client.go

package irmaclient

import (
	"crypto/rand"
	"sort"
	"strconv"
	"time"

	"github.com/credentials/go-go-gadget-paillier"
	raven "github.com/getsentry/raven-go"
	"github.com/go-errors/errors"
	"github.com/privacybydesign/gabi"
	"github.com/privacybydesign/gabi/big"
	"github.com/privacybydesign/irmago"
	"github.com/privacybydesign/irmago/internal/fs"
)

// This file contains most methods of the Client (c.f. session.go
// and updates.go).
//
// Clients are the main entry point into this package for the user of this package.
// The Client struct:
// - (De)serializes credentials and keyshare server information
// from storage, as well as logs of earlier IRMA sessions
// - it provides access to the attributes and all related information of its credentials,
// - it is the starting point for new IRMA sessions;
// - and it computes some of the messages in the client side of the IRMA protocol.
//
// The storage of credentials is split up in several parts:
//
// - The CL-signature of each credential is stored separately, so that we can
// load it on demand (i.e., during an IRMA session), instead of immediately
// at initialization.
//
// - The attributes of all credentials are stored together, as they all
// immediately need to be available anyway.
//
// - The secret key (the zeroth attribute of every credential), being the same
// across all credentials, is stored only once in a separate file (storing this
// in multiple places would be bad).

type Client struct {
	// Stuff we manage on disk
	secretkey        *secretKey
	attributes       map[irma.CredentialTypeIdentifier][]*irma.AttributeList
	credentialsCache map[irma.CredentialTypeIdentifier]map[int]*credential
	keyshareServers  map[irma.SchemeManagerIdentifier]*keyshareServer
	paillierKeyCache *paillierPrivateKey
	logs             []*LogEntry
	updates          []update

	// Where we store/load it to/from
	storage storage

	// Other state
	Preferences           Preferences
	Configuration         *irma.Configuration
	irmaConfigurationPath string
	androidStoragePath    string
	handler               ClientHandler
}

// SentryDSN should be set in the init() function
// Setting it to an empty string means no crash reports
var SentryDSN = ""

type Preferences struct {
	EnableCrashReporting bool
}

var defaultPreferences = Preferences{
	EnableCrashReporting: true,
}

// KeyshareHandler is used for asking the user for his email address and PIN,
// for enrolling at a keyshare server.
type KeyshareHandler interface {
	EnrollmentFailure(manager irma.SchemeManagerIdentifier, err error)
	EnrollmentSuccess(manager irma.SchemeManagerIdentifier)
}

type ChangePinHandler interface {
	ChangePinFailure(manager irma.SchemeManagerIdentifier, err error)
	ChangePinSuccess(manager irma.SchemeManagerIdentifier)
	ChangePinIncorrect(manager irma.SchemeManagerIdentifier, attempts int)
	ChangePinBlocked(manager irma.SchemeManagerIdentifier, timeout int)
}

// ClientHandler informs the user that the configuration or the list of attributes
// that this client uses has been updated.
type ClientHandler interface {
	KeyshareHandler
	ChangePinHandler

	UpdateConfiguration(new *irma.IrmaIdentifierSet)
	UpdateAttributes()
}

type secretKey struct {
	Key *big.Int
}

// New creates a new Client that uses the directory
// specified by storagePath for (de)serializing itself. irmaConfigurationPath
// is the path to a (possibly readonly) folder containing irma_configuration;
// androidStoragePath is an optional path to the files of the old android app
// (specify "" if you do not want to parse the old android app files),
// and handler is used for informing the user of new stuff, and when a
// enrollment to a keyshare server needs to happen.
// The client returned by this function has been fully deserialized
// and is ready for use.
//
// NOTE: It is the responsibility of the caller that there exists a (properly
// protected) directory at storagePath!
func New(
	storagePath string,
	irmaConfigurationPath string,
	androidStoragePath string,
	handler ClientHandler,
) (*Client, error) {
	var err error
	if err = fs.AssertPathExists(storagePath); err != nil {
		return nil, err
	}
	if err = fs.AssertPathExists(irmaConfigurationPath); err != nil {
		return nil, err
	}

	cm := &Client{
		credentialsCache:      make(map[irma.CredentialTypeIdentifier]map[int]*credential),
		keyshareServers:       make(map[irma.SchemeManagerIdentifier]*keyshareServer),
		attributes:            make(map[irma.CredentialTypeIdentifier][]*irma.AttributeList),
		irmaConfigurationPath: irmaConfigurationPath,
		androidStoragePath:    androidStoragePath,
		handler:               handler,
	}

	cm.Configuration, err = irma.NewConfiguration(storagePath+"/irma_configuration", irmaConfigurationPath)
	if err != nil {
		return nil, err
	}

	schemeMgrErr := cm.Configuration.ParseOrRestoreFolder()
	// If schemMgrErr is of type SchemeManagerError, we continue and
	// return it at the end; otherwise bail out now
	_, isSchemeMgrErr := schemeMgrErr.(*irma.SchemeManagerError)
	if schemeMgrErr != nil && !isSchemeMgrErr {
		return nil, schemeMgrErr
	}

	// Ensure storage path exists, and populate it with necessary files
	cm.storage = storage{storagePath: storagePath, Configuration: cm.Configuration}
	if err = cm.storage.EnsureStorageExists(); err != nil {
		return nil, err
	}

	if cm.Preferences, err = cm.storage.LoadPreferences(); err != nil {
		return nil, err
	}
	cm.applyPreferences()

	// Perform new update functions from clientUpdates, if any
	if err = cm.update(); err != nil {
		return nil, err
	}

	// Load our stuff
	if cm.secretkey, err = cm.storage.LoadSecretKey(); err != nil {
		return nil, err
	}
	if cm.attributes, err = cm.storage.LoadAttributes(); err != nil {
		return nil, err
	}
	if cm.keyshareServers, err = cm.storage.LoadKeyshareServers(); err != nil {
		return nil, err
	}
	if cm.paillierKeyCache, err = cm.storage.LoadPaillierKeys(); err != nil {
		return nil, err
	}
	if cm.paillierKeyCache == nil {
		cm.paillierKey(false)
	}

	if len(cm.UnenrolledSchemeManagers()) > 1 {
		return nil, errors.New("Too many keyshare servers")
	}

	return cm, schemeMgrErr
}

// CredentialInfoList returns a list of information of all contained credentials.
func (client *Client) CredentialInfoList() irma.CredentialInfoList {
	list := irma.CredentialInfoList([]*irma.CredentialInfo{})

	for _, attrlistlist := range client.attributes {
		for _, attrlist := range attrlistlist {
			info := attrlist.Info()
			if info == nil {
				continue
			}
			list = append(list, info)
		}
	}

	sort.Sort(list)
	return list
}

// addCredential adds the specified credential to the Client, saving its signature
// imediately, and optionally cm.attributes as well.
func (client *Client) addCredential(cred *credential, storeAttributes bool) (err error) {
	id := irma.NewCredentialTypeIdentifier("")
	if cred.CredentialType() != nil {
		id = cred.CredentialType().Identifier()
	}

	// Don't add duplicate creds
	for _, attrlistlist := range client.attributes {
		for _, attrs := range attrlistlist {
			if attrs.Hash() == cred.AttributeList().Hash() {
				return nil
			}
		}
	}

	// If this is a singleton credential type, ensure we have at most one by removing any previous instance
	if !id.Empty() && cred.CredentialType().IsSingleton {
		for len(client.attrs(id)) != 0 {
			client.remove(id, 0, false)
		}
	}

	// Append the new cred to our attributes and credentials
	client.attributes[id] = append(client.attrs(id), cred.AttributeList())
	if !id.Empty() {
		if _, exists := client.credentialsCache[id]; !exists {
			client.credentialsCache[id] = make(map[int]*credential)
		}
		counter := len(client.attributes[id]) - 1
		client.credentialsCache[id][counter] = cred
	}

	if err = client.storage.StoreSignature(cred); err != nil {
		return
	}
	if storeAttributes {
		err = client.storage.StoreAttributes(client.attributes)
	}
	return
}

func generateSecretKey() (*secretKey, error) {
	key, err := gabi.RandomBigInt(gabi.DefaultSystemParameters[1024].Lm)
	if err != nil {
		return nil, err
	}
	return &secretKey{Key: key}, nil
}

// Removal methods

func (client *Client) remove(id irma.CredentialTypeIdentifier, index int, storenow bool) error {
	// Remove attributes
	list, exists := client.attributes[id]
	if !exists || index >= len(list) {
		return errors.Errorf("Can't remove credential %s-%d: no such credential", id.String(), index)
	}
	attrs := list[index]
	client.attributes[id] = append(list[:index], list[index+1:]...)
	if storenow {
		if err := client.storage.StoreAttributes(client.attributes); err != nil {
			return err
		}
	}

	// Remove credential
	if creds, exists := client.credentialsCache[id]; exists {
		if _, exists := creds[index]; exists {
			delete(creds, index)
			client.credentialsCache[id] = creds
		}
	}

	// Remove signature from storage
	if err := client.storage.DeleteSignature(attrs); err != nil {
		return err
	}

	removed := map[irma.CredentialTypeIdentifier][]irma.TranslatedString{}
	removed[id] = attrs.Strings()

	if storenow {
		return client.addLogEntry(&LogEntry{
			Type:    actionRemoval,
			Time:    irma.Timestamp(time.Now()),
			Removed: removed,
		})
	}
	return nil
}

// RemoveCredential removes the specified credential.
func (client *Client) RemoveCredential(id irma.CredentialTypeIdentifier, index int) error {
	return client.remove(id, index, true)
}

// RemoveCredentialByHash removes the specified credential.
func (client *Client) RemoveCredentialByHash(hash string) error {
	cred, index, err := client.credentialByHash(hash)
	if err != nil {
		return err
	}
	return client.RemoveCredential(cred.CredentialType().Identifier(), index)
}

// RemoveAllCredentials removes all credentials.
func (client *Client) RemoveAllCredentials() error {
	removed := map[irma.CredentialTypeIdentifier][]irma.TranslatedString{}
	for _, attrlistlist := range client.attributes {
		for _, attrs := range attrlistlist {
			if attrs.CredentialType() != nil {
				removed[attrs.CredentialType().Identifier()] = attrs.Strings()
			}
			client.storage.DeleteSignature(attrs)
		}
	}
	client.attributes = map[irma.CredentialTypeIdentifier][]*irma.AttributeList{}
	if err := client.storage.StoreAttributes(client.attributes); err != nil {
		return err
	}

	logentry := &LogEntry{
		Type:    actionRemoval,
		Time:    irma.Timestamp(time.Now()),
		Removed: removed,
	}
	if err := client.addLogEntry(logentry); err != nil {
		return err
	}
	return client.storage.StoreLogs(client.logs)
}

// Attribute and credential getter methods

// attrs returns cm.attributes[id], initializing it to an empty slice if neccesary
func (client *Client) attrs(id irma.CredentialTypeIdentifier) []*irma.AttributeList {
	list, exists := client.attributes[id]
	if !exists {
		list = make([]*irma.AttributeList, 0, 1)
		client.attributes[id] = list
	}
	return list
}

// creds returns cm.credentials[id], initializing it to an empty map if neccesary
func (client *Client) creds(id irma.CredentialTypeIdentifier) map[int]*credential {
	list, exists := client.credentialsCache[id]
	if !exists {
		list = make(map[int]*credential)
		client.credentialsCache[id] = list
	}
	return list
}

// Attributes returns the attribute list of the requested credential, or nil if we do not have it.
func (client *Client) Attributes(id irma.CredentialTypeIdentifier, counter int) (attributes *irma.AttributeList) {
	list := client.attrs(id)
	if len(list) <= counter {
		return
	}
	return list[counter]
}

func (client *Client) credentialByHash(hash string) (*credential, int, error) {
	for _, attrlistlist := range client.attributes {
		for index, attrs := range attrlistlist {
			if attrs.Hash() == hash {
				cred, err := client.credential(attrs.CredentialType().Identifier(), index)
				return cred, index, err
			}
		}
	}
	return nil, 0, nil
}

func (client *Client) credentialByID(id irma.CredentialIdentifier) (*credential, error) {
	if _, exists := client.attributes[id.Type]; !exists {
		return nil, nil
	}
	for index, attrs := range client.attributes[id.Type] {
		if attrs.Hash() == id.Hash {
			return client.credential(attrs.CredentialType().Identifier(), index)
		}
	}
	return nil, nil
}

// credential returns the requested credential, or nil if we do not have it.
func (client *Client) credential(id irma.CredentialTypeIdentifier, counter int) (cred *credential, err error) {
	// If the requested credential is not in credential map, we check if its attributes were
	// deserialized during New(). If so, there should be a corresponding signature file,
	// so we read that, construct the credential, and add it to the credential map
	if _, exists := client.creds(id)[counter]; !exists {
		attrs := client.Attributes(id, counter)
		if attrs == nil { // We do not have the requested cred
			return
		}
		sig, err := client.storage.LoadSignature(attrs)
		if err != nil {
			return nil, err
		}
		if sig == nil {
			err = errors.New("signature file not found")
			return nil, err
		}
		pk, err := attrs.PublicKey()
		if err != nil {
			return nil, err
		}
		if pk == nil {
			return nil, errors.New("unknown public key")
		}
		cred, err := newCredential(&gabi.Credential{
			Attributes: append([]*big.Int{client.secretkey.Key}, attrs.Ints...),
			Signature:  sig,
			Pk:         pk,
		}, client.Configuration)
		if err != nil {
			return nil, err
		}
		client.credentialsCache[id][counter] = cred
	}

	return client.credentialsCache[id][counter], nil
}

// Methods used in the IRMA protocol

// Candidates returns a list of attributes present in this client
// that satisfy the specified attribute disjunction.
func (client *Client) Candidates(disjunction *irma.AttributeDisjunction) []*irma.AttributeIdentifier {
	candidates := make([]*irma.AttributeIdentifier, 0, 10)

	for _, attribute := range disjunction.Attributes {
		credID := attribute.CredentialTypeIdentifier()
		if !client.Configuration.Contains(credID) {
			continue
		}
		creds := client.attributes[credID]
		count := len(creds)
		if count == 0 {
			continue
		}
		for _, attrs := range creds {
			if !attrs.IsValid() {
				continue
			}
			id := &irma.AttributeIdentifier{Type: attribute, CredentialHash: attrs.Hash()}
			if attribute.IsCredential() {
				candidates = append(candidates, id)
			} else {
				val := attrs.UntranslatedAttribute(attribute)
				if val == nil {
					continue
				}
				if !disjunction.HasValues() {
					candidates = append(candidates, id)
				} else {
					requiredValue, present := disjunction.Values[attribute]
					if !present || requiredValue == nil || *val == *requiredValue {
						candidates = append(candidates, id)
					}
				}
			}
		}
	}

	return candidates
}

// CheckSatisfiability checks if this client has the required attributes
// to satisfy the specifed disjunction list. If not, the unsatisfiable disjunctions
// are returned.
func (client *Client) CheckSatisfiability(
	disjunctions irma.AttributeDisjunctionList,
) ([][]*irma.AttributeIdentifier, irma.AttributeDisjunctionList) {
	candidates := [][]*irma.AttributeIdentifier{}
	missing := irma.AttributeDisjunctionList{}
	for i, disjunction := range disjunctions {
		candidates = append(candidates, []*irma.AttributeIdentifier{})
		candidates[i] = client.Candidates(disjunction)
		if len(candidates[i]) == 0 {
			missing = append(missing, disjunction)
		}
	}
	return candidates, missing
}

func (client *Client) groupCredentials(choice *irma.DisclosureChoice, disjunctions irma.AttributeDisjunctionList) (
	map[irma.CredentialIdentifier][]int, irma.DisclosedAttributeIndices, error,
) {
	grouped := make(map[irma.CredentialIdentifier][]int)
	if choice == nil || choice.Attributes == nil {
		return grouped, irma.DisclosedAttributeIndices{}, nil
	}

	attributeIndices := make(irma.DisclosedAttributeIndices, len(choice.Attributes))
	for i, attribute := range choice.Attributes {
		identifier := attribute.Type
		ici := attribute.CredentialIdentifier()

		// If this is the first attribute of its credential type that we encounter
		// in the disclosure choice, then there is no slice yet at grouped[ici]
		if _, present := grouped[ici]; !present {
			indices := make([]int, 1, 1)
			indices[0] = 1 // Always include metadata
			grouped[ici] = indices
		}

		if identifier.IsCredential() {
			attributeIndices[i] = []*irma.DisclosedAttributeIndex{
				{AttributeIndex: 1, Identifier: ici},
			}
			continue // In this case we only disclose the metadata attribute, which is already handled
		}
		index, err := client.Configuration.CredentialTypes[identifier.CredentialTypeIdentifier()].IndexOf(identifier)
		if err != nil {
			return nil, nil, err
		}

		attributeIndices[i] = []*irma.DisclosedAttributeIndex{
			{AttributeIndex: index + 2, Identifier: ici},
		}

		// These indices will be used in the []*big.Int at gabi.credential.Attributes,
		// which doesn't know about the secret key and metadata attribute, so +2
		grouped[ici] = append(grouped[ici], index+2)
	}

	return grouped, attributeIndices, nil
}

// ProofBuilders constructs a list of proof builders for the specified attribute choice.
func (client *Client) ProofBuilders(choice *irma.DisclosureChoice, request irma.SessionRequest, issig bool,
) (gabi.ProofBuilderList, irma.DisclosedAttributeIndices, error) {
	todisclose, disjunctionChoices, err := client.groupCredentials(choice, request.ToDisclose())
	if err != nil {
		return nil, nil, err
	}

	builders := gabi.ProofBuilderList([]gabi.ProofBuilder{})

	for i, choice := range disjunctionChoices {
		cred, err := client.credentialByID(choice[0].Identifier)
		if err != nil {
			return nil, nil, err
		}
		choice[0].CredentialIndex = i
		builders = append(builders, cred.Credential.CreateDisclosureProofBuilder(todisclose[choice[0].Identifier]))
	}

	if issig {
		var sigs []*big.Int
		var disclosed [][]*big.Int
		var s *big.Int
		var d []*big.Int
		for _, builder := range builders {
			s, d = builder.(*gabi.DisclosureProofBuilder).TimestampRequestContributions()
			sigs = append(sigs, s)
			disclosed = append(disclosed, d)
		}
		r := request.(*irma.SignatureRequest)
		r.Timestamp, err = irma.GetTimestamp(r.Message, sigs, disclosed)
		if err != nil {
			return nil, nil, err
		}
	}

	return builders, disjunctionChoices, nil
}

// Proofs computes disclosure proofs containing the attributes specified by choice.
func (client *Client) Proofs(choice *irma.DisclosureChoice, request irma.SessionRequest, issig bool) (*irma.Disclosure, error) {
	builders, choices, err := client.ProofBuilders(choice, request, issig)
	if err != nil {
		return nil, err
	}

	return &irma.Disclosure{
		Proofs:  builders.BuildProofList(request.GetContext(), request.GetNonce(), issig),
		Indices: choices,
	}, nil
}

// generateIssuerProofNonce generates a nonce which the issuer must use in its gabi.ProofS.
func generateIssuerProofNonce() (*big.Int, error) {
	return gabi.RandomBigInt(gabi.DefaultSystemParameters[4096].Lstatzk)
}

// IssuanceProofBuilders constructs a list of proof builders in the issuance protocol
// for the future credentials as well as possibly any disclosed attributes, and generates
// a nonce against which the issuer's proof of knowledge must verify.
func (client *Client) IssuanceProofBuilders(request *irma.IssuanceRequest,
) (gabi.ProofBuilderList, irma.DisclosedAttributeIndices, *big.Int, error) {
	issuerProofNonce, err := generateIssuerProofNonce()
	if err != nil {
		return nil, nil, nil, err
	}
	builders := gabi.ProofBuilderList([]gabi.ProofBuilder{})
	for _, futurecred := range request.Credentials {
		var pk *gabi.PublicKey
		pk, err = client.Configuration.PublicKey(futurecred.CredentialTypeID.IssuerIdentifier(), futurecred.KeyCounter)
		if err != nil {
			return nil, nil, nil, err
		}
		credBuilder := gabi.NewCredentialBuilder(
			pk, request.GetContext(), client.secretkey.Key, issuerProofNonce)
		builders = append(builders, credBuilder)
	}

	disclosures, choices, err := client.ProofBuilders(request.Choice, request, false)
	if err != nil {
		return nil, nil, nil, err
	}
	builders = append(disclosures, builders...)
	return builders, choices, issuerProofNonce, nil
}

// IssueCommitments computes issuance commitments, along with disclosure proofs specified by choice,
// and also returns the credential builders which will become the new credentials upon combination with the issuer's signature.
func (client *Client) IssueCommitments(request *irma.IssuanceRequest,
) (*irma.IssueCommitmentMessage, gabi.ProofBuilderList, error) {
	builders, choices, issuerProofNonce, err := client.IssuanceProofBuilders(request)
	if err != nil {
		return nil, nil, err
	}
	return &irma.IssueCommitmentMessage{
		IssueCommitmentMessage: &gabi.IssueCommitmentMessage{
			Proofs: builders.BuildProofList(request.GetContext(), request.GetNonce(), false),
			Nonce2: issuerProofNonce,
		},
		Indices: choices,
	}, builders, nil
}

// ConstructCredentials constructs and saves new credentials using the specified issuance signature messages
// and credential builders.
func (client *Client) ConstructCredentials(msg []*gabi.IssueSignatureMessage, request *irma.IssuanceRequest, builders gabi.ProofBuilderList) error {
	if len(msg) > len(builders) {
		return errors.New("Received unexpected amount of signatures")
	}

	// First collect all credentials in a slice, so that if one of them induces an error,
	// we save none of them to fail the session cleanly
	gabicreds := []*gabi.Credential{}
	offset := 0
	for i, builder := range builders {
		credbuilder, ok := builder.(*gabi.CredentialBuilder)
		if !ok { // Skip builders of disclosure proofs
			offset++
			continue
		}
		sig := msg[i-offset]
		attrs, err := request.Credentials[i-offset].AttributeList(client.Configuration, irma.GetMetadataVersion(request.GetVersion()))
		if err != nil {
			return err
		}
		cred, err := credbuilder.ConstructCredential(sig, attrs.Ints)
		if err != nil {
			return err
		}
		gabicreds = append(gabicreds, cred)
	}

	for _, gabicred := range gabicreds {
		newcred, err := newCredential(gabicred, client.Configuration)
		if err != nil {
			return err
		}
		if err = client.addCredential(newcred, true); err != nil {
			return err
		}
	}

	return nil
}

// Keyshare server handling

// PaillierKey returns a new Paillier key (and generates a new one in a goroutine).
func (client *Client) paillierKey(wait bool) *paillierPrivateKey {
	cached := client.paillierKeyCache
	ch := make(chan bool)

	// Would just write client.paillierKeyCache instead of cached here, but the worker
	// modifies client.paillierKeyCache, and we must be sure that the boolean here and
	// the if-clause below match.
	go client.paillierKeyWorker(cached == nil && wait, ch)
	if cached == nil && wait {
		<-ch
		// generate yet another one for future calls, but no need to wait now
		go client.paillierKeyWorker(false, ch)
	}
	return client.paillierKeyCache
}

func (client *Client) paillierKeyWorker(wait bool, ch chan bool) {
	newkey, _ := paillier.GenerateKey(rand.Reader, 2048)
	client.paillierKeyCache = (*paillierPrivateKey)(newkey)
	client.storage.StorePaillierKeys(client.paillierKeyCache)
	if wait {
		ch <- true
	}
}

func (client *Client) genSchemeManagersList(enrolled bool) []irma.SchemeManagerIdentifier {
	list := []irma.SchemeManagerIdentifier{}
	for name, manager := range client.Configuration.SchemeManagers {
		if _, contains := client.keyshareServers[name]; manager.Distributed() && contains == enrolled {
			list = append(list, manager.Identifier())
		}
	}
	return list
}

func (client *Client) UnenrolledSchemeManagers() []irma.SchemeManagerIdentifier {
	return client.genSchemeManagersList(false)
}

func (client *Client) EnrolledSchemeManagers() []irma.SchemeManagerIdentifier {
	return client.genSchemeManagersList(true)
}

// KeyshareEnroll attempts to enroll at the keyshare server of the specified scheme manager.
func (client *Client) KeyshareEnroll(manager irma.SchemeManagerIdentifier, email *string, pin string, lang string) {
	go func() {
		err := client.keyshareEnrollWorker(manager, email, pin, lang)
		if err != nil {
			client.handler.EnrollmentFailure(manager, err)
		}
	}()
}

func (client *Client) keyshareEnrollWorker(managerID irma.SchemeManagerIdentifier, email *string, pin string, lang string) error {
	manager, ok := client.Configuration.SchemeManagers[managerID]
	if !ok {
		return errors.New("Unknown scheme manager")
	}
	if len(manager.KeyshareServer) == 0 {
		return errors.New("Scheme manager has no keyshare server")
	}
	if len(pin) < 5 {
		return errors.New("PIN too short, must be at least 5 characters")
	}

	transport := irma.NewHTTPTransport(manager.KeyshareServer)
	kss, err := newKeyshareServer(managerID, client.paillierKey(true), manager.KeyshareServer)
	if err != nil {
		return err
	}
	message := keyshareEnrollment{
		Email:     email,
		Pin:       kss.HashedPin(pin),
		Language:  lang,
		PublicKey: (*paillierPublicKey)(&kss.PrivateKey.PublicKey),
	}

	qr := &irma.Qr{}
	err = transport.Post("client/register", qr, message)
	if err != nil {
		return err
	}

	// We add the new keyshare server to the client here, without saving it to disk,
	// and start the issuance session for the keyshare server login attribute -
	// keyshare.go needs the relevant keyshare server to be present in the client.
	// If the session succeeds or fails, the keyshare server is stored to disk or
	// removed from the client by the keyshareEnrollmentHandler.
	client.keyshareServers[managerID] = kss
	client.newQrSession(qr, &keyshareEnrollmentHandler{
		client: client,
		pin:    pin,
		kss:    kss,
	})

	return nil
}

func (client *Client) KeyshareChangePin(manager irma.SchemeManagerIdentifier, oldPin string, newPin string) {
	go func() {
		err := client.keyshareChangePinWorker(manager, oldPin, newPin)
		if err != nil {
			client.handler.ChangePinFailure(manager, err)
		}
	}()
}

func (client *Client) keyshareChangePinWorker(managerID irma.SchemeManagerIdentifier, oldPin string, newPin string) error {
	kss, ok := client.keyshareServers[managerID]
	if !ok {
		return errors.New("Unknown keyshare server")
	}

	transport := irma.NewHTTPTransport(kss.URL)
	message := keyshareChangepin{
		Username: kss.Username,
		OldPin:   kss.HashedPin(oldPin),
		NewPin:   kss.HashedPin(newPin),
	}

	res := &keysharePinStatus{}
	err := transport.Post("users/change/pin", res, message)
	if err != nil {
		return err
	}

	switch res.Status {
	case kssPinSuccess:
		client.handler.ChangePinSuccess(managerID)
	case kssPinFailure:
		attempts, err := strconv.Atoi(res.Message)
		if err != nil {
			return err
		}
		client.handler.ChangePinIncorrect(managerID, attempts)
	case kssPinError:
		timeout, err := strconv.Atoi(res.Message)
		if err != nil {
			return err
		}
		client.handler.ChangePinBlocked(managerID, timeout)
	default:
		return errors.New("Unknown keyshare response")
	}

	return nil
}