\
INTERNET-DRAFT                                             J. M. Schanck
Intended Status: Experimental          Security Innovation & U. Waterloo
Expires: 2016-10-04                                             W. Whyte
                                                     Security Innovation
                                                                Z. Zhang
                                                     Security Innovation
                                                              2016-04-04


                 Quantum-Safe Hybrid (QSH) Ciphersuite
             for Transport Layer Security (TLS) version 1.3
                      draft-whyte-qsh-tls13-02.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 1.3.  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 2016-10-04.

   Update from last version: keeping alive till TLS WG review.




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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Modular design for quantum-safe hybrid handshake . . . . . . .  4
   3.  Data Structures and Computations . . . . . . . . . . . . . . .  7
     3.1.  Data structures for Quantum-safe Crypto Schemes  . . . . .  7
     3.2.  Client Hello Extensions  . . . . . . . . . . . . . . . . .  9
     3.3.  HelloRetryRequest Extensions . . . . . . . . . . . . . . . 11
     3.4.  Server Key Share Extension . . . . . . . . . . . . . . . . 12
   4.  Cipher Suites  . . . . . . . . . . . . . . . . . . . . . . . . 14
   5.  Specific information for Quantum Safe Scheme . . . . . . . . . 14
     5.1.  NTRUEncrypt  . . . . . . . . . . . . . . . . . . . . . . . 14
     5.2.  LWE  . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
     5.3.  HFE  . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
     5.4.  McEliece/McBits  . . . . . . . . . . . . . . . . . . . . . 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.  Compatibility with TLS 1.2 and earlier version . . . . . . . . 15
   8.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 15
   9.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 16
   10.  References  . . . . . . . . . . . . . . . . . . . . . . . . . 16
     10.1.  Normative References  . . . . . . . . . . . . . . . . . . 16
     10.2.  Informative References  . . . . . . . . . . . . . . . . . 17
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 18
   Copyright Notice . . . . . . . . . . . . . . . . . . . . . . . . . 18
























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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 1.3 [RFC2246], [RFC4346], [RFC5246],
   [TLS1.3].  ECC is enabled in RFC 4492 [RFC4492] and adopted in TLS
   version 1.2 [RFC5246] and version 1.3 [TLS1.3].  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 1.3 [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 1.3 without any
   introduction of extra cipher suites.  Yet, it allows the flexibility
   to include new and advanced quantum-safe encryption schemes at
   present and in the future.

   Extensions to TLS 1.2 [RFC5246] and earlier versions can be found in
   [QSH12].

   The remainder of this document is organized as follows.  Section 2
   provides an overview of the modular design of quantum-safe handshake
   for TLS 1.3.  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 discusses compatibility with other versions of TLS.
   Section 8 describes IANA considerations for the name spaces created
   by this document.  Section 9 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].



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

2.  Modular design for quantum-safe hybrid handshake

   This document introduces a modular approach to including new quantum-
   safe key exchange algorithms within TLS 1.3, 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
       ClientKeyShare            -------->
                                 <--------       HelloRetryRequest

       ClientHello
       ClientKeyShare            -------->
                                                       ServerHello
                                                    ServerKeyShare
                                            {EncryptedExtensions*}
                                                    {Certificate*}
                                            {CertificateRequest*+}
                                              {CertificateVerify*}
                                 <--------              {Finished}
       {Certificate*+}
       {CertificateVerify*+}
       {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 1.3 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
   HelloRetryRequest, and the ServerKeyShare messages.  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



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   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 and
   3.

   Figure 2 illustrates the data flow of a zero round trip quantum-safe
   handshake for TLS. This handshake is proceeded when 1) the classical
   key exchange is also zero round trip, and 2) the server supports the
   QSH schemes from QSHPKList.

       Client                                               Server

       ClientHelloExtension
       + qshDataExtension
         (QSHPKList)
       + qshNegotiateExtension
         (QSHSchemeIDList)       -------->
                                              EncryptedExtensions*
                                                + qshDataExtension
                                                   (QSHCipherList)
                                 <--------              {Finished}
       {Finished}                -------->

       ClassicSecret|QSHSecret   <-------> ClassicSecret|QSHSecret

             * previously known as SeverKeyShareExtensions
             + additional data

                 Figure 2: Additional cryptographic data
                   for a zero round trip TLS handshake

   In the case that the server does not support the QSH schemes from
   QSHPKList, the server will reply with a HelloRetryRequest, which
   results into a full handshake.

       Client                                               Server

       ClientHelloExtensions
       + qshDataExtension
         (QSHPKList)
       + qshNegotiateExtension
         (QSHSchemeIDList)       -------->
                                       HelloRetryRequestExtensions
                                           + qshNegotiateExtension
                                 <-------- (AcceptQSHSchemeIDList)

       ClientHelloExtensions
       + qshDataExtension



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         (QSHPKList)             -------->
                                              EncryptedExtensions*
                                                + qshDataExtension
                                                   (QSHCipherList)
                                 <--------              {Finished}
       {Finished}                -------->

       ClassicSecret|QSHSecret   <-------> ClassicSecret|QSHSecret

             * previously known as SeverKeyShareExtensions
             + additional data

                 Figure 3: Additional cryptographic data
                        for a full TLS 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). In addition there will be two
   potential extension fields, indicating qshData and qshNegotiate
   extensions.

   The ClientHelloExtension field MUST have qshData extension field:
   o   QSHPKList: a list of distinct public keys for QSH Scheme
                  from the client, each public key for a distinct
                  quantum safe encryption scheme supported by the
                  client.

   The ClientHelloExtension field MAY have qshNegotiate extension
   field:
   o   QSHSchemeIDList:
                  a list of distinct QSHSchemeIDs from the client,
                  each ID represents a quantum safe encryption
                  scheme/parameter set supported by the client

   QSHSchemeIDList must not list the scheme IDs whose public key is
   already included in the QSHPKList.

   If the server supports QSH schemes/parameter sets for the public keys
   received from QSHPKList, the server will proceed the zero round trip
   handshake, provided that the zero round trip is also permitted by
   classical handshake.  If not, the server will pick a (list of)
   QSHSchemeID(s) from the QSHSchemeIDList to form the
   AcceptQSHSchemeIDList, and request public keys for those schemes in a
   HelloRetryRequest message.  If the server does not support any of the
   QSH schemes from either QSHPKList or QSHSchemeIDList, the server will
   abort the handshake.

   The extension field of the HelloRetryRequest message MUST have an



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   qshNegotiate extension field:
   o   AcceptQSHSchemeIDList:
                  a list of distinct QSHSchemeIDs from the server,
                  each ID represents a quantum safe encryption
                  scheme/parameter set supported/selected by the server

   The ServerKeyShare message contains an indication of the classical
   cipher suite selected, and the ServerKeyShare material appropriate to
   that cipher suite.  Additionally, the ServerKeyShareExtension (a.k.a.
   EncryptedExtension) field message MUST contain a qshData extension
   field listing ciphertexts:
   o   QSHCipherList:
                  a list of ciphertests
                  [Encrypt_QSHPK1(QSHS1)]|[Encrypt_QSHPK2(QSHS2)]|...
                  where the QSH secret keying material is
                  QSHSecret = QSHS1|QSHS2|..., and QSHPKi is from
                  QSHPKList.

   The final premaster secret negotiated by the client and the server is
   the concatenation of the classical premaster secret, QSHSecret,
   QSHPK1|QSHPK2|... 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 v1.3 [TLS1.3].
   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_eess443 (0x0101),
            ntru_eess587 (0x0102),
            ntru_eess743 (0x0103),
            reserved     (0x0102..0x01FF),
            lwe_XXX      (0x0201),
            reserved     (0x0202..0x02FF),
            hfe_XXX      (0x0301),
            reserved     (0x0302..0x03FF),
            mcbits_XXX   (0x0401),



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            reserved     (0x0402..0x04FF),
            reserved     (0x0500..0xFEFF),
            (0xFFFF)
        } QSHSchemeID;

   ntru_eess443, 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.

   mcbits_XXX, etc:   Indicates parameters for McEliece encryption
      scheme instantiated with McBits parameter set.  The name of the
      parameters defined here are not specified in this document.

   See Section 5 for specific information for quantum safe scheme.

   The QSHSchemes name space is maintained by IANA [IANA].  See Section
   8 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<1..2^16-1>
        } QSHIDList;

   The QSHSchemeIDList and AcceptQSHSchemeIDList are two instances of
   QSHIDList structure. This structure defines a list of QSHSchemeIDs,
   each representing a quantum safe encryption scheme.

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

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

   The structure of public keys send from the client to the server,
   namely, QSHPK, has two fields: QSHSchemeID specifies the



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   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.

   NOTE: the QSHPK is a opaque of up to (2^24-1) bytes.  This may exceed
   the size limitation of extensions (2^16-1).

   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 send from the server to the client,
   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].

   NOTE: To support larger QSH quantum-safe cryptosystems it may be
   necessary to raise the maximum size of an extension to 2^24-1 octets.

   When these extensions are sent:

   When a client wish to negotiate a handshake using TLS_QSH approach,
   the extensions MUST be sent along with the first ClientHello message.
   Follow-up ClientHello message MAY also use these extensions when a
   zero round trip handshake failed.

   Meaning of these extensions:




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   qshNegotiate extension allows a client to send a QSHSchemeIDList that
   enumerates QSHSchemeIDs for supported quantum safe cryptosystems.
   qshData extension allows a client to send a QSHPKList of public keys
   for quantum-safe encryption schemes.

   Note:  QSHSchemeID MUST be distinct in QSHSchemeIDList.  If
   qshNegotiate extension and qshData extension are both send within a
   same ClientHello extension, QSHSchemeIDList must not enumerate
   QSHschemeIDs whose public keys are already in QSHPKList.

   Structure of the extensions:

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

        enum {
             qshNegotiate(0x18)
             qshData(0x19)
        } ExtensionType;

   qshNegotiate (Supported TLS_QSH Extension): Indicates the list of
      QSHSchemeIDs supported by the client.  For this extension, the
      opaque extension_data field MAY contain QSHSchemeIDList and its
      field can be NULL.

   qshData (Supported TLS_QSH Extension): Indicates the list of
      QSHScheme public keys supported by the client.  For this
      extension, the opaque extension_data field MUST contain QSHPKList
      and its field is not NULL.

        struct {
            select (ExtensionType) {
                case qshNegotiate:
                    QSHSchemeIDList qshSchemeIDList,
                case qshData:
                    QSHPKList       qshPKList,
            }
        } ClientHelloExtension;

   Items in both qshPKList and 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




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   An example of a qshNegotiate extension field will therefore look as
   follows:

        00 18 | extension length | 00 04 01 01 01 02 | ...

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

   Actions of the sender:

   If the ClientHello message starts a fresh handshake, a client that
   proposes TLS_QSH approach in its ClientHello message appends both
   qshNegotiate and qshData extensions (along with any others),
   enumerating the supported quantum-safe crypto systems that the client
   wish to use to negotiate keys with the server.

   If the ClientHello message is in response to a HelloRetryRequest, the
   client appends qshData extension (along with any others), enumerating
   the QSHScheme public keys supported by the server.

   Actions of the receiver:

   A server that receives a ClientHello with a TLS_QSH approach MUST
   check the extension field to use the client's enumerated capabilities
   to guide its selection of appropriate quantum safe encryption
   algorithms.  The TLS_QSH approach 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 indicated by the ClientHello message.  If the
   server supports QSHSchemes of public keys included in the qshData
   extension, the server will include a QSHCipherList in the
   EncryptedExtension field of ServerKeyShare message; if not, the
   server will select a (list of) supported QSHScheme(s), indexed by
   QSHSchemeID(s),  and form the AcceptQSHSchemeIDList with its selected
   schemes. This list will be send back to the client via the extension
   field of HelloRetryRequest.

   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 approach.
   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.  HelloRetryRequest Extensions



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   This section specifies a TLS extension that can be included with the
   HelloRetryRequest message as described in [TLS1.3].

   When this extension is sent:

   The server will send this message in response to a ClientHello
   message where the extension fields contains a extension type quantum-
   safe-hybrid, when it was able to find an acceptable set of QSHSchemes
   from qshNegotiate but not from qshData.  If it cannot find such a
   match, it will respond with a handshake failure alert.

   Meaning of this extension:

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

   Structure of this extension:

        struct {
            select (ExtensionType) {
                case qshNegotiate:
                    QSHSchemeIDList acceptQSHSchemeIDList,
            }
        } HelloRetryRequestExtension;

   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.  The QSHSchemeIDs selected MUST exist in the received
   QSHSchemeIDList.  The server form the acceptQSHSchemeIDList with the
   list of selected QSHSchemeIDs.

   Actions of the receiver:

   A client that receives a HelloRetryRequest message containing an
   extension type qshNegotiate will extract the agreed QSHSchemeIDs and
   from the acceptQSHSchemeIDList.  Those QSHSchemeIDs will be used when
   the client generates another ClientHello message.

3.4.  Server Key Share Extension

   [[This may be later on changed into *EncryptedExtensions* let's see
   how TLS 1.3 will define it]]

   NOTE: To support larger QSH quantum-safe cryptosystems it may be
   necessary to raise the maximum size of an extension to 2^24-1 octets.



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   When this message is sent:

   The server will include this extension field in response to a
   ClientHello message with extension type qshData.

   Meaning of this message:

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

   Structure of this message:

   The TLS ServerKeyShareExtension field is extended as follows.

        struct {
            select (ExtensionType) {
                case qshData:
                    QSHCipherList     encryptedQSHSecret,
            }
        } ServerKeyShare;

   Actions of the sender:


   The server extracts client's public keys QSHPK1, ..., QSHPKn from the
   qshData field in the received Client Hello extensions.  For each of
   the public keys QSHPKi, generates a secret QSHSi.  The length in
   bytes of QSHSi 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).

   The server then encrypts the QSHSi with QSHPKi, and form the
   encryptedQSHSecret with those ciphertexts.

   The QSH keying material is:
        QSHSecret = QSHS1|QSHS2|...|QSHSk

   The server will finally form the premaster secret as a concatenation
   of the classical premaster secret (negotiated via classical exchange,
   i.e., Key Share messages), QHSSecret, and QSHPK (the public keys that
   encrypts the message).  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 client processes the ServerKeyShareExtension



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   by decrypting each ciphertext in encryptedQSHSecret using the
   client's secret key and obtaining QSHSecret.

   The client will finally form the premaster secret as a concatenation
   of the classical premaster secret (negotiated via classical exchange,
   i.e., Key Share messages), QHSSecret, and QSHPK (the public keys that
   encrypts the message).  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

   The TLS_QSH approach does not introduce any additional cipher suite
   identifiers.

5.  Specific information for Quantum Safe Scheme

   Selection criteria for qauntum-safe cryptography to be used in this
   TLS_QSH approach can be found at [QSHPKC].  Also see [PQCRY] for
   initial recommendations of quantum safe cryptography from EU's
   PQCRYPTO project.

5.1.  NTRUEncrypt

   NTRUEncrypt parameter sets are identified by the values ntru_eess443
   (0x0101), ntru_eess587 (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.

        eess443  49
        eess587  76
        eess743  106

5.2.  LWE
   Encoding not defined in this document.

5.3.  HFE
   Encoding not defined in this document.



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5.4.  McEliece/McBits
   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 QSH keying material S.  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 S has enough entropy and
   remains 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

   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.  Compatibility with TLS 1.2 and earlier version

   Compatibility with TLS 1.2 and earlier version can be found in
   [QSH12].

8.  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].
   Process for determining whether a public key algorithm is in fact
   quantum-safe, and therefore entitled to a QSHSchemeId, is not



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   specified in this document and may be established by the TLS working
   group as it sees fit.  For example, TLS WG may require that
   algorithms are vetted in some sense by CFRG or have been published in
   a standard by a recognized international standards body such as IEEE
   or ANSI X9.

9.  Acknowledgements

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

   We wish to thank Douglas Stebila, [[[names]]] for helpful
   discussions.

10.  References

10.1.  Normative References

   [EESS1]    Consortium for Efficient Embedded Security, "Efficient
              Embedded Security standards (EESS) #1", March 2015,
              <https://github.com/NTRUOpenSourceProject/ntru-
              crypto/blob/master/doc/EESS1-2015v3.0.pdf/>.

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

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

   [H2020]    Lange, T., "PQCRYPTO project in the EU", April, 2015.
              <http://pqcrypto.eu.org/slides/20150403.pdf>

   [HOF15]    Hoffstein, J., Pipher, J., Schanck, J., Silverman, J.,
              Whyte, W., and Zhang, Z., "Choosing Parameters for
              NTRUEncrypt", 2015. <https://eprint.iacr.org/2015/708>

   [LIN11]    Lindner, R., and Peikert, C., "Better Key Sizes (and
              Attacks) for LWE-Based Encryption", 2011.

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

   [MCBIT]    Bernstein, D., Chou, T., and Schwabe, P., "McBits: Fast
              Constant-Time Code- Based Cryptography", 2013.

   [MCELI]    McEliece, R., "A Public-Key Cryptosystem Based On
              Algebraic Coding Theory", 1978.

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



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   [PQCRY]    PQCRYPTO, "Initial recommendations of long-term secure
              post-quantum systems".
              <http://pqcrypto.eu.org/docs/initial-recommendations.pdf>

   [QSH12]    Schanck, J., Whyte, W., and Zhang, Z., "Quantum-Safe
              Hybrid (QSH) Ciphersuite for Transport Layer Security
              (TLS) version 1.2", draft-whyte-qsh-tls12-00, July 2015.

   [QSHPKC]   Schanck, J., Whyte, W., and Zhang, Z., "Criteria for
              selection of public-key cryptographic algorithms for
              quantum-safe hybrid cryptography", draft-whyte-select-pkc-
              qsh-00.txt, Sep 2015.

   [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.

   [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.


10.2.  Informative References

   [RFC5990]  Randall, J., Kaliski, B., Brainard, J. and Turner S., "Use



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              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.

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

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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