telebit/vendor/github.com/jcmturner/gokrb5/v8/client/ASExchange.go

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2020-06-03 06:18:04 +00:00
package client
import (
"github.com/jcmturner/gokrb5/v8/crypto"
"github.com/jcmturner/gokrb5/v8/crypto/etype"
"github.com/jcmturner/gokrb5/v8/iana/errorcode"
"github.com/jcmturner/gokrb5/v8/iana/keyusage"
"github.com/jcmturner/gokrb5/v8/iana/patype"
"github.com/jcmturner/gokrb5/v8/krberror"
"github.com/jcmturner/gokrb5/v8/messages"
"github.com/jcmturner/gokrb5/v8/types"
)
// ASExchange performs an AS exchange for the client to retrieve a TGT.
func (cl *Client) ASExchange(realm string, ASReq messages.ASReq, referral int) (messages.ASRep, error) {
if ok, err := cl.IsConfigured(); !ok {
return messages.ASRep{}, krberror.Errorf(err, krberror.ConfigError, "AS Exchange cannot be performed")
}
// Set PAData if required
err := setPAData(cl, nil, &ASReq)
if err != nil {
return messages.ASRep{}, krberror.Errorf(err, krberror.KRBMsgError, "AS Exchange Error: issue with setting PAData on AS_REQ")
}
b, err := ASReq.Marshal()
if err != nil {
return messages.ASRep{}, krberror.Errorf(err, krberror.EncodingError, "AS Exchange Error: failed marshaling AS_REQ")
}
var ASRep messages.ASRep
rb, err := cl.sendToKDC(b, realm)
if err != nil {
if e, ok := err.(messages.KRBError); ok {
switch e.ErrorCode {
case errorcode.KDC_ERR_PREAUTH_REQUIRED, errorcode.KDC_ERR_PREAUTH_FAILED:
// From now on assume this client will need to do this pre-auth and set the PAData
cl.settings.assumePreAuthentication = true
err = setPAData(cl, &e, &ASReq)
if err != nil {
return messages.ASRep{}, krberror.Errorf(err, krberror.KRBMsgError, "AS Exchange Error: failed setting AS_REQ PAData for pre-authentication required")
}
b, err := ASReq.Marshal()
if err != nil {
return messages.ASRep{}, krberror.Errorf(err, krberror.EncodingError, "AS Exchange Error: failed marshaling AS_REQ with PAData")
}
rb, err = cl.sendToKDC(b, realm)
if err != nil {
if _, ok := err.(messages.KRBError); ok {
return messages.ASRep{}, krberror.Errorf(err, krberror.KDCError, "AS Exchange Error: kerberos error response from KDC")
}
return messages.ASRep{}, krberror.Errorf(err, krberror.NetworkingError, "AS Exchange Error: failed sending AS_REQ to KDC")
}
case errorcode.KDC_ERR_WRONG_REALM:
// Client referral https://tools.ietf.org/html/rfc6806.html#section-7
if referral > 5 {
return messages.ASRep{}, krberror.Errorf(err, krberror.KRBMsgError, "maximum number of client referrals exceeded")
}
referral++
return cl.ASExchange(e.CRealm, ASReq, referral)
default:
return messages.ASRep{}, krberror.Errorf(err, krberror.KDCError, "AS Exchange Error: kerberos error response from KDC")
}
} else {
return messages.ASRep{}, krberror.Errorf(err, krberror.NetworkingError, "AS Exchange Error: failed sending AS_REQ to KDC")
}
}
err = ASRep.Unmarshal(rb)
if err != nil {
return messages.ASRep{}, krberror.Errorf(err, krberror.EncodingError, "AS Exchange Error: failed to process the AS_REP")
}
if ok, err := ASRep.Verify(cl.Config, cl.Credentials, ASReq); !ok {
return messages.ASRep{}, krberror.Errorf(err, krberror.KRBMsgError, "AS Exchange Error: AS_REP is not valid or client password/keytab incorrect")
}
return ASRep, nil
}
// setPAData adds pre-authentication data to the AS_REQ.
func setPAData(cl *Client, krberr *messages.KRBError, ASReq *messages.ASReq) error {
if !cl.settings.DisablePAFXFAST() {
pa := types.PAData{PADataType: patype.PA_REQ_ENC_PA_REP}
ASReq.PAData = append(ASReq.PAData, pa)
}
if cl.settings.AssumePreAuthentication() {
// Identify the etype to use to encrypt the PA Data
var et etype.EType
var err error
var key types.EncryptionKey
var kvno int
if krberr == nil {
// This is not in response to an error from the KDC. It is preemptive or renewal
// There is no KRB Error that tells us the etype to use
etn := cl.settings.preAuthEType // Use the etype that may have previously been negotiated
if etn == 0 {
etn = int32(cl.Config.LibDefaults.PreferredPreauthTypes[0]) // Resort to config
}
et, err = crypto.GetEtype(etn)
if err != nil {
return krberror.Errorf(err, krberror.EncryptingError, "error getting etype for pre-auth encryption")
}
key, kvno, err = cl.Key(et, 0, nil)
if err != nil {
return krberror.Errorf(err, krberror.EncryptingError, "error getting key from credentials")
}
} else {
// Get the etype to use from the PA data in the KRBError e-data
et, err = preAuthEType(krberr)
if err != nil {
return krberror.Errorf(err, krberror.EncryptingError, "error getting etype for pre-auth encryption")
}
cl.settings.preAuthEType = et.GetETypeID() // Set the etype that has been defined for potential future use
key, kvno, err = cl.Key(et, 0, krberr)
if err != nil {
return krberror.Errorf(err, krberror.EncryptingError, "error getting key from credentials")
}
}
// Generate the PA data
paTSb, err := types.GetPAEncTSEncAsnMarshalled()
if err != nil {
return krberror.Errorf(err, krberror.KRBMsgError, "error creating PAEncTSEnc for Pre-Authentication")
}
paEncTS, err := crypto.GetEncryptedData(paTSb, key, keyusage.AS_REQ_PA_ENC_TIMESTAMP, kvno)
if err != nil {
return krberror.Errorf(err, krberror.EncryptingError, "error encrypting pre-authentication timestamp")
}
pb, err := paEncTS.Marshal()
if err != nil {
return krberror.Errorf(err, krberror.EncodingError, "error marshaling the PAEncTSEnc encrypted data")
}
pa := types.PAData{
PADataType: patype.PA_ENC_TIMESTAMP,
PADataValue: pb,
}
// Look for and delete any exiting patype.PA_ENC_TIMESTAMP
for i, pa := range ASReq.PAData {
if pa.PADataType == patype.PA_ENC_TIMESTAMP {
ASReq.PAData[i] = ASReq.PAData[len(ASReq.PAData)-1]
ASReq.PAData = ASReq.PAData[:len(ASReq.PAData)-1]
}
}
ASReq.PAData = append(ASReq.PAData, pa)
}
return nil
}
// preAuthEType establishes what encryption type to use for pre-authentication from the KRBError returned from the KDC.
func preAuthEType(krberr *messages.KRBError) (etype etype.EType, err error) {
//RFC 4120 5.2.7.5 covers the preference order of ETYPE-INFO2 and ETYPE-INFO.
var etypeID int32
var pas types.PADataSequence
e := pas.Unmarshal(krberr.EData)
if e != nil {
err = krberror.Errorf(e, krberror.EncodingError, "error unmashalling KRBError data")
return
}
Loop:
for _, pa := range pas {
switch pa.PADataType {
case patype.PA_ETYPE_INFO2:
info, e := pa.GetETypeInfo2()
if e != nil {
err = krberror.Errorf(e, krberror.EncodingError, "error unmashalling ETYPE-INFO2 data")
return
}
etypeID = info[0].EType
break Loop
case patype.PA_ETYPE_INFO:
info, e := pa.GetETypeInfo()
if e != nil {
err = krberror.Errorf(e, krberror.EncodingError, "error unmashalling ETYPE-INFO data")
return
}
etypeID = info[0].EType
}
}
etype, e = crypto.GetEtype(etypeID)
if e != nil {
err = krberror.Errorf(e, krberror.EncryptingError, "error creating etype")
return
}
return etype, nil
}