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Network Working Group                                         T. Taubert
Internet-Draft                                                   C. Wood
Intended status: Informational                               Apple, Inc.
Expires: September 10, 2020                                March 9, 2020

                       SPAKE2+, an Augmented PAKE


   This document describes SPAKE2+, a Password Authenticated Key
   Exchange (PAKE) protocol run between two parties for deriving a
   strong shared key with no risk of disclosing the password.  SPAKE2+
   is an augmented PAKE protocol, as only one party has knowledge of the
   password.  This method is simple to implement, compatible with any
   prime order group and is computationally efficient.

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
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   This Internet-Draft will expire on September 10, 2020.

Copyright Notice

   Copyright (c) 2020 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
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   include Simplified BSD License text as described in Section 4.e of

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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Requirements Notation . . . . . . . . . . . . . . . . . . . .   3
   3.  Definition of SPAKE2+ . . . . . . . . . . . . . . . . . . . .   3
   4.  Key Schedule and Key Confirmation . . . . . . . . . . . . . .   6
   5.  Ciphersuites  . . . . . . . . . . . . . . . . . . . . . . . .   7
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   9
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   9
   8.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .   9
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   9
   Appendix A.  Algorithm used for Point Generation  . . . . . . . .  11
   Appendix B.  Test Vectors . . . . . . . . . . . . . . . . . . . .  13
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  16

1.  Introduction

   This document describes SPAKE2+, a Password Authenticated Key
   Exchange (PAKE) protocol run between two parties for deriving a
   strong shared key with no risk of disclosing the password.  SPAKE2+
   is an augmented PAKE protocol, as only one party makes direct use of
   the password during the execution of the protocol.  The other party
   only needs a verification value at the time of the protocol execution
   instead of the password.  The verification value can be computed
   once, during an offline initialization phase.  The party using the
   password directly would typically be a client, and acts as a prover,
   while the other party would be a server, and acts as verifier.

   The protocol is augmented in the sense that it provides some
   resilience to the compromise or extraction of the verification value.
   The design of the protocol forces the adversary to recover the
   password from the verification value to successful execute the
   protocol.  Hence this protocol can be advantageously combined with a
   salted Password Hashing Function to increase the cost of the recovery
   and slow down attacks.  The verification value cannot be used
   directly to successfully run the protocol as a prover, making this
   protocol more robust than balanced PAKEs which don't benefit from
   Password Hashing Functions to the same extend.

   This augmented property is especially valuable in scenarios where the
   execution of the protocol is constrained and the adversary can not
   query the salt of the password hash function ahead of the attack.
   Constraints may consist in being in physical proximity through a
   local network or when initiation of the protocol requires a first
   authentication factor.

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   This password-based key exchange protocol is compatible with any
   group.  It only relies on group operations making it simple and
   computationally efficient.  It also has a security proof.
   Predetermined parameters for a selection of commonly used groups are
   also provided.

   This document has content split out from a related document
   specifying SPAKE2 [SPAKE2].

2.  Requirements Notation

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

3.  Definition of SPAKE2+

3.1.  Offline Initialization

   Let G be a group in which the computational Diffie-Hellman (CDH)
   problem is hard.  Suppose G has order p*h where p is a large prime; h
   will be called the cofactor.  Let I be the unit element in G, e.g.,
   the point at infinity if G is an elliptic curve group.  We denote the
   operations in the group additively.  We assume there is a
   representation of elements of G as byte strings: common choices would
   be SEC1 uncompressed or compressed [SEC1] for elliptic curve groups
   or big endian integers of a fixed (per-group) length for prime field
   DH.  We fix two elements M and N in the prime-order subgroup of G as
   defined in the table in this document for common groups, as well as a
   generator P of the (large) prime-order subgroup of G.  P is specified
   in the document defining the group, and so we do not repeat it here.

   || denotes concatenation of strings.  We also let len(S) denote the
   length of a string in bytes, represented as an eight-byte little-
   endian number.  Finally, let nil represent an empty string, i.e.,
   len(nil) = 0.

   KDF is a key-derivation function that takes as input a salt,
   intermediate keying material (IKM), info string, and derived key
   length L to derive a cryptographic key of length L.  MAC is a Message
   Authentication Code algorithm that takes a secret key and message as
   input to produce an output.  Let Hash be a hash function from
   arbitrary strings to bit strings of a fixed length.  Common choices
   for Hash are SHA256 or SHA512 [RFC6234].  Let PBKDF be a Password-
   Based Key Derivation Function designed to slow down brute-force
   attackers.  Brute-force resistance may be obtained through various

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   computation hardness parameters such as memory or CPU cycles, and are
   typically configurable.  Scrypt [RFC7914] and Argon2 are common
   examples of PBKDF functions.  PBKDF and hardness parameters selection
   for the PBKDF are out of scope of this document.  Section 5 specifies
   variants of KDF, MAC, and Hash suitable for use with the protocols
   contained herein.

   Let A and B be two parties.  A and B may also have digital
   representations of the parties' identities such as Media Access
   Control addresses or other names (hostnames, usernames, etc).  A and
   B may share Additional Authenticated Data (AAD) of length at most
   2^16 - 1 bits that is separate from their identities which they may
   want to include in the protocol execution.  One example of AAD is a
   list of supported protocol versions if SPAKE2+ were used in a higher-
   level protocol which negotiates the use of a particular PAKE.
   Including this list would ensure that both parties agree upon the
   same set of supported protocols and therefore prevent downgrade

3.2.  Protocol Flow

   SPAKE2+ is a two round protocol that establishes a shared secret with
   an additional round for key confirmation.  Prior to invocation, A and
   B are provisioned with information such as the input password needed
   to run the protocol.  A preamble exchange may occur in order to
   communicate identities, protocol version and PBKDF parameters related
   to the verification value.  Details of the preamble phase is out of
   scope of this document.  During the first round, A, the prover, sends
   a public share pA to B, the verifier, and B responds with its own
   public share pB.  Both A and B then derive a shared secret used to
   produce encryption and authentication keys.  The latter are used
   during the second round for key confirmation.  (Section 4 details the
   key derivation and confirmation steps.)  In particular, B sends a key
   confirmation message cB to A, and A responds with its own key
   confirmation message cA.  (Note that pB and cB MAY be sent in the
   same message.)  Both parties MUST NOT consider the protocol complete
   prior to receipt and validation of these key confirmation messages.

   This sample trace is shown below.

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                      A                           B

                      |         (Preamble)        |
                      |<- - - - - - - - - - - - ->|
                      |                           |
                      |       (setup protocol)    |
         (compute pA) |             pA            |
                      |             pB            | (compute pB)
                      |                           |
                      |       (derive secrets)    | (compute cB)
                      |             cB            |
         (compute cA) |             cA            |

3.3.  SPAKE2+

   This protocol appears in [TDH].  Let w0 and w1 be two integers
   derived by hashing the password pw with the identities of the two
   participants, A and B.  Specifically, w0s || w1s = PBKDF(len(pw) ||
   pw || len(A) || A || len(B) || B), and then computing w0 = w0s mod p
   and w1 = w1s mod p.  If both identities A and B are absent, then
   w0s || w1s = PBKDF(pw), i.e., the length prefix is omitted as in
   Section 3.1.  The party B stores the verification value pair L=w1*P
   and w0.

   Note that standards such as NIST.SP.800-56Ar3 suggest taking mod p of
   a hash value that is 64 bits longer than that needed to represent p
   to remove statistical bias introduced by the modulation.  Protocols
   using this specification must define the method used to compute w0
   and w1: it may be necessary to carry out various forms of
   normalization of the password before hashing [RFC8265].  The hashing
   algorithm SHOULD be a PBKDF so as to slow down brute-force attackers.

   When executing SPAKE2+, A selects x uniformly at random from the
   numbers in the range [0, p), and lets X=x*P+w0*M, then transmits pA=X
   to B.  Upon receipt of X, A computes h*X and aborts if the result is
   equal to I.  B then selects y uniformly at random from the numbers in
   [0, p), then computes Y=y*P+w0*N, and transmits pB=Y to A.

   A computes Z as h*x*(Y-w0*N), and V as h*w1*(Y-w0*N).  B computes Z
   as h*y*(X- w0*M) and V as h*y*L.  Both share Z and V as common
   values.  It is essential that both Z and V be used in combination
   with the transcript to derive the keying material.  The protocol
   transcript encoding is shown below.

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               TT = len(A) || A || len(B) || B || len(X) || X
                 || len(Y) || Y || len(Z) || Z || len(V) || V
                 || len(w0) || w0

   If an identity is absent, it is omitted from the transcript entirely.
   For example, if both A and B are absent, then TT = len(X) || X ||
   len(Y) || Y || len(Z) || Z || len(w0) || w0.  Likewise, if only A is
   absent, TT = len(B) || B || len(X) || X || len(Y) || Y || len(Z) ||
   Z || len(w0) || w0.  This must only be done for applications in which
   identities are implicit.  Otherwise, the protocol risks Unknown Key
   Share attacks (discussion of Unknown Key Share attacks in a specific
   protocol is given in [I-D.ietf-mmusic-sdp-uks].

   Upon completion of this protocol, A and B compute shared secrets Ke,
   KcA, and KcB as specified in Section 4.  B MUST send A a key
   confirmation message Fb so both parties agree upon these shared
   secrets.  This confirmation message Fb is computed as a MAC over the
   received share (pA) using KcB.  Specifically, B computes Fb =
   MAC(KcB, pA).  After receipt and verification of B's confirmation
   message, A MUST send B a confirmation message using a MAC computed
   equivalently except with the use of pB and KcA.  Key confirmation
   verification requires computing F and checking for equality against
   that which was received.

4.  Key Schedule and Key Confirmation

   The protocol transcript TT, as defined in Section Section 3.3, is
   unique and secret to A and B.  Both parties use TT to derive shared
   symmetric secrets Ke and Ka as Ke || Ka = Hash(TT).  The length of
   each key is equal to half of the digest output, e.g., |Ke| = |Ka| =
   128 bits for SHA-256.

   Both endpoints use Ka to derive subsequent MAC keys for key
   confirmation messages.  Specifically, let KcA and KcB be the MAC keys
   used by A and B, respectively.  A and B compute them as KcA || KcB =
   KDF(nil, Ka, "ConfirmationKeys" || AAD), where AAD is the associated
   data each given to each endpoint, or nil (empty string) if none was
   provided.  AAD may also include a string identifying the protocol,
   ciphersuite and all its parameters, including the definition of the
   group, and the element M and N.  It may be omitted.  The length of
   each of KcA and KcB is equal to half of the KDF output, e.g., |KcA|
   = |KcB| = 128 bits for HKDF with SHA256.

   The resulting key schedule for this protocol, given transcript TT and
   additional associated data AAD, is as follows.

           TT  -> Hash(TT) = Ka || Ke
           AAD -> KDF(nil, Ka, "ConfirmationKeys" || AAD) = KcA || KcB

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   A and B output Ke as the shared secret from the protocol.  Ka and its
   derived keys (KcA and KcB) are not used for anything except key

5.  Ciphersuites

   This section documents SPAKE2+ ciphersuite configurations.  A
   ciphersuite indicates a group, cryptographic hash algorithm, and pair
   of KDF and MAC functions, e.g., SPAKE2+-P256-SHA256-HKDF-HMAC.  This
   ciphersuite indicates a SPAKE2+ protocol instance over P-256 that
   uses SHA256 along with HKDF [RFC5869] and HMAC [RFC2104] for G, Hash,
   KDF, and MAC functions, respectively.

   |        G         |      Hash     |     KDF     |       MAC        |
   |      P-256       |     SHA256    |     HKDF    |  HMAC [RFC2104]  |
   |                  |   [RFC6234]   |  [RFC5869]  |                  |
   |                  |               |             |                  |
   |      P-256       |     SHA512    |     HKDF    |  HMAC [RFC2104]  |
   |                  |   [RFC6234]   |  [RFC5869]  |                  |
   |                  |               |             |                  |
   |      P-384       |     SHA256    |     HKDF    |  HMAC [RFC2104]  |
   |                  |   [RFC6234]   |  [RFC5869]  |                  |
   |                  |               |             |                  |
   |      P-384       |     SHA512    |     HKDF    |  HMAC [RFC2104]  |
   |                  |   [RFC6234]   |  [RFC5869]  |                  |
   |                  |               |             |                  |
   |      P-512       |     SHA512    |     HKDF    |  HMAC [RFC2104]  |
   |                  |   [RFC6234]   |  [RFC5869]  |                  |
   |                  |               |             |                  |
   |   edwards25519   |     SHA256    |     HKDF    |  HMAC [RFC2104]  |
   |    [RFC7748]     |   [RFC6234]   |  [RFC5869]  |                  |
   |                  |               |             |                  |
   |    edwards448    |     SHA512    |     HKDF    |  HMAC [RFC2104]  |
   |    [RFC7748]     |   [RFC6234]   |  [RFC5869]  |                  |
   |                  |               |             |                  |
   |      P-256       |     SHA256    |     HKDF    |   CMAC-AES-128   |
   |                  |   [RFC6234]   |  [RFC5869]  |    [RFC4493]     |
   |                  |               |             |                  |
   |      P-256       |     SHA512    |     HKDF    |   CMAC-AES-128   |
   |                  |   [RFC6234]   |  [RFC5869]  |    [RFC4493]     |

                       Table 1: SPAKE2+ Ciphersuites

   The following points represent permissible point generation seeds for
   the groups listed in the Table Table 1, using the algorithm presented

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   in Appendix A.  These bytestrings are compressed points as in [SEC1]
   for curves from [SEC1].

   For P256:

   M =
   seed: 1.2.840.10045.3.1.7 point generation seed (M)

   N =
   seed: 1.2.840.10045.3.1.7 point generation seed (N)

   For P384:

   M =
   seed: point generation seed (M)

   N =
   seed: point generation seed (N)

   For P521:

   M =
   seed: point generation seed (M)

   N =
   seed: point generation seed (N)

   For edwards25519:

   M =
   seed: edwards25519 point generation seed (M)

   N =
   seed: edwards25519 point generation seed (N)

   For edwards448:

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   M =
   seed: edwards448 point generation seed (M)

   N =
   seed: edwards448 point generation seed (N)

6.  Security Considerations

   SPAKE2+ appears in [TDH] along with a path to a proof that server
   compromise does not lead to password compromise under the DH
   assumption (though the corresponding model excludes pre-computation

   Elements received from a peer MUST be checked for group membership:
   failure to properly validate group elements can lead to attacks.
   Beyond the cofactor multiplication checks to ensure that these
   elements are in the prime order subgroup of G, it is essential that
   endpoints verify received points are members of G.

   The choices of random numbers MUST BE uniform.  Randomly generated
   values (e.g., x and y) MUST NOT be reused; such reuse may permit
   dictionary attacks on the password.

7.  IANA Considerations

   No IANA action is required.

8.  Acknowledgments

   Thanks to Ben Kaduk and Watson Ladd, from which this specification
   originally emanates.

9.  References

9.1.  Normative References

   [RFC2104]  Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed-
              Hashing for Message Authentication", RFC 2104,
              DOI 10.17487/RFC2104, February 1997,

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   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,

   [RFC4493]  Song, JH., Poovendran, R., Lee, J., and T. Iwata, "The
              AES-CMAC Algorithm", RFC 4493, DOI 10.17487/RFC4493, June
              2006, <https://www.rfc-editor.org/info/rfc4493>.

   [RFC5480]  Turner, S., Brown, D., Yiu, K., Housley, R., and T. Polk,
              "Elliptic Curve Cryptography Subject Public Key
              Information", RFC 5480, DOI 10.17487/RFC5480, March 2009,

   [RFC5869]  Krawczyk, H. and P. Eronen, "HMAC-based Extract-and-Expand
              Key Derivation Function (HKDF)", RFC 5869,
              DOI 10.17487/RFC5869, May 2010,

   [RFC6234]  Eastlake 3rd, D. and T. Hansen, "US Secure Hash Algorithms
              (SHA and SHA-based HMAC and HKDF)", RFC 6234,
              DOI 10.17487/RFC6234, May 2011,

   [RFC7748]  Langley, A., Hamburg, M., and S. Turner, "Elliptic Curves
              for Security", RFC 7748, DOI 10.17487/RFC7748, January
              2016, <https://www.rfc-editor.org/info/rfc7748>.

   [RFC7914]  Percival, C. and S. Josefsson, "The scrypt Password-Based
              Key Derivation Function", RFC 7914, DOI 10.17487/RFC7914,
              August 2016, <https://www.rfc-editor.org/info/rfc7914>.

   [RFC8032]  Josefsson, S. and I. Liusvaara, "Edwards-Curve Digital
              Signature Algorithm (EdDSA)", RFC 8032,
              DOI 10.17487/RFC8032, January 2017,

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

              Elliptic Curve Cryptography", version 2.0", May 2009.

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9.2.  Informative References

              Thomson, M. and E. Rescorla, "Unknown Key Share Attacks on
              uses of TLS with the Session Description Protocol (SDP)",
              draft-ietf-mmusic-sdp-uks-07 (work in progress), August

   [REF]      Abdalla, M. and D. Pointcheval, "Simple Password-Based
              Encrypted Key Exchange Protocols.", Feb 2005.

              Appears in A.  Menezes, editor.  Topics in Cryptography-
              CT-RSA 2005, Volume 3376 of Lecture Notes in Computer
              Science, pages 191-208, San Francisco, CA, US.  Springer-
              Verlag, Berlin, Germany.

   [RFC8265]  Saint-Andre, P. and A. Melnikov, "Preparation,
              Enforcement, and Comparison of Internationalized Strings
              Representing Usernames and Passwords", RFC 8265,
              DOI 10.17487/RFC8265, October 2017,

   [SPAKE2]   Ladd, W. and B. Kaduk, "SPAKE2, a PAKE.", Feb 2020.

              SPAKE2, a PAKE

   [TDH]      Cash, D., Kiltz, E., and V. Shoup, "The Twin-Diffie
              Hellman Problem and Applications", 2008.

              EUROCRYPT 2008.  Volume 4965 of Lecture notes in Computer
              Science, pages 127-145.  Springer-Verlag, Berlin, Germany.

Appendix A.  Algorithm used for Point Generation

   This section describes the algorithm that was used to generate the
   points (M) and (N) in the table in Section 5.

   For each curve in the table below, we construct a string using the
   curve OID from [RFC5480] (as an ASCII string) or its name, combined
   with the needed constant, for instance " point generation
   seed (M)" for P-512.  This string is turned into a series of blocks
   by hashing with SHA256, and hashing that output again to generate the
   next 32 bytes, and so on.  This pattern is repeated for each group
   and value, with the string modified appropriately.

   A byte string of length equal to that of an encoded group element is
   constructed by concatenating as many blocks as are required, starting
   from the first block, and truncating to the desired length.  The byte

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   string is then formatted as required for the group.  In the case of
   Weierstrass curves, we take the desired length as the length for
   representing a compressed point (section 2.3.4 of [SEC1]), and use
   the low-order bit of the first byte as the sign bit.  In order to
   obtain the correct format, the value of the first byte is set to 0x02
   or 0x03 (clearing the first six bits and setting the seventh bit),
   leaving the sign bit as it was in the byte string constructed by
   concatenating hash blocks.  For the [RFC8032] curves a different
   procedure is used.  For edwards448 the 57-byte input has the least-
   significant 7 bits of the last byte set to zero, and for edwards25519
   the 32-byte input is not modified.  For both the [RFC8032] curves the
   (modified) input is then interpreted as the representation of the
   group element.  If this interpretation yields a valid group element
   with the correct order (p), the (modified) byte string is the output.
   Otherwise, the initial hash block is discarded and a new byte string
   constructed from the remaining hash blocks.  The procedure of
   constructing a byte string of the appropriate length, formatting it
   as required for the curve, and checking if it is a valid point of the
   correct order, is repeated until a valid element is found.

   The following python snippet generates the above points, assuming an
   elliptic curve implementation following the interface of
   Edwards25519Point.stdbase() and Edwards448Point.stdbase() in
   Appendix A of [RFC8032]:

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  def iterated_hash(seed, n):
      h = seed
      for i in range(n):
          h = hashlib.sha256(h).digest()
      return h

  def bighash(seed, start, sz):
      n = -(-sz // 32)
      hashes = [iterated_hash(seed, i) for i in range(start, start + n)]
      return b''.join(hashes)[:sz]

  def canon_pointstr(ecname, s):
      if ecname == 'edwards25519':
          return s
      elif ecname == 'edwards448':
          return s[:-1] + bytes([s[-1] & 0x80])
          return bytes([(s[0] & 1) | 2]) + s[1:]

  def gen_point(seed, ecname, ec):
      for i in range(1, 1000):
          hval = bighash(seed, i, len(ec.encode()))
          pointstr = canon_pointstr(ecname, hval)
              p = ec.decode(pointstr)
              if p != ec.zero_elem() and p * p.l() == ec.zero_elem():
                  return pointstr, i
          except Exception:

Appendix B.  Test Vectors

   This section contains test vectors for SPAKE2+ using the P256-SHA256-
   HKDF-HMAC ciphersuite.  (Choice of PBKDF is omitted and values for w
   and w0,w1 are provided directly.)  All points are encoded using the
   uncompressed format, i.e., with a 0x04 octet prefix, specified in
   [SEC1] A and B identity strings are provided in the protocol

B.1.  SPAKE2+ Test Vectors

   SPAKE2+(A='client', B='server')
   w0 = 0x4f9e28322a64f9dc7a01b282cc51e2abc4f9ed568805ca84f4ed3ef806516
   w1 = 0x8d73e4ca273859c873d809431d15f30e2b722007964e32699160b54fda3ee
   L = 0x0491bb1e6672e71ad80b17d13f7a72ca2fe7f882d4bd734e2d140f67ab49d2

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Internet-Draft         SPAKE2+, an Augmented PAKE             March 2020

   X = 0x04879567d09560c02be565429036ed1d2fc3ca53f2eb6fadda4dba09eff3a0
   Y = 0x04b595a25588a2fba757195a756d289c191240296699f61fee8f15a7a741a4
   Z = 0x047bb4661db7085d019cffa8495aba73d22f87ab8ba22e789477ef933b916f
   V = 0x0417658e1e9707a29d429a4733d3bee703574aec222e781a6e7e5f5e504908
   TT = 0x0600000000000000636c69656e74060000000000000073657276657241000
   Ka = 0xbf800062847c5182bf5c549b05ea6cce
   Ke = 0xce9acf88ff9440777bda3e34fa4993cd
   KcA = 0x73c6a5597096e99b8025172bb45b4a2f
   KcB = 0x96a801673bd07b51d61fbaea03ef17cf
   MAC(A) = 0xcab37c89192f9ad90ca5e6b8eadb130d313b51d24b7889e2536f7c800
   MAC(B) = 0xf7076a78a3d16f0c62cb9e40bd1a91b68dee144b87016e2dae81c36e9

   SPAKE2+(A='client', B='')
   w0 = 0x4f9e28322a64f9dc7a01b282cc51e2abc4f9ed568805ca84f4ed3ef806516
   w1 = 0x8d73e4ca273859c873d809431d15f30e2b722007964e32699160b54fda3ee
   L = 0x0491bb1e6672e71ad80b17d13f7a72ca2fe7f882d4bd734e2d140f67ab49d2
   X = 0x0426fbedb3b9ccea93d609838dcc1d4baebdbb9c287763ed4cdb2d3cc76f78
   Y = 0x04d4960922990acb87809e734fed2c2ccb72fd26ed173e8207cdc6220073ac
   Z = 0x0421996ff4d9c05b2389ae05118c519679df5d6de258b31f2a17da7604c8e3
   V = 0x04729f7c6c5bd68310345b1a10b84ea7db64c70441da2255992208b7a8e0b3
   TT = 0x0600000000000000636c69656e7441000000000000000426fbedb3b9ccea9

Taubert & Wood         Expires September 10, 2020              [Page 14]

Internet-Draft         SPAKE2+, an Augmented PAKE             March 2020

   Ka = 0xfd19104b836b0ba9dfaaeab88610be57
   Ke = 0x90337374f974f673707de5ba1b98e5b8
   KcA = 0x2e10249c566677c8826b48ad10b19bb5
   KcB = 0x4fcaf8fd0bfcaeeabb9d6f48e264e4a3
   MAC(A) = 0xaaef200ea5f5c41e1fdb9b3455dde715cd8aa96f8afd3274f7159c3c5
   MAC(B) = 0x926eadbf4b720b46ea622d7100e0013eb24d1591496846a604cf90c14

   SPAKE2+(A='', B='server')
   w0 = 0x4f9e28322a64f9dc7a01b282cc51e2abc4f9ed568805ca84f4ed3ef806516
   w1 = 0x8d73e4ca273859c873d809431d15f30e2b722007964e32699160b54fda3ee
   L = 0x0491bb1e6672e71ad80b17d13f7a72ca2fe7f882d4bd734e2d140f67ab49d2
   X = 0x0463a7531acd204e7d83ac6562278d7ced01a715eff937a25520bd2220c626
   Y = 0x0433625217e2ccc0c545126f756d999c16df68b14b73b3fe473593c1d3a0d7
   Z = 0x049ef5ea46e8ca42f3e822c598858ca347bf19cc74a8a1fbfd836ec4d77bee
   V = 0x0408a70fc9dca87b70a7d4a074bdcca0222806f0caa0542d8d62aecf535ea8
   TT = 0x060000000000000073657276657241000000000000000463a7531acd204e7
   Ka = 0x5c85900898b2079c9de09ebef63cebd1
   Ke = 0x13c812476859e909682c3be7436bfef0
   KcA = 0x77bd636ab9bf153339c5724ee04f87a7
   KcB = 0x194325b27d7c291c94a689ddafeaaa3c
   MAC(A) = 0x3bb61248a1fd2946743314848fc501eb3455eb113bd8966e200de14d5
   MAC(B) = 0x3e7912bd2a85a1f56d36fbb16de29834b000d49e50d4c17f992942ee5

Taubert & Wood         Expires September 10, 2020              [Page 15]

Internet-Draft         SPAKE2+, an Augmented PAKE             March 2020


   SPAKE2+(A='', B='')
   w0 = 0x4f9e28322a64f9dc7a01b282cc51e2abc4f9ed568805ca84f4ed3ef806516
   w1 = 0x8d73e4ca273859c873d809431d15f30e2b722007964e32699160b54fda3ee
   L = 0x0491bb1e6672e71ad80b17d13f7a72ca2fe7f882d4bd734e2d140f67ab49d2
   X = 0x04f60f506cfa07506d4bfd2b3f56038b1c001fe6826374122c30e914747eab
   Y = 0x046898fafef34fff9936217608151af08313305cf8e6f9add10d721c04a018
   Z = 0x042adeeea1417cc6c592fef772da8ba0f3aea69a5fb15923d0e9ae7c3301c7
   V = 0x04845c130c8c20865828e21ed3400abea726b07fdeb7533fa6017accc37e0b
   TT = 0x410000000000000004f60f506cfa07506d4bfd2b3f56038b1c001fe682637
   Ka = 0x850a18a77b14ef5e71b4a239413630a8
   Ke = 0x4454819282b3e886a7e65b7b0de7cc62
   KcA = 0x05df6196c12d6203768c73d875e2bfc5
   KcB = 0xb58e61c322f685add02c125767e4fbb7
   MAC(A) = 0x33e50d29f8eacc67bfdab4a6c46c88d75ac3308416c64dfbb0d7fb1c0
   MAC(B) = 0x55434e5e501ad2d476aa1ae334ef27ba437a5dea87683defac575a63b

Authors' Addresses

   Tim Taubert
   Apple, Inc.

   Email: ttaubert@apple.com

   Christopher A. Wood
   Apple, Inc.

   Email: cawood@apple.com

Taubert & Wood         Expires September 10, 2020              [Page 16]

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