SPAKE2, a PAKE
draft-irtf-cfrg-spake2-13
Network Working Group W. Ladd
Internet-Draft Cloudflare
Intended status: Informational B. Kaduk, Ed.
Expires: March 13, 2021 Akamai
September 9, 2020
SPAKE2, a PAKE
draft-irtf-cfrg-spake2-13
Abstract
This document describes SPAKE2 which is a protocol for two parties
that share a password to derive a strong shared key with no risk of
disclosing the password. This method is compatible with any group,
is computationally efficient, and SPAKE2 has a security proof. This
document predated the CFRG PAKE competition and it was not selected.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on March 13, 2021.
Copyright Notice
Copyright (c) 2020 IETF Trust and the persons identified as the
document authors. All rights reserved.
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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 . . . . . . . . . . . . . . . . . . . . 2
3. Definition of SPAKE2 . . . . . . . . . . . . . . . . . . . . 2
4. Key Schedule and Key Confirmation . . . . . . . . . . . . . . 5
5. Per-User M and N . . . . . . . . . . . . . . . . . . . . . . 6
6. Ciphersuites . . . . . . . . . . . . . . . . . . . . . . . . 6
7. Security Considerations . . . . . . . . . . . . . . . . . . . 9
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 9
10. 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 means for two parties that share a
password to derive a strong shared key with no risk of disclosing the
password. This password-based key exchange protocol is compatible
with any group (requiring only a scheme to map a random input of
fixed length per group to a random group element), is computationally
efficient, and has a security proof. Predetermined parameters for a
selection of commonly used groups are also provided for use by other
protocols.
2. Requirements Notation
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"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. Setup
Let G be a group in which the gap 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
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be SEC1 [SEC1] uncompressed or compressed 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
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