blob: e1ed4ae100880f7b27821c8cde04aa0ada675f7f [file] [log] [blame]
Pragya Arya324337e2020-02-20 14:35:08 +05301package messages
2
3import (
4 "fmt"
5 "time"
6
7 "github.com/jcmturner/gofork/encoding/asn1"
8 "gopkg.in/jcmturner/gokrb5.v7/asn1tools"
9 "gopkg.in/jcmturner/gokrb5.v7/crypto"
10 "gopkg.in/jcmturner/gokrb5.v7/iana"
11 "gopkg.in/jcmturner/gokrb5.v7/iana/asnAppTag"
12 "gopkg.in/jcmturner/gokrb5.v7/iana/errorcode"
13 "gopkg.in/jcmturner/gokrb5.v7/iana/keyusage"
14 "gopkg.in/jcmturner/gokrb5.v7/iana/msgtype"
15 "gopkg.in/jcmturner/gokrb5.v7/keytab"
16 "gopkg.in/jcmturner/gokrb5.v7/krberror"
17 "gopkg.in/jcmturner/gokrb5.v7/types"
18)
19
20/*AP-REQ ::= [APPLICATION 14] SEQUENCE {
21pvno [0] INTEGER (5),
22msg-type [1] INTEGER (14),
23ap-options [2] APOptions,
24ticket [3] Ticket,
25authenticator [4] EncryptedData -- Authenticator
26}
27
28APOptions ::= KerberosFlags
29-- reserved(0),
30-- use-session-key(1),
31-- mutual-required(2)*/
32
33type marshalAPReq struct {
34 PVNO int `asn1:"explicit,tag:0"`
35 MsgType int `asn1:"explicit,tag:1"`
36 APOptions asn1.BitString `asn1:"explicit,tag:2"`
37 // Ticket needs to be a raw value as it is wrapped in an APPLICATION tag
38 Ticket asn1.RawValue `asn1:"explicit,tag:3"`
39 EncryptedAuthenticator types.EncryptedData `asn1:"explicit,tag:4"`
40}
41
42// APReq implements RFC 4120 KRB_AP_REQ: https://tools.ietf.org/html/rfc4120#section-5.5.1.
43type APReq struct {
44 PVNO int `asn1:"explicit,tag:0"`
45 MsgType int `asn1:"explicit,tag:1"`
46 APOptions asn1.BitString `asn1:"explicit,tag:2"`
47 Ticket Ticket `asn1:"explicit,tag:3"`
48 EncryptedAuthenticator types.EncryptedData `asn1:"explicit,tag:4"`
49 Authenticator types.Authenticator `asn1:"optional"`
50}
51
52// NewAPReq generates a new KRB_AP_REQ struct.
53func NewAPReq(tkt Ticket, sessionKey types.EncryptionKey, auth types.Authenticator) (APReq, error) {
54 var a APReq
55 ed, err := encryptAuthenticator(auth, sessionKey, tkt)
56 if err != nil {
57 return a, krberror.Errorf(err, krberror.KRBMsgError, "error creating Authenticator for AP_REQ")
58 }
59 a = APReq{
60 PVNO: iana.PVNO,
61 MsgType: msgtype.KRB_AP_REQ,
62 APOptions: types.NewKrbFlags(),
63 Ticket: tkt,
64 EncryptedAuthenticator: ed,
65 }
66 return a, nil
67}
68
69// Encrypt Authenticator
70func encryptAuthenticator(a types.Authenticator, sessionKey types.EncryptionKey, tkt Ticket) (types.EncryptedData, error) {
71 var ed types.EncryptedData
72 m, err := a.Marshal()
73 if err != nil {
74 return ed, krberror.Errorf(err, krberror.EncodingError, "marshaling error of EncryptedData form of Authenticator")
75 }
76 usage := authenticatorKeyUsage(tkt.SName)
77 ed, err = crypto.GetEncryptedData(m, sessionKey, uint32(usage), tkt.EncPart.KVNO)
78 if err != nil {
79 return ed, krberror.Errorf(err, krberror.EncryptingError, "error encrypting Authenticator")
80 }
81 return ed, nil
82}
83
84// DecryptAuthenticator decrypts the Authenticator within the AP_REQ.
85// sessionKey may simply be the key within the decrypted EncPart of the ticket within the AP_REQ.
86func (a *APReq) DecryptAuthenticator(sessionKey types.EncryptionKey) error {
87 usage := authenticatorKeyUsage(a.Ticket.SName)
88 ab, e := crypto.DecryptEncPart(a.EncryptedAuthenticator, sessionKey, uint32(usage))
89 if e != nil {
90 return fmt.Errorf("error decrypting authenticator: %v", e)
91 }
92 err := a.Authenticator.Unmarshal(ab)
93 if err != nil {
94 return fmt.Errorf("error unmarshaling authenticator: %v", err)
95 }
96 return nil
97}
98
99func authenticatorKeyUsage(pn types.PrincipalName) int {
100 if pn.NameString[0] == "krbtgt" {
101 return keyusage.TGS_REQ_PA_TGS_REQ_AP_REQ_AUTHENTICATOR
102 }
103 return keyusage.AP_REQ_AUTHENTICATOR
104}
105
106// Unmarshal bytes b into the APReq struct.
107func (a *APReq) Unmarshal(b []byte) error {
108 var m marshalAPReq
109 _, err := asn1.UnmarshalWithParams(b, &m, fmt.Sprintf("application,explicit,tag:%v", asnAppTag.APREQ))
110 if err != nil {
111 return krberror.Errorf(err, krberror.EncodingError, "unmarshal error of AP_REQ")
112 }
113 if m.MsgType != msgtype.KRB_AP_REQ {
114 return NewKRBError(types.PrincipalName{}, "", errorcode.KRB_AP_ERR_MSG_TYPE, errorcode.Lookup(errorcode.KRB_AP_ERR_MSG_TYPE))
115 }
116 a.PVNO = m.PVNO
117 a.MsgType = m.MsgType
118 a.APOptions = m.APOptions
119 a.EncryptedAuthenticator = m.EncryptedAuthenticator
120 a.Ticket, err = unmarshalTicket(m.Ticket.Bytes)
121 if err != nil {
122 return krberror.Errorf(err, krberror.EncodingError, "unmarshaling error of Ticket within AP_REQ")
123 }
124 return nil
125}
126
127// Marshal APReq struct.
128func (a *APReq) Marshal() ([]byte, error) {
129 m := marshalAPReq{
130 PVNO: a.PVNO,
131 MsgType: a.MsgType,
132 APOptions: a.APOptions,
133 EncryptedAuthenticator: a.EncryptedAuthenticator,
134 }
135 var b []byte
136 b, err := a.Ticket.Marshal()
137 if err != nil {
138 return b, err
139 }
140 m.Ticket = asn1.RawValue{
141 Class: asn1.ClassContextSpecific,
142 IsCompound: true,
143 Tag: 3,
144 Bytes: b,
145 }
146 mk, err := asn1.Marshal(m)
147 if err != nil {
148 return mk, krberror.Errorf(err, krberror.EncodingError, "marshaling error of AP_REQ")
149 }
150 mk = asn1tools.AddASNAppTag(mk, asnAppTag.APREQ)
151 return mk, nil
152}
153
154// Verify an AP_REQ using service's keytab, spn and max acceptable clock skew duration.
155// The service ticket encrypted part and authenticator will be decrypted as part of this operation.
156func (a *APReq) Verify(kt *keytab.Keytab, d time.Duration, cAddr types.HostAddress) (bool, error) {
157 // Decrypt ticket's encrypted part with service key
158 //TODO decrypt with service's session key from its TGT is use-to-user. Need to figure out how to get TGT.
159 //if types.IsFlagSet(&a.APOptions, flags.APOptionUseSessionKey) {
160 // //If the USE-SESSION-KEY flag is set in the ap-options field, it indicates to
161 // //the server that user-to-user authentication is in use, and that the ticket
162 // //is encrypted in the session key from the server's TGT rather than in the server's secret key.
163 // err := a.Ticket.Decrypt(tgt.DecryptedEncPart.Key)
164 // if err != nil {
165 // return false, krberror.Errorf(err, krberror.DecryptingError, "error decrypting encpart of ticket provided using session key")
166 // }
167 //} else {
168 // // Because it is possible for the server to be registered in multiple
169 // // realms, with different keys in each, the srealm field in the
170 // // unencrypted portion of the ticket in the KRB_AP_REQ is used to
171 // // specify which secret key the server should use to decrypt that
172 // // ticket.The KRB_AP_ERR_NOKEY error code is returned if the server
173 // // doesn't have the proper key to decipher the ticket.
174 // // The ticket is decrypted using the version of the server's key
175 // // specified by the ticket.
176 // err := a.Ticket.DecryptEncPart(*kt, &a.Ticket.SName)
177 // if err != nil {
178 // return false, krberror.Errorf(err, krberror.DecryptingError, "error decrypting encpart of service ticket provided")
179 // }
180 //}
181 err := a.Ticket.DecryptEncPart(kt, &a.Ticket.SName)
182 if err != nil {
183 return false, krberror.Errorf(err, krberror.DecryptingError, "error decrypting encpart of service ticket provided")
184 }
185
186 // Check time validity of ticket
187 ok, err := a.Ticket.Valid(d)
188 if err != nil || !ok {
189 return ok, err
190 }
191
192 // Check client's address is listed in the client addresses in the ticket
193 if len(a.Ticket.DecryptedEncPart.CAddr) > 0 {
194 //The addresses in the ticket (if any) are then searched for an address matching the operating-system reported
195 //address of the client. If no match is found or the server insists on ticket addresses but none are present in
196 //the ticket, the KRB_AP_ERR_BADADDR error is returned.
197 if !types.HostAddressesContains(a.Ticket.DecryptedEncPart.CAddr, cAddr) {
198 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")
199 }
200 }
201
202 // Decrypt authenticator with session key from ticket's encrypted part
203 err = a.DecryptAuthenticator(a.Ticket.DecryptedEncPart.Key)
204 if err != nil {
205 return false, NewKRBError(a.Ticket.SName, a.Ticket.Realm, errorcode.KRB_AP_ERR_BAD_INTEGRITY, "could not decrypt authenticator")
206 }
207
208 // Check CName in authenticator is the same as that in the ticket
209 if !a.Authenticator.CName.Equal(a.Ticket.DecryptedEncPart.CName) {
210 return false, NewKRBError(a.Ticket.SName, a.Ticket.Realm, errorcode.KRB_AP_ERR_BADMATCH, "CName in Authenticator does not match that in service ticket")
211 }
212
213 // Check the clock skew between the client and the service server
214 ct := a.Authenticator.CTime.Add(time.Duration(a.Authenticator.Cusec) * time.Microsecond)
215 t := time.Now().UTC()
216 if t.Sub(ct) > d || ct.Sub(t) > d {
217 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))
218 }
219 return true, nil
220}