Hi,
I went through the document draft-ietf-uta-tls13-iot-profile-14. The
document is pleasant to read, but in my opinion it should have some
stronger guidance. I provided some brief comments inline. Hope it helps.
Happy to read future versions.
Yours,
Daniel
1. Introduction
In the rapidly evolving Internet of Things (IoT) ecosystem,
communication security is a critical requirement. The Transport
Layer Security (TLS) and Datagram Transport Layer Security (DTLS)
protocols have been foundational for ensuring encryption, integrity,
and authenticity in communications. However, the constraints of a
certain class of IoT devices render conventional, off-the-shelf TLS/
DTLS implementations suboptimal for many IoT use cases. This
document addresses these limitations by specifying profiles of TLS
1.3 and DTLS 1.3, optimized for resource-constrained IoT devices.
Note that IoT devices vary widely in terms of capabilities. While
some are highly resource-constrained, others offer performance
comparable to regular desktop computers but operate without end-user
interfaces. For a detailed description of the different classes of
IoT devices, please refer to [RFC7228] and [I-D.ietf-iotops-7228bis].
It is crucial for developers to thoroughly assess the limitations of
their IoT devices and communication technologies to implement the
most suitable optimizations. The profiles in this document aim to
balance strong security with the hardware and software limitations of
IoT devices.
MGLT: I am finding the text below interesting, but I am not sure it is
needed. I think ts purpose was to explain that TLS 1.3 and TLS 1.2 have
significant differences. BUT I do not find these difference are impacting
the profile. I have the impression we should probably give more details on
what is needed by IoT that will justify some options in the profile.
TLS 1.3 has been re-designed and several previously defined
extensions are not applicable to the new version of TLS/DTLS anymore.
The following features changed with the transition from TLS 1.2 to
1.3:
Tschofenig, et al. Expires 6 November 2025 [Page 3]
Internet-Draft TLS/DTLS 1.3 IoT Profiles May 2025
* TLS 1.3 introduced the concept of post-handshake authentication
messages, which partially replaced the need for the re-negotiation
feature [RFC5746] available in earlier TLS versions. However,
rekeying defined in Section 4.6.3 of [TLS13] does not provide
forward secrecy
MGT: right. In TLS 1.3 as far as I know seems to to only update the keys as
its purpose is go over the sequence number.
and post-handshake authentication defined in
Section 4.6.2 of [TLS13] only offers client-to-server
authentication.
The "Exported Authenticator" specification, see
[RFC9261], recently added support for mutual, post-handshake
authentication but requires the Certificate, CertificateVerify and
the Finished messages to be exchanged by the application layer
protocol, as it is exercised for HTTP/2 and HTTP/3 in
[I-D.ietf-httpbis-secondary-server-certs].
MGLT: the text looks like application layer is involved, which sounds a bit
strange to rely on above-TLS layers to compleet TLS.
* Rekeying of the application traffic secret does not lead to an
update of the exporter secret (see Section 7.5 of [TLS13]) since
the derived export secret is based on the exporter_master_secret
and not on the application traffic secret.
* Flight #4, which was used by EAP-TLS 1.2 [RFC5216], does not exist
in TLS 1.3. As a consequence, EAP-TLS 1.3 [RFC9190] introduced a
dummy message.
* [RFC4279] introduced PSK-based authentication to TLS, a feature
re-designed in TLS 1.3. The "PSK identity hint" defined in
[RFC4279], which is used by the server to help the client in
selecting which PSK identity to use, is, however, not available
anymore in TLS 1.3.
* Finally, ciphersuites were depreciated and the RSA-based key
transport is not yet supported in TLS 1.3. As a consequence, only
a Diffie-Hellman-based key exchange is available.
MGLT: PSK does not require DH.
The profiles in this specification are designed to be adaptable to
the broad spectrum of IoT applications, from low-power consumer
devices to large-scale industrial deployments. It provides
guidelines for implementing TLS/DTLS 1.3 in diverse networking
contexts, including reliable, connection-oriented transport via TCP
for TLS, and lightweight, connectionless communication via UDP for
DTLS. In particular, DTLS is emphasized for scenarios where low-
latency communication is paramount, such as multi-hop mesh networks
and low-power wide-area networks, where the amount of data exchanged
needs to be minimized.
In conclusion, this document offers comprehensive guidance for
deploying secure communication in resource-constrained IoT
environments. It outlines best practices for configuring TLS/DTLS
1.3 to meet the unique needs of IoT devices, ensuring robust security
without overwhelming their limited processing, memory, and power
resources. The document plays a vital role in facilitating secure,
efficient IoT deployments, supporting the broad adoption of secure
communication standards.
Tschofenig, et al. Expires 6 November 2025 [Page 4]
Internet-Draft TLS/DTLS 1.3 IoT Profiles May 2025
2. Conventions and Terminology
...
3. Credential Types
In accordance with the recommendations in [RFC7925], a compliant
implementation MUST implement TLS_AES_128_CCM_8_SHA256. It SHOULD
implement TLS_CHACHA20_POLY1305_SHA256.
MGLT: I suspect it would be good to specify when
TLS_CHACHA20_POLY1305_SHA256 does not need to be implemented. Given that my
understanding is that we keep CCM because of hardware implementation, I am
wondering why we do not consider CCM with larger signature. It would be
good to explain why GCM is not even considered.
Note also that it is a bit distant from credential type, so i am wondering
if a dedicated section would not be appropriated.
Pre-shared key based authentication is integrated into the main TLS/
DTLS 1.3 specification and has been harmonized with session
resumption.
A compliant implementation supporting authentication based on
certificates and raw public keys MUST support digital signatures with
ecdsa_secp256r1_sha256. A compliant implementation MUST support the
key exchange with secp256r1 (NIST P-256) and SHOULD support key
exchange with X25519.
MGLT: It is not clear to me if PSK, raw, X509 are mandatory or recommended.
I think that should be clarified.
A plain PSK-based TLS/DTLS client or server MUST implement the
following extensions:
MGLT: It is my belief that plain PSK-based needs to be defined. In
particular, does it means that it is only considering PSK or simply
allowing PSK ?
Supported Version, Cookie and SNI does not seem related to PSK. Given the
sentence a plain PSK based TLS implementation I woudl have expected PSK
related extension. I think we need to explain why these extensions are
there and specific to PSK.
* Supported Versions,
* Cookie,
* Server Name Indication (SNI),
* Pre-Shared Key,
* PSK Key Exchange Modes, and
* Application-Layer Protocol Negotiation (ALPN).
For use of external pre-shared keys [RFC9258] makes the following
recommendation:
Applications SHOULD provision separate PSKs for (D)TLS 1.3 and
prior versions.
Where possible, the importer interface defined in [RFC9258] MUST be
used for external PSKs. This ensures that external PSKs used in
(D)TLS 1.3 are bound to a specific key derivation function (KDF) and
hash function.
MGLT: I think there are always bound to KDF and hash. What we want is that
both hosts uses the same KDF and hash. Suppose that one PSK is used with a
hash function that has become unsecured, I am wondering if the
recommendation would be to keep on using it over an unsecured hash function
as opposed a newly known secured hash function. Though it might be as
secured as if we had always used the secured hash function, I am wondering
it might still be better to use it this way.
Tschofenig, et al. Expires 6 November 2025 [Page 5]
Internet-Draft TLS/DTLS 1.3 IoT Profiles May 2025
The SNI extension is discussed in this document and the justification
for implementing and using the ALPN extension can be found in
[RFC9325].
For TLS/DTLS clients and servers implementing raw public keys and/or
certificates the guidance for mandatory-to-implement extensions
described in Section 9.2 of [RFC8446] MUST be followed.
4. Error Handling
...
5. Session Resumption
...
6. Compression
...
7. Forward Secrecy
...
8. Authentication and Integrity-only Cipher Suites
For a few, very specific Industrial IoT use cases [RFC9150] defines
two cipher suites that provide data authenticity, but not data
confidentiality. Please review the security and privacy
considerations about their use detailed in Section 9 of [RFC9150].
MGLT: I think this should be turned into a recommendation
9. Keep-Alive
The discussion in Section 10 of [RFC7925] is applicable.
10. Timers and ACKs
...
11. Random Number Generation
...
12. Server Name Indication
This specification mandates the implementation of the Server Name
Indication (SNI) extension. Where privacy requirements require it,
the ECH (Encrypted Client Hello) extension [I-D.ietf-tls-esni]
prevents an on-path attacker to determine the domain name the client
is trying to connect to.
Since the Encrypted Client Hello extension requires use of Hybrid
Public Key Encryption (HPKE) [RFC9180] and additional protocols
require further protocol exchanges and cryptographic operations,
there is a certain overhead associated with this privacy feature.
Note that in industrial IoT deployments the use of ECH may not be an
option because network administrators inspect DNS traffic generated
by IoT devices in order to detect malicious behaviour.
MGLT: "May not be an option" can have different different interpretation
(at least to me): not allowed or mandatory.
Besides, to avoid leaking DNS lookups from network inspection
altogether further protocols are needed, including DoH [RFC8484] and
DPRIVE [RFC7858] [RFC8094]. For use of such techniques in managed
networks, the reader is advised to keep up to date with the protocols
defined by the Adaptive DNS Discovery (add) working group [ADD].
13. Maximum Fragment Length Negotiation
...
14. Crypto Agility
The recommendations in Section 19 of [RFC7925] are applicable.
15. Key Length Recommendations
The recommendations in Section 20 of [RFC7925] are applicable.
Tschofenig, et al. Expires 6 November 2025 [Page 8]
Internet-Draft TLS/DTLS 1.3 IoT Profiles May 2025
16. 0-RTT Data
Appendix E.5 of [TLS13] establishes that:
Application protocols MUST NOT use 0-RTT data without a profile
that defines its use. That profile needs to identify which
messages or interactions are safe to use with 0-RTT and how to
handle the situation when the server rejects 0-RTT and falls back
to 1-RTT.
At the time of writing, no such profile has been defined for CoAP
[CoAP]. Therefore, 0-RTT MUST NOT be used by CoAP applications.
MGLT: I understand such profile word be needed on a PER APPLICATION basis.
I do not envision a profile that would match CoAP as a whole.
17. Certificate Profile
This section contains updates and clarifications to the certificate
profile defined in [RFC7925]. The content of Table 1 of [RFC7925]
has been split by certificate "type" in order to clarify exactly what
requirements and recommendations apply to which entity in the PKI
hierarchy.
The content is also better aligned with the IEEE 802.1AR [_8021AR]
specification, which introduces the terms Initial Device Identifier
(IDevID) and Locally Significant Device Identifiers (LDevIDs).
IDevIDs and LDevIDs are Device Identifiers (DevIDs). A DevID
consists of
MGLT: The sentence may look a bit strange. """IDevIDs and LDevIDs are
Device Identifiers (DevIDs).""" I could probably infer that one is initial
and the other is local ;-) I would maybe suggest simply saying both Device
Identifiers consists of:
* a private key,
* a certificate (containing the public key and the identifier
certified by the certificate's issuer), and
* a certificate chain up to a trust anchor. The trust anchor is
usually the root certificate).
MGLT: I was expecting some characteristics specific to DevIDs, I do not see
anything that differ from a certificate binding an identity to a private
key. The section on DevIDs does not seem necessary at that point.
Note that the trust anchor does not need to be transmitted in the TLS
Certificate message sent by the server.
The client MUST NOT use any
trust anchor provided in the Certificate message, because the trust
anchor is provisioned via out-of-band means. Therefore, transmitting
the trust anchor in the Certificate message is a waste of bandwidth.
If the trust anchor is not the root CA certificate, the server may be
unaware of which trust anchor the client has. In such cases, the
client can use the Trusted CA Indication, defined in [RFC6066], to
indicate which trust anchors it possesses.
MGLT: I believe the text above is confusing and should simply RECOMMEND not
to include the root Certificate in the Certificate and ignore
rootCertificates.
I tend to say that such recommendation is related to TLS and not
certificate, so I would move it to the TLS section.
Tschofenig, et al. Expires 6 November 2025 [Page 9]
Internet-Draft TLS/DTLS 1.3 IoT Profiles May 2025
The IDevID is typically provisioned by a manufacturer and signed by
the manufacturer CA. It is then used to obtain operational
certificates, the LDevIDs, from the operator or owner of the device.
Some protocols also introduce an additional hierarchy with
application instance certificates, which are obtained for use with
specific applications.
IDevIDs are primarily used with device onboarding or bootstrapping
protocols, such as the Bootstrapping Remote Secure Key Infrastructure
(BRSKI) protocol [RFC8995] or by LwM2M Bootstrap [LwM2M]. Hence, the
use of IDevIDs is limited in purpose even though they have a long
lifetime, or do not expire at all. While some bootstrapping
protocols use TLS (and therefore make use of the IDevID as part of
client authentication) there are other bootstrapping protocols that
do not use TLS/DTLS for client authentication, such as FIDO Device
Onboarding (FDO) [FDO]. In many cases, a profile for the certificate
content is provided by those specifications. For these reasons, this
specification focuses on the description of LDevIDs.
While the IEEE 802.1AR terminology is utilized in this document, this
specification does not claim conformance to IEEE 802.1AR since such a
compliance statement goes beyond the use of the terminology and the
certificate content and would include the use of management
protocols, fulfillment of certain hardware security requirements, and
interfaces to access these hardware security modules. Placing these
requirements on network equipment like routers may be appropriate but
designers of constrained IoT devices have opted for different
protocols and hardware security choices.
MGLT: While the DevID description is interesting, the section needs to
highlight what difference it makes to certificates.
17.1. All Certificates
To avoid repetition, this section outlines requirements on X.509
certificates applicable to all PKI entities.
17.1.1. Version
Certificates MUST be of type X.509 v3. Note that TLS 1.3 allows to
convey payloads other than X.509 certificates in the Certificate
message. The description in this section only focuses on X.509 v3
certificates and leaves the description of other formats to other
sections or even other specifications.
Tschofenig, et al. Expires 6 November 2025 [Page 10]
Internet-Draft TLS/DTLS 1.3 IoT Profiles May 2025
17.1.2. Serial Number
...
17.1.3. Signature
...
17.1.4. Issuer
...
17.1.5. Validity
In IoT deployment scenarios it is often expected that the IDevIDs
have no maximum validity period. For this purpose the use of a
special value for the notAfter date field, the GeneralizedTime value
of 99991231235959Z, is utilized.
MGLT: we should say where such value comes from.
If this is done, then the CA
certificates and the certificates of subordinate CAs cannot have a
maximum validity period either. Hence, it requires careful
consideration whether it is appropriate to issue IDevID certificates
with no maximum validity period.
MGLT: I think the text needs to be clarified. The first sentence says that
IoT are expected to have no maximum validity period. The consequence of it
is that CA, subCA also have no maximum validity. I suggest to mention what
needs to be considered carefully here. Then I suggest to simply how no
maximum validity period is enforced - i.e. 99991231235959Z.
LDevID certificates are, however, issued by the operator or owner,
and may be renewed at a regular interval using protocols, such as
Enrollment over Secure Transport (EST) [RFC7030] or the Certificate
Management Protocol (CMP) [RFC9483]. It is therefore RECOMMENDED to
limit the lifetime of these LDevID certificates using the notBefore
and notAfter fields, as described in Section 4.1.2.5 of [RFC5280].
Values MUST be expressed in Greenwich Mean Time (Zulu) and MUST
include seconds even where the number of seconds is zero.
MGLT: I think it would be good to mention different CA can be involved and
CMP can be used to switch from the CA of the IDevID to the one of the
LDevID.
Tschofenig, et al. Expires 6 November 2025 [Page 11]
Internet-Draft TLS/DTLS 1.3 IoT Profiles May 2025
Note that the validity period is defined as the period of time from
notBefore through notAfter, inclusive. This means that a
hypothetical certificate with a notBefore date of 9 June 2021 at
03:42:01 and a notAfter date of 7 September 2021 at 03:42:01 becomes
valid at the beginning of the :01 second, and only becomes invalid at
the :02 second, a period that is 90 days plus 1 second. So for a
90-day, notAfter must actually be 03:42:00.
For devices without a reliable source of time we advise the use of a
device management solution, which typically includes a certificate
management protocol, to manage the lifetime of all the certificates
used by the device. While this approach does not utilize
certificates to its widest extent, it is a solution that extends the
capabilities offered by a raw public key approach.
17.1.6. Subject Public Key Info
...
17.1.7. Certificate Revocation Checks
The guidance in Section 4.4.3 of [RFC7925] still holds: for
certificate revocation, neither the Online Certificate Status
Protocol (OCSP) nor Certificate Revocation Lists (CRLs) are used by
constrained IoT devices.
Since the publication of RFC 7925 the need for firmware update
mechanisms has been reinforced and the work on standardizing a secure
and interoperable firmware update mechanism has made substantial
progress, see [RFC9019]. RFC 7925 recommends to use a software /
firmware update mechanism to provision devices with new trust
anchors. This approach only addresses the distribution of trust
anchors and not end entity certificates or certificates of
subordinate CAs.
MGLT: The paragraph above seems more related to Trust Anchor (RootCA)
management than actually certificate revocation.
Tschofenig, et al. Expires 6 November 2025 [Page 12]
Internet-Draft TLS/DTLS 1.3 IoT Profiles May 2025
The use of device management protocols for IoT devices, which often
include an onboarding or bootstrapping mechanism, has also seen
considerable uptake in deployed devices. These protocols, some of
which are standardized,
MGLT: It is my belief that examples would be useful here.
allow for the distribution and updating of
certificates on demand. This enables a deployment model where IoT
device utilize end entity certificates with shorter lifetime making
certificate revocation protocols, like OCSP and CRLs, less relevant.
Whenever certificates are updated the TLS stack needs to be informed
since the communication endpoints need to be aware of the new
certificates. This is particularly important when long-lived TLS
connections are used. In such a case, the post-handshake
authentication exchange is triggered when the application requires
it. TLS 1.3 provides client-to-server post-handshake authentication
only. Mutual authentication via post-handshake messages is available
by the use of the "Exported Authenticator" [RFC9261] but requires the
application layer protocol to carry the payloads.
MGLT: This seems horribly complex, it would be good to know whether this is
recommended or not to use such mechanism. I believe it really depends on
the trust model since there is not a mandatory need to re-authenticate
regularly once the session has been authenticated once. Authentication is
performed at a given time, there is no commitment it remains unchanged
during the entire TLS session.
I think the only reason we need to authenticate id when the key is rogue
and we have later realized the current TLS session has been authenticated
with that rogue key. In any other cases, it seems fine, security relies on
the TSL session key not the authentication.
I see authentication as the main source of consumption, so I would like to
understand the effective gain instead of doing a reconnection.
I am wondering why we do not simply request to reconnect every X period of
time to keep things light.
Note that authenticators are mostly done to handle different identities
Hence, instead of performing certificate revocation checks on the IoT
device itself this specification recommends
MGLT: Maybe a normative language would be more appropriated: RECOMMENDS
to delegate this task to
the IoT device operator and to take the necessary action to allow IoT
devices to remain operational.
The CRL distribution points extension has been defined in RFC 5280 to
identify how CRL information is obtained. The authority information
access extension indicates how to access information like the online
certificate status service (OCSP). Both extensions SHOULD NOT be
set. If set, they MUST NOT be marked critical.
MGLT:The text above says everything we need to know regarding OCSP and CRL.
It should maybe be moved to the beginning. Since there is no revocation, we
use shorter life time certificate and update are handled in various ways -
software updates - certificate management. I think we need a
recommendations on what method is recommended here and why. The management
of TA seems to be the purpose of a dedicated section. The necessity to re
authenticate regularly as well. This latest point need to detail the
underlying security / trust model.
MGLT: I would like a section on Subject SAN.
17.2. Root CA Certificate
This section outlines the requirements for root CA certificates.
17.2.1. Subject
[RFC5280] mandates that Root CA certificates MUST have a non-empty
subject field. The subject field MUST contain the commonName, the
organizationName, and the countryName attribute and MAY contain an
organizationalUnitName attribute.
MGLT: is-it Subject instead of subject ?
17.2.2. Authority Key Identifier
Section 4.2.1.1 of [RFC5280] defines the Authority Key Identifier as
follows: "The authority key identifier extension provides a means of
identifying the public key corresponding to the private key used to
sign a certificate. This extension is used where an issuer has
multiple signing keys."
Tschofenig, et al. Expires 6 November 2025 [Page 13]
Internet-Draft TLS/DTLS 1.3 IoT Profiles May 2025
The Authority Key Identifier extension MAY be omitted. If it is set,
it MUST NOT be marked critical, and MUST contain the
subjectKeyIdentifier of this certificate.
[Editor's Note: Do we need to set the Authority Key Identifier in the
CA certificate?]
MGLT: My question is how the IoT would handle a change of key from the CA.
The configuration of the TA is part of the discussion, but we expect clear
guidance.
17.2.3. Subject Key Identifier
...
17.2.4. Key Usage
[RFC5280] defines the key usage field as follows: "The key usage
extension defines the purpose (e.g., encipherment, signature,
certificate signing) of the key contained in the certificate."
The Key Usage extension MAY be set. If it is set, it MUST be marked
critical and the keyCertSign or cRLSign purposes MUST be set.
Additional key usages MAY be set depending on the intended usage of
the public key.
[RFC5280] defines the extended key usage as follows: "This extension
indicates one or more purposes for which the certified public key may
be used, in addition to or in place of the basic purposes indicated
in the key usage extension."
MGLT: It is my beehive that we should avoid repeating the text. I would
rather just indicate where in the main specification this is specified as
well as to what extend this differs from the main specification.
This extendedKeyUsage extension MUST NOT be set in CA certificates.
17.2.5. Basic Constraints
Internet-Draft TLS/DTLS 1.3 IoT Profiles May 2025
* "The pathLenConstraint field is meaningful only if the cA boolean
is asserted and the key usage extension, if present, asserts the
keyCertSign bit. In this case, it gives the maximum number of
non-self-issued intermediate certificates that may follow this
certificate in a valid certification path."
* "A pathLenConstraint of zero indicates that no non-self-issued
intermediate CA certificates may follow in a valid certification
path."
* "Where pathLenConstraint does not appear, no limit is imposed."
* "Conforming CAs MUST include this extension in all CA certificates
that contain public keys used to validate digital signatures on
certificates and MUST mark the extension as critical in such
certificates."
The Basic Constraints extension MUST be set, MUST be marked critical,
the cA flag MUST be set to true and the pathLenConstraint MUST be
omitted.
[Editor's Note: Should we soften the requirement to: "The
pathLenConstraint field SHOULD NOT be present."]
MGLT: We need to understand the rational for having it or not. The rational
needs to balance the number of bytes versus the IoT usage and the potential
security impacts.
17.3. Subordinate CA Certificate
...
17.3.1. Subject
...
17.3.2. Authority Key Identifier
...
17.3.3. Subject Key Identifier
The Subject Key Identifier extension MUST be set, MUST NOT be marked
critical, and MUST contain the key identifier of the public key
contained in the subject public key info field.
Tschofenig, et al. Expires 6 November 2025 [Page 15]
Internet-Draft TLS/DTLS 1.3 IoT Profiles May 2025
17.3.4. Key Usage
..
17.3.5. Basic Constraints
...
17.3.6. CRL Distribution Point
...
17.3.7. Authority Information Access
...
17.4. End Entity Certificate
This section outlines the requirements for end entity certificates.
17.4.1. Subject
This section describes the use of end entity certificate primarily
for (D)TLS clients running on IoT devices. Operating (D)TLS servers
on IoT devices is possible but less common.
[RFC9525], Section 2 mandates that the subject field not be used to
identify a service. However, certain IoT applications (for example,
[I-D.ietf-anima-constrained-voucher], [_8021AR]) use the subject
field to encode the device serial number.
The requirement in Section 4.4.2 of [RFC7925] to only use EUI-64 for
end entity certificates as a subject field is lifted.
Tschofenig, et al. Expires 6 November 2025 [Page 16]
Internet-Draft TLS/DTLS 1.3 IoT Profiles May 2025
Two fields are typically used to encode a device identifier, namely
the Subject and the subjectAltName fields. Protocol specifications
tend to offer recommendations about what identifiers to use and the
deployment situation is fragmented.
The subject field MAY include a unique device serial number. If the
serial number is included, it MUST be encoded in the X520SerialNumber
attribute. e.g., [RFC8995] use requires a serial number in IDevID
certificates.
[RFC5280] defines: "The subject alternative name extension allows
identities to be bound to the subject of the certificate. These
identities may be included in addition to or in place of the identity
in the subject field of the certificate."
The subject alternative name extension MAY be set. If it is set, it
MUST NOT be marked critical, except when the subject DN contains an
empty sequence.
If the EUI-64 format is used to identify the subject of an end entity
certificate, it MUST be encoded as a Subject DN using the
X520SerialNumber attribute. The contents of the field is a string of
the form HH-HH-HH-HH-HH-HH-HH-HH where 'H' is one of the symbols
'0'-'9' or 'A'-'F'.
Per [RFC9525] domain names MUST NOT be encoded in the subject
commonName. Instead they MUST be encoded in a subjectAltName of type
DNS-ID. Domain names MUST NOT contain wildcard (*) characters. The
subjectAltName MUST NOT contain multiple names.
Note: The IEEE 802.1AR recommends to encode information about a
Trusted Platform Module (TPM), if present, in the HardwareModuleName.
This specification does not follow this recommendation.
MGLT: is HardwareModuleName defined in an RFC ? If so, we may add a
reference here.
Where IoT devices are accepting (D)TLS connections, i.e., they are
acting as a server, it is unlikely that there will be a useful name
that can go into the SNI. In general, the use of SNI for the purpose
of virtual hosting on constrained IoT devices is rare. The IoT
device cannot depend on a client providing a correct SNI, and so it
MUST ignore the extension. This implies that IoT devices cannot do
name-based virtual hosting of TLS connections. In the unlikely event
that an IoT device has multiple servers responding with different
server certificate, then the server SHOULD use different IP addresses
or port numbers.
MGLT: It is my believe that this section should come out with some
recommendations on how to name a IoT client / server. EUI-64 and FQDN are
listed, but I am wondering what about UUID or any other scheme.
Tschofenig, et al. Expires 6 November 2025 [Page 17]
Internet-Draft TLS/DTLS 1.3 IoT Profiles May 2025
17.4.2. Authority Key Identifier
...
17.4.3. Subject Key Identifier
...
17.4.4. Key Usage
The key usage extension MUST be set and MUST be marked as critical.
For signature verification keys the digitialSignature key usage
purpose MUST be specified. Other key usages are set according to the
intended usage of the key.
If enrollment of new certificates uses server-side key generation,
encrypted delivery of the private key is required. In such cases the
key usage keyEncipherment or keyAgreement MUST be set because the
encrypted delivery of the newly generated key involves encryption or
agreement of a symmetric key. On-device key generation is, however,
the preferred approach.
MGLT: I am finding this a bit orthogonal to the purpose of the draft which
is certificates for TLS. These seem to me more part of certificate
management.
In IDevID certificates, the extendedKeyUsage SHOULD NOT be present,
as it reduces the utility of the IDevID.
MGLT: If the justification for not having KE is that the key is used for
multiple purposes, we need to explicitel explain which operations are
expected by the IDevID that doe snot fit a KE. In addition multiple KE may
be added.
In locally assigned LDevID
certificates, the extendedKeyUsage, if present, MUST contain at least
one of id-kp-serverAuth or id-kp-clientAuth in order to be useable
with TLS.
18. Certificate Overhead
...
19. Ciphersuites
MGLT: In general I believe that the ciphersuiets considerations that have
been made previously should be placed in this section and only this
section.
According to Section 4.5.3 of [DTLS13], the use of AES-CCM with
8-octet authentication tags (CCM_8) is considered unsuitable for
general use with DTLS. This is because it has low integrity limits
(i.e., high sensitivity to forgeries) which makes endpoints that
negotiate ciphersuites based on such AEAD vulnerable to a trivial DoS
attack. See also Sections 5.3 and 5.4 of [I-D.irtf-cfrg-aead-limits]
for further discussion on this topic, as well as references to the
analysis supporting these conclusions.
Specifically, [DTLS13] warns that:
> TLS_AES_128_CCM_8_SHA256 MUST NOT be used in DTLS without additional
> safeguards against forgery. Implementations MUST set usage limits for
> AEAD_AES_128_CCM_8 based on an understanding of any additional forgery
> protections that are used.
Since all the ciphersuites required by [RFC7925] and [CoAP] rely on
CCM_8, there is no alternate ciphersuite available for applications
that aim to eliminate the security and availability threats related
to CCM_8 while retaining interoperability with the larger ecosystem.
In order to ameliorate the situation, it is RECOMMENDED that
implementations support the following two ciphersuites for TLS 1.3:
* TLS_AES_128_GCM_SHA256
* TLS_AES_128_CCM
and offer them as their first choice. These ciphersuites provide
confidentiality and integrity limits that are considered acceptable
in the most general settings. For the details on the exact bounds of
both ciphersuites see Section 4.5.3 of [DTLS13]. Note that the GCM-
based ciphersuite offers superior interoperability with cloud
services at the cost of a slight increase in the wire and peak RAM
footprints.
When the GCM-based ciphersuite is used with TLS 1.2, the
recommendations in Section 7.2.1 of [RFC9325] related to
deterministic nonce generation apply. In addition, the integrity
limits on key usage detailed in Section 4.4 of [RFC9325] also apply.
Table 1 summarizes the recommendations regarding ciphersuites:
--
Daniel Migault
Ericsson
_______________________________________________
Uta mailing list -- [email protected]
To unsubscribe send an email to [email protected]
