/
KDCRep.go
312 lines (296 loc) · 14.2 KB
/
KDCRep.go
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package messages
// Reference: https://www.ietf.org/rfc/rfc4120.txt
// Section: 5.4.2
import (
"fmt"
"time"
"github.com/jcmturner/gofork/encoding/asn1"
"gopkg.in/jcmturner/gokrb5.v6/config"
"gopkg.in/jcmturner/gokrb5.v6/credentials"
"gopkg.in/jcmturner/gokrb5.v6/crypto"
"gopkg.in/jcmturner/gokrb5.v6/iana/asnAppTag"
"gopkg.in/jcmturner/gokrb5.v6/iana/flags"
"gopkg.in/jcmturner/gokrb5.v6/iana/keyusage"
"gopkg.in/jcmturner/gokrb5.v6/iana/msgtype"
"gopkg.in/jcmturner/gokrb5.v6/iana/patype"
"gopkg.in/jcmturner/gokrb5.v6/krberror"
"gopkg.in/jcmturner/gokrb5.v6/types"
)
type marshalKDCRep struct {
PVNO int `asn1:"explicit,tag:0"`
MsgType int `asn1:"explicit,tag:1"`
PAData types.PADataSequence `asn1:"explicit,optional,tag:2"`
CRealm string `asn1:"generalstring,explicit,tag:3"`
CName types.PrincipalName `asn1:"explicit,tag:4"`
// Ticket needs to be a raw value as it is wrapped in an APPLICATION tag
Ticket asn1.RawValue `asn1:"explicit,tag:5"`
EncPart types.EncryptedData `asn1:"explicit,tag:6"`
}
// KDCRepFields represents the KRB_KDC_REP fields.
type KDCRepFields struct {
PVNO int
MsgType int
PAData []types.PAData
CRealm string
CName types.PrincipalName
Ticket Ticket
EncPart types.EncryptedData
DecryptedEncPart EncKDCRepPart
}
// ASRep implements RFC 4120 KRB_AS_REP: https://tools.ietf.org/html/rfc4120#section-5.4.2.
type ASRep struct {
KDCRepFields
}
// TGSRep implements RFC 4120 KRB_TGS_REP: https://tools.ietf.org/html/rfc4120#section-5.4.2.
type TGSRep struct {
KDCRepFields
}
// EncKDCRepPart is the encrypted part of KRB_KDC_REP.
type EncKDCRepPart struct {
Key types.EncryptionKey `asn1:"explicit,tag:0"`
LastReqs []LastReq `asn1:"explicit,tag:1"`
Nonce int `asn1:"explicit,tag:2"`
KeyExpiration time.Time `asn1:"generalized,explicit,optional,tag:3"`
Flags asn1.BitString `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"`
SRealm string `asn1:"generalstring,explicit,tag:9"`
SName types.PrincipalName `asn1:"explicit,tag:10"`
CAddr []types.HostAddress `asn1:"explicit,optional,tag:11"`
EncPAData types.PADataSequence `asn1:"explicit,optional,tag:12"`
}
// LastReq part of KRB_KDC_REP.
type LastReq struct {
LRType int32 `asn1:"explicit,tag:0"`
LRValue time.Time `asn1:"generalized,explicit,tag:1"`
}
// Unmarshal bytes b into the ASRep struct.
func (k *ASRep) Unmarshal(b []byte) error {
var m marshalKDCRep
_, err := asn1.UnmarshalWithParams(b, &m, fmt.Sprintf("application,explicit,tag:%v", asnAppTag.ASREP))
if err != nil {
return processUnmarshalReplyError(b, err)
}
if m.MsgType != msgtype.KRB_AS_REP {
return krberror.NewErrorf(krberror.KRBMsgError, "message ID does not indicate an AS_REP. Expected: %v; Actual: %v", msgtype.KRB_AS_REP, m.MsgType)
}
//Process the raw ticket within
tkt, err := UnmarshalTicket(m.Ticket.Bytes)
if err != nil {
return krberror.Errorf(err, krberror.EncodingError, "error unmarshaling Ticket within AS_REP")
}
k.KDCRepFields = KDCRepFields{
PVNO: m.PVNO,
MsgType: m.MsgType,
PAData: m.PAData,
CRealm: m.CRealm,
CName: m.CName,
Ticket: tkt,
EncPart: m.EncPart,
}
return nil
}
// Unmarshal bytes b into the TGSRep struct.
func (k *TGSRep) Unmarshal(b []byte) error {
var m marshalKDCRep
_, err := asn1.UnmarshalWithParams(b, &m, fmt.Sprintf("application,explicit,tag:%v", asnAppTag.TGSREP))
if err != nil {
return processUnmarshalReplyError(b, err)
}
if m.MsgType != msgtype.KRB_TGS_REP {
return krberror.NewErrorf(krberror.KRBMsgError, "message ID does not indicate an TGS_REP. Expected: %v; Actual: %v", msgtype.KRB_TGS_REP, m.MsgType)
}
//Process the raw ticket within
tkt, err := UnmarshalTicket(m.Ticket.Bytes)
if err != nil {
return krberror.Errorf(err, krberror.EncodingError, "error unmarshaling Ticket within TGS_REP")
}
k.KDCRepFields = KDCRepFields{
PVNO: m.PVNO,
MsgType: m.MsgType,
PAData: m.PAData,
CRealm: m.CRealm,
CName: m.CName,
Ticket: tkt,
EncPart: m.EncPart,
}
return nil
}
// Unmarshal bytes b into encrypted part of KRB_KDC_REP.
func (e *EncKDCRepPart) Unmarshal(b []byte) error {
_, err := asn1.UnmarshalWithParams(b, e, fmt.Sprintf("application,explicit,tag:%v", asnAppTag.EncASRepPart))
if err != nil {
// Try using tag 26
/* Ref: RFC 4120
Compatibility note: Some implementations unconditionally send an
encrypted EncTGSRepPart (application tag number 26) in this field
regardless of whether the reply is a AS-REP or a TGS-REP. In the
interest of compatibility, implementors MAY relax the check on the
tag number of the decrypted ENC-PART.*/
_, err = asn1.UnmarshalWithParams(b, e, fmt.Sprintf("application,explicit,tag:%v", asnAppTag.EncTGSRepPart))
if err != nil {
return krberror.Errorf(err, krberror.EncodingError, "error unmarshaling encrypted part within KDC_REP")
}
}
return nil
}
// DecryptEncPart decrypts the encrypted part of an AS_REP.
func (k *ASRep) DecryptEncPart(c *credentials.Credentials) (types.EncryptionKey, error) {
var key types.EncryptionKey
var err error
if c.HasKeytab() {
key, err = c.Keytab.GetEncryptionKey(k.CName.NameString, k.CRealm, k.EncPart.KVNO, k.EncPart.EType)
if err != nil {
return key, krberror.Errorf(err, krberror.DecryptingError, "error decrypting AS_REP encrypted part")
}
}
if c.HasPassword() {
key, _, err = crypto.GetKeyFromPassword(c.Password, k.CName, k.CRealm, k.EncPart.EType, k.PAData)
if err != nil {
return key, krberror.Errorf(err, krberror.DecryptingError, "error decrypting AS_REP encrypted part")
}
}
if !c.HasKeytab() && !c.HasPassword() {
return key, krberror.NewErrorf(krberror.DecryptingError, "no secret available in credentials to perform decryption of AS_REP encrypted part")
}
b, err := crypto.DecryptEncPart(k.EncPart, key, keyusage.AS_REP_ENCPART)
if err != nil {
return key, krberror.Errorf(err, krberror.DecryptingError, "error decrypting AS_REP encrypted part")
}
var denc EncKDCRepPart
err = denc.Unmarshal(b)
if err != nil {
return key, krberror.Errorf(err, krberror.EncodingError, "error unmarshaling decrypted encpart of AS_REP")
}
k.DecryptedEncPart = denc
return key, nil
}
// IsValid checks the validity of AS_REP message.
func (k *ASRep) IsValid(cfg *config.Config, creds *credentials.Credentials, asReq ASReq) (bool, error) {
//Ref RFC 4120 Section 3.1.5
if k.CName.NameType != asReq.ReqBody.CName.NameType || k.CName.NameString == nil {
return false, krberror.NewErrorf(krberror.KRBMsgError, "CName in response does not match what was requested. Requested: %+v; Reply: %+v", asReq.ReqBody.CName, k.CName)
}
for i := range k.CName.NameString {
if k.CName.NameString[i] != asReq.ReqBody.CName.NameString[i] {
return false, krberror.NewErrorf(krberror.KRBMsgError, "CName in response does not match what was requested. Requested: %+v; Reply: %+v", asReq.ReqBody.CName, k.CName)
}
}
if k.CRealm != asReq.ReqBody.Realm {
return false, krberror.NewErrorf(krberror.KRBMsgError, "CRealm in response does not match what was requested. Requested: %s; Reply: %s", asReq.ReqBody.Realm, k.CRealm)
}
key, err := k.DecryptEncPart(creds)
if err != nil {
return false, krberror.Errorf(err, krberror.DecryptingError, "error decrypting EncPart of AS_REP")
}
if k.DecryptedEncPart.Nonce != asReq.ReqBody.Nonce {
return false, krberror.NewErrorf(krberror.KRBMsgError, "possible replay attack, nonce in response does not match that in request")
}
if k.DecryptedEncPart.SName.NameType != asReq.ReqBody.SName.NameType || k.DecryptedEncPart.SName.NameString == nil {
return false, krberror.NewErrorf(krberror.KRBMsgError, "SName in response does not match what was requested. Requested: %v; Reply: %v", asReq.ReqBody.SName, k.DecryptedEncPart.SName)
}
for i := range k.CName.NameString {
if k.DecryptedEncPart.SName.NameString[i] != asReq.ReqBody.SName.NameString[i] {
return false, krberror.NewErrorf(krberror.KRBMsgError, "SName in response does not match what was requested. Requested: %+v; Reply: %+v", asReq.ReqBody.SName, k.DecryptedEncPart.SName)
}
}
if k.DecryptedEncPart.SRealm != asReq.ReqBody.Realm {
return false, krberror.NewErrorf(krberror.KRBMsgError, "SRealm in response does not match what was requested. Requested: %s; Reply: %s", asReq.ReqBody.Realm, k.DecryptedEncPart.SRealm)
}
if len(asReq.ReqBody.Addresses) > 0 {
if !types.HostAddressesEqual(k.DecryptedEncPart.CAddr, asReq.ReqBody.Addresses) {
return false, krberror.NewErrorf(krberror.KRBMsgError, "addresses listed in the AS_REP does not match those listed in the AS_REQ")
}
}
t := time.Now().UTC()
if t.Sub(k.DecryptedEncPart.AuthTime) > cfg.LibDefaults.Clockskew || k.DecryptedEncPart.AuthTime.Sub(t) > cfg.LibDefaults.Clockskew {
return false, krberror.NewErrorf(krberror.KRBMsgError, "clock skew with KDC too large. Greater than %v seconds", cfg.LibDefaults.Clockskew.Seconds())
}
// RFC 6806 https://tools.ietf.org/html/rfc6806.html#section-11
if asReq.PAData.Contains(patype.PA_REQ_ENC_PA_REP) && types.IsFlagSet(&k.DecryptedEncPart.Flags, flags.EncPARep) {
if len(k.DecryptedEncPart.EncPAData) < 2 || !k.DecryptedEncPart.EncPAData.Contains(patype.PA_FX_FAST) {
return false, krberror.NewErrorf(krberror.KRBMsgError, "KDC did not respond appropriately to FAST negotiation")
}
for _, pa := range k.DecryptedEncPart.EncPAData {
if pa.PADataType == patype.PA_REQ_ENC_PA_REP {
var pafast types.PAReqEncPARep
err := pafast.Unmarshal(pa.PADataValue)
if err != nil {
return false, krberror.Errorf(err, krberror.EncodingError, "KDC FAST negotiation response error, could not unmarshal PA_REQ_ENC_PA_REP")
}
etype, err := crypto.GetChksumEtype(pafast.ChksumType)
if err != nil {
return false, krberror.Errorf(err, krberror.ChksumError, "KDC FAST negotiation response error")
}
ab, _ := asReq.Marshal()
if !etype.VerifyChecksum(key.KeyValue, ab, pafast.Chksum, keyusage.KEY_USAGE_AS_REQ) {
return false, krberror.Errorf(err, krberror.ChksumError, "KDC FAST negotiation response checksum invalid")
}
}
}
}
return true, nil
}
// DecryptEncPart decrypts the encrypted part of an TGS_REP.
func (k *TGSRep) DecryptEncPart(key types.EncryptionKey) error {
b, err := crypto.DecryptEncPart(k.EncPart, key, keyusage.TGS_REP_ENCPART_SESSION_KEY)
if err != nil {
return krberror.Errorf(err, krberror.DecryptingError, "error decrypting TGS_REP EncPart")
}
var denc EncKDCRepPart
err = denc.Unmarshal(b)
if err != nil {
return krberror.Errorf(err, krberror.EncodingError, "error unmarshaling encrypted part")
}
k.DecryptedEncPart = denc
return nil
}
// IsValid checks the validity of the TGS_REP message.
func (k *TGSRep) IsValid(cfg *config.Config, tgsReq TGSReq) (bool, error) {
if k.CName.NameType != tgsReq.ReqBody.CName.NameType || k.CName.NameString == nil {
return false, krberror.NewErrorf(krberror.KRBMsgError, "CName type in response does not match what was requested. Requested: %+v; Reply: %+v", tgsReq.ReqBody.CName, k.CName)
}
for i := range k.CName.NameString {
if k.CName.NameString[i] != tgsReq.ReqBody.CName.NameString[i] {
return false, krberror.NewErrorf(krberror.KRBMsgError, "CName in response does not match what was requested. Requested: %+v; Reply: %+v", tgsReq.ReqBody.CName, k.CName)
}
}
if k.Ticket.Realm != tgsReq.ReqBody.Realm {
return false, krberror.NewErrorf(krberror.KRBMsgError, "realm in response ticket does not match what was requested. Requested: %s; Reply: %s", tgsReq.ReqBody.Realm, k.Ticket.Realm)
}
if k.DecryptedEncPart.Nonce != tgsReq.ReqBody.Nonce {
return false, krberror.NewErrorf(krberror.KRBMsgError, "possible replay attack, nonce in response does not match that in request")
}
//if k.Ticket.SName.NameType != tgsReq.ReqBody.SName.NameType || k.Ticket.SName.NameString == nil {
// return false, krberror.NewErrorf(krberror.KRBMsgError, "SName in response ticket does not match what was requested. Requested: %v; Reply: %v", tgsReq.ReqBody.SName, k.Ticket.SName)
//}
//for i := range k.Ticket.SName.NameString {
// if k.Ticket.SName.NameString[i] != tgsReq.ReqBody.SName.NameString[i] {
// return false, krberror.NewErrorf(krberror.KRBMsgError, "SName in response ticket does not match what was requested. Requested: %+v; Reply: %+v", tgsReq.ReqBody.SName, k.Ticket.SName)
// }
//}
//if k.DecryptedEncPart.SName.NameType != tgsReq.ReqBody.SName.NameType || k.DecryptedEncPart.SName.NameString == nil {
// return false, krberror.NewErrorf(krberror.KRBMsgError, "SName in response does not match what was requested. Requested: %v; Reply: %v", tgsReq.ReqBody.SName, k.DecryptedEncPart.SName)
//}
//for i := range k.DecryptedEncPart.SName.NameString {
// if k.DecryptedEncPart.SName.NameString[i] != tgsReq.ReqBody.SName.NameString[i] {
// return false, krberror.NewErrorf(krberror.KRBMsgError, "SName in response does not match what was requested. Requested: %+v; Reply: %+v", tgsReq.ReqBody.SName, k.DecryptedEncPart.SName)
// }
//}
if k.DecryptedEncPart.SRealm != tgsReq.ReqBody.Realm {
return false, krberror.NewErrorf(krberror.KRBMsgError, "SRealm in response does not match what was requested. Requested: %s; Reply: %s", tgsReq.ReqBody.Realm, k.DecryptedEncPart.SRealm)
}
if len(k.DecryptedEncPart.CAddr) > 0 {
if !types.HostAddressesEqual(k.DecryptedEncPart.CAddr, tgsReq.ReqBody.Addresses) {
return false, krberror.NewErrorf(krberror.KRBMsgError, "addresses listed in the TGS_REP does not match those listed in the TGS_REQ")
}
}
if time.Since(k.DecryptedEncPart.StartTime) > cfg.LibDefaults.Clockskew || k.DecryptedEncPart.StartTime.Sub(time.Now().UTC()) > cfg.LibDefaults.Clockskew {
if time.Since(k.DecryptedEncPart.AuthTime) > cfg.LibDefaults.Clockskew || k.DecryptedEncPart.AuthTime.Sub(time.Now().UTC()) > cfg.LibDefaults.Clockskew {
return false, krberror.NewErrorf(krberror.KRBMsgError, "clock skew with KDC too large. Greater than %v seconds.", cfg.LibDefaults.Clockskew.Seconds())
}
}
return true, nil
}