Internet DRAFT - draft-thomson-quic-tls
draft-thomson-quic-tls
Network Working Group M. Thomson
Internet-Draft Mozilla
Intended status: Standards Track R. Hamilton
Expires: September 22, 2016 Google
March 21, 2016
Porting QUIC to Transport Layer Security (TLS)
draft-thomson-quic-tls-00
Abstract
The QUIC experiment defines a custom security protocol. This was
necessary to gain handshake latency improvements. This document
describes how that security protocol might be replaced with TLS.
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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This Internet-Draft will expire on September 22, 2016.
Copyright Notice
Copyright (c) 2016 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
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Notational Conventions . . . . . . . . . . . . . . . . . 3
2. Protocol Overview . . . . . . . . . . . . . . . . . . . . . . 3
2.1. Handshake Overview . . . . . . . . . . . . . . . . . . . 4
3. QUIC over TLS Structure . . . . . . . . . . . . . . . . . . . 5
4. Mapping of QUIC to QUIC over TLS . . . . . . . . . . . . . . 6
4.1. Protocol and Version Negotiation . . . . . . . . . . . . 7
4.2. Source Address Validation . . . . . . . . . . . . . . . . 8
5. Record Protection . . . . . . . . . . . . . . . . . . . . . . 8
5.1. TLS Handshake Encryption . . . . . . . . . . . . . . . . 9
5.2. Key Update . . . . . . . . . . . . . . . . . . . . . . . 9
5.3. Sequence Number Reconstruction . . . . . . . . . . . . . 10
5.4. Alternative Design: Exporters . . . . . . . . . . . . . . 10
6. Pre-handshake QUIC Messages . . . . . . . . . . . . . . . . . 11
6.1. QUIC Extension . . . . . . . . . . . . . . . . . . . . . 11
6.2. Unprotected Frames Prior to Handshake Completion . . . . 15
6.2.1. STREAM Frames . . . . . . . . . . . . . . . . . . . . 15
6.2.2. ACK Frames . . . . . . . . . . . . . . . . . . . . . 15
6.2.3. WINDOW_UPDATE Frames . . . . . . . . . . . . . . . . 15
6.2.4. FEC Packets . . . . . . . . . . . . . . . . . . . . . 16
6.3. Protected Frames Prior to Handshake Completion . . . . . 16
7. Connection ID . . . . . . . . . . . . . . . . . . . . . . . . 17
8. Security Considerations . . . . . . . . . . . . . . . . . . . 18
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 18
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 18
10.1. Normative References . . . . . . . . . . . . . . . . . . 18
10.2. Informative References . . . . . . . . . . . . . . . . . 18
Appendix A. Acknowledgments . . . . . . . . . . . . . . . . . . 19
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 19
1. Introduction
QUIC [I-D.tsvwg-quic-protocol] provides a multiplexed transport for
HTTP [RFC7230] semantics that provides several key advantages over
HTTP/1.1 [RFC7230] or HTTP/2 [RFC7540] over TCP [RFC0793].
The custom security protocol designed for QUIC provides critical
latency improvements for connection establishment. Absent packet
loss, most new connections can be established with a single round
trip; on subsequent connections between the same client and server,
the client can often send application data immediately, that is, zero
round trip setup. TLS 1.3 uses a similar design and aims to provide
the same set of improvements.
This document describes how the standardized TLS 1.3 might serve as a
security layer for QUIC. The same design could work for TLS 1.2,
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though few of the benefits QUIC provides would be realized due to the
handshake latency in versions of TLS prior to 1.3.
Alternative Designs: There are other designs that are possible; and
many of these alternative designs are likely to be equally good.
The point of this document is to articulate a coherent single
design. Notes like this throughout the document are used describe
points where alternatives were considered.
Note: This is a rough draft. Many details have not been ironed out.
Ryan is not responsible for any errors or omissions.
1.1. Notational Conventions
The words "MUST", "MUST NOT", "SHOULD", and "MAY" are used in this
document. It's not shouting; when they are capitalized, they have
the special meaning defined in [RFC2119].
2. Protocol Overview
QUIC [I-D.tsvwg-quic-protocol] can be separated into several modules:
1. The basic frame envelope describes the common packet layout.
This layer includes connection identification, version
negotiation, and includes the indicators that allow the framing,
public reset, and FEC modules to be identified.
2. The public reset is an unprotected frame that allows an
intermediary (an entity that is not part of the security context)
to request the termination of a QUIC connection.
3. The forward error correction (FEC) module provides redundant
entropy that allows for frames to be repaired in event of loss.
4. Framing comprises most of the QUIC protocol. Framing provides a
number of different types of frame, each with a specific purpose.
Framing supports frames for both congestion management and stream
multiplexing. Framing additionally provides a liveness testing
capability (the PING frame).
5. Crypto provides confidentiality and integrity protection for
frames. All frames are protected after the handshake completes
on stream 1. Prior to this, data is protected with the 0-RTT
keys.
6. Multiplexed streams are the primary payload of QUIC. These
provide reliable, in-order delivery of data and are used to carry
the encryption handshake and transport parameters (stream 1),
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HTTP header fields (stream 3), and HTTP requests and responses.
Frames for managing multiplexing include those for creating and
destroying streams as well as flow control and priority frames.
7. Congestion management includes packet acknowledgment and other
signal required to ensure effective use of available link
capacity.
8. HTTP mapping provides an adaptation to HTTP that is based on
HTTP/2.
The relative relationship of these components are pictorally
represented in Figure 1.
+----+------+
| HS | HTTP |
+----+------+------------+
| Streams | Congestion |
+-----------+------------+
| Frames |
+ +------------+
| | FEC +--------+
+ +--------+------------+ Public |
| | Crypto | Reset |
+--+---------------------+--------+
| Envelope |
+---------------------------------+
| UDP |
+---------------------------------+
*HS = Crypto Handshake
Figure 1: QUIC Structure
This document describes a replacement of the cryptographic parts of
QUIC. This includes the handshake messages that are exchanged on
stream 1, plus the record protection that is used to encrypt and
authenticate all other frames.
2.1. Handshake Overview
TLS 1.3 provides two basic handshake modes of interest to QUIC:
o A full handshake in which the client is able to send application
data after one round trip and the server immediately after
receiving the first message from the client.
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o A 0-RTT handshake in which the client uses information about the
server to send immediately. This data can be replayed by an
attacker so it MUST NOT carry a self-contained trigger for any
non-idempotent action.
A simplified TLS 1.3 handshake with 0-RTT application data is shown
in Figure 2, see [I-D.ietf-tls-tls13] for more options.
Client Server
ClientHello
(Finished)
(0-RTT Application Data)
(end_of_early_data) -------->
ServerHello
{EncryptedExtensions}
{ServerConfiguration}
{Certificate}
{CertificateVerify}
{Finished}
<-------- [Application Data]
{Finished} -------->
[Application Data] <-------> [Application Data]
Figure 2: TLS Handshake with 0-RTT
Two additional variations on this basic handshake exchange are
relevant to this document:
o The server can respond to a ClientHello with a HelloRetryRequest,
which adds an additional round trip prior to the basic exchange.
This is needed if the server wishes to request a different key
exchange key from the client. HelloRetryRequest might also be
used to verify that the client is correctly able to receive
packets on the address it claims to have (see Section 4.2).
o A pre-shared key mode can be used for subsequent handshakes to
avoid public key operations. This might be the basis for 0-RTT,
even if the remainder of the connection is protected by a new
Diffie-Hellman exchange.
3. QUIC over TLS Structure
QUIC completes its cryptographic handshake on stream 1, which means
that the negotiation of keying material happens within the QUIC
protocol. QUIC over TLS does the same, relying on the ordered
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delivery guarantees provided by QUIC to ensure that the TLS handshake
packets are delivered reliably and in order.
+-----+---------+
| TLS | HTTP |
+-----+----------+------------+
| Streams | Congestion |
+----------------+------------+
| Frames |
| +------------+
| | FEC +--------+
| +----------+------------+ Public |
| | TLS Record Protection | Reset |
+-----+-----------------------+--------+
| Envelope |
+--------------------------------------+
| UDP |
+--------------------------------------+
Figure 3: QUIC over TLS
In this design the QUIC envelope carries QUIC frames until the TLS
handshake completes. After the handshake successfully completes the
key exchange, QUIC frames are then protected by TLS record
protection.
QUIC stream 1 is used to exchange TLS handshake packets. QUIC
provides for reliable and in-order delivery of the TLS handshake
messages.
Prior to the completion of the TLS handshake, QUIC frames can be
exchanged. However, these frames are not authenticated or
confidentiality protected. Section 6 covers some of the implications
of this design.
Alternative Design: TLS could be used to protect the entire QUIC
envelope. QUIC version negotiation could be subsumed by TLS and
ALPN [RFC7301]. The only unprotected packets are then public
resets and ACK frames, both of which could be given first octet
values that would easily distinguish them from other TLS packets.
This requires that the QUIC sequence numbers be moved to the
outside of the record.
4. Mapping of QUIC to QUIC over TLS
Several changes to the structure of QUIC are necessary to make a
layered design practical.
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These changes produce the handshake shown in Figure 4. In this
handshake, QUIC STREAM frames on stream 1 carry the TLS handshake.
QUIC is responsible for ensuring that the handshake packets are re-
sent in case of loss and that they can be ordered correctly.
QUIC operates without any record protection until the handshake
completes, just as TLS over TCP does not include record protection
for the handshake messages. Once complete, QUIC frames and forward
error control (FEC) messages are encapsulated in using TLS record
protection.
Client Server
QUIC STREAM Frame <stream 1>
ClientHello
+ QUIC Setup Parameters
(Finished) -------->
(Replayable QUIC Frames <any stream>)
(end_of_early_data <1>) -------->
QUIC STREAM Frame <1>
ServerHello
{EncryptedExtensions}
{ServerConfiguration}
{Certificate}
{CertificateVerify}
{Finished}
<-------- [QUIC Frames/FEC]
QUIC STREAM Frame <1>
{Finished} -------->
[QUIC Frames/FEC] <-------> [QUIC Frames/FEC]
Figure 4: QUIC over TLS Handshake
The remainder of this document describes the changes to QUIC and TLS
that allow the protocols to operate together.
4.1. Protocol and Version Negotiation
The QUIC version negotiation mechanism is used to negotiate the
version of QUIC that is used prior to the completion of the
handshake. However, this packet is not authenticated, enabling an
active attacker to force a version downgrade.
To ensure that a QUIC version downgrade is not forced by an attacker,
version information is copied into the TLS handshake, which provides
integrity protection for the QUIC negotiation. This doesn't prevent
version downgrade during the handshake, though it does prevent a
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connection from completing with a downgraded version, see
Section 6.1.
ISSUE: The QUIC version negotiation has poor performance in the
event that a client is forced to downgrade from their preferred
version.
4.2. Source Address Validation
QUIC implementations describe a source address token. This is an
opaque blob that a server provides to clients when they first use a
given source address. The client returns this token in subsequent
messages as a return routeability check. That is, the client returns
this token to prove that it is able to receive packets at the source
address that it claims.
Since this token is opaque and consumed only by the server, it can be
included in the TLS 1.3 configuration identifier for 0-RTT
handshakes. Servers that use 0-RTT are advised to provide new
configuration identifiers after every handshake to avoid passive
linkability of connections from the same client.
A server that is under load might include the same information in the
cookie extension/field of a HelloRetryRequest. (Note: the current
version of TLS 1.3 does not include the ability to include a cookie
in HelloRetryRequest.)
5. Record Protection
Each TLS record is encapsulated in the QUIC envelope. This provides
length information, which means that the length field can be dropped
from the TLS record.
The sequence number used by TLS record protection is changed to deal
with the potential for packets to be dropped or lost. The QUIC
sequence number is used in place of the monotonically increasing TLS
record sequence number. This means that the TLS record protection
employed is closer to DTLS in both its form and the guarantees that
are provided.
QUIC has a single, contiguous sequence number space. In comparison,
TLS restarts its sequence number each time that record protection
keys are changed. The sequence number restart in TLS ensures that a
compromise of the current traffic keys does not allow an attacker to
truncate the data that is sent after a key update by sending
additional packets under the old key (causing new packets to be
discarded).
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QUIC does not rely on there being a continuous sequence of
application data packets; QUIC uses authenticated repair mechansims
that operate above the layer of encryption. QUIC can therefore
operate without restarting sequence numbers.
5.1. TLS Handshake Encryption
TLS 1.3 adds encryption for handshake messages. This introduces an
additional transition between different record protection keys during
the handshake. A consequence of this is that it becomes more
important to explicitly identify the transition from one set of keys
to the next (see Section 5.2).
5.2. Key Update
Each time that the TLS record protection keys are changed, the
message initiating the change could be lost. This results in
subsequent packets being indecipherable to the peer that receives
them. Key changes happen at the conclusion of the handshake and and
immediately after a KeyUpdate message.
TLS relies on an ordered, reliable transport and therefore provides
no other mechanism to ensure that a peer receives the message
initiating a key change prior to receiving the subsequent messages
that are protected using the new key. A similar mechanism here would
introduce head-of-line blocking.
The simplest solution here is to steal a single bit from the
unprotected part of the QUIC header that signals key updates, similar
to how DTLS signals the epoch on each packet. The epoch bit is
encoded into 0x80 of the QUIC public flags.
Each time the epoch bit changes, an attempt is made to update the
keys used to read. Peers are prohibited from sending multiple
KeyUpdate messages until they see a reciprocal KeyUpdate to prevent
the chance that a transition is undetected as a result of two changes
in this bit.
The transition from cleartext to encrypted packets is exempt from
this limit of one key change. Two key changes occur during the
handshake. The server sends packets in the clear, plus packets
protected using handshake and application data keys. With only a
single bit available to discriminate between keys, packets protected
with the application data keys will have the same bit value as
cleartext packets. This condition will be easily identified and
handled, likely by discarding the application data, since the
encrypted packets will be highly unlikely to be valid.
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5.3. Sequence Number Reconstruction
Each peer maintains a 48-bit send sequence number that is incremented
with each packet that is sent (even retransmissions). The least
significant 8-, 16-, 32-, or 48-bits of this number is encoded in the
QUIC sequence number field in every packet. A 16-bit send epoch
number is maintained; the epoch is incremented each time new record
protection keying material is used. The least significant bit of the
epoch number is encoded into the epoch bit (0x80) of the QUIC public
flags.
A receiver maintains the same values, but recovers values based on
the packets it receives. This is based on the sequence number of
packets that it has received. A simple scheme predicts the receive
sequence number of an incoming packet by incrementing the sequence
number of the most recent packet to be successfully decrypted by one
and expecting the sequence number to be within a range centered on
that value. The receive epoch value is incremented each time that
the epoch bit (0x80) changes.
The sequence number used for record protection is the 64-bit value
obtained by concatenating the epoch and sequence number, both in
network byte order.
5.4. Alternative Design: Exporters
An exporter could be used to provide keying material for a QUIC-
specific record protection. This could draw on the selected cipher
suite and the TLS record protection design so that the overall effort
required to design and analyze is kept minimal.
One concern with using exporters is that TLS doesn't define an
exporter for use prior to the end of the handshake. That means the
creation of a special exporter for use in protecting 0-RTT data.
That's a pretty sharp object to leave lying around, and it's not
clear what the properties we could provide. (That doesn't mean that
there wouldn't be demand for such a thing, the possibility has
already been raised.)
An exporter-based scheme might opt not to use the handshake traffic
keys to protect QUIC packets during the handshake, relying instead on
separate protection for the TLS handshake records. This complicates
implementations somewhat, so an exporter might still be used.
In the end, using an exporter doesn't alter the design significantly.
Given the risks, a modification to the record protocol is probably
safer.
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6. Pre-handshake QUIC Messages
Implementations MUST NOT exchange data on any stream other than
stream 1 prior to the TLS handshake completing. However, QUIC
requires the use of several types of frame for managing loss
detection and recovery. In addition, it might be useful to use the
data acquired during the exchange of unauthenticated messages for
congestion management.
The actions that a peer takes as a result of receiving an
unauthenticated packet needs tobe limited. In particular, state
established by these packets cannot be retained once record
protection commences.
There are several approaches possible for dealing with
unauthenticated packets prior to handshake completion:
o discard and ignore them
o use them, but reset any state that is established once the
handshake completes
o use them and authenticate them afterwards; failing the handshake
if they can't be authenticated
o save them and use them when they can be properly authenticated
o treat them as a fatal error
Different strategies are appropriate for different types of data.
This document proposes that all strategies are possible depending on
the type of message.
o Transport parameters and options are made usable and authenticated
as part of the TLS handshake (see Section 6.1).
o Most unprotected messages are treated as fatal errors when
received except for the small number necessary to permit the
handshake to complete (see Section 6.2).
o Protected packets can be discarded, but can be saved and later
used (see Section 6.3).
6.1. QUIC Extension
A client describes characteristics of the transport protocol it
intends to conduct with the server in a new QUIC-specific extension
in its ClientHello. The server uses this information to determine
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whether it wants to continue the connection, request source address
validation, or reject the connection. Having this information
unencrypted permits this check to occur prior to committing the
resources needed to complete the initial key exchange.
If the server decides to complete the connection, it generates a
corresponding response and includes it in the EncryptedExtensions
message.
These parameters are not confidentiality-protected when sent by the
client, but the server response is protected by the handshake traffic
keys. The entire exchange is integrity protected once the handshake
completes.
This information is not used by TLS, but can be passed to the QUIC
protocol as initialization parmeters.
The "quic_parameters" extension contains a declarative set of
parameters that establish QUIC operating parameters and constrain the
behaviour of a peer. The connection identifier and version are first
negotiated using QUIC, and are included in the TLS handshake in order
to provide integrity protection.
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enum {
receive_buffer(0),
(65535)
} QuicTransportParameterType;
struct {
QuicTransportParameterType type;
uint32 value;
} QuicTransportParameter;
uint32 QuicVersion;
enum {
(65535)
} QuicOption;
struct {
uint64 connection_id;
QuicVersion quic_version;
QuicVersion supported_quic_versions<0..2^8-1>;
uint32 connection_initial_window;
uint32 stream_initial_window;
uint32 implicit_shutdown_timeout;
QuicTransportParameter transport_parameters<0..2^16-1>;
QuicOption options<0..2^8-2>;
} QuicParametersExtension;
This extension MUST be included if a QUIC version is negotiated. A
server MUST NOT negotiate QUIC if this extension is not present.
Based on the values offered by a client a server MAY use the values
in this extension to determine whether it wants to continue the
connection, request source address validation, or reject the
connection. Since this extension is initially unencrypted, the
server can use the information prior to committing the resources
needed to complete a key exchange.
If the server decides to use QUIC, this extension MUST be included in
the EncryptedExtensions message.
The parameters are:
connection_id: The 64-bit connection identifier for the connection,
as selected by the client.
quic_version: The currently selected QUIC version that is used for
the connection. This is the version negotiated using the
unauthenticated QUIC version negotiation (Section 4.1).
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supported_quic_versions: This is a list of supported QUIC versions
for each peer. A client sends an empty list if the version of
QUIC being used is their preferred version; however, a client MUST
include their preferred version if this was not negotiated using
QUIC version negotiation. A server MUST include all versions that
it supports in this list.
connection_initial_window: The initial value for the connection flow
control window for the endpoint, in octets.
connection_initial_window: The initial value for the flow control
window of new streams created by the peer endpoint, in octets.
implicit_shutdown_timeout: The time, in seconds, that a connection
can remain idle before being implicitly shutdown.
transport_parameters: A list of parameters for the QUIC connection,
expressed as key-value pairs of arbitrary length. The
QuicTransportParameterType identifies each parameter; duplicate
types are not permitted and MUST be rejected with a fatal
illegal_parameter alert. Type values are taken from a single
space that is shared by all QUIC versions.
ISSUE: There is currently no way to update the value of
parameters once the connection has started. QUIC crypto
provided a SCFG message that could be sent after the connection
was established.
options: A list of options that can be negotiated for a given
connection. These are set during the initial handshake and are
fixed thereafter. These options are used to enable or disable
optional features in the protocol. The set of features that are
supported across different versions might vary. A client SHOULD
include all options that it is willing to use. The server MAY
select any subset of those options that apply to the version of
QUIC that it selects. Only those options selected by the server
are available for use.
Note: This sort of optional behaviour seems like it could be
accommodated adequately by defining new versions of QUIC for
each experiment. However, as an evolving protocol, multiple
experiments need to be conducted concurrently and continuously.
The options parameter provides a flexible way to regulate which
experiments are enabled on a per-connection basis.
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6.2. Unprotected Frames Prior to Handshake Completion
This section describes the handling of messages that are sent and
received prior to the completion of the TLS handshake.
Sending and receiving unprotected messages is hazardous. Unless
expressly permitted, receipt of an unprotected message of any kind
MUST be treated as a fatal error.
6.2.1. STREAM Frames
"STREAM" frames for stream 1 are permitted. These carry the TLS
handshake messages.
Receiving unprotected "STREAM" frames that do not contain TLS
handshake messages MUST be treated as a fatal error.
6.2.2. ACK Frames
"ACK" frames are permitted prior to the handshake being complete.
However, an unauthenticated "ACK" frame can only be used to obtain
NACK ranges. Timestamps MUST NOT be included in an unprotected ACK
frame, since these might be modified by an attacker with the intent
of altering congestion control response. Information on FEC-revived
packets is redundant, since use of FEC in this phase is prohibited.
"ACK" frames MAY be sent a second time once record protection is
enabled. Once protected, timestamps can be included.
Editor's Note: This prohibition might be a little too strong, but
this is the only obviously safe option. If the amount of damage
that an attacker can do by modifying timestamps is limited, then
it might be OK to permit the inclusion of timestamps. Note that
an attacker need not be on-path to inject an ACK.
6.2.3. WINDOW_UPDATE Frames
Sending a "WINDOW_UPDATE" on stream 1 might be necessary to permit
the completion of the TLS handshake, particularly in cases where the
certification path is lengthy. To avoid stalling due to flow control
exhaustion, "WINDOW_UPDATE" frames with stream 1 are permitted.
Receiving a "WINDOW_UPDATE" frame on streams other than 1 MUST be
treated as a fatal error.
Stream 1 is exempt from the connection-level flow control window.
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The position of the flow control window MUST be reset to defaults
once the TLS handshake is complete. This might result in the window
position for either the connection or stream 1 being smaller than the
number of octets that have been sent on those streams. A
"WINDOW_UPDATE" frame might therefore be necessary to prevent the
connection from being stalled.
Note: This is only potentially problematic for servers, who might
need to send large certificate chains. In other cases, this is
unlikely given that QUIC - like HTTP [RFC7230] - is a protocol
where the server is unable to exercise the opportunity TLS
presents to send first.
If a server has a large certificate chain, or later modifications
or extensions to QUIC permit the server to send first, a client
might reduce the chance of stalling due to flow control in this
first round trip by setting larger values for the initial stream
and connection flow control windows using the "quic_parameters"
extension (Section 6.1).
Editor's Note: Unlike "ACK", the prohibition on "WINDOW_UPDATE" is
much less of an imposition on implementations. And, given that a
spurious "WINDOW_UPDATE" might be used to create a great deal of
memory pressure on an endpoint, the restriction seems justifiable.
Besides, I understand this one a lot better.
6.2.4. FEC Packets
FEC packets MUST NOT be sent prior to completing the TLS handshake.
Endpoints MUST treat receipt of an unprotected FEC packet as a fatal
error.
6.3. Protected Frames Prior to Handshake Completion
Due to reordering and loss, protected packets might be received by an
endpoint before the final handshake messages are received. If these
can be decrypted successfully, such packets MAY be stored and used
once the handshake is complete.
Unless expressly permitted below, encrypted packets MUST NOT be used
prior to completing the TLS handshake, in particular the receipt of a
valid Finished message and any authentication of the peer. If
packets are processed prior to completion of the handshake, an
attacker might use the willingness of an implementation to use these
packets to mount attacks.
TLS handshake messages are covered by record protection during the
handshake, once key agreement has completed. This means that
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protected messages need to be decrypted to determine if they are TLS
handshake messages or not. Similarly, "ACK" and "WINDOW_UPDATE"
frames might be needed to successfully complete the TLS handshake.
Any timestamps present in "ACK" frames MUST be ignored rather than
causing a fatal error. Timestamps on protected frames MAY be saved
and used once the TLS handshake completes successfully.
An endpoint MUST save the last protected "WINDOW_UPDATE" frame it
receives for each stream and apply the values once the TLS handshake
completes.
Editor's Note: Ugh. This last one is pretty ugly. Maybe we should
just make the TLS handshake exempt from flow control up to the
Finished message. Then we can prohibit unauthenticated
"WINDOW_UPDATE" messages. We would still likely want to account
for the packets sent and received, since to do otherwise would
create some hairy special cases. That means that stalling is
possible, but it means that we can avoid ugly rules like the
above.
7. Connection ID
The QUIC connection identifier serves to identify a connection and to
allow a server to resume an existing connection from a new client
address in case of mobility events. However, this creates an
identifier that a passive observer [RFC7258] can use to correlate
connections.
TLS 1.3 offers connection resumption using pre-shared keys, which
also allows a client to send 0-RTT application data. This mode could
be used to continue a connection rather than rely on a publicly
visible correlator. This only requires that servers produce a new
ticket on every connection and that clients do not resume from the
same ticket more than once.
The advantage of relying on 0-RTT modes for mobility events is that
this is also more robust. If the new point of attachment results in
contacting a new server instance - one that lacks the session state -
then a fallback is easy.
The main drawback with a clean restart or anything resembling a
restart is that accumulated state can be lost. Aside from progress
on incomplete requests, the state of the HPACK header compression
table could be quite valuable. Existing QUIC implementations use the
connection ID to route packets to the server that is handling the
connection, which avoids this sort of problem.
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A lightweight state resurrection extension might be used to avoid
having to recreate any expensive state.
8. Security Considerations
There are likely to be some real clangers here eventually, but the
current set of issues is well captured in the relevant sections of
the main text.
Never assume that because it isn't in the security considerations
section it doesn't affect security. Most of this document does.
9. IANA Considerations
This document has no IANA actions. Yet.
10. References
10.1. Normative References
[I-D.ietf-tls-tls13]
Rescorla, E., "The Transport Layer Security (TLS) Protocol
Version 1.3", draft-ietf-tls-tls13-11 (work in progress),
December 2015.
[I-D.tsvwg-quic-protocol]
Hamilton, R., Iyengar, J., Swett, I., and A. Wilk, "QUIC:
A UDP-Based Secure and Reliable Transport for HTTP/2",
draft-tsvwg-quic-protocol-02 (work in progress), January
2016.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
[RFC7301] 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, <http://www.rfc-editor.org/info/rfc7301>.
10.2. Informative References
[RFC0793] Postel, J., "Transmission Control Protocol", STD 7,
RFC 793, DOI 10.17487/RFC0793, September 1981,
<http://www.rfc-editor.org/info/rfc793>.
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[RFC7230] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
Protocol (HTTP/1.1): Message Syntax and Routing",
RFC 7230, DOI 10.17487/RFC7230, June 2014,
<http://www.rfc-editor.org/info/rfc7230>.
[RFC7258] Farrell, S. and H. Tschofenig, "Pervasive Monitoring Is an
Attack", BCP 188, RFC 7258, DOI 10.17487/RFC7258, May
2014, <http://www.rfc-editor.org/info/rfc7258>.
[RFC7540] Belshe, M., Peon, R., and M. Thomson, Ed., "Hypertext
Transfer Protocol Version 2 (HTTP/2)", RFC 7540,
DOI 10.17487/RFC7540, May 2015,
<http://www.rfc-editor.org/info/rfc7540>.
Appendix A. Acknowledgments
Christian Huitema's knowledge of QUIC is far better than my own.
This would be even more inaccurate and useless if not for his
assistance. This document has variously benefited from a long series
of discussions with Ryan Hamilton, Jana Iyengar, Adam Langley,
Roberto Peon, Ian Swett, and likely many others who are merely
forgotten by a faulty meat computer.
Authors' Addresses
Martin Thomson
Mozilla
Email: martin.thomson@gmail.com
Ryan Hamilton
Google
Email: rch@google.com
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