wdiff draft-ietf-tsvwg-dtls-over-sctp-bis-00.txt draft-ietf-tsvwg-dtls-over-sctp-bis-01.txt

TSVWG M. Westerlund
Internet-Draft J. Preuß Mattsson
Obsoletes: 6083 (if approved) C. Porfiri
Intended status: Standards Track Ericsson
Expires: 11 November 2021 13 January 2022 M. Tüxen
Münster Univ. of Appl. Sciences
10 May
12 July 2021

Datagram Transport Layer Security (DTLS) over Stream Control
Transmission Protocol (SCTP)
draft-ietf-tsvwg-dtls-over-sctp-bis-00
draft-ietf-tsvwg-dtls-over-sctp-bis-01

Abstract

This document describes a proposed update for the usage of the
Datagram Transport Layer Security (DTLS) protocol to protect user
messages sent over the Stream Control Transmission Protocol (SCTP).

DTLS over SCTP provides mutual authentication, confidentiality,
integrity protection, and replay protection for applications that use
SCTP as their transport protocol and allows client/server
applications to communicate in a way that is designed to give
communications privacy and to prevent eavesdropping and detect
tampering or message forgery.

Applications using DTLS over SCTP can use almost all transport
features provided by SCTP and its extensions. This document intends
to obsolete RFC 6083 and removes the 16 kB limitation on user message
size by defining a secure user message fragmentation so that multiple
DTLS records can be used to protect a single user message. It
further updates the DTLS versions to use, as well as the HMAC
algorithms for SCTP-AUTH, and simplifies the secure implementation by
some stricter requirements on the establishment procedures.

Discussion Venues

This note is to be removed before publishing as an RFC.

Discussion of this document takes place on the TSVWG Working Group
mailing list (tsvwg@ietf.org), which is archived at
https://mailarchive.ietf.org/arch/browse/tsvwg/.

Source for this draft and an issue tracker can be found at
https://github.com/gloinul/draft-westerlund-tsvwg-dtls-over-sctp-bis.

Status of This Memo

This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.

Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.

Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."

This Internet-Draft will expire on 11 November 2021. 13 January 2022.

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Please review these documents carefully, as they describe your rights
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Table of Contents

1. Introduction
1.1. Overview
1.1.1. Comparison with TLS for SCTP
1.1.2. Changes from RFC 6083
1.2. Terminology DTLS Version
1.3. Terminology
1.4. Abbreviations
2. Conventions
3. DTLS Considerations
3.1. Version of DTLS
3.2. Cipher Suites and Cryptographic Parameters
3.3. Message Sizes
3.4. Replay Protection
3.5. Path MTU Discovery
3.6. Retransmission of Messages
4. SCTP Considerations
4.1. Mapping of DTLS Records
4.2. DTLS Connection Handling
4.3. Payload Protocol Identifier Usage
4.4. Stream Usage
4.5. Chunk Handling
4.6. SCTP-AUTH Hash Function
4.7. Renegotiation
4.7.1. DTLS 1.2 Considerations
4.7.2. DTLS 1.3 Considerations
4.8. DTLS Epochs
4.8.1. DTLS 1.2 Considerations
4.8.2. DTLS 1.3 Considerations
4.9. Handling of Endpoint-Pair Shared Secrets
4.9.1. DTLS 1.2 Considerations
4.9.2. DTLS 1.3 Considerations
4.10. Shutdown
5. DTLS over SCTP Service
5.1. Adaptation Layer Indication in INIT/INIT-ACK
5.2. DTLS/SCTP "dtls_over_sctp_maximum_message_size" Extension
5.3. DTLS over SCTP Initialization
5.4.
5.3. Client Use Case
5.5.
5.4. Server Use Case
5.6.
5.5. RFC 6083 Fallback
6. IANA Socket API Considerations
6.1. Socket Option to Get the HMAC Identifier being Sent
(SCTP_SEND_HMAC_IDENT)
6.2. Exposing the HMAC Identifiers being Received
6.3. Socket Option to Expose HMAC Identifier Usage
(SCTP_EXPOSE_HMAC_IDENT_CHANGES)
7. IANA Considerations
7.1. TLS Exporter Label
6.2. DTLS "dtls_over_sctp_buffer_size_limit" Extension
6.3.
7.2. SCTP Parameter
7. Adaptation Layer Indication Code Point
8. Security Considerations
7.1.
8.1. Cryptographic Considerations
7.2.
8.2. Downgrade Attacks
7.3. DTLS/SCTP Message Sizes
7.4.
8.3. Authentication and Policy Decisions
7.5.
8.4. Privacy Considerations
7.6.
8.5. Pervasive Monitoring
8. Acknowledgments
9. Acknowledgments
10. References
9.1.
10.1. Normative References
9.2.
10.2. Informative References
Appendix A. Motivation for Changes
Authors' Addresses

1. Introduction

1.1. Overview

This document describes the usage of the Datagram Transport Layer
Security (DTLS) protocol, as defined in DTLS 1.2 [RFC6347], and DTLS
1.3 [I-D.ietf-tls-dtls13], over the Stream Control Transmission
Protocol (SCTP), as defined in [RFC4960] with Authenticated Chunks
for SCTP (SCTP-AUTH) [RFC4895].

This specification provides mutual authentication of endpoints,
confidentiality, integrity protection, and replay protection of user
messages for applications that use SCTP as their transport protocol.
Thus
Thus, it allows client/server applications to communicate in a way
that is designed to give communications privacy and to prevent
eavesdropping and detect tampering or message forgery. DTLS/SCTP
uses DTLS for mutual authentication, key exchange with perfect
forward secrecy for SCTP-AUTH, and confidentiality of user messages.
DTLS/SCTP use SCTP and SCTP-AUTH for integrity protection and replay
protection of user messages.

Applications using DTLS over SCTP can use almost all transport
features provided by SCTP and its extensions. DTLS/SCTP supports:

* preservation of message boundaries.

* a large number of unidirectional and bidirectional streams.

* ordered and unordered delivery of SCTP user messages.

* the partial reliability extension as defined in [RFC3758].

* the dynamic address reconfiguration extension as defined in
[RFC5061].

* large user messages.

The method described in this document requires that the SCTP
implementation supports the optional feature of fragmentation of SCTP
user messages as defined in [RFC4960]. To efficiently implement and
support larger user messages it The implementation is also recommended that I-DATA
chunks as defined in [RFC8260] as well as
required to have an SCTP API (for example the one described in
[RFC6458]) that supports partial user message delivery and also
recommended that I-DATA chunks as discussed defined in [RFC6458]. [RFC8260] is used to
efficiently implement and support larger user messages.

To simplify implementation and reduce the risk for security holes,
limitations have been defined such that STARTTLS as specified in
[RFC3788] is no longer supported.

1.1.1. Comparison with TLS for SCTP

TLS, from which DTLS was derived, is designed to run on top of a
byte-stream-oriented transport protocol providing a reliable, in-
sequence delivery. TLS over SCTP as described in [RFC3436] has some
serious limitations:

* It does not support the unordered delivery of SCTP user messages.

* It does not support partial reliability as defined in [RFC3758].

* It only supports the usage of the same number of streams in both
directions.

* It uses a TLS connection for every bidirectional stream, which
requires a substantial amount of resources and message exchanges
if a large number of streams is used.

1.1.2. Changes from RFC 6083

The DTLS over SCTP solution defined in RFC 6083 had the following
limitation:

* The maximum user message size is 2^14 bytes, which is a single
DTLS record limit.

This update that replaces RFC6083 RFC 6083 defines the following changes:

* Removes the limitations on user messages sizes by defining a
secure fragmentation mechanism.

* Defines a DTLS extension for the endpoints to declare the user
message size supported to be received.

* Mandates that more modern DTLS version are required (DTLS 1.2 or
1.3)

* Mandates use of modern HMAC algorithm (SHA-256) in the SCTP
authentication extension [RFC4895].

* Recommends support of [RFC8260] to enable interleaving of large
SCTP user messages to avoid scheduling issues.

* Recommends support of partial message delivery API, see [RFC6458]
if larger usage messages are intended to be used.

* Applies stricter requirements on always using DTLS for all user
messages in the SCTP association.

* Requires that SCTP-AUTH is applied to all SCTP Chunks that can be
authenticated.

1.2. Terminology

This document uses

* Requires support of partial delivery of user messages.

Mandating DTLS 1.2 or DTLS 1.3 instead to using DTLS 1.0 limits the following terms:

Association: An SCTP association.

Stream: A unidirectional stream
lifetime of an SCTP association. It is
uniquely identified by a stream identifier.

1.3. Abbreviations

DTLS: Datagram Transport Layer Security

MTU: Maximum Transmission Unit

PPID: Payload Protocol Identifier

SCTP: Stream Control Transmission Protocol

TCP: Transmission Control Protocol

TLS: Transport Layer Security

2. Conventions

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", DTLS connection and
"OPTIONAL" in this document are to the data volume which can be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.

3. DTLS Considerations

3.1. Version of
transferred over a DTLS connection. This document is based on DTLS 1.3 [I-D.ietf-tls-dtls13], but works
also for cause by:

* The number of renegotiations in DTLS 1.2 [RFC6347]. Earlier versions is limited to 65534
compared to unlimited in DTLS 1.0.

* The number of KeyUpdates in DTLS MUST NOT be
used. It 1.3 is expected that limited to 65532 and
renegotiations are not supported.

1.2. DTLS Version

DTLS/SCTP as described in defined by this document
will work with future versions of DTLS.

3.2. Cipher Suites

For can use either DTLS 1.2, 1.2
[RFC6347] or DTLS 1.3 [I-D.ietf-tls-dtls13]. Some crucial difference
between the cipher suites forbidden by [RFC7540] MUST NOT be
used. Cipher suites without encryption MUST NOT be used.

3.3. Message Sizes

DTLS/SCTP, automatically fragments and reassembles DTLS versions make it necessary for a user messages.
This specification defines how of DTLS/SCTP
to fragment make an informed choice of the user messages into DTLS records, where each version to use based on their
application's requirements. In general, DTLS 1.3 record allows is to preferred
being a maximum newer protocol that addresses known vulnerabilities and only
defines strong algorithms without known major weaknesses at the time
of 2^14
protected bytes. Each DTLS record adds publication.

However, some overhead, thus applications using
records of maximum possible size DTLS/SCTP are recommended to minimize the
overhead.

The sequence of DTLS records is then fragmented into DATA or I-DATA
Chunks to fit the path MTU by SCTP. The largest possible user
messages using the mechanism defined in this specification is 2^64-1
bytes.

The security operations semi-permanent
nature and reassembly process requires that the
protected user message, i.e. use SCTP associations with DTLS record overhead, lifetimes that are more than a
few hours, and where there is buffered
in the receiver. This buffer space will thus put a limit on the
largest size of plain text user message that can be transferred
securely.

A receiver that doesn't support partial delivery significant cost of user messages
from bringing down the
SCTP [RFC6458] will advertise its largest supported protected
message using SCTP's mechanism for Advertised Receiver Window Credit
(a_rwnd) as specified association in Section 3.3.2 of [RFC4960]. Note that the
a_rwnd value is across all user messages being delivered. order to restart it. For a receiver supporting partial delivery of user messages a_rwnd
will not limit the maximum size such DTLS/SCTP usages
that need either of:

* Periodic re-authentication of both endpoints (not only the DTLS protected user message
because the receiver can move parts
client).

* Periodic rerunning of Diffie-Hellman key-exchange to provide
Perfect Forward Secrecy (PFS) to reduce the DTLS protected user
message from impact any key-reveal.

* Perform SCTP-AUTH re-keying.

At the SCTP receiver buffer into a buffer for time of publication DTLS
processing. When each complete 1.3 does not support any of these,
where DTLS record have been received from
SCTP, it 1.2 renegotiation functionality can be processed and the plain text fragment can, provide this
functionality in its
turn, be partially delivered to the user application.

Thus, the limit context of DTLS/SCTP. The application will have
to analyze its needs and requirements on the largest user message is dependent above and based on buffering
allocated for DTLS processing as well as this
select the DTLS/SCTP API DTLS version to the
application. use.

To ensure that the sender have some understanding of
the maximum receiver size a TLS extension
"dtls_over_sctp_maximum_message_size" Section 5.2 is used address known vulnerabilities in DTLS 1.2 this document describes
and mandates implementation constraints on ciphers, protocol options
and how to signal use the endpoints receiver capability when it comes to user message size.

All implementors DTLS renegotiation mechanism.

In the rest of this specification MUST support user messages the document, unless the version of
at least 16383 bytes. Where 16383 bytes DTLS is
specifically called out the supported message
size text applies to both versions of DTLS.

1.3. Terminology

This document uses the following terms:

Association: An SCTP association.

Stream: A unidirectional stream of an SCTP association. It is
uniquely identified by a stream identifier.

1.4. Abbreviations

DTLS: Datagram Transport Layer Security

MTU: Maximum Transmission Unit

PFS: Perfect Forward Secrecy

PPID: Payload Protocol Identifier

SCTP: Stream Control Transmission Protocol

TCP: Transmission Control Protocol

TLS: Transport Layer Security

ULP: Upper Layer Protocol

2. Conventions

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in RFC 6083. By requiring this message size document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.

3. DTLS Considerations

3.1. Version of DTLS

This document defines the usage of either DTLS 1.3
[I-D.ietf-tls-dtls13], or DTLS 1.2 [RFC6347]. Earlier versions of
DTLS MUST NOT be used (see [RFC8996]). It is expected that DTLS/SCTP
as described in this document,
we ensure compatibility document will work with existing usage future versions of RFC 6083, not
requiring DTLS.

3.2. Cipher Suites and Cryptographic Parameters

For DTLS 1.2, the upper layer protocol cipher suites forbidden by [RFC7540] MUST NOT be
used. For all versions of DTLS, cryptographic parameters giving
confidentiality and Perfect Forward Secrecy (PFS) MUST be used.

3.3. Message Sizes

DTLS/SCTP, automatically fragments and reassembles user messages.
This specification defines how to implement additional features fragment the user messages into
DTLS records, where each DTLS 1.3 record allows a maximum of 2^14
protected bytes. Each DTLS record adds some overhead, thus using
records of maximum possible size are recommended to minimize the
transmitted overhead.

The sequence of DTLS records is then fragmented into DATA or requirements.

Due to SCTP's capability I-DATA
Chunks to transmit concurrent fit the path MTU by SCTP. The largest possible user
messages using the
total memory consumption mechanism defined in the receiver this specification is not bounded. In cases
where one or more user messages are affected by packet loss, 2^64-1
bytes.

The security operations and reassembly process requires that the DATA
chunks may require more data
protected user message, i.e., with DTLS record overhead, is buffered
in the receiver's buffer.

The necessary buffering receiver. This buffer space for will thus put a single user message of
dtls_over_sctp_maximum_message_size (MMS) is dependent limit on the
implementation.

When no partial data delivery is supported, the message size is
limited by the a_rwnd as this is the
largest protected size of plain text user message that can be received and then processed transferred
securely. However, by DTLS and where mandating the plain
text use of the partial delivery of
user message is expected to be messages from SCTP and assuming that no more than two messages received on
the signalled MMS.

With partial processing same stream are interleaved (as it is possible to have a receiver
implementation that is bound to use no more buffer space than MMS
(for the plaintext) plus one maximum size case when using the API
defined in [RFC6458]) the required buffering prior to DTLS record. The later
assumes that one processing
can realign be limited to a single DTLS record per used incoming stream.
This enables the start of DTLS/SCTP implementation to provide the buffer after Upper Layer
Protocol (ULP) with each DTLS
record record's content when it has been consumed. A more realistic implementation is two
maximum DTLS record sizes.

If an implementation supports partial delivery in both the SCTP API
and the ULP API,
decrypted and also its integrity been verified enabling partial processing in the DTLS/SCTP
implementation, then user
message delivery to the buffering space ULP. Implementations can trade-off buffer
memory requirements in the DTLS/SCTP DTLS layer ought
to be no more than two with transport overhead by
using smaller DTLS records. In which case the MMS to set

The DTLS/SCTP implementation is
dependent on the ULP expected to behave very similar to
just SCTP when it comes to handling of user messages and dealing with
large user messages and their reassembly and processing. Making it
the endpoints capabilities. ULP responsible for handling any resource contention related to
large user messages.

3.4. Replay Protection

SCTP-AUTH [RFC4895] does not have explicit replay protection.
However, the combination of SCTP-AUTH's protection of DATA or I-DATA
chunks and SCTP user message handling will prevent third party
attempts to inject or replay SCTP packets resulting in impact on the
received protected user message. In fact fact, this document's solution
is dependent on SCTP-AUTH and SCTP to prevent reordering reordering,
duplication, and removal of the DTLS records within each protected
user message. This includes detection of changes to what DTLS
records start and end the SCTP user message, and removal of DTLS
records before an increment to the epoch. Without SCTP-AUTH, these
would all have required explicit handling.

DTLS optionally supports record replay detection. Such replay
detection could result in the DTLS layer dropping valid messages
received outside of the DTLS replay window. As DTLS/SCTP provides
replay protection even without DTLS replay protection, the replay
detection of DTLS MUST NOT be used.

3.5. Path MTU Discovery

DTLS Path MTU Discovery MUST NOT be used. Since SCTP provides own Path
MTU discovery and fragmentation/reassembly for user messages, and
according to Section 3.3, DTLS can send maximum sized DTLS Records.

3.6. Retransmission of Messages

SCTP provides a reliable and in-sequence transport service for DTLS
messages that require it. See Section 4.4. Therefore, DTLS
procedures for retransmissions MUST NOT be used.

4. SCTP Considerations

4.1. Mapping of DTLS Records

The SCTP implementation MUST support fragmentation of user messages
using DATA [RFC4960], and optionally I-DATA [RFC8260] chunks.

DTLS/SCTP works as a shim layer between the user message API and
SCTP. The fragmentation works similar as the DTLS fragmentation of
handshake messages. On the sender side a user message fragmented
into fragments m0, m1, m2, each no larger than 2^14 - 1 = 16383
bytes.

m0 | m1 | m2 | ... = user_message

The resulting fragments are protected with DTLS and the records are
concatenated

user_message' = DTLS( m0 ) | DTLS( m1 ) | DTLS( m2 ) ...

The new user_message', i.e i.e., the protected user message, is the input
to SCTP.

On the receiving side DTLS is used to decrypt the records. If decrypt the individual records.
There are three failure cases an implementation needs to detect and
then act on:

1. Failure in decryption and integrity verification process of any
DTLS record. Due to SCTP-AUTH preventing delivery of injected or
corrupt fragments of the protected user message this should only
occur in case of implementation errors or internal hardware
failures.

2. In case the SCTP layer indicates an end to a user message, e.g.
when receiving a MSG_EOR in a recvmsg() call when using the API
described in [RFC6458], and the last buffered DTLS record length
field does not match, i.e., the DTLS record is incomplete.

3. Unable to perform the decryption processes due to lack of
resources, such as memory, and have to abandon the user message
fragment. This specification is defined such that the needed
resources for the DTLS/SCTP operations are bounded for a given
number of concurrent transmitted SCTP streams or unordered user
messages.

The above failure cases all result in the receiver failing to
recreate the full user message. This is a failure of the transport
service that is not possible to recover from in the DTLS/SCTP layer
and the sender could believe the complete message have been
delivered. This error MUST NOT be ignored, as SCTP lacks any
facility to declare a DTLS
decryption fails, failure on a specific stream or user message,
the DTLS connection and the SCTP association are SHOULD be terminated. Due A
valid exception to SCTP-AUTH preventing delivery the termination of corrupt
fragments the SCTP association is if the
receiver is capable of notifying the protected user message this should only occur ULP about the failure in
case
delivery and the ULP is capable of implementation errors recovering from this failure.

Note that if the SCTP extension for Partial Reliability (PR-SCTP)
[RFC3758] is used for a user message, user message may be partially
delivered or internal hardware failures. abandoned. These failures are not a reason for
terminating the DTLS connection and SCTP association.

The DTLS Connection ID SHOULD NOT be negotiated (Section 9 of
[I-D.ietf-tls-dtls13]). If DTLS 1.3 is used, the length field MUST
NOT
be omitted included and a 16 bit 16-bit sequence number SHOULD be used.

4.2. DTLS Connection Handling

The DTLS connection MUST be established at the beginning of the SCTP
association and be terminated when the SCTP association is
terminated, (i.e. (i.e., there's only one DTLS connection within one
association). A DTLS connection MUST NOT span multiple SCTP
associations.

As it is required to establish the DTLS connection at the beginning
of the SCTP association, either of the peers should never send any
SCTP user messages that are not protected by DTLS. So So, the case that
an endpoint receives data that is not either DTLS messages on Strea Stream
0 or protecetd protected user messages in the form of a sequence of DTLS
Records on any stream is a protocol violation. The receiver MAY
terminate the SCTP association due to this protocol violation.

4.3. Payload Protocol Identifier Usage

SCTP Payload Protocol Identifiers are assigned by IANA. Application
protocols using DTLS over SCTP SHOULD register and use a separate
Payload Protocol Identifier (PPID) and SHOULD NOT reuse the PPID that
they registered for running directly over SCTP.

Using the same PPID does not harm as long as the application can
determine whether or not DTLS is used. However, for protocol
analyzers, for example, it is much easier if a separate PPID is used.

This means, in particular, that there is no specific PPID for DTLS.

4.4. Stream Usage

All DTLS Handshake, Alert, or ChangeCipherSpec (DTLS 1.2 only)
messages MUST be transported on stream 0 with unlimited reliability
and with the ordered delivery feature.

DTLS messages of the record protocol, which carries the protected
user messages, SHOULD use multiple streams other than stream 0; they
MAY use stream 0 as long as the ordered message semantics is
acceptable. 0. On stream 0 protected user messages as well as any
DTLS messages that isn't aren't record protocol will be mixed, thus the
additional head of line blocking can occur.

4.5. Chunk Handling

DATA chunks of SCTP MUST be sent in an authenticated way as described
in [RFC4895]. All other chunks that can be authenticated, i.e. i.e., all
chunk types that can be listed in the Chunk List Parameter [RFC4895],
MUST also be sent in an authenticated way. This makes sure that an
attacker cannot modify the stream in which a message is sent or
affect the ordered/unordered delivery of the message.

If PR-SCTP as defined in [RFC3758] is used, FORWARD-TSN chunks MUST
also be sent in an authenticated way as described in [RFC4895]. This
makes sure that it is not possible for an attacker to drop messages
and use forged FORWARD-TSN, SACK, and/or SHUTDOWN chunks to hide this
dropping.

I-DATA chunk type as defined in [RFC8260] is RECOMMENDED to be
supported to avoid some of the down sides that large user messages
have on blocking transmission of later arriving high priority user
messages. However, the support is not mandated and negotiated
independently from DTLS/SCTP. If I-DATA chunks are used used, then they
MUST be sent in an authenticated way as described in [RFC4895].

4.6. SCTP-AUTH Hash Function

When using DTLS/SCTP, the SHA-256 Message Digest Algorithm MUST be
supported in the SCTP-AUTH [RFC4895] implementation. SHA-1 MUST NOT
be used when using DTLS/SCTP. [RFC4895] requires support and
inclusion of of SHA-1 in the HMAC-ALGO parameter, thus, to meet both
requirements the HMAC-ALGO parameter will include both SHA-256 and
SHA-1 with SHA-256 listed prior to SHA-1 to indicate the preference.

4.7. Renegotiation

Renegotiation

DTLS 1.2 renegotiation enables rekeying (with ephemeral Diffie-
Hellman) of both DTLS and SCTP-AUTH as well as mutual
reauthentication inside an DTLS 1.2 connection. It is up to the
upper layer to use/allow it or not. Application writers should be
aware that allowing renegotiations may result in changes of security
parameters. Renegotiation has been removed from DTLS 1.3 and partly
replaced with Post-Handshake post-handshake messages such as KeyUpdate. See
Section 7 8 for security considerations regarding rekeying.

4.7.1. DTLS 1.2 Considerations

Before sending during renegotiation a ClientHello message or
ServerHello message, the DTLS endpoint MUST ensure that all DTLS
messages using the previous epoch have been acknowledged by the SCTP
peer in a non-revokable way.

Prior to processing a received ClientHello message or ServerHello
message, all other received SCTP user messages that are buffered in
the SCTP layer and can be delivered to the DTLS layer MUST be read
and processed by DTLS.

4.7.2. DTLS 1.3 Considerations

Before sending a KeyUpdate message, the DTLS endpoint MUST ensure
that all DTLS messages have been acknowledged by the SCTP peer in a
non-revokable way. After sending the KeyUpdate message, it stops
sending DTLS messages until the corresponding Ack message has been
processed.

Prior to processing a received KeyUpdate message, all other received
SCTP user messages that are buffered in the SCTP layer and can be
delivered to the DTLS layer MUST be read and processed by DTLS.

4.8. DTLS Epochs

In general, DTLS implementations SHOULD discard records from earlier
epochs, as described
epochs. However, in Section 4.2.1 of [I-D.ietf-tls-dtls13]. To
avoid discarding messages, the processing guidelines in Section 4.2.1 context of a reliable communication this is
not appropriate.

4.8.1. DTLS 1.3 [I-D.ietf-tls-dtls13] or 1.2 Considerations

The procedures of Section 4.1 or DTLS 1.2 of [RFC6347] should MUST NOT be followed.
Instead, when currently using epoch n, for n > 1, DTLS packets from
epoch n - 1 and n MUST be processed.

4.8.2. DTLS 1.3 Considerations

The procedures of Section 4.2.1 of [I-D.ietf-tls-dtls13] are
irrelevant. When receiving DTLS packets using epoch n, no DTLS
packets from earlier epochs are received.

4.9. Handling of Endpoint-Pair Shared Secrets

SCTP-AUTH [RFC4895] is keyed using Endpoint-Pair Shared Secrets. In
SCTP associations where DTLS is used, DTLS is used to establish these
secrets. The endpoints MUST NOT use another mechanism for
establishing shared secrets for SCTP-AUTH. The endpoint-pair shared
secret for Shared Key Identifier 0 is empty and MUST be used when
establishing a DTLS connection. In

4.9.1. DTLS 1.2,
whenever 1.2 Considerations

Whenever the main master secret changes, a 64-byte shared secret is
derived from every main master secret and provided as a new endpoint-pair
shared secret by using the TLS-Exporter. In DTLS 1.3, the exporter_secret
never change. For DTLS 1.3, the exporter is TLS-Exporter described in [RFC8446].
For DTLS 1.2, [RFC5705]. The
64-byte shared secret MUST be provided to the exporter SCTP stack as soon as
the computation is described in [RFC5705]. possible. The exporter MUST use the label given
in Section Section 6 7 and no context. The new Shared Key Identifier
MUST be the old Shared Key Identifier incremented by 1. If

After sending the old one is 65535, DTLS Finished message, the active SCTP-AUTH key
MUST be switched to the new one one.

Once the initial Finished message from the peer has been processed by
DTLS, the SCTP-AUTH key with Shared Key Identifier 0 MUST be removed.
Once the Finished message using DTLS epoch n with n > 2 has been
processed by DTLS, the SCTP-AUTH key with Shared Key Identifier n - 2
MUST be removed.

4.9.2. DTLS 1.3 Considerations

When the exporter_secret can be computed, a 64-byte shared secret is
derived from it and provided as a new endpoint-pair shared secret by
using the TLS-Exporter described in [RFC8446]. The 64-byte shared
secret MUST be provided to the SCTP stack as soon as the computation
is possible. The exporter MUST use the label given in
Section Section 7 and no context. This shared secret MUST use Shared
Key Identifier 1.

Before

After sending the DTLS Finished message, the active SCTP-AUTH key
MUST be switched to the new one. use Shared Key Identifier 1.

Once the corresponding Finished message from the peer has been
received, processed by DTLS,
the old SCTP-AUTH key SHOULD with Shared Key Identifier 0 MUST be removed.

4.10. Shutdown

To prevent DTLS from discarding DTLS user messages while it is
shutting down, a CloseNotify message MUST only be sent after all
outstanding SCTP user messages have been acknowledged by the SCTP
peer and MUST NOT be revoked by the SCTP peer. in a non-revokable way.

Prior to processing a received CloseNotify, all other received SCTP
user messages that are buffered in the SCTP layer MUST be read and
processed by DTLS.

5. DTLS over SCTP Service

The adoption of DTLS over SCTP according to the current description
is meant to add to SCTP the option for transferring encrypted data.
When DTLS over SCTP is used, all data being transferred MUST be
protected by chunk authentication and DTLS encrypted. Chunks that
need to be received in an authenticated way will be specified in the
CHUNK list parameter according to [RFC4895]. Error handling for
authenticated chunks is according to [RFC4895].

5.1. Adaptation Layer Indication in INIT/INIT-ACK

At the initialization of the association, a sender of the INIT or
INIT ACK chunk that intends to use DTLS/SCTP as specified in this
specification MUST include an Adaptation Layer Indication Parameter
with the IANA assigned value TBD to inform its peer that it is able
to support DTLS over SCTP per this specification.

5.2. DTLS/SCTP "dtls_over_sctp_maximum_message_size" Extension

The endpoint's DTLS/SCTP maximum message size is declared in the
"dtls_over_sctp_maximum_message_size" TLS extension. The
ExtensionData of the extension is MessageSizeLimit:

uint64 MessageSizeLimit;

The value of MessageSizeLimit is the maximum plaintext user message
size in octets that the endpoint is willing to receive. When the
"dtls_over_sctp_maximum_message_size" extension is negotiated, an
endpoint MUST NOT send a user message larger than the
MessageSizeLimit value it receives from its peer.

This value is the length of the user message before DTLS
fragmentation and protection. The value does not account for the
expansion due to record protection, record padding, or the DTLS
header.

The "dtls_over_sctp_maximum_message_size" MUST be used to negotiate
maximum message size for DTLS/SCTP. A DTLS/SCTP endpoint MUST treat
the omission of "dtls_over_sctp_maximum_message_size" as a fatal
error unless supporting RFC 6083 fallback Section 5.6, and it SHOULD
generate an "illegal_parameter" alert. Endpoints MUST NOT send a
"dtls_over_sctp_maximum_message_size" extension with a value smaller
than 16383. An endpoint MUST treat receipt of a smaller value as a
fatal error and generate DTLS encrypted. Chunks that
need to be received in an "illegal_parameter" alert.

The "dtls_over_sctp_maximum_message_size" MUST NOT authenticated way will be send specified in TLS or the
CHUNK list parameter according to [RFC4895]. Error handling for
authenticated chunks is according to [RFC4895].

5.1. Adaptation Layer Indication in DTLS versions earlier than 1.2. In DTLS 1.3, INIT/INIT-ACK

At the server sends initialization of the
"dtls_over_sctp_maximum_message_size" extension in association, a sender of the
EncryptedExtensions message.

During resumption, INIT or
INIT ACK chunk that intends to use DTLS/SCTP as specified in this
specification MUST include an Adaptation Layer Indication Parameter
with the maximum message size IANA assigned value TBD (Section 7.2) to inform its peer
that it is renegotiated.

5.3. able to support DTLS over SCTP per this specification.

5.2. DTLS over SCTP Initialization

Initialization of DTLS/SCTP requires all the following options to be
part of the INIT/INIT-ACK handshake:

RANDOM: defined in [RFC4895]

CHUNKS: list of permitted chunks, defined in [RFC4895]

HMAC-ALGO: defined in [RFC4895]

ADAPTATION-LAYER-INDICATION: defined in [RFC5061]

When all the above options are present, the Association will start
with support of DTLS/SCTP. The set of options indicated are the
DTLS/SCTP Mandatory Options. No data transfer is permitted before
DTLS handshake is complete. Chunk bundling is permitted according to
[RFC4960]. The DTLS handshake will enable authentication of both the
peers and also have the declare their support message size.

The extension described in this document is given by the following
message exchange.

--- INIT[RANDOM; CHUNKS; HMAC-ALGO; ADAPTATION-LAYER-IND] --->
<- INIT-ACK[RANDOM; CHUNKS; HMAC-ALGO; ADAPTATION-LAYER-IND] -
------------------------ COOKIE-ECHO ------------------------>
<------------------------ COOKIE-ACK -------------------------
---------------- AUTH; DATA[DTLS Handshake] ----------------->
...
...
<--------------- AUTH; DATA[DTLS Handshake] ------------------

5.4.

5.3. Client Use Case

When a SCTP Client client initiates an SCTP Association with DTLS/SCTP DTLS protection,
i.e., the SCTP INIT containing DTSL/SCTP Mandatory Options, it can
receive an INIT-ACK also containing DTLS/SCTP Mandatory Options, in
that case the Association will proceed as specified in the previous
Section 5.3 5.2 section. If the peer replies with an INIT-ACK not
containing all DTLS/SCTP Mandatory Options, the
Client can decide to keep on working client SHOULD reply
with RFC 6083 fallback, plain
data only, or to ABORT the association.

5.5. an SCTP ABORT.

5.4. Server Use Case

If a SCTP Server supports DTLS/SCTP, i.e., per this specification,
when receiving an INIT chunk with all DTLS/SCTP Mandatory Options it must
will reply with an INIT-ACK also containing the all the DTLS/SCTP
Mandatory Options, then it must follow following the sequence for DTLS initialization
Section 5.3 5.2 and the related traffic case. If a SCTP Server that
supports DTLS, when receiving DTLS and configured to use it, receives an INIT chunk with not
without all DTLS/SCTP Mandatory Options, it can decide to
continue by creating an Association SHOULD reply with RFC 6083 fallback, plain
data only or to ABORT it.

5.6. an SCTP
ABORT.

5.5. RFC 6083 Fallback

This section discusses how an endpoint supporting this specification
can fallback to follow the DTLS/SCTP behavior in RFC 6083. RFC6083. It is
recommended to define a setting that represents the policy to allow
fallback or not. However, the possibility to use fallback is based
on the ULP can operate using user messages that are no longer than
16383 bytes and where the security issues can be mitigated or
considerd
considered acceptable. Fallback is NOT RECOMMEND to be enabled as it
enables downgrade to weaker algorithms and versions of DTLS.

An SCTP client that receives an INIT-ACK endpoint that is not compliant
according this specification may in certain cases potentially perform
an fallback to RFC 6083 behavior. The first case is when the SCTP
client receives an INIT chunk or an INIT-ACK doesn't contain the SCTP-Adaptation-
Indication parameter with the DTLS/SCTP adaptation layer codepoint
but do include the SCTP-AUTH parameters on a server that are expected
to provide services using DTLS. The second case is when the INIT-ACK
do chunk
that does not contain the SCTP-Adaptation-Indication parameter with
the correct
code point, however the HMAC-ALGO or the Chunks parameters values are
such that do not fullfil the requirement of this specification but do
meet the requirements of RFC 6083. In either of these DTLS/SCTP adaptation layer codepoint, see Section 7.2, may in
certain cases the
client could attempt DTLS per potentially perform a fallback to RFC 6083 as fallback. behavior.
However, the fallback attempt should only be performed if policy says
that is acceptable.

If fallback is allowed allowed, it is possible that the client will send plain
text user messages prior to DTLS handshake as it client will send
plain text user messages prior to DTLS handshake as it is allowed per
RFC 6083. So that needs to be part of the consideration for a policy
allowing fallback.

6. Socket API Considerations

This section describes how the socket API defined in [RFC6458] is
extended to provide a way for the application to observe the HMAC
algorithms used for sending and receiving of AUTH chunks.

Please note that this section is informational only.

A socket API implementation based on [RFC6458] is, by means of the
existing SCTP_AUTHENTICATION_EVENT event, extended to provide the
event notification whenever a new HMAC algorithm is used in a
received AUTH chunk.

Furthermore, two new socket options for the level IPPROTO_SCTP and
the name SCTP_SEND_HMAC_IDENT and SCTP_EXPOSE_HMAC_IDENT_CHANGES are
defined as described below. The first socket option is used to query
the HMAC algorithm used for sending AUTH chunks. The second enables
the monitoring of HMAC algorithms used in received AUTH chunks via
the SCTP_AUTHENTICATION_EVENT event.

Support for the SCTP_SEND_HMAC_IDENT and
SCTP_EXPOSE_HMAC_IDENT_CHANGES socket options also needs to be added
to the function sctp_opt_info().

6.1. Socket Option to Get the HMAC Identifier being Sent
(SCTP_SEND_HMAC_IDENT)

During the SCTP association establishment a HMAC Identifier is
selected which is used by an SCTP endpoint when sending AUTH chunks.
An application can access the result of this selection by using this
read-only socket option, which uses the level IPPROTO_SCTP and the
name SCTP_SEND_HMAC_IDENT.

The following structure is used to access HMAC Identifier used for
sending AUTH chunks:

struct sctp_assoc_value {
sctp_assoc_t assoc_id;
uint32_t assoc_value;
};

assoc_id: This parameter is ignored for one-to-one style sockets.
For one-to-many style sockets, the application fills in an
association identifier. It is allowed per RFC
6083. So that needs an error to be part of use
SCTP_{FUTURE|CURRENT|ALL}_ASSOC in assoc_id.

assoc_value: This parameter contains the consideration HMAC Identifier used for a policy
allowing fallback. When performing
sending AUTH chunks.

6.2. Exposing the HMAC Identifiers being Received

Section 6.1.8 of [RFC6458] defines the DTLS handshake, SCTP_AUTHENTICATION_EVENT
event, which uses the
server is required accepting that lack following structure:

struct sctp_authkey_event {
uint16_t auth_type;
uint16_t auth_flags;
uint32_t auth_length;
uint16_t auth_keynumber;
uint32_t auth_indication;
sctp_assoc_t auth_assoc_id;
};

This document updates this structure to

struct sctp_authkey_event {
uint16_t auth_type;
uint16_t auth_flags;
uint32_t auth_length;
uint16_t auth_identifier; /* formerly auth_keynumber */
uint32_t auth_indication;
sctp_assoc_t auth_assoc_id;
};

by renaming auth_keynumber to auth_identifier. auth_identifier just
replaces auth_keynumber in the context of [RFC6458]. In addition to
that, the TLS extension
"dtls_over_sctp_maximum_message_size" SCTP_AUTHENTICATION_EVENT event is extended to also
indicate when a new HMAC Identifier is received and can't treat it such reporting is
explicitly enabled as fatal
error. described in Section 6.3. In this case
auth_indication is SCTP_AUTH_NEW_HMAC and the "dtls_over_sctp_maximum_message_size" TLS
extension new HMAC identifier is present
reported in auth_identifier.

6.3. Socket Option to Expose HMAC Identifier Usage
(SCTP_EXPOSE_HMAC_IDENT_CHANGES)

This options allows the handshake application to enable and disable the server SHALL continue
reception of SCTP_AUTHENTICATION_EVENT events when a new HMAC
Identifiers has been received in an AUTH chunk (see Section 6.2).
This read/write socket option uses the
handshake including level IPPROTO_SCTP and the extension with its value also,
name SCTP_EXPOSE_HMAC_IDENT_CHANGES. It is needed to provide
backwards compatibility and from the default is that
point follow this specification. In case these events are not
reported.

The following structure is used to enable or disable the TLS option reporting of
newly received HMAC Identifiers in AUTH chunks:

struct sctp_assoc_value {
sctp_assoc_t assoc_id;
uint32_t assoc_value;
};

assoc_id: This parameter is missing
RFC 6083 applies.

6. ignored for one-to-one style sockets.
For one-to-many style sockets, the application may fill in an
association identifier or SCTP_{FUTURE|CURRENT|ALL}_ASSOC.

assoc_value: Newly received HMAC Identifiers are reported if, and
only if, this parameter is non-zero.

7. IANA Considerations

6.1.

7.1. TLS Exporter Label

RFC 6083 defined a TLS Exporter Label registry as described in
[RFC5705]. IANA is requested to update the reference for the label
"EXPORTER_DTLS_OVER_SCTP" to this specification.

6.2. DTLS "dtls_over_sctp_buffer_size_limit" Extension

This document registers the "dtls_over_sctp_maximum_message_size"
extension in the TLS "ExtensionType Values" registry established in
[RFC5246]. The "dtls_over_sctp_maximum_message_size" extension has
been assigned

7.2. SCTP Adaptation Layer Indication Code Point

[RFC5061] defined a code point of TBD. This entry [[will be|is]] marked
as recommended ([RFC8447] and marked as "Encrypted" in (D)TLS 1.3
[I-D.ietf-tls-dtls13]. The IANA registry [RFC8447] [[will
list|lists]] this extension as "Recommended" (i.e., "Y") and
indicates that it may appear for Adaptation Code Points to be
used in the ClientHello (CH) or
EncryptedExtensions (EE) messages in (D)TLS 1.3
[I-D.ietf-tls-dtls13].

6.3. SCTP Parameter Adaptation Layer Indication parameter. The registry was
at time of writing located: https://www.iana.org/assignments/sctp-
parameters/sctp-parameters.xhtml#sctp-parameters-27 IANA is requested
to assign a one Adaptation Code Point for DTLS/SCTP.

7. DTLS/SCTP per the below
proposed entry in Table 1.

+============================+=============+===========+
| Code Point (32-bit number) | Description | Reference |
+============================+=============+===========+
| 0x00000002 | DTLS/SCTP | [RFC-TBD] |
+----------------------------+-------------+-----------+

Table 1: Adaptation Code Point

RFC-Editor Note: Please replace [RFC-TBD] with the RFC number given
to this specification.

8. Security Considerations

The security considerations given in [I-D.ietf-tls-dtls13],
[RFC4895], and [RFC4960] also apply to this document.

7.1.

8.1. Cryptographic Considerations

Over the years, there have been several serious attacks on earlier
versions of Transport Layer Security (TLS), including attacks on its
most commonly used ciphers and modes of operation. [RFC7457]
summarizes the attacks that were known at the time of publishing and
BCP 195 [RFC7525] provides recommendations for improving the security
of deployed services that use TLS.

When DTLS/SCTP is used with DTLS 1.2 [RFC6347], DTLS 1.2 MUST be
configured to disable options known to provide insufficient security.
HTTP/2 [RFC7540] gives good minimum requirements based on the attacks
that where publicly known in 2015. DTLS 1.3 [I-D.ietf-tls-dtls13]
only define strong algorithms without major weaknesses at the time of
publication. Many of the TLS registries have a "Recommended" column.
Parameters not marked as "Y" are NOT RECOMMENDED to support.

DTLS 1.3 requires rekeying before algorithm specific AEAD limits have
been reached. The AEAD limits equations are equally valid for DTLS
1.2 and SHOULD be followed for DTLS/SCTP, but are not mandated by the
DTLS 1.2 specification.

HMAC-SHA-256 as used in SCTP-AUTH has a very large tag length and
very good integrity properties. The SCTP-AUTH key can be used until
the DTLS handshake is re-run at which point a new SCTP-AUTH key is
derived using the TLS-Exporter. As discussed below DTLS 1.3 does not
currently support renegotiation and lacks the capability of updating
the SCTP-AUTH key.

DTLS/SCTP is in many deployments replacing IPsec. For IPsec, NIST
(US), BSI (Germany), and ANSSI (France) recommends very frequent re-
run of Diffie-Hellman to provide Perfect Forward Secrecy. ANSSI
writes "It is recommended to force the periodic renewal of the keys,
e.g.
e.g., every hour and every 100 GB of data, in order to limit the
impact of a key compromise." [ANSSI-DAT-NT-003].

For many DTLS/SCTP deployments the DTLS connections are expected to
have very long lifetimes of months or even years. For connections
with such long lifetimes there is a need to frequently re-
authenticate both client and server.

When using DTLS 1.2 [RFC6347], AEAD limits, frequant frequent re-
authentication and frequent re-run of Diffie-Hellman can be achieved
with frequent renegotiation, see TLS 1.2 [RFC5246]. When
renegotiation is used both clients and servers MUST use the
renegotiation_info extension [RFC5746] and MUST follow the
renegotiation guidelines in BCP 195 [RFC7525]. In particular, both
clients and servers MUST NOT accept a change of identity during
renegotiation.

In DTLS 1.3 renegotiation has been removed from DTLS 1.3 and partly
replaced with Post-Handshake KeyUpdate. When using DTLS 1.3
[I-D.ietf-tls-dtls13], AEAD limits and frequent rekeying can be
achieved by sending frequent Post-Handshake post-handshake KeyUpdate messages.
Symmetric rekeying gives less protection against key leakage than re-
running Diffie-Hellman. After leakage of
application_traffic_secret_N, a passive attacker can passively
eavesdrop on all future application data sent on the connection
including application data encrypted with
application_traffic_secret_N+1, application_traffic_secret_N+2, etc.
The is no way to do Post-Handshake post-handshake server authentication or Ephemeral
Diffie-Hellman inside a DTLS 1.3 connection. Note that KeyUpdate
does not update the exporter_secret.

7.2.

For upper layer protocols where frequent re-run of Diffie-Hellman,
rekeying of SCTP-AUTH, and server reauthentication is required and
creating a new SCTP connection with DTLS 1.3 to replace the current
is not a viable option it is RECOMMENDED to use DTLS 1.2.

8.2. Downgrade Attacks

A peer supporting DTLS/SCTP according to this specification, DTLS/
SCTP according to [RFC6083] and/or SCTP without DTLS may be
vulnerable to downgrade attacks where on on-path attacker interferes
with the protocol setup to lower or disable security. If possible,
it is RECOMMENDED that the peers have a policy only allowing DTLS/
SCTP according to this specification.

7.3. DTLS/SCTP Message Sizes

The DTLS/SCTP maximum message size extension enables secure negation
of a message sizes that fit in the DTLS/SCTP buffer, which improves
security and availability. Very small plain text user fragment sizes
might generate additional work for senders and receivers, limiting
throughput and increasing exposure to denial of service.

The maximum message size extension does not protect against peer
nodes intending to negatively affect the peer node through flooding
attacks. The attacking node can both send larger messages than the
expressed capability as well as initiating a large number of
concurrent user message transmissions that never are concluded. For
the target of the attack it is more straight forward to determine
that a peer is ignoring the node's stated limitation.

7.4.

8.3. Authentication and Policy Decisions

DTLS/SCTP MUST be mutually authenticated. It is RECOMMENDED that
DTLS/SCTP is used with certificate based certificate-based authentication. All
security decisions MUST be based on the peer's authenticated
identity, not on its transport layer identity.

It is possible to authenticate DTLS endpoints based on IP addresses
in certificates. SCTP associations can use multiple IP addresses per
SCTP endpoint. Therefore, it is possible that DTLS records will be
sent from a different source IP address or to a different destination
IP address than that originally authenticated. This is not a problem
provided that no security decisions are made based on the source or
destination IP addresses.

7.5.

8.4. Privacy Considerations

[RFC6973] suggests that the privacy considerations of IETF protocols
be documented.

For each SCTP user message, the user also provides a stream
identifier, a flag to indicate whether the message is sent ordered or
unordered, and a payload protocol identifier. Although DTLS/SCTP
provides privacy for the actual user message, the other three
information fields are not confidentiality protected. They are sent
as clear text, cleartext because they are part of the SCTP DATA chunk header.

It is RECOMMENDED that DTLS/SCTP is used with certificate based
authentication in DTLS 1.3 [I-D.ietf-tls-dtls13] to provide identity
protection. DTLS/SCTP MUST be used with a key exchange method
providing Perfect Forward Secrecy. Perfect Forward Secrecy
significantly limits the amount of data that can be compromised due
to key compromise.

7.6.

8.5. Pervasive Monitoring

As required by [RFC7258], work on IETF protocols needs to consider
the effects of pervasive monitoring and mitigate them when possible.

Pervasive Monitoring is widespread surveillance of users. By
encrypting more information including user identities, DTLS 1.3
offers much better protection against pervasive monitoring.

Massive pervasive monitoring attacks relying on key exchange without
forward secrecy has been reported. By mandating perfect forward
secrecy, DTLS/SCTP effectively mitigate many forms of passive
pervasive monitoring and limits the amount of compromised data due to
key compromise.

In addition to the privacy attacks discussed above, surveillance on a
large scale may enable tracking of a user over a wider geographical
area and across different access networks. Using information from
DTLS/SCTP together with information gathered from other protocols
increases
increase the risk of identifying individual users.

9. Acknowledgments

The authors of RFC 6083 which this document is based on are Michael
Tuexen, Eric Rescorla, and Robin Seggelmann.

The RFC 6083 authors thanked Anna Brunstrom, Lars Eggert, Gorry
Fairhurst, Ian Goldberg, Alfred Hoenes, Carsten Hohendorf, Stefan
Lindskog, Daniel Mentz, and Sean Turner for their invaluable
comments.

The authors of this document want to thank GitHub user vanrein for
their contribution.

10. References

9.1.

10.1. 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/info/rfc2119>.

[RFC3758] Stewart, R., Ramalho, M., Xie, Q., Tuexen, M., and P.
Conrad, "Stream Control Transmission Protocol (SCTP)
Partial Reliability Extension", RFC 3758,
DOI 10.17487/RFC3758, May 2004,
<https://www.rfc-editor.org/info/rfc3758>.

[RFC4895] Tuexen, M., Stewart, R., Lei, P., and E. Rescorla,
"Authenticated Chunks for the Stream Control Transmission
Protocol (SCTP)", RFC 4895, DOI 10.17487/RFC4895, August
2007, <https://www.rfc-editor.org/info/rfc4895>.

[RFC4960] Stewart, R., Ed., "Stream Control Transmission Protocol",
RFC 4960, DOI 10.17487/RFC4960, September 2007,
<https://www.rfc-editor.org/info/rfc4960>.

[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246,
DOI 10.17487/RFC5246, August 2008,
<https://www.rfc-editor.org/info/rfc5246>.

[RFC5705] Rescorla, E., "Keying Material Exporters for Transport
Layer Security (TLS)", RFC 5705, DOI 10.17487/RFC5705,
March 2010, <https://www.rfc-editor.org/info/rfc5705>.

[RFC5746] Rescorla, E., Ray, M., Dispensa, S., and N. Oskov,
"Transport Layer Security (TLS) Renegotiation Indication
Extension", RFC 5746, DOI 10.17487/RFC5746, February 2010,
<https://www.rfc-editor.org/info/rfc5746>.

[RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer
Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347,
January 2012, <https://www.rfc-editor.org/info/rfc6347>.

[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/info/rfc7540>.

[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/info/rfc8174>.

[RFC8260] Stewart, R., Tuexen, M., Loreto, S., and R. Seggelmann,
"Stream Schedulers and User Message Interleaving for the
Stream Control Transmission Protocol", RFC 8260,
DOI 10.17487/RFC8260, November 2017,
<https://www.rfc-editor.org/info/rfc8260>.

[RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol
Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
<https://www.rfc-editor.org/info/rfc8446>.

[RFC8447] Salowey, J.

[RFC8996] Moriarty, K. and S. Turner, "IANA Registry Updates for Farrell, "Deprecating TLS 1.0 and DTLS", TLS
1.1", BCP 195, RFC 8447, 8996, DOI 10.17487/RFC8447, August 2018,
<https://www.rfc-editor.org/info/rfc8447>. 10.17487/RFC8996, March 2021,
<https://www.rfc-editor.org/info/rfc8996>.

[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://www.ietf.org/internet-
drafts/draft-ietf-tls-dtls13-43.txt>.

9.2.

10.2. Informative References

[RFC3436] Jungmaier, A., Rescorla, E., and M. Tuexen, "Transport
Layer Security over Stream Control Transmission Protocol",
RFC 3436, DOI 10.17487/RFC3436, December 2002,
<https://www.rfc-editor.org/info/rfc3436>.

[RFC3788] Loughney, J., Tuexen, M., Ed., and J. Pastor-Balbas,
"Security Considerations for Signaling Transport (SIGTRAN)
Protocols", RFC 3788, DOI 10.17487/RFC3788, June 2004,
<https://www.rfc-editor.org/info/rfc3788>.

[RFC5061] Stewart, R., Xie, Q., Tuexen, M., Maruyama, S., and M.
Kozuka, "Stream Control Transmission Protocol (SCTP)
Dynamic Address Reconfiguration", RFC 5061,
DOI 10.17487/RFC5061, September 2007,
<https://www.rfc-editor.org/info/rfc5061>.

[RFC6083] Tuexen, M., Seggelmann, R., and E. Rescorla, "Datagram
Transport Layer Security (DTLS) for Stream Control
Transmission Protocol (SCTP)", RFC 6083,
DOI 10.17487/RFC6083, January 2011,
<https://www.rfc-editor.org/info/rfc6083>.

[RFC6458] Stewart, R., Tuexen, M., Poon, K., Lei, P., and V.
Yasevich, "Sockets API Extensions for the Stream Control
Transmission Protocol (SCTP)", RFC 6458,
DOI 10.17487/RFC6458, December 2011,
<https://www.rfc-editor.org/info/rfc6458>.

[RFC6973] Cooper, A., Tschofenig, H., Aboba, B., Peterson, J.,
Morris, J., Hansen, M., and R. Smith, "Privacy
Considerations for Internet Protocols", RFC 6973,
DOI 10.17487/RFC6973, July 2013,
<https://www.rfc-editor.org/info/rfc6973>.

[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/info/rfc7258>.

[RFC7457] Sheffer, Y., Holz, R., and P. Saint-Andre, "Summarizing
Known Attacks on Transport Layer Security (TLS) and
Datagram TLS (DTLS)", RFC 7457, DOI 10.17487/RFC7457,
February 2015, <https://www.rfc-editor.org/info/rfc7457>.

[RFC7525] Sheffer, Y., Holz, R., and P. Saint-Andre,
"Recommendations for Secure Use of Transport Layer
Security (TLS) and Datagram Transport Layer Security
(DTLS)", BCP 195, RFC 7525, DOI 10.17487/RFC7525, May
2015, <https://www.rfc-editor.org/info/rfc7525>.

[ANSSI-DAT-NT-003]
Agence nationale de la sécurité des systèmes
d'information, ., "Recommendations for securing networks
with IPsec", ANSSI Technical Report DAT-NT-003 , August
2015,
<https://www.ssi.gouv.fr/uploads/2015/09/NT_IPsec_EN.pdf>. <<https://www.ssi.gouv.fr/uploads/2015/09/
NT_IPsec_EN.pdf>>.

Appendix A. Motivation for Changes

This document proposes a number of changes to RFC 6083 that have
various different motivations:

Supporting Large User Messages: RFC 6083 allowed only user messages
that could fit within a single DTLS record. 3GPP has run into this
limitation where they have at least four SCTP using protocols (F1,
E1, Xn, NG-C) that can potentially generate messages over the size of
16384 bytes.

New Versions: Almost 10 years has passed since RFC 6083 was written,
and significant evolution has happened in the area of DTLS and
security algorithms. Thus DTLS 1.3 is the newest version of DTLS and
also the SHA-1 HMAC algorithm of RFC 4895 is getting towards the end
of usefulness. Thus, this document mandates usage of relevant
versions and algorithms.

Clarifications: Some implementation experiences has have been gained that
motivates additional clarifications on the specification.

* Avoid unsecured messages prior to DTLS handshake have completed.

* Make clear that all messages are encrypted after DTLS handshake.

Authors' Addresses

Magnus Westerlund
Ericsson

Email: magnus.westerlund@ericsson.com

John Preuß Mattsson
Ericsson

Email: john.mattsson@ericsson.com

Claudio Porfiri
Ericsson

Email: claudio.porfiri@ericsson.com

Michael Tüxen
Münster University of Applied Sciences
Stegerwaldstrasse 39
48565 Steinfurt
Germany

Email: tuexen@fh-muenster.de