IANA Registry Updates for TLS and DTLS

Introduction This document instructs IANA to make changes to a number of the IANA registries related to Transport Layer Security (TLS) and Datagram Transport Layer Security (DTLS). These changes were almost entirely motivated by the development of TLS 1.3 . The changes introduced by this document range from simple, e.g., adding notes, to complex, e.g., changing a registry's registration policy. Instead of listing the changes and their rationale here in the introduction, each section provides rationale for the proposed change(s). This document proposes no changes to the registration policies for TLS Alerts , TLS ContentType , TLS HandshakeType , and TLS Certificate Status Types registries; the existing policies (Standards Action for the first three; IETF Review for the last), are appropriate for these one-byte code points because of their scarcity.

Terminology The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 when, and only when, they appear in all capitals, as shown here.

Adding "TLS" to Registry Names For consistency amongst TLS registries, IANA [SHALL prepend/has prepended] "TLS" to the following registries:

Application-Layer Protocol Negotiation (ALPN) Protocol IDs ,
ExtensionType Values,
Heartbeat Message Types , and
Heartbeat Modes .

IANA [SHALL update/has updated] the reference for these four registries to also refer to this document. The remainder of this document will use the registry names with the "TLS" prefix.

Aligning with RFC 8126 Many of the TLS-related IANA registries had the registration procedure "IETF Consensus", which was changed to "IETF Review" by . To align with the new terminology, IANA [SHALL update/has updated] the following registries to "IETF Review":

TLS Authorization Data Formats
TLS Supplemental Data Formats (SupplementalDataType)

This is not a universal change, as some registries originally defined with "IETF Consensus" are undergoing other changes either as a result of this document or . IANA [SHALL update/has updated] the reference for these two registries to also refer to this document.

Adding "Recommended" Column The instructions in this document update the Recommended column, originally added in to add a third value, "D", indicating that a value is "Discouraged". The permitted values are:

Y: Indicates that the IETF has consensus that the item is RECOMMENDED. This only means that the associated mechanism is fit for the purpose for which it was defined. Careful reading of the documentation for the mechanism is necessary to understand the applicability of that mechanism. The IETF could recommend mechanisms that have limited applicability, but will provide applicability statements that describe any limitations of the mechanism or necessary constraints on its use.
N: Indicates that the item has not been evaluated by the IETF and that the IETF has made no statement about the suitability of the associated mechanism. This does not necessarily mean that the mechanism is flawed, only that no consensus exists. The IETF might have consensus to leave an items marked as "N" on the basis of it having limited applicability or usage constraints.
D: Indicates that the item is discouraged and SHOULD NOT or MUST NOT be used. This marking could be used to identify mechanisms that might result in problems if they are used, such as a weak cryptographic algorithm or a mechanism that might cause interoperability problems in deployment.

Setting the Recommended item to "Y" or "D" or changing a item whose current value is "Y" or "D" requires standards action. Not all items defined in standards track documents need to be marked as Recommended. Changing the Recommended status of a standards track item requires standards action. [Note: the registries in the rest of the document will need to have the recommended column updated appropriately, specifically to deprecate MD5 and SHA-1, etc.]

Session Ticket TLS Extension The nomenclature for the registry entries in the TLS ExtensionType Values registry correspond to the presentation language field name except for entry 35. To ensure that the values in the registry are consistently identified in the registry, IANA:

[SHALL rename/has renamed] entry 35 to "session_ticket (renamed from "SessionTicket TLS")" .
[SHALL add/has added] a reference to this document in the "Reference" column for entry 35.

TLS ExtensionType Values Experience has shown that the IETF Review registry policy for TLS extensions was too strict. Based on WG consensus, the decision was taken to change the registration policy to Specification Required while reserving a small part of the code space for private use. Therefore, IANA [SHALL update/has updated] the TLS ExtensionType Values registry as follows:

Changed the registry policy to: Values with the first byte in the range 0-254 (decimal) are assigned via Specification Required . Values with the first byte 255 (decimal) are reserved for Private Use .
Updated the "Reference" to also refer to this document.

See for additional information about the designated expert pool. Despite wanting to "loosen" the registration policies for TLS extensions, it is still useful to indicate in the IANA registry which extensions the WG recommends be supported. Therefore, IANA [SHALL update/has updated] the TLS ExtensionType Values registry as follows:

Add a "Recommended" column with the contents as listed below. This table has been generated by marking Standards Track RFCs as "Y" and all others as "N". The "Recommended" column is assigned a value of "N" unless explicitly requested, and adding a value with a "Recommended" value of "Y" requires Standards Action . IESG Approval is REQUIRED for a Y->N transition.

Extension	Recommended
server_name	Y
max_fragment_length	N
client_certificate_url	Y
trusted_ca_keys	Y
truncated_hmac	Y
status_request	Y
user_mapping	Y
client_authz	N
server_authz	N
cert_type	N
supported_groups	Y
ec_point_formats	Y
srp	N
signature_algorithms	Y
use_srtp	Y
heartbeat	Y
application_layer_protocol_negotiation	Y
status_request_v2	Y
signed_certificate_timestamp	N
client_certificate_type	Y
server_certificate_type	Y
padding	Y
encrypt_then_mac	Y
extended_master_secret	Y
cached_info	Y
session_ticket	Y
renegotiation_info	Y

IANA [SHALL update/has added] the following notes:

Note:: The role of the designated expert is described in The designated expert ensures that the specification is publicly available. It is sufficient to have an Internet-Draft (that is posted and never published as an RFC) or a document from another standards body, industry consortium, university site, etc. The expert may provide more in-depth reviews, but their approval should not be taken as an endorsement of the extension.
Note:: As specified in , assignments made in the Private Use space are not generally useful for broad interoperability. It is the responsibility of those making use of the Private Use range to ensure that no conflicts occur (within the intended scope of use). For widespread experiments, temporary reservations are available.
Note:: If an item is not marked as "Recommended", it does not necessarily mean that it is flawed; rather, it indicates that the item either has not been through the IETF consensus process, has limited applicability, or is intended only for specific use cases.

The extensions added by are omitted from the above table; additionally, token_binding is omitted, since specifies the value of the "Recommended" column as for this extension. also uses the TLS ExtensionType Values registry originally created in . The following text is from and is included here to ensure alignment between these specifications.

IANA [SHALL update/has updated] this registry to include the "key_share", "pre_shared_key", "psk_key_exchange_modes", "early_data", "cookie", "supported_versions", "certificate_authorities", "oid_filters", "post_handshake_auth", and "signature_algorithms_cert", extensions with the values defined in and the "Recommended" value of "Y".
IANA [SHALL update/has updated] this registry to include a "TLS 1.3" column that lists the messages in which the extension may appear. This column [SHALL be/has been] initially populated from the table in Section 4.2 of with any extension not listed there marked as "-" to indicate that it is not used by TLS 1.3.

TLS Cipher Suites Registry Experience has shown that the IETF Consensus registry policy for TLS Cipher Suites was too strict. Based on WG consensus, the decision was taken to change the TLS Cipher Suites registry's registration policy to Specification Required while reserving a small part of the code space for experimental and private use. Therefore, IANA [SHALL update/has updated] the TLS Cipher Suites registry's policy as follows: See for additional information about the designated expert pool. The TLS Cipher Suites registry has grown significantly and will continue to do so. To better guide those not intimately involved in TLS, IANA [shall update/has updated] the TLS Cipher Suites registry as follows: [The following text needs to be update to reflect the new recommended policy]

Added a "Recommended" column to the TLS Cipher Suites registry. The cipher suites that follow in the two tables are marked as "Y". All other cipher suites are marked as "N". The "Recommended" column is assigned a value of "N" unless explicitly requested, and adding a value with a "Recommended" value of "Y" requires Standards Action . IESG Approval is REQUIRED for a Y->N transition. The cipher suites that follow are Standards Track server-authenticated (and optionally client-authenticated) cipher suites that are currently available in TLS 1.2.

RFC EDITOR: The previous paragraph is for document reviewers and is not meant for the registry. The cipher suites that follow are Standards Track ephemeral pre-shared key cipher suites that are available in TLS 1.2. RFC EDITOR: The previous paragraph is for document reviewers and is not meant for the registry. The TLS 1.3 cipher suites specified by are not listed here;
that document provides for their "Recommended" status. Despite the following behavior being misguided, experience has shown that some customers use the IANA registry as a checklist against which to measure an implementation's completeness, and some implementers blindly implement cipher suites. Therefore, IANA [SHALL add/has added] the following warning to the registry:

WARNING:: Cryptographic algorithms and parameters will be broken or weakened over time. Blindly implementing cipher suites listed here is not advised. Implementers and users need to check that the cryptographic algorithms listed continue to provide the expected level of security.

IANA [SHALL add/has added] the following note to ensure that those that focus on IANA registries are aware that TLS 1.3 uses the same registry but defines ciphers differently:

Note:: Although TLS 1.3 uses the same cipher suite space as previous versions of TLS, TLS 1.3 cipher suites are defined differently, only specifying the symmetric ciphers and hash functions, and cannot be used for TLS 1.2. Similarly, TLS 1.2 and lower cipher suite values cannot be used with TLS 1.3.

IANA [SHALL add/has added] the following notes to document the rules for populating the "Recommended" column:

Note:: CCM_8 cipher suites are not marked as "Recommended". These cipher suites have a significantly truncated authentication tag that represents a security trade-off that may not be appropriate for general environments.
Note:: If an item is not marked as "Recommended", it does not necessarily mean that it is flawed; rather, it indicates that the item either has not been through the IETF consensus process, has limited applicability, or is intended only for specific use cases.

IANA [SHALL add/has added] the following notes for additional information:

Note:: The role of the designated expert is described in [this-RFC]. The designated expert ensures that the specification is publicly available. It is sufficient to have an Internet-Draft (that is posted and never published as an RFC) or a document from another standards body, industry consortium, university site, etc. The expert may provide more in-depth reviews, but their approval should not be taken as an endorsement of the cipher suite.
Note:: As specified in , assignments made in the Private Use space are not generally useful for broad interoperability. It is the responsibility of those making use of the Private Use range to ensure that no conflicts occur (within the intended scope of use). For widespread experiments, temporary reservations are available.

IANA [SHALL update/has updated] the reference for this registry to also refer to this document.

TLS Supported Groups Similar to cipher suites, supported groups have proliferated over time, and some use the registry to measure implementations. Therefore, IANA [SHALL add/has added] a "Recommended" column with a "Y" for secp256r1, secp384r1, x25519, and x448, while all others are "N". These "Y" groups are taken from Standards Track RFCs; elevates secp256r1 and secp384r1 to Standards Track. Not all groups from , which is Standards Track, are marked as "Y"; these groups apply to TLS 1.3 and previous versions of TLS. The "Recommended" column is assigned a value of "N" unless explicitly requested, and adding a value with a "Recommended" value of "Y" requires Standards Action . IESG Approval is REQUIRED for a Y->N transition. IANA [SHALL add/has added] the following notes:

Note:: If an item is not marked as "Recommended" it does not necessarily mean that it is flawed; rather, it indicates that the item either has not been through the IETF consensus process, has limited applicability, or is intended only for specific use cases.
Note:: The role of the designated expert is described in . The designated expert ensures that the specification is publicly available. It is sufficient to have an Internet-Draft (that is posted and never published as an RFC) or a document from another standards body, industry consortium, university site, etc. The expert may provide more in-depth reviews, but their approval should not be taken as an endorsement of the supported groups.

Despite the following behavior being misguided, experience has shown that some customers use the IANA registry as a checklist against which to measure an implementation's completeness, and some implementers blindly implement supported group. Therefore, IANA [SHALL add/has added] the following warning to the registry:

WARNING:: Cryptographic algorithms and parameters will be broken or weakened over time. Blindly implementing supported groups listed here is not advised. Implementers and users need to check that the cryptographic algorithms listed continue to provide the expected level of security.

IANA [SHALL update/has updated] the reference for this registry to also refer to this document. The value 0 (0x0000) has been marked as reserved.

TLS ClientCertificateType Identifiers Experience has shown that the IETF Consensus registry policy for TLS ClientCertificateType Identifiers is too strict. Based on WG consensus, the decision was taken to change the registration policy to Specification Required while reserving some of the code space for Standards Track usage and a small part of the code space for private use. Therefore, IANA has updated the TLS ClientCertificateType Identifiers registry's policy as follows: See for additional information about the designated expert pool. IANA [SHALL add/has added] the following notes:

Note:: The role of the designated expert is described in [this-RFC]. The designated expert ensures that the specification is publicly available. It is sufficient to have an Internet-Draft (that is posted and never published as an RFC) or a document from another standards body, industry consortium, university site, etc. The expert may provide more in-depth reviews, but their approval should not be taken as an endorsement of the identifier.
Note:: As specified in , assignments made in the Private Use space are not generally useful for broad interoperability. It is the responsibility of those making use of the Private Use range to ensure that no conflicts occur (within the intended scope of use). For widespread experiments, temporary reservations are available.

New Session Ticket TLS Handshake Message Type To align with TLS implementations and to align the naming nomenclature with other Handshake message types, IANA:

[SHALL rename/has renamed] entry 4 in the TLS HandshakeType registry to "new_session_ticket (renamed from NewSessionTicket)" .
[SHALL add/has added] a reference to this document in the "Reference" column for entry 4 in the TLS HandshakeType registry.

TLS Exporter Labels Registry To aid those reviewers who start with the IANA registry, IANA [SHALL add/has added]:

The following note to the TLS Exporter Labels registry:

Note:: defines keying material exporters for TLS in terms of the TLS PRF. replaced the PRF with HKDF, thus requiring a new construction. The exporter interface remains the same; however, the value is computed differently.

A "Recommended" column to the TLS Exporter Labels registry. The table that follows has been generated by marking Standards Track RFCs as "Y" and all others as "N". The "Recommended" column is assigned a value of "N" unless explicitly requested, and adding a value with a "Recommended" value of "Y" requires Standards Action . IESG Approval is REQUIRED for a Y->N transition.

To provide additional information for the designated experts, IANA [SHALL add/has added] the following notes:

Note:: The role of the designated expert is described in . The designated expert ensures that the specification is publicly available. It is sufficient to have an Internet-Draft (that is posted and never published as an RFC) or a document from another standards body, industry consortium, university site, etc. The expert may provide more in-depth reviews, but their approval should not be taken as an endorsement of the exporter label. The expert also verifies that the label is a string consisting of printable ASCII characters beginning with "EXPORTER". IANA MUST also verify that one label is not a prefix of any other label. For example, labels "key" or "master secretary" are forbidden.
Note:: If an item is not marked as "Recommended", it does not necessarily mean that it is flawed; rather, it indicates that the item either has not been through the IETF consensus process, has limited applicability, or is intended only for specific use cases.

IANA [SHALL update/has updated] the reference for this registry to also refer to this document.

Adding Missing Item to TLS Alerts Registry IANA [SHALL add/has added] the following entry to the TLS Alerts registry; the entry was omitted from the IANA instructions in :

TLS Certificate Types Experience has shown that the IETF Consensus registry policy for TLS Certificate Types is too strict. Based on WG consensus, the decision was taken to change registration policy to Specification Required while reserving a small part of the code space for private use. Therefore, IANA [SHALL change/has changed] the TLS Certificate Types registry as follows:

Changed the registry policy to: Values in the range 0-223 (decimal) are assigned via Specification Required . Values in the range 224-255 (decimal) are reserved for Private Use .
Added a "Recommended" column to the registry. X.509 and Raw Public Key are "Y". All others are "N". The "Recommended" column is assigned a value of "N" unless explicitly requested, and adding a value with a "Recommended" value of "Y" requires Standards Action . IESG Approval is REQUIRED for a Y->N transition.

See for additional information about the designated expert pool. IANA [SHALL add/has added] the following note:

Note:: The role of the designated expert is described in [this-RFC]. The designated expert ensures that the specification is publicly available. It is sufficient to have an Internet-Draft (that is posted and never published as an RFC) or a document from another standards body, industry consortium, university site, etc. The expert may provide more in-depth reviews, but their approval should not be taken as an endorsement of the certificate type.
Note:: If an item is not marked as "Recommended", it does not necessarily mean that it is flawed; rather, it indicates that the item either has not been through the IETF consensus process, has limited applicability, or is intended only for specific use cases.

IANA [SHALL update/has updated] the reference for this registry to also refer this document.

Orphaned Registries To make it clear that (D)TLS 1.3 has orphaned certain registries (i.e., they are only applicable to version of (D)TLS protocol versions prior to 1.3), IANA:

[SHALL add/has added] the following to the TLS Compression Method Identifiers registry :

Note:: Value 0 (NULL) is the only value in this registry applicable to (D)TLS protocol version 1.3 or later.

[SHALL add/has added] the following to the TLS HashAlgorithm and TLS SignatureAlgorithm registries :

Note:: The values in this registry are only applicable to (D)TLS protocol versions prior to 1.3. (D)TLS 1.3 and later versions' values are registered in the TLS SignatureScheme registry.

[SHALL update/has updated] the "Reference" field in the TLS Compression Method Identifiers, TLS HashAlgorithm and TLS SignatureAlgorithm registries to also refer to this document.
[SHALL update/has updated] the TLS HashAlgorithm registry to list values 7 and 9-223 as "Reserved" and the TLS SignatureAlgorithm registry to list values 4-6 and 9-223 as "Reserved".
has added the following to the TLS ClientCertificateType Identifiers registry :

Note: The values in this registry are only applicable to (D)TLS protocol versions prior to 1.3. Despite the fact that the TLS HashAlgorithm and SignatureAlgorithm registries are orphaned, it is still important to warn implementers of pre-TLS1.3 implementations about the dangers of blindly implementing cryptographic algorithms. Therefore, IANA has added the following warning to the TLS HashAlgorithm and SignatureAlgorithm registries:

WARNING:: Cryptographic algorithms and parameters will be broken or weakened over time. Blindly implementing the cryptographic algorithms listed here is not advised. Implementers and users need to check that the cryptographic algorithms listed continue to provide the expected level of security.

Additional Notes IANA has added the following warning and note to the TLS SignatureScheme registry:

WARNING:: Cryptographic algorithms and parameters will be broken or weakened over time. Blindly implementing signature schemes listed here is not advised. Implementers and users need to check that the cryptographic algorithms listed continue to provide the expected level of security.
Note:: As specified in , assignments made in the Private Use space are not generally useful for broad interoperability. It is the responsibility of those making use of the Private Use range to ensure that no conflicts occur (within the intended scope of use). For widespread experiments, temporary reservations are available.

IANA has added the following notes to the TLS PskKeyExchangeMode registry:

Note:: If an item is not marked as "Recommended", it does not necessarily mean that it is flawed; rather, it indicates that the item either has not been through the IETF consensus process, has limited applicability, or is intended only for specific use cases.
Note:: The role of the designated expert is described in RFC 8447. The designated expert ensures that the specification is publicly available. It is sufficient to have an Internet-Draft (that is posted and never published as an RFC) or a document from another standards body, industry consortium, university site, etc. The expert may provide more in depth reviews, but their approval should not be taken as an endorsement of the key exchange mode.

Designated Expert Pool Specification Required registry requests are registered after a three-week review period on the tls-reg-review@ietf.org mailing list, on the advice of one or more designated experts. However, to allow for the allocation of values prior to publication, the designated experts may approve registration once they are satisfied that such a specification will be published. Registration requests sent to the mailing list for review SHOULD use an appropriate subject (e.g., "Request to register value in TLS bar registry"). Within the review period, the designated experts will either approve or deny the registration request, communicating this decision to the review list and IANA. Denials SHOULD include an explanation and, if applicable, suggestions as to how to make the request successful. Registration requests that are undetermined for a period longer than 21 days can be brought to the IESG's attention (using the iesg@ietf.org mailing list) for resolution. Criteria that SHOULD be applied by the designated experts includes determining whether the proposed registration duplicates existing functionality, whether it is likely to be of general applicability or useful only for a single application, and whether the registration description is clear. IANA MUST only accept registry updates from the designated experts and SHOULD direct all requests for registration to the review mailing list. It is suggested that multiple designated experts be appointed who are able to represent the perspectives of different applications using this specification, in order to enable broadly informed review of registration decisions. In cases where a registration decision could be perceived as creating a conflict of interest for a particular Expert, that Expert SHOULD defer to the judgment of the other Experts.

Security Considerations The change to Specification Required from IETF Review lowers the amount of review provided by the WG for cipher suites and supported groups. This change reflects reality in that the WG essentially provided no cryptographic review of the cipher suites or supported groups. This was especially true of national cipher suites. Recommended algorithms are regarded as secure for general use at the time of registration; however, cryptographic algorithms and parameters will be broken or weakened over time. It is possible that the "Recommended" status in the registry lags behind the most recent advances in cryptanalysis. Implementers and users need to check that the cryptographic algorithms listed continue to provide the expected level of security. Designated experts ensure the specification is publicly available. They may provide more in-depth reviews. Their review should not be taken as an endorsement of the cipher suite, extension, supported group, etc.

IANA Considerations This document is entirely about changes to TLS-related IANA registries.