190 lines
7.4 KiB
Go
190 lines
7.4 KiB
Go
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package client
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import (
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"gopkg.in/jcmturner/gokrb5.v7/crypto"
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"gopkg.in/jcmturner/gokrb5.v7/crypto/etype"
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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/patype"
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"gopkg.in/jcmturner/gokrb5.v7/krberror"
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"gopkg.in/jcmturner/gokrb5.v7/messages"
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"gopkg.in/jcmturner/gokrb5.v7/types"
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)
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// ASExchange performs an AS exchange for the client to retrieve a TGT.
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func (cl *Client) ASExchange(realm string, ASReq messages.ASReq, referral int) (messages.ASRep, error) {
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if ok, err := cl.IsConfigured(); !ok {
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return messages.ASRep{}, krberror.Errorf(err, krberror.ConfigError, "AS Exchange cannot be performed")
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}
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// Set PAData if required
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err := setPAData(cl, nil, &ASReq)
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if err != nil {
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return messages.ASRep{}, krberror.Errorf(err, krberror.KRBMsgError, "AS Exchange Error: issue with setting PAData on AS_REQ")
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}
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b, err := ASReq.Marshal()
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if err != nil {
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return messages.ASRep{}, krberror.Errorf(err, krberror.EncodingError, "AS Exchange Error: failed marshaling AS_REQ")
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}
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var ASRep messages.ASRep
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rb, err := cl.sendToKDC(b, realm)
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if err != nil {
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if e, ok := err.(messages.KRBError); ok {
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switch e.ErrorCode {
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case errorcode.KDC_ERR_PREAUTH_REQUIRED, errorcode.KDC_ERR_PREAUTH_FAILED:
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// From now on assume this client will need to do this pre-auth and set the PAData
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cl.settings.assumePreAuthentication = true
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err = setPAData(cl, &e, &ASReq)
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if err != nil {
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return messages.ASRep{}, krberror.Errorf(err, krberror.KRBMsgError, "AS Exchange Error: failed setting AS_REQ PAData for pre-authentication required")
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}
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b, err := ASReq.Marshal()
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if err != nil {
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return messages.ASRep{}, krberror.Errorf(err, krberror.EncodingError, "AS Exchange Error: failed marshaling AS_REQ with PAData")
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}
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rb, err = cl.sendToKDC(b, realm)
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if err != nil {
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if _, ok := err.(messages.KRBError); ok {
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return messages.ASRep{}, krberror.Errorf(err, krberror.KDCError, "AS Exchange Error: kerberos error response from KDC")
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}
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return messages.ASRep{}, krberror.Errorf(err, krberror.NetworkingError, "AS Exchange Error: failed sending AS_REQ to KDC")
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}
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case errorcode.KDC_ERR_WRONG_REALM:
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// Client referral https://tools.ietf.org/html/rfc6806.html#section-7
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if referral > 5 {
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return messages.ASRep{}, krberror.Errorf(err, krberror.KRBMsgError, "maximum number of client referrals exceeded")
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}
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referral++
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return cl.ASExchange(e.CRealm, ASReq, referral)
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default:
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return messages.ASRep{}, krberror.Errorf(err, krberror.KDCError, "AS Exchange Error: kerberos error response from KDC")
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}
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} else {
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return messages.ASRep{}, krberror.Errorf(err, krberror.NetworkingError, "AS Exchange Error: failed sending AS_REQ to KDC")
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}
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}
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err = ASRep.Unmarshal(rb)
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if err != nil {
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return messages.ASRep{}, krberror.Errorf(err, krberror.EncodingError, "AS Exchange Error: failed to process the AS_REP")
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}
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if ok, err := ASRep.Verify(cl.Config, cl.Credentials, ASReq); !ok {
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return messages.ASRep{}, krberror.Errorf(err, krberror.KRBMsgError, "AS Exchange Error: AS_REP is not valid or client password/keytab incorrect")
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}
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return ASRep, nil
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}
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// setPAData adds pre-authentication data to the AS_REQ.
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func setPAData(cl *Client, krberr *messages.KRBError, ASReq *messages.ASReq) error {
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if !cl.settings.DisablePAFXFAST() {
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pa := types.PAData{PADataType: patype.PA_REQ_ENC_PA_REP}
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ASReq.PAData = append(ASReq.PAData, pa)
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}
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if cl.settings.AssumePreAuthentication() {
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// Identify the etype to use to encrypt the PA Data
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var et etype.EType
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var err error
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var key types.EncryptionKey
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if krberr == nil {
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// This is not in response to an error from the KDC. It is preemptive or renewal
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// There is no KRB Error that tells us the etype to use
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etn := cl.settings.preAuthEType // Use the etype that may have previously been negotiated
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if etn == 0 {
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etn = int32(cl.Config.LibDefaults.PreferredPreauthTypes[0]) // Resort to config
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}
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et, err = crypto.GetEtype(etn)
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if err != nil {
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return krberror.Errorf(err, krberror.EncryptingError, "error getting etype for pre-auth encryption")
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}
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key, err = cl.Key(et, nil)
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if err != nil {
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return krberror.Errorf(err, krberror.EncryptingError, "error getting key from credentials")
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}
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} else {
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// Get the etype to use from the PA data in the KRBError e-data
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et, err = preAuthEType(krberr)
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if err != nil {
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return krberror.Errorf(err, krberror.EncryptingError, "error getting etype for pre-auth encryption")
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}
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cl.settings.preAuthEType = et.GetETypeID() // Set the etype that has been defined for potential future use
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key, err = cl.Key(et, krberr)
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if err != nil {
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return krberror.Errorf(err, krberror.EncryptingError, "error getting key from credentials")
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}
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}
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// Generate the PA data
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paTSb, err := types.GetPAEncTSEncAsnMarshalled()
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if err != nil {
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return krberror.Errorf(err, krberror.KRBMsgError, "error creating PAEncTSEnc for Pre-Authentication")
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}
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//TODO (theme: KVNO from keytab) the kvno should not be hard coded to 1 as this hampers troubleshooting.
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paEncTS, err := crypto.GetEncryptedData(paTSb, key, keyusage.AS_REQ_PA_ENC_TIMESTAMP, 1)
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if err != nil {
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return krberror.Errorf(err, krberror.EncryptingError, "error encrypting pre-authentication timestamp")
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}
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pb, err := paEncTS.Marshal()
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if err != nil {
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return krberror.Errorf(err, krberror.EncodingError, "error marshaling the PAEncTSEnc encrypted data")
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}
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pa := types.PAData{
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PADataType: patype.PA_ENC_TIMESTAMP,
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PADataValue: pb,
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}
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// Look for and delete any exiting patype.PA_ENC_TIMESTAMP
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for i, pa := range ASReq.PAData {
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if pa.PADataType == patype.PA_ENC_TIMESTAMP {
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ASReq.PAData[i] = ASReq.PAData[len(ASReq.PAData)-1]
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ASReq.PAData = ASReq.PAData[:len(ASReq.PAData)-1]
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}
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}
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ASReq.PAData = append(ASReq.PAData, pa)
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}
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return nil
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}
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// preAuthEType establishes what encryption type to use for pre-authentication from the KRBError returned from the KDC.
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func preAuthEType(krberr *messages.KRBError) (etype etype.EType, err error) {
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//The preferred ordering of the "hint" pre-authentication data that
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//affect client key selection is: ETYPE-INFO2, followed by ETYPE-INFO,
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//followed by PW-SALT.
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//A KDC SHOULD NOT send PA-PW-SALT when issuing a KRB-ERROR message
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//that requests additional pre-authentication. Implementation note:
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//Some KDC implementations issue an erroneous PA-PW-SALT when issuing a
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//KRB-ERROR message that requests additional pre-authentication.
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//Therefore, clients SHOULD ignore a PA-PW-SALT accompanying a
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//KRB-ERROR message that requests additional pre-authentication.
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var etypeID int32
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var pas types.PADataSequence
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e := pas.Unmarshal(krberr.EData)
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if e != nil {
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err = krberror.Errorf(e, krberror.EncodingError, "error unmashalling KRBError data")
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return
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}
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for _, pa := range pas {
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switch pa.PADataType {
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case patype.PA_ETYPE_INFO2:
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info, e := pa.GetETypeInfo2()
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if e != nil {
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err = krberror.Errorf(e, krberror.EncodingError, "error unmashalling ETYPE-INFO2 data")
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return
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}
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etypeID = info[0].EType
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break
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case patype.PA_ETYPE_INFO:
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info, e := pa.GetETypeInfo()
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if e != nil {
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err = krberror.Errorf(e, krberror.EncodingError, "error unmashalling ETYPE-INFO data")
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return
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}
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etypeID = info[0].EType
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}
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}
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etype, e = crypto.GetEtype(etypeID)
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if e != nil {
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err = krberror.Errorf(e, krberror.EncryptingError, "error creating etype")
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return
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}
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return etype, nil
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}
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