TCPLS: Modern Transport Services with TCP and TLS
draft-piraux-tcpls-04
| Document | Type | Active Internet-Draft (individual) | |
|---|---|---|---|
| Authors | Maxime Piraux , Florentin Rochet , Olivier Bonaventure | ||
| Last updated | 2023-10-23 | ||
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draft-piraux-tcpls-04
Network Working Group M. Piraux
Internet-Draft UCLouvain & WELRI
Intended status: Experimental F. Rochet
Expires: 25 April 2024 University of Namur
O. Bonaventure
UCLouvain & WELRI
23 October 2023
TCPLS: Modern Transport Services with TCP and TLS
draft-piraux-tcpls-04
Abstract
This document specifies a protocol leveraging TCP and TLS to provide
modern transport services such as multiplexing, connection migration
and multipath in a secure manner.
Discussion Venues
This note is to be removed before publishing as an RFC.
Source for this draft and an issue tracker can be found at
https://github.com/mpiraux/draft-piraux-tcpls.
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 25 April 2024.
Copyright Notice
Copyright (c) 2023 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
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
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions and Definitions . . . . . . . . . . . . . . . . . 5
2.1. Notational conventions . . . . . . . . . . . . . . . . . 5
3. Modern Transport Services . . . . . . . . . . . . . . . . . . 5
4. TCPLS Overview . . . . . . . . . . . . . . . . . . . . . . . 6
4.1. Multiple Streams . . . . . . . . . . . . . . . . . . . . 7
4.2. Multiple TCP connections . . . . . . . . . . . . . . . . 8
4.2.1. Joining TCP connections . . . . . . . . . . . . . . . 8
4.2.2. Robust session establishment . . . . . . . . . . . . 9
4.2.3. Failover . . . . . . . . . . . . . . . . . . . . . . 10
4.2.4. Migration . . . . . . . . . . . . . . . . . . . . . . 11
4.2.5. Multipath . . . . . . . . . . . . . . . . . . . . . . 11
4.3. Record protection . . . . . . . . . . . . . . . . . . . . 11
4.4. Authenticating TCP with Opportunistic TCP-AO . . . . . . 12
4.5. Closing a TCPLS session . . . . . . . . . . . . . . . . . 12
4.6. Zero-Copy Receive Path . . . . . . . . . . . . . . . . . 13
5. TCPLS Protocol . . . . . . . . . . . . . . . . . . . . . . . 13
5.1. TCPLS TLS Extensions . . . . . . . . . . . . . . . . . . 13
5.1.1. TCPLS . . . . . . . . . . . . . . . . . . . . . . . . 14
5.1.2. TCPLS Join . . . . . . . . . . . . . . . . . . . . . 14
5.1.3. TCPLS Token . . . . . . . . . . . . . . . . . . . . . 14
5.2. TCPLS Frames . . . . . . . . . . . . . . . . . . . . . . 15
5.2.1. Padding frame . . . . . . . . . . . . . . . . . . . . 16
5.2.2. Ping frame . . . . . . . . . . . . . . . . . . . . . 17
5.2.3. Stream frame . . . . . . . . . . . . . . . . . . . . 17
5.2.4. ACK frame . . . . . . . . . . . . . . . . . . . . . . 18
5.2.5. New Token frame . . . . . . . . . . . . . . . . . . . 18
5.2.6. Connection Reset frame . . . . . . . . . . . . . . . 19
5.2.7. New Address frame . . . . . . . . . . . . . . . . . . 19
5.2.8. Remove Address frame . . . . . . . . . . . . . . . . 20
5.2.9. Stream Change frame . . . . . . . . . . . . . . . . . 20
6. Security Considerations . . . . . . . . . . . . . . . . . . . 21
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 21
7.1. TCPLS TLS Extensions . . . . . . . . . . . . . . . . . . 21
7.2. TCPLS Frames . . . . . . . . . . . . . . . . . . . . . . 21
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 21
8.1. Normative References . . . . . . . . . . . . . . . . . . 22
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8.2. Informative References . . . . . . . . . . . . . . . . . 22
Appendix A. Alternative Designs . . . . . . . . . . . . . . . . 24
A.1. Securing new TCP connections with New Session Tickets . . 24
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 24
Change log . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
Since draft-piraux-tcpls-03 . . . . . . . . . . . . . . . . . . 24
Since draft-piraux-tcpls-02 . . . . . . . . . . . . . . . . . . 24
Since draft-piraux-tcpls-01 . . . . . . . . . . . . . . . . . . 25
Since draft-piraux-tcpls-00 . . . . . . . . . . . . . . . . . . 25
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 25
1. Introduction
The TCP/IP protocol stack continuously evolves. In the early days,
most applications were interacting with the transport layer (mainly
TCP, but also UDP) using the socket API. This is illustrated in
Figure 1.
+------------------------------+
| Application |
+------------------------------+
| TCP/UDP |
+------------------------------+
| IPv4 |
+------------------------------+
Figure 1: The classical TCP/IP protocol stack
The TCP/IP stack has slowly evolved and the figure above does not
anymore describe current Internet applications. IPv6 is now widely
deployed next to IPv4 in the network layer. In the transport layer,
protocols such as SCTP [RFC4960] or DCCP [RFC6335] and TCP extensions
including Multipath TCP [RFC8684] or tcpcrypt [RFC8548] have been
specified. The security aspects of the TCP/IP protocol suite are
much more important today than in the past [RFC7258]. Many
applications rely on TLS [RFC8446] and their stack is similar to the
one shown in Figure 2.
+------------------------------+
| Application |
+------------------------------+
| TLS |
+------------------------------+
| TCP |
+------------------------------+
| IPv4/IPv6 |
+------------------------------+
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Figure 2: Today's TCP/IP protocol stack
Recently, the IETF went one step further in improving the transport
layer with the QUIC protocol [RFC9000]. QUIC is a new secure
transport protocol primarily designed for HTTP/3. It includes the
reliability and congestion control features that are part of TCP and
integrates the security features of TLS 1.3 [RFC8446]. This close
integration between the reliability and security features brings a
lot of benefits in QUIC. QUIC runs above UDP to be able to pass
through most middleboxes and to be implementable in user space.
While QUIC reuses TLS, it does not strictly layer TLS on top of UDP
as DTLS [I-D.ietf-tls-dtls13]. This organization, illustrated in
Figure 3 provides much more flexibility than simply layering TLS
above UDP. For example, the QUIC migration capabilities enable an
application to migrate an existing QUIC session from an IPv4 path to
an IPv6 one.
+------------------------------+
| Application |
+------------------------------+
|.......... |
| TLS | QUIC ..........|
|.......... | UDP |
+------------------------------+
| IPv4/IPv6 |
+------------------------------+
Figure 3: QUIC protocol stack
In this document, we revisit how TCP and TLS 1.3 can be used to
provide modern transport services to applications. We apply a
similar principle and combine TCP and TLS 1.3 in a protocol that we
call TCPLS. TCPLS leverages the security features of TLS 1.3 like
QUIC, but without begin simply layered above a single TCP connection.
In addition, TCPLS reuses the existing TCP stacks and TCP's wider
support in current networks. A preliminary version of the TCPLS
protocol is described in [CONEXT21].
+------------------------------+
| Application |
+------------------------------+
|.......... |
| TLS | TCPLS ..........|
|.......... | TCP |
+------------------------------+
| IPv4/IPv6 |
+------------------------------+
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Figure 4: TCPLS in the TCP/IP protocol stack
In this document, we use the term TLS/TCP to refer to the TLS 1.3
protocol running over one TCP connection. We reserve the word TCPLS
for the protocol proposed in this document.
This document is organized as follows. First, Section 3 summarizes
the different types of services that modern transports expose to
application. Section 4 gives an overview of TCPLS and how it
supports these services. Finally, Section 5 describes the TCPLS in
more details and the TLS Extensions introduced in this document.
2. 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.
2.1. Notational conventions
This document uses the same conventions as defined in Section 1.3 of
[RFC9000].
This document uses network byte order (that is, big endian) values.
Fields are placed starting from the high-order bits of each byte.
3. Modern Transport Services
Application requirements and the devices they run on evolve over
time. In the early days, most applications involved single-file
transfer and ran on single-homed computers with a fixed-line network.
Today, web-based applications require exchanging multiple objects,
with different priorities, on devices that can move from one access
network to another and that often have multiple access networks
available. Security is also a key requirement of applications that
evolved from only guaranteeing the confidentiality and integrity of
application messages to also preventing pervasive monitoring.
With TCP and TLS/TCP, applications use a single connection that
supports a single bytestream in each direction. Some TCP
applications such as HTTP/2 [RFC7540] use multiple streams, but these
are mapped to a single TCP connection which leads to Head-of-Line
(HoL) blocking when packet losses occur. SCTP [RFC4960] supports
multiple truly-concurrent streams and QUIC adopted a similar approach
to prevent HoL blocking.
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Modern transport services also changed the utilization of the
underlying network. With TCP, when a host creates a connection, it
is bound to the IP addresses used by the client and the server during
the handshake. When the client moves and receives a different IP
address, it has to reestablish all TCP connections bound to the
previous address. When the client and the server are dual-stack,
they cannot easily switch from one address family to another. Happy
Eyeballs [RFC8305] provides a partial answer to this problem for web
applications with heuristics that clients can use to probe TCP
connections with different address families. With Multipath TCP, the
client and the server can learn other addresses of the remote host
and combine several TCP connections within a single Multipath TCP
connection that is exposed to the application. This supports various
use cases [RFC8041]. QUIC [RFC9000] enables applications to migrate
from one network path to another, but not to simultaneously use
different paths.
4. TCPLS Overview
In order for TCPLS to be widely compatible with middleboxes that
inspect TCP segments and TLS records, TCPLS does not modify the TCP
connection establishment and only adds a TLS extension to the TLS
handshake. Figure 5 illustrates the opening of a TCPLS session which
starts with the TCP 3-way handshake, followed by the TLS handshake.
In the Extensions of the ClientHello and in the server
EncryptedExtensions, the tcpls TLS Extension is introduced to
announce the support of TCPLS.
Client Server
| SYN |
|------------------------------------------>|
| SYN+ACK |
|<------------------------------------------|
| ACK, TLS ClientHello + tcpls |
|------------------------------------------>|
| TLS ServerHello, TLS EncryptedExtensions |
| + tcpls, ... |
|<------------------------------------------|
| TLS Finished |
|------------------------------------------>|
| |
Figure 5: Starting a TCPLS session
TCP/TLS offers a single encrypted bytestream service to the
application. To achieve this, TLS records are used to encrypt and
secure chunks of the application bytestream and are then sent through
the TCP bytestream. TCPLS leverages TLS records differently. TCPLS
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defines its own framing that allows encoding application data and
control information. A TCPLS frame is the basic unit of information
for TCPLS. A TCPLS frame always fits in a single record. One or
more TCPLS frames can be encoded in a TLS record. This TLS record is
then reliably transported by a TCP connection. Figure 6 illustrates
the relationship between TCPLS frames and TLS records.
TCPLS Data TCP Control TCPLS Data
abcdef 0010010 mnopq...
<---------> <-----------> <------------>
/ /
/ /
| /
| /
| /
| /
| /
| /
+----------------+ +-----------------+
| TLS record n | | TLS record n+1 | ....
+----------------+ +-----------------+
Figure 6: The first TLS record contains two TCPLS frames
4.1. Multiple Streams
TCPLS extends the service provided by TCP with streams. Streams are
independent bidirectional bytestreams that can be used by
applications to concurrently convey several objects over a TCPLS
session. Streams can be opened by the client and by the server.
Streams are identified by a 32-bit unsigned integer. The parity of
this number indicates the initiator of the stream. The client opens
even-numbered streams while the server opens odd-numbered streams.
Streams are opened in sequence, e.g. a client that has opened stream
0 will use stream 2 as the next one.
Data is exchanged using Stream frames whose format is described in
Section 5.2.3. Each Stream frame carries a chunk of data of a given
stream. Applications can mark the end of a stream to close it.
TCPLS enables the receiver to decrypt and process TLS records in zero
copy similarly to TLS 1.3 under circumstances discussed in
Section 4.6.
Similarly to HTTP/2 [RFC7540], conveying several streams on a single
TCP connection introduces Head-of-Line (HoL) blocking between the
streams. To alleviate this, TCPLS provides means to the application
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to choose the degree of HoL blocking resilience it needs for its
application objects by spreading streams among different underlying
TCP connections.
4.2. Multiple TCP connections
TCPLS is not restricted to using a single TCP connection to exchange
frames. A TCPLS session starts with the TCP connection that was used
to transport the TLS handshake. After this handshake, other TCP
connections can be added to a TCPLS session, either to spread the
load or for failover. TCPLS manages the utilization of the
underlying TCP connections within a TCPLS session.
Multipath TCP enables both the client and the server to establish
additional TCP connections. However, experience has shown that
additional subflows are only established by the clients. TCPLS
focuses on this deployment and only allows clients to create
additional TCP connections.
Using Multipath TCP, a client can try establishing a new TCP
connection at any time. If a server wishes to restrict the number of
TCP connections that correspond to one Multipath TCP connection, it
has to respond with RST to the in excess connection attempts.
TCPLS takes another approach. To control the number of connections
that a client can establish, a TCPLS server supplies unique tokens.
A client includes one of the server supplied tokens when it attaches
a new TCP connection to a TCPLS session. Each token can only be used
once, hence limiting the amount of additional TCP connections.
TCPLS endpoints can advertise their local addresses, allowing new TCP
connections for a given TCPLS session to be established between new
pairs of addresses. When an endpoint is no more willing new TCP
connections to use one of its advertised addresses, it can remove
this address from the TCPLS session.
4.2.1. Joining TCP connections
The TCPLS server provides tokens to the client in order to join new
TCP connections to the TCPLS session. Figure 7 illustrates a client
and server first establishing a new TCPLS session as described in
Section 4. Then the server sends a token over this connection using
the New Token frame. Each token has a sequence number (e.g. 1) and a
value (e.g. "abc"). The client uses this token to open a new TCP
connection and initiates the TCPLS handshake. It adds the token
inside the TCPLS Join TLS extension in the ClientHello.
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<-1.TCPLS Handshake->
.----------------------------------.
| <-2.New Token(1,abc) |
v v
+--------+ +--------+
| Client | | Server |
+--------+ +--------+
^ ^
| 3.TCPLS Hsh. + tcpls_join(abc)-> | Legend:
.----------------------------------. --- TCP connection
Figure 7: Joining a new TCP connection
When receiving a TCPLS Join Extension, the server validates the token
and associates the TCP connection to the TCPLS session.
Each TCP connection that is part of a TCPLS session is identified by
a 32-bit unsigned integer called its Connection ID. The first TCP
connection of a session corresponds to Connection ID 0. When joining
a new connection, the sequence number of the token, i.e. 1 in our
example, becomes the Connection ID of the connection. The Connection
ID enables the Client and the Server to identify a specific TCP
connection within a given TCPLS session.
4.2.2. Robust session establishment
The TCPLS protocol also supports robust session establishment, where
a multihomed or dual-stack client can establish a TCPLS session when
at least one network path to the server can be established. This
guarantees robustness against network failures and lowers the overall
latency of a session establishment.
Figure 8 illustrates a dual-homed client that robustly establish a
TCPLS session over two local addresses. In this example, the path
from IP b towards the server exhibits a higher delay.
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Client @ IP a Server Client @ IP b
| SYN | SYN |
|----------------------------->| /--------------|
| SYN+ACK |<-------------/ |
|<-----------------------------| SYN+ACK |
| ACK, TLS CH + tcpls |--------------\ |
|----------------------------->| \------------->|
| TLS SH, EE + tcpls, | ACK |
| tcpls_token(abc), ... |<-----------------------------|
|<-----------------------------|TLS CH + tcpls,tcpls_join(abc)|
| TLS Finished |<-----------------------------|
|----------------------------->| |
| TCPLS session established and 2nd connection can be joined. |
...
Figure 8: Robust session establishment example
The client starts by opening a TCP connection on from each of its
local addresses. The TCP connection from IP "a" towards the server
completes faster than the other. The client then starts a TCPLS
Handshake on this connection. When the other connection is
established, the client waits for receiving a TCPLS token allowing to
join it to the session being established. In addition to the New
Token frame, the TCPLS protocol enables the server to provide one
such token during the handshake using the TCPLS Token TLS extension.
The server uses this extension when sending its EncryptedExtensions
over the faster connection to provide the TCPLS token "abc". As soon
as the client has received this token, it uses it over the other
connection to join it to the session. When the TLS handshake
completes over the fastest connection, the TCPLS session is
established and the other connection can be joined to the session.
4.2.3. Failover
TCPLS supports two types of failover. In make-before-break, the
client creates a TCP connection using the procedure described in
Section 4.2.1 but only uses it once the initial connection fails.
In break-before-make, the client creates the initial TCP connection
and uses it for the TCPLS handshake and the data. The server
advertises one or more tokens over this connection. Upon failure of
the initial TCP connection, the client initiates a second TCP
connection using the server-provided token.
In both cases, some records sent by the client or the server might be
in transit when the failure occurs. Some of these records could have
been partially received but not yet delivered to the TCPLS layer when
the underlying TCP connection fails. Other records could have
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already been received, decrypted and data of their frames could have
been delivered to the application. To prevent data losses and
duplication, TCPLS includes its own acknowledgments.
A TCPLS receiver acknowledges the received records using the ACK
frame. Records are acknowledged after the record protection has been
successfully removed. This enables the sender to know which records
have been received. TCPLS enables the endpoint to send
acknowledgments for a TCP connection over any connections, e.g. not
only the receiving connection.
4.2.4. Migration
To migrate from a given TCP connection, an endpoint stops
transmitting over this TCP connection and sends the following frames
on other TCP connections. It leverages the acknowledgments to
retransmit the frames of TLS records that have not been yet
acknowledged.
When an endpoint abortfully closes a TCP connection, its peer
leverages the acknowlegments to retransmit the TLS records that were
not acknowlegded.
4.2.5. Multipath
TCPLS also supports the utilization of different TCP connections,
over different paths or interfaces, to improve throughput or spread
stream frames over different TCP connections. When the endpoints
have opened several TCP connections, they can send frames over the
connections. TCPLS can send all the stream frames belonging to a
given stream over one or more underlying TCP connections. The latter
enables bandwidth aggregation by using TCP connections established
over different network paths.
4.3. Record protection
When adding new TCP connections to a TCPLS session, an endpoint does
not complete the TLS handshake. TCPLS provides a nonce construction
for TLS record protection that is used for all connections of a
session. This reduces the cryptographic cost of adding connections.
The endpoints SHOULD send TLS messages to form an apparent complete
TLS handshake to middleboxes.
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In order to use the TLS session over multiple connections, TCPLS adds
a record sequence number space per connection that is maintained
independently at both sides. Each record sent over a TCPLS session
is identified by the Connection ID of its connection and its record
sequence number. Each record nonce is constructed as defined in
Figure 9.
N N-32 64 0
+---------------------------------------------------------------+
| client/server_write_iv |
+---------------------------------------------------------------+
XOR XOR
+-------------------+ +--------------------+
| Connection ID | | Conn. record sequ. |
+-------------------+ +--------------------+
Figure 9: TCPLS TLS record nonce construction
This construction guarantees that every TLS record sent over the TLS
session is protected with a unique nonce. As in TLS 1.3, the per-
connection record sequence is implicit.
4.4. Authenticating TCP with Opportunistic TCP-AO
The TCP packets exchanged by TCPLS endpoints can be authenticated
using the opportunistic mode for TCP-AO defined in
[I-D.piraux-tcp-ao-tls]. The TCP connection initiating the TCPLS
session follows the same procedure as described in
[I-D.piraux-tcp-ao-tls]. Then, additional TCP connections can reuse
the MKT derived from the TLS handshake. When using TCP-AO over
several TCP connections of a TCPLS session, endpoints SHOULD use
different KeyID values that appears as random to observers toi avoid
correlation. Enabling TCP-AO on TCP connections part of a TCPLS
session remains a per-connection decision.
4.5. Closing a TCPLS session
Endpoints notify their peers that they do not intend to send more
data over a given TCPLS session by sending a TLS Alert
"close_notify". The alert can be sent over one or more TCP
connections of the session. The alert MUST be sent before closing
the last TCP connection of the TCPLS session. The endpoint MAY close
its side of the TCP connections after sending the alert.
When all TCP connections of a session are closed and the TLS Alert
"close_notify" was exchanged in both directions, the TCPLS session is
considered as closed.
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We leave defining an abortful and idle session closure mechanisms for
future versions of this document.
4.6. Zero-Copy Receive Path
TCPLS enables the receiver to process TLS records in a zero-copy
manner under several conditions. When they are met, the application
data carried in TCPLS frames can be decrypted at the right place in
the application buffers.
First, zero-copy can be achieved when Stream frames of a given stream
arrive in order. When using several TCP connections, out-of-order
Stream frames cannot be processed in zero copy. A Multipath
scheduling algorithm may target the minimization of out-of-order
packets.
Second, the composition of TCPLS frames in a TLS record is impactful.
The sender SHOULD encode a single Stream Data frame as the first
frame of the record, followed by control-related frames if needed.
When the sender encodes several Stream frames, the frame at the start
of the record SHOULD be the largest, in order to maximise the use of
zero copy. When several Stream frames are included in a record, they
SHOULD belong to different streams.
5. TCPLS Protocol
5.1. TCPLS TLS Extensions
This document specifies three TLS extensions used by TCPLS. The
first, "tcpls", is used to announce the support of TCPLS. The
second, "tcpls_join", is used to join a TCP connection to a TCPLS
session. The third, "tcpls_token", is used to provide a token to the
client before the handshake completes. Their types are defined as
follows.
enum {
tcpls(TBD1),
tcpls_join(TBD2),
tcpls_token(TBD3),
(65535)
} ExtensionType;
The table below indicates the TLS messages where these extensions can
appear. "CH" indicates ClientHello while "EE" indicates
EncryptedExtensions.
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+=============+======================+
| Extension | Allowed TLS messages |
+=============+======================+
| tcpls | CH, EE |
+-------------+----------------------+
| tcpls_join | CH |
+-------------+----------------------+
| tcpls_token | EE |
+-------------+----------------------+
Table 1: TLS messages allowed to
carry TCPLS TLS Extensions
5.1.1. TCPLS
The "tcpls" extension is used by the client and the server to
announce their support of TCPLS. The extension contains no value.
When it is present in both the ClientHello and the
EncryptedExtensions, the endpoints MUST use TCPLS after completing
the TLS handshake.
5.1.2. TCPLS Join
struct {
opaque token<32>;
} TCPLSJoin;
The "tcpls_join" extension is used by the client to join the TCP
connection on which it is sent to a TCPLS session. The extension
contains a token provided by the server. The client MUST NOT send
more than one "tcpls_join" extension in its ClientHello. When
receiving a ClientHello with this extension, the server checks that
the token is valid and joins the TCP connection to the corresponding
TCPLS session. When the token is not valid, the server MUST abort
the handshake with an illegal_parameter alert.
5.1.3. TCPLS Token
struct {
opaque token<32>;
} TCPLSToken;
The "tcpls_token" extension is used by the server to provide a token
to the client during the TLS handshake. When receiving this
extension, the client associates the token value as the first token
of the TCPLS session, i.e. with a sequence number of 1. The server
MUST NOT send this extension when the corresponding ClientHello
contains a "tcpls_join" extension.
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5.2. TCPLS Frames
TCPLS uses TLS Application Data records to exchange TCPLS frames.
After decryption, the record payload consists of a sequence of TCPLS
frames. Figure 10 illustrates the manner in which TCPLS frames are
parsed from a decrypted TLS record. The receiver processes the
frames starting from the last one to the first one. The fields of
each frames are also parsed from the end towards the beginning of the
TLS Application Data content. The parsing of a frame starts with the
last byte indicating the frame type and then with type-specific
fields preceeding it, forming a Type-Value unit. Such ordering
enables a zero-copy processing of the type-specific fields as
explained in Section 4.6.
First frame start
|
0 First frame end | n
+---------------------|------------|-+
| v v |
| *------------* *------------* |
| .... | Value |Type| | Value |Type| |
| *------------* *------------* |
+------------------------------------+
Decrypted TLS record
Figure 10: Parsing TCPLS frames inside a TLS record starts from
the end.
Table 2 lists the frames specified in this document.
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+============+==================+=======+===============+
| Type value | Frame name | Rules | Definition |
+============+==================+=======+===============+
| 0x00 | Padding | N | Section 5.2.1 |
+------------+------------------+-------+---------------+
| 0x01 | Ping | | Section 5.2.2 |
+------------+------------------+-------+---------------+
| 0x02-0x03 | Stream | | Section 5.2.3 |
+------------+------------------+-------+---------------+
| 0x04 | ACK | N | Section 5.2.4 |
+------------+------------------+-------+---------------+
| 0x05 | New Token | S | Section 5.2.5 |
+------------+------------------+-------+---------------+
| 0x06 | Connection Reset | | Section 5.2.6 |
+------------+------------------+-------+---------------+
| 0x07 | New Address | | Section 5.2.7 |
+------------+------------------+-------+---------------+
| 0x08 | Remove Address | | Section 5.2.8 |
+------------+------------------+-------+---------------+
| 0x09 | Stream Change | Cs | Section 5.2.9 |
+------------+------------------+-------+---------------+
Table 2: TCPLS frames
The "Rules" column in Table 2 indicates special requirements
regarding certain frames.
N: Non-ack-eliciting. Receiving this frame does not elicit the
sending of a TCPLS acknowledgment.
S: Server only. This frame MUST NOT be sent by the client.
Cs: Connection-specific semantics. This frame is not idempotent and
has specific semantics based on the TCP connection over which it
is exchanged.
5.2.1. Padding frame
This frame has no semantic value. It can be used to mitigate traffic
analysis on the TLS records of a TCPLS session. The Padding frame
has no content.
Padding frame {
Type (8) = 0x00,
}
Figure 11: Padding frame format
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5.2.2. Ping frame
This frame is used to elicit an acknowledgment from its peer. It has
no content. When an endpoint receives a Ping frame, it acknowledges
the TLS record that contains this frame. This frame can be used by
an endpoint to check that its peer can receive TLS records over a
particular TCP connection.
Ping frame {
Type (8) = 0x01,
}
Figure 12: Ping frame format
5.2.3. Stream frame
This frame is used to carry chunks of data of a given stream.
Stream frame {
Stream Data (...),
Length (16),
Offset (64),
Stream ID (32),
FIN (1),
Type (7) = 0x01,
}
Figure 13: Stream frame format
FIN: The last bit of the frame type bit indicates that this Stream
frame ends the stream when its value is 1. The last byte of the
stream is at the sum of the Offset and Length fields of this
frame.
Stream ID: A 32-bit unsigned integer indicating the ID of the stream
this frame relates to.
Offset: A 64-bit unsigned integer indicating the offset in bytes of
the carried data in the stream.
Length: A 16-bit unsigned integer indicating the length of the
Stream Data field.
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5.2.4. ACK frame
This frame is sent by the receiver to acknowledge the receipt of TLS
records on a particular TCP connection of the TCPLS session.
Although the reliability of the data exchange on a connection is
handled by TCP, there are situations such as the failure of a TCP
connection where a sender does not know whether the TLS frames that
it sent have been correctly received by the peer. The ACK frame
allows a TCPLS receiver to indicate the highest TLS record sequence
number received on a specific connection. The ACK frame can be sent
over any TCP connection of a TCPLS session.
ACK frame {
Highest Record Sequence Received (64),
Connection ID (32),
Type (8) = 0x04,
}
Figure 14: ACK frame format
Connection ID: A 32-bit unsigned integer indicating the TCP
connection for which the acknowledgment was sent.
Highest Record Sequence Received: A 64-bit unsigned integer
indicating the highest TLS record sequence number received on the
connection indicated by the Connection ID.
5.2.5. New Token frame
This frame is used by the server to provide tokens to the client.
Each token can be used to join a new TCP connection to the TCPLS
session, as described in Section 4.2.1. Clients MUST NOT send New
Token frames.
New Token frame {
Token (256),
Sequence (8),
Type (8) = 0x05,
}
Figure 15: New Token frame format
Sequence: A 8-bit unsigned integer indicating the sequence number of
this token
Token: A 32-byte opaque value that can be used as a token by the
client.
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By controlling the amount of tokens given to the client, the server
can control the number of active TCP connections of a TCPLS session.
The server SHOULD replenish the tokens when TCP connections are
removed from the TCPLS session.
5.2.6. Connection Reset frame
This frame is used by the receiver to inform the sender that a TCP
connection has been reset.
Connection Reset frame {
Connection ID (32)
Type (8) = 0x06,
}
Figure 16: Connection Reset format
Connection ID: A 32-bit unsigned integer indicating the ID of the
connection that failed.
5.2.7. New Address frame
This frame is used by an endpoint to add a new local address to the
TCPLS session. This address can then be used to establish new TCP
connections. The server advertises addresses that the client can use
as destination when adding TCP connections. The client advertises
address that it can use as source when adding TCP connections.
New Address frame {
Port (16),
Address (..),
Address Version (8),
Address ID (8),
Type (8) = 0x07,
}
Figure 17: New Address format
Address ID: A 8-bit identifier for this address. For a given
Address ID, an endpoint receiving a frame with a content that
differs from previously received frames MUST ignore the frame. An
endpoint receiving a frame for an Address ID that was previously
removed MUST ignore the frame.
Address Version: A 8-bit value identifying the Internet address
version of this address. The number 4 indicates IPv4 while 6
indicates IPv6.
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Address: The address value. Its size depends on its version. IPv4
addresses are 32-bit long while IPv6 addresses are 128-bit long.
Port: A 16-bit value indicating the TCP port used with this address.
5.2.8. Remove Address frame
This frame is used by an endpoint to announce that it is not willing
to use a given address to establish new TCP connections. After
receiving this frame, a client MUST NOT establish new TCP connections
to the given address. After receiving this frame, an endpoint MUST
close all TCP connections using the given address.
Remove Address frame {
Address ID (8),
Type (8) = 0x08,
}
Figure 18: Remove Address format
Address ID: A 8-bit identifier for the address to remove. An
endpoint receiving a frame for an address that was nonexistent or
already removed MUST ignore the frame.
5.2.9. Stream Change frame
This frame is used by a sender to announce the Stream ID and Offset
of the next record over a given TCP connection. It can be used to
make explicit a change in stream scheduling over a connection to the
receiver, enabling a zero-copy receive path as explained in
Section 4.6. The hint contained in this frame relates to the
connection over which it was exchanged.
Stream Change frame {
Next Record Stream ID (32),
Next Offset (64),
Type (8) = 0x09,
}
Figure 19: Stream Change format
Next Record Stream ID: A 32-bit unsigned integer indicating the
Stream ID of the Stream frame in the next record .
Next Offset: A 64-bit unsigned integer indicating the Offset of the
Stream frame in the next record.
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6. Security Considerations
When issuing tokens to the client as presented in Section 4.2.1, the
server SHOULD ensure that their values appear as random to observers
and cannot be correlated together for a given TCPLS session.
The security considerations for TLS apply to TCPLS. The next
versions of this document will elaborate on other security
considerations following the guidelines of [RFC3552].
7. IANA Considerations
IANA is requested to create a new "TCPLS" heading for the new
registry described in Section 5.2. New registrations in TCPLS
registries follow the "Specification Required" policy of [RFC8126].
7.1. TCPLS TLS Extensions
IANA is requested to add the following entries to the existing "TLS
ExtensionType Values" registry.
+=======+================+=========+=============+===============+
| Value | Extension Name | TLS 1.3 | Recommended | Reference |
+=======+================+=========+=============+===============+
| TBD1 | tcpls | CH, EE | N | This document |
+-------+----------------+---------+-------------+---------------+
| TBD2 | tcpls_join | CH | N | This document |
+-------+----------------+---------+-------------+---------------+
| TBD3 | tcpls_token | EE | N | This document |
+-------+----------------+---------+-------------+---------------+
Table 3
Note that "Recommended" is set to N as these extensions are intended
for uses as described in this document.
7.2. TCPLS Frames
IANA is requested to create a new registry "TCPLS Frames Types" under
the "TCPLS" heading.
The registry governs an 8-bit space. Entries in this registry must
include a "Frame name" field containing a short mnemonic for the
frame type. The initial content of the registry is present in
Table 2, without the "Rules" column.
8. References
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8.1. Normative 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/rfc/rfc2119>.
[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/rfc/rfc8126>.
[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>.
[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/rfc/rfc8446>.
8.2. Informative References
[CONEXT21] Rochet, F., Assogba, E., Piraux, M., Edeline, K., Donnet,
B., and O. Bonaventure, "TCPLS - Modern Transport Services
with TCP and TLS", Proceedings of the 17th International
Conference on emerging Networking EXperiments and
Technologies (CoNEXT'21) , December 2021.
[I-D.ietf-tls-dtls13]
Rescorla, E., Tschofenig, H., and N. Modadugu, "The
Datagram Transport Layer Security (DTLS) Protocol Version
1.3", Work in Progress, Internet-Draft, draft-ietf-tls-
dtls13-43, 30 April 2021,
<https://datatracker.ietf.org/doc/html/draft-ietf-tls-
dtls13-43>.
[I-D.piraux-tcp-ao-tls]
Piraux, M., Bonaventure, O., and T. Wirtgen,
"Opportunistic TCP-AO with TLS", Work in Progress,
Internet-Draft, draft-piraux-tcp-ao-tls-00, 23 October
2023, <https://datatracker.ietf.org/doc/html/draft-piraux-
tcp-ao-tls-00>.
[RFC3552] Rescorla, E. and B. Korver, "Guidelines for Writing RFC
Text on Security Considerations", BCP 72, RFC 3552,
DOI 10.17487/RFC3552, July 2003,
<https://www.rfc-editor.org/rfc/rfc3552>.
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[RFC4960] Stewart, R., Ed., "Stream Control Transmission Protocol",
RFC 4960, DOI 10.17487/RFC4960, September 2007,
<https://www.rfc-editor.org/rfc/rfc4960>.
[RFC6335] Cotton, M., Eggert, L., Touch, J., Westerlund, M., and S.
Cheshire, "Internet Assigned Numbers Authority (IANA)
Procedures for the Management of the Service Name and
Transport Protocol Port Number Registry", BCP 165,
RFC 6335, DOI 10.17487/RFC6335, August 2011,
<https://www.rfc-editor.org/rfc/rfc6335>.
[RFC7258] Farrell, S. and H. Tschofenig, "Pervasive Monitoring Is an
Attack", BCP 188, RFC 7258, DOI 10.17487/RFC7258, May
2014, <https://www.rfc-editor.org/rfc/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,
<https://www.rfc-editor.org/rfc/rfc7540>.
[RFC8041] Bonaventure, O., Paasch, C., and G. Detal, "Use Cases and
Operational Experience with Multipath TCP", RFC 8041,
DOI 10.17487/RFC8041, January 2017,
<https://www.rfc-editor.org/rfc/rfc8041>.
[RFC8305] Schinazi, D. and T. Pauly, "Happy Eyeballs Version 2:
Better Connectivity Using Concurrency", RFC 8305,
DOI 10.17487/RFC8305, December 2017,
<https://www.rfc-editor.org/rfc/rfc8305>.
[RFC8548] Bittau, A., Giffin, D., Handley, M., Mazieres, D., Slack,
Q., and E. Smith, "Cryptographic Protection of TCP Streams
(tcpcrypt)", RFC 8548, DOI 10.17487/RFC8548, May 2019,
<https://www.rfc-editor.org/rfc/rfc8548>.
[RFC8684] Ford, A., Raiciu, C., Handley, M., Bonaventure, O., and C.
Paasch, "TCP Extensions for Multipath Operation with
Multiple Addresses", RFC 8684, DOI 10.17487/RFC8684, March
2020, <https://www.rfc-editor.org/rfc/rfc8684>.
[RFC9000] 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>.
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Appendix A. Alternative Designs
In this section, we discuss alternatives to mechanisms defined in
this document.
A.1. Securing new TCP connections with New Session Tickets
When adding a new TCP connection to a TCPLS session, endpoints derive
a Initial Vector based on the technique presented in Section 4.3. An
alternative is to use New Session Tickets to derive separate
cryptographic protection materials based on a pre-shared key sent by
the server. In this mode of operation, the server provides New
Session Tickets to control the amount of additional TCP connections
that can be opened by the client. The server could encode the
Connection ID in the ticket value.
Using this mechanism differs from our proposal in several ways.
While it enables to use an existing TLS mechanism for this purpose,
it has a number of differences. First, it requires the server to
compute pre-shared keys which could be more costly than computing the
TCPLS tokens defined in Section 4.2.1. Second, when used to
establish a TLS session, additional TLS messages must be computed and
exchanged to complete the handshake, which the current mechanism does
not require. Third, TLS New Session Tickets have a lifetime that is
separated from the session they are exchanged over. This is unneeded
in the context of TCPLS and may require additional protocol
specification and guidance to implementers.
Acknowledgments
This work has been partially supported by the ``Programme de
recherche d'interet général WALINNOV - MQUIC project (convention
number 1810018)'' and European Union through the NGI Pointer
programme for the TCPLS project (Horizon 2020 Framework Programme,
Grant agreement number 871528). The authors thank Quentin De Coninck
and Louis Navarre for their comments on the first version of this
draft.
Change log
Since draft-piraux-tcpls-03
* Integrated Opportunistic TCP-AO
Since draft-piraux-tcpls-02
* Added the TCPLS Token TLS extension to enable fast robust session
establishment.
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Since draft-piraux-tcpls-01
* Changed frames and fields order to enable zero-copy receiver.
Since draft-piraux-tcpls-00
* Added the addresses exchange mechanism with New Address and Remove
Address frames.
Authors' Addresses
Maxime Piraux
UCLouvain & WELRI
Email: maxime.piraux@uclouvain.be
Florentin Rochet
University of Namur
Email: florentin.rochet@unamur.be
Olivier Bonaventure
UCLouvain & WELRI
Email: olivier.bonaventure@uclouvain.be
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