draft-ietf-quic-tls.md
---
title: Using TLS to Secure QUIC
abbrev: QUIC over TLS
docname: draft-ietf-quic-tls-latest
date: {DATE}
category: std
ipr: trust200902
area: Transport
workgroup: QUIC
stand_alone: yes
pi: [toc, sortrefs, symrefs, docmapping]
author:
-
ins: M. Thomson
name: Martin Thomson
org: Mozilla
email: mt@lowentropy.net
role: editor
-
ins: S. Turner
name: Sean Turner
org: sn3rd
email: sean@sn3rd.com
role: editor
normative:
QUIC-TRANSPORT:
title: "QUIC: A UDP-Based Multiplexed and Secure Transport"
date: {DATE}
seriesinfo:
Internet-Draft: draft-ietf-quic-transport-latest
author:
-
ins: J. Iyengar
name: Jana Iyengar
org: Fastly
role: editor
-
ins: M. Thomson
name: Martin Thomson
org: Mozilla
role: editor
QUIC-RECOVERY:
title: "QUIC Loss Detection and Congestion Control"
date: {DATE}
seriesinfo:
Internet-Draft: draft-ietf-quic-recovery-latest
author:
-
ins: J. Iyengar
name: Jana Iyengar
org: Fastly
role: editor
-
ins: I. Swett
name: Ian Swett
org: Google
role: editor
informative:
AEBounds:
title: "Limits on Authenticated Encryption Use in TLS"
author:
- ins: A. Luykx
- ins: K. Paterson
date: 2016-03-08
target: "http://www.isg.rhul.ac.uk/~kp/TLS-AEbounds.pdf"
IMC:
title: "Introduction to Modern Cryptography, Second Edition"
author:
- ins: J. Katz
- ins: Y. Lindell
date: 2014-11-06
seriesinfo:
ISBN: 978-1466570269
QUIC-HTTP:
title: "Hypertext Transfer Protocol (HTTP) over QUIC"
date: {DATE}
seriesinfo:
Internet-Draft: draft-ietf-quic-http-latest
author:
-
ins: M. Bishop
name: Mike Bishop
org: Microsoft
role: editor
--- abstract
This document describes how Transport Layer Security (TLS) is used to secure
QUIC.
--- note_Note_to_Readers
Discussion of this draft takes place on the QUIC working group mailing list
(quic@ietf.org), which is archived at
<https://mailarchive.ietf.org/arch/search/?email_list=quic>.
Working Group information can be found at <https://github.com/quicwg>; source
code and issues list for this draft can be found at
<https://github.com/quicwg/base-drafts/labels/-tls>.
--- middle
# Introduction
This document describes how QUIC {{QUIC-TRANSPORT}} is secured using TLS
{{!TLS13=RFC8446}}.
TLS 1.3 provides critical latency improvements for connection establishment over
previous versions. Absent packet loss, most new connections can be established
and secured within a single round trip; on subsequent connections between the
same client and server, the client can often send application data immediately,
that is, using a zero round trip setup.
This document describes how TLS acts as a security component of QUIC.
# Notational Conventions
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.
This document uses the terminology established in {{QUIC-TRANSPORT}}.
For brevity, the acronym TLS is used to refer to TLS 1.3, though a newer version
could be used (see {{tls-version}}).
## TLS Overview
TLS provides two endpoints with a way to establish a means of communication over
an untrusted medium (that is, the Internet) that ensures that messages they
exchange cannot be observed, modified, or forged.
Internally, TLS is a layered protocol, with the structure shown below:
~~~~
+--------------+--------------+--------------+
| Handshake | Alerts | Application |
| Layer | | Data |
| | | |
+--------------+--------------+--------------+
| |
| Record Layer |
| |
+--------------------------------------------+
~~~~
Each upper layer (handshake, alerts, and application data) is carried as a
series of typed TLS records. Records are individually cryptographically
protected and then transmitted over a reliable transport (typically TCP) which
provides sequencing and guaranteed delivery.
Change Cipher Spec records cannot be sent in QUIC.
The TLS authenticated key exchange occurs between two entities: client and
server. The client initiates the exchange and the server responds. If the key
exchange completes successfully, both client and server will agree on a secret.
TLS supports both pre-shared key (PSK) and Diffie-Hellman (DH) key exchanges.
PSK is the basis for 0-RTT; the latter provides perfect forward secrecy (PFS)
when the DH keys are destroyed.
After completing the TLS handshake, the client will have learned and
authenticated an identity for the server and the server is optionally able to
learn and authenticate an identity for the client. TLS supports X.509
{{?RFC5280}} certificate-based authentication for both server and client.
The TLS key exchange is resistant to tampering by attackers and it produces
shared secrets that cannot be controlled by either participating peer.
TLS provides two basic handshake modes of interest to QUIC:
* A full 1-RTT handshake in which the client is able to send application data
after one round trip and the server immediately responds after receiving the
first handshake message from the client.
* A 0-RTT handshake in which the client uses information it has previously
learned about the server to send application data immediately. This
application data can be replayed by an attacker so it MUST NOT carry a
self-contained trigger for any non-idempotent action.
A simplified TLS handshake with 0-RTT application data is shown in {{tls-full}}.
Note that this omits the EndOfEarlyData message, which is not used in QUIC (see
{{remove-eoed}}).
~~~
Client Server
ClientHello
(0-RTT Application Data) -------->
ServerHello
{EncryptedExtensions}
{Finished}
<-------- [Application Data]
{Finished} -------->
[Application Data] <-------> [Application Data]
() Indicates messages protected by early data (0-RTT) keys
{} Indicates messages protected using handshake keys
[] Indicates messages protected using application data
(1-RTT) keys
~~~
{: #tls-full title="TLS Handshake with 0-RTT"}
Data is protected using a number of encryption levels:
- Initial Keys
- Early Data (0-RTT) Keys
- Handshake Keys
- Application Data (1-RTT) Keys
Application data may appear only in the early data and application data
levels. Handshake and Alert messages may appear in any level.
The 0-RTT handshake is only possible if the client and server have previously
communicated. In the 1-RTT handshake, the client is unable to send protected
application data until it has received all of the handshake messages sent by the
server.
# Protocol Overview
QUIC {{QUIC-TRANSPORT}} assumes responsibility for the confidentiality and
integrity protection of packets. For this it uses keys derived from a TLS
handshake {{!TLS13}}, but instead of carrying TLS records over QUIC (as with
TCP), TLS Handshake and Alert messages are carried directly over the QUIC
transport, which takes over the responsibilities of the TLS record layer, as
shown below.
~~~~
+--------------+--------------+ +-------------+
| TLS | TLS | | QUIC |
| Handshake | Alerts | | Applications|
| | | | (h3, etc.) |
+--------------+--------------+-+-------------+
| |
| QUIC Transport |
| (streams, reliability, congestion, etc.) |
| |
+---------------------------------------------+
| |
| QUIC Packet Protection |
| |
+---------------------------------------------+
~~~~
QUIC also relies on TLS for authentication and negotiation of parameters that
are critical to security and performance.
Rather than a strict layering, these two protocols are co-dependent: QUIC uses
the TLS handshake; TLS uses the reliability, ordered delivery, and record
layer provided by QUIC.
At a high level, there are two main interactions between the TLS and QUIC
components:
* The TLS component sends and receives messages via the QUIC component, with
QUIC providing a reliable stream abstraction to TLS.
* The TLS component provides a series of updates to the QUIC component,
including (a) new packet protection keys to install (b) state changes such as
handshake completion, the server certificate, etc.
{{schematic}} shows these interactions in more detail, with the QUIC packet
protection being called out specially.
~~~
+------------+ +------------+
| |<- Handshake Messages ->| |
| |<---- 0-RTT Keys -------| |
| |<--- Handshake Keys-----| |
| QUIC |<---- 1-RTT Keys -------| TLS |
| |<--- Handshake Done ----| |
+------------+ +------------+
| ^
| Protect | Protected
v | Packet
+------------+
| QUIC |
| Packet |
| Protection |
+------------+
~~~
{: #schematic title="QUIC and TLS Interactions"}
Unlike TLS over TCP, QUIC applications which want to send data do not send it
through TLS "application_data" records. Rather, they send it as QUIC STREAM
frames which are then carried in QUIC packets.
# Carrying TLS Messages {#carrying-tls}
QUIC carries TLS handshake data in CRYPTO frames, each of which consists of a
contiguous block of handshake data identified by an offset and length. Those
frames are packaged into QUIC packets and encrypted under the current TLS
encryption level. As with TLS over TCP, once TLS handshake data has been
delivered to QUIC, it is QUIC's responsibility to deliver it reliably. Each
chunk of data that is produced by TLS is associated with the set of keys that
TLS is currently using. If QUIC needs to retransmit that data, it MUST use the
same keys even if TLS has already updated to newer keys.
One important difference between TLS records (used with TCP) and QUIC CRYPTO
frames is that in QUIC multiple frames may appear in the same QUIC packet as
long as they are associated with the same encryption level. For instance, an
implementation might bundle a Handshake message and an ACK for some Handshake
data into the same packet.
Some frames are prohibited in different encryption levels, others cannot be
sent. The rules here generalize those of TLS, in that frames associated with
establishing the connection can usually appear at any encryption level, whereas
those associated with transferring data can only appear in the 0-RTT and 1-RTT
encryption levels:
- PADDING frames MAY appear in packets of any encryption level.
- CRYPTO and CONNECTION_CLOSE frames MAY appear in packets of any encryption
level except 0-RTT.
- ACK frames MAY appear in packets of any encryption level other than 0-RTT, but
can only acknowledge packets which appeared in that packet number space.
- All other frame types MUST only be sent in the 0-RTT and 1-RTT levels.
Note that it is not possible to send the following frames in 0-RTT for various
reasons: ACK, CRYPTO, NEW_TOKEN, PATH_RESPONSE, and RETIRE_CONNECTION_ID.
Because packets could be reordered on the wire, QUIC uses the packet type to
indicate which level a given packet was encrypted under, as shown in
{{packet-types-levels}}. When multiple packets of different encryption levels
need to be sent, endpoints SHOULD use coalesced packets to send them in the same
UDP datagram.
| Packet Type | Encryption Level | PN Space |
|:----------------|:-----------------|:----------|
| Initial | Initial secrets | Initial |
| 0-RTT Protected | 0-RTT | 0/1-RTT |
| Handshake | Handshake | Handshake |
| Retry | N/A | N/A |
| Short Header | 1-RTT | 0/1-RTT |
{: #packet-types-levels title="Encryption Levels by Packet Type"}
Section 17 of {{QUIC-TRANSPORT}} shows how packets at the various encryption
levels fit into the handshake process.
## Interface to TLS
As shown in {{schematic}}, the interface from QUIC to TLS consists of three
primary functions:
- Sending and receiving handshake messages
- Rekeying (both transmit and receive)
- Handshake state updates
Additional functions might be needed to configure TLS.
### Sending and Receiving Handshake Messages
In order to drive the handshake, TLS depends on being able to send and receive
handshake messages. There are two basic functions on this interface: one where
QUIC requests handshake messages and one where QUIC provides handshake packets.
Before starting the handshake QUIC provides TLS with the transport parameters
(see {{quic_parameters}}) that it wishes to carry.
A QUIC client starts TLS by requesting TLS handshake bytes from TLS. The client
acquires handshake bytes before sending its first packet. A QUIC server starts
the process by providing TLS with the client's handshake bytes.
At any given time, the TLS stack at an endpoint will have a current sending
encryption level and receiving encryption level. Each encryption level is
associated with a different flow of bytes, which is reliably transmitted to the
peer in CRYPTO frames. When TLS provides handshake bytes to be sent, they are
appended to the current flow and any packet that includes the CRYPTO frame is
protected using keys from the corresponding encryption level.
QUIC takes the unprotected content of TLS handshake records as the content of
CRYPTO frames. TLS record protection is not used by QUIC. QUIC assembles
CRYPTO frames into QUIC packets, which are protected using QUIC packet
protection.
When an endpoint receives a QUIC packet containing a CRYPTO frame from the
network, it proceeds as follows:
- If the packet was in the TLS receiving encryption level, sequence the data
into the input flow as usual. As with STREAM frames, the offset is used to
find the proper location in the data sequence. If the result of this process
is that new data is available, then it is delivered to TLS in order.
- If the packet is from a previously installed encryption level, it MUST not
contain data which extends past the end of previously received data in that
flow. Implementations MUST treat any violations of this requirement as a
connection error of type PROTOCOL_VIOLATION.
- If the packet is from a new encryption level, it is saved for later processing
by TLS. Once TLS moves to receiving from this encryption level, saved data
can be provided. When providing data from any new encryption level to TLS, if
there is data from a previous encryption level that TLS has not consumed, this
MUST be treated as a connection error of type PROTOCOL_VIOLATION.
Each time that TLS is provided with new data, new handshake bytes are requested
from TLS. TLS might not provide any bytes if the handshake messages it has
received are incomplete or it has no data to send.
Once the TLS handshake is complete, this is indicated to QUIC along with any
final handshake bytes that TLS needs to send. TLS also provides QUIC with the
transport parameters that the peer advertised during the handshake.
Once the handshake is complete, TLS becomes passive. TLS can still receive data
from its peer and respond in kind, but it will not need to send more data unless
specifically requested - either by an application or QUIC. One reason to send
data is that the server might wish to provide additional or updated session
tickets to a client.
When the handshake is complete, QUIC only needs to provide TLS with any data
that arrives in CRYPTO streams. In the same way that is done during the
handshake, new data is requested from TLS after providing received data.
Important:
: Until the handshake is reported as complete, the connection and key exchange
are not properly authenticated at the server. Even though 1-RTT keys are
available to a server after receiving the first handshake messages from a
client, the server cannot consider the client to be authenticated until it
receives and validates the client's Finished message.
: The requirement for the server to wait for the client Finished message creates
a dependency on that message being delivered. A client can avoid the
potential for head-of-line blocking that this implies by sending a copy of the
CRYPTO frame that carries the Finished message in multiple packets. This
enables immediate server processing for those packets.
### Encryption Level Changes
As keys for new encryption levels become available, TLS provides QUIC with those
keys. Separately, as TLS starts using keys at a given encryption level, TLS
indicates to QUIC that it is now reading or writing with keys at that encryption
level. These events are not asynchronous; they always occur immediately after
TLS is provided with new handshake bytes, or after TLS produces handshake bytes.
TLS provides QUIC with three items as a new encryption level becomes available:
* A secret
* An Authenticated Encryption with Associated Data (AEAD) function
* A Key Derivation Function (KDF)
These values are based on the values that TLS negotiates and are used by QUIC to
generate packet and header protection keys (see {{packet-protection}} and
{{header-protect}}).
If 0-RTT is possible, it is ready after the client sends a TLS ClientHello
message or the server receives that message. After providing a QUIC client with
the first handshake bytes, the TLS stack might signal the change to 0-RTT
keys. On the server, after receiving handshake bytes that contain a ClientHello
message, a TLS server might signal that 0-RTT keys are available.
Although TLS only uses one encryption level at a time, QUIC may use more than
one level. For instance, after sending its Finished message (using a CRYPTO
frame at the Handshake encryption level) an endpoint can send STREAM data (in
1-RTT encryption). If the Finished message is lost, the endpoint uses the
Handshake encryption level to retransmit the lost message. Reordering or loss
of packets can mean that QUIC will need to handle packets at multiple encryption
levels. During the handshake, this means potentially handling packets at higher
and lower encryption levels than the current encryption level used by TLS.
In particular, server implementations need to be able to read packets at the
Handshake encryption level at the same time as the 0-RTT encryption level. A
client could interleave ACK frames that are protected with Handshake keys with
0-RTT data and the server needs to process those acknowledgments in order to
detect lost Handshake packets.
### TLS Interface Summary
{{exchange-summary}} summarizes the exchange between QUIC and TLS for both
client and server. Each arrow is tagged with the encryption level used for that
transmission.
~~~
Client Server
Get Handshake
Initial ------------->
Rekey tx to 0-RTT Keys
0-RTT --------------->
Handshake Received
Get Handshake
<------------- Initial
Rekey rx to 0-RTT keys
Handshake Received
Rekey rx to Handshake keys
Get Handshake
<----------- Handshake
Rekey tx to 1-RTT keys
<--------------- 1-RTT
Handshake Received
Rekey rx to Handshake keys
Handshake Received
Get Handshake
Handshake Complete
Handshake ----------->
Rekey tx to 1-RTT keys
1-RTT --------------->
Handshake Received
Rekey rx to 1-RTT keys
Get Handshake
Handshake Complete
<--------------- 1-RTT
Handshake Received
~~~
{: #exchange-summary title="Interaction Summary between QUIC and TLS"}
## TLS Version {#tls-version}
This document describes how TLS 1.3 {{!TLS13}} is used with QUIC.
In practice, the TLS handshake will negotiate a version of TLS to use. This
could result in a newer version of TLS than 1.3 being negotiated if both
endpoints support that version. This is acceptable provided that the features
of TLS 1.3 that are used by QUIC are supported by the newer version.
A badly configured TLS implementation could negotiate TLS 1.2 or another older
version of TLS. An endpoint MUST terminate the connection if a version of TLS
older than 1.3 is negotiated.
## ClientHello Size {#clienthello-size}
QUIC requires that the first Initial packet from a client contain an entire
cryptographic handshake message, which for TLS is the ClientHello. Though a
packet larger than 1200 bytes might be supported by the path, a client improves
the likelihood that a packet is accepted if it ensures that the first
ClientHello message is small enough to stay within this limit.
QUIC packet and framing add at least 36 bytes of overhead to the ClientHello
message. That overhead increases if the client chooses a connection ID without
zero length. Overheads also do not include the token or a connection ID longer
than 8 bytes, both of which might be required if a server sends a Retry packet.
A typical TLS ClientHello can easily fit into a 1200 byte packet. However, in
addition to the overheads added by QUIC, there are several variables that could
cause this limit to be exceeded. Large session tickets, multiple or large key
shares, and long lists of supported ciphers, signature algorithms, versions,
QUIC transport parameters, and other negotiable parameters and extensions could
cause this message to grow.
For servers, in addition to connection IDs and tokens, the size of TLS session
tickets can have an effect on a client's ability to connect. Minimizing the
size of these values increases the probability that they can be successfully
used by a client.
A client is not required to fit the ClientHello that it sends in response to a
HelloRetryRequest message into a single UDP datagram.
The TLS implementation does not need to ensure that the ClientHello is
sufficiently large. QUIC PADDING frames are added to increase the size of the
packet as necessary.
## Peer Authentication
The requirements for authentication depend on the application protocol that is
in use. TLS provides server authentication and permits the server to request
client authentication.
A client MUST authenticate the identity of the server. This typically involves
verification that the identity of the server is included in a certificate and
that the certificate is issued by a trusted entity (see for example
{{?RFC2818}}).
A server MAY request that the client authenticate during the handshake. A server
MAY refuse a connection if the client is unable to authenticate when requested.
The requirements for client authentication vary based on application protocol
and deployment.
A server MUST NOT use post-handshake client authentication (see Section 4.6.2 of
{{!TLS13}}).
## Enabling 0-RTT {#enable-0rtt}
In order to be usable for 0-RTT, TLS MUST provide a NewSessionTicket message
that contains the "early_data" extension with a max_early_data_size of
0xffffffff; the amount of data which the client can send in 0-RTT is controlled
by the "initial_max_data" transport parameter supplied by the server. A client
MUST treat receipt of a NewSessionTicket that contains an "early_data" extension
with any other value as a connection error of type PROTOCOL_VIOLATION.
Early data within the TLS connection MUST NOT be used. As it is for other TLS
application data, a server MUST treat receiving early data on the TLS connection
as a connection error of type PROTOCOL_VIOLATION.
## Rejecting 0-RTT
A server rejects 0-RTT by rejecting 0-RTT at the TLS layer. This also prevents
QUIC from sending 0-RTT data. A server will always reject 0-RTT if it sends a
TLS HelloRetryRequest.
When 0-RTT is rejected, all connection characteristics that the client assumed
might be incorrect. This includes the choice of application protocol, transport
parameters, and any application configuration. The client therefore MUST reset
the state of all streams, including application state bound to those streams.
A client MAY attempt to send 0-RTT again if it receives a Retry or Version
Negotiation packet. These packets do not signify rejection of 0-RTT.
## HelloRetryRequest
In TLS over TCP, the HelloRetryRequest feature (see Section 4.1.4 of {{!TLS13}})
can be used to correct a client's incorrect KeyShare extension as well as for a
stateless round-trip check. From the perspective of QUIC, this just looks like
additional messages carried in the Initial encryption level. Although it is in
principle possible to use this feature for address verification in QUIC, QUIC
implementations SHOULD instead use the Retry feature (see Section 8.1 of
{{QUIC-TRANSPORT}}). HelloRetryRequest is still used to request key shares.
## TLS Errors
If TLS experiences an error, it generates an appropriate alert as defined in
Section 6 of {{!TLS13}}.
A TLS alert is turned into a QUIC connection error by converting the one-byte
alert description into a QUIC error code. The alert description is added to
0x100 to produce a QUIC error code from the range reserved for CRYPTO_ERROR.
The resulting value is sent in a QUIC CONNECTION_CLOSE frame.
The alert level of all TLS alerts is "fatal"; a TLS stack MUST NOT generate
alerts at the "warning" level.
## Discarding Unused Keys
After QUIC moves to a new encryption level, packet protection keys for previous
encryption levels can be discarded. This occurs several times during the
handshake, as well as when keys are updated (see {{key-update}}). Initial
packet protection keys are treated specially, see {{discard-initial}}.
Packet protection keys are not discarded immediately when new keys are
available. If packets from a lower encryption level contain CRYPTO frames,
frames that retransmit that data MUST be sent at the same encryption level.
Similarly, an endpoint generates acknowledgements for packets at the same
encryption level as the packet being acknowledged. Thus, it is possible that
keys for a lower encryption level are needed for a short time after keys for a
newer encryption level are available.
An endpoint cannot discard keys for a given encryption level unless it has both
received and acknowledged all CRYPTO frames for that encryption level and when
all CRYPTO frames for that encryption level have been acknowledged by its peer.
However, this does not guarantee that no further packets will need to be
received or sent at that encryption level because a peer might not have received
all the acknowledgements necessary to reach the same state.
After all CRYPTO frames for a given encryption level have been sent and all
expected CRYPTO frames received, and all the corresponding acknowledgments have
been received or sent, an endpoint starts a timer. For 0-RTT keys, which do not
carry CRYPTO frames, this timer starts when the first packets protected with
1-RTT are sent or received. To limit the effect of packet loss around a change
in keys, endpoints MUST retain packet protection keys for that encryption level
for at least three times the current Probe Timeout (PTO) interval as defined in
{{QUIC-RECOVERY}}. Retaining keys for this interval allows packets containing
CRYPTO or ACK frames at that encryption level to be sent if packets are
determined to be lost or new packets require acknowledgment.
Though an endpoint might retain older keys, new data MUST be sent at the highest
currently-available encryption level. Only ACK frames and retransmissions of
data in CRYPTO frames are sent at a previous encryption level. These packets
MAY also include PADDING frames.
Once this timer expires, an endpoint MUST NOT either accept or generate new
packets using those packet protection keys. An endpoint can discard packet
protection keys for that encryption level.
Key updates (see {{key-update}}) can be used to update 1-RTT keys before keys
from other encryption levels are discarded. In that case, packets protected
with the newest packet protection keys and packets sent two updates prior will
appear to use the same keys. After the handshake is complete, endpoints only
need to maintain the two latest sets of packet protection keys and MAY discard
older keys. Updating keys multiple times rapidly can cause packets to be
effectively lost if packets are significantly delayed. Because key updates can
only be performed once per round trip time, only packets that are delayed by
more than a round trip will be lost as a result of changing keys; such packets
will be marked as lost before this, as they leave a gap in the sequence of
packet numbers.
## Discarding Initial Keys {#discard-initial}
Packets protected with Initial secrets ({{initial-secrets}}) are not
authenticated, meaning that an attacker could spoof packets with the intent to
disrupt a connection. To limit these attacks, Initial packet protection keys
can be discarded more aggressively than other keys.
The successful use of Handshake packets indicates that no more Initial packets
need to be exchanged, as these keys can only be produced after receiving all
CRYPTO frames from Initial packets. Thus, a client MUST discard Initial keys
when it first sends a Handshake packet and a server MUST discard Initial keys
when it first successfully processes a Handshake packet. Endpoints MUST NOT
send Initial packets after this point.
This results in abandoning loss recovery state for the Initial encryption level
and ignoring any outstanding Initial packets.
# Packet Protection {#packet-protection}
As with TLS over TCP, QUIC protects packets with keys derived from the TLS
handshake, using the AEAD algorithm negotiated by TLS.
## Packet Protection Keys {#protection-keys}
QUIC derives packet protection keys in the same way that TLS derives record
protection keys.
Each encryption level has separate secret values for protection of packets sent
in each direction. These traffic secrets are derived by TLS (see Section 7.1 of
{{!TLS13}}) and are used by QUIC for all encryption levels except the Initial
encryption level. The secrets for the Initial encryption level are computed
based on the client's initial Destination Connection ID, as described in
{{initial-secrets}}.
The keys used for packet protection are computed from the TLS secrets using the
KDF provided by TLS. In TLS 1.3, the HKDF-Expand-Label function described in
Section 7.1 of {{!TLS13}} is used, using the hash function from the negotiated
cipher suite. Other versions of TLS MUST provide a similar function in order to
be used with QUIC.
The current encryption level secret and the label "quic key" are input to the
KDF to produce the AEAD key; the label "quic iv" is used to derive the IV, see
{{aead}}. The header protection key uses the "quic hp" label, see
{{header-protect}}. Using these labels provides key separation between QUIC
and TLS, see {{key-diversity}}.
The KDF used for initial secrets is always the HKDF-Expand-Label function from
TLS 1.3 (see {{initial-secrets}}).
## Initial Secrets {#initial-secrets}
Initial packets are protected with a secret derived from the Destination
Connection ID field from the client's first Initial packet of the
connection. Specifically:
~~~
initial_salt = 0xef4fb0abb47470c41befcf8031334fae485e09a0
initial_secret = HKDF-Extract(initial_salt,
client_dst_connection_id)
client_initial_secret = HKDF-Expand-Label(initial_secret,
"client in", "",
Hash.length)
server_initial_secret = HKDF-Expand-Label(initial_secret,
"server in", "",
Hash.length)
~~~
The hash function for HKDF when deriving initial secrets and keys is SHA-256
{{!SHA=DOI.10.6028/NIST.FIPS.180-4}}.
The connection ID used with HKDF-Expand-Label is the Destination Connection ID
in the Initial packet sent by the client. This will be a randomly-selected
value unless the client creates the Initial packet after receiving a Retry
packet, where the Destination Connection ID is selected by the server.
The value of initial_salt is a 20 byte sequence shown in the figure in
hexadecimal notation. Future versions of QUIC SHOULD generate a new salt value,
thus ensuring that the keys are different for each version of QUIC. This
prevents a middlebox that only recognizes one version of QUIC from seeing or
modifying the contents of packets from future versions.
The HKDF-Expand-Label function defined in TLS 1.3 MUST be used for Initial
packets even where the TLS versions offered do not include TLS 1.3.
{{test-vectors-initial}} contains test vectors for the initial packet
encryption.
Note:
: The Destination Connection ID is of arbitrary length, and it could be zero
length if the server sends a Retry packet with a zero-length Source Connection
ID field. In this case, the Initial keys provide no assurance to the client
that the server received its packet; the client has to rely on the exchange
that included the Retry packet for that property.
## AEAD Usage {#aead}
The Authentication Encryption with Associated Data (AEAD) {{!AEAD}} function
used for QUIC packet protection is the AEAD that is negotiated for use with the
TLS connection. For example, if TLS is using the TLS_AES_128_GCM_SHA256, the
AEAD_AES_128_GCM function is used.
Packets are protected prior to applying header protection ({{header-protect}}).
The unprotected packet header is part of the associated data (A). When removing
packet protection, an endpoint first removes the header protection.
All QUIC packets other than Version Negotiation and Retry packets are protected
with an AEAD algorithm {{!AEAD}}. Prior to establishing a shared secret, packets
are protected with AEAD_AES_128_GCM and a key derived from the Destination
Connection ID in the client's first Initial packet (see {{initial-secrets}}).
This provides protection against off-path attackers and robustness against QUIC
version unaware middleboxes, but not against on-path attackers.
QUIC can use any of the ciphersuites defined in {{!TLS13}} with the exception of
TLS_AES_128_CCM_8_SHA256. The AEAD for that ciphersuite, AEAD_AES_128_CCM_8
{{?CCM=RFC6655}}, does not produce a large enough authentication tag for use
with the header protection designs provided (see {{header-protect}}). All other
ciphersuites defined in {{!TLS13}} have a 16-byte authentication tag and produce
an output 16 bytes larger than their input.
The key and IV for the packet are computed as described in {{protection-keys}}.
The nonce, N, is formed by combining the packet protection IV with the packet
number. The 62 bits of the reconstructed QUIC packet number in network byte
order are left-padded with zeros to the size of the IV. The exclusive OR of the
padded packet number and the IV forms the AEAD nonce.
The associated data, A, for the AEAD is the contents of the QUIC header,
starting from the flags byte in either the short or long header, up to and
including the unprotected packet number.
The input plaintext, P, for the AEAD is the payload of the QUIC packet, as
described in {{QUIC-TRANSPORT}}.
The output ciphertext, C, of the AEAD is transmitted in place of P.
Some AEAD functions have limits for how many packets can be encrypted under the
same key and IV (see for example {{AEBounds}}). This might be lower than the
packet number limit. An endpoint MUST initiate a key update ({{key-update}})
prior to exceeding any limit set for the AEAD that is in use.
## Header Protection {#header-protect}
Parts of QUIC packet headers, in particular the Packet Number field, are
protected using a key that is derived separate to the packet protection key and
IV. The key derived using the "quic hp" label is used to provide
confidentiality protection for those fields that are not exposed to on-path
elements.
This protection applies to the least-significant bits of the first byte, plus
the Packet Number field. The four least-significant bits of the first byte are
protected for packets with long headers; the five least significant bits of the
first byte are protected for packets with short headers. For both header forms,
this covers the reserved bits and the Packet Number Length field; the Key Phase
bit is also protected for packets with a short header.
The same header protection key is used for the duration of the connection, with
the value not changing after a key update (see {{key-update}}). This allows
header protection to be used to protect the key phase.
This process does not apply to Retry or Version Negotiation packets, which do
not contain a protected payload or any of the fields that are protected by this
process.
### Header Protection Application
Header protection is applied after packet protection is applied (see {{aead}}).
The ciphertext of the packet is sampled and used as input to an encryption
algorithm. The algorithm used depends on the negotiated AEAD.
The output of this algorithm is a 5 byte mask which is applied to the protected
header fields using exclusive OR. The least significant bits of the first byte
of the packet are masked by the least significant bits of the first mask byte,
and the packet number is masked with the remaining bytes. Any unused bytes of
mask that might result from a shorter packet number encoding are unused.
{{pseudo-hp}} shows a sample algorithm for applying header protection. Removing
header protection only differs in the order in which the packet number length
(pn_length) is determined.
~~~
mask = header_protection(hp_key, sample)
pn_length = (packet[0] & 0x03) + 1
if (packet[0] & 0x80) == 0x80:
# Long header: 4 bits masked
packet[0] ^= mask[0] & 0x0f
else:
# Short header: 5 bits masked
packet[0] ^= mask[0] & 0x1f
# pn_offset is the start of the Packet Number field.
packet[pn_offset:pn_offset+pn_length] ^= mask[1:1+pn_length]
~~~
{: #pseudo-hp title="Header Protection Pseudocode"}
{{fig-sample}} shows the protected fields of long and short headers marked with
an E. {{fig-sample}} also shows the sampled fields.
~~~
Long Header:
+-+-+-+-+-+-+-+-+
|1|1|T T|E E E E|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Version -> Length Fields ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Short Header:
+-+-+-+-+-+-+-+-+
|0|1|S|E E E E E|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Destination Connection ID (0/32..144) ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Common Fields:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|E E E E E E E E E Packet Number (8/16/24/32) E E E E E E E E...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| [Protected Payload (8/16/24)] ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sampled part of Protected Payload (128) ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Protected Payload Remainder (*) ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~~~
{: #fig-sample title="Header Protection and Ciphertext Sample"}
Before a TLS ciphersuite can be used with QUIC, a header protection algorithm
MUST be specified for the AEAD used with that ciphersuite. This document
defines algorithms for AEAD_AES_128_GCM, AEAD_AES_128_CCM, AEAD_AES_256_GCM,
AEAD_AES_256_CCM (all AES AEADs are defined in {{!AEAD=RFC5116}}), and
AEAD_CHACHA20_POLY1305 {{!CHACHA=RFC8439}}. Prior to TLS selecting a
ciphersuite, AES header protection is used ({{hp-aes}}), matching the
AEAD_AES_128_GCM packet protection.
### Header Protection Sample {#hp-sample}
The header protection algorithm uses both the header protection key and a sample
of the ciphertext from the packet Payload field.
The same number of bytes are always sampled, but an allowance needs to be made
for the endpoint removing protection, which will not know the length of the
Packet Number field. In sampling the packet ciphertext, the Packet Number field
is assumed to be 4 bytes long (its maximum possible encoded length).
An endpoint MUST discard packets that are not long enough to contain a complete
sample.
To ensure that sufficient data is available for sampling, packets are padded so
that the combined lengths of the encoded packet number and protected payload is
at least 4 bytes longer than the sample required for header protection. For the
AEAD functions defined in {{?TLS13}}, which have 16-byte expansions and 16-byte
header protection samples, this results in needing at least 3 bytes of frames in
the unprotected payload if the packet number is encoded on a single byte, or 2
bytes of frames for a 2-byte packet number encoding.
The sampled ciphertext for a packet with a short header can be determined by the
following pseudocode:
~~~
sample_offset = 1 + len(connection_id) + 4
sample = packet[sample_offset..sample_offset+sample_length]
~~~
For example, for a packet with a short header, an 8 byte connection ID, and
protected with AEAD_AES_128_GCM, the sample takes bytes 13 to 28 inclusive
(using zero-based indexing).
A packet with a long header is sampled in the same way, noting that multiple
QUIC packets might be included in the same UDP datagram and that each one is
handled separately.
~~~
sample_offset = 6 + len(destination_connection_id) +
len(source_connection_id) +
len(payload_length) + 4
if packet_type == Initial:
sample_offset += len(token_length) +
len(token)
sample = packet[sample_offset..sample_offset+sample_length]
~~~
### AES-Based Header Protection {#hp-aes}
This section defines the packet protection algorithm for AEAD_AES_128_GCM,
AEAD_AES_128_CCM, AEAD_AES_256_GCM, and AEAD_AES_256_CCM. AEAD_AES_128_GCM and
AEAD_AES_128_CCM use 128-bit AES {{!AES=DOI.10.6028/NIST.FIPS.197}} in
electronic code-book (ECB) mode. AEAD_AES_256_GCM, and AEAD_AES_256_CCM use
256-bit AES in ECB mode.
This algorithm samples 16 bytes from the packet ciphertext. This value is used
as the input to AES-ECB. In pseudocode:
~~~
mask = AES-ECB(hp_key, sample)
~~~
### ChaCha20-Based Header Protection {#hp-chacha}
When AEAD_CHACHA20_POLY1305 is in use, header protection uses the raw ChaCha20
function as defined in Section 2.4 of {{!CHACHA}}. This uses a 256-bit key and
16 bytes sampled from the packet protection output.
The first 4 bytes of the sampled ciphertext are interpreted as a 32-bit number
in little-endian order and are used as the block count. The remaining 12 bytes
are interpreted as three concatenated 32-bit numbers in little-endian order and
used as the nonce.
The encryption mask is produced by invoking ChaCha20 to protect 5 zero bytes. In
pseudocode:
~~~
counter = DecodeLE(sample[0..3])
nonce = DecodeLE(sample[4..7], sample[8..11], sample[12..15])
mask = ChaCha20(hp_key, counter, nonce, {0,0,0,0,0})
~~~
## Receiving Protected Packets
Once an endpoint successfully receives a packet with a given packet number, it
MUST discard all packets in the same packet number space with higher packet
numbers if they cannot be successfully unprotected with either the same key, or
- if there is a key update - the next packet protection key (see
{{key-update}}). Similarly, a packet that appears to trigger a key update, but
cannot be unprotected successfully MUST be discarded.
Failure to unprotect a packet does not necessarily indicate the existence of a
protocol error in a peer or an attack. The truncated packet number encoding
used in QUIC can cause packet numbers to be decoded incorrectly if they are
delayed significantly.
## Use of 0-RTT Keys {#using-early-data}
If 0-RTT keys are available (see {{enable-0rtt}}), the lack of replay protection
means that restrictions on their use are necessary to avoid replay attacks on
the protocol.
A client MUST only use 0-RTT keys to protect data that is idempotent. A client
MAY wish to apply additional restrictions on what data it sends prior to the
completion of the TLS handshake. A client otherwise treats 0-RTT keys as
equivalent to 1-RTT keys, except that it MUST NOT send ACKs with 0-RTT keys.
A client that receives an indication that its 0-RTT data has been accepted by a
server can send 0-RTT data until it receives all of the server's handshake
messages. A client SHOULD stop sending 0-RTT data if it receives an indication
that 0-RTT data has been rejected.
A server MUST NOT use 0-RTT keys to protect packets; it uses 1-RTT keys to
protect acknowledgements of 0-RTT packets. A client MUST NOT attempt to
decrypt 0-RTT packets it receives and instead MUST discard them.
Note:
: 0-RTT data can be acknowledged by the server as it receives it, but any
packets containing acknowledgments of 0-RTT data cannot have packet protection
removed by the client until the TLS handshake is complete. The 1-RTT keys
necessary to remove packet protection cannot be derived until the client
receives all server handshake messages.
## Receiving Out-of-Order Protected Frames {#pre-hs-protected}
Due to reordering and loss, protected packets might be received by an endpoint
before the final TLS handshake messages are received. A client will be unable
to decrypt 1-RTT packets from the server, whereas a server will be able to
decrypt 1-RTT packets from the client.
However, a server MUST NOT process data from incoming 1-RTT protected packets
before verifying either the client Finished message or - in the case that the
server has chosen to use a pre-shared key - the pre-shared key binder (see
Section 4.2.11 of {{!TLS13}}). Verifying these values provides the server with
an assurance that the ClientHello has not been modified. Packets protected with
1-RTT keys MAY be stored and later decrypted and used once the handshake is
complete.
A server could receive packets protected with 0-RTT keys prior to receiving a
TLS ClientHello. The server MAY retain these packets for later decryption in
anticipation of receiving a ClientHello.
# Key Update
Once the 1-RTT keys are established and the short header is in use, it is
possible to update the keys. The KEY_PHASE bit in the short header is used to
indicate whether key updates have occurred. The KEY_PHASE bit is initially set
to 0 and then inverted with each key update.
The KEY_PHASE bit allows a recipient to detect a change in keying material
without necessarily needing to receive the first packet that triggered the
change. An endpoint that notices a changed KEY_PHASE bit can update keys and
decrypt the packet that contains the changed bit.
This mechanism replaces the TLS KeyUpdate message. Endpoints MUST NOT send a
TLS KeyUpdate message. Endpoints MUST treat the receipt of a TLS KeyUpdate
message as a connection error of type 0x10a, equivalent to a fatal TLS alert of
unexpected_message (see {{tls-errors}}).
An endpoint MUST NOT initiate more than one key update at a time. A new key
cannot be used until the endpoint has received and successfully decrypted a
packet with a matching KEY_PHASE.
A receiving endpoint detects an update when the KEY_PHASE bit does not match
what it is expecting. It creates a new secret (see Section 7.2 of {{!TLS13}})
and the corresponding read key and IV using the KDF function provided by TLS.
The header protection key is not updated.
If the packet can be decrypted and authenticated using the updated key and IV,
then the keys the endpoint uses for packet protection are also updated. The
next packet sent by the endpoint will then use the new keys.
An endpoint does not always need to send packets when it detects that its peer
has updated keys. The next packet that it sends will simply use the new keys.
If an endpoint detects a second update before it has sent any packets with
updated keys, it indicates that its peer has updated keys twice without awaiting
a reciprocal update. An endpoint MUST treat consecutive key updates as a fatal
error and abort the connection.
An endpoint SHOULD retain old keys for a period of no more than three times the
Probe Timeout (PTO, see {{QUIC-RECOVERY}}). After this period, old keys and
their corresponding secrets SHOULD be discarded. Retaining keys allow endpoints
to process packets that were sent with old keys and delayed in the network.
Packets with higher packet numbers always use the updated keys and MUST NOT be
decrypted with old keys.
This ensures that once the handshake is complete, packets with the same
KEY_PHASE will have the same packet protection keys, unless there are multiple
key updates in a short time frame succession and significant packet reordering.
~~~
Initiating Peer Responding Peer
@M QUIC Frames
New Keys -> @N
@N QUIC Frames
-------->
QUIC Frames @M
New Keys -> @N
QUIC Frames @N
<--------
~~~
{: #ex-key-update title="Key Update"}
A packet that triggers a key update could arrive after successfully processing a
packet with a higher packet number. This is only possible if there is a key
compromise and an attack, or if the peer is incorrectly reverting to use of old
keys. Because the latter cannot be differentiated from an attack, an endpoint
MUST immediately terminate the connection if it detects this condition.
In deciding when to update keys, endpoints MUST NOT exceed the limits for use of
specific keys, as described in Section 5.5 of {{!TLS13}}.
# Security of Initial Messages
Initial packets are not protected with a secret key, so they are subject to
potential tampering by an attacker. QUIC provides protection against attackers
that cannot read packets, but does not attempt to provide additional protection
against attacks where the attacker can observe and inject packets. Some forms
of tampering -- such as modifying the TLS messages themselves -- are detectable,
but some -- such as modifying ACKs -- are not.
For example, an attacker could inject a packet containing an ACK frame that
makes it appear that a packet had not been received or to create a false
impression of the state of the connection (e.g., by modifying the ACK Delay).
Note that such a packet could cause a legitimate packet to be dropped as a
duplicate. Implementations SHOULD use caution in relying on any data which is
contained in Initial packets that is not otherwise authenticated.
It is also possible for the attacker to tamper with data that is carried in
Handshake packets, but because that tampering requires modifying TLS handshake
messages, that tampering will cause the TLS handshake to fail.
# QUIC-Specific Additions to the TLS Handshake
QUIC uses the TLS handshake for more than just negotiation of cryptographic
parameters. The TLS handshake validates protocol version selection, provides
preliminary values for QUIC transport parameters, and allows a server to perform
return routeability checks on clients.
## Protocol and Version Negotiation {#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 does not prevent version downgrade
prior to the completion of the handshake, though it means that a downgrade
causes a handshake failure.
QUIC requires that the cryptographic handshake provide authenticated protocol
negotiation. TLS uses Application Layer Protocol Negotiation (ALPN)
{{!RFC7301}} to select an application protocol. Unless another mechanism is
used for agreeing on an application protocol, endpoints MUST use ALPN for this
purpose. When using ALPN, endpoints MUST abort a connection if an application
protocol is not negotiated.
An application-layer protocol MAY restrict the QUIC versions that it can operate
over. Servers MUST select an application protocol compatible with the QUIC
version that the client has selected. If the server cannot select a compatible
combination of application protocol and QUIC version, it MUST abort the
connection. A client MUST abort a connection if the server picks an incompatible
combination of QUIC version and ALPN identifier.
## QUIC Transport Parameters Extension {#quic_parameters}
QUIC transport parameters are carried in a TLS extension. Different versions of
QUIC might define a different format for this struct.
Including transport parameters in the TLS handshake provides integrity
protection for these values.
~~~
enum {
quic_transport_parameters(0xffa5), (65535)
} ExtensionType;
~~~
The `extension_data` field of the quic_transport_parameters extension contains a
value that is defined by the version of QUIC that is in use. The
quic_transport_parameters extension carries a TransportParameters struct when
the version of QUIC defined in {{QUIC-TRANSPORT}} is used.
The quic_transport_parameters extension is carried in the ClientHello and the
EncryptedExtensions messages during the handshake.
While the transport parameters are technically available prior to the completion
of the handshake, they cannot be fully trusted until the handshake completes,
and reliance on them should be minimized. However, any tampering with the
parameters will cause the handshake to fail.
Endpoints MUST NOT send this extension in a TLS connection that does not use
QUIC (such as the use of TLS with TCP defined in {{!TLS13}}). A fatal
unsupported_extension alert MUST be sent if this extension is received when the
transport is not QUIC.
## Removing the EndOfEarlyData Message {#remove-eoed}
The TLS EndOfEarlyData message is not used with QUIC. QUIC does not rely on
this message to mark the end of 0-RTT data or to signal the change to Handshake
keys.
Clients MUST NOT send the EndOfEarlyData message. A server MUST treat receipt
of a CRYPTO frame in a 0-RTT packet as a connection error of type
PROTOCOL_VIOLATION.
As a result, EndOfEarlyData does not appear in the TLS handshake transcript.
# 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.
## Replay Attacks with 0-RTT
As described in Section 8 of {{!TLS13}}, use of TLS early data comes with an
exposure to replay attack. The use of 0-RTT in QUIC is similarly vulnerable to
replay attack.
Endpoints MUST implement and use the replay protections described in {{!TLS13}},
however it is recognized that these protections are imperfect. Therefore,
additional consideration of the risk of replay is needed.
QUIC is not vulnerable to replay attack, except via the application protocol
information it might carry. The management of QUIC protocol state based on the
frame types defined in {{QUIC-TRANSPORT}} is not vulnerable to replay.
Processing of QUIC frames is idempotent and cannot result in invalid connection
states if frames are replayed, reordered or lost. QUIC connections do not
produce effects that last beyond the lifetime of the connection, except for
those produced by the application protocol that QUIC serves.
Note:
: TLS session tickets and address validation tokens are used to carry QUIC
configuration information between connections. These MUST NOT be used to
carry application semantics. The potential for reuse of these tokens means
that they require stronger protections against replay.
A server that accepts 0-RTT on a connection incurs a higher cost than accepting
a connection without 0-RTT. This includes higher processing and computation
costs. Servers need to consider the probability of replay and all associated
costs when accepting 0-RTT.
Ultimately, the responsibility for managing the risks of replay attacks with
0-RTT lies with an application protocol. An application protocol that uses QUIC
MUST describe how the protocol uses 0-RTT and the measures that are employed to
protect against replay attack. An analysis of replay risk needs to consider
all QUIC protocol features that carry application semantics.
Disabling 0-RTT entirely is the most effective defense against replay attack.
QUIC extensions MUST describe how replay attacks affects their operation, or
prohibit their use in 0-RTT. Application protocols MUST either prohibit the use
of extensions that carry application semantics in 0-RTT or provide replay
mitigation strategies.
## Packet Reflection Attack Mitigation {#reflection}
A small ClientHello that results in a large block of handshake messages from a
server can be used in packet reflection attacks to amplify the traffic generated
by an attacker.
QUIC includes three defenses against this attack. First, the packet containing a
ClientHello MUST be padded to a minimum size. Second, if responding to an
unverified source address, the server is forbidden to send more than three UDP
datagrams in its first flight (see Section 8.1 of {{QUIC-TRANSPORT}}). Finally,
because acknowledgements of Handshake packets are authenticated, a blind
attacker cannot forge them. Put together, these defenses limit the level of
amplification.
## Peer Denial of Service {#useless}
QUIC, TLS, and HTTP/2 all contain messages that have legitimate uses in some
contexts, but that can be abused to cause a peer to expend processing resources
without having any observable impact on the state of the connection. If
processing is disproportionately large in comparison to the observable effects
on bandwidth or state, then this could allow a malicious peer to exhaust
processing capacity without consequence.
QUIC prohibits the sending of empty `STREAM` frames unless they are marked with
the FIN bit. This prevents `STREAM` frames from being sent that only waste
effort.
While there are legitimate uses for some redundant packets, implementations
SHOULD track redundant packets and treat excessive volumes of any non-productive
packets as indicative of an attack.
## Header Protection Analysis {#header-protect-analysis}
Header protection relies on the packet protection AEAD being a pseudorandom
function (PRF), which is not a property that AEAD algorithms
guarantee. Therefore, no strong assurances about the general security of this
mechanism can be shown in the general case. The AEAD algorithms described in
this document are assumed to be PRFs.
The header protection algorithms defined in this document take the form:
~~~
protected_field = field XOR PRF(hp_key, sample)
~~~
This construction is secure against chosen plaintext attacks (IND-CPA) {{IMC}}.
Use of the same key and ciphertext sample more than once risks compromising
header protection. Protecting two different headers with the same key and
ciphertext sample reveals the exclusive OR of the protected fields. Assuming
that the AEAD acts as a PRF, if L bits are sampled, the odds of two ciphertext
samples being identical approach 2^(-L/2), that is, the birthday bound. For the
algorithms described in this document, that probability is one in 2^64.
Note:
: In some cases, inputs shorter than the full size required by the packet
protection algorithm might be used.
To prevent an attacker from modifying packet headers, the header is transitively
authenticated using packet protection; the entire packet header is part of the
authenticated additional data. Protected fields that are falsified or modified
can only be detected once the packet protection is removed.
An attacker could guess values for packet numbers and have an endpoint confirm
guesses through timing side channels. Similarly, guesses for the packet number
length can be trialed and exposed. If the recipient of a packet discards
packets with duplicate packet numbers without attempting to remove packet
protection they could reveal through timing side-channels that the packet number
matches a received packet. For authentication to be free from side-channels,
the entire process of header protection removal, packet number recovery, and
packet protection removal MUST be applied together without timing and other
side-channels.
For the sending of packets, construction and protection of packet payloads and
packet numbers MUST be free from side-channels that would reveal the packet
number or its encoded size.
## Key Diversity
In using TLS, the central key schedule of TLS is used. As a result of the TLS
handshake messages being integrated into the calculation of secrets, the
inclusion of the QUIC transport parameters extension ensures that handshake and
1-RTT keys are not the same as those that might be produced by a server running
TLS over TCP. To avoid the possibility of cross-protocol key synchronization,
additional measures are provided to improve key separation.
The QUIC packet protection keys and IVs are derived using a different label than
the equivalent keys in TLS.
To preserve this separation, a new version of QUIC SHOULD define new labels for
key derivation for packet protection key and IV, plus the header protection
keys. This version of QUIC uses the string "quic". Other versions can use a
version-specific label in place of that string.
The initial secrets use a key that is specific to the negotiated QUIC version.
New QUIC versions SHOULD define a new salt value used in calculating initial
secrets.
# IANA Considerations
This document does not create any new IANA registries, but it registers the
values in the following registries:
* TLS ExtensionsType Registry {{!TLS-REGISTRIES=RFC8447}} - IANA is to register
the quic_transport_parameters extension found in {{quic_parameters}}. The
Recommended column is to be marked Yes. The TLS 1.3 Column is to include CH
and EE.
--- back
# Sample Initial Packet Protection {#test-vectors-initial}
This section shows examples of packet protection for Initial packets so that
implementations can be verified incrementally. These packets use an 8-byte
client-chosen Destination Connection ID of 0x8394c8f03e515708. Values for both
server and client packet protection are shown together with values in
hexadecimal.
## Keys
The labels generated by the HKDF-Expand-Label function are:
client in:
: 00200f746c73313320636c69656e7420696e00
server in:
: 00200f746c7331332073657276657220696e00
quic key:
: 00100e746c7331332071756963206b657900
quic iv:
: 000c0d746c733133207175696320697600
quic hp:
: 00100d746c733133207175696320687000
The initial secret is common:
~~~
initial_secret = HKDF-Extract(initial_salt, cid)
= 4496d3903d3f97cc5e45ac5790ddc686
683c7c0067012bb09d900cc21832d596
~~~
The secrets for protecting client packets are:
~~~
client_initial_secret
= HKDF-Expand-Label(initial_secret, "client in", _, 32)
= 8a3515a14ae3c31b9c2d6d5bc58538ca
5cd2baa119087143e60887428dcb52f6
key = HKDF-Expand-Label(client_initial_secret, "quic key", _, 16)
= 98b0d7e5e7a402c67c33f350fa65ea54
iv = HKDF-Expand-Label(client_initial_secret, "quic iv", _, 12)
= 19e94387805eb0b46c03a788
hp = HKDF-Expand-Label(client_initial_secret, "quic hp", _, 16)
= 0edd982a6ac527f2eddcbb7348dea5d7
~~~
The secrets for protecting server packets are:
~~~
server_initial_secret
= HKDF-Expand-Label(initial_secret, "server in", _, 32)
= 47b2eaea6c266e32c0697a9e2a898bdf
5c4fb3e5ac34f0e549bf2c58581a3811
key = HKDF-Expand-Label(server_initial_secret, "quic key", _, 16)
= 9a8be902a9bdd91d16064ca118045fb4
iv = HKDF-Expand-Label(server_initial_secret, "quic iv", _, 12)
= 0a82086d32205ba22241d8dc
hp = HKDF-Expand-Label(server_initial_secret, "quic hp", _, 16)
= 94b9452d2b3c7c7f6da7fdd8593537fd
~~~
## Client Initial
The client sends an Initial packet. The unprotected payload of this packet
contains the following CRYPTO frame, plus enough PADDING frames to make an 1163
byte payload:
~~~
060040c4010000c003036660261ff947 cea49cce6cfad687f457cf1b14531ba1
4131a0e8f309a1d0b9c4000006130113 031302010000910000000b0009000006
736572766572ff01000100000a001400 12001d00170018001901000101010201
03010400230000003300260024001d00 204cfdfcd178b784bf328cae793b136f
2aedce005ff183d7bb14952072366470 37002b0003020304000d0020001e0403
05030603020308040805080604010501 060102010402050206020202002d0002
0101001c00024001
~~~
The unprotected header includes the connection ID and a 4 byte packet number
encoding for a packet number of 2:
~~~
c3ff000012508394c8f03e51570800449f00000002
~~~
Protecting the payload produces output that is sampled for header protection.
Because the header uses a 4 byte packet number encoding, the first 16 bytes of
the protected payload is sampled, then applied to the header:
~~~
sample = 0000f3a694c75775b4e546172ce9e047
mask = AES-ECB(hp, sample)[0..4]
= 020dbc1958
header[0] ^= mask[0] & 0x0f
= c1
header[17..20] ^= mask[1..4]
= 0dbc195a
header = c1ff000012508394c8f03e51570800449f0dbc195a
~~~
The resulting protected packet is:
~~~
c1ff000012508394c8f03e5157080044 9f0dbc195a0000f3a694c75775b4e546
172ce9e047cd0b5bee5181648c727adc 87f7eae54473ec6cba6bdad4f5982317
4b769f12358abd292d4f3286934484fb 8b239c38732e1f3bbbc6a003056487eb
8b5c88b9fd9279ffff3b0f4ecf95c462 4db6d65d4113329ee9b0bf8cdd7c8a8d
72806d55df25ecb66488bc119d7c9a29 abaf99bb33c56b08ad8c26995f838bb3
b7a3d5c1858b8ec06b839db2dcf918d5 ea9317f1acd6b663cc8925868e2f6a1b
da546695f3c3f33175944db4a11a346a fb07e78489e509b02add51b7b203eda5
c330b03641179a31fbba9b56ce00f3d5 b5e3d7d9c5429aebb9576f2f7eacbe27
bc1b8082aaf68fb69c921aa5d33ec0c8 510410865a178d86d7e54122d55ef2c2
bbc040be46d7fece73fe8a1b24495ec1 60df2da9b20a7ba2f26dfa2a44366dbc
63de5cd7d7c94c57172fe6d79c901f02 5c0010b02c89b395402c009f62dc053b
8067a1e0ed0a1e0cf5087d7f78cbd94a fe0c3dd55d2d4b1a5cfe2b68b86264e3
51d1dcd858783a240f893f008ceed743 d969b8f735a1677ead960b1fb1ecc5ac
83c273b49288d02d7286207e663c45e1 a7baf50640c91e762941cf380ce8d79f
3e86767fbbcd25b42ef70ec334835a3a 6d792e170a432ce0cb7bde9aaa1e7563
7c1c34ae5fef4338f53db8b13a4d2df5 94efbfa08784543815c9c0d487bddfa1
539bc252cf43ec3686e9802d651cfd2a 829a06a9f332a733a4a8aed80efe3478
093fbc69c8608146b3f16f1a5c4eac93 20da49f1afa5f538ddecbbe7888f4355
12d0dd74fd9b8c99e3145ba84410d8ca 9a36dd884109e76e5fb8222a52e1473d
a168519ce7a8a3c32e9149671b16724c 6c5c51bb5cd64fb591e567fb78b10f9f
6fee62c276f282a7df6bcf7c17747bc9 a81e6c9c3b032fdd0e1c3ac9eaa5077d
e3ded18b2ed4faf328f49875af2e36ad 5ce5f6cc99ef4b60e57b3b5b9c9fcbcd
4cfb3975e70ce4c2506bcd71fef0e535 92461504e3d42c885caab21b782e2629
4c6a9d61118cc40a26f378441ceb48f3 1a362bf8502a723a36c63502229a462c
c2a3796279a5e3a7f81a68c7f81312c3 81cc16a4ab03513a51ad5b54306ec1d7
8a5e47e2b15e5b7a1438e5b8b2882dbd ad13d6a4a8c3558cae043501b68eb3b0
40067152337c051c40b5af809aca2856 986fd1c86a4ade17d254b6262ac1bc07
7343b52bf89fa27d73e3c6f3118c9961 f0bebe68a5c323c2d84b8c29a2807df6
63635223242a2ce9828d4429ac270aab 5f1841e8e49cf433b1547989f419caa3
c758fff96ded40cf3427f0761b678daa 1a9e5554465d46b7a917493fc70f9ec5
e4e5d786ca501730898aaa1151dcd318 29641e29428d90e6065511c24d3109f7
cba32225d4accfc54fec42b733f95852 52ee36fa5ea0c656934385b468eee245
315146b8c047ed27c519b2c0a52d33ef e72c186ffe0a230f505676c5324baa6a
e006a73e13aa8c39ab173ad2b2778eea 0b34c46f2b3beae2c62a2c8db238bf58
fc7c27bdceb96c56d29deec87c12351b fd5962497418716a4b915d334ffb5b92
ca94ffe1e4f78967042638639a9de325 357f5f08f6435061e5a274703936c06f
c56af92c420797499ca431a7abaa4618 63bca656facfad564e6274d4a741033a
ca1e31bf63200df41cdf41c10b912bec
~~~
## Server Initial
The server sends the following payload in response, including an ACK frame, a
CRYPTO frame, and no PADDING frames:
~~~
0d0000000018410a020000560303eefc e7f7b37ba1d1632e96677825ddf73988
cfc79825df566dc5430b9a045a120013 0100002e00330024001d00209d3c940d
89690b84d08a60993c144eca684d1081 287c834d5311bcf32bb9da1a002b0002
0304
~~~
The header from the server includes a new connection ID and a 2-byte packet
number encoding for a packet number of 1:
~~~
c1ff00001205f067a5502a4262b50040740001
~~~
As a result, after protection, the header protection sample is taken starting
from the third protected octet:
~~~
sample = c4c2a2303d297e3c519bf6b22386e3d0
mask = 75f7ec8b62
header = c4ff00001205f067a5502a4262b5004074f7ed
~~~
The final protected packet is then:
~~~
c4ff00001205f067a5502a4262b50040 74f7ed5f01c4c2a2303d297e3c519bf6
b22386e3d0bd6dfc6612167729803104 1bb9a79c9f0f9d4c5877270a660f5da3
6207d98b73839b2fdf2ef8e7df5a51b1 7b8c68d864fd3e708c6c1b71a98a3318
15599ef5014ea38c44bdfd387c03b527 5c35e009b6238f831420047c7271281c
cb54df7884
~~~
# Change Log
> **RFC Editor's Note:** Please remove this section prior to publication of a
> final version of this document.
Issue and pull request numbers are listed with a leading octothorp.
## Since draft-ietf-quic-tls-18
- Increased the set of permissible frames in 0-RTT (#2344, #2355)
## Since draft-ietf-quic-tls-17
- Endpoints discard initial keys as soon as handshake keys are available (#1951,
#2045)
- Use of ALPN or equivalent is mandatory (#2263, #2284)
## Since draft-ietf-quic-tls-14
- Update the salt used for Initial secrets (#1970)
- Clarify that TLS_AES_128_CCM_8_SHA256 isn't supported (#2019)
- Change header protection
- Sample from a fixed offset (#1575, #2030)
- Cover part of the first byte, including the key phase (#1322, #2006)
- TLS provides an AEAD and KDF function (#2046)
- Clarify that the TLS KDF is used with TLS (#1997)
- Change the labels for calculation of QUIC keys (#1845, #1971, #1991)
- Initial keys are discarded once Handshake are avaialble (#1951, #2045)
## Since draft-ietf-quic-tls-13
- Updated to TLS 1.3 final (#1660)
## Since draft-ietf-quic-tls-12
- Changes to integration of the TLS handshake (#829, #1018, #1094, #1165, #1190,
#1233, #1242, #1252, #1450)
- The cryptographic handshake uses CRYPTO frames, not stream 0
- QUIC packet protection is used in place of TLS record protection
- Separate QUIC packet number spaces are used for the handshake
- Changed Retry to be independent of the cryptographic handshake
- Limit the use of HelloRetryRequest to address TLS needs (like key shares)
- Changed codepoint of TLS extension (#1395, #1402)
## Since draft-ietf-quic-tls-11
- Encrypted packet numbers.
## Since draft-ietf-quic-tls-10
- No significant changes.
## Since draft-ietf-quic-tls-09
- Cleaned up key schedule and updated the salt used for handshake packet
protection (#1077)
## Since draft-ietf-quic-tls-08
- Specify value for max_early_data_size to enable 0-RTT (#942)
- Update key derivation function (#1003, #1004)
## Since draft-ietf-quic-tls-07
- Handshake errors can be reported with CONNECTION_CLOSE (#608, #891)
## Since draft-ietf-quic-tls-05
No significant changes.
## Since draft-ietf-quic-tls-04
- Update labels used in HKDF-Expand-Label to match TLS 1.3 (#642)
## Since draft-ietf-quic-tls-03
No significant changes.
## Since draft-ietf-quic-tls-02
- Updates to match changes in transport draft
## Since draft-ietf-quic-tls-01
- Use TLS alerts to signal TLS errors (#272, #374)
- Require ClientHello to fit in a single packet (#338)
- The second client handshake flight is now sent in the clear (#262, #337)
- The QUIC header is included as AEAD Associated Data (#226, #243, #302)
- Add interface necessary for client address validation (#275)
- Define peer authentication (#140)
- Require at least TLS 1.3 (#138)
- Define transport parameters as a TLS extension (#122)
- Define handling for protected packets before the handshake completes (#39)
- Decouple QUIC version and ALPN (#12)
## Since draft-ietf-quic-tls-00
- Changed bit used to signal key phase
- Updated key phase markings during the handshake
- Added TLS interface requirements section
- Moved to use of TLS exporters for key derivation
- Moved TLS error code definitions into this document
## Since draft-thomson-quic-tls-01
- Adopted as base for draft-ietf-quic-tls
- Updated authors/editors list
- Added status note
# Acknowledgments
{:numbered="false"}
This document has benefited from input from Dragana Damjanovic, Christian
Huitema, Jana Iyengar, Adam Langley, Roberto Peon, Eric Rescorla, Ian Swett, and
many others.
# Contributors
{:numbered="false"}
Ryan Hamilton was originally an author of this specification.
