Quantum-Safe Hybrid (QSH) Ciphersuite for Transport Layer Security (TLS) version 1.2
draft-whyte-qsh-tls12-02

Versions: 00 01 02                                                      
INTERNET-DRAFT                                             J. M. Schanck
Intended Status: Experimental          Security Innovation & U. Waterloo
Expires: 21 Jan 2017                                            W. Whyte
                                                     Security Innovation
                                                                Z. Zhang
                                                     Security Innovation
                                                            22 July 2016


               Quantum-Safe Hybrid (QSH) Ciphersuite for
               Transport Layer Security (TLS) version 1.2
                      draft-whyte-qsh-tls12-02.txt


Abstract

   This document describes the Quantum-Safe Hybrid ciphersuite, a new
   cipher suite providing modular design for quantum-safe cryptography
   to be adopted in the handshake for the Transport Layer Security (TLS)
   protocol version 1.2.  In particular, it specifies the use of the
   NTRUEncrypt encryption scheme in a TLS handshake.




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), its areas, and its working groups.  Note that
   other groups may also distribute working documents as Internet-
   Drafts.

   The list of current Internet-Drafts can be accessed at
   http://www.ietf.org/1id-abstracts.html.

   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html.

   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 21 Jan, 2017.




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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Modular design for quantum-safe hybrid handshake . . . . . . .  4
   3.  Data Structures and Computations . . . . . . . . . . . . . . .  6
     3.1.  Data structures for Quantum-safe Crypto Schemes  . . . . .  7
     3.2.  Client Hello Extensions  . . . . . . . . . . . . . . . . .  8
     3.3.  Server Hello Extension . . . . . . . . . . . . . . . . . . 10
     3.4.  Server Key Exchange  . . . . . . . . . . . . . . . . . . . 11
     3.5.  Client Key Exchange  . . . . . . . . . . . . . . . . . . . 13
   4.  Cipher Suites  . . . . . . . . . . . . . . . . . . . . . . . . 14
   5.  Specific information for Quantum Safe Scheme . . . . . . . . . 14
     5.1   NTRUEncrypt  . . . . . . . . . . . . . . . . . . . . . . . 14
     5.2.  LWE  . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
     5.3.  HFE  . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
   6.  Security Considerations  . . . . . . . . . . . . . . . . . . . 15
     6.1.  Security, Authenticity and Forward Secrecy . . . . . . . . 15
     6.2.  Quantum Security and Quantum Forward Secrecy . . . . . . . 15
     6.3.  Quantum Authenticity . . . . . . . . . . . . . . . . . . . 15
   7.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 16
   8.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 16
   9.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 16
     9.1.  Normative References . . . . . . . . . . . . . . . . . . . 16
     8.2.  Informative References . . . . . . . . . . . . . . . . . . 17
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 18
   Copyright Notice . . . . . . . . . . . . . . . . . . . . . . . . . 19

























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1.  Introduction

   Quantum computers pose a significant threat to modern cryptography.
   Two most widely adopted public key cryptosystems, namely, RSA [PKCS1]
   and Elliptic Curve Cryptography (ECC) [SECG], will be broken by
   general purpose quantum computers.  RSA is adopted in TLS from
   Version 1.0 and to TLS Version 1.2 [RFC2246], [RFC4346], [RFC5246],
   [TLS1.3].  ECC is enabled in RFC 4492 [RFC4492] and adopted in TLS
   version 1.2 [RFC5246].  On the other hand, there exist several
   quantum-safe cryptosystems, such as the NTRUEncrypt cryptosystem
   [EESS1], that deliver similar performance, yet are conjectured to be
   robust against quantum computers.

   This document describes a modular design that allows one or many
   quantum-safe cryptosystems to be adopted in the handshake protocol,
   applicable to TLS Version 1.0 to Version 1.3 [RFC2246], [RFC4346],
   [RFC5246], [TLS1.3].  It uses a hybrid approach that combines a
   classical handshake mechanism with key encapsulation mechanisms
   instantiated with quantum-safe encryption schemes.  The modular
   design provides quantum-safe features to TLS with an introduction of
   only one new cipher suite.  Yet, it allows the flexibility to include
   new and advanced quantum-safe encryption schemes at present and in
   the future.

   The remainder of this document is organized as follows.  Section 2
   provides an overview of the modular design of quantum-safe handshake
   for TLS.  Section 3 specifies various data structures needed for a
   quantum safe handshake, their encoding in TLS messages, and the
   processing of those messages.  Section 4 defines new TLS_QSH cipher
   suites.  Section 5 provides specific information for quantum safe
   encryption schemes.  Section 6 discusses security considerations.
   Section 7 describes IANA considerations for the name spaces created
   by this document.  Section 8 gives acknowledgements.

   This is followed by the lists of normative and informative references
   cited in this document, the authors' contact information, and
   statements on intellectual property rights and copyrights.

   Implementation of this specification requires familiarity with TLS
   [RFC2246], [RFC4346], [RFC5246], [TLS1.3], TLS extensions [RFC4366],
   and knowledge of the corresponding quantum-safe cryptosystem.

   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].

   Well-known abbreviations and acronyms can be found at RFC Editor
   Abbreviations List [REAL].



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2.  Modular design for quantum-safe hybrid handshake

   This document introduces a modular approach to including new quantum-
   safe key exchange algorithms within TLS, while maintaining the
   assurance that comes from the use of already established cipher
   suites.  It allows the TLS premaster secret to be agreed using both
   an established classical cipher suite and a quantum-safe key
   encapsulation mechanism.

          Client                                        Server
          ------                                        ------
          ClientHello          -------->
                                                   ServerHello
                                                  Certificate*
                                            ServerKeyExchange*
                                          CertificateRequest*+
                               <--------       ServerHelloDone
          Certificate*+
          ClientKeyExchange
          CertificateVerify*+
          [ChangeCipherSpec]
          Finished             -------->
                                            [ChangeCipherSpec]
                               <--------              Finished

          Application Data     <------->      Application Data

             * message is not sent under some conditions
             + message is not sent unless client authentication
               is desired

           Figure 1: Message flow in a full TLS 1.2 handshake

   Figure 1 shows all messages involved in the TLS key establishment
   protocol (aka full handshake).  The addition of quantum-safe
   cryptography has direct impact only on the ClientHello, the
   ServerHello, the ServerKeyExchange, and the ClientKeyExchange.  In
   the rest of this document, we describe each quantum-safe key exchange
   data structure in greater detail in terms of the content and
   processing of these messages.

   The authentication is provided by classical cryptography.  The
   introduction of quantum-safe encryption schemes delivers forward
   secrecy against quantum attackers.  The additional cryptographic data
   exchanged between the client and the server is shown in Figure 2.






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          Client                                        Server
          ------                                        ------
          ClientHelloExtension
          (SerPKReq|
          QSHSchemeIDList|
          [CliPKList])         -------->
                                          ServerHelloExtension
                                                 ([SerPKList])
                                             ServerKeyExchange
                               <--------     ([SerCipherList])
          ClientKeyExchange
          ([CliCipherList])    -------->

          ClassicS|SerS|CliS   <------->    ClassicS|SerS|CliS

             [struct]: struct is optional

          Figure 2: Additional cryptographic data in handshake

   As usual, the ClientHello message includes the list of classical
   cipher suites the client wishes to negotiate (e.g.,
   TLS_ECDH_ECDSA_WITH_NULL_SHA), as well as a new cipher suite
   identifier TLS_QSH (short for TLS with Quantum Safe Hybrid
   handshake).  This new identifier SHOULD appear first in the list of
   cipher suites.

   The ClientHelloExtension field MAY have three additional fields:
   o   SerPKReq:  a request for server's public key; also indicates the
                  number of server's public keys the client wishes to
                  receive
   o   QSHSchemeIDList:
                  a list of distinct QSHSchemeIDs from the client,
                  each ID represents a quantum safe encryption
                  scheme/parameter set supported by the client
   o   CliPKList: a list of client's public keys [CPK1]|[CPK2]|...
                  each corresponding to a distinct QSHScheme in
                  QSHSchemeIDList

   Note: The client does not need to provide public keys for all
   QSSchemes from the list. The client indicates that it does not wish
   to contribute a public key for certain QSScheme by omitting the
   corresponding public key field.

   The ServerHelloExtension field MAY have one additional field:
   o   SerPKList: a list of Server's public keys [SPK1]|[SPK2]|...
                  each corresponding to a QSHScheme in
                  QSHSchemeIDList




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   Note: SerPKList is a list of public key structures QSHPK.  For each
   structure, there is a QSHSchemeID field identifying the corresponding
   encryption scheme.  This QSHSchemeID MUST exist in QSHSchemeIDList.

   The ServerKeyExchange message MAY contain an additional list of
   ciphertexts:
   o   SerCipherList:
                  a list of ciphertexts
                  [Encrypt_CPK1(SerS1)]|[Encrypt_CPK2(SerS2)]|...
                  where the server-contributed secret keying material
                  is SerS = SerS1|SerS2|..., and CPKi is selected from
                  CliPKList.
   At least one of SerPKList and SerCipherList MUST have at least one
   entry.

   Additionally, the ServerKeyExchange contains an indication of the
   classical cipher suite selected, and the ServerKeyExchange material
   appropriate to that cipher suite.

   If SerPKList was provided, the ClientKeyExchange message MUST contain
   an additional list of ciphertexts:
   o   CliCipherList:
                  a list of ciphertexts
                  [Encrypt_SPK1(CliS1)]|[Encrypt_SPK2(CliS2)]|...
                  where the client-contributed secret keying material
                  is CliS = CliS1|CliS2|... , and SPKi is from
                  SerPKList.

   The client MUST use all public keys from SerPKList.

   Additionally, the ClientKeyExchange contains the ServerKeyExchange
   material appropriate to the selected classical cipher suite.

   SerS and CliS cannot be both NULL.

   The final premaster secret negotiated by the client and the server is
   the concatenation of the classical premaster secret, SerS, and CliS
   in that order.
   A 48 bytes fixed length master secret is derived from the premaster
   secret at the end of the handshake, using a pseudo random function
   specified by the classical cipher suite (see Section 8.1. RFC 5246
   [RFC5246]).

3.  Data Structures and Computations

   This section specifies the data structures and computations used by
   TLS_QSH cipher suite specified in Sections 2.  The presentation
   language used here is the same as that used in TLS [RFC2246],



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   [RFC4346], [RFC5246].  Since this specification extends TLS, these
   descriptions should be merged with those in the TLS specification and
   any others that extend TLS.  This means that enum types may not
   specify all possible values, and structures with multiple formats
   chosen with a select() clause may not indicate all possible cases.

3.1.  Data structures for Quantum-safe Crypto Schemes

        enum {
            ntru_eess439 (0x0101),
            ntru_eess593 (0x0102),
            ntru_eess743 (0x0103),
            reserved     (0x0102..0x01FF),
            lwe_XXX      (0x0201),
            reserved     (0x0202..0x02FF),
            hfe_XXX      (0x0301),
            reserved     (0x0302..0x03FF),
            reserved     (0x0400..0xFEFF),
            (0xFFFF)
        } QSHSchemeID;

   ntru_eess439, etc:   Indicates parameter set to be used for the
      NTRUEncrypt encryption scheme.  The name of the parameter sets
      defined here are those specified in [EESS1].

   lwe_XXX, etc:   Indicates parameters for Learning With Error (LWE)
      encryption scheme.  The name of the parameters defined here are
      not specified in this document.

   hfe_XXX, etc:   Indicates parameters for Hidden Field Equotion (HFE)
      encryption scheme.  The name of the parameters defined here are
      not specified in this document.

   The QSHSchemes name space is maintained by IANA [IANA].  See Section
   6 for information on how new schemes are added.

   The server implementation SHOULD support all of the above QSHSchemes,
   and client implementation SHALL support at least one of them.

        struct {
            QSHSchemeID   id,
            opaque        pubKey<1..2^16-1>
        } QSHPK;

        struct {
            QSHPK         keys<1..2^24-1>
        } QSHPKList;




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   The structure of public keys exchanged by the client and the server,
   namely, QSHPK, has two fields: QSHSchemeID specifies the
   corresponding quantum safe encryption scheme, and an opaque encodes
   the actual public key data following the specification of the
   corresponding quantum safe encryption scheme.  Any entity that
   reserves a new quantum safe encryption scheme identifier MUST specify
   how the keys and ciphertexts for that scheme are encoded.  See
   Section 5 for definitions of the encodings of the schemes specified
   in this document.

   The QSHPKList is a list of QSHPKs.

        struct {
            QSHSchemeID   id,
            opaque        encryptedKey<1..2^16-1>
        } QSHCipher;

        struct {
            QSHCipher     encryptedKeys<1..2^24-1>
        } QSHCipherList;

   The structure of ciphertext exchanged by the client and the server,
   namely QSHCipher, has two fields: QSHSchemeID specifies the
   corresponding quantum safe encryption scheme, and an opaque encodes
   the actual ciphertext following the specification of the
   corresponding quantum safe encryption scheme.

   The QSHCipherList is a list of ciphertexts.


3.2.  Client Hello Extensions

   This section specifies a TLS extension that can be included with the
   ClientHello message as described in RFC 4366 [RFC4366].

   When these extensions are sent:

   The extensions MUST be sent along with any ClientHello message that
   proposes TLS_QSH cipher suites.

   Meaning of these extensions:

   These extensions allow a client to send a request for server's public
   key, a list that enumerates QSHSchemeIDs for supported quantum safe
   cryptosystems, and/or public keys corresponding to QSHSchemeIDs.

   Note: QSHSchemeID MUST be distinct in QSHSchemeIDList.  For each
   QSHSchemeID there MUST be at most one public key CPKi.



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   Structure of the extension:

   The general structure of TLS extensions is described in [RFC4366],
   and this specification adds a new type to ExtensionType.

       enum { quantum-safe-hybrid(0x18)} ExtensionType;

   quantum-safe-hybrid (Supported TLS_QSH Extension): Indicates the list
      of QSHSchemeIDs supported by the client.  For this extension, the
      opaque extension_data field may contain SrvPkReq, QSHSchemeIDList
      and CliPKList.

        struct {
            select (CipherSuite) {
                case TLS_QSH:
                    QSHSchemeIDList qshSchemeIDList,
                    QSHPKList       cliPKList,
                    SerPkReqType    serPkReq,
        } ClientHelloExtension;

   SerPKReqType is defined as follows:

        struct {
            int    min,
            int    max
        } SerPkReqType;

   serPKReq.min MUST not be greater than serPKReq.max.  Either field
   MUST not be greater than the maximum number that is supported by the
   protocol (this may due to the size of the extensions and size of the
   encoded public keys, etc).  If the serPKReq.min equal serPKReq.max,
   the client requires specifically serPKReq.min number of public keys.
   When both field are zero, the client do not wish to receive any
   public keys. When 0 <= serPKReq.min < serPKReq.max, the client lets
   the server to decide the number of public keys (between serPKReq.min
   and serPKReq.max).

   Items in qshSchemeIDList are ordered according to the client's
   preferences (favorite choice first).

   As an example, a client that only supports ntru_eess439 (0x0101) and
   ntru_eess593 (0x0102) and prefers to use ntru_eess439 would encode
   its qshSchemeIDList as follows:

        04 01 01 01 02

   The client MAY append a list of public keys corresponding to each
   crypto system. If serPKReq is (0,0), the client MUST list all public



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   keys corresponding to each qshSchemeID form qshSchemeIDList.

        00 18 | extension length | 00 04 01 01 01 02 | CliPKList length
        | CPK1 | CPK2 | CPK3 | ... | 00 |

   Note: the extension type value appearing in these examples is
   tentative.

   Actions of the sender:

   A client that proposes TLS_QSH cipher suites in its ClientHello
   message appends these extensions (along with any others), indicating
   whether the client wishes the server to contribute its quantum-safe
   public key, enumerating the supported quantum-safe crypto systems,
   and/or the public key corresponding to each crypto system.

   Actions of the receiver:

   A server that receives a ClientHello with a TLS_QSH cipher suite MUST
   check the extension field to use the client's enumerated capabilities
   to guide its selection of an appropriate cipher suite.  The TLS_QSH
   cipher suite must be negotiated only if the server can successfully
   complete the handshake while using the listed quantum-safe
   cryptosystems from the client.

   The server will carry out a classic handshake with the client using a
   classical cipher suite (other than TLS_QSH) indicated by the client.
   The server will also select a (list of) supported QSHScheme(s),
   indexed by QSHSchemeID(s).  If server's public key(s) is required,
   the server will generate public/private keys corresponding to these
   QSHSchemeIDs.

   If a server does not understand the Extension, does not understand
   the list of quantum-safe encryption schemes, or is unable to complete
   the TLS_QSH handshake while restricting itself to the enumerated
   cryptosystems, it MUST NOT negotiate the use of a TLS_QSH cipher
   suite.   Depending on what other cipher suites are proposed by the
   client and supported by the server, this may result in a fatal
   handshake failure alert due to the lack of common cipher suites.

3.3.  Server Hello Extension

   This section specifies a TLS extension that can be included with the
   ServerHello message as described in RFC 4366 [RFC4366].

   When this extension is sent:

   The extensions MUST be sent along with any ServerHello message that



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   accepts TLS_QSH cipher suites.

   Meaning of this extension:

   This extension allows a server to notify the client the ID(s) and
   public key(s) for the quantum-safe encryption scheme(s) it chooses
   from the QSHSchemeIDList.

   Structure of this extension:

        struct {
            select (CipherSuite) {
                case TLS_QSH:
                    QSHPKList       serPKList
        } ServerHelloExtension;

   Actions of the sender:

   The server selects a number of QSHSchemeIDs in response to a
   ClientHelloExtension message.  The selection is based on client's
   preference and ReqSerPK field.  The QSHSchemeIDs selected MUST exist
   in the received QSHSchemeIDList.  For each scheme, the server sets
   QSHPK.id to the QSHSchemeID that it selects.  If the server is
   willing/requested to contribute its public key, the server will
   generate a pair of public/private keys, and set QSHPK.pubKey to this
   the public key; otherwise this field will be empty.  The server form
   the SerPKList with the list of QSHPK.

   Note: if the server sends no public keys in the Server Hello
   Extension, it MUST send at least one ciphertext in the EncryptedSerS
   at the Server Key Exchange message.

   Actions of the receiver:

   A client that receives a ServerHello message containing an extension
   will extract the agreed QSHSchemeIDs and the server's public keys
   from serPKList.  The client-generated secrets will be encrypted with
   server's ephemeral public keys as described in Section 3.5.

3.4.  Server Key Exchange

   When this message is sent:

   This message is sent in all implementations of this cipher suite.

   Meaning of this message:

   This message is used to send classical key exchange information to



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   the client.  It MAY also be used to send key material (encrypted by
   one or many of the client's public keys) to the client.

   Structure of this message:

   The TLS ServerKeyExchange message is extended as follows.

        struct {
            select (KeyExchangeAlgorithm) {
                case TLS_QSH:
                    QSHCipherList     encryptedSerS,
                    CipherSuite       classical_ciphersuite,
                    ServerKeyExchange classical_exchange
            } exchange_keys;
        } ServerKeyExchange;

   Actions of the sender:

   The server sets the CipherSuite field to the classical cipher suite.
   This MUST be one of the next preferable cipher suites other than
   TLS_QSH that was received in the ClientHello.

   The server sets classical_exchange to have the contents appropriate
   for the indicated classical cipher suite.

   If a number of client's public keys CPK1,...CPKn were received in the
   Client Hello Extension, the server:

        1. Selects k<=n of these public keys.

        2. For each of the public keys CPKi, generates a secret SerSi.
        The length in bytes of SerSi MUST be the lesser of (a) 48, the
        length of the classical master secret, and (b) the maximum
        plaintext input length for the corresponding encryption scheme
        (see Section 5).

        3. Encrypts the SerSi with PKi.

        4. Creates a QSHCipherList structure containing the encrypted
        secrets.

   Note: since it is required that each of the public keys in the
   ClientHelloExtension is for a distinct quantum-safe encryption
   scheme, the QSHCipherList unambiguously identifies which client
   public key corresponds to which server-generated ciphertext.

   The server-contributed keying material is:
        SerS = SerS1|SerS2|...|SerSk



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   Actions of the receiver:

   The client processes the ServerKeyExchange with KeyExchangeAlgorithm
   as in a classical handshake.  If EncryptedSerS is not NULL, the
   client decrypts each ciphertext in encryptedSerS using the client's
   secret key identified by QSHIDs from SerPKList (received from
   ServerHelloExtension) and obtains SerS. Otherwise, the client sets
   SerS to NULL.

3.5.  Client Key Exchange

   When this message is sent:

   This message is sent in all key exchange algorithms.

   Meaning of the message:

   This message is used to convey ephemeral data relating to the key
   exchange belonging to the client (such as its ephemeral ECDH public
   key).  It is also used to send client's quantum-safe keying material
   to the server.

   Structure of this message:

   The TLS ClientKeyExchange message is extended as follows.

        struct {
            select (KeyExchangeAlgorithm) {
                case QSH:
                    QSHcipher         encryptedCliS,
                    ClientKeyExchange classical_exchange
            } exchange_keys;
        } ClientKeyExchange;

   Actions of the sender:

   The client sets classical_exchange to have the contents appropriate
   for the indicated classical cipher suite.

   If a number of server's public keys SPK1,...SPKk were received in the
   Server Hello Extension, the client:

        1. For each of the public keys SPKi, generates a secret CliSi.
        The length in bytes of CliSi should be the lesser of (a) 48, the
        length of the classical master secret, and (b) the maximum
        plaintext input length for the corresponding encryption scheme
        (see Section 5).




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        2. Encrypts the CliSi with SPKi.

        3. Creates a QSHCipherList structure containing the encrypted
        secrets.

   Note: since it is required that each of the public keys in the Client
   Hello Extension is for a distinct quantum-safe encryption scheme, the
   QSHCipherList unambiguously identifies which server public key
   corresponds to which client-generated ciphertext.

   The client-contributed keying material is:
        CliS = CliS1|CliS2|...|CliSk.


   The final premaster secret negotiated by the client and the server is
   the concatenation of the classical premaster secret, SerS, and CliS
   in that order. A 48 bytes fixed length master secret is derived from
   the premaster secret at the end of the handshake, using a pseudo
   random function specified by the classical cipher suite (see Section
   8.1. RFC 5246 [RFC5246]).


   Actions of the receiver:

   The server processes the ClientKeyExchange with KeyExchangeAlgorithm
   as in a classical handshake.  If EncryptedCliS is received, the
   server decrypts the ciphertext(s) with the appropriate private secret
   key(s) and obtains CliS.  Otherwise, the server sets CliS to NULL.

   The final premaster secret negotiated by the client and the server is
   the concatenation of the classical premaster secret, SerS, and CliS
   in that order. A 48 bytes fixed length master secret is derived from
   the premaster secret at the end of the handshake, using a pseudo
   random function specified by the classical cipher suite (see Section
   8.1. RFC 5246 [RFC5246]).

4.  Cipher Suites

        CipherSuite TLS_QSH  = { 0x66 0x26 }

   Implementations that support this cipher suite MUST support at least
   one classical cipher suite.

5.  Specific information for Quantum Safe Scheme

5.1   NTRUEncrypt

   NTRUEncrypt parameter sets are identified by the values ntru_eess439



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   (0x0101), ntru_eess593 (0x0102), ntru_eess743 (0x0103) assigned in
   this document.

   For each of these parameter sets, the public key and ciphertext are
   Ring Elements as defined in [EESS1].  The encoded public key and
   ciphertext are the result of encoding the relevant Ring Element with
   RE2BSP as defined in [EESS1].

   For each parameter set the the maximum plaintext input length in
   bytes is as follows. This is used when determining the length of the
   client/server-generated secrets CliSi and SerSi as specified in
   sections 3.4 and 3.5.

        eess439  65
        eess593  86
        eess743  106

5.2.  LWE
   Encoding not defined in this document.

5.3.  HFE
   Encoding not defined in this document.

6.  Security Considerations

6.1.  Security, Authenticity and Forward Secrecy

   Security, authenticity and forward secrecy against classical
   computers are inherent from classical handshake mechanism.

6.2.  Quantum Security and Quantum Forward Secrecy

   The proposed handshake mechanism provides quantum security and
   quantum forward secrecy.

   Quantum resistant feature of QSHSchemes ensures a quantum attacker
   will not learn SerS and/or CliS.  A quantum attacker may learn
   classic handshake information.  Given an input X, the leftover hash
   lemma [LHL] ensures that one can extract Y bits that are almost
   uniformly distributed, where Y is asymptotic to the min-entropy of X.
   An adversary who has some partial knowledge about X, will have almost
   no knowledge about Y.  This guarantees the attacker will not learn
   the final premaster secret so long as SerS and/or CliS have enough
   entropy and remain secret.  This also guarantees the premaster secret
   is secure even if the client's and/or the server's long term keys are
   compromised.

6.3.  Quantum Authenticity



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   The proposed approach relies on the classical cipher suite for
   authenticity.  Thus, an attacker with quantum computing capability
   will be able to break the authenticity.

7.  IANA Considerations

   This document describes a new name spaces for use with the TLS
   protocol:

   o  QSHSchemeID

   Any additional assignments require IETF Consensus action [RFC2434].

8.  Acknowledgements

   Funding for the RFC Editor function is provided by the IETF
   Administrative Support Activity (IASA).


9.  References

9.1.  Normative References

   [EESS1]    Consortium for Efficient Embedded Security, "Efficient
              Embedded Security Standard #1: Implementation Aspects of
              NTRUEncrypt", March 2015.
              <https://github.com/NTRUOpenSourceProject/ntru-
              crypto/raw/master/doc/EESS1-2015v3.0.pdf>

   [FIPS180]  NIST, "Secure Hash Standard", FIPS 180-2, 2002.

   [FIPS186]  NIST, "Digital Signature Standard", FIPS 186-2, 2000.

   [LHL]      Impagliazzo, R., Levin, L., and Luby, M., "Pseudo-random
              generation from one-way functions", 1989.

   [PKCS1]    RSA Laboratories, "PKCS#1: RSA Encryption Standard version
              1.5", PKCS 1, November 1993

   [REAL]     "RFC Editor Abbreviations List", September 2013,
              <https://www.rfc-editor.org/rfc-style-
              guide/abbrev.expansion.txt/>.

   [RFC2119]  Bradner, S., "Key Words for Use in RFCs to Indicate
              Requirement Levels", RFC 2119, March 1997.

   [RFC2246]  Dierks, T. and C. Allen, "The TLS Protocol Version 1.0",
              RFC 2246, January 1999.



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   [RFC2434]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in RFCs", RFC 2434, October
              1998.

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

   [RFC4366]  Blake-Wilson, S., Nysrom, M., Hopwood, D., Mikkelsen, J.,
              and T. Wright, "Transport Layer Security (TLS)
              Extensions", RFC 4366, April 2006.

   [RFC4492]  Blake-Wilson, S., Bolyard, N., Gupta, V., Hawk, C., and B.
              Moeller, "Elliptic Curve Cryptography (ECC) Cipher Suites
              for Transport Layer Security (TLS)", RFC 4492, May 2006.

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

   [TLS1.3]   E. Rescorla, "The Transport Layer Security (TLS) Protocol
              Version 1.3", draft-ietf-tls-tls13-05, March 2015.


8.2.  Informative References

   [RFC5990]  Randall, J., Kaliski, B., Brainard, J. and Turner S., "Use
              of the RSA-KEM Key Transport Algorithm in the
              Cryptographic Message Syntax (CMS)", RFC 5990, September
              2010.

   [RFC5859]  Krawczyk, H., Eronen, P., "HMAC-based Extract-and-Expand
              Key Derivation Function (HKDF)", RFC 5859, May 2010.




















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Authors' Addresses

   John M. Schanck
   Security Innovation, US
   and
   University of Waterloo, Canada
   jschanck@securityinnovation.com


   William Whyte
   Security Innovation, US
   wwhyte@securityinnovation.com


   Zhenfei Zhang
   Security Innovation, US
   zzhang@securityinnovation.com


































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Copyright Notice

   IETF Trust Legal Provisions of 28-dec-2009, Section 6.b(i), paragraph
   2: Copyright (c) 2015 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   IETF Trust Legal Provisions of 28-dec-2009, Section 6.b(ii),
   paragraph 3: 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.






































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