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  TLS Working Group                                            P. Urien
  Internet Draft                                          Telecom Paris
  Intended status: Experimental

                                                           June 24 2020
  Expires: December 2020

                    Identity Module for TLS Version 1.3
                         draft-urien-tls-im-00.txt


Abstract

   TLS 1.3 will be deployed in the Internet of Things ecosystem. In
   many IoT frameworks, TLS or DTLS protocols, based on pre-shared key
   (PSK), are used for device authentication. So PSK tamper resistance,
   is a critical market request, in order to prevent hijacking issues.
   If DH exchange is used with certificate bound to DH ephemeral public
   key, there is also a benefit to protect its signature procedure. The
   TLS identity module (im) MAY be based on secure element; it realizes
   some HKDF operations bound to PSK, and cryptographic signature if
   certificates are used. Secure Element form factor could be
   standalone chip, or embedded in SOC like eSIM.

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.

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 December 2020.

   .





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Copyright Notice

   Copyright (c) 2020 IETF Trust and the persons identified as the
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   This document is subject to BCP 78 and the IETF Trust's Legal
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                 Identity Module for TLS Version 1.3      June 2020

Table of Contents
   Abstract........................................................... 1
   Requirements Language.............................................. 1
   Status of this Memo................................................ 1
   Copyright Notice................................................... 2
   1 Overview......................................................... 4
   2 Protecting the Key Schedule for PSK.............................. 4
      2.1 Context..................................................... 4
      2.2 Identity Module Procedures.................................. 4
      2.3 KSGS: Keys Secure Generation and Storage.................... 5
      2.4 Identity Module Key Procedures (IMKP)....................... 5
          2.4.1 CETS: Client Early Traffic Secret .................... 5
          2.4.2 EEMS: Early Exporter Master Secret ................... 5
          2.4.3 HEDSK: HKDF-Extract from Derived Secret Key .......... 5
          2.4.4 HBSK: HMAC from Binder Key Secret .................... 6
   3. Asymmetric Signature............................................ 6
      3.1 GENKEY...................................................... 6
      3.2 GETPUB...................................................... 6
      3.3 SIGN........................................................ 6
   4. Secure Element as Identity Module............................... 7
      4.1 Administrative mode......................................... 7
      4.2 User Mode................................................... 7
      4.3 KSGS: Keys Secure Generation and Storage.................... 7
          4.3.1 Example .............................................. 8
      4.4 CETS: Client Early Traffic Secret........................... 8
          4.4.1 Example .............................................. 8
      4.5 EEMS: Early Exporter Master Secret.......................... 8
          4.5.1 Example .............................................. 9
      4.6 HEDSK: HKDF-Extract from Derived Secret Key................. 9
          4.6.1 Example .............................................. 9
   5 IANA Considerations.............................................. 9
   6 Security Considerations.......................................... 9
   7 References....................................................... 9
      7.1 Normative References........................................ 9
      7.2 Informative References..................................... 10
   8 Authors' Addresses.............................................. 10
















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                 Identity Module for TLS Version 1.3      June 2020

1 Overview

   TLS 1.3 [RFC8446] will be deployed in the Internet of Things
   ecosystem. In many IoT frameworks, TLS or DTLS protocols, based on
   pre-shared key (PSK), are used for device authentication. So PSK
   tamper resistance, is a critical market request, in order to prevent
   hijacking issues. If DH exchange is used with certificate bound to
   DH ephemeral public key, there is also a benefit to protect its
   signature procedure. The TLS identity module (im) MAY be based on
   secure element [ISO7816]; it realizes some HKDF [RFC5869] operations
   bound to PSK, and cryptographic signature if certificates are used.
   Secure Element form factor could be standalone chip or embedded in
   SOC like eSIM.


                       +-----------+      +----------+
                       | Processor |      | Identity |
                       |  TLS 1.3  +------+  Module  |
                       |           |      |    im    |
                       +-----------+      +----------+

   Figure 1. TLS 1.3 Identity Module (im)


2 Protecting the Key Schedule for PSK

2.1 Context

   According to [RFC8446] external PSKs MAY be provisioned outside of
   TLS.

   The Early Secret (ESK) is computed according to relation:
   ESK =HKDF-Extract(salt=0s,PSK) = HMAC(salt=0s,PSK)

   The Binder Key (BSK) for outside provisioning is computed according
   to the relation:
   BSK = Derive-Secret(ESK, "ext binder", "")

   The Derived Secret (DSK) is computed according to the relation:
   DSK= Derive-Secret(ESK, "derived", "")

2.2 Identity Module Procedures

   The identity module MUST provide a KSGS (Keys Secure Generation and
   Storage) procedure, which computes and securely stores ESK, BSK and
   DSK keys.

   This procedure MUST require administrative rights.

   A set IMKP (Identity Module Key Procedures) of four procedures is
   required, in order to protect from public exposure ESK, BSK and DSK:

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                 Identity Module for TLS Version 1.3      June 2020

   - CETS: Client Early Traffic Secret
   - EEMS: Early Exporter Master Secret
   - HEDSK: HKDF-Extract from Derived Secret Key
   - HBSK: HMAC from Binder Key Secret

   These procedures MAY require user rights.

2.3 KSGS: Keys Secure Generation and Storage

   The Identity module MUST provide a KSGS procedure, requiring
   administrative rights, which computes and securely stores ESK, BSK,
   DSK

   Input: salt and PSK
   Output: Success or Failure

   ESK, DSK, and BSK secret values are stored in the identity module

   ESK= HMAC(salt=0s,PSK)
   DSK= HMAC(ESK,Hash-Length || 0d746c73313320646572697665640001)
   BSK= HMAC(ESK,Hash-Length || 10746c733133206578742062696e6465720001)


2.4 Identity Module Key Procedures (IMKP)

  2.4.1 CETS: Client Early Traffic Secret

   Input: Length, Message
   Output: Client Early Traffic Secret or Failure

   CETS(ClientHello) = Derive-Secret(ESK, "c e traffic", Message)
   = HMAC(ESK, Length || 11746c733133206320652074726166666963 ||
   Message || 01)

  2.4.2 EEMS: Early Exporter Master Secret

   Input: Length, Message
   Output: Early Exporter Master Secret or Failure

   EEMS(ClientHello) = Derive-Secret(ESK, "e exp master", Message)
   = HMAC(ESK, Length || 12746c733133206520657870206d6173746572 ||
   Message || 01)

  2.4.3 HEDSK: HKDF-Extract from Derived Secret Key

   Input: DHE
   Output: Handshake Secret or Failure

   EDSK(DHE)= HKDF-Extract(DHE, DSK) = HMAC(DHE, DSK)



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  2.4.4 HBSK: HMAC from Binder Key Secret

   Input: data
   Output: HMAC(BSK, data) or Failure

   HBSK(data) = HMAC(BSK, data)

3. Asymmetric Signature

   The identity module MUST provide a GENKEY (GENKEY: Generate Key)
   procedure, in order to store or generate private asymmetric key and
   associated public key.

   This procedure MUST require administrative rights.

   The procedure GETPUB (GETPUB: Get Public Key) is required in order
   to read the public key value.

   This procedure MAY require user rights.

   The procedure SIGN (SIGN: Signature) is required in order to perform
   a raw signature for a digest value, computed from certificate.

   This procedure MAY require user rights.

3.1 GENKEY

   Input: None
   Output: Success or Failure

   A private key is generated and store in the identity module. A
   public key is computed from the private key.

3.2 GETPUB

   Input: None
   Output: Public Key Value or Failure

3.3 SIGN

   Input: DigestValue
   Output: Signature Value or Failure










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4. Secure Element as Identity Module

   Secure elements are defined according to [ISO7816] standards. They
   support hash functions (sha256, sha384, sha512) and associated HMAC
   procedures. They also provide DH procedures in Z/pZ* and elliptic
   curves. Open software can be released thanks to the Javacard
   standards, such as JC3.04, JC3.05.

   Below is an illustration of binary encoding rules for secure element
   according to the T=1 ISO7816 protocol.

   An ISO7816 command (TAPDU) is a set of bytes comprising a five byte
   header and an optional payload (up to 255 bytes)

   The header comprises the following five bytes
   - CLA, Class
   - INS, Instruction code
   - P1, P1 byte
   - P2, P2 byte
   - P3, length of the payload, or number of expected bytes

   The response comprises a payload (up to 256 bytes) and a two bytes
   status word (SW1, SW2), 9000 meaning successful operation.

4.1 Administrative mode

   The [ISO7816] command VERIFY (INS=0x20) SHOULD be used to enter the
   administrative mode

   Tx: CLA=00 INS=20 P1=00 P2=Adm P3=PIN-Length [PIN-Value]
   Rx: 9000

4.2 User Mode

   The [ISO7816] command VERIFY SHOULD be used to enter the user mode

   Tx: CLA=00 INS=20 P1=00 P2=User P3=PIN-Length [PIN-Value]
   Rx: 9000


4.3 KSGS: Keys Secure Generation and Storage

   Length= 2 + Salt-Length + PSK-Length

   Tx: CLA=00 INS=TLS13 P1=0 P2=KSGS P3=Length Salt-Length [Salt-Value]
   PSK-Length [PSK-Value]
   Rx: 9000

   This procedure computes and stores ESK, BSK and DSK.



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  4.3.1 Example

   PSK=0102030405060708090A0B0C0D0E0F101112131415161718191A1B1C1D1E1F20

   Tx: CLA=00 INS=85 P1=00 P2=0A P3=23 01 00 20
   0102030405060708090A0B0C0D0E0F101112131415161718191A1B1C1D1E1F20
   Rx:9000

   ESK= HMAC-SHA256(0,PSK)
   ESK=
   23499E7EDF0FBE6BAA137DF0F23BECAEFA722AD19FC262855409DE8CD8B3C897

   DSK= HMAC-SHA256(ESK,0020 0d746c7331332064657269766564 00 01)
   DSK=
   98EEAA27F7D77499E5FBC63A413CD8C395CAE42D850B65A5AE6A63807368A3F5

   BSK = HMAC-SHA256(ESK,0020 10746c733133206578742062696e646572 00 01)
   BSK=
   4B6B423D2B92D840CC9A1A30D457BC5A4B10918587BBFF96380E91CE20A5FA2C

4.4 CETS: Client Early Traffic Secret

   Length = 2 + Messages-Length
   Hash-Length: the hash length (2 bytes)

   Tx: CLA INS=TLS13 P1=CETS P2=ESK P3=Length Hash-Length Messages-
   Length [Messages]
   Rx:[Client Early Traffic Secret] 9000

  4.4.1 Example

   Tx: CLA=00 INS=85 P1=00 P2=0B P3=03 0020 00
   Rx: 0738A2B6F6FAA2AF5CDD9B6F0F2B232F19B3256A5926EAC600B911F91E98D2D4
   9000

   Message= NULL = 0s
   [Client Early Traffic Secret] =
   HMAC-SHA256(ESK, 0020 11746c733133206320652074726166666963 00 01)


4.5 EEMS: Early Exporter Master Secret

   Length = 2 + Messages-Length
   Hash-Length: the hash length (2 bytes)

   Tx: CLA INS=TLS13 P1=EEMS P2=ESK P3=Length Hash-Length Messages-
   Length [Messages]
   Rx: [Early Exporter Master Secret] 9000




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  4.5.1 Example

   Tx: CLA=00 INS=85 P1=01 P2=0B P3=03 0020 00
   Rx: 9B7FC6A8F854C16A301DFC566859931DB5EE9A22793142A0C67159C445E7BEAB
   9000

   Message= NULL = 0s
   [Early Exporter Master Secret] =
   HMAC-SHA256(ESK, 0020 12746c733133206520657870206d6173746572 00 01)

4.6 HEDSK: HKDF-Extract from Derived Secret Key

   Tx: CLA INS=TLS13 P1=0 P2=HEDSK P3=Data-Length [Data]
   Rx: [HMAC(Data,DSK)] 9000

  4.6.1 Example

   Tx: CLA=00 INS=85 P1=00 P2=0E P3=01 00
   Rx: 3074777017FA405DB00BF0F4E24E5A3E0A5F8CE357472BEA4F442D7754E13BF2
   900

   DHE=NULL=0s
   HMAC-256(DHE,DSK)= HMAC-256(0s,DSK)


5 IANA Considerations

   TODO

6 Security Considerations

   TODO

7 References

7.1 Normative References

   [RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol
   Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
   https://www.rfc-editor.org/info/rfc8446.

   [RFC5869]  Krawczyk, H. and P. Eronen, "HMAC-based Extract-and-
   Expand Key Derivation Function (HKDF)", RFC 5869, DOI
   10.17487/RFC5869, May 2010,
   <https://www.rfc-editor.org/info/rfc5869>.

   [ISO7816] ISO 7816, "Cards Identification - Integrated Circuit Cards
   with Contacts", The International Organization for Standardization
   (ISO).



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7.2 Informative References


8 Authors' Addresses

   Pascal Urien
   Telecom Paris
   19 place Marguerite Perey
   91120 Palaiseau           Phone: NA
   France                    Email: Pascal.Urien@telecom-paris.fr










































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