Internet DRAFT - draft-farrell-decade-ni
draft-farrell-decade-ni
Internet Engineering Task Force S. Farrell
Internet-Draft Trinity College Dublin
Intended status: Standards Track D. Kutscher
Expires: February 4, 2013 NEC
C. Dannewitz
University of Paderborn
B. Ohlman
A. Keranen
Ericsson
P. Hallam-Baker
Comodo Group Inc.
August 3, 2012
Naming Things with Hashes
draft-farrell-decade-ni-10
Abstract
This document defines a set of ways to identify a thing (a digital
object in this case) using the output from a hash function,
specifying a new URI scheme for this, a way to map those to http
URLs, and 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. This work
is motivated as a way to standardise current uses of hash outputs in
URLs and to support new information-centric applications and other
uses of hash outputs in protocols.
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
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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
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on February 4, 2013.
Copyright Notice
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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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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 . . . . . . . . . . . . . . 6
3.1. Content Type Query String Attribute . . . . . . . . . . . 8
4. .well-known URI . . . . . . . . . . . . . . . . . . . . . . . 9
5. URL Segment Format . . . . . . . . . . . . . . . . . . . . . . 10
6. Binary Format . . . . . . . . . . . . . . . . . . . . . . . . 10
7. Human-speakable (nih) URI Format . . . . . . . . . . . . . . . 11
8. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
8.1. Hello World! . . . . . . . . . . . . . . . . . . . . . . . 13
8.2. Public Key Examples . . . . . . . . . . . . . . . . . . . 13
8.3. nih Usage Example . . . . . . . . . . . . . . . . . . . . 14
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15
9.1. Assignment of ni URI Scheme . . . . . . . . . . . . . . . 15
9.2. Assignment of nih URI Scheme . . . . . . . . . . . . . . . 15
9.3. Assignment of .well-known 'ni' URI . . . . . . . . . . . . 16
9.4. Creation of Named Information Hash Algorithm Registry . . 16
9.5. Creation of Named Information Parameter Registry . . . . . 17
10. Security Considerations . . . . . . . . . . . . . . . . . . . 18
11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 20
12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 20
12.1. Normative References . . . . . . . . . . . . . . . . . . . 20
12.2. Informative References . . . . . . . . . . . . . . . . . . 21
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 22
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1. Introduction
Identifiers -- names or locators -- are used in various protocols to
identify resources. In many scenarios, those identifiers contain
values that are obtained from hash functions. Different deployments
have chosen different ways to include the hash function outputs in
their identifiers, resulting in interoperability problems.
This document defines a "Named Information" identifier, which
provides a set of standard ways to use hash function outputs in
names. We begin with a few example uses for various ways to include
hash function output in a name, with the specifics defined later in
this document. Figure 1 shows an example of the Named Information
(ni) URI scheme that this document defines.
ni:///sha-256;UyaQV-Ev4rdLoHyJJWCi11OHfrYv9E1aGQAlMO2X_-Q
Figure 1: Example ni URI
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. In yet other situations people may have
to speak such values, e.g., in a voice call, (see Section 8.3), in
order to confirm the presence or absence of a resource.
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
verification that a resource representation that has been obtained
actually corresponds to the name that was used to request the
resource, i.e., verifying the binding between the data and the name,
which is here termed name-data integrity.
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 used 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 thry are presented in a standard way.
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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 Named Identifier can be represented in a number of ways: using
the "ni" URI scheme that we specifically define for the name (which
is very similar to the "magnet link" that is informally defined in
other protocols [magnet]), or using other mechanisms also defined
herein. However it is represented, the Named Identifier *names* a
resource, and the mechanism used to dereference the name and to
*locate* the named resource needs to be known by the entity that
dereferences it.
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
[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 comparing two names of the form defined here, an implementation
MUST only consider the digest algorithm and the digest value, i.e.,
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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 [SHA-256] 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. 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. A 32-bit truncated hash is
essentially useless for security in almost all cases, but might be
useful for naming. With current best practices [RFC3766] very few,
if any, applications making use of names with less than 100 bit long
hashes will have useful security properties.
When a hash value is truncated to N bits the left-most N bits, that
is, the most significant N bits in network byte order, 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 2.
128-bit hash: 0x265357902fe1b7e2a04b897c6025d7a2
32-bit truncated hash: 0x26535790
Figure 2: 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. 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.
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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 nine
components:
Scheme Name The scheme name is 'ni'.
Colon and Slashes The literal "://"
Authority The optional authority component may assist applications
in accessing the object named by an ni URI. There is no default
value for the authority field. (See [RFC3986] Section 3.2.2 for
details.) While ni names with and without an authority differ
syntactically from ni names with different authorities, all three
refer to the same object if and only if the digest algorithm,
length, and value are the same.
One slash The literal "/"
Digest Algorithm The name of the digest algorithm, as specified in
the IANA registry defined in Section 9.4 below.
Separator The literal ";"
Digest Value The digest value MUST be encoded using the base64url
[RFC4648] encoding, with no "=" padding characters.
Query Parameter separator '?' The query parameter separator acts as
a separator between the digest value and the query parameters (if
specified). For compatibility with IRIs, non-ASCII characters in
the query part MUST be encoded as UTF-8, and the resulting octets
MUST be %-encoded (see [RFC3986] Section 2.1).
Query Parameters 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.
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Escaping of characters follows the rules in RFC 3986. This means
that %-encoding is used to distinguish between reserved and
unreserved functions of the same character in the same URI component.
As an example, an ampersand ('&') is used in the query part to
separate attribute-value pairs; an ampersand in a value therefore has
to be escaped as '%26'. Note that the set of reserved characters
differs for each component, as an example, a slash ('/') does not
have any reserved function in a query part and therefore does not
have to be escaped. However, it can still appear escaped as '%2f' or
'%2F', and implementations have to be able to understand such escaped
forms. Also note that any characters outside those allowed in the
respective URI component have to be escaped.
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 3: URI syntax
Adapting that for the Named Information URI:
NI-URI = ni-scheme ":" ni-hier-part [ "?" query ]
; adapted from "URI" in RFC 3986
; query is from RFC 3986, Section 3.4
ni-scheme = "ni"
ni-hier-part = "//" [ authority ] "/" alg-val
; authority is from RFC 3986, Section 3.2
alg-val = alg ";" val
; adapted from "hier-part" in RFC 3986
alg = 1*unreserved
val = 1*unreserved
; unreserved is from RFC 3986, Section 2.3
Figure 4: ni Name syntax
The "val" field MUST contain the output of base64url encoding (with
no "=" padding characters) 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.
Relative ni URIs can occur. In such cases, the algorithm in
[RFC3986] Section 5 applies. As an example, in Figure 5, the
absolute URI for "this third document" is
"ni://example.com/sha-256-128;...".
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<html>
<head>
<title>ni: relative URI test</title>
<base href="ni://example.com">
</head>
<body>
<p>Please check <a href="sha-256;f4OxZX...">this document</a>.
and <a href="sha-256;UyaQV...">this other document</a>.
and <a href="sha-256-128;...">this third document</a>.
</p>
</body>
</html>
Figure 5: Example HTML with relative ni URI
The authority field in an ni URI is not quite the same as that from
an HTTP URL, even though the same values (e.g., DNS names) may be
usefully used in both. For an ni URI, the authority does not control
nearly as much of the structure of the "right hand side" of the URI.
With ni URIs we also define standard query string attributes and of
cousrse have a strictly defined way to include the hash value.
Internationalisation of strings within ni names is handled exactly as
for http URIs - see [I-D.ietf-httpbis-p1-messaging] Section 2.7.
3.1. Content Type Query String Attribute
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. The Content Type
"ct" parameter specifies the MIME Content Type of the associated data
as defined in [I-D.ietf-appsawg-media-type-regs]. See Section 9.5
for the associated IANA registry for ni parameter names. as shown in
Figure 6. Implementations of this specification MUST support parsing
the ct= query string attribute name.
ni:///sha-256-32;f4OxZQ?ct=text/plain
Figure 6: Example ni URI with Content Type
Protocols making use of ni URIs will need to specify how to verify
name-data integrity for the MIME Content Types that they need to
process and will need to take into account possible Content-Transfer-
Encodings and other aspects of MIME encoding.
Implementations of this specification SHOULD support name-data
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integrity validation for at least the application/octet-stream
Content Type with no explicit Content-Transfer-Encoding (which is
equivalent to binary). Additional Content Types and Content-
Transfer- Encodings can of course also be supported, but are
OPTIONAL. Note that the hash is calculated after the Content
Transfer Encoding is removed, so it is applied to the raw data.
If a) the user agent is sensitive to the Content Type and b) the ni
name used has a ct= query string attribute and c) the object is
retrieved (from a server) using a protocol that specifies a Content
Type, then, if the two Content Types match, all is well. If, in this
situation, the Content Types do not match, then the client SHOULD
handle that situation as a potential security error. Content Type
matching rules are defined in [RFC2045] Section 5.1.
4. .well-known URI
We define a mapping between URIs following the ni URI scheme and HTTP
[RFC2616] or HTTPS [RFC2818] 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 with
support for ni URIs are not available.
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 will often receive a 3xx HTTP re-
direction response. A server responding to a request for a .well-
known/ni URL will often therefore return a 3xx response and a client
sending such a request MUST be able to handle that, as should any
fully compliant HTTP [RFC2616] client.
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 via
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.
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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 can 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 for example in the
pathname, query string or even fragment components 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.
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 binary format of a name is shown
in Figure 7.
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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 7: Binary Name Format
The Res field is a reserved 2-bit field for future use and MUST be
set to zero for this specification and ignored on receipt.
The hash algorithm and truncation length are specified by the Suite
ID. For maintaining efficient encoding for the binary format, only a
few hash algorithms and truncation lengths are supported. See
Section 9.4 for details.
A hash value that is truncated to 120 bits will result in the overall
name being a 128-bit value which may be useful for protocols that can
easily use 128-bit identifiers.
7. Human-speakable (nih) URI Format
Sometimes a resource may need to be referred to via a name in a
format that is easy for humans to read out, and less likely to be
ambiguous when heard. This is intended to be usable for example over
the phone in order to confirm the (current or future) presence or
absence of a resource. This "confirmation" use-case described
further in Section 8.3 is the main current use-case for nih URIs.
The ni URI format is not well-suited for this, as, for example,
base64url uses both upper and lower case which can easily cause
confusion. For this particular purpose, ("speaking" the value of a
hash output) the more verbose but less ambiguous (when spoken) nih
URI scheme is defined. "nih" stands for "Named Information for
Humans." (Or possibly "Not Invented Here," which is clearly false,
and therefore worth including [RFC5513]:-)
The justification for nih being a URI scheme is that that can help a
user agent for the speaker to better display the value, or help a
machine to better speak or recognise the value when spoken. We do
not include the query string since there is no way to ensure that its
value might be spoken unambiguously, and similarly for the authority,
where e.g., some internationalised forms of domain name might not be
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easy to speak and comprehend easily. This leaves the hash value as
the only part of the ni URI that we feel can be usefully included.
But since speakers or listeners (or speech recognition) may err, we
also include a check-digit to catch common errors, and allow for the
inclusion of "-" separators to make nih URIs more easy to read out.
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
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. Separators ("-" characters) MAY be
interspersed in the hash value in any way to make those easier to
read, typically grouping four or six characters with a separator
between.
The hash value MAY be 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., "sepval" in
the ABNF production below) but with all "-" separator characters
first stripped out. This maps the ASCII-HEX so that
'0'=0,...'9'=9,'a'=10,...'f'=15. None of the other fields, nor any
"-" separators, are input when calculating the checkdigit.
humanname = "nih:" alg-sepval [ ";" checkdigit ]
alg-sepval = alg ";" sepval
sepval = 1*(ahlc / "-")
ahlc = DIGIT / "a" / "b" / "c" / "d" / "e" / "f"
; DIGIT is defined in RFC 5234 and is 0-9
checkdigit = ahlc
Figure 8: Human-speakable syntax
For algorithms that have a Suite ID reserved (see Figure 11), the alg
field MAY contain the ID value as a ASCII 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 format.
There is no such thing as a relative nih URI.
8. Examples
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8.1. Hello World!
The following ni URI is generated from 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
8.2. Public Key Examples
Given the DER-encoded SubjectPublicKeyInfo in Figure 9 we derive the
names shown in Figure 10 for this value.
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 9: 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-speakable form of a name for this key (truncated to 120 bits|
| in length) with checkdigit: |
| nih:sha-256-120;5326-9057-e12f-e2b7-4ba0-7c89-2560-a2;f |
+-------------------------------------------------------------------+
| Human-speakable form of a name for this key (truncated to 32 bits |
| in length) with checkdigit and no "-" separators: |
| nih:sha-256-32;53269057;b |
+-------------------------------------------------------------------+
| Human-speakable form using decimal presentation of the |
| algorithm ID (sha-256-120) with checkdigit: |
| nih:3;532690-57e12f-e2b74b-a07c89-2560a2;f |
+-------------------------------------------------------------------+
Figure 10: Example Names
8.3. nih Usage Example
Alice has set up a server node with an RSA key pair. She uses an ni
URI as the name for the public key that corresponds to the private
key on that box. Alice's node might identify itself using that ni
URI in some protocol.
Bob would like to believe that its really Alice's node when his node
interacts with the network and asks his friend Alice to tell him what
public key she uses. Alice hits the "tell someone the name of the
public key" button on her admin user interface, and that displays the
nih URI and says "tell this to your buddy." She phones Bob and reads
the nih URI to him.
Bob types that in to his "manage known nodes" admin application, (or
lets that application listen to part of the call), which can
regenerate the ni URI and store that or some equivalent. Then when
Bob's node interacts with Alice's node it can more safely accept a
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signature or encrypt data to Alice's node.
9. IANA Considerations
9.1. Assignment of 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
Applications/protocols that use this URI scheme name: General
applicability.
Interoperability considerations: Defined here.
Security considerations: See Section 10
Contact: Stephen Farrell, stephen.farrell@cs.tcd.ie
Author/Change controller: IETF
References: As specified in this document
9.2. Assignment of 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
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Applications/protocols that use this URI scheme name: General
applicability.
Interoperability considerations: Defined here.
Security considerations: See Section 10
Contact: Stephen Farrell, stephen.farrell@cs.tcd.ie
Author/Change controller: IETF
References: As specified in this document
9.3. Assignment of .well-known 'ni' URI
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
Change controller: IETF
Specification document(s): This document
Related information: None
9.4. Creation of Named Information Hash Algorithm Registry
IANA is requested to create a new registry for hash algorithms as
used in the name formats specified here and called the "Named
Information Hash Algorithm Registry". Future assignments are to be
made through Expert Review [RFC5226]. This registry has five fields,
the suite ID, the hash algorithm name string, the truncation length,
the underlying algorithm reference and a status field that indicates
if algorithm is current or deprecated and should no longer be used.
The status field can have the value "current" or "deprecated". Other
values are reserved for possible future definition.
If the status is "current", 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.
A request to mark an entry as "deprecated" can be done by sending a
mail to the Designated Expert. Before approving the request, the
community MUST be consulted via a "call for comments" of at least two
weeks by sending a mail to the IETF discussion list.
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Initial values are specified below. The Designated Expert SHOULD
generally approve additions that reference hash algorithms that are
widely used in other IETF protocols. In addition, the Designated
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. See
for example [RFC6149],[RFC6150] and [RFC6151] for some hash functions
that are considered obsolete in this sense.
The 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 Designated Expert MAY allow for later allocation of a suite
ID, if that appears warranted. The Designated Expert MAY consult the
community via a "call for comments" by sending a mail to the IETF
discussion list before allocating a suite ID.
ID Hash name string Value length Reference Status
0 Reserved
1 sha-256 256 bits [SHA-256] current
2 sha-256-128 128 bits [SHA-256] current
3 sha-256-120 120 bits [SHA-256] current
4 sha-256-96 96 bits [SHA-256] current
5 sha-256-64 64 bits [SHA-256] current
6 sha-256-32 32 bits [SHA-256] current
32 Reserved
Figure 11: 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 meets the "specification required" rule."
9.5. Creation of Named Information Parameter Registry
IANA is requested to create a new registry entitled "Named
Information URI Parameter Definitions".
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The policy for future assignments to the registry is Expert Review,
and as for the ni Hash Algorithm Registry above, the Designated
Expert is responsible for ensuring that the document referenced for
the paramater definition meets the "specification required" rule."
The fields in this registry are the parameter name, a description and
a reference. The parameter name MUST be such that it is suitable for
use as a query string parameter name in an ni URI. (See Section 3.)
The initial contents of the registry are:
Parameter Meaning Reference
----------- -------------------------------------------- ---------
ct Content Type [RFC-THIS]
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
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.
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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.
The 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. Application developers
MUST NOT assume any relationship between the registrant of the domain
name that is part of an ni URI and some matching content just because
the ni URI matches that content.
If name-data integrity is successfully validated, and the hash is
strong and long enough, then the "web origin" [RFC6454] for the bytes
of the named object is really going to be the place from which you
got the ni name and not the place from which you got the bytes of the
object. This appears to offer a potential benefit if using ni names
for, for example, scripts included from a HTML page accessed via
server-authenticated https. If name-data integrity is not validated
(and it is optional), or fails, then the web origin is, as usual, the
place from which the object bytes were received. Applications making
use of ni names SHOULD take this into account in their trust models.
Some implementations might mis-handle ni URIs that include non-base64
characters, whitespace or other non-conforming strings and that could
lead to erroneously considering names to be the same when they are
not. An ni URI that is malformed in such ways MUST NOT be treated as
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matching any other ni URI. Implementers need to check the behaviour
of libraries for such parsing problems.
11. Acknowledgments
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 Carsten Bormann, Martin Durst,
Tobias Heer, Bjoern Hoehrmann, Tero Kivinen, Barry Leiba, Larry
Masinter, David McGrew, Alexey Melnikov, Bob Moskowitz, Jonathan
Rees, Eric Rescorla, Zach Shelby, Martin Thomas, for their comments
and input to the document. Thanks, in particular, to James Manger
for correcting the examples.
12. References
12.1. Normative References
[I-D.ietf-appsawg-media-type-regs]
Freed, N., Klensin, J., and T. Hansen, "Media Type
Specifications and Registration Procedures",
draft-ietf-appsawg-media-type-regs-14 (work in progress),
June 2012.
[I-D.ietf-httpbis-p1-messaging]
Fielding, R., Lafon, Y., and J. Reschke, "HTTP/1.1, part
1: Message Routing and Syntax"",
draft-ietf-httpbis-p1-messaging-20 (work in progress),
July 2012.
[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>.
[RFC2045] Freed, N. and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part One: Format of Internet Message
Bodies", RFC 2045, November 1996.
[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.,
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Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext
Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.
[RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000.
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66,
RFC 3986, January 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
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.
[SHA-256] NIST, "United States National Institute of Standards and
Technology (NIST), FIPS 180-3: Secure Hash Standard",
October 2008, <http://csrc.nist.gov/publications/fips/
fips180-3/fips180-3_final.pdf>.
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-03
(work in progress), June 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-23 (work in
progress), June 2012.
[I-D.ietf-websec-strict-transport-sec]
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Hodges, J., Jackson, C., and A. Barth, "HTTP Strict
Transport Security (HSTS)",
draft-ietf-websec-strict-transport-sec-11 (work in
progress), July 2012.
[RFC3766] Orman, H. and P. Hoffman, "Determining Strengths For
Public Keys Used For Exchanging Symmetric Keys", BCP 86,
RFC 3766, April 2004.
[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.
[RFC5513] Farrel, A., "IANA Considerations for Three Letter
Acronyms", RFC 5513, April 1 2009.
[RFC6149] Turner, S. and L. Chen, "MD2 to Historic Status",
RFC 6149, March 2011.
[RFC6150] Turner, S. and L. Chen, "MD4 to Historic Status",
RFC 6150, March 2011.
[RFC6151] Turner, S. and L. Chen, "Updated Security Considerations
for the MD5 Message-Digest and the HMAC-MD5 Algorithms",
RFC 6151, March 2011.
[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
Workshop , December 2008.
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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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