Hybrid Public Key Encryption
draft-irtf-cfrg-hpke-05

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Network Working Group                                        R.L. Barnes
Internet-Draft                                                     Cisco
Intended status: Informational                              K. Bhargavan
Expires: 31 January 2021                                         B. Lipp
                                                                   Inria
                                                               C.A. Wood
                                                              Cloudflare
                                                            30 July 2020

                      Hybrid Public Key Encryption
                        draft-irtf-cfrg-hpke-05

Abstract

   This document describes a scheme for hybrid public-key encryption
   (HPKE).  This scheme provides authenticated public key encryption of
   arbitrary-sized plaintexts for a recipient public key.  HPKE works
   for any combination of an asymmetric key encapsulation mechanism
   (KEM), key derivation function (KDF), and authenticated encryption
   with additional data (AEAD) encryption function.  We provide
   instantiations of the scheme using widely-used and efficient
   primitives, such as Elliptic Curve Diffie-Hellman key agreement,
   HKDF, and SHA2.

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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   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on 31 January 2021.

Copyright Notice

   Copyright (c) 2020 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

Barnes, et al.           Expires 31 January 2021                [Page 1]
Internet-Draft                    HPKE                         July 2020

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents (https://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
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   provided without warranty as described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Requirements Notation . . . . . . . . . . . . . . . . . . . .   4
   3.  Notation  . . . . . . . . . . . . . . . . . . . . . . . . . .   4
   4.  Cryptographic Dependencies  . . . . . . . . . . . . . . . . .   5
     4.1.  DH-Based KEM  . . . . . . . . . . . . . . . . . . . . . .   7
   5.  Hybrid Public Key Encryption  . . . . . . . . . . . . . . . .  10
     5.1.  Creating the Encryption Context . . . . . . . . . . . . .  11
       5.1.1.  Encryption to a Public Key  . . . . . . . . . . . . .  14
       5.1.2.  Authentication using a Pre-Shared Key . . . . . . . .  14
       5.1.3.  Authentication using an Asymmetric Key  . . . . . . .  15
       5.1.4.  Authentication using both a PSK and an Asymmetric
               Key . . . . . . . . . . . . . . . . . . . . . . . . .  15
     5.2.  Encryption and Decryption . . . . . . . . . . . . . . . .  16
     5.3.  Secret Export . . . . . . . . . . . . . . . . . . . . . .  17
   6.  Single-Shot APIs  . . . . . . . . . . . . . . . . . . . . . .  18
   7.  Algorithm Identifiers . . . . . . . . . . . . . . . . . . . .  18
     7.1.  Key Encapsulation Mechanisms (KEMs) . . . . . . . . . . .  19
       7.1.1.  Serialize/Deserialize . . . . . . . . . . . . . . . .  19
       7.1.2.  DeriveKeyPair . . . . . . . . . . . . . . . . . . . .  19
       7.1.3.  Validation of Inputs and Outputs  . . . . . . . . . .  20
     7.2.  Key Derivation Functions (KDFs) . . . . . . . . . . . . .  21
       7.2.1.  Input Length Restrictions . . . . . . . . . . . . . .  21
     7.3.  Authenticated Encryption with Associated Data (AEAD)
           Functions . . . . . . . . . . . . . . . . . . . . . . . .  23
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  23
     8.1.  Security Properties . . . . . . . . . . . . . . . . . . .  23
     8.2.  Security Requirements on a KEM used within HPKE . . . . .  26
     8.3.  Security Requirements on a KDF  . . . . . . . . . . . . .  26
     8.4.  Pre-Shared Key Recommendations  . . . . . . . . . . . . .  26
     8.5.  Domain Separation . . . . . . . . . . . . . . . . . . . .  27