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Allow specifying OPRF client seed #5

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15 changes: 9 additions & 6 deletions examples_test.go
View file
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Original file line number Diff line number Diff line change
Expand Up @@ -106,7 +106,7 @@ func Example_serverSetup() {
log.Fatalln(err)
}

if err := server.SetKeyMaterial(serverID, serverPrivateKey, serverPublicKey, secretOprfSeed); err != nil {
if err := server.SetKeyMaterial(serverID, serverPrivateKey, serverPublicKey, secretOprfSeed, nil); err != nil {
log.Fatalln(err)
}

Expand Down Expand Up @@ -232,13 +232,16 @@ func Example_registration() {
// The server creates a database entry for the client and creates a credential identifier that must absolutely
// be unique among all clients.
credID = opaque.RandomBytes(64)
pks, err := server.Deserialize.DecodeAkePublicKey(serverPublicKey)
if err != nil {

if err = server.SetKeyMaterial(serverID, serverPrivateKey, serverPublicKey, secretOprfSeed, nil); err != nil {
log.Fatalln(err)
}

// The server uses its public key and secret OPRF seed created at the setup.
response := server.RegistrationResponse(request, pks, credID, secretOprfSeed)
response, err := server.RegistrationResponse(request, credID)
if err != nil {
log.Fatalln(err)
}

// The server responds with its serialized response.
message2 = response.Serialize()
Expand Down Expand Up @@ -308,7 +311,7 @@ func Example_loginKeyExchange() {
log.Fatalln(err)
}

if err := server.SetKeyMaterial(serverID, serverPrivateKey, serverPublicKey, secretOprfSeed); err != nil {
if err := server.SetKeyMaterial(serverID, serverPrivateKey, serverPublicKey, secretOprfSeed, nil); err != nil {
log.Fatalln(err)
}

Expand Down Expand Up @@ -424,7 +427,7 @@ func Example_fakeResponse() {
log.Fatalln(err)
}

if err := server.SetKeyMaterial(serverID, serverPrivateKey, serverPublicKey, secretOprfSeed); err != nil {
if err := server.SetKeyMaterial(serverID, serverPrivateKey, serverPublicKey, secretOprfSeed, nil); err != nil {
log.Fatalln(err)
}

Expand Down
79 changes: 57 additions & 22 deletions server.go
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Original file line number Diff line number Diff line change
Expand Up @@ -58,6 +58,11 @@ type keyMaterial struct {
serverSecretKey *ecc.Scalar
serverPublicKey []byte
oprfSeed []byte
oprfClientSeed []byte
}

type OPRFSeedOptions struct {
OPRFSeed []byte
}

// NewServer returns a Server instantiation given the application Configuration.
Expand All @@ -84,49 +89,67 @@ func (s *Server) GetConf() *internal.Configuration {
return s.conf
}

func (s *Server) oprfResponse(element *ecc.Element, oprfSeed, credentialIdentifier []byte) *ecc.Element {
seed := s.conf.KDF.Expand(
oprfSeed,
encoding.SuffixString(credentialIdentifier, tag.ExpandOPRF),
internal.SeedLength,
)
func (s *Server) oprfResponse(element *ecc.Element, credentialIdentifier []byte) (*ecc.Element, error) {
if s.keyMaterial == nil {
return nil, fmt.Errorf("key material must be specified")
}
seed := s.keyMaterial.oprfClientSeed
if seed == nil {
if s.keyMaterial.oprfSeed == nil {
return nil, fmt.Errorf("OPRF seed must be specified")
}
seed = s.conf.KDF.Expand(
s.keyMaterial.oprfSeed,
encoding.SuffixString(credentialIdentifier, tag.ExpandOPRF),
internal.SeedLength,
)
}
ku := s.conf.OPRF.DeriveKey(seed, []byte(tag.DeriveKeyPair))

return s.conf.OPRF.Evaluate(ku, element)
return s.conf.OPRF.Evaluate(ku, element), nil
}

// RegistrationResponse returns a RegistrationResponse message to the input RegistrationRequest message and given
// identifiers.
func (s *Server) RegistrationResponse(
req *message.RegistrationRequest,
serverPublicKey *ecc.Element,
credentialIdentifier, oprfSeed []byte,
) *message.RegistrationResponse {
z := s.oprfResponse(req.BlindedMessage, oprfSeed, credentialIdentifier)
credentialIdentifier []byte,
) (*message.RegistrationResponse, error) {
z, err := s.oprfResponse(req.BlindedMessage, credentialIdentifier)
if err != nil {
return nil, err
}

serverPublicKey := s.conf.Group.NewElement()
if err := serverPublicKey.Decode(s.keyMaterial.serverPublicKey); err != nil {
return nil, fmt.Errorf("invalid server public key: %w", err)
}

return &message.RegistrationResponse{
EvaluatedMessage: z,
Pks: serverPublicKey,
}
}, nil
}

func (s *Server) credentialResponse(
req *message.CredentialRequest,
serverPublicKey []byte,
record *message.RegistrationRecord,
credentialIdentifier, oprfSeed, maskingNonce []byte,
) *message.CredentialResponse {
z := s.oprfResponse(req.BlindedMessage, oprfSeed, credentialIdentifier)
credentialIdentifier, maskingNonce []byte,
) (*message.CredentialResponse, error) {
z, err := s.oprfResponse(req.BlindedMessage, credentialIdentifier)
if err != nil {
return nil, err
}

maskingNonce, maskedResponse := masking.Mask(
s.conf,
maskingNonce,
record.MaskingKey,
serverPublicKey,
s.keyMaterial.serverPublicKey,
record.Envelope,
)

return message.NewCredentialResponse(z, maskingNonce, maskedResponse)
return message.NewCredentialResponse(z, maskingNonce, maskedResponse), nil
}

// GenerateKE2Options enable setting optional values for the session, which default to secure random values if not
Expand Down Expand Up @@ -166,7 +189,7 @@ func getGenerateKE2Options(options []GenerateKE2Options) (*ake.Options, []byte)
// - serverSecretKey is the server's secret AKE key.
// - serverPublicKey is the server's public AKE key to the serverSecretKey.
// - oprfSeed is the long-term OPRF input seed.
func (s *Server) SetKeyMaterial(serverIdentity, serverSecretKey, serverPublicKey, oprfSeed []byte) error {
func (s *Server) SetKeyMaterial(serverIdentity, serverSecretKey, serverPublicKey, oprfSeed []byte, oprfClientSeed []byte) error {
sks := s.conf.Group.NewScalar()
if err := sks.Decode(serverSecretKey); err != nil {
return fmt.Errorf("invalid server AKE secret key: %w", err)
Expand All @@ -176,7 +199,15 @@ func (s *Server) SetKeyMaterial(serverIdentity, serverSecretKey, serverPublicKey
return ErrZeroSKS
}

if len(oprfSeed) != s.conf.Hash.Size() {
if oprfSeed != nil {
if len(oprfSeed) != s.conf.Hash.Size() {
return ErrInvalidOPRFSeedLength
}
} else if oprfClientSeed != nil {
if len(oprfClientSeed) != internal.SeedLength {
return ErrInvalidOPRFSeedLength
}
} else {
return ErrInvalidOPRFSeedLength
}

Expand All @@ -193,6 +224,7 @@ func (s *Server) SetKeyMaterial(serverIdentity, serverSecretKey, serverPublicKey
serverSecretKey: sks,
serverPublicKey: serverPublicKey,
oprfSeed: oprfSeed,
oprfClientSeed: oprfClientSeed,
}

return nil
Expand All @@ -217,8 +249,11 @@ func (s *Server) GenerateKE2(

op, maskingNonce := getGenerateKE2Options(options)

response := s.credentialResponse(ke1.CredentialRequest, s.serverPublicKey,
record.RegistrationRecord, record.CredentialIdentifier, s.oprfSeed, maskingNonce)
response, err := s.credentialResponse(ke1.CredentialRequest,
record.RegistrationRecord, record.CredentialIdentifier, maskingNonce)
if err != nil {
return nil, err
}

identities := ake.Identities{
ClientIdentity: record.ClientIdentity,
Expand Down
24 changes: 14 additions & 10 deletions tests/client_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -44,15 +44,19 @@ func TestClientRegistrationFinalize_InvalidPks(t *testing.T) {
t.Fatal(err)
}

_, pks := conf.conf.KeyGen()
sks, pks := conf.conf.KeyGen()
oprfSeed := internal.RandomBytes(conf.conf.Hash.Size())
r1 := client.RegistrationInit([]byte("yo"))

pk := server.GetConf().Group.NewElement()
if err = pk.Decode(pks); err != nil {
panic(err)
}
r2 := server.RegistrationResponse(r1, pk, credID, oprfSeed)
server.SetKeyMaterial([]byte("server"), sks, pks, oprfSeed, nil)
r2, err := server.RegistrationResponse(r1, credID)
if err != nil {
t.Fatalf("failed to generate registration response: %v", err)
}

// message length
badr2 := internal.RandomBytes(15)
Expand Down Expand Up @@ -131,11 +135,11 @@ func TestClientFinish_BadMaskedResponse(t *testing.T) {
sks, pks := conf.conf.KeyGen()
oprfSeed := internal.RandomBytes(conf.conf.Hash.Size())

if err = server.SetKeyMaterial(nil, sks, pks, oprfSeed); err != nil {
if err := server.SetKeyMaterial(nil, sks, pks, oprfSeed, nil); err != nil {
t.Fatal(err)
}

rec := buildRecord(credID, oprfSeed, []byte("yo"), pks, client, server)
rec := buildRecord(credID, oprfSeed, []byte("yo"), sks, pks, client, server, false)

ke1 := client.GenerateKE1([]byte("yo"))
ke2, _ := server.GenerateKE2(ke1, rec)
Expand Down Expand Up @@ -177,11 +181,11 @@ func TestClientFinish_InvalidEnvelopeTag(t *testing.T) {
sks, pks := conf.conf.KeyGen()
oprfSeed := internal.RandomBytes(conf.conf.Hash.Size())

if err = server.SetKeyMaterial(nil, sks, pks, oprfSeed); err != nil {
if err := server.SetKeyMaterial(nil, sks, pks, oprfSeed, nil); err != nil {
t.Fatal(err)
}

rec := buildRecord(credID, oprfSeed, []byte("yo"), pks, client, server)
rec := buildRecord(credID, oprfSeed, []byte("yo"), sks, pks, client, server, false)

ke1 := client.GenerateKE1([]byte("yo"))
ke2, _ := server.GenerateKE2(ke1, rec)
Expand Down Expand Up @@ -235,11 +239,11 @@ func TestClientFinish_InvalidKE2KeyEncoding(t *testing.T) {
sks, pks := conf.conf.KeyGen()
oprfSeed := internal.RandomBytes(conf.conf.Hash.Size())

if err := server.SetKeyMaterial(nil, sks, pks, oprfSeed); err != nil {
if err := server.SetKeyMaterial(nil, sks, pks, oprfSeed, nil); err != nil {
t.Fatal(err)
}

rec := buildRecord(credID, oprfSeed, []byte("yo"), pks, client, server)
rec := buildRecord(credID, oprfSeed, []byte("yo"), sks, pks, client, server, false)

ke1 := client.GenerateKE1([]byte("yo"))
ke2, _ := server.GenerateKE2(ke1, rec)
Expand Down Expand Up @@ -318,11 +322,11 @@ func TestClientFinish_InvalidKE2Mac(t *testing.T) {
sks, pks := conf.conf.KeyGen()
oprfSeed := internal.RandomBytes(conf.conf.Hash.Size())

if err := server.SetKeyMaterial(nil, sks, pks, oprfSeed); err != nil {
if err := server.SetKeyMaterial(nil, sks, pks, oprfSeed, nil); err != nil {
log.Fatal(err)
}

rec := buildRecord(credID, oprfSeed, []byte("yo"), pks, client, server)
rec := buildRecord(credID, oprfSeed, []byte("yo"), sks, pks, client, server, false)

ke1 := client.GenerateKE1([]byte("yo"))
ke2, _ := server.GenerateKE2(ke1, rec)
Expand Down
15 changes: 13 additions & 2 deletions tests/helper_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -167,9 +167,10 @@ func getBadScalar(t *testing.T, c *configuration) []byte {
}

func buildRecord(
credID, oprfSeed, password, pks []byte,
credID, oprfSeed, password, sks, pks []byte,
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RegistrationResponse doesn't use sks, so no need to provide it here, you can leave sks out

client *opaque.Client,
server *opaque.Server,
noServerID bool,
) *opaque.ClientRecord {
conf := server.GetConf()
r1 := client.RegistrationInit(password)
Expand All @@ -178,8 +179,18 @@ func buildRecord(
if err := pk.Decode(pks); err != nil {
panic(err)
}
var serverID []byte
if !noServerID {
serverID = []byte("server")
}

r2 := server.RegistrationResponse(r1, pk, credID, oprfSeed)
if err := server.SetKeyMaterial(serverID, sks, pks, oprfSeed, nil); err != nil {
panic(err)
}
r2, err := server.RegistrationResponse(r1, credID)
if err != nil {
panic(err)
}
r3, _ := client.RegistrationFinalize(r2)

return &opaque.ClientRecord{
Expand Down
10 changes: 6 additions & 4 deletions tests/opaque_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -96,13 +96,15 @@ func testRegistration(t *testing.T, p *testParams) (*opaque.Client, *opaque.Serv
}

credID = internal.RandomBytes(32)
pks, err := server.Deserialize.DecodeAkePublicKey(p.serverPublicKey)

if err := server.SetKeyMaterial(p.serverID, p.serverSecretKey, p.serverPublicKey, p.oprfSeed, nil); err != nil {
t.Fatalf(dbgErr, err)
}
respReg, err := server.RegistrationResponse(m1, credID)
if err != nil {
t.Fatalf(dbgErr, err)
}

respReg := server.RegistrationResponse(m1, pks, credID, p.oprfSeed)

m2s = respReg.Serialize()
}

Expand Down Expand Up @@ -163,7 +165,7 @@ func testAuthentication(
var state []byte
server, _ := p.Server()
{
if err := server.SetKeyMaterial(p.serverID, p.serverSecretKey, p.serverPublicKey, p.oprfSeed); err != nil {
if err := server.SetKeyMaterial(p.serverID, p.serverSecretKey, p.serverPublicKey, p.oprfSeed, nil); err != nil {
t.Fatal(err)
}

Expand Down
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