draft-ietf-teep-otrp-over-http.txt

TEEP WG                                                        D. Thaler
Internet-Draft                                                 Microsoft
Intended status: Standards Track                           27 March 2023
Expires: 28 September 2023


  HTTP Transport for Trusted Execution Environment Provisioning: Agent
                        Initiated Communication
                   draft-ietf-teep-otrp-over-http-15

Abstract

   The Trusted Execution Environment Provisioning (TEEP) Protocol is
   used to manage code and configuration data in a Trusted Execution
   Environment (TEE).  This document specifies the HTTP transport for
   TEEP communication where a Trusted Application Manager (TAM) service
   is used to manage code and data in TEEs on devices that can initiate
   communication to the TAM.

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 28 September 2023.

Copyright Notice

   Copyright (c) 2023 IETF Trust and the persons identified as the
   document authors.  All rights reserved.











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   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents (https://trustee.ietf.org/
   license-info) in effect on the date of publication of this document.
   Please review these documents carefully, as they describe your rights
   and restrictions with respect to this document.  Code Components
   extracted from this document must include Simplified BSD License text
   as described in Section 4.e of the Trust Legal Provisions and are
   provided without warranty as described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   4
   3.  TEEP Broker . . . . . . . . . . . . . . . . . . . . . . . . .   4
     3.1.  Use of Abstract APIs  . . . . . . . . . . . . . . . . . .   5
   4.  Use of HTTP as a Transport  . . . . . . . . . . . . . . . . .   5
   5.  TEEP/HTTP Client Behavior . . . . . . . . . . . . . . . . . .   6
     5.1.  Receiving a request to install a new Trusted
           Application . . . . . . . . . . . . . . . . . . . . . . .   6
       5.1.1.  Session Creation  . . . . . . . . . . . . . . . . . .   7
     5.2.  Receiving a notification that a Trusted Application is no
           longer needed . . . . . . . . . . . . . . . . . . . . . .   7
     5.3.  Getting a TAM URI and message back from a TEEP Agent  . .   8
     5.4.  Receiving an HTTP response  . . . . . . . . . . . . . . .   8
     5.5.  Handling checks for policy changes  . . . . . . . . . . .   9
     5.6.  Error handling  . . . . . . . . . . . . . . . . . . . . .  10
   6.  TEEP/HTTP Server Behavior . . . . . . . . . . . . . . . . . .  10
     6.1.  Receiving an HTTP POST request  . . . . . . . . . . . . .  10
     6.2.  Getting an empty message back from the TAM  . . . . . . .  11
     6.3.  Getting a message from the TAM  . . . . . . . . . . . . .  11
     6.4.  Error handling  . . . . . . . . . . . . . . . . . . . . .  11
   7.  Sample message flow . . . . . . . . . . . . . . . . . . . . .  11
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  13
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  13
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  13
     10.1.  Normative References . . . . . . . . . . . . . . . . . .  13
     10.2.  Informative References . . . . . . . . . . . . . . . . .  14
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  14

1.  Introduction

   A Trusted Execution Environment (TEE) is an environment that enforces
   that any code within that environment cannot be tampered with, and
   that any data used by such code cannot be read or tampered with by
   any code outside that environment.  The Trusted Execution Environment
   Provisioning (TEEP) protocol is designed to provision authorized code
   and configuration into TEEs.




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   To be secure against malware, a TEEP implementation (referred to as a
   TEEP "Agent" on the client side is expected to run inside a TEE, and
   a "Trusted Application Manager (TAM)" on the server side) might or
   might not run inside a TEE.  However, the transport for TEEP, along
   with the underlying TCP/IP stack, does not necessarily run inside a
   TEE.  This split allows the set of highly trusted code to be kept as
   small as possible, including allowing code (e.g., TCP/IP or QUIC
   [RFC9000]) that only sees encrypted messages, to be kept out of the
   TEE.  See section 6.2 of [I-D.ietf-teep-architecture] for a depiction
   of various implementation models.

   The TEEP specification [I-D.ietf-teep-protocol] describes the
   behavior of TEEP Agents and TAMs, but does not specify the details of
   the transport.  The purpose of this document is to provide such
   details.  That is, a TEEP-over-HTTP (TEEP/HTTP) implementation
   delivers messages up to a TEEP implementation, and accepts messages
   from the TEEP implementation to be sent over a network.  The TEEP-
   over-HTTP implementation can be implemented either outside a TEE
   (i.e., in a TEEP "Broker") or inside a TEE.

   There are two topological scenarios (among others) in which TEEP
   could be deployed:

   1.  TAMs are reachable on the Internet, and Agents are on networks
       that might be behind a firewall or stateful NAT, so that
       communication must be initiated by an Agent.  Thus, the Agent has
       an HTTP Client and the TAM has an HTTP Server.

   2.  Agents are reachable on the Internet, and TAMs are on networks
       that might be behind a firewall or stateful NAT, so that
       communication must be initiated by a TAM.  Thus, the Agent has an
       HTTP Server and the TAM has an HTTP Client.

   The remainder of this document focuses primarily on the first
   scenario as depicted in Figure 1, but some sections (Section 4 and
   Section 8) may apply to the second scenario as well.  A more complete
   discussion of the second scenario may be handled by a separate
   document.













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      +------------------+           TEEP           +------------------+
      |    TEEP Agent    | <----------------------> |        TAM       |
      +------------------+                          +------------------+
               |                                              |
      +------------------+      TEEP-over-HTTP      +------------------+
      | TEEP/HTTP Client | <----------------------> | TEEP/HTTP Server |
      +------------------+                          +------------------+
               |                                              |
      +------------------+           HTTP           +------------------+
      |    HTTP Client   | <----------------------> |    HTTP Server   |
      +------------------+                          +------------------+

                 Figure 1: Agent Initiated Communication

   This document specifies the middle layer (TEEP-over-HTTP), whereas
   the top layer (TEEP) is specified in [I-D.ietf-teep-protocol] and the
   bottom layer (HTTP) is specified in [RFC9110].

2.  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 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

   This document also uses various terms defined in
   [I-D.ietf-teep-architecture], including Trusted Execution Environment
   (TEE), Trusted Application (TA), Trusted Application Manager (TAM),
   TEEP Agent, TEEP Broker, and Rich Execution Environment (REE).

3.  TEEP Broker

   Section 6 of the TEEP architecture [I-D.ietf-teep-architecture]
   defines a TEEP "Broker" as being a component on the device, but
   outside the TEE, that facilitates communication with a TAM.  That
   document further explains that the protocol layer at which the TEEP
   broker operates may vary by implementation, and it depicts several
   exemplary models.  An implementation is free to choose any of these
   models, although model A is the one we will use in our examples.

   Passing information from an REE component to a TEE component is
   typically spoken of as being passed "in" to the TEE, and information
   passed in the opposite direction is spoken of as being passed "out".
   In the protocol layering sense, information is typically spoken of as
   being passed "up" or "down" the stack.  Since the layer at which
   information is passed in/out may vary by implementation, we will
   generally use "up" and "down" in this document.



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3.1.  Use of Abstract APIs

   This document refers to various APIs between a TEEP implementation
   and a TEEP/HTTP implementation in the abstract, meaning the literal
   syntax and programming language are not specified, so that various
   concrete APIs can be designed (outside of the IETF) that are
   compliant.

   Some TEE architectures (e.g., SGX) may support API calls both into
   and out of a TEE.  In other TEE architectures, there may be no calls
   out from a TEE, but merely data returned from calls into a TEE.  This
   document attempts to be agnostic as to the concrete API architecture
   for Broker/Agent communication.  Since in model A, the Broker/Agent
   communication is done at the layer between the TEEP and TEEP/HTTP
   implementations, and there may be some architectures that do not
   support calls out of the TEE (which would be downcalls from TEEP in
   model A), we will refer to passing information up to the TEEP
   implementation as API calls, but will simply refer to "passing data"
   back down from a TEEP implementation.  A concrete API might pass data
   back via an API downcall or via data returned from an API upcall.

   This document will also refer to passing "no" data back out of a TEEP
   implementation.  In a concrete API, this might be implemented by not
   making any downcall, or by returning 0 bytes from an upcall, for
   example.

4.  Use of HTTP as a Transport

   This document uses HTTP [RFC9110] as a transport.  For the motivation
   behind the HTTP recommendations in this document, see the discussion
   of HTTP as a transport in [RFC9205].

   Redirects MUST NOT be automatically followed.  Cookies are not used.

   Content is not intended to be treated as active by browsers and so
   HTTP responses with content MUST have the following header fields as
   explained in Section 4.13 of [RFC9205] (using the TEEP media type
   defined in [I-D.ietf-teep-protocol]):

       Content-Type: application/teep+cbor
       X-Content-Type-Options: nosniff
       Content-Security-Policy: default-src 'none'
       Referrer-Policy: no-referrer

   Only the POST method is specified for TAM resources exposed over
   HTTP.  Since POST responses without explicit freshness information
   are uncacheable (see Section 9.3.3 of [RFC9110]), the Cache-Control
   header MUST NOT be used.



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   A URI of such a resource is referred to as a "TAM URI".  A TAM URI
   can be any HTTP(S) URI.  The URI to use is configured in a TEEP Agent
   via an out-of-band mechanism, as discussed in the next section.

   It is RECOMMENDED that implementations use HTTPS.  Although TEEP is
   protected end-to-end inside of HTTP, there is still value in using
   HTTPS for transport, since HTTPS can provide additional protections
   as discussed in Section 6 of [RFC9205].

   However, there may be constrained nodes where code space is an issue.
   [RFC7925] provides TLS profiles that can be used in many constrained
   nodes, but in rare cases the most constrained nodes might need to use
   HTTP without a TLS stack, relying on the end-to-end security provided
   by the TEEP protocol.  See Sections 4.4.2 and 6 of [RFC9205] for more
   discussion of additional security considerations that apply in this
   case.

   When HTTPS is used, clients MUST use the procedures detailed in
   Section 4.3.4 of [RFC9110] to verify the authenticity of the server.
   See [BCP195] for additional TLS recommendations and [RFC7925] for TLS
   recommendations related to IoT devices.

5.  TEEP/HTTP Client Behavior

5.1.  Receiving a request to install a new Trusted Application

   In some environments, an application installer can determine (e.g.,
   from an application manifest) that the application being installed or
   updated has a dependency on a given Trusted Application (TA) being
   available in a given type of TEE.  In such a case, it will notify a
   TEEP Broker, where the notification will contain the following:

   *  A unique identifier of the TA

   *  Optionally, any metadata to provide to the TEEP Agent.  This might
      include a TAM URI provided in the application manifest, for
      example.

   *  Optionally, any requirements that may affect the choice of TEE, if
      multiple are available to the TEEP Broker.

   When a TEEP Broker receives such a notification, it first identifies
   in an implementation-dependent way which TEE (if any) is most
   appropriate based on the constraints expressed.  If there is only one
   TEE, the choice is obvious.  Otherwise, the choice might be based on
   factors such as capabilities of available TEE(s) compared with TEE
   requirements in the notification.  Once the TEEP Broker picks a TEE,
   it passes the notification to the TEEP/HTTP Client for that TEE.



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   The TEEP/HTTP Client then informs the TEEP Agent in that TEE by
   invoking an appropriate "RequestTA" API that identifies the TA needed
   and any other associated metadata.  The TEEP/HTTP Client need not
   know whether the TEE already has such a TA installed or whether it is
   up to date.

   The TEEP Agent will either (a) pass no data back, (b) pass back a TAM
   URI to connect to, or (c) pass back a message and TAM URI to send it
   to.  The TAM URI passed back may or may not be the same as the TAM
   URI, if any, provided by the TEEP/HTTP Client, depending on the TEEP
   Agent's configuration.  If they differ, the TEEP/HTTP Client MUST use
   the TAM URI passed back.

5.1.1.  Session Creation

   If no data is passed back, the TEEP/HTTP Client simply informs its
   caller (e.g., the application installer) of success.

   If the TEEP Agent passes back a TAM URI with no message, the TEEP/
   HTTP Client attempts to create session state, then sends an HTTP(S)
   POST to the TAM URI with an Accept header field with the TEEP media
   type specified in [I-D.ietf-teep-protocol], and an empty body.  The
   HTTP request is then associated with the TEEP/HTTP Client's session
   state.

   If the TEEP Agent instead passes back a TAM URI with a message, the
   TEEP/HTTP Client attempts to create session state and handles the
   message as specified in Section 5.3.

   Session state consists of:

   *  Any context (e.g., a handle) that the TEEP Agent wishes to be
      provided back to it in any later conceptual API calls into it
      related to this session.

   *  Any context that identifies an HTTP request, if one is
      outstanding.  Initially, none exists.

5.2.  Receiving a notification that a Trusted Application is no longer
      needed

   In some environments, an application installer can determine (e.g.,
   from an application manifest) that a given Trusted Application is no
   longer needed, such as if the application that previously depended on
   the TA is uninstalled or updated in a way that removes the
   dependency.  In such a case, it will notify a TEEP Broker, where the
   notification will contain the following:




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   *  A unique identifier of the TA

   *  Optionally, any metadata to provide to the TEEP Agent.  This might
      include a TAM URI provided in the original application manifest,
      for example.

   *  Optionally, any requirements that may affect the choice of TEE, if
      multiple are available to the TEEP Broker.

   When a TEEP Broker receives such a notification, it first identifies
   in an implementation-dependent way which TEE (if any) is believed to
   contain the TA that is no longer needed, similar to the process in
   Section 5.1.  Once the TEEP Broker picks a TEE, it passes the
   notification to the TEEP/HTTP Client for that TEE.

   The TEEP/HTTP Client then informs the TEEP Agent in that TEE by
   invoking an appropriate "UnrequestTA" API that identifies the
   unneeded TA.  The TEEP/HTTP Client need not know whether the TEE
   actually has the TA installed.

   Finally, the TEEP Agent responds to the TEEP/HTTP Client as in
   Section 5.1.  Specifically, the TEEP Agent will either (a) pass no
   data back, (b) pass back a TAM URI to connect to, or (c) pass back a
   message and TAM URI to send it to.  The TAM URI passed back may or
   may not be the same as the TAM URI, if any, provided by the TEEP/HTTP
   Client, depending on the TEEP Agent's configuration.  If they differ,
   the TEEP/HTTP Client MUST use the TAM URI passed back.

   Processing then continues as in Section 5.1.1.

5.3.  Getting a TAM URI and message back from a TEEP Agent

   When a TEEP Agent passes a TAM URI and optionally a message to a
   TEEP/HTTP Client, the TEEP/HTTP Client MUST do the following, using
   the TEEP/HTTP Client's session state associated with its API call to
   the TEEP Agent.

   The TEEP/HTTP Client sends an HTTP POST request to the TAM URI with
   Accept and Content-Type header fields with the TEEP media type, and a
   body containing the TEEP message (if any) provided by the TEEP Agent.
   The HTTP request is then associated with the TEEP/HTTP Client's
   session state.

5.4.  Receiving an HTTP response

   When an HTTP response is received in response to a request associated
   with a given session state, the TEEP/HTTP Client MUST do the
   following.



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   If the HTTP response body is empty, the TEEP/HTTP Client's task is
   complete, and it can delete its session state, and its task is done.

   If instead the HTTP response body is not empty, the TEEP/HTTP Client
   passes (e.g., using the "ProcessTeepMessage" API as mentioned in
   Section 6.2.1 of [I-D.ietf-teep-architecture]) the response body up
   to the TEEP Agent associated with the session.  The TEEP Agent will
   then either pass no data back, or pass back a message.

   If no data is passed back, the TEEP/HTTP Client's task is complete,
   and it can delete its session state, and inform its caller (e.g., the
   application installer) of success.

   If instead the TEEP Agent passes back a message, the TEEP/HTTP Client
   handles the message as specified in Section 5.3.

5.5.  Handling checks for policy changes

   An implementation MUST provide a way to periodically check for TAM
   policy changes, such as a Trusted Application needing to be deleted
   from a TEE because it is no longer permitted, or needing to be
   updated to a later version.  This can be done in any implementation-
   specific manner, such as any of the following or a combination
   thereof:

   A) The TEEP/HTTP Client might call up to the TEEP Agent at an
   interval previously specified by the TEEP Agent.  This approach
   requires that the TEEP/HTTP Client be capable of running a periodic
   timer.

   B) The TEEP/HTTP Client might be informed when an existing TA is
   invoked, and call up to the TEEP Agent if more time has passed than
   was previously specified by the TEEP Agent.  This approach allows the
   device to go to sleep for a potentially long period of time.

   C) The TEEP/HTTP Client might be informed when any attestation
   attempt determines that the device is out of compliance, and call up
   to the TEEP Agent to remediate.

   The TEEP/HTTP Client informs the TEEP Agent by invoking an
   appropriate "RequestPolicyCheck" API.  The TEEP Agent will either (a)
   pass no data back, (b) pass back a TAM URI to connect to, or (c) pass
   back a message and TAM URI to send it to.  Processing then continues
   as specified in Section 5.1.1.







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   The TEEP Agent might need to talk to multiple TAMs, however, as shown
   in Figure 1 of [I-D.ietf-teep-architecture].  To accomplish this, the
   TEEP/HTTP Client keeps invoking the "RequestPolicyCheck" API until
   the TEEP Agent passes no data back, so that the TEEP Agent can return
   each TAM URI in response to a separate API call.

5.6.  Error handling

   If any local error occurs where the TEEP/HTTP Client cannot get a
   message (empty or not) back from the TEEP Agent, the TEEP/HTTP Client
   deletes its session state, and informs its caller (if any, e.g., the
   application installer) of a failure.  Note that no timeout check is
   used at the TEEP/HTTP Client layer; any timeout would be done inside
   the TEEP Agent.

   If any HTTP request results in an HTTP error response or a lower
   layer error (e.g., network unreachable), the TEEP/HTTP Client calls
   the TEEP Agent's "ProcessError" API, and then deletes its session
   state and informs its caller of a failure.

6.  TEEP/HTTP Server Behavior

6.1.  Receiving an HTTP POST request

   If the TAM does not receive the appropriate Content-Type header field
   value, the TAM SHOULD fail the request, returning a 415 Unsupported
   Media Type response.  Similarly, if an appropriate Accept header
   field is not present, the TAM SHOULD fail the request with an
   appropriate error response.  (This is for consistency with common
   implementation practice to allow the HTTP server to choose a default
   error response, since in some implementations the choice is done at
   the HTTP layer rather than the layer at which TEEP-over-HTTP would be
   implemented.)  Otherwise, processing continues as follows.

   When an HTTP POST request is received with an empty body, this
   indicates a request for a new TEEP session, and the TEEP/HTTP Server
   invokes the TAM's "ProcessConnect" API.  The TAM will then pass back
   a message.

   When an HTTP POST request is received with a non-empty body, this
   indicates a message on an existing TEEP session, and the TEEP/HTTP
   Server passes the request body to the TAM (e.g., using the
   "ProcessTeepMessage" API mentioned in [I-D.ietf-teep-architecture]).
   The TAM will then pass back a (possibly empty) message.







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6.2.  Getting an empty message back from the TAM

   If the TAM passes back an empty message, the TEEP/HTTP Server sends a
   successful (2xx) response with no body.  It SHOULD be status 204 (No
   Content).

6.3.  Getting a message from the TAM

   If the TAM passes back a non-empty message, the TEEP/HTTP Server
   generates a successful (2xx) response with a Content-Type header
   field with the TEEP media type, and with the message as the body.

6.4.  Error handling

   If any error occurs where the TEEP/HTTP Server cannot get a message
   (empty or not) back from the TAM, the TEEP/HTTP Server generates an
   appropriate HTTP 5xx error response.  Note that no timeout check is
   used at the TEEP/HTTP Client layer; any timeout would be handled
   inside the TEEP Agent.

7.  Sample message flow

   The following shows a sample TEEP message flow that uses application/
   teep+cbor as the Content-Type.

   1.   An application installer determines (e.g., from an application
        manifest) that the application has a dependency on TA "X", and
        passes this notification to the TEEP Broker.  The TEEP Broker
        picks a TEE (e.g., the only one available) based on this
        notification, and passes the information to the TEEP/HTTP Client
        for that TEE.

   2.   The TEEP/HTTP Client calls the TEEP Agent's "RequestTA" API,
        passing TA Needed = X.

   3.   The TEEP Agent finds that no such TA is already installed, but
        that it can be obtained from a given TAM.  The TEEP Agent passes
        back the TAM URI (e.g., "https://example.com/tam") to the TEEP/
        HTTP Client.

   4.   The TEEP/HTTP Client sends an HTTP POST request to the TAM URI:

              POST /tam HTTP/1.1
              Host: example.com
              Accept: application/teep+cbor
              Content-Length: 0
              User-Agent: Foo/1.0




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        where the TEEP/HTTP Client fills in an implementation-specific
        value in the User-Agent header field.

   5.   On the TAM side, the TEEP/HTTP Server receives the HTTP POST
        request, and calls the TAM's "ProcessConnect" API.

   6.   The TAM generates a TEEP message (where typically QueryRequest
        is the first message) and passes it to the TEEP/HTTP Server.

   7.   The TEEP/HTTP Server sends an HTTP successful response with the
        TEEP message in the body:

              HTTP/1.1 200 OK
              Content-Type: application/teep+cbor
              Content-Length: [length of TEEP message here]
              Server: Bar/2.2
              X-Content-Type-Options: nosniff
              Content-Security-Policy: default-src 'none'
              Referrer-Policy: no-referrer

              [TEEP message here]

        where the TEEP/HTTP Server fills in an implementation-specific
        value in the Server header field.

   8.   Back on the TEEP Agent side, the TEEP/HTTP Client gets the HTTP
        response, extracts the TEEP message and passes it up to the TEEP
        Agent.

   9.   The TEEP Agent processes the TEEP message, and generates a TEEP
        response (e.g., QueryResponse) which it passes back to the TEEP/
        HTTP Client.

   10.  The TEEP/HTTP Client gets the TEEP message and sends an HTTP
        POST request to the TAM URI, with the TEEP message in the body:

             POST /tam HTTP/1.1
             Host: example.com
             Accept: application/teep+cbor
             Content-Type: application/teep+cbor
             Content-Length: [length of TEEP message here]
             User-Agent: Foo/1.0

             [TEEP message here]

   11.  The TEEP/HTTP Server receives the HTTP POST request, and passes
        the payload up to the TAM.




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   12.  Steps 6-11 are then repeated until the TAM passes no data back
        to the TEEP/HTTP Server in step 6.

   13.  The TEEP/HTTP Server sends an HTTP successful response with no
        body:

             HTTP/1.1 204 No Content
             Server: Bar/2.2

   14.  The TEEP/HTTP Client deletes its session state.

8.  Security Considerations

   Section 4 discussed security recommendations for HTTPS transport of
   TEEP messages.  See Section 6 of [RFC9205] for additional discussion
   of HTTP(S) security considerations.  See section 9 of
   [I-D.ietf-teep-architecture] for security considerations specific to
   the use of TEEP.  See Section 7 of [RFC3986] for security
   considerations on dereferencing URIs.

9.  IANA Considerations

   This document has no actions for IANA.

10.  References

10.1.  Normative References

   [BCP195]   Sheffer, Y., Saint-Andre, P., and T. Fossati,
              "Recommendations for Secure Use of Transport Layer
              Security (TLS) and Datagram Transport Layer Security
              (DTLS)", BCP 195, RFC 9325, DOI 10.17487/RFC9325, November
              2022, <https://www.rfc-editor.org/rfc/rfc9325>.

   [I-D.ietf-teep-protocol]
              Tschofenig, H., Pei, M., Wheeler, D. M., Thaler, D., and
              A. Tsukamoto, "Trusted Execution Environment Provisioning
              (TEEP) Protocol", Work in Progress, Internet-Draft, draft-
              ietf-teep-protocol-12, 13 March 2023,
              <https://datatracker.ietf.org/doc/html/draft-ietf-teep-
              protocol-12>.

   [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/rfc/rfc2119>.





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   [RFC3986]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
              Resource Identifier (URI): Generic Syntax", STD 66,
              RFC 3986, DOI 10.17487/RFC3986, January 2005,
              <https://www.rfc-editor.org/rfc/rfc3986>.

   [RFC7925]  Tschofenig, H., Ed. and T. Fossati, "Transport Layer
              Security (TLS) / Datagram Transport Layer Security (DTLS)
              Profiles for the Internet of Things", RFC 7925,
              DOI 10.17487/RFC7925, July 2016,
              <https://www.rfc-editor.org/rfc/rfc7925>.

   [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/rfc/rfc8174>.

   [RFC9110]  Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke,
              Ed., "HTTP Semantics", STD 97, RFC 9110,
              DOI 10.17487/RFC9110, June 2022,
              <https://www.rfc-editor.org/rfc/rfc9110>.

10.2.  Informative References

   [I-D.ietf-teep-architecture]
              Pei, M., Tschofenig, H., Thaler, D., and D. M. Wheeler,
              "Trusted Execution Environment Provisioning (TEEP)
              Architecture", Work in Progress, Internet-Draft, draft-
              ietf-teep-architecture-19, 24 October 2022,
              <https://datatracker.ietf.org/doc/html/draft-ietf-teep-
              architecture-19>.

   [RFC9000]  Iyengar, J., Ed. and M. Thomson, Ed., "QUIC: A UDP-Based
              Multiplexed and Secure Transport", RFC 9000,
              DOI 10.17487/RFC9000, May 2021,
              <https://www.rfc-editor.org/rfc/rfc9000>.

   [RFC9205]  Nottingham, M., "Building Protocols with HTTP", BCP 56,
              RFC 9205, DOI 10.17487/RFC9205, June 2022,
              <https://www.rfc-editor.org/rfc/rfc9205>.

Author's Address

   Dave Thaler
   Microsoft

   Email: dthaler@microsoft.com






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