P2PSIP M. Petit-Huguenin
Internet-Draft Impedance Mismatch
Intended status: Standards Track February 16, 2013
Expires: August 20, 2013
Configuration of Access Control Policy in REsource LOcation And
Discovery (RELOAD) Base Protocol
draft-ietf-p2psip-access-control-00
Abstract
This document describes an extension to the REsource LOcation And
Discovery (RELOAD) base protocol to distribute the code of new Access
Control Policies without having to upgrade the RELOAD implementations
in an overlay.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on August 20, 2013.
Copyright Notice
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document authors. All rights reserved.
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This document may not be modified, and derivative works of it may not
be created, except to format it for publication as an RFC or to
translate it into languages other than English.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Processing . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. Security Considerations . . . . . . . . . . . . . . . . . . . 6
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
6. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
6.1. Normative References . . . . . . . . . . . . . . . . . . 7
6.2. Informative References . . . . . . . . . . . . . . . . . 8
Appendix A. Examples . . . . . . . . . . . . . . . . . . . . . . 8
A.1. Standard Access Control Policies . . . . . . . . . . . . 8
A.1.1. USER-MATCH . . . . . . . . . . . . . . . . . . . . . 8
A.1.2. NODE-MATCH . . . . . . . . . . . . . . . . . . . . . 9
A.1.3. USER-NODE-MATCH . . . . . . . . . . . . . . . . . . . 9
A.1.4. NODE-MULTIPLE . . . . . . . . . . . . . . . . . . . . 9
A.2. Service Discovery Access Control Policy NODE-ID-MATCH . . 10
A.3. VIPR Access Control Policy . . . . . . . . . . . . . . . 11
A.4. ShaRe Access Control Policy USER-CHAIN-ACL . . . . . . . 12
Appendix B. Release notes . . . . . . . . . . . . . . . . . . . 12
B.1. Modifications between ietf-p2psip-reload-access-control
and petithuguenin-p2psip-access-control-05 . . . . . . . 12
B.2. Running Code Considerations . . . . . . . . . . . . . . . 13
B.3. TODO List . . . . . . . . . . . . . . . . . . . . . . . . 13
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 13
1. Introduction
The RELOAD base protocol specifies an Access Control Policy as
"defin[ing] whether a request from a given node to operate on a given
value should succeed or fail." The paragraph continues saying that
"[i]t is anticipated that only a small number of generic access
control policies are required", but there is indications that this
assumption will not hold. On all the RELOAD Usages defined in other
documents than the RELOAD base protocol, roughly 50% defines a new
Access Control Policy.
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The problem with a new Access Control Policy is that, because it is
executed when a Store request is processed, it needs to be
implemented by all the peers and so requires an upgrade of the
software. This is something that is probably not possible in large
overlays or on overlays using different implementations. For this
reason, this document proposes an extension to the RELOAD
configuration document that permits to transport the code of a new
Access Control Policy to each peer.
This extension defines a new element <code> that can be optionally
added to a <configuration> element in the configuration document.
The <code> element contains ECMAScript [ECMA-262] code that will be
called for each StoredData object that use this access control
policy. The code receives four parameters, corresponding to the
Resource-ID, Signature, Kind and StoredDataValue of the value to
store. The code returns true or false to signal to the
implementation if the request should succeed or fail.
For example the USER-MATCH Access Control Policy defined in the base
protocol could be identically defined by inserting the following code
in an <code> element:
return resource.equalsHash(signer.user_name.bytes());
The <kind> parameters are also passed to the code, so the NODE-
MULTIPLE Access Control Policy could be implemented like this:
for (var i = 0; i < kind.max_node_multiple; i++) {
if (resource.equalsHash(signer.node_id, i.width(4))) {
return true;
}
}
return false;
2. Terminology
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 [RFC2119] with the
caveat that "SHOULD", "SHOULD NOT", "RECOMMENDED", and "NOT
RECOMMENDED" are appropriate when valid exceptions to a general
requirement are known to exist or appear to exist, and it is
infeasible or impractical to enumerate all of them. However, they
should not be interpreted as permitting implementors to fail to
implement the general requirement when such failure would result in
interoperability failure.
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3. Processing
A peer receiving a configuration document containing one or more
<code> elements, either by retrieving it from the configuration
server or in a ConfigUpdateReq message, MUST reject this
configuration if is not is not signed or if the signature
verification fails.
The Compact Relax NG Grammar for this element is:
namespace acp = "urn:ietf:params:xml:ns:p2p:access-control"
parameter &= element acp:code {
attribute name { xsd:string },
xsd:base64Binary
}?
All peers in an overlay MUST implement this specification. One way
to do this is to add a <mandatory-extension> element containing the
"urn:ietf:params:xml:ns:p2p:access-control" namespace in the
configuration document.
The mandatory "name" attribute identifies the access control policy
and can be used in the "name" attribute of a <kind> element as if it
was defined by IANA.
If the <code> element is present in the namespace allocated to this
specification, and the Access Control Policy is not natively
implemented, then the code inside the element MUST be called for each
DataValue found in a received StoreReq for a Kind that is defined
with this access control policy. The content of the <code> element
MUST be decoded using the base64 [RFC4648] encoding, uncompressed
using gzip [RFC1952] then converted to characters using UTF-8.
<code> elements that are not encoded using UTF-8, compressed with
gzip or finally converted to the base64 format MUST be ignored.
For each call to the code, the following ECMAScript objects,
properties and functions MUST be available:
configuration.instance_name: The name of the overlay, as a String
object.
configuration.topology_plugin: The overlay algorithm, as a String
object.
configuration.node_id_length: The length of a NodeId in bytes, as a
Number object.
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configuration.kinds: An array of kinds (with the same definition
than the kind object), indexed by id and eventually by name.
configuration.evaluate(String, String, String): A function that
evaluates the first parameter as an XPath expression against the
configuration element, and returns the result as a String object.
The second parameter contains a namespace prefix and the third
parameter contains a namespace.
kind.id: The id of the Kind associated with the entry, as a Number
object.
kind.name: If the Kind associated with the entry is registered by
IANA, contains the name as a String object. If not, this property
is undefined.
kind.data_model: The name of the Data Model associated with the
entry, as a String object.
kind.access_control: The name of the Access Control Policy
associated with the entry, as a String object.
kind.max_count: The value of the max-count element in the
configuration file, as a Number object.
kind.max_size: The value of the max-size element in the
configuration file as a Number object.
kind.max_node_multiple: If the Access Control is MULTIPLE-NODE,
contains the value of the max-node-multiple element in the
configuration file, as a Number object. If not, this property is
undefined.
kind.evaluate(String, String, String): A function that evaluates the
first parameter as an XPath expression against the kind element,
and returns the result as a String object. The second parameter
must contain a namespace prefix and the third parameter must
contain a namespace.
resource: An opaque object representing the Resource-ID, as an array
of bytes.
resource.entries: An array of arrays of entry objects, with the
first array level indexed by Kind-Id and kind names, and the
second level indexed by index, key or nothing, depending on the
data model of the kind. This permits to retrieve all the values
of all Kinds stored at the same Resource-ID than the entry
currently processed.
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resource.equalsHash(Object...): A function that returns true if
hashing the concatenation of the arguments according to the
mapping function of the overlay algorithm is equal to the
Resource-ID. Each argument is an array of bytes.
entry.index: If the Data Model is ARRAY, contains the index of the
entry, as a Number object. If not, this property is undefined.
entry.key: If the Data Model is DICTIONARY, contains the key of the
entry, as an array of bytes. If not, this property is undefined.
entry.storage_time: The date and time used to store the entry, as a
Date object.
entry.lifetime: The validity for the entry in seconds, as a Number
object.
entry.exists: Indicates if the entry value exists, as Boolean
object.
entry.value: This property contains an opaque object that represents
the whole data, as an array of bytes.
entry.signer.user_name: The rfc822Name stored in the certificate
that was used to sign the request, as a String object.
entry.signer.node_id: The Node-ID stored in the certificate that was
used to sign the request, as an array of bytes.
The properties SHOULD NOT be modifiable or deletable and if they are,
modifying or deleting them MUST NOT modify or delete the equivalent
internal values (in other words, the code cannot be used to modify
the elements that will be stored).
The value returned by the code is evaluated to true or false,
according to the ECMAScript rules. If the return value of one of the
call to the code is evaluated to false, then the StoreReq fails, the
state MUST be rolled back and an Error_Forbidden MUST be returned.
4. Security Considerations
Because the configuration document containing the ECMAScript code is
under the responsibility of the same entity that will sign it, using
a scripting language does not introduce any additional risk if the
RELOAD implementers follow the rules in this document (no side effect
when modifying the parameters, only base classes of ECMAScript
implemented, etc...). It is even possible to deal with less than
perfect implementations as long as they do not accept a configuration
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file that is not signed correctly. One way for the signer to enforce
this would be to deliberately send in a ConfigUpdate an incorrectly
signed version of the configuration file and blacklist all the nodes
that accepted it in a newly issued configuration file.
By permitting multiple overlay implementations to interoperate inside
one overlay, RELOAD helps build overlays that are not only resistant
to hardware or communication failures, but also to programmer errors.
Distributing the access control policy code inside the configuration
document reintroduces this single point of failure. To mitigate this
problem, new access control policies should be implemented natively
as soon as possible, but if all implementations uses the ECMAscript
code as a blueprint for the native code, an hidden bug can be
unwillingly duplicated. This is why developers should implement new
access control policies from the normative text instead of looking at
the code itself. To help developers do the right thing the code in
the configuration document is obfuscated by compressing and encoding
it as a base64 character string.
5. IANA Considerations
This section requests IANA to register the following URN in the "XML
Namespaces" class of the "IETF XML Registry" in accordance with
[RFC3688].
URI: urn:ietf:params:xml:ns:p2p:access-control
Registrant Contact: The IESG
XML: This specification.
6. References
6.1. Normative References
[RFC1952] Deutsch, P., "GZIP file format specification version 4.3",
RFC 1952, May 1996.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3688] Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
January 2004.
[RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data
Encodings", RFC 4648, October 2006.
[I-D.ietf-p2psip-base]
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Jennings, C., Lowekamp, B., Rescorla, E., Baset, S., and
H. Schulzrinne, "REsource LOcation And Discovery (RELOAD)
Base Protocol", draft-ietf-p2psip-base-24 (work in
progress), January 2013.
[ECMA-262]
Ecma, , "ECMAScript Language Specification 3rd Edition",
December 2009.
6.2. Informative References
[I-D.ietf-p2psip-service-discovery]
Maenpaa, J. and G. Camarillo, "Service Discovery Usage for
REsource LOcation And Discovery (RELOAD)", draft-ietf-
p2psip-service-discovery-06 (work in progress), April
2013.
[I-D.petithuguenin-vipr-reload-usage]
Petit-Huguenin, M., Rosenberg, J., and C. Jennings, "A
Usage of Resource Location and Discovery (RELOAD) for
Public Switched Telephone Network (PSTN) Verification",
draft-petithuguenin-vipr-reload-usage-04 (work in
progress), March 2012.
[I-D.ietf-p2psip-share]
Knauf, A., Schmidt, T., Hege, G., and M. Waehlisch, "A
Usage for Shared Resources in RELOAD (ShaRe)", draft-ietf-
p2psip-share-00 (work in progress), April 2013.
Appendix A. Examples
A.1. Standard Access Control Policies
This section shows the ECMAScript code that could be used to
implement the standard Access Control Policies defined in
[I-D.ietf-p2psip-base].
A.1.1. USER-MATCH
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String.prototype['bytes'] = function () {
var bytes = [];
for (var i = 0; i < this.length; i++) {
bytes[i] = this.charCodeAt(i);
}
return bytes;
};
return resource.equalsHash(entry.signer.user_name.bytes());
A.1.2. NODE-MATCH
return resource.equalsHash(entry.signer.node_id);
A.1.3. USER-NODE-MATCH
String.prototype['bytes'] = function () {
var bytes = [];
for (var i = 0; i < this.length; i++) {
bytes[i] = this.charCodeAt(i);
}
return bytes;
};
var equals = function (a, b) {
if (a.length !== b.length) return false;
for (var i = 0; i < a.length; i++) {
if (a[i] !== b[i]) return false;
}
return true;
};
return resource.equalsHash(entry.signer.user_name.bytes())
&& equals(entry.key, entry.signer.node_id);
A.1.4. NODE-MULTIPLE
Number.prototype['width'] = function (w) {
var bytes = [];
for (var i = 0; i < w; i++) {
bytes[i] = (this >>> ((w - i - 1) * 8)) & 255;
}
return bytes;
};
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for (var i = 0; i < kind.max_node_multiple; i++) {
if (resource.equalsHash(entry.signer.node_id, i.width(4))) {
return true;
}
}
return false;
A.2. Service Discovery Access Control Policy NODE-ID-MATCH
[I-D.ietf-p2psip-service-discovery] defines a new Access Control
Policy (NODE-ID-MATCH) that need to access the content of the entry
to be written. If implemented as specified by this document, the
ECMAScript code would look something like this:
/* Insert here the code from
http://jsfromhell.com/classes/bignumber
*/
var toBigNumber = function (node_id) {
var bignum = new BigNumber(0);
for (var i = 0; i < node_id.length; i++) {
bignum = bignum.multiply(256).add(node_id[i]);
}
return bignum;
};
var checkIntervals = function (node_id, level, node, factor) {
var size = new BigNumber(2).pow(128);
var node = toBigNumber(node_id);
for (var f = 0; f < factor; f++) {
var temp = size.multiply(new BigNumber(f)
.pow(new BigNumber(level).negate()));
var min = temp.multiply(node.add(new BigNumber(f)
.divide(factor)));
var max = temp.multiply(node.add(new BigNumber(f + 1)
.divide(factor)));
if (node.compare(min) === -1 || node.compare(max) == 1
|| node.compare(max) == 0) return false;
}
return true;
};
var equals = function (a, b) {
if (a.length !== b.length) return false;
for (var i = 0; i < a.length; i++) {
if (a[i] !== b[i]) return false;
}
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return true;
};
var level = function (value) {
var length = value[16] * 256 + value[17];
return value[18 + length] * 256 + value[18 + length + 1];
};
var node = function (value) {
var length = value[16] * 256 + value[17];
return value[18 + length + 2] * 256
+ value[18 + length + 3];
};
var namespace = function (value) {
var length = value[16] * 256 + value[17];
return String.fromCharCode.apply(null,
value.slice(18, length + 18));
};
var branching_factor =
kind.evaluate('/branching-factor',
'redir', 'urn:ietf:params:xml:ns:p2p:redir');
return equals(entry.key, entry.signer.node_id)
&& (!entry.exists || checkIntervals(entry.key,
level(entry.value), node(entry.value),
branching_factor))
&& (!entry.exists
|| resource.equalsHash(namespace(entry.value),
level(entry.value), node(entry.value)));
Note that the code for the BigNumber object was removed from this
example, as the licensing terms are unclear. The code is available
at [1].
A.3. VIPR Access Control Policy
[I-D.petithuguenin-vipr-reload-usage] defines a new Access Control
Policy. If implemented as specified by this document, the ECMAScript
code would look something like this:
var equals = function (a, b) {
if (a.length !== b.length) return false;
for (var i = 0; i < a.length; i++) {
if (a[i] !== b[i]) return false;
}
return true;
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};
var length = configuration.node_id_length;
return equals(entry.key.slice(0, length),
entry.value.slice(4, length + 4))
&& equals(entry.key.slice(0, length), entry.signer.node_id);
A.4. ShaRe Access Control Policy USER-CHAIN-ACL
[I-D.ietf-p2psip-share] defines a new Access Control Policy, USER-
CHAIN-ACL. If implemented as specified by this document, the
ECMAScript code would look something like this:
var pattern = kind.evaluate('/share:pattern',
'share', 'urn:ietf:params:xml:ns:p2p:config-share');
var username = entry.signer.user_name.match(/^([^@]+)@(.+)$/);
var new_pattern = new RegExp(
pattern.replace('$USER', username[1])
.replace('$DOMAIN', username[2]));
var length = entry.value[0] * 256 + entry.value[1];
var resource_name = String.fromCharCode.apply(null,
entry.value.slice(2, length + 2));
return new_pattern.test(resource_name);\n"));
[[Note: the code is incomplete]]
Appendix B. Release notes
This section must be removed before publication as an RFC.
B.1. Modifications between ietf-p2psip-reload-access-control and
petithuguenin-p2psip-access-control-05
o Removed inconsistency in the terminology section.
o Updated the IANA section and added reference to RFC 3688.
o Removed "This is probably not legal..." in the security section.
o Renamed "access-control-code" to simply "code" as it has to be
prefixed by the namespace anyway, so there is no risk of conflict.
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B.2. Running Code Considerations
o Reference Implementation and Access Control Policy script tester
(<http://debian.implementers.org/testing/source/reload.tar.gz>).
Marc Petit-Huguenin. Implements version -03.
B.3. TODO List
o Finish the code for ShaRe.
o Update the reference implementation.
Author's Address
Marc Petit-Huguenin
Impedance Mismatch
Email: petithug@acm.org
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