[Docs] [txt|pdf|xml] [Tracker] [WG] [Email] [Diff1] [Diff2] [Nits]

Versions: 00 01 02 03 04 05 06

NTP Working Group                                              D. Sibold
Internet-Draft                                                       PTB
Intended status: Standards Track                             S. Roettger
Expires: September 7, 2015                                   Google Inc.
                                                              K. Teichel
                                                                     PTB
                                                              R. Housley
                                                          Vigil Security
                                                          March 06, 2015


Protecting Network Time Security Messages with the Cryptographic Message
                              Syntax (CMS)
               draft-ietf-ntp-cms-for-nts-message-02.txt

Abstract

   This document describes a convention for using the Cryptographic
   Message Syntax (CMS) to protect the messages in the Network Time
   Security (NTS) protocol.  NTS provides authentication of time servers
   as well as integrity protection of time synchronization messages
   using Network Time Protocol (NTP) or Precision Time Protocol (PTP).

Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].

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 September 7, 2015.






Sibold, et al.          Expires September 7, 2015               [Page 1]


Internet-Draft                   CMS4NTS                      March 2015


Copyright Notice

   Copyright (c) 2015 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  CMS Conventions for NTS Message Protection  . . . . . . . . .   3
     2.1.  Fields of the employed CMS Content Types  . . . . . . . .   5
       2.1.1.  ContentInfo . . . . . . . . . . . . . . . . . . . . .   5
       2.1.2.  SignedData  . . . . . . . . . . . . . . . . . . . . .   6
       2.1.3.  EnvelopedData . . . . . . . . . . . . . . . . . . . .   8
   3.  Implementation Notes: ASN.1 Structures and Use of the CMS . .   9
     3.1.  Preliminaries . . . . . . . . . . . . . . . . . . . . . .   9
     3.2.  Unicast Messages  . . . . . . . . . . . . . . . . . . . .   9
       3.2.1.  Association Messages  . . . . . . . . . . . . . . . .   9
       3.2.2.  Cookie Messages . . . . . . . . . . . . . . . . . . .  10
       3.2.3.  Time Synchronization Messages . . . . . . . . . . . .  11
     3.3.  Broadcast Messages  . . . . . . . . . . . . . . . . . . .  11
       3.3.1.  Broadcast Parameter Messages  . . . . . . . . . . . .  11
       3.3.2.  Broadcast Time Synchronization Message  . . . . . . .  12
       3.3.3.  Broadcast Keycheck  . . . . . . . . . . . . . . . . .  13
   4.  Certificate Conventions . . . . . . . . . . . . . . . . . . .  13
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  14
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  14
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  14
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .  14
     7.2.  Informative References  . . . . . . . . . . . . . . . . .  14
   Appendix A.  ASN.1 Module . . . . . . . . . . . . . . . . . . . .  15
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  15

1.  Introduction

   This document provides details on how to construct NTS messages in
   practice.  NTS provides secure time synchronization with time servers
   using Network Time Protocol (NTP) [RFC5905] or Precision Time
   Protocol (PTP) [IEEE1588].  Among other things, this document



Sibold, et al.          Expires September 7, 2015               [Page 2]


Internet-Draft                   CMS4NTS                      March 2015


   describes a convention for using the Cryptographic Message Syntax
   (CMS) [RFC5652] to protect messages in the Network Time Security
   (NTS) protocol.  Encryption is used to provide confidentiality of
   secrets, and digital signatures are used to provide authentication
   and integrity of content.

   Sometimes CMS is used in an exclusively ASN.1 [ASN1] environment.  In
   this case, the NTS message may use any syntax that facilitates easy
   implementation.

2.  CMS Conventions for NTS Message Protection

   Regarding the usage of CMS, we differentiate between four archetypes
   according to which the NTS message types can be structured.  They are
   presented below.  Note that the NTS Message Object that is at the
   core of each structure does not necessarily contain all the data
   needed for the particular message type, but may contain only that
   data which needs to be secured directly with cryptographic operations
   using the CMS.  Specific information about what is included can be
   found in Section 3.

   NTS-Plain:  This archetype is used for actual time synchronization
      messages (explicitly, the following message types: time_request,
      time_response, server_broad, see
      [I-D.ietf-ntp-network-time-security], Section 6) as well as for
      the very first messages of a unicast or a broadcast exchange
      (client_assoc or client_bpar, respectively) and the broadcast
      keycheck exchange (client_keycheck and server_keycheck).  This
      archetype does not make use of any CMS structures.  Figure 1
      illustrates this structure.

      +---------------------------------------------------------+
      |                                                         |
      | ContentInfo                                             |
      |                                                         |
      | +-----------------------------------------------------+ |
      | |                                                     | |
      | | NTS Message Object                                  | |
      | |                                                     | |
      | |                                                     | |
      | +-----------------------------------------------------+ |
      |                                                         |
      +---------------------------------------------------------+

   NTS-Encrypted-and-Signed:  This archetype is used for secure
      transmission of the cookie (only for the server_cook message type,
      see [I-D.ietf-ntp-network-time-security], Section 6).  For this,
      the following CMS structure is used:



Sibold, et al.          Expires September 7, 2015               [Page 3]


Internet-Draft                   CMS4NTS                      March 2015


         First, the NTS message MUST be encrypted using the
         EnvelopedData content type.  EnvelopedData supports nearly any
         form of key management.  In the NTS protocol the client
         provides a certificate in an unprotected message, and the
         public key from this certificate, if it is valid, will be used
         to establish a pairwise symmetric key for the encryption of the
         protected NTS message.

         Second, the EnvelopedData content MUST be digitally signed
         using the SignedData content type.  SignedData supports nearly
         any form of digital signature, and in the NTS protocol the
         server will include its certificate within the SignedData
         content type.

         Third, the SignedData content type MUST be encapsulated in a
         ContentInfo content type.

      Figure 2 illustrates this structure.

      +---------------------------------------------------------+
      |                                                         |
      | ContentInfo                                             |
      |                                                         |
      | +-----------------------------------------------------+ |
      | |                                                     | |
      | | SignedData                                          | |
      | |                                                     | |
      | | +-------------------------------------------------+ | |
      | | |                                                 | | |
      | | | EnvelopedData                                   | | |
      | | |                                                 | | |
      | | | +---------------------------------------------+ | | |
      | | | |                                             | | | |
      | | | | NTS Message Object                          | | | |
      | | | |                                             | | | |
      | | | |                                             | | | |
      | | | +---------------------------------------------+ | | |
      | | |                                                 | | |
      | | +-------------------------------------------------+ | |
      | |                                                     | |
      | +-----------------------------------------------------+ |
      |                                                         |
      +---------------------------------------------------------+

   NTS-Signed:  This archetype is used for server_assoc and server_bpar
      message types.  It uses the following CMS structure:





Sibold, et al.          Expires September 7, 2015               [Page 4]


Internet-Draft                   CMS4NTS                      March 2015


         First, the NTS message object MUST be wrapped in a SignedData
         content type.  The messages MUST be digitally signed, and
         certificates included.  SignedData supports nearly any form of
         digital signature, and in the NTS protocol the server will
         include its certificate within the SignedData content type.

         Second, the SignedData content type MUST be encapsulated in a
         ContentInfo content type.

      Figure 3 illustrates this structure.

      +---------------------------------------------------------+
      |                                                         |
      | ContentInfo                                             |
      |                                                         |
      | +-----------------------------------------------------+ |
      | |                                                     | |
      | | SignedData                                          | |
      | |                                                     | |
      | | +-------------------------------------------------+ | |
      | | |                                                 | | |
      | | | NTS Message Object                              | | |
      | | |                                                 | | |
      | | |                                                 | | |
      | | +-------------------------------------------------+ | |
      | |                                                     | |
      | +-----------------------------------------------------+ |
      |                                                         |
      +---------------------------------------------------------+

   NTS-Certified:  This archetype is used for the client_cook message
      type.  It uses a CMS structure much like the NTS-Signed archetype
      (see Figure 3), with the only difference being that messages
      SHOULD NOT be digitally signed.  This archetype employs the CMS
      structure merely in order to transport certificates.

2.1.  Fields of the employed CMS Content Types

   Overall, three CMS content types are used for NTS messages by the
   archetypes above.  Explicitly, those content types are ContentInfo,
   SignedData and EnvelopedData.  The following is a description of how
   the fields of those content types are used in detail.

2.1.1.  ContentInfo

   The ContentInfo content type is used in all four archetypes.  The
   fields of the SignedData content type are used as follows:




Sibold, et al.          Expires September 7, 2015               [Page 5]


Internet-Draft                   CMS4NTS                      March 2015


      contentType -- indicates the type of the associated content.  For
      the archetype NTS-Plain, it MUST identify the NTS message object
      that is included.  For all other archetypes (NTS-Certified, NTS-
      Signed and NTS-Encrypted-and-Signed), it MUST contain the object
      identifier for the SignedData content type:

           id-signedData OBJECT IDENTIFIER ::= { iso(1) member-body(2)
              us(840) rsadsi(113549) pkcs(1) pkcs7(7) 2 }

      content is the associated content.  For the NTS-Plain archetype,
      it MUST contain the DER encoded NTS message object.  For all other
      archetypes, it MUST contain the DER encoded SignedData content
      type.

2.1.2.  SignedData

   The SignedData content type is used in the NTS-Certified, NTS-Signed
   and NTS-Encrypted-and-Signed archetypes, but not in the NTS-Plain
   archetype.  The fields of the SignedData content type are used as
   follows:

      version -- the appropriate value depends on the optional items
      that are included.  In the NTS protocol, the signer certificate
      MUST be included and other items MAY be included.  The
      instructions in [RFC5652] Section 5.1 MUST be followed to set the
      correct value.

      digestAlgorithms -- is a collection of message digest algorithm
      identifiers.  In the NTS protocol, there MUST be exactly one
      algorithm identifier present.  The instructions in Section 5.4 of
      [RFC5652] MUST be followed.

      encapContentInfo -- this structure is always present.  In the NTS
      protocol, it MUST follow these conventions:

         eContentType -- is an object identifier.  In the NTS protocol,
         for the NTS-Certified and NTS-Signed archetypes, it MUST
         identify the type of the NTS message that was encapsulated.
         For the NTS-Encrypted-and-Signed archetype, it MUST contain the
         object identifier for the EnvelopedData content type:

         id-envelopedData OBJECT IDENTIFIER ::= { iso(1) member-body(2)
                us(840) rsadsi(113549) pkcs(1) pkcs7(7) 3 }.

         eContent is the content itself, carried as an octet string.
         For the NTS-Certified and NTS-Signed archetypes, it MUST
         contain the DER encoded encapsulated NTS message object.  The
         instructions in Section 6.3 of [RFC5652] MUST be followed.  For



Sibold, et al.          Expires September 7, 2015               [Page 6]


Internet-Draft                   CMS4NTS                      March 2015


         the NTS-Encrypted-and-Signed archetype, it MUST contain the DER
         encoded EnvelopedData content type.

      certificates -- is a collection of certificates.  In the NTS
      protocol, it MUST contain the DER encoded certificate [RFC5280] of
      the sender.  It is intended that the collection of certificates be
      sufficient for the recipient to construct a certification path
      from a recognized "root" or "top-level certification authority" to
      the certificate used by the sender.

      crls -- is a collection of revocation status information.  In the
      NTS protocol, it MAY contain one or more DER encoded CRLs
      [RFC5280].  It is intended that the collection contain information
      sufficient to determine whether the certificates in the
      certificates field are valid.

      signerInfos -- is a collection of per-signer information.  In the
      NTS protocol, for the NTS-Certified archetype, this SHOULD be left
      out.  For both the NTS-Signed and the NTS-Encrypted-and-Signed
      archetypes, there MUST be exactly one SignerInfo structure
      present.  The details of the SignerInfo type are discussed in
      Section 5.3 of [RFC5652].  In the NTS protocol, it MUST follow
      these conventions:

         version -- is the syntax version number.  In the NTS protocol,
         the SignerIdentifier is subjectKeyIdentifier, therefore the
         version MUST be 3.

         sid -- identifies the signer's certificate.  In the NTS
         protocol, the "sid" field contains the subjectKeyIdentifier
         from the signer's certificate.

         digestAlgorithm -- identifies the message digest algorithm and
         any associated parameters used by the signer.  In the NTS
         protocol, the identifier MUST match the single algorithm
         identifier present in the digestAlgorithms.

         signedAttrs -- is a collection of attributes that are signed.
         In the NTS protocol, it MUST be present, and it MUST contain
         the following attributes:

            Content Type -- see Section 11.1 of [RFC5652].

            Message Digest -- see Section 11.2 of [RFC5652].

         In addition, it MAY contain the following attributes:

            Signing Time -- see Section 11.3 of [RFC5652].



Sibold, et al.          Expires September 7, 2015               [Page 7]


Internet-Draft                   CMS4NTS                      March 2015


            Binary Signing Time -- see Section 3 of [RFC5652].

         signatureAlgorithm -- identifies the signature algorithm and
         any associated parameters used by the signer to generate the
         digital signature.

         signature is the result of digital signature generation using
         the message digest and the signer's private key.  The
         instructions in Section 5.5 of [RFC5652] MUST be followed.

         unsignedAttrs -- is an optional collection of attributes that
         are not signed.  In the NTS protocol, it MUST be absent.

2.1.3.  EnvelopedData

   The EnvelopedData content type is used only in the NTS-Encrypted-and-
   Signed archetype.  The fields of the EnvelopedData content type are
   used as follows:

      version -- the appropriate value depends on the type of key
      management that is used.  The instructions in [RFC5652]
      Section 6.1 MUST be followed to set the correct value.

      originatorInfo -- this structure is present only if required by
      the key management algorithm.  In the NTS protocol, it MUST be
      present when a key agreement algorithm is used, and it MUST be
      absent when a key transport algorithm is used.  The instructions
      in Section 6.1 of [RFC5652] MUST be followed.

      recipientInfos -- this structure is always present.  In the NTS
      protocol, it MUST contain exactly one entry that allows the client
      to determine the key used to encrypt the NTS message.  The
      instructions in Section 6.2 of [RFC5652] MUST be followed.

      encryptedContentInfo -- this structure is always present.  In the
      NTS protocol, it MUST follow these conventions:

         contentType -- indicates the type of content.  In the NTS
         protocol, it MUST identify the type of the NTS message that was
         encrypted.

         contentEncryptionAlgorithm -- identifies the content-encryption
         algorithm and any associated parameters used to encrypt the
         content.

         encryptedContent -- is the encrypted content.  In the NTS
         protocol, it MUST contain the encrypted NTS message.  The
         instructions in Section 6.3 of [RFC5652] MUST be followed.



Sibold, et al.          Expires September 7, 2015               [Page 8]


Internet-Draft                   CMS4NTS                      March 2015


      unprotectedAttrs -- this structure is optional.  In the NTS
      protocol, it MUST be absent.

3.  Implementation Notes: ASN.1 Structures and Use of the CMS

   This section presents some hints about the structures of the NTS
   message objects for the different message types when one wishes to
   implement the security mechanisms.

3.1.  Preliminaries

   The following ASN.1 coded data type "NTSNonce" is needed for other
   types used below for NTS messages.  It specifies a 128 bit nonce as
   required in several message types:

   NTSNonce ::= OCTET STRING (SIZE(16))

3.2.  Unicast Messages

3.2.1.  Association Messages

3.2.1.1.  Message Type: "client_assoc"

   This message is structured according to the NTS-Plain archetype.
   There is no data necessary besides that which is transported in the
   NTS message object, which is an ASN.1 object of type
   "ClientAssocData" and structured as follows:

   ClientAssocData ::= SEQUENCE {
       nonce            NTSNonce,
       clientId         SubjectKeyIdentifier,
       digestAlgos      DigestAlgorithmIdentifiers,
       keyEncAlgos      KeyEncryptionAlgorithms,
       contentEncAlgos  ContentEncryptionAlgorithms
   }

3.2.1.2.  Message Type: "server_assoc"

   This message is structured according to the NTS-Signed archetype.
   There is no data necessary besides that which is transported in the
   NTS message object, which is an ASN.1 object of type
   "ServerAssocData" and structured as follows:









Sibold, et al.          Expires September 7, 2015               [Page 9]


Internet-Draft                   CMS4NTS                      March 2015


   ServerAssocData ::= SEQUENCE {
       nonce                 NTSNonce,
       clientId              SubjectKeyIdentifier,
       digestAlgos           DigestAlgorithmIdentifiers,
       choiceDigestAlgo      DigestAlgorithmIdentifier,
       keyEncAlgos           KeyEncryptionAlgorithms,
       choiceKeyEncAlgo      KeyEncryptionAlgorithmIdentifier,
       contentEncAlgos       ContentEncryptionAlgorithms
       choiceContentEncAlgo  ContentEncryptionAlgorithmIdentifier
   }

3.2.2.  Cookie Messages

3.2.2.1.  Message Type: "client_cook"

   This message is structured according to the NTS-Certified archetype.
   There is no data necessary besides that which is transported in the
   NTS message object, which is an ASN.1 object of type
   "ClientCookieData" and structured as follows:

   ClientCookieData ::= SEQUENCE {
       nonce       NTSNonce,
       signAlgo    SignatureAlgorithmIdentifier,
       digestAlgo  DigestAlgorithmIdentifier,
       encAlgo     ContentEncryptionAlgorithmIdentifier,
       keyEncAlgo  KeyEncryptionAlgorithmIdentifier
   }

   It is identified by the following object identifier (fictional
   values):

   id-clientCookieData OBJECT IDENTIFIER ::=
       {nts(??) cookie(3) clientcookiedata(1)}

3.2.2.2.  Message Type: "server_cook"

   This message is structured according to the "NTS-Encrypted-and-
   Signed" archetype.  There is no data necessary besides that which is
   transported in the NTS message object, which is an ASN.1 object of
   type "ServerCookieData" and structured as follows:

   ServerCookieData ::= SEQUENCE {
       nonce     NTSNonce,
       cookie    OCTET STRING (SIZE(16))
   }

   It is identified by the following object identifier (fictional
   values):



Sibold, et al.          Expires September 7, 2015              [Page 10]


Internet-Draft                   CMS4NTS                      March 2015


   id-serverCookieData OBJECT IDENTIFIER ::=
       {nts(??) cookie(3) servercookiedata(2)}

3.2.3.  Time Synchronization Messages

3.2.3.1.  Message Type: "time_request"

   This message is structured according to the "NTS-Plain" archetype.

   This message type requires additional data to that which is included
   in the NTS message object, namely it requires regular time
   synchronization data, as an unsecured packet from a client to a
   server would contain.  The NTS message object itself is an ASN.1
   object of type "TimeRequestSecurityData", whose structure is as
   follows:

   TimeRequestSecurityData ::=
   SEQUENCE {
       nonce_t           NTSNonce,
       digestAlgo        DigestAlgorithmIdentifier,
       hashOfClientCert  BIT STRING
   }

3.2.3.2.  Message Type: "time_response"

   This message is also structured according to "NTS-Plain".

   It requires two items of data in addition to that which is
   transported in the NTS message object.  Like "time_request", it
   requires regular time synchronization data.  Furthermore, it requires
   the Message Authentication Code (MAC) to be generated over the whole
   rest of the packet (including the NTS message object) and transported
   in some way.  The NTS message object itself is an ASN.1 object of
   type "TimeResponseSecurityData", with the following structure:

   TimeResponseSecurityData ::=
   SEQUENCE {
       nonce_t  NTSNonce,
   }

3.3.  Broadcast Messages

3.3.1.  Broadcast Parameter Messages








Sibold, et al.          Expires September 7, 2015              [Page 11]


Internet-Draft                   CMS4NTS                      March 2015


3.3.1.1.  Message Type: "client_bpar"

   This first broadcast message is structured according to the NTS-Plain
   archetype.  There is no data necessary besides that which is
   transported in the NTS message object, which is an ASN.1 object of
   type "BroadcastParameterRequest" and structured as follows:

   BroadcastParameterRequest ::=
   SEQUENCE {
       nonce     NTSNonce,
       clientId  SubjectKeyIdentifier
   }

3.3.1.2.  Message Type: "server_bpar"

   This message is structured according to "NTS-Signed".  There is no
   data necessary besides that which is transported in the NTS message
   object, which is an ASN.1 object of type "BroadcastParameterResponse"
   and structured as follows:

   BroadcastParameterResponse ::=
   SEQUENCE {
       nonce               NTSNonce,
       oneWayAlgo1         DigestAlgorithmIdentifier,
       oneWayAlgo2         DigestAlgorithmIdentifier,
       lastKey             OCTET STRING (SIZE (16)),
       intervalDuration    BIT STRING,
       disclosureDelay     INTEGER,
       nextIntervalTime    BIT STRING,
       nextIntervalIndex   INTEGER
   }

3.3.2.  Broadcast Time Synchronization Message

3.3.2.1.  Message Type: "server_broad"

   This message is structured according to the "NTS-Plain" archetype.
   It requires regular broadcast time synchronization data in addition
   to that which is carried in the NTS message object.  Like
   "time_response", this message type also requires a MAC, generated
   over all other data, to be transported within the packet.  The NTS
   message object itself is an ASN.1 object of type "BroadcastTime".  It
   has the following structure:








Sibold, et al.          Expires September 7, 2015              [Page 12]


Internet-Draft                   CMS4NTS                      March 2015


   BroadcastTime ::=
   SEQUENCE {
       thisIntervalIndex   INTEGER,
       disclosedKey        OCTET STRING (SIZE (16)),
   }

3.3.3.  Broadcast Keycheck

3.3.3.1.  Message Type: "client_keycheck"

   This message is structured according to the "NTS-Plain" archetype.
   There is no data necessary besides that which is transported in the
   NTS message object, which is an ASN.1 object of type
   "ClientKeyCheckSecurityData" and structured as follows:

   ClientKeyCheckSecurityData ::=
   SEQUENCE {
       nonce_k           NTSNonce,
       interval_number   INTEGER,
       digestAlgo        DigestAlgorithmIdentifier,
       hashOfClientCert  BIT STRING
   }

3.3.3.2.  Message Type: "server_keycheck"

   This message is also structured according to "NTS-Plain".  It
   requires only a MAC, generated over the NTS message object, to be
   included in the packet in addition to what the NTS message object
   itself contains.  The latter is an ASN.1 object of type
   "ServerKeyCheckSecurityData", which is structured as follows:

   ServerKeyCheckSecurityData ::=
   SEQUENCE {
       nonce_t           NTSNonce,
       interval_number   INTEGER
   }

4.  Certificate Conventions

   The syntax and processing rules for certificates are specified in
   [RFC5652].  In the NTS protocol, the server certificate MUST contain
   the following extensions:

      Subject Key Identifier -- see Section 4.2.1.2 of [RFC5652].

      Key Usage -- see Section 4.2.1.3 of [RFC5652].

      Extended Key Usage -- see Section 4.2.1.22 of [RFC5652].



Sibold, et al.          Expires September 7, 2015              [Page 13]


Internet-Draft                   CMS4NTS                      March 2015


   The Extended Key Usage extension MUST include the id-kp-NTSserver
   object identifier.  When a certificate issuer includes this object
   identifier in the extended key usage extension, it provides an
   attestation that the certificate subject is a time server that
   supports the NTS protocol.

   The id-kp-NTSserver object identifier is:

         id-kp-NTSserver OBJECT IDENTIFIER ::= { TBD }

5.  IANA Considerations

   IANA needs to assign an object identifier for the id-kp-NTSserver key
   purpose and another one for the ASN.1 module in the appendix.

6.  Security Considerations

   To be written.

7.  References

7.1.  Normative References

   [ASN1]     International Telecommunication Union, "Abstract Syntax
              Notation One (ASN.1): Specification of basic notation",
              ITU-T Recommendation X.680, November 2008.

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

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

7.2.  Informative References

   [I-D.ietf-ntp-network-time-security]
              Sibold, D., Roettger, S., and K. Teichel, "Network Time
              Security", draft-ietf-ntp-network-time-security-07 (work
              in progress), March 2015.

   [IEEE1588]
              IEEE Instrumentation and Measurement Society. TC-9 Sensor
              Technology, "IEEE standard for a precision clock
              synchronization protocol for networked measurement and
              control systems", 2008.






Sibold, et al.          Expires September 7, 2015              [Page 14]


Internet-Draft                   CMS4NTS                      March 2015


   [RFC5905]  Mills, D., Martin, J., Burbank, J., and W. Kasch, "Network
              Time Protocol Version 4: Protocol and Algorithms
              Specification", RFC 5905, June 2010.

Appendix A.  ASN.1 Module

   The ASN.1 module contained in this appendix defines the id-kp-
   NTSserver object identifier.

      NTSserverKeyPurpose
        { TBD }

      DEFINITIONS IMPLICIT TAGS ::=
      BEGIN

      id-kp-NTSserver OBJECT IDENTIFIER ::= { TBD }

      END

Authors' Addresses

   Dieter Sibold
   Physikalisch-Technische Bundesanstalt
   Bundesallee 100
   Braunschweig  D-38116
   Germany

   Phone: +49-(0)531-592-8420
   Fax:   +49-531-592-698420
   Email: dieter.sibold@ptb.de


   Stephen Roettger
   Google Inc.

   Email: stephen.roettger@googlemail.com


   Kristof Teichel
   Physikalisch-Technische Bundesanstalt
   Bundesallee 100
   Braunschweig  D-38116
   Germany

   Phone: +49-(0)531-592-8421
   Email: kristof.teichel@ptb.de





Sibold, et al.          Expires September 7, 2015              [Page 15]


Internet-Draft                   CMS4NTS                      March 2015


   Russ Housley
   Vigil Security

















































Sibold, et al.          Expires September 7, 2015              [Page 16]


Html markup produced by rfcmarkup 1.124, available from https://tools.ietf.org/tools/rfcmarkup/