266 lines
10 KiB
Go
266 lines
10 KiB
Go
package messages
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import (
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"crypto/rand"
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"fmt"
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"log"
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"time"
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"github.com/jcmturner/gofork/encoding/asn1"
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"gopkg.in/jcmturner/gokrb5.v7/asn1tools"
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"gopkg.in/jcmturner/gokrb5.v7/crypto"
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"gopkg.in/jcmturner/gokrb5.v7/iana"
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"gopkg.in/jcmturner/gokrb5.v7/iana/adtype"
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"gopkg.in/jcmturner/gokrb5.v7/iana/asnAppTag"
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"gopkg.in/jcmturner/gokrb5.v7/iana/errorcode"
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"gopkg.in/jcmturner/gokrb5.v7/iana/flags"
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"gopkg.in/jcmturner/gokrb5.v7/iana/keyusage"
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"gopkg.in/jcmturner/gokrb5.v7/keytab"
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"gopkg.in/jcmturner/gokrb5.v7/krberror"
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"gopkg.in/jcmturner/gokrb5.v7/pac"
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"gopkg.in/jcmturner/gokrb5.v7/types"
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)
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// Reference: https://www.ietf.org/rfc/rfc4120.txt
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// Section: 5.3
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// Ticket implements the Kerberos ticket.
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type Ticket struct {
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TktVNO int `asn1:"explicit,tag:0"`
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Realm string `asn1:"generalstring,explicit,tag:1"`
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SName types.PrincipalName `asn1:"explicit,tag:2"`
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EncPart types.EncryptedData `asn1:"explicit,tag:3"`
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DecryptedEncPart EncTicketPart `asn1:"optional"` // Not part of ASN1 bytes so marked as optional so unmarshalling works
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}
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// EncTicketPart is the encrypted part of the Ticket.
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type EncTicketPart struct {
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Flags asn1.BitString `asn1:"explicit,tag:0"`
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Key types.EncryptionKey `asn1:"explicit,tag:1"`
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CRealm string `asn1:"generalstring,explicit,tag:2"`
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CName types.PrincipalName `asn1:"explicit,tag:3"`
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Transited TransitedEncoding `asn1:"explicit,tag:4"`
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AuthTime time.Time `asn1:"generalized,explicit,tag:5"`
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StartTime time.Time `asn1:"generalized,explicit,optional,tag:6"`
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EndTime time.Time `asn1:"generalized,explicit,tag:7"`
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RenewTill time.Time `asn1:"generalized,explicit,optional,tag:8"`
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CAddr types.HostAddresses `asn1:"explicit,optional,tag:9"`
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AuthorizationData types.AuthorizationData `asn1:"explicit,optional,tag:10"`
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}
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// TransitedEncoding part of the ticket's encrypted part.
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type TransitedEncoding struct {
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TRType int32 `asn1:"explicit,tag:0"`
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Contents []byte `asn1:"explicit,tag:1"`
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}
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// NewTicket creates a new Ticket instance.
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func NewTicket(cname types.PrincipalName, crealm string, sname types.PrincipalName, srealm string, flags asn1.BitString, sktab *keytab.Keytab, eTypeID int32, kvno int, authTime, startTime, endTime, renewTill time.Time) (Ticket, types.EncryptionKey, error) {
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etype, err := crypto.GetEtype(eTypeID)
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if err != nil {
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return Ticket{}, types.EncryptionKey{}, krberror.Errorf(err, krberror.EncryptingError, "error getting etype for new ticket")
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}
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ks := etype.GetKeyByteSize()
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kv := make([]byte, ks, ks)
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rand.Read(kv)
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sessionKey := types.EncryptionKey{
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KeyType: eTypeID,
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KeyValue: kv,
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}
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etp := EncTicketPart{
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Flags: flags,
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Key: sessionKey,
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CRealm: crealm,
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CName: cname,
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Transited: TransitedEncoding{},
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AuthTime: authTime,
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StartTime: startTime,
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EndTime: endTime,
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RenewTill: renewTill,
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}
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b, err := asn1.Marshal(etp)
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if err != nil {
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return Ticket{}, types.EncryptionKey{}, krberror.Errorf(err, krberror.EncodingError, "error marshalling ticket encpart")
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}
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b = asn1tools.AddASNAppTag(b, asnAppTag.EncTicketPart)
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skey, err := sktab.GetEncryptionKey(sname, srealm, kvno, eTypeID)
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if err != nil {
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return Ticket{}, types.EncryptionKey{}, krberror.Errorf(err, krberror.EncryptingError, "error getting encryption key for new ticket")
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}
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ed, err := crypto.GetEncryptedData(b, skey, keyusage.KDC_REP_TICKET, kvno)
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if err != nil {
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return Ticket{}, types.EncryptionKey{}, krberror.Errorf(err, krberror.EncryptingError, "error encrypting ticket encpart")
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}
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tkt := Ticket{
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TktVNO: iana.PVNO,
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Realm: srealm,
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SName: sname,
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EncPart: ed,
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}
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return tkt, sessionKey, nil
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}
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// Unmarshal bytes b into a Ticket struct.
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func (t *Ticket) Unmarshal(b []byte) error {
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_, err := asn1.UnmarshalWithParams(b, t, fmt.Sprintf("application,explicit,tag:%d", asnAppTag.Ticket))
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return err
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}
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// Marshal the Ticket.
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func (t *Ticket) Marshal() ([]byte, error) {
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b, err := asn1.Marshal(*t)
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if err != nil {
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return nil, err
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}
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b = asn1tools.AddASNAppTag(b, asnAppTag.Ticket)
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return b, nil
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}
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// Unmarshal bytes b into the EncTicketPart struct.
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func (t *EncTicketPart) Unmarshal(b []byte) error {
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_, err := asn1.UnmarshalWithParams(b, t, fmt.Sprintf("application,explicit,tag:%d", asnAppTag.EncTicketPart))
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return err
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}
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// unmarshalTicket returns a ticket from the bytes provided.
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func unmarshalTicket(b []byte) (t Ticket, err error) {
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err = t.Unmarshal(b)
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return
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}
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// UnmarshalTicketsSequence returns a slice of Tickets from a raw ASN1 value.
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func unmarshalTicketsSequence(in asn1.RawValue) ([]Ticket, error) {
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//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
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//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.
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b := in.Bytes
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// 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
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p := 1 + asn1tools.GetNumberBytesInLengthHeader(in.Bytes)
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var tkts []Ticket
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var raw asn1.RawValue
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for p < (len(b)) {
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_, err := asn1.UnmarshalWithParams(b[p:], &raw, fmt.Sprintf("application,tag:%d", asnAppTag.Ticket))
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if err != nil {
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return nil, fmt.Errorf("unmarshaling sequence of tickets failed getting length of ticket: %v", err)
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}
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t, err := unmarshalTicket(b[p:])
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if err != nil {
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return nil, fmt.Errorf("unmarshaling sequence of tickets failed: %v", err)
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}
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p += len(raw.FullBytes)
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tkts = append(tkts, t)
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}
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MarshalTicketSequence(tkts)
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return tkts, nil
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}
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// MarshalTicketSequence marshals a slice of Tickets returning an ASN1 raw value containing the ticket sequence.
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func MarshalTicketSequence(tkts []Ticket) (asn1.RawValue, error) {
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raw := asn1.RawValue{
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Class: 2,
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IsCompound: true,
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}
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if len(tkts) < 1 {
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// There are no tickets to marshal
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return raw, nil
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}
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var btkts []byte
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for i, t := range tkts {
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b, err := t.Marshal()
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if err != nil {
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return raw, fmt.Errorf("error marshaling ticket number %d in sequence of tickets", i+1)
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}
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btkts = append(btkts, b...)
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}
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// The ASN1 wrapping consists of 2 bytes:
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// 1st byte -> Identifier Octet - In this case an OCTET STRING (ASN TAG
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// 2nd byte -> The length (this will be the size indicated in the input bytes + 2 for the additional bytes we add here.
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// Application Tag:
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//| Byte: | 8 | 7 | 6 | 5 | 4 | 3 | 2 | 1 |
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//| Value: | 0 | 1 | 1 | From the RFC spec 4120 |
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//| Explanation | Defined by the ASN1 encoding rules for an application tag | A value of 1 indicates a constructed type | The ASN Application tag value |
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btkts = append(asn1tools.MarshalLengthBytes(len(btkts)), btkts...)
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btkts = append([]byte{byte(32 + asn1.TagSequence)}, btkts...)
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raw.Bytes = btkts
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// If we need to create the full bytes then identifier octet is "context-specific" = 128 + "constructed" + 32 + the wrapping explicit tag (11)
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//fmt.Fprintf(os.Stderr, "mRaw fb: %v\n", raw.FullBytes)
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return raw, nil
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}
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// DecryptEncPart decrypts the encrypted part of the ticket.
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// The sname argument can be used to specify which service principal's key should be used to decrypt the ticket.
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// If nil is passed as the sname then the service principal specified within the ticket it used.
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func (t *Ticket) DecryptEncPart(keytab *keytab.Keytab, sname *types.PrincipalName) error {
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if sname == nil {
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sname = &t.SName
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}
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key, err := keytab.GetEncryptionKey(*sname, t.Realm, t.EncPart.KVNO, t.EncPart.EType)
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if err != nil {
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return NewKRBError(t.SName, t.Realm, errorcode.KRB_AP_ERR_NOKEY, fmt.Sprintf("Could not get key from keytab: %v", err))
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}
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return t.Decrypt(key)
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}
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// Decrypt decrypts the encrypted part of the ticket using the key provided.
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func (t *Ticket) Decrypt(key types.EncryptionKey) error {
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b, err := crypto.DecryptEncPart(t.EncPart, key, keyusage.KDC_REP_TICKET)
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if err != nil {
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return fmt.Errorf("error decrypting Ticket EncPart: %v", err)
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}
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var denc EncTicketPart
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err = denc.Unmarshal(b)
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if err != nil {
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return fmt.Errorf("error unmarshaling encrypted part: %v", err)
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}
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t.DecryptedEncPart = denc
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return nil
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}
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// GetPACType returns a Microsoft PAC that has been extracted from the ticket and processed.
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func (t *Ticket) GetPACType(keytab *keytab.Keytab, sname *types.PrincipalName, l *log.Logger) (bool, pac.PACType, error) {
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var isPAC bool
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for _, ad := range t.DecryptedEncPart.AuthorizationData {
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if ad.ADType == adtype.ADIfRelevant {
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var ad2 types.AuthorizationData
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err := ad2.Unmarshal(ad.ADData)
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if err != nil {
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l.Printf("PAC authorization data could not be unmarshaled: %v", err)
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continue
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}
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if ad2[0].ADType == adtype.ADWin2KPAC {
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isPAC = true
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var p pac.PACType
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err = p.Unmarshal(ad2[0].ADData)
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if err != nil {
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return isPAC, p, fmt.Errorf("error unmarshaling PAC: %v", err)
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}
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if sname == nil {
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sname = &t.SName
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}
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key, err := keytab.GetEncryptionKey(*sname, t.Realm, t.EncPart.KVNO, t.EncPart.EType)
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if err != nil {
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return isPAC, p, NewKRBError(t.SName, t.Realm, errorcode.KRB_AP_ERR_NOKEY, fmt.Sprintf("Could not get key from keytab: %v", err))
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}
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err = p.ProcessPACInfoBuffers(key, l)
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return isPAC, p, err
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}
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}
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}
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return isPAC, pac.PACType{}, nil
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}
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// Valid checks it the ticket is currently valid. Max duration passed endtime passed in as argument.
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func (t *Ticket) Valid(d time.Duration) (bool, error) {
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// Check for future tickets or invalid tickets
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time := time.Now().UTC()
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if t.DecryptedEncPart.StartTime.Sub(time) > d || types.IsFlagSet(&t.DecryptedEncPart.Flags, flags.Invalid) {
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return false, NewKRBError(t.SName, t.Realm, errorcode.KRB_AP_ERR_TKT_NYV, "service ticket provided is not yet valid")
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}
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// Check for expired ticket
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if time.Sub(t.DecryptedEncPart.EndTime) > d {
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return false, NewKRBError(t.SName, t.Realm, errorcode.KRB_AP_ERR_TKT_EXPIRED, "service ticket provided has expired")
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}
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return true, nil
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}
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