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Ticket.go
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Ticket.go
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package messages
import (
"crypto/rand"
"fmt"
"github.com/jcmturner/asn1"
"github.com/jcmturner/gokrb5/asn1tools"
"github.com/jcmturner/gokrb5/crypto"
"github.com/jcmturner/gokrb5/iana"
"github.com/jcmturner/gokrb5/iana/adtype"
"github.com/jcmturner/gokrb5/iana/asnAppTag"
"github.com/jcmturner/gokrb5/iana/errorcode"
"github.com/jcmturner/gokrb5/iana/keyusage"
"github.com/jcmturner/gokrb5/keytab"
"github.com/jcmturner/gokrb5/krberror"
"github.com/jcmturner/gokrb5/pac"
"github.com/jcmturner/gokrb5/types"
"time"
)
// Reference: https://www.ietf.org/rfc/rfc4120.txt
// Section: 5.3
// Ticket implements the Kerberos ticket.
type Ticket struct {
TktVNO int `asn1:"explicit,tag:0"`
Realm string `asn1:"generalstring,explicit,tag:1"`
SName types.PrincipalName `asn1:"explicit,tag:2"`
EncPart types.EncryptedData `asn1:"explicit,tag:3"`
DecryptedEncPart EncTicketPart `asn1:"optional"` // Not part of ASN1 bytes so marked as optional so unmarshalling works
}
// EncTicketPart is the encrypted part of the Ticket.
type EncTicketPart struct {
Flags asn1.BitString `asn1:"explicit,tag:0"`
Key types.EncryptionKey `asn1:"explicit,tag:1"`
CRealm string `asn1:"generalstring,explicit,tag:2"`
CName types.PrincipalName `asn1:"explicit,tag:3"`
Transited TransitedEncoding `asn1:"explicit,tag:4"`
AuthTime time.Time `asn1:"generalized,explicit,tag:5"`
StartTime time.Time `asn1:"generalized,explicit,optional,tag:6"`
EndTime time.Time `asn1:"generalized,explicit,tag:7"`
RenewTill time.Time `asn1:"generalized,explicit,optional,tag:8"`
CAddr types.HostAddresses `asn1:"explicit,optional,tag:9"`
AuthorizationData types.AuthorizationData `asn1:"explicit,optional,tag:10"`
}
// TransitedEncoding part of the ticket's encrypted part.
type TransitedEncoding struct {
TRType int `asn1:"explicit,tag:0"`
Contents []byte `asn1:"explicit,tag:1"`
}
// NewTicket creates a new Ticket instance.
func NewTicket(cname types.PrincipalName, crealm string, sname types.PrincipalName, srealm string, flags asn1.BitString, sktab keytab.Keytab, eTypeID, kvno int, authTime, startTime, endTime, renewTill time.Time) (Ticket, types.EncryptionKey, error) {
etype, err := crypto.GetEtype(eTypeID)
if err != nil {
return Ticket{}, types.EncryptionKey{}, krberror.Errorf(err, krberror.EncryptingError, "Error getting etype for new ticket")
}
ks := etype.GetKeyByteSize()
kv := make([]byte, ks, ks)
rand.Read(kv)
sessionKey := types.EncryptionKey{
KeyType: eTypeID,
KeyValue: kv,
}
etp := EncTicketPart{
Flags: flags,
Key: sessionKey,
CRealm: crealm,
CName: cname,
Transited: TransitedEncoding{},
AuthTime: authTime,
StartTime: startTime,
EndTime: endTime,
RenewTill: renewTill,
}
b, err := asn1.Marshal(etp)
b = asn1tools.AddASNAppTag(b, asnAppTag.EncTicketPart)
skey, err := sktab.GetEncryptionKey(sname.NameString, srealm, kvno, eTypeID)
if err != nil {
return Ticket{}, types.EncryptionKey{}, krberror.Errorf(err, krberror.EncryptingError, "Error getting encryption key for new ticket")
}
ed, err := crypto.GetEncryptedData(b, skey, keyusage.KDC_REP_TICKET, kvno)
if err != nil {
return Ticket{}, types.EncryptionKey{}, krberror.Errorf(err, krberror.EncryptingError, "Error encrypting ticket encpart")
}
tkt := Ticket{
TktVNO: iana.PVNO,
Realm: srealm,
SName: sname,
EncPart: ed,
}
return tkt, sessionKey, nil
}
// Unmarshal bytes b into a Ticket struct.
func (t *Ticket) Unmarshal(b []byte) error {
_, err := asn1.UnmarshalWithParams(b, t, fmt.Sprintf("application,explicit,tag:%d", asnAppTag.Ticket))
return err
}
// Marshal the Ticket.
func (t *Ticket) Marshal() ([]byte, error) {
b, err := asn1.Marshal(*t)
if err != nil {
return nil, err
}
b = asn1tools.AddASNAppTag(b, asnAppTag.Ticket)
return b, nil
}
// Unmarshal bytes b into the EncTicketPart struct.
func (t *EncTicketPart) Unmarshal(b []byte) error {
_, err := asn1.UnmarshalWithParams(b, t, fmt.Sprintf("application,explicit,tag:%d", asnAppTag.EncTicketPart))
return err
}
// UnmarshalTicket returns a ticket from the bytes provided.
func UnmarshalTicket(b []byte) (t Ticket, err error) {
_, err = asn1.UnmarshalWithParams(b, &t, fmt.Sprintf("application,explicit,tag:%d", asnAppTag.Ticket))
return
}
// UnmarshalTicketsSequence returns a slice of Tickets from a raw ASN1 value.
func UnmarshalTicketsSequence(in asn1.RawValue) ([]Ticket, error) {
//This is a workaround to a asn1 decoding issue in golang - https://github.com/golang/go/issues/17321. It's not pretty I'm afraid
//We pull out raw values from the larger raw value (that is actually the data of the sequence of raw values) and track our position moving along the data.
b := in.Bytes
// Ignore the head of the asn1 stream (1 byte for tag and those for the length) as this is what tells us its a sequence but we're handling it ourselves
p := 1 + asn1tools.GetNumberBytesInLengthHeader(in.Bytes)
var tkts []Ticket
var raw asn1.RawValue
for p < (len(b)) {
_, err := asn1.UnmarshalWithParams(b[p:], &raw, fmt.Sprintf("application,tag:%d", asnAppTag.Ticket))
if err != nil {
return nil, fmt.Errorf("Unmarshaling sequence of tickets failed geting length of ticket: %v", err)
}
t, err := UnmarshalTicket(b[p:])
if err != nil {
return nil, fmt.Errorf("Unmarshaling sequence of tickets failed: %v", err)
}
p += len(raw.FullBytes)
tkts = append(tkts, t)
}
MarshalTicketSequence(tkts)
return tkts, nil
}
// MarshalTicketSequence marshals a slice of Tickets returning an ASN1 raw value containing the ticket sequence.
func MarshalTicketSequence(tkts []Ticket) (asn1.RawValue, error) {
raw := asn1.RawValue{
Class: 2,
IsCompound: true,
}
if len(tkts) < 1 {
// There are no tickets to marshal
return raw, nil
}
var btkts []byte
for i, t := range tkts {
b, err := t.Marshal()
if err != nil {
return raw, fmt.Errorf("Error marshaling ticket number %d in seqence of tickets", i+1)
}
btkts = append(btkts, b...)
}
// The ASN1 wrapping consists of 2 bytes:
// 1st byte -> Identifier Octet - In this case an OCTET STRING (ASN TAG
// 2nd byte -> The length (this will be the size indicated in the input bytes + 2 for the additional bytes we add here.
// Application Tag:
//| Byte: | 8 | 7 | 6 | 5 | 4 | 3 | 2 | 1 |
//| Value: | 0 | 1 | 1 | From the RFC spec 4120 |
//| Explanation | Defined by the ASN1 encoding rules for an application tag | A value of 1 indicates a constructed type | The ASN Application tag value |
btkts = append(asn1tools.MarshalLengthBytes(len(btkts)), btkts...)
btkts = append([]byte{byte(32 + asn1.TagSequence)}, btkts...)
raw.Bytes = btkts
// If we need to create the full bytes then identifier octet is "context-specific" = 128 + "constructed" + 32 + the wrapping explicit tag (11)
//fmt.Fprintf(os.Stderr, "mRaw fb: %v\n", raw.FullBytes)
return raw, nil
}
// DecryptEncPart decrypts the encrypted part of the ticket.
func (t *Ticket) DecryptEncPart(keytab keytab.Keytab, sa string) error {
var upn []string
if sa != "" {
upn = []string{sa}
} else {
upn = t.SName.NameString
}
key, err := keytab.GetEncryptionKey(upn, t.Realm, t.EncPart.KVNO, t.EncPart.EType)
if err != nil {
return NewKRBError(t.SName, t.Realm, errorcode.KRB_AP_ERR_NOKEY, fmt.Sprintf("Could not get key from keytab: %v", err))
}
b, err := crypto.DecryptEncPart(t.EncPart, key, keyusage.KDC_REP_TICKET)
if err != nil {
return fmt.Errorf("Error decrypting Ticket EncPart: %v", err)
}
var denc EncTicketPart
err = denc.Unmarshal(b)
if err != nil {
return fmt.Errorf("Error unmarshaling encrypted part: %v", err)
}
t.DecryptedEncPart = denc
return nil
}
// GetPACType returns a Microsoft PAC that has been extracted from the ticket and processed.
func (t *Ticket) GetPACType(keytab keytab.Keytab, sa string) (bool, pac.PACType, error) {
var isPAC bool
for _, ad := range t.DecryptedEncPart.AuthorizationData {
if ad.ADType == adtype.ADIfRelevant {
var ad2 types.AuthorizationData
err := ad2.Unmarshal(ad.ADData)
if err != nil {
continue
}
if ad2[0].ADType == adtype.ADWin2KPAC {
isPAC = true
var pac pac.PACType
err = pac.Unmarshal(ad2[0].ADData)
if err != nil {
return isPAC, pac, fmt.Errorf("Error unmarshaling PAC: %v", err)
}
var upn []string
if sa != "" {
upn = []string{sa}
} else {
upn = t.SName.NameString
}
key, err := keytab.GetEncryptionKey(upn, t.Realm, t.EncPart.KVNO, t.EncPart.EType)
if err != nil {
return isPAC, pac, NewKRBError(t.SName, t.Realm, errorcode.KRB_AP_ERR_NOKEY, fmt.Sprintf("Could not get key from keytab: %v", err))
}
err = pac.ProcessPACInfoBuffers(key)
return isPAC, pac, err
}
}
}
return isPAC, pac.PACType{}, nil
}