserved / pct-encoded )
unreserved = ALPHA / DIGIT / "-" / "." / "_" / "~"
; directly from RFC 3986
; "authority" and "pct-encoded" are also from RFC 3986
</artwork>
</figure>
<t>Note that "unreserved" is defined in the URI specification <xref
target="RFC3986"/> Section 2.3, in the way shown above. The "authority" and
"query" types are also from the URI specification. <xref target="RFC3986"/>
</t>
<t>
The "val" field MUST contain the output 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.
</t>
</section>
<section title=".well-known URL Format">
<t>
We define a mapping between URIs following the ni URI scheme and HTTP <xref target="RFC2616"/> or
HTTPS <xref target="RFC2617"/> URLs that makes use of the .well-known URI <xref target="RFC5785"/> by defining an
"ni" suffix (see <xref target="IANACons"/>).
</t>
<t>
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.
</t>
<t>
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
<xref target="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.
</t>
<t>
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.
</t>
<t>
When mapping from a 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. In general however, whether to use "http" or "https" is something
that needs to be decided by the application.
</t>
</section>
<section anchor="url-frag" title="URL Segment Format">
<t>Some applications may benefit from using hashes in existing HTTP URLs or
other URLs. To do this one simply uses the "algval" production from the
ni name scheme ABNF which may be included in the pathname component of
HTTP URLs. <xref target="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 "algval" 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.
</t>
</section>
<section anchor="binary-format" title="Binary Format">
<t> When a more space-efficient version of the name is needed, we
can use a binary format. 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 <xref
target="fig-format"/>. </t>
<figure anchor="fig-format" title="Binary Name Format">
<artwork align="center">
<![CDATA[
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 /
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/ ... /
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/ ... |
+-+-+-+-+-+-+-+-+
]]></artwork></figure>
<t> The Res field is a reserved 2-bit field for future use and MUST
be set to zero for this specification.</t>
<t> 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
<xref target="IANAbin"/> for details.</t>
<t>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.</t>
</section>
<section anchor="nihsyntax" title="Human-readable Format">
<!--
<t>[[Comment on apps-discuss asked about using "ni:" for this, but
might be that then the abnf is too complex and easily confused, so
I think a different scheme is warranted here, so how about "nih"?
Hard-to-resist acronym anyway:-) ]] </t>
-->
<t> 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 :-) </t>
<t>
As with the ni URI format, nih URI fields 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
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 <xref target="RFC4648"/>
except using lower-case letters.
</t>
<t> The hash value is OPTIONALLY followed by a checksum. The
checksum MUST be calculated as a crc16 over the following parts
(encoded as UTF-8 <xref target="RFC3629"/>): the URI scheme and
separator ("nih:"), the algorithm string, the first delimiter, (";")
the hash value, and the second delimiter (also ";"). The 16-bit
result of the crc16 is encoded using network byte order and, like
the hash value, with lower-case ASCII hex characters. </t>
<t>The crc16 MUST use the CRC-CCITT polynomial: x^16 + x^12 + x^5 +
1.</t>
<!--
<t>[[CCITT crc16 needs a proper reference]]</t>
-->
<figure title="Human-readable syntax" anchor="fig_human">
<artwork type="abnf">
humanname = "nih:" algval [ ";" checksum ]
algval = alg ";" val
alg = 1*unreserved
val = 1*unreserved
checksum = 1*unreserved
</artwork>
</figure>
<t> For algorithms that have a Suite ID reserved (see <xref
target="fig-ids"/>), 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. Note that using the decimal presentation instead of
the hash name string results in a different checksum for the same
name. </t>
</section>
<section title="Examples">
<t>
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:
</t>
<t>ni:///sha-256;f4OxZX_x_FO5LcGBSKHWXfwtSx-j1ncoSt3SABJtkGk</t>
<t>ni://example.com/sha-256;f4OxZX_x_FO5LcGBSKHWXfwtSx-j1ncoSt3SABJtkGk</t>
<t>The following HTTP URL represents a mapping from the
previous ni name based on the algorithm outlined above.
</t>
<t>http://example.com/.well-known/ni/sha-256/f4OxZX_x_FO5LcGBSKHWXfwtSx-j1ncoSt3SABJtkGk</t>
<t> Given the SubjectPublicKeyInfo in <xref target="eg-spki"/>
we derive the names shown in <xref target="eg-names"/> for
this value.</t>
<figure anchor="eg-spki" title="A SubjectPublicKeyInfo used in examples and its sha-256 hash">
<artwork>
<![CDATA[
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
]]></artwork></figure>
<figure anchor="eg-names" title="Example Names">
<artwork>
<![CDATA[
+-------------------------------------------------------------------+
| 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 checksum: |
| nih:sha-256-120;53269057e12fe2b74ba07c892560a2;8628 |
+-------------------------------------------------------------------+
| Human-readable form of a name for this key (truncated to 32 bits |
| in length) with checksum: |
| nih:sha-256-32;53269057;5cab |
+-------------------------------------------------------------------+
| Human-readable form using decimal presentation of the |
| algorithm ID (sha-256-120) with checksum: |
| nih:3;53269057e12fe2b74ba07c892560a2;1535 |
+-------------------------------------------------------------------+
]]></artwork></figure>
</section>
<section title="IANA Considerations" anchor="IANACons">
<section anchor="IANAscheme" title="Assignment of Named Information (ni) URI Scheme">
<t>
The procedures for registration of a URI scheme are specified in
<xref target="RFC4395">RFC 4395</xref>. The following is the proposed
assignment template.
</t>
<t>
URI scheme name: ni
</t>
<t>
Status: Permanent
</t>
<t>
URI scheme syntax. See <xref target="syntax" />
</t>
<t>
URI scheme semantics. See <xref target="syntax" />
</t>
<t>
Encoding considerations. See <xref target="syntax" />
</t>
<t>
Applications/protocols that use this URI scheme name:
General applicability with initial use cases provided by CoAP
and DECADE
</t>
<t>
Interoperability considerations: Defined here.
</t>
<t>
Security considerations: See <xref target="sec_cons" />
</t>
<t>
Contact: stephen.farrell@cs.tcd.ie
</t>
<t>
Author/Change controller: IETF
</t>
<t>
References: As specified in this document
</t>
</section>
<section anchor="IANAschemeh" title="Assignment of Named Information for Humans (nih) URI Scheme">
<t>
The procedures for registration of a URI scheme are specified in
<xref target="RFC4395">RFC 4395</xref>. The following is the proposed
assignment template.
</t>
<t>
URI scheme name: nih
</t>
<t>
Status: Permanent
</t>
<t>
URI scheme syntax. See <xref target="nihsyntax" />
</t>
<t>
URI scheme semantics. See <xref target="nihsyntax" />
</t>
<t>
Encoding considerations. See <xref target="nihsyntax" />
</t>
<t>
Applications/protocols that use this URI scheme name:
General applicability with initial use cases provided by CoAP
and DECADE
</t>
<t>
Interoperability considerations: Defined here.
</t>
<t>
Security considerations: See <xref target="sec_cons" />
</t>
<t>
Contact: stephen.farrell@cs.tcd.ie
</t>
<t>
Author/Change controller: IETF
</t>
<t>
References: As specified in this document
</t>
</section>
<section title="Assignment of Well Known URI prefix ni">
<t>
The procedures for registration of a Well Known URI entry
are specified in <xref target="RFC5785">RFC 5785</xref>.
The following is the proposed
assignment template.
</t>
<t>
URI suffix: ni
</t>
<t>
Change controller: IETF
</t>
<t>
Specification document(s): This document
</t>
<t>
Related information: None
</t>
</section>
<section anchor="IANAbin" title="Hash Name Algorithm Registry">
<t>
IANA is requested to create a new registry for hash algorithms as used in the
name formats specified here. 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. If the status is not "deprecated,"
then that does not necessarily mean that an 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."
</t>
<t>
Future assignments are to be made through expert review <xref
target="RFC5226"/>. 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.
</t>
<t>
Since there are only 64 possible binary suite ID field values allowed by the
binary format specified here, the suite ID field value is OPTIONAL. 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.
</t>
<t>
<figure anchor="fig-ids" title="Suite Identifiers">
<artwork align="center">
<![CDATA[
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
]]></artwork></figure>
</t>
<t> The Suite ID value 32 is reserved for compatibility with ORCHIDs
<xref target="RFC4843"/>.
</t>
<t>
The referenced hash algorithm matching to the Suite ID, truncated to the length
indicated, according to the description given in <xref target="basics"/>, is
used for generating the hash. The document referenced for the hash algorithm
MUST be such that it would be acceptable were the "specification required" rule
applied.
</t>
<!--
<t>[[Do we need sha-1 here? Its been asked for, but in a new standards
track spec is dodgy...]]</t>
-->
</section>
</section>
<section title="Security Considerations" anchor="sec_cons">
<t>
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.
</t>
<t>
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.
</t>
<t>
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.
</t>
<t>
If a truncated hash value is used, certain security properties
will be affected.
In general a hash algorithm is designed to produce 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.
</t>
</section>
<section title="Acknowledgements">
<t>
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.
</t>
<t> The authors would also like to thank Bob Moskowitz, Tero Kivinen,
Zach Shelby, Carsten Bormann, David McGrew, Eric Rescorla, Tobias Heer, Martin
Thomas and James Manger for their comments and input to the document. </t>
</section>
</middle>
<back>
<references title="Normative References">
<!--&RFC1035;-->
&RFC2119;
&RFC2616;
&RFC2617;
&RFC3629;
&RFC3986;
<!--&RFC4033;-->
&RFC4055;
&RFC4395;
&RFC4648;
<!--&RFC5395;-->
<!--&RFC5698;-->
&RFC5280;
&RFC5234;
&RFC5785;
</references>
<references title="Informative References">
&RFC4843;
&RFC5226;
&I-D.hallambaker-decade-ni-params;
<reference anchor="ref.netinf-design">
<front>
<title>Design Considerations for a Network of Information</title>
<author surname="Ahlgren" fullname="Bengt Ahlgren"></author>
<author surname="D'Ambrosio" fullname="Matteo D'Ambrosio"></author>
<author surname="Dannewitz" fullname="Christian Dannewitz"></author>
<author surname="Marchisio" fullname="Marco Marchisio"></author>
<author surname="Marsh" fullname="Ian Marsh"></author>
<author surname="Ohlman" fullname="Boerje Ohlman"></author>
<author surname="Pentikousis" fullname="Kostas Pentikousis"></author>
<author surname="Rembarz" fullname="Rene Rembarz"></author>
<author surname="Strandberg" fullname="Ove Strandberg"></author>
<author surname="Vercellone" fullname="Vinicio Vercellone"></author>
<date month="December" year="2008"/>
</front>
<seriesInfo name="Re-Arch 2008 Workshop" value=""/>
</reference>
<reference anchor="ref.ccn">
<front>
<title>Networking Named Content</title>
<author surname="Jacobsen" fullname="Van Jacobsen"></author>
<author surname="K" fullname="Diana K. Smetters"></author>
<author surname="D" fullname="James D. Thornton"></author>
<author surname="F" fullname="Michael F. Plass"></author>
<author surname="H" fullname="Nicholas H. Briggs"></author>
<author surname="L" fullname="Rebecca L. Braynard"></author>
<date month="December" year="2009"/>
</front>
<seriesInfo name="CoNEXT 2009" value=""/>
</reference>
&RFC6454;
&I-D.ietf-dane-protocol;
<reference anchor="magnet" target="http://en.wikipedia.org/wiki/Magnet_link">
<front>
<title>Magnet URI Scheme</title>
<author surname="Wikipedia article" fullname="Wikipedia"/>
<date month="April" year="2012"/>
</front>
</reference>
</references>
</back>
</rfc>
| PAFTECH AB 2003-2026 | 2026-04-24 13:40:35 |