Compatible Version Negotiation for QUIC
draft-ietf-quic-version-negotiation-06
The information below is for an old version of the document.
| Document | Type | Active Internet-Draft (quic WG) | |
|---|---|---|---|
| Authors | David Schinazi , Eric Rescorla | ||
| Last updated | 2022-03-08 (Latest revision 2021-10-25) | ||
| Replaces | draft-schinazi-quic-version-negotiation | ||
| Stream | Internet Engineering Task Force (IETF) | ||
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draft-ietf-quic-version-negotiation-06
QUIC D. Schinazi
Internet-Draft Google LLC
Intended status: Standards Track E. Rescorla
Expires: 8 September 2022 Mozilla
7 March 2022
Compatible Version Negotiation for QUIC
draft-ietf-quic-version-negotiation-06
Abstract
QUIC does not provide a complete version negotiation mechanism but
instead only provides a way for the server to indicate that the
version the client offered is unacceptable. This document describes
a version negotiation mechanism that allows a client and server to
select a mutually supported version. Optionally, if the original and
negotiated version share a compatible first flight format, the
negotiation can take place without incurring an extra round trip.
Discussion Venues
This note is to be removed before publishing as an RFC.
Discussion of this document takes place on the QUIC Working Group
mailing list (quic@ietf.org), which is archived at
https://mailarchive.ietf.org/arch/browse/quic/.
Source for this draft and an issue tracker can be found at
https://github.com/quicwg/version-negotiation.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on 8 September 2022.
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Copyright Notice
Copyright (c) 2022 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 (https://trustee.ietf.org/
license-info) in effect on the date of publication of this document.
Please review these documents carefully, as they describe your rights
and restrictions with respect to this document. Code Components
extracted from this document must include Revised BSD License text as
described in Section 4.e of the Trust Legal Provisions and are
provided without warranty as described in the Revised BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Conventions and Definitions . . . . . . . . . . . . . . . 3
2. Version Negotiation Mechanism . . . . . . . . . . . . . . . . 3
2.1. Incompatible Version Negotiation . . . . . . . . . . . . 4
2.2. Compatible Versions . . . . . . . . . . . . . . . . . . . 4
2.3. Compatible Version Negotiation . . . . . . . . . . . . . 5
2.4. Connections and Version Negotiation . . . . . . . . . . . 6
2.5. Client Choice of Original Version . . . . . . . . . . . . 7
3. Version Information . . . . . . . . . . . . . . . . . . . . . 7
4. Version Downgrade Prevention . . . . . . . . . . . . . . . . 8
5. Server Deployments of QUIC . . . . . . . . . . . . . . . . . 9
6. Considerations for Future Versions . . . . . . . . . . . . . 11
6.1. Interaction with Retry . . . . . . . . . . . . . . . . . 11
6.2. Interaction with TLS resumption . . . . . . . . . . . . . 12
6.3. Interaction with 0-RTT . . . . . . . . . . . . . . . . . 12
7. Security Considerations . . . . . . . . . . . . . . . . . . . 12
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13
8.1. QUIC Transport Parameter . . . . . . . . . . . . . . . . 13
8.2. QUIC Transport Error Code . . . . . . . . . . . . . . . . 13
9. Normative References . . . . . . . . . . . . . . . . . . . . 13
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 14
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 14
1. Introduction
The version-invariant properties of QUIC [INV] define a Version
Negotiation packet but do not specify how an endpoint reacts when it
receives one. QUIC version 1 [QUIC] allows the server to use a
Version Negotiation packet to indicate that the version the client
offered is unacceptable, but doesn't allow the client to safely make
use of that information to create a new connection with a mutually
supported version.
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With proper safety mechanisms in place, the Version Negotiation
packet can be part of a mechanism to allow two QUIC implementations
to negotiate between two totally disjoint versions of QUIC. This
document specifies version negotiation using Version Negotiation
packets, which adds an extra round trip to connection establishment
if needed.
It is beneficial to avoid additional round trips whenever possible,
especially given that most incremental versions are broadly similar
to the the previous version. This specification also defines a
simple version negotiation mechanism which leverages similarities
between versions and can negotiate between the set of "compatible"
versions without additional round trips.
1.1. Conventions and Definitions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
In this document, the Maximum Segment Lifetime (MSL) represents the
time a QUIC packet can exist in the network. Implementations can
make this configurable, and a RECOMMENDED value is one minute.
2. Version Negotiation Mechanism
This document specifies two means of performing version negotiation:
one "incompatible" which requires a round trip and is applicable to
all versions, and one "compatible" that allows saving the round trip
but only applies when the versions are compatible.
The client initiates a QUIC connection by sending a first flight of
QUIC packets with a long header to the server [INV]. We'll refer to
the version of those packets as the "original version". The client's
first flight includes Version Information (see Section 3) which will
be used to optionally enable compatible version negotation (see
Section 2.3), and to prevent version downgrade attacks (see
Section 4).
Upon receiving this first flight, the server verifies whether it
knows how to parse first flights from the original version. If it
does not, then it starts incompatible version negotiation, see
Section 2.1. If the server can parse the first flight, it can either
establish the connection using the original version, or it MAY
attempt compatible version negotiation, see Section 2.3.
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Note that it is possible for a server to have the ability to parse
the first flight of a given version without fully supporting it, in
the sense that it implements enough of the version's specification to
parse first flight packets but not enough to fully establish a
connection using that version.
2.1. Incompatible Version Negotiation
The server starts incompatible version negotiation by sending a
Version Negotiation packet. This packet SHALL include each entry
from the server's set of Offered Versions (see Section 5) in a
Supported Version field. The server MAY add reserved versions (as
defined in Section 6.3 of [QUIC]) in Supported Version fields.
Clients will ignore a Version Negotiation packet if it contains the
original version attempted by the client. The client also ignores a
Version Negotiation packet that contains incorrect connection ID
fields; see Section 6 of [INV].
Upon receiving the Version Negotiation packet, the client will search
for a version it supports in the list provided by the server. If it
doesn't find one, it aborts the connection attempt. Otherwise, it
selects a mutually supported version and sends a new first flight
with that version - we refer to this version as the "negotiated
version".
The new first flight will allow the endpoints to establish a
connection using the negotiated version. The handshake of the
negotiated version will exchange version information (see Section 3)
required to ensure that version negotiation was genuine, i.e. that no
attacker injected packets in order to influence the version
negotiation process, see Section 4.
2.2. Compatible Versions
If A and B are two distinct versions of QUIC, A is said to be
"compatible" with B if it is possible to take a first flight of
packets from version A and convert it into a first flight of packets
from version B. As an example, if versions A and B are absolutely
equal in their wire image and behavior during the handshake but
differ after the handshake, then A is compatible with B and B is
compatible with A. Note that the conversion of the first flight can
be lossy: some data such as QUIC version 1 0-RTT packets could be
ignored during conversion and retransmitted later.
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Version compatibility is not symmetric: it is possible for version A
to be compatible with version B and for B not to be compatible with
A. This could happen for example if version B is a strict superset
of version A.
Note that version compatibility does not mean that every single
possible instance of a first flight will succeed in conversion to the
other version. A first flight using version A is said to be
"compatible" with version B if two conditions are met: first that
version A is compatible with version B, and second that the
conversion of this first flight to version B is well-defined. For
example, if version B is equal to A in all aspects except it
introduced a new frame in its first flight that version A cannot
parse or even ignore, then B could still be compatible with A as
conversions would succeed for connections where that frame is not
used. In this example, first flights using version B that carry this
new frame would not be compatible with version A.
When a new version of QUIC is defined, it is assumed to not be
compatible with any other version unless otherwise specified.
Similarly, no other version is compatible with the new version unless
otherwise specified. Implementations MUST NOT assume compatibility
between versions unless explicitly specified.
Note that both endpoints might disagree on whether two versions are
compatible or not. For example, two versions could have been defined
concurrently and then specified as compatible in a third document
much later - in that scenario one endpoint might be aware of the
compatibility document while the other may not.
When a client creates a QUIC connection, its goal is to use an
application layer protocol. Therefore, when considering which
versions are compatible, clients will only consider versions that
support one of the intended application layer protocols. For
example, if the client's first flight advertises multiple Application
Layer Protocol Negotiation (ALPN) [ALPN] tokens and multiple
compatible versions, the server needs to ensure that the ALPN token
that it selects can run over the QUIC version that it selects.
2.3. Compatible Version Negotiation
When the server can parse the client's first flight using the
original version, it can extract the client's Version Information
structure (see Section 3). This contains the list of versions that
the client knows its first flight is compatible with.
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If the server supports one of the client's compatible versions, and
the server also knows that the original version is compatible with
this version, and the client's first flight is compatible with this
version, then the server converts the client's first flight to that
version and replies to the client as if it had received the converted
first flight. Note that this conversion process cannot fail by
definition of the first flight being compatible. The version used by
the server in its reply is refered to as the "negotiated version".
The server MUST NOT reply with a version that is not present in the
client's compatible versions, unless it is the original version.
Clients will be made aware of compatible version negotiation by
seeing a change in the QUIC long header Version field. It is
possible for the server to initially send packets with the original
version before switching to the negotiated version (for example, this
can happen when the client's Version Information structured spans
multiple packets; in that case the server might acknowledge the first
packet in the original version and later switch to a different
negotiated version).
Note that, after the first flight is converted to the negotiated
version, the handshake completes in the negotiated version. The
entire handshake (including the converted first flight) needs to
conform to the rules of the negotiated version. For instance, if the
negotiated version requires that the 5-tuple remain stable for the
entire handshake (as QUIC version 1 does), then this applies to the
entire handshake, including the first flight.
Note also that the client can disable compatible version negotiation
by only including the Chosen Version in the Other Versions field of
the Version Information Transport Parameter.
If the server does not find a compatible version, it will use the
original version if it supports it, and if it doesn't then the server
will perform incompatible version negotiation instead, see
Section 2.1.
2.4. Connections and Version Negotiation
QUIC connections are shared state between a client and a server
[INV]. The compatible version negotiation mechanism defined in this
document (see Section 2.3) is performed as part of a single QUIC
connection; that is, the packets with the original version are part
of the same connection as the packets with the negotiated version.
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In comparison, the incompatible version negotiation mechanism, which
leverages QUIC Version Negotiation packets (see Section 2.1)
conceptually operates across two QUIC connections: the connection
attempt prior to receiving the Version Negotiation packet is distinct
from the connection with the incompatible version that follows.
2.5. Client Choice of Original Version
The client's first connection attempt SHOULD be made using the
version that the server is most likely to support. The client
selects the version most likely to be supported from the versions
that are compatible with the client's most preferred version.
Without additional information this could mean selecting the oldest
version that the client supports.
3. Version Information
During the handshake, endpoints will exchange Version Information,
which consists of a chosen version and a list of other versions. Any
version of QUIC that supports this mechanism MUST provide a mechanism
to exchange Version Information in both directions during the
handshake, such that this data is authenticated.
In QUIC version 1, the Version Information is transmitted using a new
transport parameter, version_information. The contents of Version
Information are shown below (using the notation from the "Notational
Conventions" section of [QUIC]):
Version Information {
Chosen Version (32),
Other Versions (32) ...,
}
Figure 1: Version Information Format
The content of each field is described below:
Chosen Version: The version that the sender has chosen to use for
this connection. In most cases, this field will be equal to the
value of the Version field in the long header that carries this
data.
The contents of the Other Versions field depends on whether it is
sent by the client or by the server.
Client-Sent Other Versions: When sent by a client, the Other
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Versions field lists all the versions that this first flight is
compatible with, ordered by descending preference. Note that the
version in the Chosen Version field MUST be included in this list
to allow the client to communicate the chosen version's
preference. Note that this preference is only advisory, servers
MAY choose to use their own preference instead.
Server-Sent Other Versions: When sent by a server, the Other
Versions field lists all the Fully-Deployed Versions of this
server deployment, see Section 5. Note that the version in the
Chosen Version field is not necessarily included in this list,
because the server operator could be in the process of removing
support for this version. For the same reason, the Other Versions
field MAY be empty.
Clients and servers MAY both include versions following the pattern
0x?a?a?a?a in their Other Versions list. Those versions are reserved
to exercise version negotiation (see the Versions section of [QUIC]),
and will never be selected when choosing a version to use.
4. Version Downgrade Prevention
Clients MUST ignore any received Version Negotiation packets that
contain the version that they initially attempted. A client that
makes a connection attempt based on information received from a
Version Negotiation packet MUST ignore any Version Negotiation
packets it receives in response to that connection attempt.
Both endpoints MUST parse their peer's Version Information during the
handshake. If parsing the Version Information failed (for example,
if it is too short or if its length is not divisible by four), then
the endpoint MUST close the connection; if the connection was using
QUIC version 1, that connection closure MUST use a transport error of
type TRANSPORT_PARAMETER_ERROR. If an endpoint receives a Chosen
Version equal to zero, or any Other Version equal to zero, it MUST
treat it as a parsing failure.
Every QUIC version that supports version negotiation MUST define a
method for closing the connection with a version negotiation error.
For QUIC version 1, version negotiation errors are signaled using a
transport error of type VERSION_NEGOTIATION_ERROR; see Section 8.2.
If the Version Information was missing, the endpoints MAY complete
the handshake. However, if a client has reacted to a Version
Negotiation packet and the Version Information was missing, the
client MUST close the connection with a version negotiation error.
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If the client received and acted on a Version Negotiation packet, the
client MUST validate the server's Other Versions field. The Other
Versions field is validated by confirming that the client would have
attempted the same version with knowledge of the versions the server
supports. That is, the client would have selected the same version
if it received a Version Negotiation packet that listed the versions
in the server's Other Versions field, plus the negotiated version.
If the client would have selected a different version, the client
MUST close the connection with a version negotiation error. In
particular, if the client reacted to a Version Negotiation packet and
the server's Other Versions field is empty, the client MUST close the
connection with a version negotiation error. These connection
closures prevent an attacker from being able to use forged Version
Negotiation packets to force a version downgrade.
This validation of Other Versions is not sufficient to prevent
downgrade. Downgrade prevention also depends on the client ignoring
Version Negotiation packets that contain the original version; see
Section 2.1.
After the process of version negotiation in this document completes,
the version in use for the connection is the version that the server
sent in the Chosen Version field of its Version Information. That
remains true even if other versions were used in the Version field of
long headers at any point in the lifetime of the connection. In
particular, since during compatible version negotiation the client is
made aware of the negotiated version by the QUIC long header version
(see Section 2.3), clients MUST validate that the server's Chosen
Version is equal to the negotiated version; if they do not match, the
client MUST close the connection with a version negotiation error.
This prevents an attacker's ability to influence version negotiation
by forging the Version long header field.
5. Server Deployments of QUIC
While this document mainly discusses a single QUIC server, it is
common for deployments of QUIC servers to include a fleet of multiple
server instances. We therefore define the following terms:
Acceptable Versions: This is the set of versions supported by a
given server instance. More specifically, these are the versions
that a given server instance will use if a client sends a first
flight using them.
Offered Versions: This is the set of versions that a given server
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instance will send in a Version Negotiation packet if it receives
a first flight from an unknown version. This set will most often
be equal to the Acceptaple Versions set, except during short
transitions while versions are added or removed (see below).
Fully-Deployed Versions: This is the set of QUIC versions that is
supported and negotiated by every single QUIC server instance in
this deployment. If a deployment only contains a single server
instance, then this set is equal to the Offered Versions set,
except during short transitions while versions are added or
removed (see below).
If a deployment contains multiple server instances, software updates
may not happen at exactly the same time on all server instances.
Because of this, a client might receive a Version Negotiation packet
from a server instance that has already been updated and the client's
resulting connection attempt might reach a different server instance
which hasn't been updated yet.
However, even when there is only a single server instance, it is
still possible to receive a stale Version Negotiation packet if the
server performs its software update while the Version Negotiation
packet is in flight.
This could cause the version downgrade prevention mechanism described
in Section 4 to falsely detect a downgrade attack. To avoid that,
server operators SHOULD perform a three-step process when they wish
to add or remove support for a version:
When adding support for a new version:
* The first step is to progressively add support for the new version
to all server instances. This step updates the Acceptable
Versions but not the Offered Versions nor the Fully-Deployed
Versions. Once all server instances have been updated, operators
wait for at least one MSL to allow any in-flight Version
Negotiation packets to arrive.
* Then, the second step is to progressively add the new version to
Offered Versions on all server instances. Once complete,
operators wait for at least another MSL.
* Finally, the third step is to progressively add the new version to
Fully-Deployed Versions on all server instances.
When removing support for a version:
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* The first step is to progressively remove the version from Fully-
Deployed Versions on all server instances. Once it has been
removed on all server instances, operators wait for at least one
MSL to allow any in-flight Version Negotiation packets to arrive.
* Then, the second step is to progressively remove the version from
Offered Versions on all server instances. Once complete,
operators wait for at least another MSL.
* Finally, the third step is to progressively remove support for the
version from all server instances. That step updates the
Acceptable Versions.
Note that this opens connections to version downgrades (but only for
partially-deployed versions) during the update window, since those
could be due to clients communicating with both updated and non-
updated server instances.
6. Considerations for Future Versions
In order to facilitate the deployment of future versions of QUIC,
designers of future versions SHOULD attempt to design their new
version such that commonly deployed versions are compatible with it.
QUIC version 1 defines multiple features which are not documented in
the QUIC invariants. Since at the time of writing QUIC version 1 is
widely deployed, this section discusses considerations for future
versions to help with compatibility with QUIC version 1.
6.1. Interaction with Retry
QUIC version 1 features Retry packets, which the server can send to
validate the client's IP address before parsing the client's first
flight. A server that sends a Retry packet can do so before parsing
the client's first flight. A server that sends a Retry packet
therefore might not have processed the client's Version Information
before doing so.
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If a future document wishes to define compatibility between two
versions that support retry, that document MUST specify how version
negotiation (both compatible and incompatible) interacts with retry
during a handshake that requires both. For example, that could be
accomplished by having the server send a Retry packet in the original
version first and therefore validating the client's IP address before
attempting compatible version negotiation. If both versions support
authenticating Retry packets, the compatibility defition needs to
define how to authenticate the Retry in the negotiated version
handshake even though the Retry itself was sent using the original
version.
6.2. Interaction with TLS resumption
QUIC version 1 uses TLS 1.3, which supports session resumption by
sending session tickets in one connection that can be used in a later
connection; see Section 2.2 of [TLS]. New versions that also use TLS
1.3 SHOULD mandate that their session tickets are rightly scoped to
one version of QUIC; i.e., require that clients not use them across
version and that servers validate this client requirement.
6.3. Interaction with 0-RTT
QUIC version 1 allows sending data from the client to the server
during the handshake, by using 0-RTT packets. If a future document
wishes to define compatibility between two versions that support
0-RTT, that document MUST address the scenario where there are 0-RTT
packets in the client's first flight. For example, this could be
accomplished by defining which transformations are applied to 0-RTT
packets. Alternatively, that document could specify that compatible
version negotiation causes 0-RTT data to be rejected by the server.
7. Security Considerations
The security of this version negotiation mechanism relies on the
authenticity of the Version Information exchanged during the
handshake. In QUIC version 1, transport parameters are authenticated
ensuring the security of this mechanism. Negotiation between
compatible versions will have the security of the weakest common
version.
The requirement that versions not be assumed compatible mitigates the
possibility of cross-protocol attacks, but more analysis is still
needed here.
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8. IANA Considerations
8.1. QUIC Transport Parameter
This document registers a new value in the QUIC Transport Parameter
Registry maintained at https://www.iana.org/assignments/quic/
quic.xhtml#quic-transport.
Value: 0xFF73DB
Parameter Name: version_information
Status: provisional
Specification: This document
When this document is approved, it will request permanent allocation
of a codepoint in the 0-63 range to replace the provisional codepoint
described above.
8.2. QUIC Transport Error Code
This document registers a new value in the QUIC Transport Error Codes
Registry maintained at https://www.iana.org/assignments/quic/
quic.xhtml#quic-transport-error-codes.
Value: 0x53F8
Code: VERSION_NEGOTIATION_ERROR
Description: Error negotiating version
Status: provisional
Specification: This document
When this document is approved, it will request permanent allocation
of a codepoint in the 0-63 range to replace the provisional codepoint
described above.
9. Normative References
[ALPN] Friedl, S., Popov, A., Langley, A., and E. Stephan,
"Transport Layer Security (TLS) Application-Layer Protocol
Negotiation Extension", RFC 7301, DOI 10.17487/RFC7301,
July 2014, <https://www.rfc-editor.org/rfc/rfc7301>.
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[INV] Thomson, M., "Version-Independent Properties of QUIC",
RFC 8999, DOI 10.17487/RFC8999, May 2021,
<https://www.rfc-editor.org/rfc/rfc8999>.
[QUIC] Iyengar, J., Ed. and M. Thomson, Ed., "QUIC: A UDP-Based
Multiplexed and Secure Transport", RFC 9000,
DOI 10.17487/RFC9000, May 2021,
<https://www.rfc-editor.org/rfc/rfc9000>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/rfc/rfc2119>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/rfc/rfc8174>.
[TLS] Rescorla, E., "The Transport Layer Security (TLS) Protocol
Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
<https://www.rfc-editor.org/rfc/rfc8446>.
Acknowledgments
The authors would like to thank Nick Banks, Mike Bishop, Ryan
Hamilton, Roberto Peon, Anthony Rossi, and Martin Thomson for their
input and contributions.
Authors' Addresses
David Schinazi
Google LLC
1600 Amphitheatre Parkway
Mountain View, California 94043,
United States of America
Email: dschinazi.ietf@gmail.com
Eric Rescorla
Mozilla
Email: ekr@rtfm.com
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