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client.go
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client.go
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// SPDX-License-Identifier: MIT
//
// Copyright (C) 2020-2022 Daniel Bourdrez. All Rights Reserved.
//
// This source code is licensed under the MIT license found in the
// LICENSE file in the root directory of this source tree or at
// https://spdx.org/licenses/MIT.html
package opaque
import (
"errors"
"fmt"
group "github.com/bytemare/crypto"
"github.com/bytemare/opaque/internal"
"github.com/bytemare/opaque/internal/ake"
"github.com/bytemare/opaque/internal/encoding"
"github.com/bytemare/opaque/internal/keyrecovery"
"github.com/bytemare/opaque/internal/masking"
"github.com/bytemare/opaque/internal/oprf"
"github.com/bytemare/opaque/internal/tag"
"github.com/bytemare/opaque/message"
)
var (
// errInvalidMaskedLength happens when unmasking a masked response.
errInvalidMaskedLength = errors.New("invalid masked response length")
// errKe1Missing happens when GenerateKE3 is called and the client has no Ke1 in state.
errKe1Missing = errors.New("missing KE1 in client state")
)
// Client represents an OPAQUE Client, exposing its functions and holding its state.
type Client struct {
Deserialize *Deserializer
OPRF *oprf.Client
Ake *ake.Client
conf *internal.Configuration
}
// NewClient returns a new Client instantiation given the application Configuration.
func NewClient(c *Configuration) (*Client, error) {
if c == nil {
c = DefaultConfiguration()
}
conf, err := c.toInternal()
if err != nil {
return nil, err
}
return &Client{
OPRF: conf.OPRF.Client(),
Ake: ake.NewClient(),
Deserialize: &Deserializer{conf: conf},
conf: conf,
}, nil
}
// GetConf returns the internal configuration.
func (c *Client) GetConf() *internal.Configuration {
return c.conf
}
// buildPRK derives the randomized password from the OPRF output.
func (c *Client) buildPRK(evaluation *group.Element) []byte {
output := c.OPRF.Finalize(evaluation)
stretched := c.conf.KSF.Harden(output, c.conf.KSFSalt, c.conf.Hash.Size())
return c.conf.KDF.Extract(nil, encoding.Concat(output, stretched))
}
// ClientRegistrationInitOptions enables setting internal client values for the client registration.
type ClientRegistrationInitOptions struct {
// OPRFBlind: optional
OPRFBlind *group.Scalar
}
func getClientRegistrationInitBlind(options []ClientRegistrationInitOptions) *group.Scalar {
if len(options) == 0 {
return nil
}
return options[0].OPRFBlind
}
// RegistrationInit returns a RegistrationRequest message blinding the given password.
func (c *Client) RegistrationInit(
password []byte,
options ...ClientRegistrationInitOptions,
) *message.RegistrationRequest {
m := c.OPRF.Blind(password, getClientRegistrationInitBlind(options))
return &message.RegistrationRequest{
BlindedMessage: m,
}
}
// ClientRegistrationFinalizeOptions enables setting optional client values for the client registration.
type ClientRegistrationFinalizeOptions struct {
// ClientIdentity: optional
ClientIdentity []byte
// ServerIdentity: optional
ServerIdentity []byte
// EnvelopeNonce : optional
EnvelopeNonce []byte
}
func initClientRegistrationFinalizeOptions(options []ClientRegistrationFinalizeOptions) *keyrecovery.Credentials {
if len(options) == 0 {
return &keyrecovery.Credentials{
ClientIdentity: nil,
ServerIdentity: nil,
EnvelopeNonce: nil,
}
}
return &keyrecovery.Credentials{
ClientIdentity: options[0].ClientIdentity,
ServerIdentity: options[0].ServerIdentity,
EnvelopeNonce: options[0].EnvelopeNonce,
}
}
// RegistrationFinalize returns a RegistrationRecord message given the identities and the server's RegistrationResponse.
func (c *Client) RegistrationFinalize(
resp *message.RegistrationResponse,
options ...ClientRegistrationFinalizeOptions,
) (record *message.RegistrationRecord, exportKey []byte) {
credentials := initClientRegistrationFinalizeOptions(options)
randomizedPassword := c.buildPRK(resp.EvaluatedMessage)
maskingKey := c.conf.KDF.Expand(randomizedPassword, []byte(tag.MaskingKey), c.conf.KDF.Size())
envelope, clientPublicKey, exportKey := keyrecovery.Store(c.conf, randomizedPassword, resp.Pks, credentials)
return &message.RegistrationRecord{
PublicKey: clientPublicKey,
MaskingKey: maskingKey,
Envelope: envelope.Serialize(),
}, exportKey
}
// GenerateKE1Options enables setting optional values for the session, which default to secure random values if not
// set.
type GenerateKE1Options struct {
// Blind: optional
Blind *group.Scalar
// KeyShareSeed: optional
KeyShareSeed []byte
// Nonce: optional
Nonce []byte
// NonceLength: optional
NonceLength uint
}
func (c GenerateKE1Options) get() (*group.Scalar, ake.Options) {
return c.Blind, ake.Options{
KeyShareSeed: c.KeyShareSeed,
Nonce: c.Nonce,
NonceLength: c.NonceLength,
}
}
func getGenerateKE1Options(options []GenerateKE1Options) (*group.Scalar, ake.Options) {
if len(options) != 0 {
return options[0].get()
}
return nil, ake.Options{
KeyShareSeed: nil,
Nonce: nil,
NonceLength: internal.NonceLength,
}
}
// GenerateKE1 initiates the authentication process, returning a KE1 message blinding the given password.
func (c *Client) GenerateKE1(password []byte, options ...GenerateKE1Options) *message.KE1 {
blind, akeOptions := getGenerateKE1Options(options)
m := c.OPRF.Blind(password, blind)
ke1 := c.Ake.Start(c.conf.Group, akeOptions)
ke1.CredentialRequest = message.NewCredentialRequest(m)
c.Ake.Ke1 = ke1.Serialize()
return ke1
}
// GenerateKE3Options enables setting optional client values for the client registration.
type GenerateKE3Options struct {
// ClientIdentity: optional
ClientIdentity []byte
// ServerIdentity: optional
ServerIdentity []byte
}
func initGenerateKE3Options(options []GenerateKE3Options) *ake.Identities {
if len(options) == 0 {
return &ake.Identities{
ClientIdentity: nil,
ServerIdentity: nil,
}
}
return &ake.Identities{
ClientIdentity: options[0].ClientIdentity,
ServerIdentity: options[0].ServerIdentity,
}
}
// GenerateKE3 returns a KE3 message given the server's KE2 response message and the identities. If the idc
// or ids parameters are nil, the client and server's public keys are taken as identities for both.
func (c *Client) GenerateKE3(
ke2 *message.KE2, options ...GenerateKE3Options,
) (ke3 *message.KE3, exportKey []byte, err error) {
if len(c.Ake.Ke1) == 0 {
return nil, nil, errKe1Missing
}
// This test is very important as it avoids buffer overflows in subsequent parsing.
if len(ke2.MaskedResponse) != c.conf.Group.ElementLength()+c.conf.EnvelopeSize {
return nil, nil, errInvalidMaskedLength
}
identities := initGenerateKE3Options(options)
// Finalize the OPRF.
randomizedPassword := c.buildPRK(ke2.EvaluatedMessage)
// Decrypt the masked response.
serverPublicKey, serverPublicKeyBytes,
envelope, err := masking.Unmask(c.conf, randomizedPassword, ke2.MaskingNonce, ke2.MaskedResponse)
if err != nil {
return nil, nil, fmt.Errorf("unmasking: %w", err)
}
// Recover the client keys.
clientSecretKey, clientPublicKey,
exportKey, err := keyrecovery.Recover(
c.conf,
randomizedPassword,
serverPublicKeyBytes,
identities.ClientIdentity,
identities.ServerIdentity,
envelope)
if err != nil {
return nil, nil, fmt.Errorf("key recovery: %w", err)
}
// Finalize the AKE.
identities.SetIdentities(clientPublicKey, serverPublicKeyBytes)
ke3, err = c.Ake.Finalize(c.conf, identities, clientSecretKey, serverPublicKey, ke2)
if err != nil {
return nil, nil, fmt.Errorf("finalizing AKE: %w", err)
}
return ke3, exportKey, nil
}
// SessionKey returns the session key if the previous call to GenerateKE3() was successful.
func (c *Client) SessionKey() []byte {
return c.Ake.SessionKey()
}