KITTEN W. Mills
Internet-Draft T. Showalter
Intended status: Standards Track Yahoo Inc.
Expires: August 20, 2011 H. Tschofenig
Nokia Siemens Networks
February 16, 2011
A SASL Mechanism for OAuth
draft-mills-kitten-sasl-oauth-01.txt
Abstract
Simple Authentication and Security Layer (SASL) is a framework for
providing authentication and data security services in connection-
oriented protocols via replaceable mechanisms. OAuth is a protocol
framework for delegated HTTP authentication and thereby provides a
method for clients to access a protected resource on behalf of a
resource owner.
This document defines the use of HTTP authentication over SASL, and
additionally defines authoriation and token issuing endpoint
discovery. Thereby, it enables schemes defined within the OAuth
framework for non-HTTP-based application protocols. A future version
of this document will describe the integration into the Generic
Security Services Application Program Interface (GSS-APIO).
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
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Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on August 20, 2011.
Copyright Notice
Copyright (c) 2011 IETF Trust and the persons identified as the
document authors. All rights reserved.
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This document is subject to BCP 78 and the IETF Trust's Legal
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. The OAuth SASL Mechanism . . . . . . . . . . . . . . . . . . . 6
3.1. Channel Binding . . . . . . . . . . . . . . . . . . . . . 6
3.2. Initial Client Response . . . . . . . . . . . . . . . . . 6
3.3. Server's Response . . . . . . . . . . . . . . . . . . . . 7
3.4. Discovery Information . . . . . . . . . . . . . . . . . . 7
3.5. Use of Signature Type Authorization . . . . . . . . . . . 9
4. Implementation Requirements . . . . . . . . . . . . . . . . . 10
5. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
5.1. Successful Bearer Token Exchange . . . . . . . . . . . . . 11
5.2. Failed Exchange . . . . . . . . . . . . . . . . . . . . . 11
6. Security Considerations . . . . . . . . . . . . . . . . . . . 13
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14
7.1. SASL Registration . . . . . . . . . . . . . . . . . . . . 14
7.2. Link Type Registration . . . . . . . . . . . . . . . . . . 14
7.2.1. OAuth 2 Authentication Endpoint . . . . . . . . . . . 14
7.2.2. OAuth 2 Token Endpoint . . . . . . . . . . . . . . . . 14
7.2.3. OAuth 1.0a Request Initiation Endpoint . . . . . . . . 15
7.2.4. OAuth 1.0a Authorization Endpoint . . . . . . . . . . 15
7.2.5. OAuth 1.0a Token Endpoint . . . . . . . . . . . . . . 15
8. Appendix A -- Document History . . . . . . . . . . . . . . . . 16
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 17
9.1. Normative References . . . . . . . . . . . . . . . . . . . 17
9.2. Informative References . . . . . . . . . . . . . . . . . . 17
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 19
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1. Introduction
OAuth [I-D.ietf-oauth-v2] offers a standard mechanism for delegating
authentication typically used for the purpose of control access to
resources. The core OAuth specification defines a framework for
authentication and token usage in an HTTP-based environment. The
HTTP authorization schemes and tokens in this model are defined
separately, some are deined within the OAuth 2 framework such as
OAuth 2.0 Protocol: Bearer Tokens [I-D.ietf-oauth-v2-bearer], and
some are free standing with OAuth 2 frameowrk bindings such as MAC
Authentication [I-D.hammer-oauth-v2-mac-token] tokens. This
mechanism takes advantage of the OAuth protocol and infrastructure to
provide a way to use SASL [RFC4422] for access to resources for non-
HTTP-based protocols such as IMAP [RFC3501], which is what this memo
uses in the examples.
The general authentication flow is that the application will first
obtain an access token from an OAuth token service for the resource.
Once the client has obtained an OAuth access token it then connects
and authenticated using this SASL mechanism.
Figure 1 shows the relationship between SASL and OAuth graphically.
Item (1) denotes the part of the OAuth exchange that remains
unchanged from [I-D.ietf-oauth-v2], i.e. where the client obtains and
refreshes Access Tokens. This document focuses on item (2) where the
Access Token is presented to the resource server over SASL.
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----+
+--------+ +---------------+ |
| |--(C)-- Authorization Request --->| Resource | |
| | | Owner | |Plain
| |<-(D)------ Access Grant ---------| | |OAuth
| | +---------------+ |2.0
| | |(1)
| | Client Credentials & +---------------+ |
| |--(E)------ Access Grant -------->| Authorization | |
| Client | | Server | |
| |<-(F)------ Access Token ---------| | |
| | (w/ Optional Refresh Token) +---------------+ |
| | ----+
| |
| | ----+
| | (Optional discovery) +---------------+ |
| |--(A)------- User Name --------->| | |
| Client | | | |
| |<-(B)------ Authentication -------| | |
| | endpoint information | Resource | |OAuth
| | | Server | |over
| |--(G)------ Access Token -------->| | |SASL
| | | | |
| |<-(H)---- Protected Resource -----| | |(2)
+--------+ +---------------+ |
----+
Figure 1: Interworking Architecture
Note: The discovery procedure in OAuth is still work in progress.
Hence, the discovery components described in this document should
be considered incomplete and a tentative proposal. In general,
there is a tradeoff between a generic, externally available
defined discovery mechanisms (such as Webfinger using host-meta
[I-D.hammer-hostmeta]) and configuration information exchanged
inband between the protocol endpoints.
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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].
The reader is assumed to be familiar with the terms used in the OAuth
2.0 specification.
In examples, "C:" and "S:" indicate lines sent by the client and
server respectively. Line breaks have been inserted for readability.
Note that the IMAP SASL specification requires base64 encoding
message, not this memo.
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3. The OAuth SASL Mechanism
SASL is used as a generalized authentication method in a variety of
protocols. This document defines a mechanism to allow HTTP
Authorization schemes in the OAuth framework to be used within the
SASL framework. In this model a client authenticates to an OAuth-
capable authorization server over HTTPS. This server then issues
tokens after successfully authenticating the resource owner.
Subsequently, the obtained token may be presented in an OAuth-
authenticated request to the resource server. This mechanism further
provides compatibility with OAuth 1.0a [RFC5849] and the "OAuth"
authentication scheme defined there.
3.1. Channel Binding
[[TODO: Make this much better and define the channel binding variant
for the mechanism.]]
Channel binding for this mechanism is defined in order to allow
satifying the security requirements of the authorization schemes
used. If the specification for the underlying authorization scheme
requires a security layer such as TLS [RFC5246] the server SHOULD
only provide that scheme in a mechanism with channel binding enabled.
3.2. Initial Client Response
The client response is formatted as an HTTP [RFC2616] request. The
HTTP request is limited in that the path MUST be "/" and no query
string is allowed. The following header lines are defined in the
client response:
User (OPTIONAL): Contains the user identifier being
authenticated, and is provided to allow correct discovery
information to be returned.
Host (REQUIRED): Contains the host name to which the client
connected.
Authorization (REQUIRED): An HTTP Authorization header..
The user name is provided by the client to allow the discovery
information to be customised for the user, a given server could allow
multiple authenticators and it needs to return the correct one. For
instance, a large ISP could provide mail service for several domains
who manage their own user information. For instance, users at foo-
example.com could be authenticated by an OAuth service at
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https://oauth.foo-example.com/, and users at bar-example.com could be
authenticated by https://oauth.bar-example.com, but both could be
served by a hypothetical IMAP server running at a third domain,
imap.example.net.
3.3. Server's Response
The server validates the response per the specification for the
authorization scheme used. If the authorization scheme used includes
signing of the request parameters the client must provide a complete
HTTP style request that satisfies the data requirements for the
scheme in use.
The server responds to a successful OAuth authentication by
completing the SASL negotiation. The authentication scheme MUST
carry the user ID to be authenticated. The server MUST use that ID
as the user being authenticated, that is the user assertion we accept
and not other information such as from the URL or "User:" header.
The server responds to failed authentication by sending discovery
information and then failing the authentication.
3.4. Discovery Information
The server MUST send discovery information in response to a failed
authentication exchange or a request with an empty Authorization
header. If discovery information is returned it MUST include an
authentication endpoint appropriate for the user. If the "User"
header is present the discovery information MUST be for that user.
Discovery information is provided by the server to the client to
allow a client to discover the appropriate OAuth authentication and
token endpoints. The client then uses that information to obtain the
access token needed for OAuth authentication. The client SHOULD
cache and re-use the user specific discovery information for service
endpoints.
Discovery information makes use of both the WWW-Authenticate header
as defined in HTTP Authentication: Basic and Digest Access
Authentication [RFC2617] and Link headers as defined in [RFC5988].
The following elements are defined for discovery information:
WWW-Authenticate A WWW-Authenticate header for each authentication
scheme supported by the server. Authentication scheme names are
case insensitive. The following [RFC2617] authentication
parameters are defined:
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realm REQUIRED -- (as defined by RFC2617)
scope OPTIONAL -- A quoted string. This provides the client an
OAuth 2 scope known to be valid for the resource.
oauth2-authenticator An [RFC5988] Link header specifying the
[I-D.ietf-oauth-v2] authentication endpoint. This link has an
OPTIONAL link-extension "scheme", if included this link applies
ONLY to the specified scheme.
oauth2-token An [RFC5988] Link header specifying the
[I-D.ietf-oauth-v2] token endpoint. This link has an OPTIONAL
link-extension "scheme", if included this link applies ONLY to the
specified scheme.
oauth-initiate (Optional) An [RFC5988] Link header specifying the
Oauth 1.0a [RFC5849] initiation endpoint. The server MUST send
this if "OAuth" is included in the supported list of HTTP
authentication schemes for the server.
oauth-authorize (Optional) An [RFC5988] Link header specifying the
Oauth 1.0a [RFC5849] authentication endpoint. The server MUST
send this if "OAuth" is included in the supported list of HTTP
authentication schemes for the server.
oauth-token (Optional) An [RFC5988] Link header specifying the Oauth
1.0a [RFC5849] token endpoint. The server MUST send this if
"OAuth" is included in the supported list of HTTP authentication
schemes for the server. This link type has one link-extenstion
"grant-types" which is a space separated list of the the OAuth 2.0
grant types that can be used at the token endpoint to obtain a
token.
Usage of the URLs provided in the discovery information is defined in
the relevant specifications. If the server supports multiple
authenticators the discovery information returned for unknown users
MUST be consistent with the discovery information for known users to
prevent user enumeration. The OAuth 2.0 specification
[I-D.ietf-oauth-v2] supports multiple types of authentication schemes
and the server MUST specify at least one supported authentication
scheme in the discovery information. The server MAY support multiple
schemes and MAY support schemes not listed in the discovery
information.
If the resource server provides a scope the client SHOULD always
request scoped tokens from the token endpoint. The client MAY use a
scope other than the one provided by the resource server. Scopes
other than those advertised by the resource server must be defined by
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the resource owner and provided in service documentation (which is
beyond the scope of this memo).
3.5. Use of Signature Type Authorization
This mechanism supports authorization using signatures, which
requires that both client and server construct the string to be
signed. OAuth 2 is designed for authentication/authorization to
access specific URIs. SASL is designed for user authentication, and
has no facility for being more specific. In this mechanism we
require an HTTP style format specifically to support signature type
authentication, but this is extremely limited. The HTTP style
request is limited to a path of "/" without a query string. This
mechanism is in the SASL model, but is designed so that no changes
are needed if there is a revision of SASL which supports more
specific resource authorization, e.g. IMAP access to a specific
folder or FTP access limited to a specific directory.
Using the example in the MAC specification
[I-D.hammer-oauth-v2-mac-token] as a starting point, on an IMAP
server running on port 143 and given the MAC style authorization
request (with long lines wrapped for readability) below:
GET / HTTP/1.1
Host: server.example.com
User: user@example.com
Authorization: MAC token="h480djs93hd8",timestamp="137131200",
nonce="dj83hs9s",signature="YTVjyNSujYs1WsDurFnvFi4JK6o="
The normalized request string would be constructed per the MAC
specifcation [I-D.hammer-oauth-v2-mac-token]. In this example the
normalized request string with the new line separator character is
represented by "\n" for display purposes only would be:
h480djs93hd8\n
137131200\n
dj83hs9s\n
\n
GET\n
server.example.com\n
143\n
/\n
\n
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4. Implementation Requirements
Tokens typically have a restricted lifetime. In addition, the policy
of a client MAY revoke a previously obtained token at any time. The
client MAY request a new access token for each connection to a
resource server, but it SHOULD cache and re-use access credentials
that appear to be valid. Credential lifetime and how that is
communicated to the client is defined in the authentication scheme
specifications. Clients MAY implement any of the OAuth 2 profiles
since they are largely outside the scope of this specification, and
the mentioned profiles in this document are just examples.
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5. Examples
[[TODO: fix these]]
[[NOTE: The Bearer token spec is still in flux. presuming that the
scheme name is BEARER for these examples, but -1 of the spec uses
OAuth2 as the scheme name.]]
These example illustrate exchanges between an IMAP client and an IMAP
server.
5.1. Successful Bearer Token Exchange
This example shows a successful OAuth 2.0 bearer token exchange with
an initial client response. Note that line breaks are inserted for
readability.
S: * IMAP4rev1 Server Ready
C: t0 CAPABILITY
S: * CAPABILITY IMAP4rev1 AUTH=OAUTH
S: t0 OK Completed
C: t1 AUTHENTICATE OAUTH R0VUIC8gSFRUUC8xLjENCkhvc3Q6IGltYXAuZXhhbXBs
ZS5jb20NCkF1dGhvcml6YXRpb246IEJFQVJFUiAidkY5ZGZ0NHFtVGMyTnZiM1J
sY2tCaGJIUmhkbWx6ZEdFdVkyOXRDZz09Ig0KDQo=
S: +
S: t1 OK SASL authentication succeeded
As required by IMAP [RFC3501], the payloads are base64-encoded. The
decoded initial client response is:
GET / HTTP/1.1
Host: imap.example.com
Authorization: BEARER "vF9dft4qmTc2Nvb3RlckBhbHRhdmlzdGEuY29tCg=="
The line conaining just a "+" and a space is an empty response from
the server. This response contains discovery information, and in the
success case no discovery information is necessary so the response is
empty. Like other messages, and in accordance with the IMAP SASL
binding, the empty response is base64-encoded.
5.2. Failed Exchange
This example shows a failed exchange because of the empty
Authorization header, which is how a client can query for discovery
information. Note that line breaks are inserted for readability.
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S: * CAPABILITY IMAP4rev1 AUTH=OAUTH SASL-IR IMAP4rev1 Server Ready
S: t0 OK Completed
C: t1 AUTHENTICATE OAUTH R0VUIC8gSFRUUC8xLjENClVzZXI6IHNjb290ZXJAYW
x0YXZpc3RhLmNvbQ0KSG9zdDogaW1hcC55YWhvby5jb20NCkF1dGhlbnRpY2F0ZT
ogDQoNCg==
S: + SFRUUC8xLjEgNDAxIFVuYXV0aG9yaXplZA0KV1dXLUF1dGhlbnRpY2F0ZTogQk
VBUkVSIHJlYWxtPSJleGFtcGxlLmNvbSINCkxpbms6IDxodHRwczovL2xvZ2luLn
lhaG9vLmNvbS9vYXV0aD4gcmVsPSJvYXV0aDItYXV0aGVudGljYXRvciIgIA0KTG
luazogPGh0dHBzOi8vbG9naW4ueWFob28uY29tL29hdXRoPiByZWw9Im91YXRoMi
10b2tlbiINCg0K
S: t1 NO SASL authentication failed
The decoded initial client response is:
GET / HTTP/1.1
User: alice@example.com
Host: imap.example.com
Authorization:
The decoded server discovery response is:
HTTP/1.1 401 Unauthorized
WWW-Authenticate: BEARER realm="example.com"
Link: <https://login.yahoo.com/oauth> rel="oauth2-authenticator"
Link: <https://login.yahoo.com/oauth> rel="ouath2-token"
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6. Security Considerations
This mechanism does not provide a security layer, but does provide a
provision for channel binding. The OAuth 2 specification
[I-D.ietf-oauth-v2] allows for a variety of usages, and the security
properties of these profiles vary. The usage of bearer tokens, for
example, provide security features similar to cookies. Applications
using this mechanism SHOULD exercise the same level of care using
this mechanism as they would in using the SASL PLAIN mechanism. In
particular, TLS 1.2 MUST be implemented and its usage is RECOMMENDED
unless tokens expire quickly.
A significant benefit of OAuth for usage in clients that usually
store passwords is that the password is not stored in the client, a
token is. This means that the password is not exposed, what we risk
is a token that can be more limited or can be easily revoked.
It is possible that SASL will be authenticating a connection and the
life of that connection may outlast the life of the token used to
authenticate it. This is a common problem in application protocols
where connections are long-lived, and not a problem with this
mechanism per se. Servers MAY unilaterally disconnect clients in
accordance with the application protocol.
It is possible for an application server running on Evil.example.com
to tell a client to request a token from Good.example.org. A client
following these instructions will pass a token from Good to Evil.
This is by design, since it is possible that Good and Evil are merely
names, not descriptive, and that this is an innocuous activity
between cooperating two servers in different domains. For instance,
a site might operate their authentication service in-house, but
outsource their mail systems to an external entity.
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7. IANA Considerations
7.1. SASL Registration
The IANA is requested to register the following SASL profile:
SASL mechanism profile: OAUTH
Security Considerations: See this document
Published Specification: See this document
For further information: Contact the authors of this document.
Owner/Change controller: the IETF
Note: None
7.2. Link Type Registration
Pursuant to [RFC5988] The following link type registrations [[will
be]] registered by mail to link-relations@ietf.org.
7.2.1. OAuth 2 Authentication Endpoint
o Relation Name: oauth2-authenticator
o Description: An OAuth 2.0 authentication endpoint.
o Reference:
o Notes: This link type indicates an OAuth 2.0 authentication
endpoint that can be used for user authentication/authorization
for the endpoint providing the link.
o Application Data: [optional]
7.2.2. OAuth 2 Token Endpoint
o Relation Name: oauth2-token
o Description: The OAuth token endpoint used to get tokens for
access.
o Reference:
o Notes: The OAuth 2.0 token enpoint to be used for obtaining tokens
to access the endpoint providing the link.
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o Application Data: This link type has one link-extenstion "grant-
types" which is the OAuth 2.0 grant types that can be used at the
token endpoint to obtain a token. This is not an exclusive list,
it provides a hint to the application of what SHOULD be valid. A
token endpoint MAY support additional grant types not advertised
by a resource endpoint.
7.2.3. OAuth 1.0a Request Initiation Endpoint
o Relation Name: oauth-initiate
o Description: The OAuth 1.0a request initiation endpoint used to
get tokens for access.
o Reference:
o Notes: The OAuth 1.0a enpoint used to initiate the sequence, this
temporary request is what the user approves to grant access to the
resource.
o Application Data:
7.2.4. OAuth 1.0a Authorization Endpoint
o Relation Name: oauth-authorize
o Description: The OAuth 1.0a authorization endpoint used to approve
an access request.
o Reference:
o Notes:
o Application Data:
7.2.5. OAuth 1.0a Token Endpoint
o Relation Name: oauth-token
o Description: The OAuth 1.0a token endpoint used to get tokens for
access.
o Reference:
o Notes:
o Application Data:
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8. Appendix A -- Document History
[[ to be removed by RFC editor before publication as an RFC ]]
-01
o Bringing this into line with rdraft 12 of the core spec, the
bearer token spec, and references the MAC token spec
o Changing discovery over to using the Link header construct from
RFC5988.
o Added the seeds of channel binding.
-00
o Initial revision
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9. References
9.1. Normative References
[I-D.hammer-oauth-v2-mac-token]
Hammer-Lahav, E., "HTTP Authentication: MAC
Authentication", draft-hammer-oauth-v2-mac-token-02 (work
in progress), January 2011.
[I-D.ietf-oauth-v2]
Hammer-Lahav, E., Recordon, D., and D. Hardt, "The OAuth
2.0 Authorization Protocol", draft-ietf-oauth-v2-12 (work
in progress), January 2011.
[I-D.ietf-oauth-v2-bearer]
Jones, M., Hardt, D., and D. Recordon, "The OAuth 2.0
Protocol: Bearer Tokens", draft-ietf-oauth-v2-bearer-02
(work in progress), January 2011.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext
Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.
[RFC2617] Franks, J., Hallam-Baker, P., Hostetler, J., Lawrence, S.,
Leach, P., Luotonen, A., and L. Stewart, "HTTP
Authentication: Basic and Digest Access Authentication",
RFC 2617, June 1999.
[RFC4422] Melnikov, A. and K. Zeilenga, "Simple Authentication and
Security Layer (SASL)", RFC 4422, June 2006.
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246, August 2008.
[RFC5849] Hammer-Lahav, E., "The OAuth 1.0 Protocol", RFC 5849,
April 2010.
[RFC5988] Nottingham, M., "Web Linking", RFC 5988, October 2010.
9.2. Informative References
[I-D.hammer-hostmeta]
Hammer-Lahav, E., "Web Host Metadata",
draft-hammer-hostmeta-13 (work in progress), June 2010.
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[RFC3501] Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL - VERSION
4rev1", RFC 3501, March 2003.
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Authors' Addresses
William Mills
Yahoo Inc.
Phone:
Email: wmills@yahoo-inc.com
Tim Showalter
Yahoo Inc.
Phone:
Email: timshow@yahoo-inc.com
Hannes Tschofenig
Nokia Siemens Networks
Linnoitustie 6
Espoo 02600
Finland
Phone: +358 (50) 4871445
Email: Hannes.Tschofenig@gmx.net
URI: http://www.tschofenig.priv.at
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