Internet DRAFT - draft-ietf-quic-version-aliasing
draft-ietf-quic-version-aliasing
QUIC M. Duke
Internet-Draft F5 Networks, Inc.
Intended status: Experimental April 6, 2020
Expires: October 8, 2020
QUIC Version Aliasing
draft-ietf-quic-version-aliasing-00
Abstract
The QUIC transport protocol [QUIC-TRANSPORT] preserves its future
extensibility partly by specifying its version number. There will be
a relatively small number of published version numbers for the
foreseeable future. This document provides a method for clients and
servers to negotiate the use of other version numbers in subsequent
connections. If a sizeable subset of QUIC connections use this
mechanism, this should prevent middlebox ossification around the
current set of published version numbers and the contents of QUIC
Initial packets.
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
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Internet-Drafts are draft documents valid for a maximum of six months
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on October 8, 2020.
Copyright Notice
Copyright (c) 2020 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
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to this document. Code Components extracted from this document must
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
2. Protocol Overview . . . . . . . . . . . . . . . . . . . . . . 3
3. The Version Alias Transport Parameter . . . . . . . . . . . . 4
3.1. Version Number Generation . . . . . . . . . . . . . . . . 4
3.2. Salt Generation . . . . . . . . . . . . . . . . . . . . . 4
3.3. Expiration Time . . . . . . . . . . . . . . . . . . . . . 5
3.4. Format . . . . . . . . . . . . . . . . . . . . . . . . . 5
4. Client Behavior . . . . . . . . . . . . . . . . . . . . . . . 6
5. Server Actions on Non-standard Version Numbers . . . . . . . 6
6. Considerations for Retry Packets . . . . . . . . . . . . . . 7
7. Security and Privacy Considerations . . . . . . . . . . . . . 8
7.1. Version Downgrade . . . . . . . . . . . . . . . . . . . . 8
7.2. Increased Linkability . . . . . . . . . . . . . . . . . . 8
7.3. Seed Polling Attack . . . . . . . . . . . . . . . . . . . 8
7.4. Increased Processing of Garbage UDP Packets . . . . . . . 9
7.5. Increased Retry Overhead . . . . . . . . . . . . . . . . 9
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 10
9.1. Normative References . . . . . . . . . . . . . . . . . . 10
9.2. Informative References . . . . . . . . . . . . . . . . . 10
Appendix A. Acknowledgments . . . . . . . . . . . . . . . . . . 10
Appendix B. Change Log . . . . . . . . . . . . . . . . . . . . . 10
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 11
1. Introduction
The QUIC version number is critical to future extensibility of the
protocol. Past experience with other protocols, such as TLS1.3
[RFC8446], shows that middleboxes might attempt to enforce that QUIC
packets use versions known at the time the middlebox was implemented.
This has a chilling effect on deploying experimental and standard
versions on the internet.
Each version of QUIC has a "salt" [QUIC-TLS] that is used to derive
the keys used to encrypt Initial packets. As each salt is published
in a standards document, any observer can decrypt these packets and
inspect the contents, including a TLS Client Hello. A subsidiary
mechanism like Encrypted SNI [ENCRYPTED-SNI] might protect some of
the TLS fields inside a TLS Client Hello.
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This document proposes "QUIC Version Aliasing," a standard way of
servers advertising the availability of other versions inside the
cryptographic protection of a QUIC handshake. These versions are
syntactically identical to the QUIC version in which the
communication takes place, but use a different salt. In subsequent
communications, the client uses the new version number and encrypts
its Initial packets with a key derived from the provided salt. These
version numbers and salts are unique to the client.
If a large subset of QUIC traffic adopts his technique, middleboxes
will be unable to enforce particular version numbers or policy based
on Client Hello contents without incurring unacceptable penalties on
users. This would simultaneously protect the protocol against
ossification and improve its privacy properties.
1.1. 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 RFC 2119 [RFC2119].
In this document, these words will appear with that interpretation
only when in ALL CAPS. Lower case uses of these words are not to be
interpreted as carrying significance described in RFC 2119.
A "syntax version" is a QUIC version that would be advertised in a
QUIC version negotiation and conforms to a specification. Any
aliased version corresponds to a syntax version in all its formats
and behaviors, except for the version number field in long headers.
An "aliased version" is a version with a number generated in
accordance with this document. Except for the version field in long
headers, it conforms entirely to the specification of the syntax
version.
2. Protocol Overview
When they instantiate a connection, servers select an alternate
32-bit version number for the next connection at random and securely
derive a salt from that version number using a repeatable process.
They communicate this using a transport parameter extension including
the version, salt, and an expiration time for that value.
The next time a client connects to that server, if it is within the
indicated expiration time, it MAY use the provided version number and
encrypt its Initial Packets using a key derived from the provided
salt. The server can reconstruct the salt from the requested version
and proceed with the connection normally.
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3. The Version Alias Transport Parameter
3.1. Version Number Generation
Servers MUST use a random process to generate version numbers. This
version number MUST NOT correspond to a QUIC version the server
advertises in QUIC Version Negotiation packets.
Servers MAY encode the syntax version as long as this information is
cryptographically protected. For example, a server advertises
support for QUIC version 1 and QUIC version 2 in Version Negotiation
packets, each corresponding to a particular packet syntax. In a
Version 1 connection, it might provide an aliased version in the
transport parameter, 0x45f3213b, that encodes the fact the syntax
version is 1. When the client initiates a connection using version
0x45f3213b, the server knows the Initial Packet is formatted in
accordance with QUIC version 1. A subsequent aliased version
provided in the transport parameters would also encode version 1,
even though this is sent in a connection ostensibly of version
0x45f3213b.
Servers MUST NOT use client-controlled information (e.g. the client
IP address) in the random process, see Section 7.3.
Servers MUST NOT advertise these versions in QUIC Version Negotiation
packets.
If multiple servers represent the same entity behind a load balancer,
all such servers SHOULD have a common configuration for how to encode
and extract syntax version to use. They MUST NOT generate version
numbers that any of them would advertise in a Version Negotiation
Packet.
3.2. Salt Generation
The salt is an opaque 20-octet field. It is used to generate a
Initial connection keys using the process described in {QUIC-TLS}.
Servers MUST generate the SALT using a cryptographic method that uses
the version number and only server state that is persistent across
connections. That is, servers MUST implement a method that it can
repeat deterministically at a later time to derive the salt from the
incoming version number. It MUST NOT use client controlled
information other than the version number; for example, the client's
IP address and port.
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3.3. Expiration Time
Servers should select an expiration time in seconds, measured from
the instant the transport parameter is first sent. This time SHOULD
be less than the time until the server expects to support new QUIC
versions, rotate the keys used to encode information in the version
number, or rotate the keys use in salt generation.
Furthermore, the expiration time SHOULD be short enough to frustrate
a seed polling attack Section 7.3.
Conversely, an extremely short expiration time will often force the
client to use standard QUIC version numbers and salts.
3.4. Format
This document defines a new transport parameter extension for QUIC
with identifier 0x5641. The contents of the value field are
indicated below.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Version (32) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| |
+ +
| Salt (160) |
+ +
| |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Expiration (i) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: Version Alias Transport Parameter value
The definition of the fields is described above. Note that the
"Expiration" field is in seconds, and its length is encoded using the
Variable Length Integer encoding from Section 16 of [QUIC-TRANSPORT].
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4. Client Behavior
When a client receives the Version Alias Transport Parameter, it MAY
cache the version number, salt, and the expiration of this value. It
MAY use the version number in a subsequent connection and compute the
initial keys using the provided salt.
Clients SHOULD NOT attempt to use the provided version number and
salt after the provided Expiration time has elapsed.
Clients SHOULD NOT use the provided version number or salt in more
than one connection, particularly if its IP address has changed
between two connection attempts. Using a consistent version number
can link the client across IP address changes.
Clients MUST use the same syntax version to format the Initial Packet
as the syntax version used in the connection that provided the
aliased version.
If the response to an Initial packet using the provided version is a
Version Negotiation Packet, the client SHOULD cease attempting to use
that version and salt to the server unless it later determines that
the packet was the result of a version downgrade, see Section 7.1.
5. Server Actions on Non-standard Version Numbers
When a server receives an Initial Packet with an unknown version
number, it SHOULD send a Version Negotiation Packet if it is
specifically configured not to generate that version number at
random. Otherwise, it derives a salt from the version number using
the algorithm and inputs it uses to generate salts to put in
transport parameters.
If the syntax version was encoded in the version number, the server
extracts it so that it can properly parse the packet. If not, it can
try trial parsing of the packet for each syntax version it supports.
If the computed seed results in a packet that fails authentication,
or the encoded syntax version is not supported at the server, or
trial parsing fails for all supported versions, the server SHOULD
send a Version Negotiation Packet.
Servers SHOULD provide a new Version Alias transport parameter, with
a new version number and salt, each time a client connects, to reduce
linkability for the client. However, issuing version numbers to a
client SHOULD be rate-limited to mitigate the seed polling attack
Section 7.3.
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6. Considerations for Retry Packets
QUIC Retry packets reduce the load on servers during periods of
stress by forcing the client to prove it possesses the IP address
before the server decrypts any Initial Packets or establishing any
connection state. Version aliasing substantially complicates the
process.
If a server has to send a Retry packet, the required format is
ambiguous without understanding which syntax version to use. If all
supported syntax versions use the same Retry format, it simply uses
that format with the provided version number.
If the supported syntax versions use different Retry formats, the
server MUST either extract the syntax version from the version field
and format the Retry accordingly using the aliased version number, or
it MUST send a valid Retry packet for each supported version using
the syntax version number instead of the aliased version number. It
MUST NOT do both.
The Retry integrity Tag of a Retry Packet for an aliased version uses
the procedure in Section 5.8 of [QUIC-TLS]. However, the secret key
K uses the first 16 octets of the aliased salt instead of the key
provided in the specification.
Clients MUST accept Retry packets that contain either the aliased
version or syntax version. It MUST ignore Retry packets with other
syntax versions. It it receives Retry packets with both the aliased
version and the correct syntax version, it MUST discard the second
one it receives in accordance with section 17.2.5 of [QUIC-TRANSPORT]
unless the other one failed integrity validation.
After a client receives a Retry, it sends a new Initial Packet with
the provided Retry token. It MAY use the aliased version and salt or
the syntax version and salt, regardless of which type of Retry it
received. Note that if the server is not able to generate the
correct salt for an aliased version due to lost keys or other errors,
this might result in a Version Negotiation packet, which violates the
usual order of server responses (QUIC servers would normally send
Version Negotiation before Retry).
Clients that receive a Version Negotiation packet in response to an
Initial with a valid Retry token MAY interpret this to mean that the
server can no longer process the aliased version. They can retry the
connection with a syntax version number, but see Section 7.1. These
MUST include the Retry token so that the client can verify that the
Retry was authentic.
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7. Security and Privacy Considerations
This document intends to improve the existing security and privacy
properties of QUIC by dramatically improving the secrecy of QUIC
Initial Packets. However, there are new attacks against this
mechanism.
7.1. Version Downgrade
A countermeasure against version aliasing is the downgrade attack.
Middleboxes may drop a packet containing a random version and imitate
the server's failure to correctly process it. Clients and servers
MUST implement the parts of [QUIC-VERSION-NEGOTIATION] relevant to
downgrade detection.
Note that downgrade detection only works after receiving a response
from the server. If a client immediately responds to a Version
Negotiation Packet with an Initial Packet with a syntax version
number, it will have exposed its request in a format readable to
observers before it discovers if the Version Negotiation Packet is
authentic. A client SHOULD wait for an interval to see if a valid
response comes from the server before assuming the version
negotiation is valid. The client MAY also alter its Initial Packet
(e.g., its ALPN field) to sanitize sensitive information and obtain
another aliased version before proceeding with its true request.
Servers that support version aliasing SHOULD be liberal about the
Initial Packet formats they receive, keeping the connection open long
enough to deliver their transport parameters, to support this
mechanism.
7.2. Increased Linkability
As each version number is theoretically unique to each client, if a
client uses one twice, those two connections are extremely likely to
be from the same host. If the client has changed IP address, this is
a significant increase in linkability relative to QUIC with a
standard version numbers.
7.3. Seed Polling Attack
Observers that wish to decode Initial Packets might open a large
number of connections to the server in an effort to obtain a large
portion of the mapping of version numbers to salts to a server.
While storage-intensive, this attack could increase the probability
that at least some version-aliased connections are observable. There
are two mitigations servers can execute against this attack:
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o rate-limit transport parameters sent to a particular client; and/
or
o set a low expiration time to reduce the lifetime of the attacker's
database.
Segmenting the version number space based on client information, i.e.
using only a subset of version numbers for a certain IP address
range, would significantly amplify an attack. Observers will
generally be on the path to the client and be able to mimic having an
identical IP address. Segmentation in this way would dramatically
reduce the search space for attackers. Thus, servers are prohibited
from using these mechanisms.
7.4. Increased Processing of Garbage UDP Packets
As QUIC shares the UDP protocol number with other UDP applications,
in some deployments it may be possible for traffic intended for other
UDP applications to arrive at a QUIC server endpoint. When servers
support a finite set of version numbers, a valid version number field
is a strong indicator the packet is, in fact, QUIC. If the version
number is invalid, a QUIC Version Negotiation is a low-cost response
that triggers very early in packet processing.
However, a server that provides version aliasing is prepared to
accept almost any version number. As a result, many more
sufficiently sized UDP payloads with the first bit set to '1' are
potential QUIC Initial Packets that require generation of a salt,
some initial connection state, and a decryption operation.
While not a more potent attack then simply sending valid Initial
Packets, servers may have to provision additional resources to
address this possibility.
7.5. Increased Retry Overhead
This document requires two small cryptographic operations to build a
Retry packet instead of one, placing more load on servers when
already under load.
8. IANA Considerations
This draft chooses a transport parameter (0x5641) to minimize the
risk of collision. IANA should assign a permanent value from the
QUIC Transport Parameter Registry.
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9. References
9.1. Normative References
[ENCRYPTED-SNI]
Rescorla, E., Ed., Oku, K., Ed., Sullivan, N., Ed., and C.
Wood, Ed., "Encrypted Server Name Indication for TLS 1.3",
draft-ietf-tls-esni-latest (work in progress).
[QUIC-TLS]
Thomson, M., Ed. and S. Turner, Ed., "Using Transport
Layer Security (TLS) to Secure QUIC", draft-ietf-quic-tls-
latest (work in progress).
[QUIC-TRANSPORT]
Iyengar, J., Ed. and M. Thomson, Ed., "QUIC: A UDP-Based
Multiplexed and Secure Transport", draft-ietf-quic-
transport (work in progress).
[QUIC-VERSION-NEGOTIATION]
Schinazi, D., Ed. and E. Rescorla, Ed., "Compatible
Version Negotiation for QUIC", draft-ietf-quic-version-
negotiation-latest (work in progress).
9.2. Informative References
[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/info/rfc2119>.
[RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol
Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
<https://www.rfc-editor.org/info/rfc8446>.
Appendix A. Acknowledgments
Marten Seemann was the original progenitor of the version aliasing
approach.
Appendix B. Change Log
*RFC Editor's Note:* Please remove this section prior to
publication of a final version of this document.
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Author's Address
Martin Duke
F5 Networks, Inc.
Email: martin.h.duke@gmail.com
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