attributes.go 11.7 KB
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package irmago

import (
	"crypto/sha256"
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	"encoding/binary"
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	"encoding/json"
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	"errors"
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	"math/big"
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	"time"
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	"github.com/mhe/gabi"
)

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const (
	// ExpiryFactor is the precision for the expiry attribute. Value is one week.
	ExpiryFactor = 60 * 60 * 24 * 7
	// ValidityDefault is the default validity of new credentials (half a year).
	ValidityDefault = 52 / 2
	metadataLength  = 1 + 3 + 2 + 2 + 16
)

var (
	metadataVersion = []byte{0x02}

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	versionField     = metadataField{1, 0}
	signingDateField = metadataField{3, 1}
	validityField    = metadataField{2, 4}
	keyCounterField  = metadataField{2, 6}
	credentialID     = metadataField{16, 8}
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)

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// metadataField contains the length and offset of a field within a metadata attribute.
type metadataField struct {
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	length int
	offset int
}

// MetadataAttribute represent a metadata attribute. Contains the credential type, signing date, validity, and the public key counter.
type MetadataAttribute struct {
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	Int   *big.Int
	pk    *gabi.PublicKey
	store *ConfigurationStore
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}

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// AttributeList contains attributes, excluding the secret key,
// providing convenient access to the metadata attribute.
type AttributeList struct {
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	*MetadataAttribute `json:"-"`
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	Ints               []*big.Int
	strings            []string
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	info               *CredentialInfo
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}

func (al *AttributeList) MarshalJSON() ([]byte, error) {
	return json.Marshal(al.Ints)
}

func (al *AttributeList) UnmarshalJSON(bytes []byte) error {
	ints := []*big.Int{}
	if err := json.Unmarshal(bytes, &ints); err != nil {
		return err
	}
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	list, err := NewAttributeListFromInts(ints)
	if err != nil {
		return err
	}
	*al = *list
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	return nil
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}

// NewAttributeListFromInts initializes a new AttributeList from a list of bigints.
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func NewAttributeListFromInts(ints []*big.Int, store *ConfigurationStore) (*AttributeList, error) {
	meta := MetadataFromInt(ints[0], store)
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	if ints[0] == nil || meta.CredentialType() == nil {
		return nil, errors.New("Encountered credential of unknown type")
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	}

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	return &AttributeList{
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		Ints:              ints,
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		MetadataAttribute: meta,
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	}, nil
}

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func (al *AttributeList) Info() *CredentialInfo {
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	if al.info == nil {
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		al.info = NewCredentialInfo(al.Ints)
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	}
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	return al.info
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}

// Strings converts the current instance to human-readable strings.
func (al *AttributeList) Strings() []string {
	if al.strings == nil {
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		al.strings = make([]string, len(al.Ints)-1)
		for index, num := range al.Ints[1:] { // skip metadata
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			al.strings[index] = string(num.Bytes())
		}
	}
	return al.strings
}
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// Attribute returns the content of the specified attribute, or "" if not present in this attribute list.
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func (al *AttributeList) Attribute(identifier AttributeTypeIdentifier) string {
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	if al.CredentialType().Identifier() != identifier.CredentialTypeIdentifier() {
		return ""
	}
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	for i, desc := range al.CredentialType().Attributes {
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		if desc.ID == string(identifier.Name()) {
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			return al.Strings()[i]
		}
	}
	return ""
}

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// MetadataFromInt wraps the given Int
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func MetadataFromInt(i *big.Int, store *ConfigurationStore) *MetadataAttribute {
	return &MetadataAttribute{Int: i, store: store}
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}

// NewMetadataAttribute constructs a new instance containing the default values:
// 0x02 as versionField
// now as signing date
// 0 as keycounter
// ValidityDefault (half a year) as default validity.
func NewMetadataAttribute() *MetadataAttribute {
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	val := MetadataAttribute{new(big.Int), nil, nil}
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	val.setField(versionField, metadataVersion)
	val.setSigningDate()
	val.setKeyCounter(0)
	val.setValidityDuration(ValidityDefault)
	return &val
}

// Bytes returns this metadata attribute as a byte slice.
func (attr *MetadataAttribute) Bytes() []byte {
	bytes := attr.Int.Bytes()
	if len(bytes) < metadataLength {
		bytes = append(bytes, make([]byte, metadataLength-len(bytes))...)
	}
	return bytes
}

// PublicKey extracts identifier of the Idemix public key with which this instance was signed,
// and returns this public key.
func (attr *MetadataAttribute) PublicKey() *gabi.PublicKey {
	if attr.pk == nil {
		attr.pk = MetaStore.PublicKey(attr.CredentialType().IssuerIdentifier(), attr.KeyCounter())
	}
	return attr.pk
}

// Version returns the metadata version of this instance
func (attr *MetadataAttribute) Version() byte {
	return attr.field(versionField)[0]
}

// SigningDate returns the time at which this instance was signed
func (attr *MetadataAttribute) SigningDate() time.Time {
	bytes := attr.field(signingDateField)
	bytes = bytes[1:] // The signing date field is one byte too long
	timestamp := int64(binary.BigEndian.Uint16(bytes)) * ExpiryFactor
	return time.Unix(timestamp, 0)
}

func (attr *MetadataAttribute) setSigningDate() {
	attr.setField(signingDateField, shortToByte(int(time.Now().Unix()/ExpiryFactor)))
}

// KeyCounter return the public key counter of the metadata attribute
func (attr *MetadataAttribute) KeyCounter() int {
	return int(binary.BigEndian.Uint16(attr.field(keyCounterField)))
}

func (attr *MetadataAttribute) setKeyCounter(i int) {
	attr.setField(keyCounterField, shortToByte(i))
}

// ValidityDuration returns the amount of epochs during which this instance is valid
func (attr *MetadataAttribute) ValidityDuration() int {
	return int(binary.BigEndian.Uint16(attr.field(validityField)))
}

func (attr *MetadataAttribute) setValidityDuration(weeks int) {
	attr.setField(validityField, shortToByte(weeks))
}

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func (attr *MetadataAttribute) setExpiryDate(timestamp *Timestamp) error {
	expiry := time.Time(*timestamp).Unix()
	if expiry%ExpiryFactor != 0 {
		return errors.New("Expiry date does not match an epoch boundary")
	}
	signing := attr.SigningDate().Unix()
	attr.setValidityDuration(int((expiry - signing) / ExpiryFactor))
	return nil
}

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// CredentialType returns the credential type of the current instance
// using the MetaStore.
func (attr *MetadataAttribute) CredentialType() *CredentialType {
	return MetaStore.hashToCredentialType(attr.field(credentialID))
}

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func (attr *MetadataAttribute) setCredentialTypeIdentifier(id string) {
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	bytes := sha256.Sum256([]byte(id))
	attr.setField(credentialID, bytes[:16])
}

// Expiry returns the expiry date of this instance
func (attr *MetadataAttribute) Expiry() time.Time {
	expiry := attr.SigningDate().Unix() + int64(attr.ValidityDuration()*ExpiryFactor)
	return time.Unix(expiry, 0)
}

// IsValidOn returns whether this instance is still valid at the given time
func (attr *MetadataAttribute) IsValidOn(t time.Time) bool {
	return attr.Expiry().After(t)
}

// IsValid returns whether this instance is valid.
func (attr *MetadataAttribute) IsValid() bool {
	return attr.IsValidOn(time.Now())
}

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func (attr *MetadataAttribute) field(field metadataField) []byte {
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	return attr.Bytes()[field.offset : field.offset+field.length]
}

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func (attr *MetadataAttribute) setField(field metadataField, value []byte) {
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	if len(value) > field.length {
		panic("Specified metadata field too large")
	}

	bytes := attr.Bytes()

	// Push the value to the right within the field. Graphical representation:
	// --xxxXXX----
	// "-" indicates a byte of another field
	// "X" is a byte of the value and "x" of our field
	// In this example, our field has offset 2, length 6,
	// but the specified value is only 3 bytes long.
	startindex := field.length - len(value)
	for i := 0; i < field.length; i++ {
		if i < startindex {
			bytes[i+field.offset] = 0
		} else {
			bytes[i+field.offset] = value[i-startindex]
		}
	}

	attr.Int.SetBytes(bytes)
}

func shortToByte(x int) []byte {
	bytes := make([]byte, 2)
	binary.BigEndian.PutUint16(bytes, uint16(x))
	return bytes
}
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// A DisclosureChoice contains the attributes chosen to be disclosed.
type DisclosureChoice struct {
	Attributes []*AttributeIdentifier
}

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// An AttributeDisjunction encapsulates a list of possible attributes, one
// of which should be disclosed.
type AttributeDisjunction struct {
	Label      string
	Attributes []AttributeTypeIdentifier
	Values     map[AttributeTypeIdentifier]string

	selected *AttributeTypeIdentifier
}

// An AttributeDisjunctionList is a list of AttributeDisjunctions.
type AttributeDisjunctionList []*AttributeDisjunction

// HasValues indicates if the attributes of this disjunction have values
// that should be satisfied.
func (disjunction *AttributeDisjunction) HasValues() bool {
	return disjunction.Values != nil && len(disjunction.Values) != 0
}

// Satisfied indicates if this disjunction has a valid chosen attribute
// to be disclosed.
func (disjunction *AttributeDisjunction) Satisfied() bool {
	if disjunction.selected == nil {
		return false
	}
	for _, attr := range disjunction.Attributes {
		if *disjunction.selected == attr {
			return true
		}
	}
	return false
}

// MatchesStore returns true if all attributes contained in the disjunction are
// present in the MetaStore.
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func (disjunction *AttributeDisjunction) MatchesStore(store *ConfigurationStore) bool {
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	for ai := range disjunction.Values {
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		creddescription, exists := store.Credentials[ai.CredentialTypeIdentifier()]
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		if !exists {
			return false
		}
		if !creddescription.ContainsAttribute(ai) {
			return false
		}
	}
	return true
}

// Satisfied indicates whether each contained attribute disjunction has a chosen attribute.
func (dl AttributeDisjunctionList) Satisfied() bool {
	for _, disjunction := range dl {
		if !disjunction.Satisfied() {
			return false
		}
	}
	return true
}

// Find searches for and returns the disjunction that contains the specified attribute identifier, or nil if not found.
func (dl AttributeDisjunctionList) Find(ai AttributeTypeIdentifier) *AttributeDisjunction {
	for _, disjunction := range dl {
		for _, attr := range disjunction.Attributes {
			if attr == ai {
				return disjunction
			}
		}
	}
	return nil
}

// MarshalJSON marshals the disjunction to JSON.
func (disjunction *AttributeDisjunction) MarshalJSON() ([]byte, error) {
	if !disjunction.HasValues() {
		temp := struct {
			Label      string                    `json:"label"`
			Attributes []AttributeTypeIdentifier `json:"attributes"`
		}{
			Label:      disjunction.Label,
			Attributes: disjunction.Attributes,
		}
		return json.Marshal(temp)
	}

	temp := struct {
		Label      string                             `json:"label"`
		Attributes map[AttributeTypeIdentifier]string `json:"attributes"`
	}{
		Label:      disjunction.Label,
		Attributes: disjunction.Values,
	}
	return json.Marshal(temp)
}

// UnmarshalJSON unmarshals an attribute disjunction from JSON.
func (disjunction *AttributeDisjunction) UnmarshalJSON(bytes []byte) error {
	if disjunction.Values == nil {
		disjunction.Values = make(map[AttributeTypeIdentifier]string)
	}
	if disjunction.Attributes == nil {
		disjunction.Attributes = make([]AttributeTypeIdentifier, 0, 3)
	}

	// We don't know if the json element "attributes" is a list, or a map.
	// So we unmarshal it into a temporary struct that has interface{} as the
	// type of "attributes", so that we can check which of the two it is.
	temp := struct {
		Label      string      `json:"label"`
		Attributes interface{} `json:"attributes"`
	}{}
	json.Unmarshal(bytes, &temp)
	disjunction.Label = temp.Label

	switch temp.Attributes.(type) {
	case map[string]interface{}:
		temp := struct {
			Label      string            `json:"label"`
			Attributes map[string]string `json:"attributes"`
		}{}
		json.Unmarshal(bytes, &temp)
		for str, value := range temp.Attributes {
			id := NewAttributeTypeIdentifier(str)
			disjunction.Attributes = append(disjunction.Attributes, id)
			disjunction.Values[id] = value
		}
	case []interface{}:
		temp := struct {
			Label      string   `json:"label"`
			Attributes []string `json:"attributes"`
		}{}
		json.Unmarshal(bytes, &temp)
		for _, str := range temp.Attributes {
			disjunction.Attributes = append(disjunction.Attributes, NewAttributeTypeIdentifier(str))
		}
	default:
		return errors.New("could not parse attribute disjunction: element 'attributes' was incorrect")
	}

	return nil
}