Configuration

OPAQUE-3DH is currently parameterized with a tuple (OPRF, KDF, MAC, Hash, KSF, Group)

A shorter representation could be (OPRF, Hash, MHF, KSF), given that some parameters are the same.

Prime-order Groups	Hashing	Key-Stretching Functions	Envelope Mode
Ristretto255 P256 P384 P384	SHA2-256 SHA2-512 SHA3-256 SHA3-256	Argon2id Scrypt PBKDF2Sha512 Bcrypt	Internal External

Prime-order Groups

OPRF

designates an OPRF ciphersuite (a group + hashing to curve algorithm) used in the base mode. Default is Ristretto255-SHA512.

Group

identifies the prime-order group to be used for the 3DH-AKE. It's usually the same as the one in the OPRF ciphersuite. Default is Ristretto255.

Hashing

KDF, MAC, and Hash

are hash function identifiers. These are defined separately for finer tunability, but they are usually all the same. Defaults are HKDF for KDF, and HMAC for MAC, and all three over SHA-512.

Key-Stretching functions

The key-stretching function that will be executed on the client. Default is Scrypt(32768,8,1).

Usage

Applications should use only one set of parameters throughout the application lifecycle, but the EnvelopeMode must absolutely stay the same, or the client enumeration protection may get compromised.

The best way is still to use the default configuration, which is optimal in terms of performance and offers a great security level.

import "github.com/bytemare/opaque"

conf := opaque.DefaultConfiguration()

Or you can brew your own configuration like the following:

import (
  "github.com/bytemare/cryptotools/group/ciphersuite"
  "github.com/bytemare/cryptotools/hash"
  "github.com/bytemare/cryptotools/mhf"
  "github.com/bytemare/opaque"
)

conf := &opaque.Configuration{
	  OprfCiphersuite: opaque.P256Sha256,
	  KDF:             hash.SHA512,
	  MAC:             hash.SHA512,
	  Hash:            hash.SHA512,
	  MHF:             mhf.Scrypt,
	  AKEGroup:        ciphersuite.P256Sha256,
	  NonceLen:        32,
	}