221 lines
8.6 KiB
Go
221 lines
8.6 KiB
Go
package messages
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import (
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"fmt"
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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/asnAppTag"
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"gopkg.in/jcmturner/gokrb5.v7/iana/errorcode"
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"gopkg.in/jcmturner/gokrb5.v7/iana/keyusage"
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"gopkg.in/jcmturner/gokrb5.v7/iana/msgtype"
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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/types"
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)
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/*AP-REQ ::= [APPLICATION 14] SEQUENCE {
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pvno [0] INTEGER (5),
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msg-type [1] INTEGER (14),
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ap-options [2] APOptions,
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ticket [3] Ticket,
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authenticator [4] EncryptedData -- Authenticator
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}
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APOptions ::= KerberosFlags
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-- reserved(0),
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-- use-session-key(1),
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-- mutual-required(2)*/
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type marshalAPReq struct {
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PVNO int `asn1:"explicit,tag:0"`
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MsgType int `asn1:"explicit,tag:1"`
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APOptions asn1.BitString `asn1:"explicit,tag:2"`
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// Ticket needs to be a raw value as it is wrapped in an APPLICATION tag
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Ticket asn1.RawValue `asn1:"explicit,tag:3"`
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EncryptedAuthenticator types.EncryptedData `asn1:"explicit,tag:4"`
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}
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// APReq implements RFC 4120 KRB_AP_REQ: https://tools.ietf.org/html/rfc4120#section-5.5.1.
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type APReq struct {
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PVNO int `asn1:"explicit,tag:0"`
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MsgType int `asn1:"explicit,tag:1"`
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APOptions asn1.BitString `asn1:"explicit,tag:2"`
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Ticket Ticket `asn1:"explicit,tag:3"`
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EncryptedAuthenticator types.EncryptedData `asn1:"explicit,tag:4"`
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Authenticator types.Authenticator `asn1:"optional"`
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}
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// NewAPReq generates a new KRB_AP_REQ struct.
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func NewAPReq(tkt Ticket, sessionKey types.EncryptionKey, auth types.Authenticator) (APReq, error) {
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var a APReq
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ed, err := encryptAuthenticator(auth, sessionKey, tkt)
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if err != nil {
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return a, krberror.Errorf(err, krberror.KRBMsgError, "error creating Authenticator for AP_REQ")
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}
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a = APReq{
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PVNO: iana.PVNO,
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MsgType: msgtype.KRB_AP_REQ,
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APOptions: types.NewKrbFlags(),
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Ticket: tkt,
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EncryptedAuthenticator: ed,
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}
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return a, nil
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}
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// Encrypt Authenticator
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func encryptAuthenticator(a types.Authenticator, sessionKey types.EncryptionKey, tkt Ticket) (types.EncryptedData, error) {
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var ed types.EncryptedData
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m, err := a.Marshal()
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if err != nil {
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return ed, krberror.Errorf(err, krberror.EncodingError, "marshaling error of EncryptedData form of Authenticator")
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}
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usage := authenticatorKeyUsage(tkt.SName)
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ed, err = crypto.GetEncryptedData(m, sessionKey, uint32(usage), tkt.EncPart.KVNO)
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if err != nil {
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return ed, krberror.Errorf(err, krberror.EncryptingError, "error encrypting Authenticator")
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}
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return ed, nil
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}
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// DecryptAuthenticator decrypts the Authenticator within the AP_REQ.
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// sessionKey may simply be the key within the decrypted EncPart of the ticket within the AP_REQ.
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func (a *APReq) DecryptAuthenticator(sessionKey types.EncryptionKey) error {
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usage := authenticatorKeyUsage(a.Ticket.SName)
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ab, e := crypto.DecryptEncPart(a.EncryptedAuthenticator, sessionKey, uint32(usage))
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if e != nil {
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return fmt.Errorf("error decrypting authenticator: %v", e)
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}
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err := a.Authenticator.Unmarshal(ab)
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if err != nil {
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return fmt.Errorf("error unmarshaling authenticator: %v", err)
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}
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return nil
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}
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func authenticatorKeyUsage(pn types.PrincipalName) int {
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if pn.NameString[0] == "krbtgt" {
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return keyusage.TGS_REQ_PA_TGS_REQ_AP_REQ_AUTHENTICATOR
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}
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return keyusage.AP_REQ_AUTHENTICATOR
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}
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// Unmarshal bytes b into the APReq struct.
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func (a *APReq) Unmarshal(b []byte) error {
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var m marshalAPReq
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_, err := asn1.UnmarshalWithParams(b, &m, fmt.Sprintf("application,explicit,tag:%v", asnAppTag.APREQ))
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if err != nil {
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return krberror.Errorf(err, krberror.EncodingError, "unmarshal error of AP_REQ")
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}
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if m.MsgType != msgtype.KRB_AP_REQ {
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return NewKRBError(types.PrincipalName{}, "", errorcode.KRB_AP_ERR_MSG_TYPE, errorcode.Lookup(errorcode.KRB_AP_ERR_MSG_TYPE))
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}
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a.PVNO = m.PVNO
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a.MsgType = m.MsgType
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a.APOptions = m.APOptions
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a.EncryptedAuthenticator = m.EncryptedAuthenticator
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a.Ticket, err = unmarshalTicket(m.Ticket.Bytes)
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if err != nil {
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return krberror.Errorf(err, krberror.EncodingError, "unmarshaling error of Ticket within AP_REQ")
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}
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return nil
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}
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// Marshal APReq struct.
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func (a *APReq) Marshal() ([]byte, error) {
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m := marshalAPReq{
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PVNO: a.PVNO,
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MsgType: a.MsgType,
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APOptions: a.APOptions,
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EncryptedAuthenticator: a.EncryptedAuthenticator,
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}
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var b []byte
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b, err := a.Ticket.Marshal()
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if err != nil {
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return b, err
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}
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m.Ticket = asn1.RawValue{
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Class: asn1.ClassContextSpecific,
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IsCompound: true,
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Tag: 3,
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Bytes: b,
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}
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mk, err := asn1.Marshal(m)
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if err != nil {
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return mk, krberror.Errorf(err, krberror.EncodingError, "marshaling error of AP_REQ")
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}
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mk = asn1tools.AddASNAppTag(mk, asnAppTag.APREQ)
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return mk, nil
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}
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// Verify an AP_REQ using service's keytab, spn and max acceptable clock skew duration.
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// The service ticket encrypted part and authenticator will be decrypted as part of this operation.
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func (a *APReq) Verify(kt *keytab.Keytab, d time.Duration, cAddr types.HostAddress) (bool, error) {
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// Decrypt ticket's encrypted part with service key
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//TODO decrypt with service's session key from its TGT is use-to-user. Need to figure out how to get TGT.
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//if types.IsFlagSet(&a.APOptions, flags.APOptionUseSessionKey) {
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// //If the USE-SESSION-KEY flag is set in the ap-options field, it indicates to
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// //the server that user-to-user authentication is in use, and that the ticket
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// //is encrypted in the session key from the server's TGT rather than in the server's secret key.
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// err := a.Ticket.Decrypt(tgt.DecryptedEncPart.Key)
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// if err != nil {
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// return false, krberror.Errorf(err, krberror.DecryptingError, "error decrypting encpart of ticket provided using session key")
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// }
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//} else {
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// // Because it is possible for the server to be registered in multiple
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// // realms, with different keys in each, the srealm field in the
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// // unencrypted portion of the ticket in the KRB_AP_REQ is used to
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// // specify which secret key the server should use to decrypt that
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// // ticket.The KRB_AP_ERR_NOKEY error code is returned if the server
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// // doesn't have the proper key to decipher the ticket.
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// // The ticket is decrypted using the version of the server's key
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// // specified by the ticket.
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// err := a.Ticket.DecryptEncPart(*kt, &a.Ticket.SName)
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// if err != nil {
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// return false, krberror.Errorf(err, krberror.DecryptingError, "error decrypting encpart of service ticket provided")
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// }
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//}
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err := a.Ticket.DecryptEncPart(kt, &a.Ticket.SName)
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if err != nil {
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return false, krberror.Errorf(err, krberror.DecryptingError, "error decrypting encpart of service ticket provided")
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}
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// Check time validity of ticket
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ok, err := a.Ticket.Valid(d)
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if err != nil || !ok {
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return ok, err
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}
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// Check client's address is listed in the client addresses in the ticket
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if len(a.Ticket.DecryptedEncPart.CAddr) > 0 {
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//The addresses in the ticket (if any) are then searched for an address matching the operating-system reported
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//address of the client. If no match is found or the server insists on ticket addresses but none are present in
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//the ticket, the KRB_AP_ERR_BADADDR error is returned.
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if !types.HostAddressesContains(a.Ticket.DecryptedEncPart.CAddr, cAddr) {
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return false, NewKRBError(a.Ticket.SName, a.Ticket.Realm, errorcode.KRB_AP_ERR_BADADDR, "client address not within the list contained in the service ticket")
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}
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}
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// Decrypt authenticator with session key from ticket's encrypted part
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err = a.DecryptAuthenticator(a.Ticket.DecryptedEncPart.Key)
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if err != nil {
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return false, NewKRBError(a.Ticket.SName, a.Ticket.Realm, errorcode.KRB_AP_ERR_BAD_INTEGRITY, "could not decrypt authenticator")
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}
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// Check CName in authenticator is the same as that in the ticket
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if !a.Authenticator.CName.Equal(a.Ticket.DecryptedEncPart.CName) {
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return false, NewKRBError(a.Ticket.SName, a.Ticket.Realm, errorcode.KRB_AP_ERR_BADMATCH, "CName in Authenticator does not match that in service ticket")
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}
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// Check the clock skew between the client and the service server
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ct := a.Authenticator.CTime.Add(time.Duration(a.Authenticator.Cusec) * time.Microsecond)
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t := time.Now().UTC()
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if t.Sub(ct) > d || ct.Sub(t) > d {
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return false, NewKRBError(a.Ticket.SName, a.Ticket.Realm, errorcode.KRB_AP_ERR_SKEW, fmt.Sprintf("clock skew with client too large. greater than %v seconds", d))
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}
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return true, nil
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}
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