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Versions: (draft-pritikin-est) 00 01 02 03 04 05 06 07 08 09 RFC 7030

PKIX                                                    M. Pritikin, Ed.
Internet-Draft                                       Cisco Systems, Inc.
Intended status: Standards Track                             P. Yee, Ed.
Expires: February 15, 2014                                  AKAYLA, Inc.
                                                         D. Harkins, Ed.
                                                          Aruba Networks
                                                         August 13, 2013


                    Enrollment over Secure Transport
                      draft-ietf-pkix-est-09

Abstract

   This document profiles certificate enrollment for clients using
   Certificate Management over CMS (CMC) messages over a secure
   transport.  This profile, called Enrollment over Secure Transport
   (EST), describes a simple yet functional certificate management
   protocol targeting Public Key Infrastructure (PKI) clients that need
   to acquire client certificates and associated Certification Authority
   (CA) certificate(s).  It also supports client-generated public/
   private key pairs as well as key pairs generated by the CA.

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."

   This Internet-Draft will expire on February 15, 2014.

Copyright Notice

   Copyright (c) 2013 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



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   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   4
   2.  Operational Scenario Overviews  . . . . . . . . . . . . . . .   5
     2.1.  Obtaining CA Certificates . . . . . . . . . . . . . . . .   6
     2.2.  Initial Enrollment  . . . . . . . . . . . . . . . . . . .   7
       2.2.1.  Certificate TLS authentication  . . . . . . . . . . .   7
       2.2.2.  Certificate-less TLS authentication . . . . . . . . .   8
       2.2.3.  HTTP-based client authentication  . . . . . . . . . .   8
     2.3.  Client Certificate Re-issuance  . . . . . . . . . . . . .   8
     2.4.  Server Key Generation . . . . . . . . . . . . . . . . . .   8
     2.5.  Full PKI Request messages . . . . . . . . . . . . . . . .   8
     2.6.  Certificate Signing Request (CSR) Attributes Request  . .   9
   3.  Protocol Design and Layering  . . . . . . . . . . . . . . . .   9
     3.1.  Application Layer . . . . . . . . . . . . . . . . . . . .  12
     3.2.  HTTP Layer  . . . . . . . . . . . . . . . . . . . . . . .  13
       3.2.1.  HTTP headers for control  . . . . . . . . . . . . . .  13
       3.2.2.  HTTP URIs for control . . . . . . . . . . . . . . . .  14
       3.2.3.  HTTP-Based Client Authentication  . . . . . . . . . .  15
       3.2.4.  Message types . . . . . . . . . . . . . . . . . . . .  16
     3.3.  TLS Layer . . . . . . . . . . . . . . . . . . . . . . . .  17
       3.3.1.  TLS-Based Server Authentication . . . . . . . . . . .  18
       3.3.2.  TLS-Based Client Authentication . . . . . . . . . . .  18
       3.3.3.  Certificate-less TLS Mutual Authentication  . . . . .  19
     3.4.  Proof-of-Possession . . . . . . . . . . . . . . . . . . .  20
     3.5.  Linking Identity and PoP information  . . . . . . . . . .  20
     3.6.  Server Authorization  . . . . . . . . . . . . . . . . . .  21
       3.6.1.  Client use of Explicit TA Database  . . . . . . . . .  22
       3.6.2.  Client use of Implicit TA Database  . . . . . . . . .  22
     3.7.  Client Authorization  . . . . . . . . . . . . . . . . . .  22
   4.  Protocol Exchange Details . . . . . . . . . . . . . . . . . .  22
     4.1.  Distribution of CA certificates . . . . . . . . . . . . .  23
       4.1.1.  Bootstrap Distribution of CA certificates . . . . . .  23
       4.1.2.  CA certificates request . . . . . . . . . . . . . . .  23
       4.1.3.  CA certificates response  . . . . . . . . . . . . . .  24
     4.2.  Client Certificate Request Functions  . . . . . . . . . .  25
       4.2.1.  Simple Enrollment of Clients  . . . . . . . . . . . .  26
       4.2.2.  Simple Re-Enrollment of Clients . . . . . . . . . . .  26
       4.2.3.  Simple Enroll and Re-Enroll Response  . . . . . . . .  27
     4.3.  Full CMC  . . . . . . . . . . . . . . . . . . . . . . . .  27



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       4.3.1.  Full CMC Request  . . . . . . . . . . . . . . . . . .  28
       4.3.2.  Full CMC Response . . . . . . . . . . . . . . . . . .  28
     4.4.  Server-side Key Generation  . . . . . . . . . . . . . . .  28
       4.4.1.  Server-side Key Generation Request  . . . . . . . . .  29
         4.4.1.1.  Requests for Symmetric Key Encryption of the
                   Private Key . . . . . . . . . . . . . . . . . . .  30
         4.4.1.2.  Requests for Asymmetric Encryption of the Private
                   Key . . . . . . . . . . . . . . . . . . . . . . .  30
       4.4.2.  Server-side Key Generation Response . . . . . . . . .  31
     4.5.  CSR Attributes  . . . . . . . . . . . . . . . . . . . . .  32
       4.5.1.  CSR Attributes Request  . . . . . . . . . . . . . . .  33
       4.5.2.  CSR Attributes Response . . . . . . . . . . . . . . .  33
   5.  Contributors/Acknowledgements . . . . . . . . . . . . . . . .  34
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  34
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  36
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  38
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .  38
     8.2.  Informative References  . . . . . . . . . . . . . . . . .  41
   Appendix A.  Operational Scenario Example Messages  . . . . . . .  42
     A.1.  Obtaining CA Certificates . . . . . . . . . . . . . . . .  42
     A.2.  CSR Attributes  . . . . . . . . . . . . . . . . . . . . .  44
     A.3.  Enroll/Reenroll . . . . . . . . . . . . . . . . . . . . .  44
     A.4.  Server Key Generation . . . . . . . . . . . . . . . . . .  47
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  49

1.  Introduction

   This document profiles certificate enrollment for clients using
   Certificate Management over CMS (CMC) [RFC5272] messages over a
   secure transport.  Enrollment over Secure Transport (EST) describes
   the use of Transport Layer Security (TLS) 1.1 [RFC4346] (or a later
   version) and Hypertext Transfer Protocol (HTTP) [RFC2616] to provide
   an authenticated and authorized channel for Simple PKI (Public Key
   Infrastructure) Requests and Responses [RFC5272].

   Architecturally, the EST service is located between a Certification
   Authority (CA) and a client.  It performs several functions
   traditionally allocated to the RA (Registration Authority) role in a
   PKI.  The nature of communication between an EST server and a CA is
   not described in this document.

   EST adopts the Certificate Management Protocol (CMP) [RFC4210] model
   for CA certificate rollover, but does not use the CMP message syntax
   or protocol.  EST servers are extensible in that new functions may be
   defined to provide additional capabilities not specified in CMC
   [RFC5272], and this document defines two such extensions, one for
   requesting Certificate Signing Request attributes, and another for
   requesting server-generated keys.



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   EST specifies how to transfer messages securely via HTTP over TLS
   (HTTPS) [RFC2818], where the HTTP headers and media types are used in
   conjunction with TLS.  HTTPS operates over TCP; this document does
   not specify EST over HTTP/Datagram Transport Layer Security/User
   Datagram Protocol (HTTP/DTLS/UDP).  With a suitable specification for
   combining HTTP, DTLS, and UDP, there are no EST requirements that
   would prevent it from working over such a stack.  Figure 1 shows how
   the layers build upon each other.

   EST Layering:

   Protocols:
   +--------------------------------------------+
   |                                            |
   | EST request/response messages              |
   |                                            |
   +--------------------------------------------+
   |                                            |
   | HTTP for message transfer and signaling    |
   |                                            |
   +--------------------------------------------+
   |                                            |
   | TLS for transport security                 |
   |                                            |
   +--------------------------------------------+
   |                                            |
   | TCP for transport                          |
   |                                            |
   +--------------------------------------------+

                                 Figure 1

1.1.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in
   [RFC2119].

   It is assumed that the reader is familiar with the terms and concepts
   described in Public Key Cryptography Standard (PKCS) #10 [RFC2986],
   HTTPS [RFC2818], CMP [RFC4210], CMC [RFC5272][RFC5273][RFC5274], and
   TLS [RFC4346].

   In addition to the terms defined in the terminology section of CMC
   [RFC5272] the following terms are defined for clarity:





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   EST CA:  For certificate issuing services, the EST CA is reached
      through the EST Server; the CA could be logically "behind" the EST
      Server or embedded within it.

   Third-Party Trust Anchor:  Any Trust Anchor (TA) that is not
      authoritative for the PKI hierarchy the EST server is providing
      services for.

   Explicit Trust Anchor:  Any Trust Anchor that is explicitly
      configured on the client or server for use during EST TLS
      authentication.  For example a TA that is manually configured on
      the EST client or bootstrapped as described in Section 4.1.1.
      (See more details in Section 3.6 and Section 7).

   Implicit Trust Anchor:  Any third-party Trust Anchor that is
      available on the client or server for use during TLS
      authentication but is not specifically indicated for use during
      EST TLS authentication.  For example TAs commonly used by web
      browsers to authenticate web servers, or TAs used by servers to
      authenticate manufacturer-installed client credentials (such as
      certificates populated into cable modem or routers in the
      factory).  The authorization model for these TAs is different from
      the authorization model for Explicit Trust Anchors.  (See more
      details in Section 3.6.1, Section 3.6.2, and Section 7).

   Certificate-less TLS:  Certificate-less TLS cipher suites provide a
      way to perform mutual authentication in situations where neither
      the client nor server have certificates or are willing to use
      them.  The credential used for authentication is a word, phrase,
      code, or key that is shared between the client and server.  The
      credential must be uniquely shared between the client and server
      in order to provide authentication of an individual client and an
      individual server.

2.  Operational Scenario Overviews

   This section provides an informative overview of the operational
   scenarios to better introduce the reader to the protocol discussion.

   Both the EST clients and server are configured with information that
   provides the basis for bidirectional authentication and for
   authorization.  The specific initialization data depends on the
   methods available in the client and server, but can include shared
   secrets, network service names and locations (e.g., a Uniform
   Resource Identifier (URI) [RFC3986]), trust anchor information (e.g.,
   a CA certificate or a hash of a TA's certificate), and enrollment
   keys and certificates.  Depending on an enterprise's acquisition and
   network management practices, some initialization may be performed by



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   the vendor prior to delivery of client hardware and software.  In
   that case, the client vendor may provide data, such as trust anchors,
   to the enterprise via a secure procedure.  The distribution of this
   initial information is out of scope.

   Distribution of trust anchors and other certificates can be effected
   via the EST server.  However, nothing can be inferred about the
   authenticity of this data until an out-of-band mechanism is used to
   verify them.

   Sections 2.1-2.3 very closely mirror the text of the Scenarios
   Appendix of [RFC6403] with such modifications as are appropriate for
   this profile.  Sections 2.1-2.6, below, enumerate the set of EST
   functions (see Figure 5) and provide an informative overview of EST's
   capabilities.

   The general client/server interaction proceeds as follows: The client
   initiates a TLS-secured HTTP session with an EST server.  A specific
   EST service is requested based on a portion of the URI used for the
   session.  The client and server authenticate each other.  The client
   verifies that the server is authorized to serve this client.  The
   server verifies that the client is authorized to make use of this
   server and the request that the client has made.  The server acts
   upon the client request.

2.1.  Obtaining CA Certificates

   The EST client can request a copy of the current EST CA
   certificate(s) from the EST server.  The EST client is assumed to
   perform this operation before performing other operations.

   Throughout this document we assume the EST CA has a certificate that
   is used by the client to verify signed objects issued by the CA,
   e.g., certificates and certificate revocation lists (CRLs), and that
   a separate end-entity (EE) certificate is used when EST protocol
   communication requires additional encryption.

   The EST client authenticates and verifies the authorization scope of
   the EST server when requesting the current CA certificate(s).  As
   detailed in Section 3.3.1 and Section 3.3.3, available options
   include:

   o  Verifying the EST server's HTTPS URI against the EST server's
      certificate using Implicit TAs (similar to a common HTTPS
      exchange).  This allows the EST server and client to leverage
      existing TAs that might be known to the EST client.





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   o  The client can leverage a previously distributed trust anchor
      specific to the EST server.  This allows the EST client to use an
      existing, potentially older, CA certificate to request a current
      CA certificate.

   o  For bootstrapping, the EST client can rely upon manual
      authentication performed by the end user as detailed in
      Section 4.1.1.

   Client authentication is not required for this exchange, so it is
   trivially supported by the EST server.

2.2.  Initial Enrollment

   After authenticating an EST server and verifying that it is
   authorized to provide services to the client, an EST client can
   acquire a certificate for itself by submitting an enrollment request
   to that server.

   The EST server authenticates and authorizes the EST client as
   specified in Section 3.3.2, Section 3.3.3 and Section 3.7.  The
   methods described in the normative text that are discussed in this
   overview include:

   o  TLS with a previously issued client certificate (e.g., an existing
      certificate issued by the EST CA);

   o  TLS with a previously installed certificate (e.g., manufacturer
      installed certificate or a certificate issued by some other
      party);

   o  Certificate-less TLS (e.g., with a shared credential distributed
      out-of-band);

   o  HTTP-based with a username/password distributed out-of-band.

2.2.1.  Certificate TLS authentication

   If the EST client has a previously installed certificate issued by a
   third party CA, this certificate can be used to authenticate the
   client's request for a certificate from the EST server (if that CA is
   recognized by the EST server).  An EST client responds to the EST
   server's TLS certificate request message with the existing
   certificate already held by the client.  The EST server will verify
   the client's existing certificate and authorize the client's request
   as described in Section 3.3.2.





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2.2.2.  Certificate-less TLS authentication

   The EST client and EST server can be mutually authenticated using a
   certificate-less TLS cipher suite (see Section 3.3.3).

2.2.3.  HTTP-based client authentication

   The EST server can optionally also request that the EST client submit
   a username/password using the HTTP Basic or Digest Authentication
   methods (see Section 3.2.3).  This approach is desirable if the EST
   client cannot be authenticated during the TLS handshake (see
   Section 3.3.2) or the EST server policy requires additional
   authentication information.  See Section 3.2.3.  In all cases, HTTP-
   based client authentication is only to be performed over a TLS-
   protected transport (see Section 3.3).

2.3.  Client Certificate Re-issuance

   An EST client can renew/rekey its existing client certificate by
   submitting a re-enrollment request to an EST server.

   When the current EST client certificate can be used for TLS client
   authentication (Section 3.3.2) the client presents this certificate
   to the EST server for client authentication.  When the to be re-
   issued EST client certificate cannot be used for TLS client
   authentication, any of the authentication methods used for initial
   enrollment can be used.

   For example if the client has an alternative certificate issued by
   the EST CA that can be used for TLS client authentication, then it
   can be used.

   The certificate request message includes the same Subject and
   SubjectAltName as the current certificate.  Name changes are
   requested as specified in Section 4.2.2.

2.4.  Server Key Generation

   The EST client can request a server-generated certificate and key
   pair (see Section 4.4).

2.5.  Full PKI Request messages









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   Full PKI Request [RFC5272] messages can be transported via EST using
   the Full CMC Request function.  This affords access to functions not
   provided by the Simple Enrollment functions.  Full PKI Request
   messages are defined in Sections 3.2 and 4.2 of [RFC5272].  See
   Section 4.3 for a discussion of how EST provides a transport for
   these messages.

2.6.  Certificate Signing Request (CSR) Attributes Request

   Prior to sending an enrollment request to an EST server, an EST
   client can query the EST server for a set of additional attribute(s)
   that the client is requested to use in a subsequent enrollment
   request.

   These attributes can provide additional descriptive information that
   the EST server cannot access itself, such as the Media Access Control
   (MAC) address of an interface of the EST client.  Alternatively,
   these attributes can indicate the kind of enrollment request, such as
   a specific elliptic curve or a specific hash function that the client
   is expected to use when generating the CSR.

3.  Protocol Design and Layering

   Figure 2 provides an expansion of Figure 1 describing how the layers
   are used.  Each aspect is described in more detail in the sections
   that follow.

   EST Layering:

   Protocols and uses:
   +----------------------------------------------------+
   |                                                    |
   | Message types:                                     |
   |   - "Simple PKI" messages                          |
   |     (incorporates proof-of-possession)             |
   |   - CA certificate retrieval                       |
   |   - "Full PKI" messages (OPTIONAL)                 |
   |     (incorporates proof-of-possession)             |
   |   - CSR attribute request (OPTIONAL)               |
   |   - Server-generated key request (OPTIONAL)        |
   |                                                    |
   +----------------------------------------------------+
   |                                                    |
   | HTTP:                                              |
   |   - HTTP headers and URIs for control              |
   |      - Content-Type headers specify message type   |
   |      - Headers for control/error messages          |
   |      - URIs for selecting functions                |



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   |   - Basic or Digest authentication (OPTIONAL)      |
   |                                                    |
   +----------------------------------------------------+
   |                                                    |
   | TLS for transport security                         |
   |   - Authentication of the EST server               |
   |   - Authentication of the EST client (OPTIONAL)    |
   |   - Provides communications integrity              |
   |     and confidentiality                            |
   |   - Supplies channel Binding [RFC5929] information |
   |     to link proof-of-identity with message-based   |
   |     proof-of-possession. (OPTIONAL)                |
   |                                                    |
   +----------------------------------------------------+

                                 Figure 2

   Specifying HTTPS as the secure transport for enrollment messages
   introduces two 'layers' to communicate authentication and control
   messages: TLS and HTTP.

   The TLS layer provides integrity and confidentiality during
   transport.  The proof-of-identity is supplied by TLS handshake
   authentication and optionally also by the HTTP layer headers.  The
   message type and control/error messages are included in the HTTP
   headers.

   CMC [RFC5272] Section 3.1 notes that "the Simple PKI Request MUST NOT
   be used if a proof-of-identity needs to be included".  Since the TLS
   and HTTP layers can provide proof-of-identity for EST clients and
   servers the Simple PKI message types are used.

   The TLS layer certificate exchange provides a method for authorizing
   client enrollment requests using existing certificates.  Such
   certificates may have been issued by the CA (from which the client is
   requesting a certificate) or they may have been issued under a
   distinct PKI (e.g., an IEEE 802.1AR IDevID [IDevID] credential).

   Proof-of-possession (PoP) is a distinct issue from proof-of-identity
   and is included in the Simple PKI message type as described in
   Section 3.4.  A method of linking proof-of-identity and proof-of-
   possession is described in Section 3.5.

   This document also defines transport for CMC [RFC5272] that complies
   with CMC Transport Protocols [RFC5273].  CMC's PoP and proof-of-
   identity mechanisms are defined in CMC, but the mechanisms here can
   also be used in conjunction with those mechanisms in "Full PKI"
   messages.



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   During protocol exchanges different certificates can be used.  The
   following table provides an informative overview.  End-entities can
   have one or more certificates of each type listed in Figure 3 and use
   one or more Trust Anchor databases of each type listed in Figure 4.

   Certificates and their corresponding uses:
   +--------------+--------------------+-------------------------------+
   | Certificate  | Issuer             | Use and section references    |
   +==============+====================+===============================+
   | EST server   | The CA served by   | Presented by the EST server   |
   | certificate  | the EST server     | during the TLS handshake      |
   |              |                    |                               |
   |              |                    | Section 3.3.1                 |
   +--------------+--------------------+-------------------------------+
   | EST server   | A CA               | Presented by the EST server   |
   | certificate  | authenticatable by | during the TLS handshake      |
   |              | a third-party TA   |                               |
   |              | e.g., a web server | Section 3.3.1, and            |
   |              | CA                 | Security Considerations       |
   +--------------+--------------------+-------------------------------+
   | Third-Party  | A CA               | Presented by the EST client   |
   | EST client   | authenticatable by | to the EST server by clients  |
   | certificate  | a third-party TA   | that have not yet enrolled    |
   |              | e.g., a device     |                               |
   |              | manufacturer       | Section 3.3.2                 |
   +--------------+--------------------+-------------------------------+
   | EST client   | The CA served by   | Presented to the EST server   |
   | certificate  | the EST server     | during future EST operations. |
   |              |                    |                               |
   |              |                    | Section 3.3.2                 |
   +--------------+--------------------+-------------------------------+
   | End-Entity   | The CA served by   | Clients can obtain certs      |
   | certificate  | the EST server     | that are intended for         |
   |              |                    | non-EST uses. This includes   |
   |              |                    | certs that cannot be used     |
   |              |                    | for EST operations.           |
   |              |                    |                               |
   |              |                    | Section 4.2.3                 |
   +--------------+--------------------+-------------------------------+


                                 Figure 3

   Trust Anchor databases and their corresponding uses:
   +--------------+----------------------------------------------------+
   | TA database  | Use and section references                         |
   +==============+====================================================+
   | EST server   | EST servers use this TA database to authenticate   |



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   | Explicit     | certificates issued by the EST CA, including EST   |
   | TA database  | client certificates during enroll/re-enroll        |
   |              | operations                                         |
   |              |                                                    |
   |              | Section 3.3.2                                      |
   +--------------+----------------------------------------------------+
   | EST server   | EST servers use this TA database to authenticate   |
   | Implicit     | certificates issued by third-party TAs.            |
   | TA database  | e.g., EST client certificates issued by a device   |
   |              | manufacturer                                       |
   |              | An Implicit TA database can be disabled.           |
   |              |                                                    |
   |              | Section 3.3.2                                      |
   +--------------+----------------------------------------------------+
   | EST client   | EST clients use this TA database to authenticate   |
   | Explicit     | certificates issued by the EST CA, including EST   |
   | TA database  | server certificates.                               |
   |              |                                                    |
   |              | Section 3.1, Section 3.3.1, Section 3.6.1 and      |
   |              | Section 4.1.1                                      |
   +--------------+----------------------------------------------------+
   | EST client   | EST clients use this trust anchor database to      |
   | Implicit     | authenticate an EST server that uses an externally |
   | TA database  | issued certificate.                                |
   |              | An Implicit TA database can be disabled.           |
   |              |                                                    |
   |              | Section 3.1, Section 3.3.1, Section 3.6.2          |
   |              | and Security Considerations                        |
   +--------------+----------------------------------------------------+


                                 Figure 4

3.1.  Application Layer

   The EST client MUST be capable of generating and parsing Simple PKI
   messages (see Section 4.2).  Generating and parsing Full PKI messages
   is OPTIONAL (see Section 4.3).  The client MUST also be able to
   request CA certificates from the EST server and parse the returned
   "bag" of certificates (see Section 4.1).  Requesting CSR attributes
   and parsing the returned list of attributes is OPTIONAL (see
   Section 4.5).

   Details of the EST client application configuration are out of scope
   of the protocol discussion but are necessary for understanding the
   prerequisites of initiating protocol operations.  The EST client is
   RECOMMENDED to be configured with TA databases for Section 3.3.1 or
   with a secret key for Section 3.3.3.  Implementations conforming to



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   this standard MUST provide the ability to designate Explicit TAs.
   For human usability reasons a "fingerprint" of an Explicit TA
   database entry can be configured for bootstrapping as discussed in
   Section 4.1.1.  Configuration of an Implicit TA database, perhaps by
   its inclusion within the EST client distribution or available from
   the operating system, provides flexibility along with the caveats
   detailed in Section 7.  Implementations conforming to this standard
   MUST provide the ability to disable use of any Implicit TA database.

   The EST client is configured with sufficient information to form the
   EST server URI.  This can be the full operation path segment (e.g.
   https://www.example.com/.well-known/est/ or https://www.example.com/
   .well-known/est/arbitraryLabel1) or the EST client can be configured
   with a tuple composed of the authority portion of the URI along with
   the OPTIONAL label (e.g.  "www.example.com:80", "arbitraryLabel1") or
   just the authority portion of the URI.

3.2.  HTTP Layer

   HTTP is used to transfer EST messages.  URIs are defined for handling
   each media type (i.e., message type) as described in Section 3.2.2.
   HTTP is also used for client authentication services when TLS client
   authentication is not available, due to lack of a client certificate
   suitable for use by TLS (see Section 3.2.3).  HTTP authentication can
   also be used in addition to TLS client authentication if the EST
   server wishes additional authentication information, as noted in
   Section 2.2.3.  Registered media types are used to convey EST
   messages as specified in Figure 6.

   HTTP 1.1 [RFC2616] and above support persistent connections.  As
   described in Section 8.1 of that RFC, persistent connections may be
   used to reduce network and processing load associated with multiple
   HTTP requests.  EST does not require or preclude persistent HTTP
   connections.

3.2.1.  HTTP headers for control

   The HTTP Status value is used to communicate success or failure of an
   EST function.  HTTP authentication is used by a client when requested
   by the server.

   The media types indicated in the HTTP content-type header indicates
   which EST message is being transferred.  Media types used by EST are
   specified in Section 3.2.4.

   HTTP redirections (3xx status codes) to the same web origin (see
   [RFC6454]) SHOULD be handled by the client without user input so long
   as all applicable security checks (Section 3.3 and Section 3.6) have



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   been enforced on the initial connection.  The client initiates a new
   TLS connection and performs all applicable security checks when
   redirected to other web origin servers.  Redirections to other web
   origins require the EST client to obtain user input for non-GET or
   HEAD requests as specified in [RFC2616].  Additionally if the client
   has already generated a CSR that includes Linking Identity and POP
   information (Section 3.5) then the CSR will need to be recreated to
   incorporate the tls-unique from the new, redirected session.  Note:
   the key pair need not be regenerated.  These are processing and
   interface burdens on the client.  EST server administrators are
   advised to take this into consideration.

3.2.2.  HTTP URIs for control

   The EST server MUST use the [RFC5785] defined path-prefix of "/.well-
   known/" and the registered name of "est".  Thus a valid EST server
   URI path begins with "https://www.example.com/.well-known/est".  Each
   EST operation is indicated by a path-suffix that indicates the
   intended operation:

   Operations and their corresponding URIs:
   +------------------------+-----------------+-------------------+
   | Operation              |Operation Path   | Details           |
   +========================+=================+===================+
   | Distribution of CA     | /cacerts        | Section 4.1       |
   | certificates (MUST)    |                 |                   |
   +------------------------+-----------------+-------------------+
   | Enrollment of new      | /simpleenroll   | Section 4.2.      |
   | clients (MUST)         |                 |                   |
   +------------------------+-----------------+-------------------+
   | Re-Enrollment of       | /simplereenroll | Section 4.2.2     |
   | existing clients (MUST)|                 |                   |
   +------------------------+-----------------+-------------------+
   | Full CMC (OPTIONAL)    | /fullcmc        | Section 4.3       |
   +------------------------+-----------------+-------------------+
   | Server-side Key        | /serverkeygen   | Section 4.4       |
   | Generation (OPTIONAL)  |                 |                   |
   +------------------------+-----------------+-------------------+
   | Request CSR attributes | /csrattrs       | Section 4.5       |
   | (OPTIONAL)             |                 |                   |
   +------------------------+-----------------+-------------------+

                                 Figure 5

   The operation path (Figure 5) is appended to the path-prefix to form
   the URI used with HTTP GET or POST to perform the desired EST
   operation.  An example valid URI absolute path for the "/cacerts"
   operation is "/.well-known/est/cacerts".  To retrieve the CA's



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   certificates, the EST client would use the following HTTP request-
   line:

   GET /.well-known/est/cacerts HTTP/1.1


   Likewise, to request a new certificate in this example scheme, the
   EST client would use the following request-line:

   POST /.well-known/est/simpleenroll HTTP/1.1


   The use of distinct operation paths simplifies implementation for
   servers that do not perform client authentication when distributing
   /cacerts responses.

   An EST server MAY provide service for multiple CAs as indicated by an
   OPTIONAL additional path segment between the registered application
   name and the operation path.  To avoid conflict the CA label MUST NOT
   be the same as any defined operation path segment.  The EST server
   MUST provide services regardless of whether the additional path
   segment is present.  The following are three example valid URIs:

   1.  https://www.example.com/.well-known/est/cacerts

   2.  https://www.example.com/.well-known/est/arbitraryLabel1/cacerts

   3.  https://www.example.com/.well-known/est/arbitraryLabel2/cacerts

   In this specification the distinction between enroll and renew/rekey
   is explicitly indicated by the HTTP URI.  When requesting /fullcmc
   operations CMC [RFC5272] uses the same messages for certificate
   renewal and certificate rekey.

   An EST server can provide additional services using other URIs.

3.2.3.  HTTP-Based Client Authentication














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   The EST server MAY request HTTP-based client authentication.  This
   request can be in addition to successful TLS client authentication
   (Section 3.3.2) if EST server policy requires additional
   authentication.  (For example the EST server may require that an EST
   client "knows" a password in addition to "having" an existing client
   certificate).  Or HTTP-based client authentication can be an EST
   server policy specified fallback in situations where the EST client
   did not successfully complete the TLS client authentication.  (This
   might arise if the EST client is enrolling for the first time or if
   the certificates available to an EST client cannot be used for TLS
   client authentication).

   HTTP Basic and Digest authentication MUST only be performed over TLS
   1.1 [RFC4346] or later versions.  NULL and anon cipher suites MUST
   NOT be used because they do not provide confidentiality or support
   mutual Certificate-based or Certificate-less authentication,
   respectively.  As specified in CMC: Transport Protocols [RFC5273] the
   server "MUST NOT assume client support for any type of HTTP
   authentication such as cookies, Basic authentication, or Digest
   authentication".  Clients SHOULD support the Basic and Digest
   authentication mechanism.

   Servers that wish to use Basic and Digest authentication reject the
   HTTP request using the HTTP defined WWW-Authenticate response-header
   ([RFC2616], Section 14.47).  The client is expected to retry the
   request, including the appropriate Authorization Request Header
   ([RFC2617], Section 3.2.2), if the client is capable of using the
   Basic or Digest authentication.  If the client is not capable of
   retrying the request or it is not capable of Basic or Digest
   authentication, then the client MUST terminate the connection.

   A client MAY set the username to the empty string ("") if it is
   presenting a password that is not associated with a username.

   Support for HTTP-based client authentication has security
   ramifications as discussed in Section 7.  The client MUST NOT respond
   to the server's HTTP authentication request unless the client has
   authorized the EST server (as per Section 3.6).

3.2.4.  Message types

   This document uses existing media types for the messages as specified
   by [RFC2585], [RFC5967], and CMC [RFC5272].  To support distribution
   of multiple certificates for a CA certificate path, the [RFC2046]
   multipart/mixed media type is used.

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



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   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        |                   |
   +====================+==========================+===================+
   | CA certificate     | N/A                      | Section 4.1       |
   | request            | application/pkcs7-mime   | Section 4.1.1     |
   |                    | [RFC5751]                |                   |
   | /cacerts           |                          |                   |
   +--------------------+--------------------------+-------------------+
   | Cert enroll/renew/ | application/pkcs10       | Section 4.2/4.2.1 |
   | rekey              | application/pkcs7-mime   | Section 4.2.2     |
   |                    | [RFC5967] [RFC5751]      |                   |
   | /simpleenroll      |                          |                   |
   +--------------------+--------------------------+-------------------+
   | Full CMC           | application/pkcs7-mime   | Section 4.3.1     |
   |                    | application/pkcs7-mime   | Section 4.3.2     |
   | /fullcmc           | [RFC5751]                |                   |
   +--------------------+--------------------------+-------------------+
   | Server-side Key    | application/pkcs10       | Section 4.4.1     |
   | Generation         | multipart/mixed          | Section 4.4.2     |
   |                    | (application/pkcs7-mime &|                   |
   |                    | application/pkcs8)       |                   |
   |                    | [RFC5967] [RFC5751] &    |                   |
   | /serverkeygen      | [RFC5958]                |                   |
   +--------------------+--------------------------+-------------------+
   | Request CSR        | N/A                      | Section 4.5.1     |
   | attributes         | application/csrattrs     | Section 4.5.2     |
   |                    | (This document)          |                   |
   | /csrattrs          |                          |                   |
   +--------------------+--------------------------+-------------------+


                                 Figure 6

3.3.  TLS Layer

   TLS provides authentication, which in turn enables authorization
   decisions.  The EST server and EST client are responsible for
   ensuring that an acceptable cipher suite is negotiated and that
   bidirectional authentication has been performed.  TLS authentication
   is most commonly enabled with the use of certificates [RFC5280].
   Alternately, certificate-less TLS authentication, where neither the
   client nor server present a certificate, is also an acceptable method
   for EST mutual authentication (Section 3.3.3.  The EST server MUST be



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   authenticated during the TLS handshake unless the client is
   requesting Bootstrap Distribution of CA certificates (Section 4.1.1)
   or Full CMC (Section 4.3).

   HTTPS [RFC2818] specifies how HTTP messages are carried over TLS.
   HTTPS MUST be used.  TLS 1.1 [RFC4346] (or a later version) MUST be
   used for all EST communications.  TLS session resumption [RFC5077]
   SHOULD be supported.

   TLS channel binding information can be inserted into a certificate
   request as detailed in Section 3.5 in order to provide the EST server
   with assurance that the authenticated TLS client has access to the
   private key for the certificate being requested.  The EST server MUST
   implement Section 3.5.

3.3.1.  TLS-Based Server Authentication

   TLS server authentication with certificates MUST be supported.

   The EST client authenticates the EST server as defined for the cipher
   suite negotiated.  The following text provides details assuming a
   certificate-based cipher suite, such as the TLS 1.1 [RFC4346]
   mandatory cipher suite (TLS_RSA_WITH_3DES_EDE_CBC_SHA).

   Certificate validation MUST be performed as per [RFC5280].  The EST
   server certificate MUST conform to the [RFC5280] certificate profile.

   The client validates the TLS server certificate using the EST client
   Explicit and, if enabled, Implicit TA database(s).  The client MUST
   maintain a distinction between the use of Explicit and Implicit TA
   databases during authentication in order to support proper
   authorization.  The EST client MUST perform authorization checks as
   specified in Section 3.6.

   If certificate validation fails, the client MAY follow the procedure
   outlined in Section 4.1.1 for bootstrap distribution of CA
   certificates.

3.3.2.  TLS-Based Client Authentication

   TLS client authentication is the RECOMMENDED method for identifying
   EST clients.  HTTP-Based Client Authentication (Section 3.2.3) MAY be
   used.








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   The EST server authenticates the EST client as defined for the cipher
   suite negotiated.  The following text provides details assuming a
   certificate-based cipher suite such as the TLS 1.1 [RFC4346]
   mandatory cipher suite (TLS_RSA_WITH_3DES_EDE_CBC_SHA).  The EST
   server MUST support certificate-based client authentication.

   Generally, the client will use an existing certificate for renew or
   rekey operations.  If the certificate to be renewed or rekeyed is
   appropriate for the negotiated cipher suite, then the client MUST use
   it for the TLS handshake, otherwise the client SHOULD use an
   alternate certificate that is suitable for the cipher suite and
   contains the same subject identity information.  When requesting an
   enroll operation the client MAY use a third-party issued client
   certificate to authenticate itself.

   Certificate validation MUST be performed as per [RFC5280].  The EST
   client certificate MUST conform to the [RFC5280] certificate profile.

   The server validates the TLS server certificate using the EST server
   Explicit and, if enabled, Implicit TA database(s).  The server MUST
   maintain a distinction between the use of Explicit and Implicit TA
   databases during authentication in order to support proper
   authorization.

   The EST server MUST perform authorization checks as specified in
   Section 3.7.

   If a client does not support TLS client authentication, then it MUST
   support HTTP-based client authentication (Section 3.2.3) or
   certificate-less TLS authentication (Section 3.3.3).

3.3.3.  Certificate-less TLS Mutual Authentication

   Certificate-less TLS cipher suites provide a way to perform mutual
   authentication in situations where neither the client nor server have
   certificates, do not desire to use certificates, or do not have the
   trust anchors necessary to verify a certificate.  The client and
   server MAY negotiate a certificate-less cipher suite for mutual
   authentication.

   When using certificate-less mutual authentication in TLS for
   enrollment, the cipher suite MUST be based on a protocol that is
   resistant to dictionary attack and MUST be based on a zero knowledge
   protocol.  TLS-SRP cipher suites, i.e., those with _SRP_ in the name,
   listed in section 2.7 of [RFC5054] are suitable for this purpose.
   Section 7 lists the characteristics of a cipher suite that are
   suitable for use in certificate-less mutual authentication for
   enrollment.



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   Successful authentication using a certificate-less cipher suite
   proves knowledge of a pre-shared secret which implicitly authorizes a
   peer in the exchange.

3.4.  Proof-of-Possession

   As defined in Section 2.1 of CMC [RFC5272], Proof-of-possession (POP)
   "refers to a value that can be used to prove that the private key
   corresponding to the public key is in the possession of and can be
   used by an end-entity."

   The signed enrollment request provides a signature-based proof-of-
   possession.  The mechanism described in Section 3.5 strengthens this
   by optionally including "Direct"-based proof-of-possession [RFC5272]
   by including TLS session-specific information within the data covered
   by the enrollment request signature (thus linking the enrollment
   request to the authenticated end-point of the TLS connection).

3.5.  Linking Identity and PoP information

   Server policy will determine whether clients are required to use the
   mechanism specified in this section.  This specification provides a
   method of linking identity and proof-of-possession by including
   information specific to the current authenticated TLS session within
   the signed certification request.  The client can determine if the
   server requires the linking of identity and PoP by examining the CSR
   Attributes Response (see Section 4.5.2).  Regardless of the CSR
   Attributes Response, clients SHOULD link identity and PoP by
   embedding tls-unique information in the certification request.  If
   tls-unique information is included by the client, the server MUST
   verify it.  The EST server MAY reject requests without tls-unique
   information as indicated by server policy.

   Linking identity and proof-of-possession proves to the server that
   the authenticated TLS client has possession of the private key
   associated with the certification request and that the client was
   able to sign the certification request after the TLS session was
   established.  This is an alternative to the [RFC5272]
   Section 6.3-defined "Linking Identity and POP information" method
   available if Full PKI messages are used.

   The client generating the CSR obtains the tls-unique value from the
   TLS subsystem as described in Channel Bindings for TLS [RFC5929].
   The EST client operations between obtaining the tls_unique value
   through generation of the CSR that contains the current tls_unique
   value and the subsequent verification of this value by the EST server
   are the "phases of the application protocol during which application-
   layer authentication occurs" that are protected by the



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   synchronization interoperability mechanism described in the Channel
   Bindings for TLS [RFC5929] section 3.1 interoperability notes.  When
   performing renegotiation, TLS "secure_renegotiation" [RFC5746] MUST
   be used.

   The tls-unique value is base 64-encoded as specified in Section 4 of
   [RFC4648] and the resulting string is placed in the certification
   request challenge-password field ([RFC2985], Section 5.4.1).  The
   challenge-password field is limited to 255 bytes (section 7.4.9 of
   [RFC5246] indicates that no existing cipher suite would result in an
   issue with this limitation).  If tls-unique information is not
   embedded within the certification request the challenge-password
   field MUST be empty to indicate that the client did not include the
   optional channel-binding information (any value submitted is verified
   by the server as tls-unique information).

   If the EST server makes use of a back-end infrastructure for
   processing, it is RECOMMENDED that the results of this verification
   be communicated.  (For example this communication might use the CMC
   [RFC5272] "RA POP Witness Control" in a CMC Full PKI Request message.
   Or an EST server might TLS-authenticate an EST client as being a
   trusted infrastructure element that does not forward invalid
   requests.  A detailed discussion of back-end processing is out of
   scope).

   When rejecting requests, the EST server response is as described for
   all enroll responses (Section 4.2.3).  If a Full PKI Response is
   included, the CMCFailInfo MUST be set to popFailed.  If a human
   readable reject message is included it SHOULD include an informative
   text message indicating that linking of identity and POP information
   is required.

3.6.  Server Authorization

   The client MUST check EST server authorization before accepting any
   server responses or responding to HTTP authentication requests.

   The EST client authorization method depends on which method was used
   to authenticate the server.  When the Explicit TA database is used to
   authenticate the EST server then Section 3.6.1 applies.  When the
   Implicit TA database is used to authenticate the EST server then
   Section 3.6.2 applies.  Successful authentication using a
   certificate-less cipher suite implies authorization of the server.

   The client MAY perform bootstrapping as specified in Section 4.1.1
   even if these checks fail.





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3.6.1.  Client use of Explicit TA Database

   When the EST client Explicit TA database is used to validate the EST
   server certificate the client MUST check either the configured URI or
   the most recent HTTP redirection URI against the server's identity
   according to the rules specified in [RFC6125], Section 6.4, or the
   EST server certificate MUST contain the id-kp-cmcRA [RFC6402]
   extended key usage extension.

3.6.2.  Client use of Implicit TA Database

   When the EST client Implicit TA database is used to validate the EST
   server certificate, the client MUST check the configured URI and each
   HTTP redirection URI according to the rules specified in [RFC6125],
   Section 6.4.  The provisioned URI or the most recent HTTP redirection
   URI provides the basis for authorization, and the server's
   authenticated identity confirms it is the authorized server.

3.7.  Client Authorization

   The decision to issue a certificate to a client is always controlled
   by local CA policy.  The EST server configuration reflects this CA
   policy.  This document does not specify any constraints on such
   policy.  EST provides the EST server access to each client's
   authenticated identity -- e.g., the TLS client's certificate in
   addition to any HTTP user authentication credentials -- to help in
   implementing such policy.

   If the client's certificate was issued by the EST CA, and it includes
   the id-kp-cmcRA [RFC6402] extended key usage extension, then the
   client is a Registration Authority (RA) as described in [RFC5272] and
   [RFC6402].  In this case the EST server SHOULD apply authorization
   policy consistent with an RA client.  For example, when handling
   /simpleenroll requests the EST server could be configured to accept
   PoP linking information that does not match the current TLS session
   because the authenticated EST client RA has verified this information
   when acting as an EST server (as specified in Section 3.5).  More
   specific RA mechanisms are available if the EST client uses /fullcmc
   methods.

4.  Protocol Exchange Details

   Before processing a request, an EST server determines if the client
   is authorized to receive the requested services.  Likewise, the
   client determines if it will make requests to the EST server.  These
   authorization decisions are described in the next two sections.
   Assuming that both sides of the exchange are authorized, then the
   actual operations are as described in subsequent sections.



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4.1.  Distribution of CA certificates

   The EST client can request a copy of the current CA certificates.
   This function is generally performed before other EST functions.

4.1.1.  Bootstrap Distribution of CA certificates

   It is possible that the client was not configured with the TA
   database(s) necessary to validate the EST server certificate.  This
   section describes a method by which minimally configured EST clients
   can populate their Explicit TA database.

   If the EST client application does not specify either an Explicit TA
   database or a Implicit TA database then the initial TLS server
   authentication and authorization will fail.  The client MAY
   provisionally continue the TLS handshake to completion for the
   purposes of accessing the /cacerts or /fullcmc method.  If the EST
   client continues with an unauthenticated connection, the client MUST
   extract the HTTP content data from the response (Section 4.1.3 or
   Section 4.3.2) and engage a human user to authorize the CA
   certificate using out-of-band data such as a CA certificate
   "fingerprint" (e.g., a SHA-256 or SHA-512 [SHS] hash on the whole CA
   certificate).  In a /fullcmc response it is the Publish Trust Anchors
   control (CMC [RFC5272], Section 6.15) within the Full PKI Response
   that must be accepted manually.  It is incumbent on the user to
   properly verify the TA information, or to provide the "fingerprint"
   data during configuration that is necessary to verify the TA
   information.

   HTTP authentication requests MUST NOT be responded to if the server
   has not been authenticated as specified in Section 3.3.1 or
   Section 3.3.3 if the optional Certificate-less authentication is
   used.

   The EST client uses the /cacerts response to establish an Explicit
   Trust Anchor database for subsequent TLS authentication of the EST
   server.  EST clients MUST NOT engage in any other protocol exchange
   until after the /cacerts response has been accepted and a new TLS
   session has been established (using TLS certificate-based
   authentication).

4.1.2.  CA certificates request









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   EST clients request the EST CA TA database information of the CA (in
   the form of certificates) with an HTTPS GET message using an
   operation path of "/cacerts".  EST clients and servers MUST support
   the /cacerts function.  Clients SHOULD request an up-to-date response
   before stored information has expired in order to ensure the EST CA
   TA database is up to date.

   The EST server SHOULD NOT require client authentication or
   authorization to reply to this request.

   The client MUST authenticate the EST server as specified in
   Section 3.3.1 if certificate-based authentication is used or
   Section 3.3.3 if the optional certificate-less authentication is used
   and check the server's authorization as given in Section 3.6 or
   follow the procedure outlined in Section 4.1.1.

4.1.3.  CA certificates response

   If successful, the server response MUST have an HTTP 200 response
   code.  Any other response code indicates an error and the client MUST
   abort the protocol.

   A successful response MUST be a certs-only CMC Simple PKI Response,
   as defined in [RFC5272], containing the certificates described in the
   following paragraph.  The HTTP content-type of "application/
   pkcs7-mime" is used.  The Simple PKI response is sent with a Content-
   Transfer-Encoding of "base64" [RFC2045].

   The EST server MUST include the current root CA certificate in the
   response.  The EST server MUST include any additional certificates
   the client would need to build a chain from an EST CA issued
   certificate to the current EST CA TA.  For example if the EST CA is a
   subordinate CA then all the appropriate subordinate CA certificates
   necessary to build a chain to the root EST CA are included in the
   response.

   The EST server SHOULD include the three "Root CA Key Update"
   certificates OldWithOld, OldWithNew, and NewWithOld in the response
   chain.  These are defined in Section 4.4 of CMP [RFC4210].  The EST
   client MUST be able to handle these certificates in the response.
   The EST CA's most recent self-signed certificate (e.g. NewWithNew
   certificate) is self-signed and has the latest NotAfter date.  If the
   EST server does not include these in the response then after the
   current EST CA certificate expires the EST clients will need to be
   reinitialized with the PKI using the Bootstrap Distribution of CA
   certificates (Section 4.1.1) method, which involves user interaction.





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   After out-of-band validation occurs, all the other certificates MUST
   be validated using normal [RFC5280] certificate path validation
   (using the most recent CA certificate as the TA) before they can be
   used to build certificate paths during certificate validation.

   The EST client MUST store the extracted EST CA certificate as an
   Explicit TA database entry for subsequent EST server authentication.
   The EST client SHOULD disable use of Implicit TA database entries for
   this EST server, now that an Explicit TA database entry is available.
   If the client disables the Implicit TA database, and if the EST
   server certificate was verified using an Implicit TA database entry,
   then the client MUST include the "Trusted CA Indication" extension in
   future TLS sessions [RFC6066].  This indicates to the server that
   only an EST Server certificate authenticatable by the Explicit TA
   database entry is now acceptable (otherwise the EST server might
   continue to use a server certificate that is only verifiable by a now
   disabled Implicit TA).

   The EST client SHOULD also make the CA Certificate response
   information available to the end-entity software for use when
   validating peer certificates.

4.2.  Client Certificate Request Functions

   EST clients request a certificate from the EST server with an HTTPS
   POST using the operation path value of "/simpleenroll".  EST clients
   request a renew/rekey of existing certificates with an HTTP POST
   using the operation path value of "/simplereenroll".  EST servers
   MUST support the /simpleenroll and /simplereenroll functions.

   It is RECOMMENDED that a client obtain the current CA certificates,
   as described in Section 4.1, before performing certificate request
   functions.  This ensures that the client will be able to validate the
   EST server certificate.  The client MUST authenticate the EST server
   as specified in Section 3.3.1 if certificate-based authentication is
   used or Section 3.3.3 if the optional certificate-less authentication
   is used.  The client MUST verify the authorization of the EST server
   as specified in Section 3.6.

   The server MUST authenticate the client as specified in Section 3.3.2
   if certificate-based authentication is used or Section 3.3.3 if the
   optional certificate-less authentication is used.  The server MUST
   verify client authorization as specified in Section 3.7.  The EST
   server MUST check the tls-unique value as described in Section 3.5 if
   one is submitted by the client.






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   The server MAY accept a certificate request for manual authorization
   checking by an administrator.  (Section 4.2.3 describes the use of an
   HTTP 202 response to the EST client if this occurs).

4.2.1.  Simple Enrollment of Clients

   When HTTPS POSTing to /simpleenroll the client MUST include a Simple
   PKI Request as specified in CMC [RFC5272] Section 3.1 (i.e., a
   PKCS#10 Certification Request [RFC2986]).

   The Certification Signing Request (CSR) signature provides proof-of-
   possession of the client possessed private key to the EST server.  If
   the CSR KeyUsage extension indicates the private key can be used to
   generate digital signatures then the client MUST generate the CSR
   signature using the private key.  If the key can be used to generate
   digital signatures but the requested CSR KeyUsage extension prohibits
   generation of digital signatures then the CSR signature MAY still be
   generated using the private key but the key MUST NOT be used for any
   other signature operations (this is consistent with the
   recommendations concerning submission of proof-of-possession to an RA
   or CA as described in [SP-800-57-Part-1]).  The use of /fullcmc
   operations provides access to more advanced proof-of-possession
   methods that are used when the key pair cannot be used for digital
   signature generation (see Section 4.3).

   The HTTP content-type of "application/pkcs10" is used here.  The
   format of the message is as specified in [RFC5967] with a Content-
   Transfer-Encoding of "base64" [RFC2045].

   The EST client MAY request additional certificates even when using an
   existing certificate in the TLS client authentication.  For example
   the client can use an existing certificate for TLS client
   authentication when requesting a certificate that cannot be used for
   TLS client authentication.

4.2.2.  Simple Re-Enrollment of Clients

   EST clients renew/rekey certificates with an HTTPS POST using the
   operation path value of "/simplereenroll".

   A certificate request employs the same format as the "simpleenroll"
   request, using the same HTTP content-type.  The request Subject field
   and SubjectAltName extension MUST be identical to the corresponding
   fields in the certificate being renewed/rekeyed.  The
   ChangeSubjectName attribute, as defined in [RFC6402], MAY be included
   in the CSR to request that these fields be changed in the new
   certificate.




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   If the Subject Public Key Info in the certification request is the
   same as the current client certificate then the EST server renews the
   client certificate.  If the public key information in the
   certification request is different than the current client
   certificate then the EST server rekeys the client certificate.

4.2.3.  Simple Enroll and Re-Enroll Response

   If the enrollment is successful, the server response MUST contain an
   HTTP 200 response code with a content-type of "application/
   pkcs7-mime".

   A successful response MUST be a certs-only CMC Simple PKI Response,
   as defined in [RFC5272], containing only the certificate that was
   issued.  The HTTP content-type of "application/pkcs7-mime" with an
   smime-type parameter "certs-only" is used, as specified in [RFC5273].

   The server MUST answer with a suitable 4xx or 5xx HTTP [RFC2616]
   error code when a problem occurs.  A Simple PKI Response with an HTTP
   content-type of "application/pkcs7-mime" (see Section 4.3.2) MAY be
   included in the response data to convey an error response.  If the
   content-type is not set the response data MUST be a plain text human-
   readable error message containing explanatory information describing
   why the request was rejected (for example indicating that CSR
   attributes are incomplete).

   If the server responds with an HTTP [RFC2616] 202, this indicates
   that the request has been accepted for processing but that a response
   is not yet available.  The server MUST include a Retry-After header
   as defined for HTTP 503 responses.  The server also MAY include
   informative human-readable content.  The client MUST wait at least
   the specified 'retry-after' time before repeating the same request.
   The client repeats the initial enrollment request after the
   appropriate 'retry-after' interval has expired.  The client SHOULD
   log or inform the end user of this event.  The server is responsible
   for maintaining all state necessary to recognize and handle retry
   operations as the client is stateless in this regard; it simply sends
   the same request repeatedly until it receives a different response
   code.  All other return codes are handled as specified in HTTP
   [RFC2616].

   The EST client MAY also make the certificate response, and associated
   private key, available to end-entity software for use as an end-
   entity certificate.

4.3.  Full CMC





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   An EST client can request a certificate from an EST server with an
   HTTPS POST using the operation path value of "/fullcmc".  Support for
   the /fullcmc function is OPTIONAL for both clients and servers.

4.3.1.  Full CMC Request

   If the HTTP POST to /fullcmc is not a valid Full PKI Request, the
   server MUST reject the message.  The HTTP content-type used is
   "application/pkcs7-mime" with an smime-type parameter "CMC-request",
   as specified in [RFC5273].  The body of the message is the binary
   value of the encoding of the PKI Request with a Content-Transfer-
   Encoding of "base64" [RFC2045].

4.3.2.  Full CMC Response

   If the enrollment is successful, the server response MUST include an
   HTTP 200 response code with a content-type of "application/
   pkcs7-mime" as specified in [RFC5273].  The response data includes
   either the Simple PKI Response with an smime-type parameter of
   "certs-only" or the Full PKI Response with an smime-type parameter
   "CMC-response", as specified in Section 3.2.1 of [RFC5751].  The body
   of the message is the binary value of the encoding of the PKI
   Response with a Content-Transfer-Encoding of "base64" [RFC2045].

   When rejecting a request, the server MUST specify either an HTTP 4xx
   error or an HTTP 5xx error.  A CMC response with content-type of
   "application/pkcs7-mime" SHOULD be included in the response data for
   any CMC error response.  If the content-type is not set the response
   data MUST be a plain text human-readable error message containing
   informative information describing why the request was rejected (for
   example indicating that CSR attributes are incomplete).

   All other return codes are handled as specified in Section 4.2.3 or
   HTTP [RFC2616].  For example, a client interprets an HTTP 404 or 501
   response to indicate that this service is not implemented.

4.4.  Server-side Key Generation

   An EST client may request a private key and associated certificate
   from an EST server using an HTTPS POST with an operation path value
   of "/serverkeygen".  Support for the /serverkeygen function is
   OPTIONAL.

   A client MUST authenticate an EST server as specified in
   Section 3.3.1 if certificate-based authentication is used or
   Section 3.3.3 if the optional certificate-less authentication is used
   and check the server's authorization as given in Section 3.6.




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   The EST server MUST authenticate the client as specified in
   Section 3.3.2 if certificate-based authenticated is used or
   Section 3.3.3 if the optional certificate-less authentication is used
   and check the client's authorization as given in Section 3.7.  The
   EST server applies whatever authorization or logic it chooses to
   determine if the private key and certificate should be provided.

   Cipher suites which have a NULL confidentiality algorithm MUST NOT be
   used as they will disclose the contents of an unprotected private
   key.

   Proper random number and key generation [RFC4086] is a server
   implementation responsibility and server archiving of generated keys
   is determined by CA policy.  The key pair and certificate are
   transferred over the TLS session.  The cipher suite used to return
   the private key and certificate MUST offer confidentiality
   commensurate with the private key being delivered to the client.

   The EST client MAY request additional certificates even when using an
   existing certificate in the TLS client authentication.  For example
   the client can use an existing certificate for TLS client
   authentication when requesting a certificate that cannot be used for
   TLS client authentication.

4.4.1.  Server-side Key Generation Request

   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.

   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.

   If the client desires to receive the private key with encryption that
   exists outside of and in addition to that of the TLS transport used
   by EST or if server policy requires that the key be delivered in such
   a form, the client MUST include an attribute in the CSR indicating
   the encryption key to be used.  Both symmetric and asymmetric
   encryption are supported as described in the following subsections.
   The client MUST also include an SMIMECapabilities attribute
   ([RFC2633], Section 2.5) in the CSR to indicate the key encipherment
   algorithms the client is willing to use.

   It is strongly RECOMMENDED that the clients request that the returned
   private key be afforded the additional security of the CMS



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   EnvelopedData in addition to the TLS-provided security to protect
   against unauthorized disclosure.

4.4.1.1.  Requests for Symmetric Key Encryption of the Private Key

   To specify a symmetric encryption key to be used to encrypt the
   server-generated private key, the client MUST include a
   DecryptKeyIdentifier attribute (as defined in Section 2.2.5,
   [RFC4108]) specifying the identifier of the secret key to be used by
   the server to encrypt the private key.  While that attribute was
   originally designated for specifying a firmware encryption key, it
   exactly mirrors the requirements for specifying a secret key to
   encrypt a private key.  If the server does not have a secret key
   matching the identifier specified by the client, the request MUST be
   terminated and an error returned to the client.  Distribution of the
   key specified by the DecryptKeyIdentifier to the key generator and
   the client is outside the scope of this document.

4.4.1.2.  Requests for Asymmetric Encryption of the Private Key

   To specify an asymmetric encryption key to be used to encrypt the
   server-generated private key, the client MUST include an
   AsymmetricDecryptKeyIdentifier attribute.  The
   AsymmetricDecryptKeyIdentifier attribute is defined as:

   id-aa-asymmDecryptKeyID OBJECT IDENTIFIER ::= {
       id-pkix TBD }


   The asymmetric-decrypt-key-identifier attribute values have ASN.1
   type AsymmetricDecryptKeyIdentifier:

    AsymmetricDecryptKeyIdentifier ::= OCTET STRING


   If the server does not have a public key matching the identifier
   specified by the client, the request MUST be terminated and an error
   returned to the client.  Distribution of the key specified by the
   AysmmetricDecryptKeyIdentifier to the key generator and the client is
   outside the scope of this document.  If the key identified is bound
   to an X.509 certificate, then the key MUST either explicitly support
   keyTransport or keyAgreement or its use MUST be unrestricted.









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4.4.2.  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 "multipart/mixed" consisting
   of two parts.  One part is the private key data and the other part is
   the certificate data.

   The format in which the private key data part is returned is
   dependent on whether the private key is being returned with
   additional encryption on top of that provided by TLS.

   If additional encryption is not being employed, the private key data
   MUST be placed in an "application/pkcs8".  An "application/pkcs8"
   part consists of the base 64-encoded DER-encoded PrivateKeyInfo with
   a Content-Transfer-Encoding of "base64" [RFC2045].

   If additional encryption is being employed, the private key is placed
   inside of a CMS SignedData.  The SignedData is signed by the party
   that generated the private key, which may or may not be the EST
   server or the EST CA.  The SignedData is further protected by placing
   it inside of a CMS EnvelopedData, as described in Section 4 of
   [RFC5958].  The following list shows how the EncryptedData is used,
   depending on the type of protection key specified by the client.

   o  If the client specified a symmetric encryption key to protect the
      server-generated private key, the EnvelopedData content is
      encrypted using the secret key identified in the request.  The
      EnvelopedData RecipientInfo field MUST indicate the kekri (Key
      Encryption Key Recipient Info) key management technique.  The
      values are: version is set to 4, kekid is set to the value of the
      DecryptKeyIdentifier from Section 4.4.1.1, keyEncryptionAlgorithm
      is set to one of the key wrap algorithms that the client included
      in the SMIMECapabilities accompanying the request, and
      encryptedKey is the encrypted key.

   o  If the client specified an asymmetric encryption key suitable for
      key transport operations to protect the server-generated private
      key, the EnvelopedData content is encrypted using a randomly-
      generated symmetric encryption key.  The cryptographic strength of
      the symmetric encryption key SHOULD be equivalent to the client-
      specified asymmetric key.  The EnvelopedData RecipientInfo field
      MUST indicate the ktri (KeyTransRecipientInfo) key management
      technique.  In KeyTransRecipientInfo, rid is either the
      subjectKeyIdentifier copied from the attribute defined in
      Section 4.4.1.2 or the server determines an associated
      issuerAndSerialNumber from the attribute. version is derived from
      the choice of rid [RFC5652], keyEncryptionAlgorithm is set to one
      of the key wrap algorithms that the client included in the



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      SMIMECapabilities accompanying the request, and encryptedKey is
      the encrypted key.

   o  If the client specified an asymmetric encryption key suitable for
      key agreement operations to protect the server-generated private
      key, the EnvelopedData content is encrypted using a randomly-
      generated symmetric encryption key.  The cryptographic strength of
      the symmetric encryption key SHOULD be equivalent to the client-
      specified asymmetric key.  The EnvelopedData RecipientInfo field
      MUST indicate the kari (KeyAgreeRecipientInfo) key management
      technique.  In the KeyAgreeRecipientInfo type, version,
      originator, and ukm are as in [RFC5652] and keyEncryptionAlgorithm
      is set to one of the key wrap algorithms that the client included
      in the SMIMECapabilities accompanying the request.  The
      recipient's key identifier is either copied from the attribute
      defined in Section 4.4.1.2 to subjectKeyIdentifier or the server
      determines an IssuerAndSerialNumber that corresponds to the value
      provided in the attribute.

   In all three additional encryption cases, the EnvelopedData is
   returned in the response as an "application/pkcs7-mime" part, with an
   smime-type parameter of "server-generated-key", and with a Content-
   Transfer-Encoding of "base64".

   The certificate data part is an "application/pkcs7-mime" and exactly
   matches the certificate response to /simpleenroll.

   When rejecting a request, the server MUST specify either an HTTP 4xx
   error, or an HTTP 5xx error.  If the content-type is not set, the
   response data MUST be a plain text human-readable error message.

4.5.  CSR Attributes

   CA policy may allow inclusion of client-provided attributes in
   certificates that it issues, and some of these attributes may
   describe information that is not available to the CA.  In addition, a
   CA may desire to certify a certain type of public key and a client
   may not have a priori knowledge of that fact.  Therefore, clients
   SHOULD request a list of expected attributes that are required, or
   desired, by the CA in an enrollment request, or if dictated by local
   policy.

   The EST server SHOULD NOT require client authentication or
   authorization to reply to this request.

   Requesting CSR Attributes is optional but clients are advised that
   CA's may refuse enrollment requests that are not encoded according to
   the CA's policy.



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4.5.1.  CSR Attributes Request

   The EST client requests a list of CA-desired CSR attributes from the
   CA by sending an HTTPS GET message to the EST server with an
   operations path of "/csrattrs".

4.5.2.  CSR Attributes Response

   If locally configured policy for an authenticated EST client
   indicates a CSR Attributes Response is to be provided, the server
   response MUST include an HTTP 200 response code.  An HTTP response
   code of 204 or 404 indicates that a CSR Attributes Response is not
   available.  Regardless of the response code, the EST server and CA
   MAY reject any subsequent enrollment requests for any reason, e.g.,
   incomplete CSR attributes in the request.

   If the CA requires a particular crypto system (e.g., certification of
   a public key based on a certain elliptic curve) it MUST provide that
   information in the CSR Attributes response.  If an EST server
   requires the linking of identity and PoP information (see
   Section 3.5) it MUST include the challengePassword OID in the CSR
   Attributes response.

   Responses to attribute request messages MUST be encoded as content-
   type of "application/csrattrs" with a Content-Transfer-Encoding of
   "base64" [RFC2045].  The syntax for application/csrattrs body is as
   follows:

   id-aa-asymmDecryptKeyID OBJECT IDENTIFIER ::= {
       id-pkix TBD }
   CsrAttrs ::= SEQUENCE SIZE (0..MAX) OF AttrOrOID

   AttrOrOID ::= CHOICE (oid OBJECT IDENTIFIER, attribute Attribute }

   Attribute { ATTRIBUTE:IOSet } ::= SEQUENCE {
        type   ATTRIBUTE.&id({IOSet}),
        values SET SIZE(1..MAX) OF ATTRIBUTE.&Type({IOSet}{@type}) }


   An EST server includes zero or more OIDs that it requests the client
   to use in the certification request.  The server MAY include zero or
   more Attributes [RFC2986] providing additional information to the
   client.  The client MUST ignore any OID or Attribute it does not
   recognize.  When the server encodes CsrAttrs as an empty SEQUENCE it
   means that the server has no specific additional information it
   desires in a client certification request (this is functionally
   equivalent to an HTTP response code of 204 or 404).  The sequence is
   Distinguished Encoding Rules (DER) encoded and then base 64 encoded



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   (section 4 of [RFC4648]).  The resulting text forms the application/
   csrattr body, without headers.

   For example, if a CA requests a client to submit a certification
   request containing the Media Access Control (MAC) address [RFC2397]
   of a device, the challengePassword (indicating that Linking of
   Identity and POP information is requested, see Section 3.5), to use
   the secp384r1 elliptic curve, and to use the SH384 hash function then
   it sends the following object identifiers:

   o  macAddress: 1.3.6.1.1.1.1.22

   o  challengePassword: 1.2.840.113549.1.9.7

   o  the secp384r1 elliptic curve: 1.3.132.0.34

   o  the SHA384 hash function: 2.16.840.1.101.3.4.2.2

   and encodes them into an ASN.1 SEQUENCE to produce:

       30 26 06 07 2B 06 01 01 01 01 16 06 09 2A 86 48 86 F7 0D 01 09 07
       06 05 2B 81 04 00 22 06 09 60 86 48 01 65 03 04 02 02

   and then base 64 encodes the resulting ASN.1 SEQUENCE to produce:

       MCYGBysGAQEBARYGCSqGSIb3DQEJBwYFK4EEACIGCWCGSAFlAwQCAg==

   The EST client parses the OID's in the response and handles each OID
   independently.  When an OID indicates a known descriptive CSR
   attribute type, or a common PKIX OID, the client SHOULD include the
   requested information or use the indicated algorithm in the
   subsequent CSR that it submits, either in the CSR attributes or in
   any other appropriate CSR field.  When an OID indicates a particular
   way to generate the CSR, the client SHOULD generate its CSR according
   to the parsed OID.  The Attributes in the response contain additional
   information for the client as defined by the Attribute type.

5.  Contributors/Acknowledgements

   The editors would like to thank Stephen Kent, Vinod Arjun, Jan
   Vilhuber, Sean Turner, Russ Housley, and others for their feedback
   and prototypes of early drafts.  Our thanks also go the authors of
   [RFC6403] around whose document we structured part of this
   specification.

6.  IANA Considerations





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   There is one OID in Section 4.4.1.2 that needs to be assigned in an
   arc delegated by the IANA to the PKIX working group.  No action by
   the IANA is necessary for this OID or assignment or any anticipated
   updates.

   IANA is requested to register the following:

   IANA is to update the well-known URI registry with the following
   filled-in template from [RFC5785].

      URI suffix: est

      Change controller: IETF

   IANA is to update the Application Media Types registry with the
   following filled-in templates from [RFC6838].

   The media subtype for CSR Attributes in a CSR Attributes response is
   application/csrattrs.

       Type name: application

       Subtype name: csrattrs

       Required parameters: None

       Optional parameters: None

       Encoding considerations: binary;

       Security Considerations:

         Clients request a list of attributes that servers wish to be in
         certification requests.  The request/response is normally done
         in a TLS-protected tunnel.

       Interoperability considerations: None

       Published specification: This memo.

       Applications which use this media type: Enrollment over Secure
       Transport (EST)

       Additional information:

         Magic number(s): None

         File extension: .csrattrs



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         Macintosh File Type Code(s):

       Person & email address to contact for further information:

         Dan Harkins <dharkins@arubanetworks.com>

       Restrictions on usage: None

       Author: Dan Harkins <dharkins@arubanetworks.com>

       Intended usage: COMMON

       Change controller: The IESG <iesg@ietf.org>

   The application/pkcs7-mime content type defines the optional "smime-
   type" parameter [RFC5751].  The smime-type parameter for Server-side
   Key Generation Response is server-generated-key.

7.  Security Considerations

   Support for Basic authentication as specified in HTTP [RFC2617]
   allows the server access to a client's cleartext password.  This
   provides support for legacy username/password databases but requires
   exposing the plaintext password to the EST server.  Use of a PIN or
   one-time-password can help mitigate such exposure, but it is
   RECOMMENDED that EST clients use such credentials only once to obtain
   a client certificate (that will be used during future interactions
   with the EST server).

   When a client uses the Implicit TA database for certificate
   validation (see Section 3) then authorization proceeds as specified
   in Section 3.6.2.  In this situation, the client has validated the
   server as being a certified-by-a-third-party responder for the URI
   configured, but cannot verify that the responder is authorized to act
   as an RA for the PKI in which the client is trying to enroll.
   Clients using an implicit trust anchor database are RECOMMENDED to
   only use TLS-based client authentication (to prevent exposing HTTP-
   based Client Authentication information).  It is RECOMMENDED that
   such clients include "Linking Identity and POP information"
   (Section 3.5) in requests (to prevent such requests from being
   forwarded to a real EST server by a MITM).  It is RECOMMENDED that
   the implicit trust anchor database used for EST server authentication
   be carefully managed, to reduce the chance of a third-party CA with
   poor certification practices from being trusted.  Disabling the
   implicit trust anchor database after successfully receiving the
   Distribution of CA Certificates response (Section 4.1.3) limits any
   vulnerability to the first TLS exchange.




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   Certificate-less TLS cipher suites that maintain security and perform
   the mutual authentication necessary for enrollment have the following
   properties:

   o  the only information leaked by an active attack is whether a
      single guess of the secret is correct or not.

   o  any advantage an adversary gains is through interaction and not
      computation.

   o  it is possible to perform countermeasures, such as exponential
      backoff after a certain number of failed attempts, to frustrate
      repeated active attacks.

   Using a certificate-less cipher suite that does not have the
   properties listed above would render the results of enrollment void
   and potentially result in certificates being issued to
   unauthenticated and/or unauthorized entities.

   When using a certificate-less TLS cipher suite, the shared secret
   used for authentication and authorization cannot be shared with an
   entity that is not a party to the exchange: someone other than the
   client and the server.  Any additional sharing of secrets voids the
   security afforded by a certificate-less cipher suite.  Exposure of a
   shared secret used by a certificate-less cipher suite to a third-
   party enables client impersonation that can results in corruption of
   a client's trust anchor database.

   TLS cipher suites that include "_EXPORT_" and "_DES_" in their names
   MUST NOT be used.  These ciphers do not offer a sufficient level of
   protection; 40-bit crypto in 2013 doesn't offer acceptable protection
   and the use of DES is deprecated.

   As described in CMC Section 6.7 [RFC5272], "For keys that can be used
   as signature keys, signing the certification request with the private
   key serves as a POP on that key pair".  The inclusion of tls-unique
   within the certification request links the proof-of-possession to the
   TLS proof-of-identity by enforcing that the POP operation occurred
   while the TLS session was active.  This implies to the server that
   the authenticated client currently has access to the private key.  If
   the authenticated client is known to have specific capabilities, such
   as hardware protection for authentication credentials and key
   storage, this implication is strengthened but not proven.

   The server-side key generation method allows keys to be transported
   over the TLS connection to the client without any application layer
   protection.  The distribution of private key material is inherently
   risky.  Private key distribution uses the encryption mode of the



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   negotiated TLS cipher suite.  Keys are not protected by preferred key
   wrapping methods such as AES Key Wrap [RFC3394] or as specified in
   [RFC5958] as encryption of the private key beyond that provided by
   TLS is optional.  It is RECOMMENDED that EST servers not support this
   operation by default.  It is RECOMMENDED that clients not request
   this service unless there is a compelling operational benefit.  Use
   of an implicit trust anchor database is NOT RECOMMENDED when server-
   side key generation is employed.  The use of an encrypted CMS Server-
   side Key Generation Response is RECOMMENDED.

   Regarding the CSR attributes that the CA may list for inclusion in an
   enrollment request, there are no real inherent security issues with
   the content being conveyed but an adversary who is able to interpose
   herself into the conversation could exclude attributes that a server
   may want, include attributes that a server may not want, and render
   meaningless other attributes that a server may want.

   ASN.1 encoding rules (e.g., DER and BER) have a type-length-value
   structure, and it is easy to construct malicious content with invalid
   length fields that can cause buffer overrun conditions.  ASN.1
   encoding rules allows for arbitrary levels of nesting, which may make
   it possible to construct malicious content that will cause a stack
   overflow.  Interpreters of ASN.1 structures should be aware of these
   issues and should take appropriate measures to guard against buffer
   overflows and stack overruns in particular and malicious content in
   general.

8.  References

8.1.  Normative References

   [RFC2045]  Freed, N. and N. Borenstein, "Multipurpose Internet Mail
              Extensions (MIME) Part One: Format of Internet Message
              Bodies", RFC 2045, November 1996.

   [RFC2046]  Freed, N. and N. Borenstein, "Multipurpose Internet Mail
              Extensions (MIME) Part Two: Media Types", RFC 2046,
              November 1996.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC2585]  Housley, R. and P. Hoffman, "Internet X.509 Public Key
              Infrastructure Operational Protocols: FTP and HTTP", RFC
              2585, May 1999.






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   [RFC2616]  Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
              Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext
              Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.

   [RFC2617]  Franks, J., Hallam-Baker, P., Hostetler, J., Lawrence, S.,
              Leach, P., Luotonen, A., and L. Stewart, "HTTP
              Authentication: Basic and Digest Access Authentication",
              RFC 2617, June 1999.

   [RFC2633]  Ramsdell, B., "S/MIME Version 3 Message Specification",
              RFC 2633, June 1999.

   [RFC2986]  Nystrom, M. and B. Kaliski, "PKCS #10: Certification
              Request Syntax Specification Version 1.7", RFC 2986,
              November 2000.

   [RFC3986]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
              Resource Identifier (URI): Generic Syntax", STD 66, RFC
              3986, January 2005.

   [RFC4086]  Eastlake, D., Schiller, J., and S. Crocker, "Randomness
              Requirements for Security", BCP 106, RFC 4086, June 2005.

   [RFC4108]  Housley, R., "Using Cryptographic Message Syntax (CMS) to
              Protect Firmware Packages", RFC 4108, August 2005.

   [RFC4210]  Adams, C., Farrell, S., Kause, T., and T. Mononen,
              "Internet X.509 Public Key Infrastructure Certificate
              Management Protocol (CMP)", RFC 4210, September 2005.

   [RFC4346]  Dierks, T. and E. Rescorla, "The Transport Layer Security
              (TLS) Protocol Version 1.1", RFC 4346, April 2006.

   [RFC4648]  Josefsson, S., "The Base16, Base32, and Base64 Data
              Encodings", RFC 4648, October 2006.

   [RFC5077]  Salowey, J., Zhou, H., Eronen, P., and H. Tschofenig,
              "Transport Layer Security (TLS) Session Resumption without
              Server-Side State", RFC 5077, January 2008.

   [RFC5246]  Dierks, T. and E. Rescorla, "The Transport Layer Security
              (TLS) Protocol Version 1.2", RFC 5246, August 2008.

   [RFC5272]  Schaad, J. and M. Myers, "Certificate Management over CMS
              (CMC)", RFC 5272, June 2008.

   [RFC5273]  Schaad, J. and M. Myers, "Certificate Management over CMS
              (CMC): Transport Protocols", RFC 5273, June 2008.



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   [RFC5274]  Schaad, J. and M. Myers, "Certificate Management Messages
              over CMS (CMC): Compliance Requirements", RFC 5274, June
              2008.

   [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, May 2008.

   [RFC5652]  Housley, R., "Cryptographic Message Syntax (CMS)", STD 70,
              RFC 5652, September 2009.

   [RFC5746]  Rescorla, E., Ray, M., Dispensa, S., and N. Oskov,
              "Transport Layer Security (TLS) Renegotiation Indication
              Extension", RFC 5746, February 2010.

   [RFC5751]  Ramsdell, B. and S. Turner, "Secure/Multipurpose Internet
              Mail Extensions (S/MIME) Version 3.2 Message
              Specification", RFC 5751, January 2010.

   [RFC5785]  Nottingham, M. and E. Hammer-Lahav, "Defining Well-Known
              Uniform Resource Identifiers (URIs)", RFC 5785, April
              2010.

   [RFC5929]  Altman, J., Williams, N., and L. Zhu, "Channel Bindings
              for TLS", RFC 5929, July 2010.

   [RFC5958]  Turner, S., "Asymmetric Key Packages", RFC 5958, August
              2010.

   [RFC6066]  Eastlake, D., "Transport Layer Security (TLS) Extensions:
              Extension Definitions", RFC 6066, January 2011.

   [RFC6125]  Saint-Andre, P. and J. Hodges, "Representation and
              Verification of Domain-Based Application Service Identity
              within Internet Public Key Infrastructure Using X.509
              (PKIX) Certificates in the Context of Transport Layer
              Security (TLS)", RFC 6125, March 2011.

   [RFC6402]  Schaad, J., "Certificate Management over CMS (CMC)
              Updates", RFC 6402, November 2011.

   [RFC6454]  Barth, A., "The Web Origin Concept", RFC 6454, December
              2011.

   [RFC6838]  Freed, N., Klensin, J., and T. Hansen, "Media Type
              Specifications and Registration Procedures", BCP 13, RFC
              6838, January 2013.



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   [X.680]    ITU-T Recommendation, "ITU-T Recommendation X.680
              Abstract Syntax Notation One (ASN.1): Specification of
              basic notation", November 2008,
              <http://www.itu.int/rec/T-REC-X.680-200811-I/en>.

   [X.690]    ITU-T Recommendation, "ITU-T Recommendation X.690 ASN.1
              encoding rules: Specification of Basic Encoding Rules
              (BER), Canonical Encoding Rules (CER) and Distinguished
              Encoding Rules (DER)", November 2008,
              <http://www.itu.int/rec/T-REC-X.690-200811-I/en>.

8.2.  Informative References

   [IDevID]   IEEE Std, "IEEE 802.1AR Secure Device Identifier",
              December 2009, <http://standards.ieee.org/findstds/
              standard/802.1AR-2009.html>.

   [RFC2397]  Masinter, L., "The "data" URL scheme", RFC 2397, August
              1998.

   [RFC2818]  Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000.

   [RFC2985]  Nystrom, M. and B. Kaliski, "PKCS #9: Selected Object
              Classes and Attribute Types Version 2.0", RFC 2985,
              November 2000.

   [RFC3394]  Schaad, J. and R. Housley, "Advanced Encryption Standard
              (AES) Key Wrap Algorithm", RFC 3394, September 2002.

   [RFC5054]  Taylor, D., Wu, T., Mavrogiannopoulos, N., and T. Perrin,
              "Using the Secure Remote Password (SRP) Protocol for TLS
              Authentication", RFC 5054, November 2007.

   [RFC5967]  Turner, S., "The application/pkcs10 Media Type", RFC 5967,
              August 2010.

   [RFC6403]  Zieglar, L., Turner, S., and M. Peck, "Suite B Profile of
              Certificate Management over CMS", RFC 6403, November 2011.

   [SHS]      National Institute of Standards and Technology,
              "Federal Information Processing Standard Publication
              180-4: Secure Hash Standard (SHS)", March 2012, <http://
              csrc.nist.gov/publications/fips/fips180-4/fips-180-4.pdf>.

   [SP-800-57-Part-1]
              National Institute of Standards and Technology,
              "Recommendation for Key Management - Part 1: General
              (Revision 3)", July 2012, <http://csrc.nist.gov/



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              publications/nistpubs/800-57/
              sp800-57_part1_rev3_general.pdf>.

   [X.520]    ITU-T Recommendation, "ITU-T Recommendation X.520 The
              Directory: Selected attribute types", November 2008,
              <http://www.itu.int/rec/T-REC-X.520-200811-I/en>.

Appendix A.  Operational Scenario Example Messages

   (informative)

   This section expands on the Operational Scenario Overviews by
   providing detailed examples of the messages at each TLS layer.

A.1.  Obtaining CA Certificates

   The following is an example of a valid /cacerts exchange.

   During the initial TLS handshake the client can ignore the optional
   server generated "certificate request" and can instead proceed with
   the HTTP GET request:

   GET /.well-known/est/cacerts HTTP/1.1
   User-Agent: curl/7.22.0 (i686-pc-linux-gnu) libcurl/7.22.0 OpenS
   SL/1.0.1 zlib/1.2.3.4 libidn/1.23 librtmp/2.3
   Host: 192.0.2.1:8085
   Accept: */*


   In response the server provides the current CA certificates:

   HTTP/1.1 200 OK
   Status: 200 OK
   Content-Type: application/pkcs7-mime
   Content-Transfer-Encoding: base64
   Content-Length: 4246

   MIIMOQYJKoZIhvcNAQcCoIIMKjCCDCYCAQExADALBgkqhkiG9w0BBwGgggwMMIIC
   +zCCAeOgAwIBAgIJAJpY3nUZO3qcMA0GCSqGSIb3DQEBBQUAMBsxGTAXBgNVBAMT
   EGVzdEV4YW1wbGVDQSBPd08wHhcNMTMwNTA5MDM1MzMxWhcNMTQwNTA5MDM1MzMx
   WjAbMRkwFwYDVQQDExBlc3RFeGFtcGxlQ0EgT3dPMIIBIjANBgkqhkiG9w0BAQEF
   AAOCAQ8AMIIBCgKCAQEAwDqpiHopaICubpRqbpEN7LqTIqWELFIA9qDDheHIKuyO
   HW/ZAP7Rl4S5ZU6gaLW/ksseBUxdmox3KNyvtyjehIofTu28eZWhgy6/LCEGWR3P
   K+fgPBA0l0JfJR/8oeXZa70oLVQc3hI4kCeqjFMs+biYH0vp/RluhftyZ5kzQyH1
   EGsRkw1/qUKkTZ8PCF8VFlYfqmUoqsaRTyZbjII4J+Y6/jEG+p7QreW9zcz4sPe8
   3c/uhwMLOWQkZtKsQtgo5CpfYMjuAmk4Q2joQq2vcxlc+WNKHf+wbrDb11ORZril
   9ISlI94oumcRz3uBG1Yg7z83hdDfasmdfbp8gOSNFQIDAQABo0IwQDAPBgNVHRMB
   Af8EBTADAQH/MB0GA1UdDgQWBBQITTKxMqATXrfc4ffpCIbt6Gsz0jAOBgNVHQ8B



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   Af8EBAMCAQYwDQYJKoZIhvcNAQEFBQADggEBACPnQPu5WReUGuCMS0nBOGa2tXh6
   uZP4mS3J1qEfDePam/IiU9ssyYdcDwhVvKMoP4gI/yu4XFqhdpIoy/PyD4T15MT7
   KADCxXkh5rM1IqMui7FvBKLWYGdy9sjEf90wAkBjHBe/TMO1NNw3uELyONSkHIvo
   X0pu6aPmm/moIMyGi46niFse1iWlXXldGLkOQsh0e7U+wpBX07QpOr2KB2+Yf+uA
   KY1SWzEG23bUxXlvcbUMgANDGj5r6z+niKL0VlApip/iCuVEEOcZ91UlmJjVLQWA
   x6ie+v84oM+pIojiGM0C4XWcVlKKEgcMOsN3S4lvm8Ptpq0GLoIJY8NTD20wggMD
   MIIB66ADAgECAgEBMA0GCSqGSIb3DQEBBQUAMBsxGTAXBgNVBAMTEGVzdEV4YW1w
   bGVDQSBPd08wHhcNMTMwNTA5MDM1MzMyWhcNMTQwNTA5MDM1MzMyWjAbMRkwFwYD
   VQQDExBlc3RFeGFtcGxlQ0EgTndPMIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIB
   CgKCAQEAnn3rZ3rMJHwf7MD9K4mubxHAvtdnrsQf5OfgtMhRIL4aePNhAdgPyj8C
   loxOgD3UTV+dQ1ViOzVxPN7acikoOnkIdRpjpOpkyMo+KkvHMQXGnQTbsMAv1qWt
   9S12DMpo0GOA1e4Ge3ud5YPOTR/q6PvjN51IEwYKksG7CglwZwB+5JbwhYr2D/0u
   btGltriRVixPWrvt+wz/ITp5rcjh/8RS3LE8tQy3kTNhJF3Y/esR2sSgOiPNgIto
   CATysbaINEPr4MemqML4tDpR/aG9y+8Qe7s1LyMFvDletp2mmBykAC/7nOat/pwU
   lB0sN524D1XAgz8ZKvWrkh+ZaOr3hwIDAQABo1IwUDAOBgNVHQ8BAf8EBAMCBLAw
   HQYDVR0OBBYEFLHEaeZbowSn2Jejizu/uWqyMkI8MB8GA1UdIwQYMBaAFAhNMrEy
   oBNet9zh9+kIhu3oazPSMA0GCSqGSIb3DQEBBQUAA4IBAQCLDkL7aLNV6hSOkIqH
   q+shV9YLO56/tj00vY/jV5skgDHk5d0B+OGortKVuGa57+v0avTrlJns3bNW8Ntv
   zkDEhmd00Ak02aPsi4wRHLFgttUf9HdEHAuTkAESPTU43DiptjkfHhtBMfsFrCkd
   sxWzCz+prDOMHYfUEkhRVV++1zyGEX6ov1Ap2IU2p3E+ASihL/amxTEQAsbwjUTI
   R52zoL6nMPzpbKeZi2M0eEBVF8sDueA9Hjo6woLjgJqV0/yc5vC2HAxUOhx0cWTY
   GcRBgL/yOyQLKiY5TKBH951OjQ4vhF2HmcoO7DkcNLYJOge16ssx4ogBHul20VgF
   XJJjMIIDAzCCAeugAwIBAgIBAjANBgkqhkiG9w0BAQUFADAbMRkwFwYDVQQDExBl
   c3RFeGFtcGxlQ0EgTndOMB4XDTEzMDUwOTAzNTMzMloXDTE0MDUwOTAzNTMzMlow
   GzEZMBcGA1UEAxMQZXN0RXhhbXBsZUNBIE93TjCCASIwDQYJKoZIhvcNAQEBBQAD
   ggEPADCCAQoCggEBAMA6qYh6KWiArm6Uam6RDey6kyKlhCxSAPagw4XhyCrsjh1v
   2QD+0ZeEuWVOoGi1v5LLHgVMXZqMdyjcr7co3oSKH07tvHmVoYMuvywhBlkdzyvn
   4DwQNJdCXyUf/KHl2Wu9KC1UHN4SOJAnqoxTLPm4mB9L6f0ZboX7cmeZM0Mh9RBr
   EZMNf6lCpE2fDwhfFRZWH6plKKrGkU8mW4yCOCfmOv4xBvqe0K3lvc3M+LD3vN3P
   7ocDCzlkJGbSrELYKOQqX2DI7gJpOENo6EKtr3MZXPljSh3/sG6w29dTkWa4pfSE
   pSPeKLpnEc97gRtWIO8/N4XQ32rJnX26fIDkjRUCAwEAAaNSMFAwDgYDVR0PAQH/
   BAQDAgSwMB0GA1UdDgQWBBQITTKxMqATXrfc4ffpCIbt6Gsz0jAfBgNVHSMEGDAW
   gBSxxGnmW6MEp9iXo4s7v7lqsjJCPDANBgkqhkiG9w0BAQUFAAOCAQEALhDaE6Mp
   BINBsJozdbXlijrWxL1CSv8f4GwpUFk3CgZjibt/qW9UoaNR4E58yRopuEhjwFZK
   2w8YtRqx8IZoFhcoLkpBDfgLLwhoztzbYvOVKQMidjBlkBEVNR5MWdrs7F/AxWuy
   iZ2+8AnR8GwqEIbCD0A7xIghmWEMh/BVI9C7GLqd6PxKrTAjuDfEpfdWhU/uYKmK
   cL3XDbSwr30j2EQyaTV/3W0Tn2UfuxdwDQ4ZJs9G+Mw50s7AG6CpISyOIFmX6/bU
   DpJXGLiLwfJ9C/aum9nylYuGCJ68BuTrCs9567KGfXEXI0mdFFCL7TaVR43kjsg3
   c43kZ7369MeEZzCCAvswggHjoAMCAQICCQDprp3DmjOyETANBgkqhkiG9w0BAQUF
   ADAbMRkwFwYDVQQDExBlc3RFeGFtcGxlQ0EgTndOMB4XDTEzMDUwOTAzNTMzMloX
   DTE0MDUwOTAzNTMzMlowGzEZMBcGA1UEAxMQZXN0RXhhbXBsZUNBIE53TjCCASIw
   DQYJKoZIhvcNAQEBBQADggEPADCCAQoCggEBAJ5962d6zCR8H+zA/SuJrm8RwL7X
   Z67EH+Tn4LTIUSC+GnjzYQHYD8o/ApaMToA91E1fnUNVYjs1cTze2nIpKDp5CHUa
   Y6TqZMjKPipLxzEFxp0E27DAL9alrfUtdgzKaNBjgNXuBnt7neWDzk0f6uj74zed
   SBMGCpLBuwoJcGcAfuSW8IWK9g/9Lm7Rpba4kVYsT1q77fsM/yE6ea3I4f/EUtyx
   PLUMt5EzYSRd2P3rEdrEoDojzYCLaAgE8rG2iDRD6+DHpqjC+LQ6Uf2hvcvvEHu7
   NS8jBbw5XradppgcpAAv+5zmrf6cFJQdLDeduA9VwIM/GSr1q5IfmWjq94cCAwEA
   AaNCMEAwDwYDVR0TAQH/BAUwAwEB/zAdBgNVHQ4EFgQUscRp5lujBKfYl6OLO7+5



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   arIyQjwwDgYDVR0PAQH/BAQDAgEGMA0GCSqGSIb3DQEBBQUAA4IBAQBCz/CWdYvn
   GM/SdCdEiom5A1VxaW8nKgCWg/EyWtAIiaHQuViB+jTUAE9lona2MbJoFHW8U5e8
   9dCP0rJpA9UYXXhWvFQzd5ZWpms4wUYt1j3gqqd36KorJIAuPigVng13yKytxM7c
   VmxQnh0aux3aEnEyRGAhGalHp0RaKdgPRzUaGtipJTNBkSV5S4kD4yDCPHMNbBu+
   OcluerwEpbz6GvE7CpXl2jrTBZSqBsFelq0iz4kk9++9CnwZwrVgdzklhRfJ1Z4j
   NkLruwbQ+o4NvBZsXiKxNfn3K2o3SK8AuaEyDWkq18+5rjcfprRO8x4YTW+6mXPq
   jM0MAGNDEW+1oQAxAA==


A.2.  CSR Attributes

   The following is an example of a valid /csrattrs exchange.  During
   this exchange the EST client authenticates itself using an existing
   certificate issued by the CA the EST server provides services for.

   The initial TLS handshake is identical to the enrollment example
   handshake.  The HTTP GET request:

   GET /.well-known/est/csrattrs HTTP/1.1
   User-Agent: curl/7.22.0 (i686-pc-linux-gnu) libcurl/7.22.0 OpenS
   SL/1.0.1 zlib/1.2.3.4 libidn/1.23 librtmp/2.3
   Host: 192.0.2.1:8085
   Accept: */*



   In response the server provides suggested attributes that are
   appropriate for the authenticated client.  In this example the EST
   server also includes two example Attributes which the client would
   ignore unless the attribute type is known to the client:

   HTTP/1.1 200 OK
   Status: 200 OK
   Content-Type: application/csrattrs
   Content-Transfer-Encoding: base64
   Content-Length: 171

   MHwGBysGAQEBARYwIgYDiDcBMRsTGVBhcnNlIFNFVCBhcyAyLjk5OS4xIGRhdGEG
   CSqGSIb3DQEJBzAsBgOINwIxJQYDiDcDBgOINwQTGVBhcnNlIFNFVCBhcyAyLjk5
   OS4yIGRhdGEGCSskAwMCCAEBCwYJYIZIAWUDBAIC


A.3.  Enroll/Reenroll

   The following is an example of a valid /simpleenroll exchange.  The
   data messages for /simplereenroll are similar.





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   During this exchange the EST client uses an out-of-band distributed
   username/password to authenticate itself to the EST server.  This is
   the normal HTTP WWW-Authenticate behavior and is included here for
   informative purposes.  When an existing TLS client certificate is
   used the server might skip requesting the HTTP WWW-Authenticate
   header, such as during a /simplereenroll operation.

   During the initial TLS handshake the client can ignore the optional
   server generated "certificate request" and can instead proceed with
   the HTTP POST request.  In response to the initial HTTP POST attempt
   the server requests WWW-Authenticate from the client (this might
   occur even if the client used a client certificate, as detailed in
   the normative text above):

   HTTP/1.1 401 Unauthorized
   Content-Length: 0
   WWW-Authenticate: Digest qop="auth", realm="estrealm",
   nonce="1368141352"


   In the subsequent HTTP POST the username/password is included, along
   with the complete application/pkcs10 content:





























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   POST /.well-known/est/simpleenroll HTTP/1.1
   Authorization: Digest username="estuser", realm="estrealm", nonc
   e="1368141352", uri="/.well-known/est/simpleenroll", cnonce="M
   TYwMzg3", nc=00000001, qop="auth", response="144cc27f96046f1d70e
   b16db20f75f22"
   Host: 192.0.2.1:8085
   Accept: */*
   Content-Type: application/pkcs10
   Content-Transfer-Encoding: base64
   Content-Length: 882

   MIIChTCCAW0CAQAwHzEdMBsGA1UEAxMUZGVtb3N0ZXA0IDEzNjgxNDEzNTIwggEi
   MA0GCSqGSIb3DQEBAQUAA4IBDwAwggEKAoIBAQClNp+kdz+Nj8XpEp9kaumWxDZ3
   eFYJpQKz9ddD5e5OzUeCm103ZIXQIxc0eVtMCatnRr3dnZRCAxGjwbqoB3eKt29/
   XSQffVv+odbyw0WdkQOIbntCQry8YdcBZ+8LjI/N7M2krmjmoSLmLwU2V4aNKf0Y
   MLR5Krmah3Ik31jmYCSvwTnv6mx6pr2pTJ82JavhTEIIt/fAYq1RYhkM1CXoBL+y
   hEoDanN7TzC94skfS3VV+f53J9SkUxTYcy1Rw0k3VXfxWwy+cSKEPREl7I6k0YeK
   tDEVAgBIEYM/L1S69RXTLujirwnqSRjOquzkAkD31BE961KZCxeYGrhxaR4PAgMB
   AAGgITAfBgkqhkiG9w0BCQcxEhMQK3JyQ2lyLzcrRVl1NTBUNDANBgkqhkiG9w0B
   AQUFAAOCAQEARBv0AJeXaHpl1MFIdzWqoi1dOCf6U+qaYWcBzpLADvJrPK1qx5pq
   wXM830A1O+7RvrFv+nyd6VF2rl/MrNp+IsKuA9LYWIBjVe/LXoBO8dB/KxrYl16c
   VUS+Yydi1m/a+DaftYSRGolMLtWeiqbc2SDBr2kHXW1TR130hIcpwmr29kC2Kzur
   5thsuj276FGL1vPu0dRfGQfx4WWa9uAHBgz6tW37CepZsrUKe/0pfVhr2oHxApYh
   cHGBQDQHVTFVjHccdUjAXicrtbsVhU5o1lPv7f4lEApv3SBQmJcaq5O832BzHw7n
   PyMFcM15E9gtUVee5C62bVwuk/tbnGsbwQ==


   The EST server uses the username/password to perform authentication/
   authorization and responds with the issued certificate:

   HTTP/1.1 200 OK
   Status: 200 OK
   Content-Type: application/pkcs7-mime; smime-type=certs-only
   Content-Transfer-Encoding: base64
   Content-Length: 1122

   MIIDOAYJKoZIhvcNAQcCoIIDKTCCAyUCAQExADALBgkqhkiG9w0BBwGgggMLMIID
   BzCCAe+gAwIBAgIBFTANBgkqhkiG9w0BAQUFADAbMRkwFwYDVQQDExBlc3RFeGFt
   cGxlQ0EgTndOMB4XDTEzMDUwOTIzMTU1M1oXDTE0MDUwOTIzMTU1M1owHzEdMBsG
   A1UEAxMUZGVtb3N0ZXA0IDEzNjgxNDEzNTIwggEiMA0GCSqGSIb3DQEBAQUAA4IB
   DwAwggEKAoIBAQClNp+kdz+Nj8XpEp9kaumWxDZ3eFYJpQKz9ddD5e5OzUeCm103
   ZIXQIxc0eVtMCatnRr3dnZRCAxGjwbqoB3eKt29/XSQffVv+odbyw0WdkQOIbntC
   Qry8YdcBZ+8LjI/N7M2krmjmoSLmLwU2V4aNKf0YMLR5Krmah3Ik31jmYCSvwTnv
   6mx6pr2pTJ82JavhTEIIt/fAYq1RYhkM1CXoBL+yhEoDanN7TzC94skfS3VV+f53
   J9SkUxTYcy1Rw0k3VXfxWwy+cSKEPREl7I6k0YeKtDEVAgBIEYM/L1S69RXTLuji
   rwnqSRjOquzkAkD31BE961KZCxeYGrhxaR4PAgMBAAGjUjBQMA4GA1UdDwEB/wQE
   AwIEsDAdBgNVHQ4EFgQU/qDdB6ii6icQ8wGMXvy1jfE4xtUwHwYDVR0jBBgwFoAU
   scRp5lujBKfYl6OLO7+5arIyQjwwDQYJKoZIhvcNAQEFBQADggEBACmxg1hvL6+7



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   a+lFTARoxainBx5gxdZ9omSb0L+qL+4PDvg/+KHzKsDnMCrcU6M4YP5n0EDKmGa6
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   rEs9Mlh2CjA/ocSC/WxmMvd+Eqnt/FpggRy+F8IZSRvBaRUCtGE1lgDmu6AFUxce
   R4POrT2xz8ChADEA


A.4.  Server Key Generation

   The following is an example of a valid /serverkeygen exchange.
   During this exchange the EST client authenticates itself using an
   existing certificate issued by the CA the EST server provides
   services for.

   The initial TLS handshake is identical to the enrollment example
   handshake.  An example HTTP POSTed message is:

   POST /.well-known/est/serverkeygen HTTP/1.1
   Host: 192.0.2.1:8085
   Accept: */*
   Expect: 100-continue
   Content-Type: application/pkcs10
   Content-Transfer-Encoding: base64
   Content-Length: 963

   MIICwTCCAakCAQAwWzE+MDwGA1UEAxM1c2VydmVyS2V5R2VuIHJlcSBieSBjbGll
   bnQgaW4gZGVtbyBzdGVwIDEyIDEzNjgxNDE5NTUxGTAXBgNVBAUTEFBJRDpXaWRn
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   3/L32Suyzbf28LM9y8CQfp0aepa7o20BSfluvm8HXR44mlV+wpieM8H5n3Ub3RIo
   RUun/FllIzK9uV7UrkqJ3Yzmq2NOoTd4C+OPsV/RPTu873dhFrssDk3P4NIphlSS
   sSIkt5rhz7wYbCqCFR5Aphe/30Jx7D+xBI5Rs8e6vRS8IpuImh71BHiLfhq9AFhz
   4ZJsOUSVpUmqUogFsM7SOQ6XI4dl+djhpjT+YTJ6hQ2PXrqdch3KsTQ8c6aKs+e2
   5QJxh7O8JHVlPHo4YIxXtAYSutcbbTN5TXWFCWSrWDJ+zuMmk2yU+dio1oW7YR7V
   ftAvazJ3laQbAgMBAAGgITAfBgkqhkiG9w0BCQcxEhMQZEZzQVhtSm5qb2tCdER2
   cjANBgkqhkiG9w0BAQUFAAOCAQEAR+I0EQB+hSjrLCAjnVH6bZdHUNGszIdwx1iu
   L4n+0XK3SfEzeOMkC4T74yFGKj3redS1Ht9atYUPb0D1Qi9Jf9Co8eLblo1l19A6
   GaS798ofxIF0Pl0Dr6/GqjheqJEIbcDTAJq+kvDihyQ4GQnhosygIZHvKppQlebA
   gvp2RJSnMroPCe6RgTU9E2fmI9rin/9PyXeWFF1namp+lYbTGwjv1aE1ikhjCLlH
   veHhCdgOExPw+fqhKhHjp+0ZKBlo2bC3pqRWvDTiZuwt9UpFFfGtuxvpTp44oS/j
   M/965hWIw/5dshY/wQjIfYs07bbq2ERbpJiw9bAQY34gyoVmEQ==


   Because the DecryptKeyIdentifier attribute is not included in this
   request the response does not include additional encryption beyond
   the TLS session.  The EST server response is:

   HTTP/1.1 200 OK



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   Status: 200 OK
   Content-Type: multipart/mixed ; boundary=estServerExampleBoundary
   Content-Length: 3219

   This is the preamble. It is to be ignored, though it
   is a handy place for estServer to include an explanatory note
   including contact or support information.
   --estServerExampleBoundary
   Content-Type: application/pkcs8
   Content-Transfer-Encoding: base64

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   FGq93yOhAgMBAAECggEBALQ5az/nYjd5x9Y3f7NMUffwl+jRRfMHCMTRx/u4AEAo
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   vylUd9HCerzgYaA7rixieQ0sxTvtxhL6PXlM2NEBFQbV16hPFL6/IiG4F0u9oHNo
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   wER+XIy4C2UByCANv9csaXulIOdXlXNbaCGPfOm5dWrm5ddLMf33MO9vaSRe+ku3
   Q4nbgsGLwPp1ZQZ+QZNZpMi7W6306yp4GdAJ5Pb+oww/ST0VqW5OB7dILyK4A9S4
   zkiNrf+Rsl8GM/vsDhc9rsuDwqofIAq/VHVBHNzJAoGBAOHQof5L6iGHOHcxLazx
   4MGvRTpmzU/PX6Q3QxqpetEGFEDZAaL58L67SSS3fFBnKrVAidF6llC1bAH1aoRa
   fYHUDi45xBoroy0hBwrnTKRxppua4UK75FUH5PPJfR6cCvw5stRkzIevTZHhozkX
   pM7PYH/x4BiBmgQ3bhOqTp4H
   --estServerExampleBoundary
   Content-Type: application/pkcs7-mime; smime-type=certs-only
   Content-Transfer-Encoding: base64

   MIIDRQYJKoZIhvcNAQcCoIIDNjCCAzICAQExADALBgkqhkiG9w0BBwGgggMYMIID
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   t/BVKdHpy2240k7nePCqRFuvhc5HrgGpzxmTANcCsq2Mvaw+bUDjiVPwgVYVKyE8



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   mC2TWFHuGoG6XEdMDLa0a9hOfDLvMEPNK8pOp5C+wjpOWSEHTUcZXZOwxb6QPOWJ
   9bLbpqBkbVS1udYl3k0tS7V8IblG/4+i3bN77wIidkomdGN68T5ZyVchZkfDH9kw
   To87har2v1Sw9mskI4GhhI6tmVh13pUADmejd5awoaIxChRqvd8joQIDAQABo1Iw
   UDAOBgNVHQ8BAf8EBAMCBLAwHQYDVR0OBBYEFKeZixu9F+appDX2SS5HaxmV6Jr4
   MB8GA1UdIwQYMBaAFLHEaeZbowSn2Jejizu/uWqyMkI8MA0GCSqGSIb3DQEBBQUA
   A4IBAQBHhLmRAKrnTapqqBObDM9IQDQPuwW+fW1gYwZKlSm/IWIwHEZL1igXhpjj
   rf4xqpIkiJMmkaOeoXA8PFniX0/lZM9FQSM/j89CUf5dMoAqWj8s17xuXu9L/hVe
   XjjXHsL40WuDG6tMPN9vcT8tE3ruor608MKSHFX/NEM6+AaNVSUPTmB33BgYB1Wa
   E7pn3JMN6pjIxsHnF4pKi8qvoTSVVjaCEwUe8Q/fw1yvjoHoYJtyMn4v5Kb3Rt+m
   s8Yie1tcfVQrjQutqr34/IJsKdPziZwi92KZa+1958A6M9O/p5OI0up9ZXKg2DEC
   1O9qT0GyYJ6sxAyKiGTOxk6jMddDoQAxAA==
   --estServerExampleBoundary--
   This is the epilogue. It is also to be ignored.


Authors' Addresses

   Max Pritikin (editor)
   Cisco Systems, Inc.
   510 McCarthy Drive
   Milpitas, CA  95035
   USA

   Email: pritikin@cisco.com


   Peter E. Yee (editor)
   AKAYLA, Inc.
   7150 Moorland Drive
   Clarksville, MD  21029
   USA

   Email: peter@akayla.com


   Dan Harkins (editor)
   Aruba Networks
   1322 Crossman Avenue
   Sunnyvale, CA  94089-1113
   USA

   Email: dharkins@arubanetworks.com









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