// RunMessageLoop handles messages from a client on a given message stream until
// it gets an error trying to read a message.
func (m *ResourceMaster) RunMessageLoop(ms util.MessageStream, programPolicy *ProgramPolicy) error {
for {
var msg Message
if err := ms.ReadMessage(&msg); err != nil {
return err
}
var fop FileOperation
t := *msg.Type
if t == MessageType_CREATE || t == MessageType_DELETE || t == MessageType_READ || t == MessageType_WRITE {
if err := proto.Unmarshal(msg.Data, &fop); err != nil {
log.Printf("Couldn't unmarshal FileOperation for operation %d\n", t)
continue
}
if err := m.checkFileAuth(&msg, &fop); err != nil {
log.Printf("The file operation %d didn't pass authorization: %s\n", t, err)
continue
}
}
switch *msg.Type {
case MessageType_AUTH_CERT:
cert, err := m.AuthenticatePrincipal(ms, &msg, programPolicy)
if err != nil {
log.Printf("Failed to authenticate a principal: %s\n", err)
continue
}
owner, err := principalNameFromDERCert(cert)
if err != nil {
log.Printf("Couldn't get the owner name from the cert: %s\n", err)
continue
}
_, err = m.InsertPrincipal(owner, cert, Authenticated)
if err != nil {
log.Printf("Couldn't set the principal as authenticated")
}
case MessageType_CREATE:
if err := m.Create(ms, &fop); err != nil {
log.Printf("Couldn't create the file %s: %s\n", *fop.Name, err)
}
case MessageType_READ:
if err := m.Read(ms, &fop, programPolicy.SymKeys); err != nil {
log.Printf("Couldn't create the file %s: %s\n", *fop.Name, err)
}
case MessageType_WRITE:
if err := m.Write(ms, &fop, programPolicy.SymKeys); err != nil {
log.Printf("Couldn't create the file %s: %s\n", *fop.Name, err)
}
default:
if err := sendResult(ms, false); err != nil {
log.Printf("Couldn't signal failure for the invalid operation: %s", err)
}
log.Printf("Invalid initial message type %d\n", *msg.Type)
}
}
}
// checkResponse waits for a RollbackResponse and checks to make sure it's not
// an ERROR response from the server.
func checkResponse(ms *util.MessageStream) error {
var rr RollbackResponse
if err := ms.ReadMessage(&rr); err != nil {
return err
}
if *rr.Type == RollbackMessageType_ERROR {
return fmt.Errorf("couldn't set the counter on the remote server")
}
return nil
}
func sendError(err error, ms *util.MessageStream) {
var errStr = ""
if err != nil {
errStr = err.Error()
}
resp := &domain_service.DomainServiceResponse{ErrorMessage: &errStr}
if _, err := ms.WriteMessage(resp); err != nil {
log.Printf("domain_server: Error sending resp on the channel: %s\n ", err)
}
}
func SendMessage(ms *util.MessageStream, msg *SimpleMessage) error {
out, err := proto.Marshal(msg)
if err != nil {
return errors.New("SendRequest: Can't encode response")
}
send := string(out)
_, err = ms.WriteString(send)
if err != nil {
return errors.New("SendResponse: Writestring error")
}
return nil
}
// recvResult waits for a OperationResult on a MessageStream
func recvResult(ms util.MessageStream) (bool, error) {
var m Message
if err := ms.ReadMessage(&m); err != nil {
return false, err
}
var res OperationResult
if err := proto.Unmarshal(m.Data, &res); err != nil {
return false, err
}
return *res.Result, nil
}
func GetMessage(ms *util.MessageStream) (*SimpleMessage,
error) {
resp, err := ms.ReadString()
if err != nil {
return nil, err
}
msg := new(SimpleMessage)
err = proto.Unmarshal([]byte(resp), msg)
if err != nil {
return nil, errors.New("GetResponse: Can't unmarshal message")
}
return msg, nil
}
// SetCounter sets the remote counter for this program.
func SetCounter(ms *util.MessageStream, counter uint64) error {
rm := &RollbackMessage{
Type: RollbackMessageType_SET_COUNTER.Enum(),
Data: EncodeCounter(counter),
}
if _, err := ms.WriteMessage(rm); err != nil {
return err
}
// TODO(tmroeder): we currently ignore the value of the counter returned
// by the server.
return checkResponse(ms)
}
// readResult reads an OperationResult and returns its value or an error.
func readResult(ms util.MessageStream) (bool, error) {
// Read the response wrapper message.
var arm Message
if err := ms.ReadMessage(&arm); err != nil {
return false, err
}
if *arm.Type != MessageType_OP_RES {
return false, fmt.Errorf("didn't receive OP_RES from the server")
}
var opr OperationResult
if err := proto.Unmarshal(arm.Data, &opr); err != nil {
return false, err
}
return *opr.Result, nil
}
// sendResult sends an OperationResult with the given value on the given stream.
func sendResult(ms util.MessageStream, result bool) error {
res := &OperationResult{Result: proto.Bool(result)}
ar := &Message{
Type: MessageType_OP_RES.Enum(),
}
var err error
if ar.Data, err = proto.Marshal(res); err != nil {
return err
}
if _, err := ms.WriteMessage(ar); err != nil {
return err
}
return nil
}
func (conn *Conn) sendCredentials(ms util.MessageStream) {
if conn.Authenticate && conn.delegation != nil {
ms.WriteString("delegation")
ms.WriteMessage(conn.delegation)
} else if conn.Authenticate {
ms.WriteString("key")
} else {
ms.WriteString("anonymous")
}
}
// RunMessageLoop handles incoming messages for the RollbackMaster and passes
// them to the appropriate functions.
func (r *RollbackMaster) RunMessageLoop(ms *util.MessageStream, programPolicy *ProgramPolicy, name string) error {
for {
var msg RollbackMessage
if err := ms.ReadMessage(&msg); err != nil {
return err
}
switch *msg.Type {
case RollbackMessageType_SET_COUNTER:
i, err := decodeCounter(msg.Data)
if err != nil {
log.Printf("failed to decode counter for SET_COUNTER: %s", err)
continue
}
if err = r.SetCounter(ms, name, i); err != nil {
log.Printf("failed to set the counter on the RollbackMaster: %s", err)
continue
}
case RollbackMessageType_GET_COUNTER:
if err := r.GetCounter(ms, name); err != nil {
log.Printf("failed to get the counter for program %s", name)
continue
}
case RollbackMessageType_SET_HASH:
var rh RollbackHash
if err := proto.Unmarshal(msg.Data, &rh); err != nil {
log.Printf("failed to unmarshal the parameters for SET_HASH: %s", err)
continue
}
if err := r.SetHash(ms, name, *rh.Item, rh.Hash); err != nil {
log.Printf("failed to set the hash for item %s on program %s: %s", *rh.Item, name, err)
continue
}
case RollbackMessageType_GET_HASHED_VERIFIER:
if err := r.GetHashedVerifier(ms, name, string(msg.Data)); err != nil {
log.Printf("failed to get the hashed verifier for program %s: %s", name, err)
continue
}
default:
log.Printf("unknown rollback message %d", *msg.Type)
}
}
}
// SetHash sets the value of a hash for a given item for this program.
func SetHash(ms *util.MessageStream, item string, hash []byte) error {
rh := &RollbackHash{
Item: proto.String(item),
Hash: hash,
}
rhb, err := proto.Marshal(rh)
if err != nil {
return err
}
rm := &RollbackMessage{
Type: RollbackMessageType_SET_HASH.Enum(),
Data: rhb,
}
if _, err := ms.WriteMessage(rm); err != nil {
return err
}
return checkResponse(ms)
}
// GetCounter implements RollbackMessageType_GET_COUNTER and returns the current
// value of a counter to the requestor.
func (r *RollbackMaster) GetCounter(ms *util.MessageStream, name string) error {
var emptyData []byte
rr := &RollbackResponse{
Type: RollbackMessageType_ERROR.Enum(),
Data: emptyData,
}
p := r.FindRollbackProgram(name)
if p == nil {
if _, err := ms.WriteMessage(rr); err != nil {
return err
}
return fmt.Errorf("couldn't find a rollback program with name %s", name)
}
rr.Type = RollbackMessageType_GET_COUNTER.Enum()
rr.Data = EncodeCounter(p.MonotonicCounter)
_, err := ms.WriteMessage(rr)
return err
}
// GetHashedVerifier gets the hash of the counter and the item hash for a given
// item.
func GetHashedVerifier(ms *util.MessageStream, item string) ([]byte, error) {
rm := &RollbackMessage{
Type: RollbackMessageType_GET_HASHED_VERIFIER.Enum(),
Data: []byte(item),
}
if _, err := ms.WriteMessage(rm); err != nil {
return nil, err
}
// We can't use checkResponse here since we need to get the value out of
// the response to read the hash.
var rr RollbackResponse
if err := ms.ReadMessage(&rr); err != nil {
return nil, err
}
if *rr.Type == RollbackMessageType_ERROR {
return nil, fmt.Errorf("couldn't set the counter on the remote server")
}
return rr.Data, nil
}
// sendOperation is a helper method that sets up the data structures needed for
// a FileOperation message like CREATE, WRITE, or READ, and sends this message
// on the MessageStream.
func sendOperation(ms util.MessageStream, mt MessageType, cert []byte, name string) error {
fop := &FileOperation{
Subject: cert,
Name: proto.String(name),
}
fopb, err := proto.Marshal(fop)
if err != nil {
return err
}
m := &Message{
Type: mt.Enum(),
Data: fopb,
}
if _, err := ms.WriteMessage(m); err != nil {
return err
}
return nil
}
// SetCounter sets the monotonic counter for a given program to a higher value.
// It returns an error if the program doesn't exist or if the new value of the
// counter is less than the current value of the counter.
func (r *RollbackMaster) SetCounter(ms *util.MessageStream, name string, counter uint64) error {
var emptyData []byte
rr := &RollbackResponse{
Type: RollbackMessageType_ERROR.Enum(),
Data: emptyData,
}
p := r.FindRollbackProgram(name)
if p == nil {
if _, err := ms.WriteMessage(rr); err != nil {
return err
}
return fmt.Errorf("couldn't find a rollback program with name %s", name)
}
if p.MonotonicCounter > counter {
if _, err := ms.WriteMessage(rr); err != nil {
return err
}
return fmt.Errorf("couldn't write a smaller counter value %d for %s", counter, name)
}
// TODO(tmroeder): this needs synchronization for any real application.
p.MonotonicCounter = counter
rr.Type = RollbackMessageType_SET_COUNTER.Enum()
rr.Data = EncodeCounter(p.MonotonicCounter)
if _, err := ms.WriteMessage(rr); err != nil {
return err
}
return nil
}
// GetCounter gets the current value of the monotonic counter for a given
// program name.
func GetCounter(ms *util.MessageStream) (uint64, error) {
// The name of the program is managed by the rollback server, not the
// client, so it doesn't need to be passed in the message.
rm := &RollbackMessage{
Type: RollbackMessageType_GET_COUNTER.Enum(),
Data: make([]byte, 0),
}
if _, err := ms.WriteMessage(rm); err != nil {
return 0, err
}
// We can't use checkResponse here since we need to get the value out of
// the response to read the counter.
var rr RollbackResponse
if err := ms.ReadMessage(&rr); err != nil {
return 0, err
}
if *rr.Type == RollbackMessageType_ERROR {
return 0, fmt.Errorf("couldn't set the counter on the remote server")
}
return decodeCounter(rr.Data)
}
// SetHash implements RollbackMessageType_SET_HASH by setting the value of the
// hash for a given item to a given hash value.
func (r *RollbackMaster) SetHash(ms *util.MessageStream, name string, item string, h []byte) error {
var emptyData []byte
rr := &RollbackResponse{
Type: RollbackMessageType_ERROR.Enum(),
Data: emptyData,
}
p := r.FindRollbackProgram(name)
if p == nil {
if _, err := ms.WriteMessage(rr); err != nil {
return err
}
return fmt.Errorf("couldn't find a rollback program with name %s", name)
}
// Set the hash.
if err := p.AddRollbackHashEntry(item, h); err != nil {
if _, e := ms.WriteMessage(rr); e != nil {
return e
}
return err
}
rh := &RollbackHash{
Item: proto.String(item),
Hash: h,
}
rhb, err := proto.Marshal(rh)
if err != nil {
if _, e := ms.WriteMessage(rr); e != nil {
return e
}
return err
}
// TODO(tmroeder): Do you need to update the counter when you update the
// hash?
rr.Type = RollbackMessageType_SET_HASH.Enum()
rr.Data = rhb
_, err = ms.WriteMessage(rr)
return err
}
// AuthenticatePrincipal is a client method used to send a request to a
// ResourceMaster to authenticate a principal with a given certificate and a
// given set of keys.
func AuthenticatePrincipal(ms util.MessageStream, key *tao.Keys, derCert []byte) error {
// Send the authentication request, which supposes that a server is
// waiting to receive this request.
c := &Message{
Type: MessageType_AUTH_CERT.Enum(),
Data: derCert,
}
if _, err := ms.WriteMessage(c); err != nil {
return err
}
// Receive a challenge nonce from the server.
var nc Message
if err := ms.ReadMessage(&nc); err != nil {
return err
}
if *nc.Type != MessageType_NONCE_CHALL {
return fmt.Errorf("didn't receive NONCE_CHALL from the server")
}
// Sign the nonce.
sn := &Message{
Type: MessageType_SIGNED_NONCE.Enum(),
}
var err error
if sn.Data, err = key.SigningKey.Sign(nc.Data, ChallengeContext); err != nil {
return err
}
if _, err := ms.WriteMessage(sn); err != nil {
return err
}
// Get the result from the server after verificaton.
res, err := readResult(ms)
if err != nil {
return err
}
if !res {
return fmt.Errorf("the signed nonce failed verification")
}
return nil
}
// GetHashedVerifier gets a version of the hash for a given item along with the
// current monotonic counter.
func (r *RollbackMaster) GetHashedVerifier(ms *util.MessageStream, name string, item string) error {
var emptyData []byte
rr := &RollbackResponse{
Type: RollbackMessageType_ERROR.Enum(),
Data: emptyData,
}
p := r.FindRollbackProgram(name)
if p == nil {
if _, err := ms.WriteMessage(rr); err != nil {
return err
}
return fmt.Errorf("couldn't find a rollback program with name %s", name)
}
h := p.FindRollbackHashEntry(item)
if h == nil {
if _, err := ms.WriteMessage(rr); err != nil {
return err
}
return fmt.Errorf("couldn't find an item with name '%s' in program '%s'", item, name)
}
// Return SHA-256(Counter || Hash || Counter).
// TODO(tmroeder): what is the justification for this protocol?
sha256Hash := sha256.New()
b := EncodeCounter(p.MonotonicCounter)
sha256Hash.Write(b)
sha256Hash.Write(h)
sha256Hash.Write(b)
hash := sha256Hash.Sum(nil)
rr.Type = RollbackMessageType_GET_HASHED_VERIFIER.Enum()
rr.Data = hash[:]
_, err := ms.WriteMessage(rr)
return err
}
// SendFile reads a file from disk and streams it to a receiver across a
// MessageStream. If there are sufficient bytes in the keys (at least
// hmacKeySize+aesKeySize), then it will attempt to check the integrity of the
// file with HMAC-SHA256 and decrypt it with AES-CTR-128.
func SendFile(ms util.MessageStream, dir string, filename string, keys []byte) error {
fullpath := path.Join(dir, filename)
fileInfo, err := os.Stat(fullpath)
if err != nil {
return fmt.Errorf("in SendFile: no file '%s' found: %s", fullpath, err)
}
file, err := os.Open(fullpath)
if err != nil {
return fmt.Errorf("in SendFile: can't open file '%s': %s", fullpath, err)
}
defer file.Close()
// This encryption scheme uses AES-CTR with HMAC-SHA256 for integrity
// protection.
var hm hash.Hash
var ctr cipher.Stream
iv := make([]byte, ivSize)
hasKeys := len(keys) >= minKeySize
// The variable "left" gives the total number of bytes left to read from
// the (maybe encrypted) file.
left := fileInfo.Size()
buf := make([]byte, bufferSize)
if hasKeys {
dec, err := aes.NewCipher(keys[:aesKeySize])
if err != nil || dec == nil {
return fmt.Errorf("can't create AES cipher in SendFile: %s", err)
}
if _, err := file.Read(iv); err != nil {
return err
}
// Remove the IV from the number of remaining bytes to decrypt.
left = left - ivSize
// Take all the remaining key bytes for the HMAC key.
hm = hmac.New(sha256.New, keys[aesKeySize:])
hmacSize := hm.Size()
// The HMAC input starts with the IV.
hm.Write(iv)
ctr = cipher.NewCTR(dec, iv)
if ctr == nil {
return fmt.Errorf("can't create AES-CTR encryption")
}
// Remove the HMAC-SHA256 output from the bytes to check.
left = left - int64(hmacSize)
// Secure decryption in this case requires reading the file
// twice: once to check the MAC, and once to decrypt the bytes.
// The MAC must be checked before *any* decryption occurs and
// before *any* decrypted bytes are sent to the receiver.
for {
// Figure out how many bytes to read on this iteration.
readSize := int64(bufferSize)
final := false
if left <= bufferSize {
readSize = left
final = true
}
// Read the (maybe encrypted) bytes from the file.
n, err := file.Read(buf[:readSize])
if err != nil {
return err
}
left = left - int64(n)
hm.Write(buf[:n])
if final {
break
}
}
computed := hm.Sum(nil)
original := buf[:hmacSize]
// Read the file's version of the HMAC and check it securely
// against the computed version.
if _, err := file.Read(original); err != nil {
return err
}
if !hmac.Equal(computed, original) {
return fmt.Errorf("invalid file HMAC on decryption for file '%s'", fullpath)
}
// Go back to the beginning of the file (minus the IV) for
// decryption.
if _, err := file.Seek(ivSize, 0); err != nil {
return fmt.Errorf("couldn't seek back to the beginning of file '%s': %s", fullpath, err)
}
// Reset the number of bytes so it only includes the encrypted
// bytes.
left = fileInfo.Size() - int64(ivSize+hmacSize)
}
// The input buffer, and a temporary buffer for holding decrypted
// plaintext.
temp := make([]byte, bufferSize)
// Set up a framing message to use to send the data.
m := &Message{
Type: MessageType_FILE_NEXT.Enum(),
}
// Now that the integrity of the data has been verified, if needed, send
// the data (after decryption, if necessary) to the receiver.
for {
// Figure out how many bytes to read on this iteration.
readSize := int64(bufferSize)
final := false
if left <= bufferSize {
readSize = left
final = true
m.Type = MessageType_FILE_LAST.Enum()
}
// Read the (maybe encrypted) bytes from the file.
n, err := file.Read(buf[:readSize])
if err != nil {
return err
}
left = left - int64(n)
if hasKeys {
ctr.XORKeyStream(temp[:n], buf[:n])
m.Data = temp[:n]
} else {
m.Data = buf[:n]
}
// Send the decrypted data to the receiver.
if _, err := ms.WriteMessage(m); err != nil {
return err
}
if final {
break
}
}
return nil
}
// GetFile receives bytes from a sender and optionally encrypts them and adds
// integrity protection, and writes them to disk.
func GetFile(ms util.MessageStream, dir string, filename string, keys []byte) error {
fullpath := path.Join(dir, filename)
file, err := os.Create(fullpath)
if err != nil {
return fmt.Errorf("can't create file '%s' in GetFile", fullpath)
}
defer file.Close()
var ctr cipher.Stream
var hm hash.Hash
iv := make([]byte, ivSize)
hasKeys := len(keys) >= minKeySize
if hasKeys {
enc, err := aes.NewCipher(keys[:aesKeySize])
if err != nil || enc == nil {
return fmt.Errorf("couldn't create an AES cipher: %s", err)
}
// Use the remaining bytes of the key slice for the HMAC key.
hm = hmac.New(sha256.New, keys[aesKeySize:])
if _, err := rand.Read(iv); err != nil {
return fmt.Errorf("couldn't read random bytes for a fresh IV: %s", err)
}
// The first bytes of the HMAC input are the IV.
hm.Write(iv)
ctr = cipher.NewCTR(enc, iv)
if ctr == nil {
return fmt.Errorf("couldn't create a new instance of AES-CTR-128")
}
if _, err = file.Write(iv); err != nil {
return err
}
}
// temp holds temporary encrypted ciphertext before it's written to
// disk.
temp := make([]byte, bufferSize)
for {
var m Message
if err := ms.ReadMessage(&m); err != nil {
return nil
}
// Sanity check: this must be FILE_LAST or FILE_NEXT.
t := *m.Type
if !(t == MessageType_FILE_LAST || t == MessageType_FILE_NEXT) {
return fmt.Errorf("received invalid message type %d during file streaming in GetFile", t)
}
if hasKeys {
l := len(m.Data)
ctr.XORKeyStream(temp, m.Data)
hm.Write(temp[:l])
if _, err = file.Write(temp[:l]); err != nil {
return err
}
} else {
if _, err = file.Write(m.Data); err != nil {
return err
}
}
// FILE_LAST corresponds to receiving the final bytes of the
// file.
if *m.Type == MessageType_FILE_LAST {
break
}
}
// Write the MAC at the end of the file.
if hasKeys {
hmacBytes := hm.Sum(nil)
if _, err = file.Write(hmacBytes[:]); err != nil {
return err
}
}
return nil
}
func (conn *Conn) recvCredentials(ms util.MessageStream) {
m, err := ms.ReadString()
if err != nil {
return
}
if m == "delegation" {
var a Attestation
if err = ms.ReadMessage(&a); err != nil {
return
}
// Validate the peer certificate
peerCert := conn.ConnectionState().PeerCertificates[0]
p, err := ValidatePeerAttestation(&a, peerCert)
if err != nil {
ms.SetErr(err)
return
}
if conn.guard != nil {
if conn.verifier != nil {
if err = AddEndorsements(conn.guard, &a, conn.verifier); err != nil {
ms.SetErr(err)
return
}
}
if !conn.guard.IsAuthorized(p, "Connect", nil) {
ms.SetErr(errors.New("principal delegator in client attestation is not authorized to connect"))
return
}
}
conn.peer = &p
} else if m == "key" {
peerCert := conn.ConnectionState().PeerCertificates[0]
v, err := FromX509(peerCert)
if err != nil {
ms.SetErr(errors.New("can't decode key from peer certificate"))
return
}
p := v.ToPrincipal()
conn.peer = &p
} else if m == "anonymous" {
if conn.guard != nil {
err = errors.New("peer did not provide tao delegation")
ms.SetErr(err)
return
}
} else {
err = errors.New("unrecognized authentication handshake: " + m)
ms.SetErr(err)
return
}
}
func sendResponse(ms util.MessageStream, resp *taoca.Response) {
_, err := ms.WriteMessage(resp)
if err != nil {
fmt.Printf("error writing response: %s\n", err)
}
}
// AuthenticatePrincipal runs a synchronous protocol to authenticate a single
// principal on a single channel. In this toy implementation, it is assumed that
// there are no other principals on the channel and that there are no other
// simultaneous channels.
func (m *ResourceMaster) AuthenticatePrincipal(ms util.MessageStream, msg *Message, programPolicy *ProgramPolicy) ([]byte, error) {
// The certificate message is passed in by the caller as the first
// message.
// Process the certificate. For AUTH_CERT, the data is just the
// certificate.
cert, err := x509.ParseCertificate([]byte(msg.Data))
if err != nil {
log.Printf("couldn't Parse Certificate in AuthenticatePrincipal\n")
return nil, err
}
// Set up a nonce challenge for the reply. For NONCE_CHALL, the data is
// also just the message itself.
reply := &Message{
Type: MessageType_NONCE_CHALL.Enum(),
Data: make([]byte, NonceSize),
}
if _, err = rand.Read(reply.Data); err != nil {
return nil, err
}
// Step 1: Send a nonce to the principal.
if _, err := ms.WriteMessage(reply); err != nil {
return nil, err
}
// Step 2: Wait for the signed response.
var s Message
if err := ms.ReadMessage(&s); err != nil {
return nil, err
}
if *s.Type != MessageType_SIGNED_NONCE {
return nil, fmt.Errorf("received message was not SIGNED_NONCE")
}
// Verify the certificate against the root.
// TODO(tmroeder): move the VerifyOptions up into the ResourceMaster.
var opts x509.VerifyOptions
roots := x509.NewCertPool()
policyCert, err := x509.ParseCertificate(programPolicy.PolicyCert)
if err != nil || policyCert == nil {
return nil, err
}
roots.AddCert(policyCert)
opts.Roots = roots
chains, err := cert.Verify(opts)
if chains == nil || err != nil {
return nil, err
}
v, err := tao.FromX509(cert)
if err != nil {
return nil, err
}
ok, err := v.Verify(reply.Data, ChallengeContext, s.Data)
if err != nil {
return nil, err
}
if err := sendResult(ms, ok); err != nil {
return nil, fmt.Errorf("failed to return a result to the client")
}
if !ok {
return nil, fmt.Errorf("the nonce signature did not pass verification")
}
return msg.Data, nil
}