Strong Assertions of IoT Network Access Requirements

Introduction Under , devices report a URL to a MUD manager in the network. RFC 8520 envisions different approaches for conveying the information from the device to the network such as: DHCP, IEEE802.1AB Link Layer Discovery Protocol (LLDP), and IEEE 802.1X whereby the URL to the MUD file would be contained in the certificate used in an EAP method. The MUD manager then uses the URL to fetch the MUD file, which contains access and network functionality required for a device to properly function. The MUD manager must trust the service from which the MUD file is fetched to return an authentic copy of the MUD file. This concern may be mitigated using the optional signature reference in the MUD file. The MUD manager must also trust the device to report a correct URL. In case of DHCP and LLDP the URL is unprotected. When the URL to the MUD file is included in a certificate then it is authenticated and integrity protected. A certificate created for use with network access authentication is typically not signed by the entity that wrote the software and configured the device, which leads to conflation of local network access rights with rights to assert all network access requirements. There is a need to bind the entity that creates the software and configuration to the MUD file because only that entity can attest the network access requirements of the device. This specification defines an extension to the Software Updates for Internet of Things (SUIT) manifest format to include a MUD file (by reference or by value). When combining a MUD file with a manifest used for software/firmware updates (potentially augmented with attestation) then a network operator can get more confidence in the description of the access and network functionality required for a device to properly function.

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.

Workflow The intended workflow is as follows: At the time of onboarding, devices report their manifest in use to the MUD manager via attestation evidence. If the SUIT_MUD_container, see , has been severed, the MUD manager can use the suit-reference-uri to retrieve the complete SUIT manifest. The manifest authenticity is verified by the MUD manager, which enforces that the MUD file presented is also authentic and as intended by the device software vendor. Each time a device is updated, rebooted, or otherwise substantially changed, it will execute an attestation. Among other claims in the Entity Attestation Token (EAT) , the device will report its software digest(s), configuration digest(s), manifest URI, and manifest digest to the MUD manager. The MUD manager can then validate these attestation reports in order to check that the device is operating with the expected version of software and configuration. Since the manifest digest is reported, the MUD manager can look up the corresponding manifest. If the MUD manager does not already have a full copy of the manifest, it can be acquired using the reference URI. Once a full copy of the manifest is provided, the MUD manager can verify the device attestation report The MUD manager acquires the MUD file from the MUD URL. The MUD manager verifies the MUD file signature using the provided Subject Key Identifier. Then, the MUD manager can apply any appropriate policy as described by the MUD file.

Advantages over previous MUD URL reporting mechanisms Binding within the manifest has several advantages over other MUD URL reporting mechanisms: The MUD URL is tightly coupled to device software/firmware version. The device does not report the URL, so the device cannot tamper with the URL. The onus is placed on the software/firmware author to provide a MUD file that describes the behavior of the software running on a device. The author explicitly authorizes a key to sign MUD files, providing a tight coupling between the party that knows device behavior best (the author of the software/firmware) and the party that declares device behavior (MUD file signer). Network operators do not need to know, a priori, which MUD URL to use for each device; this can be harvested from the device's manifest and only replaced if necessary. A network operator can still replace a MUD URL: By providing a manifest that overrides the MUD URL. By replacing the MUD URL in their network infrastructure. Devices can be quarantined if they do not attest a known software/firmware version. Devices cannot lie about which MUD URL to use.

Extensions to SUIT To enable strong assertions about the network access requirements that a device should have for a particular software/configuration pair a MUD URL is added to the SUIT manifest along with a subject key identifier (ski). The subject key identifier MUST be generated according to the process defined in . The following CDDL describes the extension to the SUIT_Manifest structure:

SUIT_Digest / SUIT_MUD_container ) ]]> The SUIT_Envelope is also amended:

bstr .cbor SUIT_MUD_container ) ]]> The SUIT_MUD_container structure is defined as follows:

#6.32(tstr), suit-mud-ski => SUIT_Digest, } ]]>

Security Considerations This specification links MUD files to other IETF technologies, particularly to SUIT manifests, for improving security protection and ease of use. By including MUD files (by reference or by value) in SUIT manifests an extra layer of protection has been created and synchronization risks can be minimized. If the MUD file and the software/firmware loaded onto the device gets out-of-sync a device may be firewalled and, with firewalling by networks in place, the device may stop functioning.

IANA Considerations IANA is requested to add a new value to the SUIT manifest elements registry created with : Label: TBD1 [[Value allocated from the standards action address range]] Name: Manufacturer Usage Description (MUD) Reference: [[TBD: This document]] IANA is requested to add a new value to the SUIT envelope elements registry created with : Label: TBD2 [[Value allocated from the standards action address range]] Name: Manufacturer Usage Description (MUD) Reference: [[TBD: This document]]