irmaconfig.go 47.4 KB
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package irma
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import (
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	"crypto/rsa"
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	"encoding/base64"
	"encoding/xml"
	"io/ioutil"
	"os"
	"path/filepath"
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	"reflect"
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	"regexp"
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	"strconv"
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	"time"
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	"crypto/sha256"

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	"fmt"

	"strings"

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	"sort"

	"bytes"

	"encoding/hex"

	"crypto/ecdsa"
	"crypto/x509"
	"encoding/asn1"
	"encoding/pem"
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	gobig "math/big"
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	"github.com/dgrijalva/jwt-go"
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	"github.com/go-errors/errors"
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	"github.com/jasonlvhit/gocron"
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	"github.com/privacybydesign/gabi"
	"github.com/privacybydesign/gabi/big"
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	"github.com/privacybydesign/irmago/internal/fs"
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)

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// Configuration keeps track of scheme managers, issuers, credential types and public keys,
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// dezerializing them from an irma_configuration folder, and downloads and saves new ones on demand.
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type Configuration struct {
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	SchemeManagers  map[SchemeManagerIdentifier]*SchemeManager
	Issuers         map[IssuerIdentifier]*Issuer
	CredentialTypes map[CredentialTypeIdentifier]*CredentialType
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	AttributeTypes  map[AttributeTypeIdentifier]*AttributeType
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	// Path to the irma_configuration folder that this instance represents
	Path string

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	// DisabledSchemeManagers keeps track of scheme managers that did not parse  succesfully
	// (i.e., invalid signature, parsing error), and the problem that occurred when parsing them
	DisabledSchemeManagers map[SchemeManagerIdentifier]*SchemeManagerError
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	Warnings []string

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	kssPublicKeys map[SchemeManagerIdentifier]map[int]*rsa.PublicKey
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	publicKeys    map[IssuerIdentifier]map[int]*gabi.PublicKey
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	privateKeys   map[IssuerIdentifier]*gabi.PrivateKey
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	reverseHashes map[string]CredentialTypeIdentifier
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	initialized   bool
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	assets        string
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	readOnly      bool
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	cronchan      chan bool
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	scheduler     *gocron.Scheduler
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}

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// ConfigurationFileHash encodes the SHA256 hash of an authenticated
// file under a scheme manager within the configuration folder.
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type ConfigurationFileHash []byte

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// SchemeManagerIndex is a (signed) list of files under a scheme manager
// along with their SHA266 hash
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type SchemeManagerIndex map[string]ConfigurationFileHash

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type SchemeManagerStatus string

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type SchemeManagerError struct {
	Manager SchemeManagerIdentifier
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	Status  SchemeManagerStatus
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	Err     error
}

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type UnknownIdentifierError struct {
	ErrorType
	Missing *IrmaIdentifierSet
}

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const (
	SchemeManagerStatusValid               = SchemeManagerStatus("Valid")
	SchemeManagerStatusUnprocessed         = SchemeManagerStatus("Unprocessed")
	SchemeManagerStatusInvalidIndex        = SchemeManagerStatus("InvalidIndex")
	SchemeManagerStatusInvalidSignature    = SchemeManagerStatus("InvalidSignature")
	SchemeManagerStatusParsingError        = SchemeManagerStatus("ParsingError")
	SchemeManagerStatusContentParsingError = SchemeManagerStatus("ContentParsingError")
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	pubkeyPattern  = "%s/%s/%s/PublicKeys/*.xml"
	privkeyPattern = "%s/%s/%s/PrivateKeys/*.xml"
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)

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func (sme SchemeManagerError) Error() string {
	return fmt.Sprintf("Error parsing scheme manager %s: %s", sme.Manager.Name(), sme.Err.Error())
}

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// NewConfiguration returns a new configuration. After this
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// ParseFolder() should be called to parse the specified path.
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func NewConfiguration(path string) (*Configuration, error) {
	return newConfiguration(path, "")
}

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// NewConfigurationReadOnly returns a new configuration whose representation on disk
// is never altered. ParseFolder() should be called to parse the specified path.
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func NewConfigurationReadOnly(path string) (*Configuration, error) {
	conf, err := newConfiguration(path, "")
	if err != nil {
		return nil, err
	}
	conf.readOnly = true
	return conf, nil
}

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// NewConfigurationFromAssets returns a new configuration, copying the schemes out of the assets folder to path.
// ParseFolder() should be called to parse the specified path.
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func NewConfigurationFromAssets(path, assets string) (*Configuration, error) {
	return newConfiguration(path, assets)
}

func newConfiguration(path string, assets string) (conf *Configuration, err error) {
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	conf = &Configuration{
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		Path:   path,
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		assets: assets,
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	}
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	if conf.assets != "" { // If an assets folder is specified, then it must exist
		if err = fs.AssertPathExists(conf.assets); err != nil {
			return nil, errors.WrapPrefix(err, "Nonexistent assets folder specified", 0)
		}
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	}
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	if err = fs.EnsureDirectoryExists(conf.Path); err != nil {
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		return nil, err
	}
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	// Init all maps
	conf.clear()

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	return
}

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func (conf *Configuration) clear() {
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	conf.SchemeManagers = make(map[SchemeManagerIdentifier]*SchemeManager)
	conf.Issuers = make(map[IssuerIdentifier]*Issuer)
	conf.CredentialTypes = make(map[CredentialTypeIdentifier]*CredentialType)
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	conf.AttributeTypes = make(map[AttributeTypeIdentifier]*AttributeType)
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	conf.DisabledSchemeManagers = make(map[SchemeManagerIdentifier]*SchemeManagerError)
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	conf.kssPublicKeys = make(map[SchemeManagerIdentifier]map[int]*rsa.PublicKey)
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	conf.publicKeys = make(map[IssuerIdentifier]map[int]*gabi.PublicKey)
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	conf.privateKeys = make(map[IssuerIdentifier]*gabi.PrivateKey)
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	conf.reverseHashes = make(map[string]CredentialTypeIdentifier)
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}

// ParseFolder populates the current Configuration by parsing the storage path,
// listing the containing scheme managers, issuers and credential types.
func (conf *Configuration) ParseFolder() (err error) {
	// Init all maps
	conf.clear()
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	// Copy any new or updated scheme managers out of the assets into storage
	if conf.assets != "" {
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		err = iterateSubfolders(conf.assets, func(dir string, _ os.FileInfo) error {
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			scheme := NewSchemeManagerIdentifier(filepath.Base(dir))
			uptodate, err := conf.isUpToDate(scheme)
			if err != nil {
				return err
			}
			if !uptodate {
				_, err = conf.CopyManagerFromAssets(scheme)
			}
			return err
		})
		if err != nil {
			return err
		}
	}

	// Parse scheme managers in storage
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	var mgrerr *SchemeManagerError
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	err = iterateSubfolders(conf.Path, func(dir string, _ os.FileInfo) error {
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		manager := NewSchemeManager(filepath.Base(dir))
		err := conf.ParseSchemeManagerFolder(dir, manager)
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		if err == nil {
			return nil // OK, do next scheme manager folder
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		}
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		// If there is an error, and it is of type SchemeManagerError, return nil
		// so as to continue parsing other managers.
		var ok bool
		if mgrerr, ok = err.(*SchemeManagerError); ok {
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			conf.DisabledSchemeManagers[manager.Identifier()] = mgrerr
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			return nil
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		}
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		return err // Not a SchemeManagerError? return it & halt parsing now
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	})
	if err != nil {
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		return
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	}
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	conf.initialized = true
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	if mgrerr != nil {
		return mgrerr
	}
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	return
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}

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// ParseOrRestoreFolder parses the irma_configuration folder, and when possible attempts to restore
// any broken scheme managers from their remote.
// Any error encountered during parsing is considered recoverable only if it is of type *SchemeManagerError;
// In this case the scheme in which it occured is downloaded from its remote and re-parsed.
// If any other error is encountered at any time, it is returned immediately.
// If no error is returned, parsing and possibly restoring has been succesfull, and there should be no
// disabled scheme managers.
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func (conf *Configuration) ParseOrRestoreFolder() error {
	err := conf.ParseFolder()
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	// Only in case of a *SchemeManagerError might we be able to recover
	if _, isSchemeMgrErr := err.(*SchemeManagerError); !isSchemeMgrErr {
		return err
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	}
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	if err != nil && (conf.assets == "" || conf.readOnly) {
		return err
	}
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	for id := range conf.DisabledSchemeManagers {
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		if err = conf.ReinstallSchemeManager(conf.SchemeManagers[id]); err == nil {
			continue
		}
		if _, err = conf.CopyManagerFromAssets(id); err != nil {
			return err // File system error, too serious, bail out now
		}
		name := id.String()
		if err = conf.ParseSchemeManagerFolder(filepath.Join(conf.Path, name), NewSchemeManager(name)); err == nil {
			delete(conf.DisabledSchemeManagers, id)
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		}
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	}
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	return err
}

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// ParseSchemeManagerFolder parses the entire tree of the specified scheme manager
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// If err != nil then a problem occured
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func (conf *Configuration) ParseSchemeManagerFolder(dir string, manager *SchemeManager) (err error) {
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	// From this point, keep it in our map even if it has an error. The user must check either:
	// - manager.Status == SchemeManagerStatusValid, aka "VALID"
	// - or equivalently, manager.Valid == true
	// before using any scheme manager for anything, and handle accordingly
	conf.SchemeManagers[manager.Identifier()] = manager

	// Ensure we return a SchemeManagerError when any error occurs
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	defer func() {
		if err != nil {
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			err = &SchemeManagerError{
				Manager: manager.Identifier(),
				Err:     err,
				Status:  manager.Status,
			}
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		}
	}()

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	// Verify signature and read scheme manager description
	if err = conf.VerifySignature(manager.Identifier()); err != nil {
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		return
	}
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	if manager.index, err = conf.parseIndex(filepath.Base(dir), manager); err != nil {
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		manager.Status = SchemeManagerStatusInvalidIndex
		return
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	}
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	exists, err := conf.pathToDescription(manager, dir+"/description.xml", manager)
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	if err != nil {
		manager.Status = SchemeManagerStatusParsingError
		return
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	}
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	if !exists {
		manager.Status = SchemeManagerStatusParsingError
		return errors.New("Scheme manager description not found")
	}
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	if err = conf.validateScheme(manager, dir); err != nil {
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		return
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	}
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	// Verify that all other files are validly signed
	err = conf.VerifySchemeManager(manager)
	if err != nil {
		manager.Status = SchemeManagerStatusInvalidSignature
		return
	}
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	// Read timestamp indicating time of last modification
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	ts, exists, err := readTimestamp(dir + "/timestamp")
	if err != nil || !exists {
		return errors.WrapPrefix(err, "Could not read scheme manager timestamp", 0)
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	}
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	manager.Timestamp = *ts
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	// Parse contained issuers and credential types
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	err = conf.parseIssuerFolders(manager, dir)
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	if err != nil {
		manager.Status = SchemeManagerStatusContentParsingError
		return
	}
	manager.Status = SchemeManagerStatusValid
	manager.Valid = true
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	return
}

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// PrivateKey returns the specified private key, or nil if not present in the Configuration.
func (conf *Configuration) PrivateKey(id IssuerIdentifier) (*gabi.PrivateKey, error) {
	if sk := conf.privateKeys[id]; sk != nil {
		return sk, nil
	}

	path := fmt.Sprintf(privkeyPattern, conf.Path, id.SchemeManagerIdentifier().Name(), id.Name())
	files, err := filepath.Glob(path)
	if err != nil {
		return nil, err
	}
	if len(files) == 0 {
		return nil, nil
	}

	// List private keys and get highest counter
	counters := make([]int, 0, len(files))
	for _, file := range files {
		filename := filepath.Base(file)
		count := filename[:len(filename)-4]
		i, err := strconv.Atoi(count)
		if err != nil {
			return nil, err
		}
		counters = append(counters, i)
	}
	sort.Ints(counters)
	counter := counters[len(counters)-1]

	// Read private key
	file := strings.Replace(path, "*", strconv.Itoa(counter), 1)
	sk, err := gabi.NewPrivateKeyFromFile(file)
	if err != nil {
		return nil, err
	}
	if int(sk.Counter) != counter {
		return nil, errors.Errorf("Private key %s of issuer %s has wrong <Counter>", file, id.String())
	}
	conf.privateKeys[id] = sk

	return sk, nil
}

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// PublicKey returns the specified public key, or nil if not present in the Configuration.
func (conf *Configuration) PublicKey(id IssuerIdentifier, counter int) (*gabi.PublicKey, error) {
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	var haveIssuer, haveKey bool
	var err error
	_, haveIssuer = conf.publicKeys[id]
	if haveIssuer {
		_, haveKey = conf.publicKeys[id][counter]
	}

	// If we have not seen this issuer or key before in conf.publicKeys,
	// try to parse the public key folder; new keys might have been put there since we last parsed it
	if !haveIssuer || !haveKey {
		if err = conf.parseKeysFolder(id); err != nil {
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			return nil, err
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		}
	}
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	return conf.publicKeys[id][counter], nil
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}

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// KeyshareServerKeyFunc returns a function that returns the public key with which to verify a keyshare server JWT,
// suitable for passing to jwt.Parse() and jwt.ParseWithClaims().
func (conf *Configuration) KeyshareServerKeyFunc(scheme SchemeManagerIdentifier) func(t *jwt.Token) (interface{}, error) {
	return func(t *jwt.Token) (i interface{}, e error) {
		var kid int
		if kidstr, ok := t.Header["kid"].(string); ok {
			var err error
			if kid, err = strconv.Atoi(kidstr); err != nil {
				return nil, err
			}
		}
		return conf.KeyshareServerPublicKey(scheme, kid)
	}
}

// KeyshareServerPublicKey returns the i'th public key of the specified scheme.
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func (conf *Configuration) KeyshareServerPublicKey(scheme SchemeManagerIdentifier, i int) (*rsa.PublicKey, error) {
	if _, contains := conf.kssPublicKeys[scheme]; !contains {
		conf.kssPublicKeys[scheme] = make(map[int]*rsa.PublicKey)
	}
	if _, contains := conf.kssPublicKeys[scheme][i]; !contains {
		pkbts, err := ioutil.ReadFile(filepath.Join(conf.Path, scheme.Name(), fmt.Sprintf("kss-%d.pem", i)))
		if err != nil {
			return nil, err
		}
		pkblk, _ := pem.Decode(pkbts)
		genericPk, err := x509.ParsePKIXPublicKey(pkblk.Bytes)
		if err != nil {
			return nil, err
		}
		pk, ok := genericPk.(*rsa.PublicKey)
		if !ok {
			return nil, errors.New("Invalid keyshare server public key")
		}
		conf.kssPublicKeys[scheme][i] = pk
	}
	return conf.kssPublicKeys[scheme][i], nil
}

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func (conf *Configuration) addReverseHash(credid CredentialTypeIdentifier) {
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	hash := sha256.Sum256([]byte(credid.String()))
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	conf.reverseHashes[base64.StdEncoding.EncodeToString(hash[:16])] = credid
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}

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func (conf *Configuration) hashToCredentialType(hash []byte) *CredentialType {
	if str, exists := conf.reverseHashes[base64.StdEncoding.EncodeToString(hash)]; exists {
		return conf.CredentialTypes[str]
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	}
	return nil
}

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// IsInitialized indicates whether this instance has successfully been initialized.
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func (conf *Configuration) IsInitialized() bool {
	return conf.initialized
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}

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// Prune removes any invalid scheme managers and everything they own from this Configuration
func (conf *Configuration) Prune() {
	for _, manager := range conf.SchemeManagers {
		if !manager.Valid {
			_ = conf.RemoveSchemeManager(manager.Identifier(), false) // does not return errors
		}
	}
}

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func (conf *Configuration) parseIssuerFolders(manager *SchemeManager, path string) error {
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	return iterateSubfolders(path, func(dir string, _ os.FileInfo) error {
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		issuer := &Issuer{}
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		exists, err := conf.pathToDescription(manager, dir+"/description.xml", issuer)
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		if err != nil {
			return err
		}
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		if !exists {
			return nil
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		}
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		if issuer.XMLVersion < 4 {
			return errors.New("Unsupported issuer description")
		}
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		if err = conf.validateIssuer(manager, issuer, dir); err != nil {
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			return err
		}

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		conf.Issuers[issuer.Identifier()] = issuer
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		issuer.Valid = conf.SchemeManagers[issuer.SchemeManagerIdentifier()].Valid
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		return conf.parseCredentialsFolder(manager, issuer, dir+"/Issues/")
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	})
}

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func (conf *Configuration) DeleteSchemeManager(id SchemeManagerIdentifier) error {
	delete(conf.SchemeManagers, id)
	delete(conf.DisabledSchemeManagers, id)
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	name := id.String()
	for iss := range conf.Issuers {
		if iss.Root() == name {
			delete(conf.Issuers, iss)
		}
	}
	for iss := range conf.publicKeys {
		if iss.Root() == name {
			delete(conf.publicKeys, iss)
		}
	}
	for cred := range conf.CredentialTypes {
		if cred.Root() == name {
			delete(conf.CredentialTypes, cred)
		}
	}
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	if !conf.readOnly {
		return os.RemoveAll(filepath.Join(conf.Path, id.Name()))
	}
	return nil
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}

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// parse $schememanager/$issuer/PublicKeys/$i.xml for $i = 1, ...
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func (conf *Configuration) parseKeysFolder(issuerid IssuerIdentifier) error {
	manager := conf.SchemeManagers[issuerid.SchemeManagerIdentifier()]
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	conf.publicKeys[issuerid] = map[int]*gabi.PublicKey{}
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	path := fmt.Sprintf(pubkeyPattern, conf.Path, issuerid.SchemeManagerIdentifier().Name(), issuerid.Name())
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	files, err := filepath.Glob(path)
	if err != nil {
		return err
	}

	for _, file := range files {
		filename := filepath.Base(file)
		count := filename[:len(filename)-4]
		i, err := strconv.Atoi(count)
		if err != nil {
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			return err
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		}
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		relativepath, err := filepath.Rel(conf.Path, file)
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		if err != nil {
			return err
		}
		bts, found, err := conf.ReadAuthenticatedFile(manager, relativepath)
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		if err != nil || !found {
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			return err
		}
		pk, err := gabi.NewPublicKeyFromBytes(bts)
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		if err != nil {
			return err
		}
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		if int(pk.Counter) != i {
			return errors.Errorf("Public key %s of issuer %s has wrong <Counter>", file, issuerid.String())
		}
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		pk.Issuer = issuerid.String()
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		conf.publicKeys[issuerid][i] = pk
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	}
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	return nil
}

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func (conf *Configuration) PublicKeyIndices(issuerid IssuerIdentifier) (i []int, err error) {
	return conf.matchKeyPattern(issuerid, pubkeyPattern)
}

func (conf *Configuration) matchKeyPattern(issuerid IssuerIdentifier, pattern string) (i []int, err error) {
	pkpath := fmt.Sprintf(pattern, conf.Path, issuerid.SchemeManagerIdentifier().Name(), issuerid.Name())
	files, err := filepath.Glob(pkpath)
	if err != nil {
		return
	}
	for _, file := range files {
		var count int
		base := filepath.Base(file)
		if count, err = strconv.Atoi(base[:len(base)-4]); err != nil {
			return
		}
		i = append(i, count)
	}
	sort.Ints(i)
	return
}

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// parse $schememanager/$issuer/Issues/*/description.xml
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func (conf *Configuration) parseCredentialsFolder(manager *SchemeManager, issuer *Issuer, path string) error {
	var foundcred bool
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	err := iterateSubfolders(path, func(dir string, _ os.FileInfo) error {
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		cred := &CredentialType{}
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		exists, err := conf.pathToDescription(manager, dir+"/description.xml", cred)
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		if err != nil {
			return err
		}
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		if !exists {
			return nil
		}
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		if err = conf.validateCredentialType(manager, issuer, cred, dir); err != nil {
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			return err
		}
		foundcred = true
		cred.Valid = conf.SchemeManagers[cred.SchemeManagerIdentifier()].Valid
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		credid := cred.Identifier()
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		conf.CredentialTypes[credid] = cred
		conf.addReverseHash(credid)
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		for index, attr := range cred.AttributeTypes {
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			attr.Index = index
			attr.SchemeManagerID = cred.SchemeManagerID
			attr.IssuerID = cred.IssuerID
			attr.CredentialTypeID = cred.ID
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			conf.AttributeTypes[attr.GetAttributeTypeIdentifier()] = attr
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		}
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		return nil
	})
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	if !foundcred {
		conf.Warnings = append(conf.Warnings, fmt.Sprintf("Issuer %s has no credential types", issuer.Identifier().String()))
	}
	return err
}

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// iterateSubfolders iterates over the subfolders of the specified path,
// calling the specified handler each time. If anything goes wrong, or
// if the caller returns a non-nil error, an error is immediately returned.
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func iterateSubfolders(path string, handler func(string, os.FileInfo) error) error {
	return iterateFiles(path, true, handler)
}

func iterateFiles(path string, onlyDirs bool, handler func(string, os.FileInfo) error) error {
	files, err := filepath.Glob(filepath.Join(path, "*"))
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	if err != nil {
		return err
	}

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	for _, file := range files {
		stat, err := os.Stat(file)
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		if err != nil {
			return err
		}
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		if onlyDirs && !stat.IsDir() {
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			continue
		}
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		if filepath.Base(file) == ".git" {
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			continue
		}
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		err = handler(file, stat)
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		if err != nil {
			return err
		}
	}

	return nil
}

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// walkDir recursively walks the file tree rooted at path, following symlinks (unlike filepath.Walk).
// Avoiding loops is the responsibility of the caller.
func walkDir(path string, handler func(string, os.FileInfo) error) error {
	return iterateFiles(path, false, func(p string, info os.FileInfo) error {
		if info.IsDir() {
			if err := handler(p, info); err != nil {
				return err
			}
			return walkDir(p, handler)
		}
		return handler(p, info)
	})
}

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func (conf *Configuration) pathToDescription(manager *SchemeManager, path string, description interface{}) (bool, error) {
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	if _, err := os.Stat(path); err != nil {
		return false, nil
	}

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	relativepath, err := filepath.Rel(conf.Path, path)
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	if err != nil {
		return false, err
	}
	bts, found, err := conf.ReadAuthenticatedFile(manager, relativepath)
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	if !found {
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		if manager.index.Scheme() != manager.Identifier() {
			return false, errors.Errorf("Folder must be called %s, not %s", manager.index.Scheme(), manager.ID)
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		}
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		return false, errors.Errorf("File %s not present in scheme index", relativepath)
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	}
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	if err != nil {
		return true, err
	}

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	err = xml.Unmarshal(bts, description)
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	if err != nil {
		return true, err
	}

	return true, nil
}
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// ContainsCredentialType checks if the configuration contains the specified credential type.
func (conf *Configuration) ContainsCredentialType(cred CredentialTypeIdentifier) bool {
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	return conf.SchemeManagers[cred.IssuerIdentifier().SchemeManagerIdentifier()] != nil &&
		conf.Issuers[cred.IssuerIdentifier()] != nil &&
		conf.CredentialTypes[cred] != nil
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}
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func (conf *Configuration) ContainsAttributeType(attr AttributeTypeIdentifier) bool {
	_, contains := conf.AttributeTypes[attr]
	return contains && conf.ContainsCredentialType(attr.CredentialTypeIdentifier())
}

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func (conf *Configuration) isUpToDate(scheme SchemeManagerIdentifier) (bool, error) {
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	if conf.assets == "" || conf.readOnly {
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		return true, nil
	}
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	name := scheme.String()
	newTime, exists, err := readTimestamp(filepath.Join(conf.assets, name, "timestamp"))
	if err != nil || !exists {
		return true, errors.WrapPrefix(err, "Could not read asset timestamp of scheme "+name, 0)
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	}
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	// The storage version of the manager does not need to have a timestamp. If it does not, it is outdated.
	oldTime, exists, err := readTimestamp(filepath.Join(conf.Path, name, "timestamp"))
	if err != nil {
		return true, err
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	}
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	return exists && !newTime.After(*oldTime), nil
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}

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func (conf *Configuration) CopyManagerFromAssets(scheme SchemeManagerIdentifier) (bool, error) {
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	if conf.assets == "" || conf.readOnly {
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		return false, nil
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	}
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	// Remove old version; we want an exact copy of the assets version
	// not a merge of the assets version and the storage version
	name := scheme.String()
	if err := os.RemoveAll(filepath.Join(conf.Path, name)); err != nil {
		return false, err
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	}
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	return true, fs.CopyDirectory(
		filepath.Join(conf.assets, name),
		filepath.Join(conf.Path, name),
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	)
}

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// DownloadSchemeManager downloads and returns a scheme manager description.xml file
// from the specified URL.
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func DownloadSchemeManager(url string) (*SchemeManager, error) {
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	if !strings.HasPrefix(url, "http://") && !strings.HasPrefix(url, "https://") {
		url = "https://" + url
	}
	if url[len(url)-1] == '/' {
		url = url[:len(url)-1]
	}
	if strings.HasSuffix(url, "/description.xml") {
		url = url[:len(url)-len("/description.xml")]
	}
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	b, err := NewHTTPTransport(url).GetBytes("description.xml")
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	if err != nil {
		return nil, err
	}
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	manager := NewSchemeManager("")
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	if err = xml.Unmarshal(b, manager); err != nil {
		return nil, err
	}

	manager.URL = url // TODO?
	return manager, nil
}

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// RemoveSchemeManager removes the specified scheme manager and all associated issuers,
// public keys and credential types from this Configuration.
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func (conf *Configuration) RemoveSchemeManager(id SchemeManagerIdentifier, fromStorage bool) error {
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	// Remove everything falling under the manager's responsibility
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	for credid := range conf.CredentialTypes {
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		if credid.IssuerIdentifier().SchemeManagerIdentifier() == id {
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			delete(conf.CredentialTypes, credid)
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		}
	}
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	for issid := range conf.Issuers {
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		if issid.SchemeManagerIdentifier() == id {
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			delete(conf.Issuers, issid)
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		}
	}
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	for issid := range conf.publicKeys {
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		if issid.SchemeManagerIdentifier() == id {
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			delete(conf.publicKeys, issid)
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		}
	}
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	delete(conf.SchemeManagers, id)
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	if fromStorage || !conf.readOnly {
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		return os.RemoveAll(fmt.Sprintf("%s/%s", conf.Path, id.String()))
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	}
	return nil
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}

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func (conf *Configuration) ReinstallSchemeManager(manager *SchemeManager) (err error) {
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	if conf.readOnly {
		return errors.New("cannot install scheme into a read-only configuration")
	}

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	// Check if downloading stuff from the remote works before we uninstall the specified manager:
	// If we can't download anything we should keep the broken version
	manager, err = DownloadSchemeManager(manager.URL)
	if err != nil {
		return
	}
	if err = conf.DeleteSchemeManager(manager.Identifier()); err != nil {
		return
	}
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	err = conf.InstallSchemeManager(manager, nil)
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	return
}

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// InstallSchemeManager downloads and adds the specified scheme manager to this Configuration,
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// provided its signature is valid.
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func (conf *Configuration) InstallSchemeManager(manager *SchemeManager, publickey []byte) error {
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	if conf.readOnly {
		return errors.New("cannot install scheme into a read-only configuration")
	}

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	name := manager.ID
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	if err := fs.EnsureDirectoryExists(filepath.Join(conf.Path, name)); err != nil {
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		return err
	}
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	t := NewHTTPTransport(manager.URL)
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	path := fmt.Sprintf("%s/%s", conf.Path, name)
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	if err := t.GetFile("description.xml", path+"/description.xml"); err != nil {
		return err
	}
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	if publickey != nil {
		if err := fs.SaveFile(path+"/pk.pem", publickey); err != nil {
			return err
		}
	} else {
		if err := t.GetFile("pk.pem", path+"/pk.pem"); err != nil {
			return err
		}
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	}
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	if err := conf.DownloadSchemeManagerSignature(manager); err != nil {
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		return err
	}
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	conf.SchemeManagers[manager.Identifier()] = manager
	if err := conf.UpdateSchemeManager(manager.Identifier(), nil); err != nil {
		return err
	}
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	return conf.ParseSchemeManagerFolder(filepath.Join(conf.Path, name), manager)
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}

// DownloadSchemeManagerSignature downloads, stores and verifies the latest version
// of the index file and signature of the specified manager.
func (conf *Configuration) DownloadSchemeManagerSignature(manager *SchemeManager) (err error) {
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	if conf.readOnly {
		return errors.New("cannot download into a read-only configuration")
	}

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	t := NewHTTPTransport(manager.URL)
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	path := fmt.Sprintf("%s/%s", conf.Path, manager.ID)
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	index := filepath.Join(path, "index")
	sig := filepath.Join(path, "index.sig")

	if err = t.GetFile("index", index); err != nil {
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		return
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	}
	if err = t.GetFile("index.sig", sig); err != nil {
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		return
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	}
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	err = conf.VerifySignature(manager.Identifier())
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	return
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}
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func (e *UnknownIdentifierError) Error() string {
	return "unknown identifiers: " + e.Missing.String()
}

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// Download downloads the issuers, credential types and public keys specified in set
// if the current Configuration does not already have them,  and checks their authenticity
// using the scheme manager index.
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func (conf *Configuration) Download(session SessionRequest) (downloaded *IrmaIdentifierSet, err error) {
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	if conf.readOnly {
		return nil, errors.New("cannot download into a read-only configuration")
	}
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	missing, err := conf.checkIdentifiers(session)
	if err != nil {
		return nil, err
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	}
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	if len(missing.SchemeManagers) > 0 {
		return nil, &UnknownIdentifierError{ErrorUnknownSchemeManager, missing}
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	}

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	// Update the scheme  found above and parse them, if necessary
	downloaded = newIrmaIdentifierSet()
	for id := range missing.allSchemes() {
		if err = conf.UpdateSchemeManager(id, downloaded); err != nil {
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			return
		}
	}
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	if !downloaded.Empty() {
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		if err = conf.ParseFolder(); err != nil {
			return nil, err
		}
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	}
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	// Check again if all identifiers are known in the Configuration
	if missing, err = conf.checkIdentifiers(session); err != nil {
		return nil, err
	}
	if !missing.Empty() {
		return nil, &UnknownIdentifierError{ErrorUnknownIdentifier, missing}
	}

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	return
}

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func (conf *Configuration) checkCredentialTypes(session SessionRequest, missing *IrmaIdentifierSet) {
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	var typ *CredentialType
	var contains bool

	switch s := session.(type) {
	case *IssuanceRequest:
		for _, credreq := range s.Credentials {
			// First check if we have this credential type
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			typ, contains = conf.CredentialTypes[credreq.CredentialTypeID]
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			if !contains {
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				missing.CredentialTypes[credreq.CredentialTypeID] = struct{}{}
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				continue
			}
			newAttrs := make(map[string]string)
			for k, v := range credreq.Attributes {
				newAttrs[k] = v
			}
			// For each of the attributes in the credentialtype, see if it is present; if so remove it from newAttrs
			// If not, check that it is optional; if not the credentialtype must be updated
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			for _, attrtyp := range typ.AttributeTypes {
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				_, contains = newAttrs[attrtyp.ID]
				if !contains && !attrtyp.IsOptional() {
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					missing.CredentialTypes[credreq.CredentialTypeID] = struct{}{}
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					break
				}
				delete(newAttrs, attrtyp.ID)
			}
			// If there is anything left in newAttrs, then these are attributes that are not in the credentialtype
			if len(newAttrs) > 0 {
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				missing.CredentialTypes[credreq.CredentialTypeID] = struct{}{}
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			}
		}
	}

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	_ = session.Disclosure().Disclose.Iterate(func(attr *AttributeRequest) error {
		credid := attr.Type.CredentialTypeIdentifier()
		if typ, contains = conf.CredentialTypes[credid]; !contains {
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			missing.CredentialTypes[credid] = struct{}{}
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			return nil
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		}
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		if !attr.Type.IsCredential() && !typ.ContainsAttribute(attr.Type) {
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			missing.CredentialTypes[credid] = struct{}{}
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		}
		return nil
	})
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	return
}

func (conf *Configuration) checkIdentifiers(session SessionRequest) (*IrmaIdentifierSet, error) {
	missing := newIrmaIdentifierSet()
	conf.checkSchemes(session, missing)
	if err := conf.checkIssuers(session.Identifiers(), missing); err != nil {
		return nil, err
	}
	conf.checkCredentialTypes(session, missing)
	return missing, nil
}

// CheckSchemes verifies that all schemes occuring in the specified session request occur in this
// instance.
func (conf *Configuration) checkSchemes(session SessionRequest, missing *IrmaIdentifierSet) {
	for id := range session.Identifiers().SchemeManagers {
		scheme, contains := conf.SchemeManagers[id]
		if !contains || !scheme.Valid {
			missing.SchemeManagers[id] = struct{}{}
		}
	}
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}

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func (conf *Configuration) checkIssuers(set *IrmaIdentifierSet, missing *IrmaIdentifierSet) error {
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	for issid := range set.Issuers {
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		if _, contains := conf.Issuers[issid]; !contains {
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			missing.Issuers[issid] = struct{}{}
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		}
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	}
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	for issid, keyids := range set.PublicKeys {
		for _, keyid := range keyids {
			pk, err := conf.PublicKey(issid, keyid)
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			if err != nil {
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				return err
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			}
			if pk == nil {
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				missing.PublicKeys[issid] = append(missing.PublicKeys[issid], keyid)
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			}
		}
	}
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	return nil
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}

func (i SchemeManagerIndex) String() string {
	var paths []string
	var b bytes.Buffer

	for path := range i {
		paths = append(paths, path)
	}
	sort.Strings(paths)

	for _, path := range paths {
		b.WriteString(hex.EncodeToString(i[path]))
		b.WriteString(" ")
		b.WriteString(path)
		b.WriteString("\n")
	}

	return b.String()
}

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// FromString populates this index by parsing the specified string.
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func (i SchemeManagerIndex) FromString(s string) error {
	for j, line := range strings.Split(s, "\n") {
		if len(line) == 0 {
			continue
		}
		parts := strings.Split(line, " ")
		if len(parts) != 2 {
			return errors.Errorf("Scheme manager index line %d has incorrect amount of parts", j)
		}
		hash, err := hex.DecodeString(parts[0])
		if err != nil {
			return err
		}
		i[parts[1]] = hash
	}

	return nil
}

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func (i SchemeManagerIndex) Scheme() SchemeManagerIdentifier {
	for p := range i {
		return NewSchemeManagerIdentifier(p[0:strings.Index(p, "/")])
	}
	return NewSchemeManagerIdentifier("")
}

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// parseIndex parses the index file of the specified manager.
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func (conf *Configuration) parseIndex(name string, manager *SchemeManager) (SchemeManagerIndex, error) {
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	path := filepath.Join(conf.Path, name, "index")
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	if err := fs.AssertPathExists(path); err != nil {
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		return nil, fmt.Errorf("Missing scheme manager index file; tried %s", path)
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	}
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	indexbts, err := ioutil.ReadFile(path)
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	if err != nil {
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		return nil, err
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	}
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	index := SchemeManagerIndex(make(map[string]ConfigurationFileHash))
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	if err = index.FromString(string(indexbts)); err != nil {
		return nil, err
	}

	return index, conf.checkUnsignedFiles(name, index)
}

func (conf *Configuration) checkUnsignedFiles(name string, index SchemeManagerIndex) error {
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	return walkDir(filepath.Join(conf.Path, name), func(path string, info os.FileInfo) error {
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		relpath, err := filepath.Rel(conf.Path, path)
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		if err != nil {
			return err
		}
		for _, ex := range sigExceptions {
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			if ex.MatchString(filepath.ToSlash(relpath)) {
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<