EST (Enrollment over Secure Transport) Extensions
draft-turner-est-extensions-11

Versions: 00 01 02 03 04 05 06 07 08 09 10 11            Standards Track
Network Working Group                                        Sean Turner
Internet Draft                                                     sn3rd
Intended Status: Standards Track                      September 29, 2017
Expires: April 2, 2018

           EST (Enrollment over Secure Transport) Extensions
                   draft-turner-est-extensions-10.txt

Abstract

   The EST (Enrollment over Secure Transport) protocol defined a Well-
   Known URI (Uniform Resource Identifier): /.well-known/est along with
   a number of other path components that clients use for PKI (Public
   Key Infrastructure) services, namely certificate enrollment (e.g.,
   /simpleenroll).  This document defines a number of other PKI services
   as additional path components, specifically firmware and trust
   anchors as well as symmetric, asymmetric, and encrypted keys.  This
   document also specifies the PAL (Package Availability List), which is
   an XML (Extensible Markup Language) file or JSON (JavaScript Object
   Notation) object that clients use to retrieve packages available and
   authorized for them.  This document extends the EST server path
   components to provide these additional services.

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 http://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."

Copyright Notice

   Copyright (c) 2017 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://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



Turner                   Expires April 2, 2018                  [Page 1]


Internet-Draft               EST Extensions           September 29, 2017


   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 . . . . . . . . . . . . . . . . . . . . . . . . .  3
     1.1.  Definitions  . . . . . . . . . . . . . . . . . . . . . . .  5
     1.2.  Authentication and Authorization . . . . . . . . . . . . .  6
     1.3.  TLS Cipher Suites  . . . . . . . . . . . . . . . . . . . .  6
     1.4.  URI Configuration  . . . . . . . . . . . . . . . . . . . .  6
     1.5.  Message Types  . . . . . . . . . . . . . . . . . . . . . .  6
     1.6.  Key Words  . . . . . . . . . . . . . . . . . . . . . . . .  8
   2.  Locate Available Packages  . . . . . . . . . . . . . . . . . .  9
     2.1.  PAL Format . . . . . . . . . . . . . . . . . . . . . . . . 11
       2.1.1.  PAL Package Types  . . . . . . . . . . . . . . . . . . 12
       2.1.2.  PAL XML Schema . . . . . . . . . . . . . . . . . . . . 17
       2.1.3.  PAL JSON Object  . . . . . . . . . . . . . . . . . . . 20
     2.2.  Request PAL  . . . . . . . . . . . . . . . . . . . . . . . 21
     2.3.  Provide PAL  . . . . . . . . . . . . . . . . . . . . . . . 21
   3.  Distribute EE Certificates . . . . . . . . . . . . . . . . . . 22
     3.1.  EE Certificate Request . . . . . . . . . . . . . . . . . . 23
     3.2.  EE Certificate Response  . . . . . . . . . . . . . . . . . 23
   4.  Distribute CRLs and ARLs . . . . . . . . . . . . . . . . . . . 23
     4.1.  CRL Request  . . . . . . . . . . . . . . . . . . . . . . . 23
     4.2.  CRL Response . . . . . . . . . . . . . . . . . . . . . . . 24
   5. Symmetric Keys, Receipts, and Errors  . . . . . . . . . . . . . 24
     5.1.  Symmetric Keys . . . . . . . . . . . . . . . . . . . . . . 24
       5.1.1.  Distribute Symmetric Keys  . . . . . . . . . . . . . . 25
       5.1.2.  Symmetric Key Response . . . . . . . . . . . . . . . . 25
     5.2.  Symmetric Key Receipts and Errors  . . . . . . . . . . . . 26
       5.2.1.  Provide Symmetric Key Receipt or Error . . . . . . . . 27
       5.2.2.  Symmetric Key Receipt or Error Response  . . . . . . . 28
   6.  Firmware, Receipts, and Errors . . . . . . . . . . . . . . . . 28
     6.1.  Firmware . . . . . . . . . . . . . . . . . . . . . . . . . 28
       6.1.1.  Distribute Firmware  . . . . . . . . . . . . . . . . . 28
       6.1.2.  Firmware Response  . . . . . . . . . . . . . . . . . . 29
     6.2.  Firmware Receipts and Errors . . . . . . . . . . . . . . . 29
       6.2.1.  Provide Firmware Receipt or Error  . . . . . . . . . . 30
       6.2.2.  Firmware Receipt or Error Response . . . . . . . . . . 30
   7.  Trust Anchor Management Protocol . . . . . . . . . . . . . . . 30
     7.1.  TAMP Status Query, Trust Anchor Update, Apex Trust
           Anchor Update, . . . . . . . . . . . . . . . . . . . . . . 31
         Community Update, and Sequence Number Adjust . . . . . . . . 31
       7.1.1.  Request TAMP Packages  . . . . . . . . . . . . . . . . 31
       7.1.2.  Return TAMP Packages . . . . . . . . . . . . . . . . . 31



Turner                   Expires April 2, 2018                  [Page 2]


Internet-Draft               EST Extensions           September 29, 2017


     7.2.  TAMP Response, Confirm, and Errors . . . . . . . . . . . . 32
       7.2.1.  Provide TAMP Response, Confirm, or Error . . . . . . . 32
       7.2.2.  TAMP Response, Confirm, and Error Response . . . . . . 32
   8.  Asymmetric Keys, Receipts, and Errors  . . . . . . . . . . . . 33
     8.1.  Asymmetric Key Encapsulation . . . . . . . . . . . . . . . 33
     8.2.  Asymmetric Key Package Receipts and Errors . . . . . . . . 34
     8.3.  PKCS#12  . . . . . . . . . . . . . . . . . . . . . . . . . 35
       8.3.1.  Server-Side Key Generation Request . . . . . . . . . . 35
       8.3.2.  Server-Side Key Generation Response  . . . . . . . . . 35
   9.  PAL & Certificate Enrollment . . . . . . . . . . . . . . . . . 36
   10.  Security Considerations . . . . . . . . . . . . . . . . . . . 38
   11.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . 39
     11.1.  PAL Name Space  . . . . . . . . . . . . . . . . . . . . . 39
     11.2.  PAL XML Schema  . . . . . . . . . . . . . . . . . . . . . 39
     11.3.  PAL Package Types . . . . . . . . . . . . . . . . . . . . 40
   12.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . 40
   13.  References  . . . . . . . . . . . . . . . . . . . . . . . . . 40
     13.1.  Normative References  . . . . . . . . . . . . . . . . . . 40
     13.2.  Informative References  . . . . . . . . . . . . . . . . . 45
   Appendix A.  Example Use of PAL  . . . . . . . . . . . . . . . . . 45
   Appendix B.  Additional CSR Attributes . . . . . . . . . . . . . . 47
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 48


1.  Introduction

   The EST (Enrollment over Secure Transport) protocol [RFC7030] defines
   the Well-Known URI (Uniform Resource Identifier) /.well-known/est to
   support selected PKI (Public Key Infrastructure) related services
   with path components (PCs) such as simple enrollment with
   /simpleenroll, rekey or renew with /simplereenroll, etc.  A server
   that wishes to support additional PKI-related services and other
   security-related packages could use the same .well-known URI by
   defining additional PCs.  This document defines six such PCs:

     o /pal - The PAL (Package Availability List) provides a list of all
       known packages available and authorized for a client.  By
       accessing the service provided by this PC first, the client can
       walk through the PAL and download all the packages necessary to
       begin operating securely.  The PAL essentially points to other
       PCs including the ones defined in this document as well as those
       defined in [RFC7030], which include /cacerts, /simpleenroll,
       /simplereenroll, /fullcmc, /serverkeygen, and /csrattrs.  The
       /pal PC is described in Section 2.

     o /eecerts - EE (End-Entity) certificates [RFC5280] are needed by
       the client when they invoke a security protocol for communicating
       with a peer (i.e., they become operational and do something



Turner                   Expires April 2, 2018                  [Page 3]


Internet-Draft               EST Extensions           September 29, 2017


       meaningful as opposed to just communicating with the
       infrastructure).  If the infrastructure knows the certificate(s)
       needed by the client, then providing the peer's certificate
       avoids the client having to discover the peer's certificate.
       This service is not meant to be a general purpose repository to
       which clients query a "repository" and then get a response; this
       is purely a push mechanism.  The /eecerts PC is described in
       Section 3.

     o /crls - CRLs (Certificate Revocation Lists) and Authority
       Revocation Lists (ARLs) [RFC5280] are also needed by the client
       when they validate certificate paths.  CRLs (and ARLs) from TAs
       (Trust Anchors) and intermediate CAs (Certification Authorities)
       are needed to validate the certificates used to generate the
       client's certificate or the peer's certificate, which is provided
       by the /eecerts PC, and providing them saves the client from
       having to "discover" them and then retrieve them.  CRL
       "discovery" is greatly aided by the inclusion of the CRL
       Distribution Point certificate extension [RFC5280], but this
       extension is not always present in certificates and requires
       another connection to retrieve them.  Like the /eecerts PC, this
       service is not meant to be a general purpose repository to which
       clients query a repository and then get a response; this is
       purely a push mechanism.  The /crls PC is described in Section 4.

     o /symmetrickeys - In some cases, clients use symmetric keys
       [RFC6031] when communicating with their peers.  If the client's
       peers are known by the server a priori, then providing them saves
       the client or an administrator from later having to find,
       retrieve and install them.  Like the /eecerts and /crls PCs, this
       service is not meant to be a general purpose repository to which
       clients query a repository and then get a response; this is
       purely a push mechanism for the keys themselves.  However, things
       do not always go as planned and clients need to inform the server
       about any errors.  If things did go well, then the client, if
       requested, needs to provide a receipt [RFC7191].  The
       /symmetrickeys and /symmetrickeys/return PCs are described in
       Section 5.

     o /firmware - Some client firmware and software support automatic
       update mechanisms and some do not.  For those that do not, the
       /firmware PC provides a mechanism for the infrastructure to
       inform the client that firmware and software updates [RFC4108]
       are available.  Because updates do not always go as planned and
       because sometimes the server needs to know whether the firmware
       was received and processed, this PC also provides a mechanism to
       return errors and receipts.  The /firmware and /firmware/return
       PCs are defined in Section 6.



Turner                   Expires April 2, 2018                  [Page 4]


Internet-Draft               EST Extensions           September 29, 2017


     o /tamp - To control the TAs in client TA databases, servers use
       the /tamp PC to request that clients retrieve a TAMP (Trust
       Anchor Management Protocol) query, update, and adjust packages
       [RFC5934] and clients use the /tamp/return PC to return TAMP
       response, confirm, and error [RFC5934]. The /tamp and
       /tamp/return PCs are defined in Section 7.

   This document also extends the /est/serverkeygen PC [RFC7030] to
   support (see Section 8):

     o Returning asymmetric key package receipts and errors [RFC7191].

     o Encapsulating returned asymmetric keys in additional CMS content
       types [RFC7193].

     o Returning server-generated public key pairs encapsulated in
       PKCS#12 [RFC7292].

   While the motivation is to provide packages to clients during
   enrollment so that they can perform securely after enrollment, the
   services defined in this specification can be used after enrollment.

1.1.  Definitions

   Familiarity with Using Cryptographic Message Syntax (CMS) to Protect
   Firmware Packages [RFC4108], Certificate Management over CMS (CMC)
   [RFC5272], Cryptographic Message Syntax (CMS) Encrypted Key Package
   [RFC6032], Cryptographic Message Syntax (CMS) [RFC5652][RFC6268],
   Trust Anchor Management Protocol (TAMP) [RFC5934], Cryptographic
   Message Syntax (CMS) Content Constraints Extension [RFC6010], CMS
   Symmetric Key Package Content Type [RFC6031], Enrollment over Secure
   Transport protocol [RFC7030], CMS Key Package Receipt and Error
   Content Types [RFC7191] is assumed.  Also, familiarity with the CMS
   protecting content types signed data and encrypted data is assumed;
   CMS signed data and encrypted data are defined in [RFC5652] and CMS
   encrypted key package is defined in [RFC6032].

   In addition to the definitions found in [RFC7030], the following
   definitions are used in this document:

   Agent: An entity that performs functions on behalf of a client.
   Agents can service a) one or more clients on the same network as the
   server, b) clients on non-IP based networks, or c) clients that have
   a non-electronic air gap [RFC4949] between themselves and the server.
    Interactions between the agent and client in the last two cases are
   beyond the scope of this document.  Before an agent can service
   clients, the agent must have a trust relationship with the server, be
   authorized to act on behalf of clients.



Turner                   Expires April 2, 2018                  [Page 5]


Internet-Draft               EST Extensions           September 29, 2017


   Client: A device that ultimately consumes and uses the packages to
   enable communications.  In other words, the client is the end-point
   for the packages and an agent may have one or more clients.  To avoid
   confusion, this document henceforth uses the term client to refer to
   both agents and clients.

   Package: An object that contains one or more content types.  There
   are numerous types of packages: Asymmetric Keys, Symmetric Keys,
   Encrypted Keys, CRLs, Public Key Certificate Management, Firmware,
   Public Key Certificates, and TAMP packages.  All of these packages
   are digitally signed by their creator and encapsulated in a CMS
   signed data [RFC5652][RFC6268] (except the public key certificates
   and CRLs that are already digitally signed by a CA); Firmware
   receipts and errors, TAMP responses, confirms, and errors, as well as
   Key Package receipts and errors that can be optionally signed.
   Certificate and CRLs are included in a package that uses signed data,
   which is often referred to as a degenerate CMS or "certs-only" or
   "crls-only" message [RFC5751][RFC6268], but no signature or content
   is present; hence the name certs-only and crls-only.

   Note: As per [RFC7030], the creator may or may not be the EST server
   or the EST CA.

1.2.  Authentication and Authorization

   Client and server authentication as well as client and server
   authorization are as defined in [RFC7030].  The requirements for each
   are discussed in the request and response sections of each of the PCs
   defined by this document.

   The requirements for the TA databases are as specified in [RFC7030]
   as well.

1.3.  TLS Cipher Suites

   TLS cipher suite and issues associated with them are as defined in
   [RFC7030].

1.4.  URI Configuration

   As specified in Section 3.1 of [RFC7030], the client is configured
   with sufficient information to form the server URI [RFC3986].  Like
   EST, this configuration mechanism is beyond the scope of this
   document.

1.5.  Message Types

   This document uses existing media types for the messages as specified



Turner                   Expires April 2, 2018                  [Page 6]


Internet-Draft               EST Extensions           September 29, 2017


   by "Internet X.509 Public Key Infrastructure Protocol: FTP and HTTP"
   [RFC2585], "The application/pkcs10 Media Type" [RFC5967], and CMC
   [RFC5272].

   For consistency with [RFC5273], each distinct EST message type uses
   an HTTP Content-Type header with a specific media type.

   The EST messages and their corresponding media types for each
   operation are:

   +--------------------+--------------------------+-------------------+
   | Message type       | Request media type       | Request section(s)|
   |                    | Response media type(s)   | Response section  |
   | (per operation)    | Source(s) of types       |                   |
   +====================+==========================+===================+
   | Locate Available   | N/A                      | Section 2.2       |
   | Packages           | application/xml or       | Section 2.3       |
   |                    | application/json         |                   |
   |                    | [RFC7303][RFC7159]       |                   |
   | /pal               |                          |                   |
   +====================+==========================+===================+
   | Distribute EE      | N/A                      | Section 3.1       |
   | Certificates       | application/pkcs7-mime   | Section 3.2       |
   |                    | [RFC5751]                |                   |
   | /eecerts           |                          |                   |
   +====================+==========================+===================+
   | Distribute CRLs    | N/A                      | Section 4.1       |
   |                    | application/pkcs7-mime   | Section 4.2       |
   |                    | [RFC5751]                |                   |
   | /crls              |                          |                   |
   +====================+==========================+===================+
   | Symmetric Key      | N/A                      | Section 5.1.1     |
   | Distribution       | application/cms          | Section 5.1.2     |
   |                    | [RFC7193]                |                   |
   | /symmetrickeys     |                          |                   |
   +====================+==========================+===================+
   | Return Symmetric   | application/cms          | Section 5.2.1     |
   | Key                | N/A                      | Section 5.2.2     |
   | Receipts/Errors    | [RFC7193]                |                   |
   |                    |                          |                   |
   | /symmetrickeys/    |                          |                   |
   |    return          |                          |                   |
   +====================+==========================+===================+
   | Firmware           | N/A                      | Section 6.1.1     |
   | Distribution       | application/cms          | Section 6.1.2     |
   |                    | [RFC7193]                |                   |
   | /firmware          |                          |                   |
   +====================+==========================+===================+



Turner                   Expires April 2, 2018                  [Page 7]


Internet-Draft               EST Extensions           September 29, 2017


   | Return Firmware    | application/cms          | Section 6.2.1     |
   | Receipts/Errors    | N/A                      | Section 6.2.2     |
   |                    | [RFC7193]                |                   |
   | /firmware/return   |                          |                   |
   +====================+==========================+===================+
   | Trust Anchor       | N/A                      | Section 7.1.1     |
   | Management         | application/             | Section 7.1.2     |
   |                    |   tamp-status-query      |                   |
   |                    |   tamp-update            |                   |
   |                    |   tamp-apex-update       |                   |
   |                    |   tamp-community-update  |                   |
   |                    |   tamp-sequence-adjust   |                   |
   |                    | [RFC5934]                |                   |
   | /tamp              |                          |                   |
   +====================+==========================+===================+
   | Return TAMP        | application/             | Section 7.2.1     |
   | Responses/         |   tamp-status-query-response    |            |
   | Confirms/          |   tamp-update-confirm           |            |
   | Errors             |   tamp-apex-update-confirm      |            |
   |                    |   tamp-community-update-confirm |            |
   |                    |   tamp-sequence-adjust-confirm  |            |
   |                    |   tamp-error                    |            |
   |                    | N/A                      | Section 7.2.2     |
   |                    | [RFC5934]                |                   |
   | /tamp/return       |                          |                   |
   +====================+==========================+===================+
   | Server-Side Key    | application/pkcs10 with  | Section 8.1       |
   | Generation         | content type attribute   |                   |
   |                    | CSR                      |                   |
   |                    | application/cms          | Section 8.1       |
   | /serverkeygen      | [RFC7193]                |                   |
   +====================+==========================+===================+
   | Return Asymmetric  | application/cms          | Section 8.2       |
   | Key                | N/A                      | Section 8.2       |
   | Receipts/Errors    | [RFC7193]                |                   |
   |                    |                          |                   |
   | /serverkeygen/     |                          |                   |
   |    return          |                          |                   |
   +====================+==========================+===================+
   | Server-Side Key    | application/pkcs10       | Section 8.3.1     |
   | Generation:        | application/pkcs12       | Section 8.3.2     |
   | PKCS#12            |                          |                   |
   |                    |                          |                   |
   | /serverkeygen      | [RFC7193]                |                   |
   +====================+==========================+===================+

1.6.  Key Words




Turner                   Expires April 2, 2018                  [Page 8]


Internet-Draft               EST Extensions           September 29, 2017


   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
   [RFC2119].

2.  Locate Available Packages

   The PAL (Package Availability List) is either an XML (Extensible
   Markup Language) [XML] or JSON (JavasScript Object Notation)
   [RFC7159] object available through the /pal PC that furnishes the
   following information to clients:

     o Advertisements for available packages that can be retrieved from
       the server;

     o Notifications to begin public key certificate management or to
       return package receipts and errors; and

     o Advertisement for another PAL.

   After being configured (see Section 1.4), the client can use this
   service to retrieve their PAL (see Section 2.1) that, if properly
   constructed (see Section 2.3), allows the client to determine some or
   all of the security-related packages needed for bootstrapping.  Each
   PAL entry refers to other PCs, defined in this document as well as
   those defined in [RFC7030], that clients use to retrieve packages,
   e.g., CA certificates, firmware, trust anchors, symmetric keys, and
   asymmetric keys, available for it or to be notified to initiate
   public key certificate enrollment.  PAL entries can also be used to
   notify clients they are to return receipts or errors for certain
   packages (see Section 2.1.1).  Placing these entries after entries
   that clients used to retrieve the packages is the same as requesting
   receipts in the originally distributed package.  Figure 1 provides a
   ladder diagram for the /pal PC protocol flow.  Appendix A provides a
   detailed example.

                      |                      |
            Client    |     Establish TLS    |    Server
                      |        Session       |
                      |<-------------------->|
                      |                      |
                      |          Request PAL |
                      |   (HTTP GET Request) |
                      |--------------------->|
                      |<---------------------|
                      | Deliver PAL          |
                      | (HTTP GET Response)  |
                      |                      |



Turner                   Expires April 2, 2018                  [Page 9]


Internet-Draft               EST Extensions           September 29, 2017


                      | Request package by   |
                      | specified URI        |
                      | (HTTP GET or POST    |
                      |  Request)            |
                      |--------------------->|
                      |<---------------------|
                      | Deliver requested    |
                      | CMS package product  |
                      | (HTTP GET or POST    |
                      |  Response)           |
                      |                      |

                        repeat as necessary

                    Figure 1 - /pal Message Sequence

   PALs are designed to support an arbitrary number of entries, but for
   PALs that need to be divided for whatever reason there is a special
   PAL entry type, which are collectively referred to as PAL Package
   Types (see Sections 2.1 and 2.1.1), number 0001 is defined that
   refers to another PAL.  If present, the 0001 package type is always
   last because other entries after it are ignored.  Also, the 0001
   package type cannot be the only PAL entry to avoid needlessly
   dereferencing URIs.

   In addition to using the PAL during bootstrapping, clients can be
   configured to periodically poll the server to determine if there are
   updated packages available for it.  Note that the mechanism to
   configure how often clients poll the server is out-of-scope.
   However, there are some services that support indicating when to
   return (e.g., simple enrollment and re-enroll responses include the
   Retry-After header [RFC7030]).

   As noted earlier, the PAL support two variants: XML and JSON.
   Clients include the HTTP Accept header [RFC7231] when they connect to
   the server to indicate whether they support XML or JSON.

   The client MUST authenticate the server as specified in [RFC7030] and
   the client MUST check the server's authorization as specified in
   [RFC7030].

   The server MUST authenticate the client as specified in [RFC7030] and
   the server MUST check the client's authorization as specified in
   [RFC7030].

   PAL support is OPTIONAL.  It is shown in figures throughout this
   document but clients need not support the PAL to access services
   offered by the server.



Turner                   Expires April 2, 2018                 [Page 10]


Internet-Draft               EST Extensions           September 29, 2017


2.1.  PAL Format

   Each PAL is composed of zero or more entries.  Each entry is composed
   of four fields, type, date, size, and info, whose semantics follow:

     Note: Both XML elements and JSON values are described below. XML
     elements are enclosed in angle brackets <> and JSON values are
     enclosed in single quotes ''.  When described together they are
     enclosed in brackets [] separated by |.

     o [<type> | 'type'] uniquely identifies each package that a client
       may retrieve from the server with a 4-digit string.
       [<type> | 'type'] MUST be present.  The PAL Package Types are
       defined in Section 2.1.1.

     o [<date> | 'date'] either indicates:

       * The date and time that the client last successfully downloaded
         the identified package from the server.  [<date> | 'date'] MUST
         be represented as Generalized Time with 20 characters:
         YYYY-MM-DDTHH:MM:SSZ; <date> matches the dateTime production in
         "canonical representation" [XMLSCHEMA]; 'date' is a string.
         Implementations SHOULD NOT rely on time resolution finer than
         seconds and MUST NOT generate time instants that specify leap
         seconds.

       * The omission of [<date> | 'date'] indicates that:

         - There is no indication the client has successfully downloaded
           the identified package, or

         - The PAL entry corresponds to a pointer to the next PAL or the
           server is requesting a package from the client (e.g.,
           certification request, receipt, error).

     o [<size> | 'size'] indicates the size in bytes of the package;
       <size> is a nonNegativeInteger and 'size' is a number.  A package
       size of zero (i.e., "0" without the quotes) indicates that the
       client needs to begin a transaction or return an error or
       receipt.  [<size> | 'size'] MUST be present.

     o [<info> | 'info'] provides either an SKI (Subject Key
       Identifier), a DN (Distinguished Name), an Issuer and Serial
       Number tuple or a URI, i.e., it is a choice between these four
       all of which are defined in [RFC5280].  When a URI [RFC3986] is
       included, [<uri> | 'uri'] indicates the location where the
       identified package can be retrieved.  When a DN, an SKI, or an
       Issuer Name and Serial Number tuple is included it points to a



Turner                   Expires April 2, 2018                 [Page 11]


Internet-Draft               EST Extensions           September 29, 2017


       certificate that is the subject of the notification (i.e., the
       certificate to be rekeyed or renewed); [<dn> | 'dn'] is encoded
       as a string with the format defined in [RFC4514]; <ski> is a
       hexBinary and 'ski' is a string of hex digits (i.e., 0-9, a-f,
       and A-F); [<iasn> | 'iasn'] includes both [<issuer> | 'issuer']
       and [<serial> | 'serial'] as a complexType in XML and an object
       in JSON.  [<issuer> | 'issuer'] is a DN encoded as a string with
       the format defined in [RFC4514]; <serial> is a positiveInteger
       and 'serial' is a number.  [<info> | 'info'] MUST be present and
       [<info> | 'info'] MUST include exactly one [<dn> | 'dn'],
       [<ski> | 'ski'], [<iasn> | 'iasn'], or [<uri> | 'uri'].

   Clients are often limited by the size of objects they can consume,
   the PAL is not immune to these limitations.  As opposed to picking a
   limit for all clients, a special package type is defined, see Section
   2.1.1, to indicate that another PAL is available.   Servers can use
   this value to limit the size of the PALs provided to clients.  The
   mechanism for servers to know client PAL size limits is beyond the
   scope of the document; one possible solution is through provisioned
   information.

2.1.1.  PAL Package Types

   Table 1 lists the PAL package types that are defined by this
   document:

   NOTE: CSR is Certificate Signing Request, DS is Digital Signature and
   KE is Key Establishment.

   Package    Package Description
   Number
   --------   ---------------------------------------------------
   0000:      Reserved
   0001:      Additional PAL value present
   0002:      X.509 CA certificate
   0003:      X.509 EE certificate
   0004:      X.509 ARL
   0005:      X.509 CRL
   0006:      Start DS certificate enrollment with CSR attribute
   0007:      Start DS certificate enrollment
   0008:      DS certificate enrollment (success)
   0009:      DS certificate enrollment (failure)
   0010:      Start DS certificate re-enrollment
   0011:      DS certificate re-enrollment (success)
   0012:      DS certificate re-enrollment (failure)
   0013:      Start KE certificate enrollment with CSR attribute
   0014:      Start KE certificate enrollment
   0015:      KE certificate enrollment (success)



Turner                   Expires April 2, 2018                 [Page 12]


Internet-Draft               EST Extensions           September 29, 2017


   0016:      KE certificate enrollment (failure)
   0017:      Start KE certificate re-enrollment
   0018:      KE certificate re-enrollment (success)
   0019:      KE certificate re-enrollment (failure)
   0020:      Asymmetric Key Package (PKCS#8)
   0021:      Asymmetric Key Package (CMS)
   0022:      Asymmetric Key Package (PKCS#12)
   0023:      Asymmetric Key Package Receipt or Error
   0024:      Symmetric Key Package
   0025:      Symmetric Key Package Receipt or Error
   0026:      Firmware Package
   0027:      Firmware Package Receipt or Error
   0028:      TAMP Status Query
   0029:      TAMP Status Query Response or Error
   0030:      Trust Anchor Update
   0031:      Trust Anchor Update Confirm or Error
   0032:      Apex Trust Anchor Update
   0033:      Apex Trust Anchor Update Confirm or Error
   0034:      Community Update
   0035:      Community Update Confirm or Error
   0036:      Sequence Number Adjust
   0037:      Sequence Number Adjust Confirm or Error

                      Table 1 - PAL Package Types

   PAL package types are essentially hints about the type of package the
   client is about to retrieve or is asked to return.  Savvy clients can
   parse the packages to determine what has been provided, but in some
   instances it is better to know before retrieving the package.  The
   hint provided here does not obviate the need for clients to check the
   type of package provided before they store it possibly in specially
   allocated locations (i.e., some clients might store Root ARLs
   separately from intermediate CRLs).  For packages provided by the
   client, the server is asking the client to provide an enrollment
   package, receipt, response, confirm or error.

   The PAL package types have the following meaning:

   NOTE: The semantics behind Codes 0002 and 0006-0021 are defined in
   [RFC7030].

   0000 Reserved: Reserved for future use.

   0001 Additional PAL value present: Indicates that this PAL entry
          refers to another PAL by referring to another /pal URI, which
          is defined in this section.  This PAL package type limits the
          size of PALs to a more manageable size for clients.  If this
          PAL Package Type appears it MUST be the last entry in the PAL.



Turner                   Expires April 2, 2018                 [Page 13]


Internet-Draft               EST Extensions           September 29, 2017


           Additionally, this PAL Package Type MUST NOT the only entry
          to avoid endless dereferencing URIs.

   0002 X.509 CA certificate: Indicates that one or more CA certificates
          [RFC5280] are available for the client by pointing to a
          /cacerts URI, which is defined in [RFC7030].

   0003 X.509 EE certificate: Indicates that one or more EE certificate
          [RFC5280] is available for the client by pointing to an
          /eecerts URI, which is defined in Section 3.

   0004 X.509 ARL: Indicates that one or more ARL (Authority Revocation
          List) [RFC5280] is available for the client by pointing to a
          /crls URI, which is defined in Section 4.

   0005 X.509 CRL: Indicates that one or more CRL (Certificate
          Revocation List) [RFC5280] is available for the client by
          pointing to a /crls URI, which is defined in Section 4.

   NOTE:  See Section 9 for additional information about PAL and
   certificate enrollment interaction.  See Appendix B for additional
   informative information.

   0006 Start DS (Digital Signature) certificate enrollment with CSR:
          Indicates that the client begin enrolling their DS certificate
          (i.e., those certificates for which the key usage extension
          will have digital signature set) using a template provided by
          the server with a CSR (Certificate Signing Request) attribute
          (see Appendix B).  The PAL entry points to a /csrattrs URI,
          which is defined in [RFC7030].

   0007 Start DS (Digital Signature) certificate enrollment: Indicates
          that the client begin enrolling their DS certificate.  The PAL
          entry points to a /simpleenroll URI, which is defined in
          [RFC7030].

   0008 DS certificate enrollment (success): Indicates that the client
          retrieve a successful certification response.  The PAL entry
          points to a /simpleenroll or a /fullcmc URI, which are both
          defined in [RFC7030].

   0009 DS certificate enrollment (failure): Indicates that the client
          retrieve a failed certification response for a DS certificate.
           This PAL entry points to a /simpleenroll or a /fullcmc URI.

   0010 Start DS certificate re-enrollment: Indicates that the client
          rekey or renew a DS certificate.   The PAL entry points to a
          /simplereenroll or a /fullcmc URI.



Turner                   Expires April 2, 2018                 [Page 14]


Internet-Draft               EST Extensions           September 29, 2017


   0011 DS certificate re-enrollment (success): See PAL package type
          0008.

   0012 DS certificate re-enrollment (failure): See PAL package type
          0009.

   NOTE: The KE (Key Establishment) responses that follow use the same
   URIs as DS certificates except in the requested certificates the key
   usage extension request will have only either key agreement or key
   transport set.

   0013 Start KE certificate enrollment with CSR: See PAL package type
          0006.

   0014 Start KE certificate enrollment: See PAL package type 0007.

   0015 KE certificate enrollment (success): See PAL package type 0008.

   0016 KE certificate enrollment (failure): See PAL package type 0009.

   0017 Start KE certificate re-enrollment: See PAL package type 0010.

   0018 KE certificate re-enrollment (success): See PAL package type
          0008.

   0019 KE certificate re-enrollment (failure): See PAL package type
          0009.

   NOTE: The variations on the asymmetric key packages is due to the
   number of CMS content types that can be used to protect the
   asymmetric key; the syntax for the asymmetric key is the same but
   additional ASN.1 is needed to include it in a signed data (i.e., the
   ASN.1 needs to be a CMS content type not the private key info type).
   See Section 8 of this document for additional information.

   0020 Asymmetric Key Package (PKCS#8):  Indicates that an asymmetric
          key generated by the server is available for the client; the
          package is an asymmetric key without additional encryption as
          specified in Section 4.4.2 of [RFC7030].  The PAL entry points
          to a /serverkeygen or a /fullcmc URI, which are defined in
          [RFC7030].

   0021 Asymmetric Key Package (CMS): See PAL package type 0020.  The
          difference being that the package available is an asymmetric
          key package [RFC5958] that is signed and encapsulated in a
          signed data content type, as specified in Section 4.4.2 of
          [RFC7030].  Also, see Section 8.1 of this document.




Turner                   Expires April 2, 2018                 [Page 15]


Internet-Draft               EST Extensions           September 29, 2017


   0022 Asymmetric Key Package (PKCS#12): See PAL package type 0020.
          The difference being that the package available is PKCS12
          [RFC7292] content type.  See Section 8.3 of this document.

   0023 Asymmetric Key Package Receipt or Error: Indicates that the
          server wants the client to return a key package receipt or
          error [RFC7191] to the /serverkeygen/return URI, which is
          defined in Section 8.

   0024 Symmetric Key Package: Indicates that a symmetric key package
          [RFC6031] is available for the client by pointing to a
          /symmetrickeys URI, which is defined in Section 5.

   0025 Symmetric Key Package Receipt or Error: Indicates that the
          server wants the client to return a key package receipt or an
          error [RFC7191] to the /symmetrickeys/return URI, which is
          defined in Section 5.

   0026 Firmware Package: Indicates that a firmware package [RFC4108] is
          available for the client using the /firmware URI, which is
          defined in Section 6.

   0027 Firmware Package Receipt or Error: Indicates that the server
          wants the client to return a firmware package load receipt or
          error [RFC4108] to the /firmware/return URI, which is defined
          in Section 6.

   NOTE: The /tamp and tamp/return URIs are defined in Section 7.

   0028 TAMP Status Query: Indicates that a TAMP Status Query package
          [RFC5934] is available for the client using the /tamp URI.

   0029 TAMP Status Query Response or Error: Indicates that the server
          wants the client to return a TAMP Status Query Response or
          Error [RFC5934] to the /tamp/return URI.

   0030 Trust Anchor Update: Indicates that a Trust Anchor Update
          package [RFC5934] is available for the client using the /tamp
          URI.

   0031 Trust Anchor Update Confirm or Error: Indicates that the server
          wants the client to return a Trust Anchor Update Confirm or
          Error [RFC5934] to the /tamp/return URI.

   0032 Apex Trust Anchor Update: Indicates that an Apex Trust Anchor
          Update package [RFC5934] is available for the client using the
          /tamp URI.




Turner                   Expires April 2, 2018                 [Page 16]


Internet-Draft               EST Extensions           September 29, 2017


   0033 Apex Trust Anchor Update Confirm or Error: Indicates that the
          server wants the client to return an Apex Trust Anchor Update
          Confirm or Error [RFC5934] to the /tamp/return URI.

   0034 Community Update: Indicates that a Community Update package
          [RFC5934] is available for the client using the /tamp URI.

   0035 Community Update Confirm or Error: Indicates that the server
          wants the client to return a Community Update Confirm or Error
          [RFC5934] to the /tamp/return URI.

   0036 Sequence Number Adjust: Indicates that a Sequence Number Adjust
          package [RFC5934] is available for the client using the /tamp
          URI.

   0037 Sequence Number Adjust Confirm or Error: Indicates that the
          server wants the client to return a Sequence Number Adjust
          Confirm or Error [RFC5934] to the /tamp/return URI.

2.1.2.  PAL XML Schema

   The name space is specified in Section 11.1.  The fields in the
   schema were discussed earlier in Sections 2.1 and 2.1.1.

   <?xml version="1.0" encoding="UTF-8"?>
   <xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema"
     xmlns:pal="urn:ietf:params:xml:ns:pal"
     targetNamespace="urn:ietf:params:xml:ns:pal"
     elementFormDefault="qualified" attributeFormDefault="unqualified"
     version="1.0">
     <xsd:annotation>
       <xsd:documentation>
         This schema defines the types and elements needed
         to retrieve client packages from the server or for the
         client to post packages to the server.
       </xsd:documentation>
     </xsd:annotation>

     <!-- ===== Element Declarations ===== -->

     <xsd:element name="pal" type="pal:PAL" />

     <!-- ===== Complex Data Element Type Definitions ===== -->

     <xsd:complexType name="PAL">
       <xsd:annotation>
         <xsd:documentation>
           This type defines the Package Availability List (PAL).



Turner                   Expires April 2, 2018                 [Page 17]


Internet-Draft               EST Extensions           September 29, 2017


         </xsd:documentation>
       </xsd:annotation>
       <xsd:sequence>
         <xsd:element name="message" type="pal:PALEntry"
           minOccurs="0" maxOccurs="unbounded">
           <xsd:annotation>
             <xsd:documentation>
               Contains information about the package and a link that
               the client uses to download or post the package.
             </xsd:documentation>
           </xsd:annotation>
         </xsd:element>
       </xsd:sequence>
     </xsd:complexType>

     <xsd:complexType name="PALEntry">
       <xsd:annotation>
         <xsd:documentation>
           This type defines a product in the PAL.
         </xsd:documentation>
       </xsd:annotation>
       <xsd:sequence>
         <xsd:element name="type" type="pal:PackageType" />
         <xsd:element name="date" type="pal:GeneralizedTimeType"
           minOccurs="0" />
         <xsd:element name="size" type="xsd:nonNegativeInteger">
           <xsd:annotation>
             <xsd:documentation>
               Indicates the package's size.
             </xsd:documentation>
           </xsd:annotation>
         <xsd:element name="info" type="pal:PackageInfoType" />
       </xsd:sequence>
     </xsd:complexType>

     <xsd:complexType name="PackageInfoType">
       <xsd:annotation>
         <xsd:documentation>
           This type allows a choice of X.500 Distinguished Name,
           Subject Key Identifier, Issuer and Serial Number tuple,
           or URI.
         </xsd:documentation>
       </xsd:annotation>
       <xsd:choice>
         <xsd:element name="dn"   type="pal:DistinguishedName" />
         <xsd:element name="ski"  type="pal:SubjectKeyIdentifier" />
         <xsd:element name="iasn" type="pal:IssuerAndSerialNumber" />
         <xsd:element name="uri"  type="pal:ThisURI" />



Turner                   Expires April 2, 2018                 [Page 18]


Internet-Draft               EST Extensions           September 29, 2017


       </xsd:choice>
     </xsd:complexType>

     <xsd:complexType name="IssuerAndSerialNumber">
       <xsd:annotation>
         <xsd:documentation>
           This type holds the issuer Distinguished Name and
           serial number of a referenced certificate.
         </xsd:documentation>
       </xsd:annotation>
       <xsd:sequence>
         <xsd:element name="issuer" type="pal:DistinguishedName" />
         <xsd:element name="serial" type="xsd:positiveInteger" />
       </xsd:sequence>
     </xsd:complexType>

     <!-- =====Simple Data Element Type Definitions ===== -->

     <xsd:simpleType name="PackageType">
       <xsd:annotation>
         <xsd:documentation>
           Identifies each package that a client may retrieve from
           the server with a 4-digit string.
         </xsd:documentation>
       </xsd:annotation>
       <xsd:restriction base="xsd:string">
         <xsd:pattern value="d{4}" />
       </xsd:restriction>
     </xsd:simpleType>

     <xsd:simpleType name="GeneralizedTimeType">
       <xsd:annotation>
         <xsd:documentation>
           Indicates the date and time (YYYY-MM-DDTHH:MM:SSZ) the
           client last acknowledged successful receipt of the
           package or is absent if a) there is no indication
           the package has been downloaded or b) the PAL entry
           corresponds to a pointer to the next PAL.
         </xsd:documentation>
       </xsd:annotation>
       <xsd:restriction base="xsd:dateTime">
         <xsd:pattern value=".*:d{2}Z" />
         <xsd:minInclusive value="2013-05-23T00:00:00Z" />
       </xsd:restriction>
     </xsd:simpleType>

     <xsd:simpleType name="DistinguishedName">
       <xsd:annotation>



Turner                   Expires April 2, 2018                 [Page 19]


Internet-Draft               EST Extensions           September 29, 2017


         <xsd:documentation>
           This type holds an X.500 Distinguished Name.
         </xsd:documentation>
       </xsd:annotation>
       <xsd:restriction base="xsd:string">
         <xsd:maxLength value="1024" />
       </xsd:restriction>
     </xsd:simpleType>

     <xsd:simpleType name="SubjectKeyIdentifier">
       <xsd:annotation>
         <xsd:documentation>
           This type holds a hex string representing the value of a
           certificate's SubjectKeyIdentifier.
         </xsd:documentation>
       </xsd:annotation>
       <xsd:restriction base="xsd:hexBinary">
         <xsd:maxLength value="1024" />
       </xsd:restriction>
     </xsd:simpleType>

     <xsd:simpleType name="ThisURI">
       <xsd:annotation>
         <xsd:documentation>
           This type holds a URI, but is length limited.
         </xsd:documentation>
       </xsd:annotation>
       <xsd:restriction base="xsd:anyURI" />
       <xsd:maxLength value="1024" />
     </xsd:simpleType>

   </xsd:schema>

2.1.3.  PAL JSON Object

   The following is an example PAL JSON object.  The fields in the
   object were discussed earlier in Sections 2.1 and 2.1.1.

   [
     {
       "type": "0003",
       "date": "2016-12-29T09:28:00Z",
       "size": 1234,
       "info":
        {
         "uri": "https://www.example.com/.well-known/est/eecerts/1234"
        }
     },



Turner                   Expires April 2, 2018                 [Page 20]


Internet-Draft               EST Extensions           September 29, 2017


     {
       "type": "0006",
       "date": "2016-12-29T09:28:00Z",
       "size": 1234,
       "info":
        {
         "iasn":
          {
           "issuer": "CN=Sean Turner,O=sn3rd,C=US",
           "sn": 0
          }
        }
     }
   ]

2.2.  Request PAL

   Clients request their PAL with an HTTP GET [RFC7231] using an
   operation path of "/pal".  Clients indicate whether they would prefer
   XML or JSON by including the HTTP Accept header [RFC7231] with either
   "application/xml" or "application/json", respectively.

2.3.  Provide PAL

   If the server has a PAL for the client, the server response MUST
   contain an HTTP 200 response code with a content-type of
   "application/xml" [RFC7303] or "application/json" [RFC7159].

   When the server constructs a PAL, an order of precedence for PAL
   offerings is based on the following rationale:

     o /cacerts and /crls packages are the most important because they
       support validation decisions on certificates used to sign and
       encrypt other listed PAL items.

     o /csrattrs are the next in importance, since they provide
       information that the server would like the client to include in
       its certificate enrollment request.

     o /simpleenroll, /simplereenroll, and /fullcmc packages items are
       next in importance, since they can impact a certificate used by
       the client to sign CMS content or a certificate to establish keys
       for encrypting content exchanged with the client.

       * A client engaged in a certificate management SHOULD accept and
         process CA-provided transactions as soon as possible to avoid
         undue delays that might lead to protocol failure.




Turner                   Expires April 2, 2018                 [Page 21]


Internet-Draft               EST Extensions           September 29, 2017


     o /symmetrickeys, /firmware, /tamp, and /eecerts packages
       containing keys and other types of products are last.  Precedence
       SHOULD be given to packages that the client has not previously
       downloaded.  The items listed in a PAL may not identify all of
       the packages available for a device.  This can be for any of the
       following reasons:

       * The server may temporarily withhold some outstanding PAL items
         to simplify client processing.

       * If a CA has more than one certificate ready for the client, the
         server will provide a notice for one at a time.  Pending
         notices will be serviced in order of the earliest date when the
         certificate will be used.

   When rejecting a request the server specifies either an HTTP 4xx
   error, or an HTTP 5xx error.

   All other return codes are handled as specified in Section 4.2.3 of
   [RFC7030] (i.e., 202 handling and all other HTTP response codes).

3.  Distribute EE Certificates

   Numerous mechanisms exist for clients to query repositories for
   certificates.  The service provided by the /eecerts PC is different
   in that it is not a general purpose query for client certificates
   instead it allows the server to provide peer certificates to a client
   that the server knows through an out-of-band mechanism that the
   client will be communicating with.  For example, a router being
   provisioned that connects to two peers can be provisioned with not
   only its certificate but also with the peers' certificates.

   The server need not authenticate or authorize the client for
   distributing an EE certificate because the package contents are
   already signed by a CA (i.e., the certificate(s) in a certs-only
   message have already been signed by a CA).  The message flow is
   similar to Figure 1 except that the connection need not be HTTPS:

                      |                      |
            Client    |    Establish TLS     |    Server
                      |       Session        |
                      |<-------------------->|
                      |                      |
                      |          Request PAL |
                      |   (HTTP GET Request) |
                      |--------------------->|
                      |<---------------------|
                      | Deliver PAL          |



Turner                   Expires April 2, 2018                 [Page 22]


Internet-Draft               EST Extensions           September 29, 2017


                      | (HTTP GET Response)  |
                      |                      |
                      |   Request EE Cert(s) |
                      |   (HTTP GET Request) |
                      |--------------------->|
                      |<---------------------|
                      | Deliver EE Cert(s)   |
                      | (HTTP GET Response)  |
                      |                      |

                  Figure 2 - /eecerts Message Sequence

3.1.  EE Certificate Request

   Clients request EE certificates with an HTTP GET [RFC7231] using an
   operation path of "/eecerts".

3.2.  EE Certificate Response

   The response and processing of the returned error codes is identical
   to that in Section 4.1.3 of [RFC7030] except that the certificate
   provided is not the one issued to the client but instead one or more
   client's peer certificates is returned in the certs-only message.

   Clients MUST reject EE certificates that do not validate to an
   authorized TA.

4.  Distribute CRLs and ARLs

   CRLs (and ARLs) are needed in many instances to perform certificate
   path validation [RFC5280].  They can be obtained from repositories if
   their location is provided in the certificate.  However, the client
   needs to parse the certificate and perform an additional round trip
   to retrieve them.  Providing CRLs at the time of bootstrap obviates
   the need for the client to parse certificate and aid those clients
   who might be unable to retrieve the CRL.  Clients are free to obtain
   CRLs on which they rely from sources other than the server (e.g., a
   local directory).  The /crls PC allows servers to distribute CRLs at
   the same time clients retrieve their certificate(s) and CA
   certificate(s) as well as peer certificates.

   The server need not authenticate or authorize the client for
   distributing a CRL because the package content is already signed by a
   CA (i.e., the CRLs in a crls-only message have already been signed by
   a CA).  The message flow is as depicted in Figure 2 but with "CRL(s)"
   instead of "EE Cert(s)".

4.1.  CRL Request



Turner                   Expires April 2, 2018                 [Page 23]


Internet-Draft               EST Extensions           September 29, 2017


   Clients request CRLs with an HTTP GET [RFC7231] using an operation
   path of "/crls".

4.2.  CRL Response

   The response and processing of the response is identical to that in
   Section 4.1.3 of [RFC7030] except that instead of providing the
   issued certificate one of more CRLs are returned in the crls-only
   message.

   Clients MUST reject CRLs that do not validate to an authorized TA.

5. Symmetric Keys, Receipts, and Errors

   In addition to public keys, clients often need one or more symmetric
   keys to communicate with their peers.  The /symmetrickeys PC allows
   the server to distribute symmetric keys to clients.

   Distribution of keys does not always work as planned and clients need
   a way to inform the server that something has gone wrong; they also
   need a way to inform the server, if asked, that the distribution
   process has successfully completed.  The /symmetrickeys/return PC
   allows client to provide errors and receipts.

   Clients MUST authenticate the server and clients MUST check the
   server's authorization.

   The server MUST authenticate clients and the server MUST check the
   client's authorization.

   HTTP GET [RFC7231] is used when the server provides the key to the
   client (see Section 5.1) using the /symmetrickeys PC; HTTP POST
   [RFC7231] is used when the client provides a receipt (see Section
   5.2) or an error (see Section 5.2) to the server with the
   /symmetrickeys/return PC.

5.1.  Symmetric Keys

   Servers use /symmetrickeys to provide clients symmetric keys;
   symmetric key package is defined in [RFC6031].

   As with the /serverkeygen PC defined in [RFC7030], the default
   distribution method of the symmetric key uses the encryption mode of
   the negotiated TLS cipher suite.  Keys are not protected by preferred
   key wrapping methods such as AES Key Wrap [RFC3394] or AES Key Wrap
   with Padding [RFC5649] because encryption of the symmetric key beyond
   that provided by TLS is OPTIONAL.  Therefore, the cipher suite used
   to return the symmetric key MUST offer commensurate cryptographic



Turner                   Expires April 2, 2018                 [Page 24]


Internet-Draft               EST Extensions           September 29, 2017


   strength with the symmetric key being delivered to the client.  The
   cipher suite used MUST NOT have NULL encryption algorithm as this
   will disclose the unprotected symmetric key.  It is strongly
   RECOMMENDED that servers always return encrypted symmetric keys.

   The following depicts the protocol flow:

                      |                      |
            Client    |    Establish TLS     |    Server
                      |       Session        |
                      |<-------------------->|
                      |                      |
                      |          Request PAL |
                      |   (HTTP GET Request) |
                      |--------------------->|
                      |<---------------------|
                      | Deliver PAL          |
                      | (HTTP GET Response)  |
                      |                      |
                      |    Req Symmetric Key |
                      |   (HTTP GET Request) |
                      |--------------------->|
                      |<---------------------|
                      | Res Symmetric Key    |
                      | (HTTP GET Response)  |
                      |                      |

               Figure 3 - /symmetrickeys Message Sequence

5.1.1.  Distribute Symmetric Keys

   Clients request the symmetric key from the server with an HTTP GET
   [RFC7231] using an operation path of "/symmetrickeys".

5.1.2.  Symmetric Key Response

   If the request is successful, the server response MUST have an HTTP
   200 response code with a Content-Type of application/cms [RFC7193].
   The optional application/cms encapsulatingContent and innerContent
   parameters SHOULD be included with the Content-Type to indicate the
   protection afforded to the returned symmetric key.  The returned
   content varies:

     o If additional encryption is not being employed, the content
       associated with application/cms is a DER-encoded [X.690]
       symmetric key package.

     o If additional encryption is employed, the content associated with



Turner                   Expires April 2, 2018                 [Page 25]


Internet-Draft               EST Extensions           September 29, 2017


       application/cms is DER-encoded enveloped data that encapsulates a
       signed data that further encapsulates a symmetric key package.

     o If additional encryption and origin authentication are employed,
       the content associated with application/cms is a DER-encoded
       signed data that encapsulates an enveloped data that encapsulates
       a signed data that further encapsulates a symmetric key package.

     o If CCC (CMS Content Constraints) [RFC6010] is supported the
       content associated with application/cms is a DER-encoded
       encrypted key package [RFC6032].  Encrypted key package provides
       three choices to encapsulate keys: encrypted data, enveloped
       data, and authenticated enveloped data.  Prior to employing one
       of these three encryption choices the key package can be
       encapsulated in a signed data.

   How the server knows whether the client supports the encrypted key
   package is beyond the scope of this document.

   When rejecting a request, the server specifies either an HTTP 4xx
   error, or an HTTP 5xx error.

   If a symmetric key package (which might be signed) or an encrypted
   key package (which might be signed before and after encryption) is
   digitally signed, the client MUST reject it if the digital signature
   does not validate back to an authorized TA.

   Note: absent a policy on the client side requiring signature, a
   malicious EST server can simply strip the signature, thus bypassing
   that check. In that case, this requirement is merely a sanity check,
   serving to detect mis-signed packages or misconfigured clients.

   [RFC3370], [RFC5753], [RFC5754], [RFC6033], [RFC6160], and [RFC6161]
   provide algorithm details for use when protecting the symmetric key
   package and encrypted key package.

5.2.  Symmetric Key Receipts and Errors

   Clients use /symmetrickeys/return to provide symmetric key package
   receipts; the key package receipt content type is defined in
   [RFC7191].  Clients can be configured to automatically return
   receipts after processing a symmetric key package, return receipts
   based on processing of the key-package-identifier-and-receipt-request
   attribute [RFC7191], or return receipts when prompted by a PAL entry.

   Servers can indicate that clients return a receipt by including the
   key-package-identifier-and-receipt-request attribute in a signed data
   as a signed attribute.  However, this attribute only appears when



Turner                   Expires April 2, 2018                 [Page 26]


Internet-Draft               EST Extensions           September 29, 2017


   additional encryption is employed (see Section 5.1.2).

   Clients also use /symmetrickeys/return to return symmetric key
   package errors; the key package error content type is defined in
   [RFC7191].  Clients can be configured to automatically return errors
   after processing a symmetric key package or based on a PAL entry.

   The following depicts the protocol flow:

                      |                      |
            Client    |    Establish TLS     |    Server
                      |       Session        |
                      |<-------------------->|
                      |                      |
                      |          Request PAL |
                      |   (HTTP GET Request) |
                      |--------------------->|
                      |<---------------------|
                      | Deliver PAL          |
                      | (HTTP GET Response)  |
                      |                      |
                      | Return Receipt/Error |
                      |  (HTTP POST Request) |
                      |--------------------->|
                      |<---------------------|
                      | (HTTP POST Response) |
                      | status code only     |
                      | no content           |
                      |                      |

           Figure 4 - /symmetrickeys/return Message Sequence

5.2.1.  Provide Symmetric Key Receipt or Error

   Clients return symmetric key receipts and errors to the server with
   an HTTP POST [RFC7231] using an operation path of
   "/symmetrickeys/return".  The returned content varies:

     o The key package receipt is digitally signed [RFC7191], the
       Content-Type is application/cms [RFC7193] and the associated
       content is signed data, which encapsulates a key package receipt.

     o If the key package error is not digitally signed, the Content-
       Type is application/cms and the associated content is key package
       error.  If the key package error is digitally signed, the
       Content-Type is application/cms and the associated content is
       signed data, which encapsulates a key package error.




Turner                   Expires April 2, 2018                 [Page 27]


Internet-Draft               EST Extensions           September 29, 2017


   The optional application/cms encapsulatingContent and innerContent
   parameters SHOULD be included with the Content-Type to indicate the
   protection afforded to the receipt or error.

   [RFC3370], [RFC5753], [RFC5754], and [RFC7192] provide algorithm
   details for use when protecting the key package receipt or key
   package error.

5.2.2.  Symmetric Key Receipt or Error Response

   If the client successfully provides a receipt or error, the server
   response has an HTTP 204 response code (i.e., no content is
   returned).

   When rejecting a request, the server specifies either an HTTP 4xx
   error, or an HTTP 5xx error.

   If a key package receipt or key package error is digitally signed,
   the server MUST reject it if the digital signature does not validate
   back to an authorized TA.

6.  Firmware, Receipts, and Errors

   Servers can distribute object code for cryptographic algorithms and
   software with the firmware package [RFC4108].

   Clients MUST authenticate the server and clients MUST check the
   server's authorization.

   The server MUST authenticate the client and the server MUST check the
   client's authorization.

   The /firmware PC uses an HTTP GET [RFC7231] and the /firmware/return
   PC uses an HTTP POST [RFC7231].  GET is used when the client
   retrieves firmware from the server (see Section 6.1); POST is used
   when the client provides a receipt (see Section 6.2) or an error (see
   Section 6.2).

6.1.  Firmware

   The /firmware URI is used by servers to provide firmware packages to
   clients.

   The message flow is as depicted in Figure 3 modulo replacing
   "Symmetric Key" with "Firmware Package".

6.1.1.  Distribute Firmware




Turner                   Expires April 2, 2018                 [Page 28]


Internet-Draft               EST Extensions           September 29, 2017


   Clients request firmware from the server with an HTTP GET [RFC7231]
   using an operation path of "/firmware".

6.1.2.  Firmware Response

   If the request is successful, the server response MUST have an HTTP
   200 response code with a Content-Type of "application/cms" [RFC7193].
    The optional encapsulatingContent and innerContent parameters SHOULD
   be included with Content-Type to indicate the protection afforded to
   the returned firmware.  The returned content varies:

     o If the firmware is unprotected, then the Content-Type is
       application/cms and the content is the DER-encoded [X.690]
       firmware package.

     o If the firmware is compressed, then the Content-Type is
       application/cms and the content is the DER-encoded [X.690]
       compressed data that encapsulates the firmware package.

     o If the firmware is encrypted, then the Content-Type is
       application/cms and the content is the DER-encoded [X.690]
       encrypted data that encapsulates the firmware package (which
       might be compressed prior to encryption).

     o If the firmware is signed, then the Content-Type is
       application/cms and the content is the DER-encoded [X.690] signed
       data that encapsulates the firmware package (which might be
       compressed, encrypted, or compressed and then encrypted prior to
       signature).

   How the server knows whether the client supports the unprotected,
   signed, compressed and/or encrypted firmware package is beyond the
   scope of this document

   When rejecting a request, the server specifies either an HTTP 4xx
   error, or an HTTP 5xx error.

   If a firmware package is digitally signed, the client MUST reject it
   if the digital signature does not validate back to an authorized TA.

   [RFC3370], [RFC5753], and [RFC5754] provide algorithm details for use
   when protecting the firmware package.

6.2.  Firmware Receipts and Errors

   Clients use the /firmware/return PC to provide firmware package load
   receipts and errors [RFC4108].  Clients can be configured to
   automatically return receipts and errors after processing a firmware



Turner                   Expires April 2, 2018                 [Page 29]


Internet-Draft               EST Extensions           September 29, 2017


   package or based on a PAL entry.

   The message flow is as depicted in Figure 4 modulo the receipt or
   error is for a firmware package.

6.2.1.  Provide Firmware Receipt or Error

   Clients return firmware receipts and errors to the server with an
   HTTP POST [RFC7231] using an operation path of "/firmware/return".
   The optional encapsulatingContent and innerContent parameters SHOULD
   be included with Content-Type to indicate the protection afforded to
   the returned firmware receipt or error.  The returned content varies:

     o If the firmware receipt is not digitally signed, the Content-Type
       is application/cms [RFC7193] and the content is the DER-encoded
       firmware receipt.

     o If the firmware receipt is digitally signed, the Content-Type is
       application/cms and the content is the DER-encoded signed data
       encapsulating the firmware receipt.

     o If the firmware error is not digitally signed, the Content-Type
       is application/cms and the content is the DER-encoded firmware
       error.

     o If the firmware error is digitally signed, the Content-Type is
       application/cms and the content is the DER-encoded signed data
       encapsulating the firmware error.

   [RFC3370], [RFC5753], and [RFC5754] provide algorithm details for use
   when protecting the firmware receipt or firmware error.

6.2.2.  Firmware Receipt or Error Response

   If the request is successful, the server response MUST have an HTTP
   204 response code (i.e., no content is returned).

   When rejecting a request, the server MUST specify either an HTTP 4xx
   error, or an HTTP 5xx error.

   If a firmware receipt or firmware error is digitally signed, the
   server MUST reject it if the digital signature does not validate back
   to an authorized TA.

7.  Trust Anchor Management Protocol

   Servers distribute TAMP packages to manage TAs in a client's trust
   anchor databases; TAMP packages are defined in [RFC5934].  TAMP will



Turner                   Expires April 2, 2018                 [Page 30]


Internet-Draft               EST Extensions           September 29, 2017


   allow the flexibility for a device to load authorities while
   maintaining an operational state.  Unlike other systems that require
   new software loads when new PKI Roots are authorized for use, TAMP
   allows for automated management of roots for provisioning or
   replacement as needed.

   Clients MUST authenticate the server and clients MUST check the
   server's authorization.

   The server MUST authenticate the client and the server MUST check the
   client's authorization.

   The /tamp PC uses an HTTP GET [RFC7231] and the tamp/return PC uses
   an HTTP POST [RFC7231].  GET is used when the server requests that
   the client retrieve a TAMP package (see Section 7.1); POST is used
   when the client provides a confirm (see Section 7.2), provides a
   response (see Section 7.2), or provides an error (see Section 7.2)
   for the TAMP package.

7.1.  TAMP Status Query, Trust Anchor Update, Apex Trust Anchor Update,
      Community Update, and Sequence Number Adjust

   Clients use the /tamp PC to retrieve the TAMP packages: TAMP Status
   Query, Trust Anchor Update, Apex Trust Anchor Update, Community
   Update, and Sequence Number Adjust.  Clients can be configured to
   periodically poll the server for these packages or contact the server
   based on a PAL entry.

   The message flow is as depicted in Figure 3 modulo replacing
   "Symmetric Key" with the appropriate TAMP message.

7.1.1.  Request TAMP Packages

   Clients request the TAMP packages from the server with an HTTP GET
   [RFC7231] using an operation path of "/tamp".

7.1.2.  Return TAMP Packages

   If the request is successful, the server response MUST have an HTTP
   200 response code and a Content-Type of:
     o application/tamp-status-query for TAMP Status Query
     o application/tamp-update for Trust Anchor Update
     o application/tamp-apex-update for Apex Trust Anchor Update
     o application/tamp-community-update for Community Update
     o application/tamp-sequence-adjust for Sequence Number Adjust

   As specified in [RFC5934], these content types are digitally signed
   and clients must support validating the packages directly signed by



Turner                   Expires April 2, 2018                 [Page 31]


Internet-Draft               EST Extensions           September 29, 2017


   TAs.  For this specification, clients MUST support validation with a
   certificate and clients MUST reject it if the digital signature does
   not validate back to an authorized TA.

   [RFC3370], [RFC5753], and [RFC5754] provide algorithm details for use
   when protecting the TAMP packages.

7.2.  TAMP Response, Confirm, and Errors

   Clients return the TAMP Status Query Response, Trust Anchor Update
   Confirm, Apex Trust Anchor Update Confirm, Community Update Confirm,
   Sequence Number Adjust Confirm, and TAMP Error to servers using the
   /tamp/return PC.  Clients can be configured to automatically return
   responses, confirms, and errors after processing a TAMP package or
   based on a PAL entry.

   The message flow is as depicted in Figure 4 modulo replacing
   "Receipt/Error" with the appropriate TAMP response, confirm, or
   error.

7.2.1.  Provide TAMP Response, Confirm, or Error

   Clients provide the TAMP responses, confirms, and errors to the
   server with an HTTP POST using an operation path of "/tamp/return".
   Content-Type is:

     o application/tamp-status-query-response for TAMP Status Query
       Response
     o application/tamp-update-confirm for Trust Anchor Update Confirm
     o application/tamp-apex-update-confirm for Apex Trust Anchor Update
       Confirm
     o application/tamp-community-update-confirm for Community Update
       Confirm
     o application/tamp-sequence-adjust-confirm for Sequence Number
       Adjust Confirm
     o application/tamp-error for TAMP Error

   As specified in [RFC5934], these content types should be signed.  If
   signed, a signed data encapsulates the TAMP content.

   [RFC3370], [RFC5753], and [RFC5754] provide algorithm details for use
   when protecting the TAMP packages.

7.2.2.  TAMP Response, Confirm, and Error Response

   If the request is successful, the server response MUST have an HTTP
   204 response code (i.e., no content is returned).




Turner                   Expires April 2, 2018                 [Page 32]


Internet-Draft               EST Extensions           September 29, 2017


   When rejecting a request, the server MUST specify either an HTTP 4xx
   error, or an HTTP 5xx error.

   If the package is digitally signed, the server MUST reject it if
   digital signature does not validate back to an authorized TA.

8.  Asymmetric Keys, Receipts, and Errors

   [RFC7030] defines the /serverkeygen PC to support server-side
   generation of asymmetric keys.  Keys are returned either as an
   unprotected PKCS#8 when additional security beyond TLS is not
   employed or as a CMS asymmetric key package content type that is
   encapsulated in a signed data content type that is further
   encapsulated in an enveloped data content type when additional
   security beyond TLS is requested.  Some implementations prefer the
   use of other CMS content types to encapsulate the asymmetric key
   package; this document extends the content types that can be returned
   in Section 8.1.

   [RFC7191] defines content types for key package receipts and errors.
   This document defines the /serverkeygen/return PC to add support for
   returning receipts and errors for asymmetric key packages in Section
   8.2.

   PKCS#12 [RFC7292], sometimes referred to as "PFX" (Personal
   inFormation eXchange), "P12", and "PKCS#12" files, are often used to
   distribute asymmetric private keys and the associated certificate.
   This document extends the /serverkeygen PC to allow servers to
   distribute using PKCS#12 server-generated asymmetric private keys and
   the associated certificate to clients in Section 8.3.

8.1.  Asymmetric Key Encapsulation

   CMS supports a number of content types to encapsulate other CMS
   content types; [RFC7030] includes one such possibility; note that
   when only relying on TLS the returned key is not a CMS content type.
   This document extends the CMS content types that can be returned.

   If the client supports CCC [RFC6010], then the client can indicate
   that it supports encapsulated asymmetric keys in the encrypted key
   package [RFC5958] by including the encrypted key package's OID in a
   content type attribute [RFC2985] in the CSR (Certificate Signing
   Request), aka the certification request, it provides to the server.
   If the client knows a priori that the server supports the encrypted
   key package content type, then the client need not include the
   content type attribute in the CSR.

   In all instances defined herein, the Content-Type is



Turner                   Expires April 2, 2018                 [Page 33]


Internet-Draft               EST Extensions           September 29, 2017


   "application/cms" [RFC7193].  The optional encapsulatingContent and
   innerContent parameters SHOULD be included with Content-Type to
   indicate the protection afforded to the returned asymmetric key
   package.

   If additional encryption and origin authentication is employed, the
   content associated with application/cms is a DER-encoded signed data
   that encapsulates an enveloped data that encapsulates a signed data
   that further encapsulates an asymmetric key package.

   If CCC (CMS Content Constraints) is supported and additional
   encryption is employed, the content associated with application/cms
   is a DER-encoded encrypted key package [RFC6032] content type that
   encapsulates a signed data that further encapsulates an asymmetric
   key package.

   If CCC is supported and additional encryption and additional origin
   authentication is employed, the content associated with
   application/cms is a DER-encoded signed data that encapsulates an
   encrypted key package content type that encapsulates a signed data
   that further encapsulates an asymmetric key package.

   Encrypted key package [RFC6032] provides three choices to encapsulate
   keys, encrypted data, enveloped data, and authenticated data, with
   enveloped data being the mandatory to implement choice.

   When rejecting a request, the server specifies either an HTTP 4xx
   error, or an HTTP 5xx error.

   If an asymmetric key package or an encrypted key package is digitally
   signed, the client MUST reject it if the digital signature does not
   validate back to an authorized TA.

   Note: absent a policy on the client side requiring signature, a
   malicious EST server can simply strip the signature, thus bypassing
   that check.  In that case, this requirement is merely a sanity check,
   serving to detect mis-signed packages or misconfigured clients.

   [RFC3370], [RFC5753], [RFC5754], [RFC6033], [RFC6161], and [RFC6162]
   provide algorithm details for use when protecting the asymmetric key
   package and encrypted key package.

8.2.  Asymmetric Key Package Receipts and Errors

   Clients can be configured to automatically return receipts after
   processing an asymmetric key package, return receipts based on
   processing of the key-package-identifier-and-receipt-request
   attribute [RFC7191], or return receipts when prompted by a PAL entry.



Turner                   Expires April 2, 2018                 [Page 34]


Internet-Draft               EST Extensions           September 29, 2017


   Servers can indicate that clients return a receipt by including the
   key-package-identifier-and-receipt-request attribute [RFC7191] in a
   signed data as a signed attribute.

   The protocol flow is identical to that depicted in Figure 4 modulo
   the receipt or error is for asymmetric keys.

   The server and client processing is as described in Section 5.2.1 and
   5.2.2 modulo the PC, which for Asymmetric Key Packages is
   "/serverkeygen/return".

8.3.  PKCS#12

   PFX is widely deployed and supports protecting keys in the same
   fashion as CMS but it does so differently.

8.3.1.  Server-Side Key Generation Request

   Similar to the other server-generated asymmetric keys provided
   through the /serverkeygen PC:

     o The certificate request is HTTPS POSTed and is the same format as
       for the "/simpleenroll" and "/simplereenroll" path extensions
       with the same content-type and transfer encoding.

     o In all respects, the server SHOULD treat the CSR as it would any
       enroll or re-enroll CSR; the only distinction here is that the
       server MUST ignore the public key values and signature in the
       CSR.  These are included in the request only to allow re-use of
       existing codebases for generating and parsing such requests.

   PBE (password based encryption) shrouding of PKCS#12 is supported and
   this specification makes no attempt to alter this de facto standard.
   As such, there is no support of the DecryptKeyIdentifier specified in
   [RFC7030] for use with PKCS#12 (i.e., "enveloping" is not supported).
    NOTE: Use of PBE requires the password be distributed to the client;
   methods to distribute this password are out-of-scope.

8.3.2.  Server-Side Key Generation Response

   If the request is successful, the server response MUST have an HTTP
   200 response code with a content-type of "application/pkcs12" that
   consists of a base64-encoded DER-encoded [X.690] PFX [RFC7292].

   Note that this response is different than the response returned in
   Section 4.4.2 of [RFC7030] because here the private key and the
   certificate are included in the same PFX.




Turner                   Expires April 2, 2018                 [Page 35]


Internet-Draft               EST Extensions           September 29, 2017


   When rejecting a request, the server MUST specify either an HTTP 4xx
   error or an HTTP 5xx error.  The response data's content-type MAY be
   "text/plain" [RFC2046] to convey human-readable error messages.

9.  PAL & Certificate Enrollment

   The /fullcmc PC is defined in [RFC7030]; the CMC (Certificate
   Management over Cryptographic Message Syntax) requirements and
   packages are defined in [RFC5272], [RFC5273], [RFC5274], and
   [RFC6402].  This section describes PAL interactions.

   Under normal circumstances the client-server interactions for PKI
   enrollment are as follows:

           Client                       Server
                 --------------------->
             POST req: PKIRequest
             Content-Type: application/pkcs10
            or
             POST req: PKIRequest
             Content-Type: application/pkcs7-mime
                           smime-type=CMC-request

                  <--------------------
                         POST res: PKIResponse
                         Content-Type: application/pkcs7-mime
                                       smime-type=certs-only
                        or
                         POST res: PKIResponse
                         Content-Type: application/pkcs7-mime
                                       smime-type=CMC-response

   if the response is rejected during the same session:

           Client                       Server
                  --------------------->
              POST req: PKIRequest
              Content-Type: application/pkcs10
             or
              POST req: PKIRequest
              Content-Type: application/pkcs7-mime
                            smime-type=CMC-request

                  <--------------------
                         POST res: empty
                         HTTPS Status Code
                        or
                         POST res: PKIResponse



Turner                   Expires April 2, 2018                 [Page 36]


Internet-Draft               EST Extensions           September 29, 2017


                         Content-Type: application/pkcs7-mime
                                      smime-type=CMC-response

   if the request is to be filled later:

           Client                       Server
                  --------------------->
              POST req: PKIRequest
              Content-Type: application/pkcs10
             or
              POST req: PKIRequest
              Content-Type: application/pkcs7-mime
                            smime-type=CMC-request

                  <--------------------
                         POST res: empty
                         HTTPS Status Code
                         + Retry-After
                        or
                         POST res: PKIResponse (pending)
                         Content-Type: application/pkcs7-mime
                                      smime-type=CMC-response

                  --------------------->
              POST req: PKIRequest (same request)
              Content-Type: application/pkcs10
             or
              POST req: PKIRequest (CMC Status Info only)
              Content-Type: application/pkcs7-mime
                            smime-type=CMC-request

                  <--------------------
                         POST res: PKIResponse
                         Content-Type: application/pkcs7-mime
                                       smime-type=certs-only
                        or
                         POST res: PKIResponse
                         Content-Type: application/pkcs7-mime
                                       smime-type=CMC-response


   With the PAL, the client begins after pulling the PAL and a Start
   Issuance PAL package type essentially adding the following before the
   request:

           Client                       Server
                 --------------------->
             GET req: PAL



Turner                   Expires April 2, 2018                 [Page 37]


Internet-Draft               EST Extensions           September 29, 2017


                  <--------------------
                         GET res: PAL
                         Content-Type: application/xml

   The client then proceeds as above with a simple PKI Enroll, Full CMC
   Enrollment, or begin enrollment assisted with a CSR:

           Client                       Server
                 --------------------->
             GET req: DS certificate with CSR

                  <--------------------
                         GET res: PAL
                         Content-Type: application/csr-attrs

   For immediately rejected request, CMC works well.  If the server
   prematurely closes the connection, then the procedures in Section
   8.2.4 of [RFC7231] apply.  But, this might leave the client and
   server in a different state.  The client could merely resubmit the
   request but another option, documented herein, is for the client to
   instead download the PAL to see if the server has processed the
   request.  Clients might also use this process when they are unable to
   remain connected to the server for the entire enrollment process; if
   the server does not or is not able to return a PKIData indicating a
   status of pending, then the client will not know whether the request
   was received.  If a client uses the PAL and reconnects to determine
   if the certification or rekey or renew request was processed:

     o Clients MUST authenticate the server and clients MUST check the
       server's authorization.

     o Server MUST authenticate the client and the server MUST check the
       client's authorization.

     o Clients retrieve the PAL using the /pal URI.

     o Clients and servers use the operation path of "/simpleenroll",
       "simplereenroll", or "/fullcmc", based on the PAL entry, with an
       HTTP GET [RFC7231] to get the success or failure response.

   Responses are as specified in [RFC7030].

10.  Security Considerations

   This document relies on many other specifications; however, all of
   the security considerations [RFC7030] apply.  For HTTP, HTTPS, and
   TLS security considerations see  [RFC7231], [RFC2818], and [RFC5246];
   for URI security considerations see [RFC3986]; for content type



Turner                   Expires April 2, 2018                 [Page 38]


Internet-Draft               EST Extensions           September 29, 2017


   security considerations see [RFC4073], [RFC4108], [RFC5272],
   [RFC5652], [RFC5751], [RFC5934], [RFC5958] [RFC6031], [RFC6032],
   [RFC6268], [RFC6402], [RFC7191], and [RFC7292]; for algorithms used
   to protect packages see [RFC3370], [RFC5649], [RFC5753], [RFC5754],
   [RFC5959], [RFC6033], [RFC6160], [RFC6161], [RFC6162] and [RFC7192];
   for random numbers see [RFC4086]; for server-generated asymmetric key
   pairs see [RFC7030].

11.  IANA Considerations

   IANA is requested to create the PAL Package Type registry and perform
   three registrations: PAL Name Space, PAL XML Schema, and PAL Package
   Types.

11.1.  PAL Name Space

   This section registers a new XML namespace [XMLNS],
   "urn:ietf:params:xml:ns:pal" per the guidelines in [RFC3688]:

      URI:  urn:ietf:params:xml:ns:pal
      Registrant Contact: Sean Turner (sean@sn3rd.com)
      XML:
         BEGIN
            <?xml version="1.0"?>
            <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
               "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
            <html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en">
            <head>
               <title>Package Availability List</title>
            </head>
            <body>
               <h1>Namespace for Package Availability List</h1>
               <h2>urn:ietf:params:xml:ns:pal</h2>
               <p>See RFC TBD</p>
            </body>
            </html>
         END

11.2.  PAL XML Schema

   This section registers an XML schema as per the guidelines in
   [RFC3688].

      URI: urn:ietf:params:xml:schema:pal

      Registrant Contact:  Sean Turner sean@sn3rd.com

      XML: See Section 2.1.2.



Turner                   Expires April 2, 2018                 [Page 39]


Internet-Draft               EST Extensions           September 29, 2017


11.3.  PAL Package Types

   IANA is kindly requested to create a new registry named: PAL Package
   Type.  This registry is for PAL Package Types whose initial values
   are found in Section 2.1.1.  Future PAL Package Types registrations
   are to be subject to Expert Review, as defined in RFC 8126 [RFC8126].
    Package types MUST be paired with a media type; package types
   specify the path component to be used that in turn specify the media
   type used.

12.  Acknowledgements

   Thanks in no particular order go to Alexey Melnikov, Paul Hoffman,
   Brad McInnis, Max Pritikin, Francois Rousseau, Chris Bonatti, and
   Russ Housley for taking time to provide comments.

13.  References

13.1.  Normative References

   [RFC2045] Freed, N. and N. Borenstein, "Multipurpose Internet Mail
             Extensions (MIME) Part One: Format of Internet Message
             Bodies", RFC 2045, DOI 10.17487/RFC2045, November 1996,
             <http://www.rfc-editor.org/info/rfc2045>.

   [RFC2046] Freed, N. and N. Borenstein, "Multipurpose Internet Mail
             Extensions (MIME) Part Two: Media Types", RFC 2046, DOI
             10.17487/RFC2046, November 1996, <http://www.rfc-
             editor.org/info/rfc2046>.

   [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
             Requirement Levels", BCP 14, RFC 2119, DOI
             10.17487/RFC2119, March 1997, <http://www.rfc-
             editor.org/info/rfc2119>.

   [RFC2585] Housley, R. and P. Hoffman, "Internet X.509 Public Key
             Infrastructure Operational Protocols: FTP and HTTP",
             RFC 2585, DOI 10.17487/RFC2585, May 1999, <http://www.rfc-
             editor.org/info/rfc2585>.

   [RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818, DOI
             10.17487/RFC2818, May 2000, <http://www.rfc-
             editor.org/info/rfc2818>.

   [RFC2985] Nystrom, M. and B. Kaliski, "PKCS #9: Selected Object
             Classes and Attribute Types Version 2.0", RFC 2985, DOI
             10.17487/RFC2985, November 2000, <http://www.rfc-
             editor.org/info/rfc2985>.



Turner                   Expires April 2, 2018                 [Page 40]


Internet-Draft               EST Extensions           September 29, 2017


   [RFC3370] Housley, R., "Cryptographic Message Syntax (CMS)
             Algorithms", RFC 3370, DOI 10.17487/RFC3370, August 2002,
             <http://www.rfc-editor.org/info/rfc3370>.

   [RFC3394] Schaad, J. and R. Housley, "Advanced Encryption Standard
             (AES) Key Wrap Algorithm", RFC 3394, DOI 10.17487/RFC3394,
             September 2002, <http://www.rfc-editor.org/info/rfc3394>.

   [RFC3688] Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
             DOI 10.17487/RFC3688, January 2004, <http://www.rfc-
             editor.org/info/rfc3688>.

   [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,
             <http://www.rfc-editor.org/info/rfc3986>.

   [RFC4073] Housley, R., "Protecting Multiple Contents with the
             Cryptographic Message Syntax (CMS)", RFC 4073, DOI
             10.17487/RFC4073, May 2005, <http://www.rfc-
             editor.org/info/rfc4073>.

   [RFC4108] Housley, R., "Using Cryptographic Message Syntax (CMS) to
             Protect Firmware Packages", RFC 4108, DOI 10.17487/RFC4108,
             August 2005, <http://www.rfc-editor.org/info/rfc4108>.

   [RFC4514] Zeilenga, K., Ed., "Lightweight Directory Access Protocol
             (LDAP): String Representation of Distinguished Names",
             RFC 4514, DOI 10.17487/RFC4514, June 2006, <http://www.rfc-
             editor.org/info/rfc4514>.

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

   [RFC5272] Schaad, J. and M. Myers, "Certificate Management over CMS
             (CMC)", RFC 5272, DOI 10.17487/RFC5272, June 2008,
             <http://www.rfc-editor.org/info/rfc5272>.

   [RFC5273] Schaad, J. and M. Myers, "Certificate Management over CMS
             (CMC): Transport Protocols", RFC 5273, DOI
             10.17487/RFC5273, June 2008, <http://www.rfc-
             editor.org/info/rfc5273>.

   [RFC5274] Schaad, J. and M. Myers, "Certificate Management Messages
             over CMS (CMC): Compliance Requirements", RFC 5274, DOI
             10.17487/RFC5274, June 2008, <http://www.rfc-



Turner                   Expires April 2, 2018                 [Page 41]


Internet-Draft               EST Extensions           September 29, 2017


             editor.org/info/rfc5274>.

   [RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
             Housley, R., and W. Polk, "Internet X.509 Public Key
             Infrastructure Certificate and Certificate Revocation List
             (CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008,
             <http://www.rfc-editor.org/info/rfc5280>.

   [RFC5649] Housley, R. and M. Dworkin, "Advanced Encryption Standard
             (AES) Key Wrap with Padding Algorithm", RFC 5649, DOI
             10.17487/RFC5649, September 2009, <http://www.rfc-
             editor.org/info/rfc5649>.

   [RFC5652] Housley, R., "Cryptographic Message Syntax (CMS)", STD 70,
             RFC 5652, DOI 10.17487/RFC5652, September 2009,
             <http://www.rfc-editor.org/info/rfc5652>.

   [RFC5751] Ramsdell, B. and S. Turner, "Secure/Multipurpose Internet
             Mail Extensions (S/MIME) Version 3.2 Message
             Specification", RFC 5751, DOI 10.17487/RFC5751, January
             2010, <http://www.rfc-editor.org/info/rfc5751>.

   [RFC5753] Turner, S. and D. Brown, "Use of Elliptic Curve
             Cryptography (ECC) Algorithms in Cryptographic Message
             Syntax (CMS)", RFC 5753, DOI 10.17487/RFC5753, January
             2010, <http://www.rfc-editor.org/info/rfc5753>.

   [RFC5754] Turner, S., "Using SHA2 Algorithms with Cryptographic
             Message Syntax", RFC 5754, DOI 10.17487/RFC5754, January
             2010, <http://www.rfc-editor.org/info/rfc5754>.

   [RFC5934] Housley, R., Ashmore, S., and C. Wallace, "Trust Anchor
             Management Protocol (TAMP)", RFC 5934, DOI
             10.17487/RFC5934, August 2010, <http://www.rfc-
             editor.org/info/rfc5934>.

   [RFC5958] Turner, S., "Asymmetric Key Packages", RFC 5958, DOI
             10.17487/RFC5958, August 2010, <http://www.rfc-
             editor.org/info/rfc5958>.

   [RFC5959] Turner, S., "Algorithms for Asymmetric Key Package Content
             Type", RFC 5959, DOI 10.17487/RFC5959, August 2010,
             <http://www.rfc-editor.org/info/rfc5959>.

   [RFC5967] Turner, S., "The application/pkcs10 Media Type", RFC 5967,
             DOI 10.17487/RFC5967, August 2010, <http://www.rfc-
             editor.org/info/rfc5967>.




Turner                   Expires April 2, 2018                 [Page 42]


Internet-Draft               EST Extensions           September 29, 2017


   [RFC6010] Housley, R., Ashmore, S., and C. Wallace, "Cryptographic
             Message Syntax (CMS) Content Constraints Extension",
             RFC 6010, DOI 10.17487/RFC6010, September 2010,
             <http://www.rfc-editor.org/info/rfc6010>.

   [RFC6031] Turner, S. and R. Housley, "Cryptographic Message Syntax
             (CMS) Symmetric Key Package Content Type", RFC 6031, DOI
             10.17487/RFC6031, December 2010, <http://www.rfc-
             editor.org/info/rfc6031>.

   [RFC6032] Turner, S. and R. Housley, "Cryptographic Message Syntax
             (CMS) Encrypted Key Package Content Type", RFC 6032, DOI
             10.17487/RFC6032, December 2010, <http://www.rfc-
             editor.org/info/rfc6032>.

   [RFC6033] Turner, S., "Algorithms for Cryptographic Message Syntax
             (CMS) Encrypted Key Package Content Type", RFC 6033, DOI
             10.17487/RFC6033, December 2010, <http://www.rfc-
             editor.org/info/rfc6033>.

   [RFC6160] Turner, S., "Algorithms for Cryptographic Message Syntax
             (CMS) Protection of Symmetric Key Package Content Types",
             RFC 6160, DOI 10.17487/RFC6160, April 2011,
             <http://www.rfc-editor.org/info/rfc6160>.

   [RFC6161] Turner, S., "Elliptic Curve Algorithms for Cryptographic
             Message Syntax (CMS) Encrypted Key Package Content Type",
             RFC 6161, DOI 10.17487/RFC6161, April 2011,
             <http://www.rfc-editor.org/info/rfc6161>.

   [RFC6162] Turner, S., "Elliptic Curve Algorithms for Cryptographic
             Message Syntax (CMS) Asymmetric Key Package Content Type",
             RFC 6162, DOI 10.17487/RFC6162, April 2011,
             <http://www.rfc-editor.org/info/rfc6162>.

   [RFC6268] Schaad, J. and S. Turner, "Additional New ASN.1 Modules for
             the Cryptographic Message Syntax (CMS) and the Public Key
             Infrastructure Using X.509 (PKIX)", RFC 6268, DOI
             10.17487/RFC6268, July 2011, <http://www.rfc-
             editor.org/info/rfc6268>.

   [RFC6402] Schaad, J., "Certificate Management over CMS (CMC)
             Updates", RFC 6402, DOI 10.17487/RFC6402, November 2011,
             <http://www.rfc-editor.org/info/rfc6402>.

   [RFC7303] Thompson, H. and C. Lilley, "XML Media Types", RFC 7303,
             DOI 10.17487/RFC7303, July 2014, <http://www.rfc-
             editor.org/info/rfc7303>.



Turner                   Expires April 2, 2018                 [Page 43]


Internet-Draft               EST Extensions           September 29, 2017


   [RFC7030] Pritikin, M., Ed., Yee, P., Ed., and D. Harkins, Ed.,
             "Enrollment over Secure Transport", RFC 7030, DOI
             10.17487/RFC7030, October 2013, <http://www.rfc-
             editor.org/info/rfc7030>.

   [RFC7159] Bray, T., Ed., "The JavaScript Object Notation (JSON) Data
             Interchange Format", RFC 7159, DOI 10.17487/RFC7159, March
             2014, <http://www.rfc-editor.org/info/rfc7159>.

   [RFC7191] Housley, R., "Cryptographic Message Syntax (CMS) Key
             Package Receipt and Error Content Types", RFC 7191, DOI
             10.17487/RFC7191, April 2014, <http://www.rfc-
             editor.org/info/rfc7191>.

   [RFC7192] Turner, S., "Algorithms for Cryptographic Message Syntax
             (CMS) Key Package Receipt and Error Content Types",
             RFC 7192, DOI 10.17487/RFC7192, April 2014,
             <http://www.rfc-editor.org/info/rfc7192>.

   [RFC7193] Turner, S., Housley, R., and J. Schaad, "The
             application/cms Media Type", RFC 7193, DOI
             10.17487/RFC7193, April 2014, <http://www.rfc-
             editor.org/info/rfc7193>.

   [RFC7231] Fielding, R., Ed., and J. Reschke, Ed., "Hypertext Transfer
             Protocol (HTTP/1.1): Semantics and Content", RFC 7231, DOI
             10.17487/RFC7231, June 2014, <http://www.rfc-
             editor.org/info/rfc7231>.

   [RFC7292] Moriarty, K., Ed., Nystrom, M., Parkinson, S., Rusch, A.,
             and M. Scott, "PKCS #12: Personal Information Exchange
             Syntax v1.1", RFC 7292, DOI 10.17487/RFC7292, July 2014,
             <http://www.rfc-editor.org/info/rfc7292>.

   [RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
             Writing an IANA Considerations Section in RFCs", BCP 26,
             RFC 8126, DOI 10.17487/RFC8126, June 2017, <http://www.rfc-
             editor.org/info/rfc8126>.

   [XML]     W3C, "Extensible Markup Language (XML) 1.0 (Fifth
             Edition)", W3C Recommendation, November 2008,
             <http://www.w3.org/TR/2006/REC-xml-20060816/>.

   [XMLSCHEMA]
             Malhotra, A. and P. Biron, "XML Schema Part 2: Datatypes
             Second Edition", World Wide Web Consortium Recommendation
             REC-xmlschema-2-20041082, October 2004,
             <http://www.w3.org/TR/2004/REC-xmlschema-2-20041028>.



Turner                   Expires April 2, 2018                 [Page 44]


Internet-Draft               EST Extensions           September 29, 2017


   [X.690]   ITU-T Recommendation X.690 (2002) | ISO/IEC 8825-1:2002.
             Information Technology - ASN.1 encoding rules:
             Specification of Basic Encoding Rules (BER), Canonical
             Encoding Rules (CER) and Distinguished Encoding Rules
             (DER).

13.2.  Informative References

   [RFC2985] Nystrom, M. and B. Kaliski, "PKCS #9: Selected Object
             Classes and Attribute Types Version 2.0", RFC 2985, DOI
             10.17487/RFC2985, November 2000, <http://www.rfc-
             editor.org/info/rfc2985>.

   [RFC4086] Eastlake 3rd, D., Schiller, J., and S. Crocker, "Randomness
             Requirements for Security", BCP 106, RFC 4086, DOI
             10.17487/RFC4086, June 2005, <http://www.rfc-
             editor.org/info/rfc4086>.

   [RFC4949] Shirey, R., "Internet Security Glossary, Version 2", FYI
             36, RFC 4949, DOI 10.17487/RFC4949, August 2007,
             <http://www.rfc-editor.org/info/rfc4949>.


   [XMLNS]   Hollander, D., Bray, T., and A. Layman, "Namespaces in
             XML", World Wide Web Consortium First Edition REC-xml-
             names-19990114, January 1999,
             <http://www.w3.org/TR/1999/REC-xml-names-19990114>.

Appendix A.  Example Use of PAL

   This is an informative appendix.  It includes examples protocol
   flows.

   Steps for using a PAL include:
    1. Access PAL
    2. Process PAL entries
      2.1. Get CA Certificates
      2.2. Get CRLs
      2.3. Get CSR attributes
      2.4. Enroll: simple enrollment, re-enrollment, or full CMC
      2.5. Get Firmware, TAMP, Symmetric Keys, or EE Certificates

   Client                      Server
         --------------------->                     -+
   GET req:                                          | /pal
         <---------------------                      |
                       GET res: PAL                  |
                       Content-Type: application/xml |



Turner                   Expires April 2, 2018                 [Page 45]


Internet-Draft               EST Extensions           September 29, 2017


                                                     |
         --------------------->                     -+
   GET req:                                          | /cacerts
         <---------------------                      |
               GET res: CA Certificates              |
               Content-Type: application/pkcs7-smime |
                             smime-type=certs-only   |
                                                     |
         --------------------->                     -+
   GET req:                                          | /crls
         <---------------------                      |
               GET res: CRLs                         |
               Content-Type: application/pkcs7-smime |
                             smime-type=crls-only    |
                                                     |
         --------------------->                     -+
   GET req:                                          | /csrattrs
         <---------------------                      |
                           GET res: attributes       |
         --------------------->                     -+
   POST req: PKIRequest                              | /simpleenroll &
   Content-Type: application/pkcs10                  | /simplereenroll
                                                     |
   Content-Type: application/pkcs7-mime              | /fullcmc
                 smime-type=CMC-request              |
                                                     |
         <--------------------                       |
              (success or failure)                   |
              POST res: PKIResponse                  | /simpleenroll
              Content-Type: application/pkcs7-mime   | /simplereenroll
                            smime-type=certs-only    | /fullcmc
                                                     |
              Content-Type: application/pkcs7-mime   | /fullcmc
                            smime-type=CMC-response  |
                                                     |
         -------------------->                      -+
   GET req:                                          | /firmware
         <--------------------                       | /tamp
               GET res:  Firmware, TAMP Query        | /symmetrickeys
                         + Updates, Symmetric Keys   |
                Content-Type: application/cms        |
                                                     |
         --------------------->                     -+
   POST res: Firmware Receipts or Errors,            | /firmware/return
   TAMP Response or Confirms or Errors,              | /tamp/return
   Symmetric Key Receipts or Errors,                 | /symmetrickeys/
                                                     |      return
                                                     |



Turner                   Expires April 2, 2018                 [Page 46]


Internet-Draft               EST Extensions           September 29, 2017


   Content-Type: application/cms                     |
         <--------------------                       |
               POST res: empty                       |
                (success or failure)                 |
         -------------------->                      -+
   GET req:                                          | /eecerts
         <--------------------                       |
               GET res:  Other EE certificates       |
                Content-Type: application/pkcs7-mime |
                              smime-type=certs-only  |

   The figure above shows /eecerts after /*/return, but this is for
   illustrative purposes only.

Appendix B.  Additional CSR Attributes

   This is an informative appendix.

   In some cases, the client is severely limited in its ability to
   encode and decode ASN.1 objects.  If the client knows a csr template
   is being provided during enrollment, then it can peel the returned
   csr attribute, generate its keys, place the public key in the
   certification request, and then sign the request.  To accomplish
   this, the server returns a PKCS7PDU attribute [RFC2985] in as part of
   the /csrattrs (the following is pseudo ASN.1 and is only meant to
   show the fields needed to accomplish returning a template
   certification request):

     pKCS7PDU ATTRIBUTE ::= {
       WITH SYNTAX ContentInfo
       ID pkcs-9-at-pkcs7PDU
       }

     pkcs-9-at-pkcs7PDU OBJECT IDENTIFIER ::= {
       iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs9(9)
       at(25) 5
       }

   The ContentInfo is a PKIData:

     PKIData ::= SEQUENCE {
       reqSequence        SEQUENCE SIZE(0..MAX) OF TaggedRequest,
       }

   Where TaggedRequest is a choice between the PKCS #10 or CRMF
   requests.

     TaggedRequest ::= CHOICE {



Turner                   Expires April 2, 2018                 [Page 47]


Internet-Draft               EST Extensions           September 29, 2017


       tcr               [0] TaggedCertificationRequest,
       crm               [1] CertReqMsg,
       }

   Or, the Content Info can be a signed data content type that further
   encapsulates a PKIData.

Authors' Addresses

   Sean Turner
   sn3rd

   EMail: sean@sn3rd.com






































Turner                   Expires April 2, 2018                 [Page 48]