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Crypto Forum hpke hybrid encryption KDF SHA3 This document defines Secure Hashing Algorithm-3 (SHA-3) options for Hybrid Public-Key Encryption (HPKE) as registered KDFs. About This Document The latest revision of this draft can be found at . Status information for this document may be found at . Discussion of this document takes place on the Crypto Forum mailing list (), which is archived at . Subscribe at . Source for this draft and an issue tracker can be found at .

Introduction TODO Introduction

Conventions and Definitions 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 when, and only when, they appear in all capitals, as shown here.

Security Considerations TODO Security

IANA Considerations This document requests/registers three new entries to the "HPKE KDF Identifiers" registry.

Value:

0x0004 (please) KDF:

SHA3-256 Nh: The output size of the Extract function in bytes

32 Reference:

Value:

0x0005 (please) KDF:

SHA3-384 Nh: The output size of the Extract function in bytes

48 Reference:

Value:

0x0006 (please) KDF:

SHA3-512 Nh: The output size of the Extract function in bytes

64 Reference:

Normative References This document describes a scheme for hybrid public key encryption (HPKE). This scheme provides a variant of public key encryption of arbitrary-sized plaintexts for a recipient public key. It also includes three authenticated variants, including one that authenticates possession of a pre-shared key and two optional ones that authenticate possession of a key encapsulation mechanism (KEM) private key. HPKE works for any combination of an asymmetric KEM, key derivation function (KDF), and authenticated encryption with additional data (AEAD) encryption function. Some authenticated variants may not be supported by all KEMs. We provide instantiations of the scheme using widely used and efficient primitives, such as Elliptic Curve Diffie-Hellman (ECDH) key agreement, HMAC-based key derivation function (HKDF), and SHA2. This document is a product of the Crypto Forum Research Group (CFRG) in the IRTF. National Institute of Standards and Technology (U.S.) In many standards track documents several words are used to signify the requirements in the specification. These words are often capitalized. This document defines these words as they should be interpreted in IETF documents. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements. RFC 2119 specifies common key words that may be used in protocol specifications. This document aims to reduce the ambiguity by clarifying that only UPPERCASE usage of the key words have the defined special meanings.

Acknowledgments TODO acknowledge.