khenaidoo | 106c61a | 2021-08-11 18:05:46 -0400 | [diff] [blame] | 1 | package messages |
| 2 | |
| 3 | // Reference: https://www.ietf.org/rfc/rfc4120.txt |
| 4 | // Section: 5.4.2 |
| 5 | |
| 6 | import ( |
| 7 | "fmt" |
| 8 | "time" |
| 9 | |
| 10 | "github.com/jcmturner/gofork/encoding/asn1" |
| 11 | "github.com/jcmturner/gokrb5/v8/asn1tools" |
| 12 | "github.com/jcmturner/gokrb5/v8/config" |
| 13 | "github.com/jcmturner/gokrb5/v8/credentials" |
| 14 | "github.com/jcmturner/gokrb5/v8/crypto" |
| 15 | "github.com/jcmturner/gokrb5/v8/iana/asnAppTag" |
| 16 | "github.com/jcmturner/gokrb5/v8/iana/flags" |
| 17 | "github.com/jcmturner/gokrb5/v8/iana/keyusage" |
| 18 | "github.com/jcmturner/gokrb5/v8/iana/msgtype" |
| 19 | "github.com/jcmturner/gokrb5/v8/iana/patype" |
| 20 | "github.com/jcmturner/gokrb5/v8/krberror" |
| 21 | "github.com/jcmturner/gokrb5/v8/types" |
| 22 | ) |
| 23 | |
| 24 | type marshalKDCRep struct { |
| 25 | PVNO int `asn1:"explicit,tag:0"` |
| 26 | MsgType int `asn1:"explicit,tag:1"` |
| 27 | PAData types.PADataSequence `asn1:"explicit,optional,tag:2"` |
| 28 | CRealm string `asn1:"generalstring,explicit,tag:3"` |
| 29 | CName types.PrincipalName `asn1:"explicit,tag:4"` |
| 30 | // Ticket needs to be a raw value as it is wrapped in an APPLICATION tag |
| 31 | Ticket asn1.RawValue `asn1:"explicit,tag:5"` |
| 32 | EncPart types.EncryptedData `asn1:"explicit,tag:6"` |
| 33 | } |
| 34 | |
| 35 | // KDCRepFields represents the KRB_KDC_REP fields. |
| 36 | type KDCRepFields struct { |
| 37 | PVNO int |
| 38 | MsgType int |
| 39 | PAData []types.PAData |
| 40 | CRealm string |
| 41 | CName types.PrincipalName |
| 42 | Ticket Ticket |
| 43 | EncPart types.EncryptedData |
| 44 | DecryptedEncPart EncKDCRepPart |
| 45 | } |
| 46 | |
| 47 | // ASRep implements RFC 4120 KRB_AS_REP: https://tools.ietf.org/html/rfc4120#section-5.4.2. |
| 48 | type ASRep struct { |
| 49 | KDCRepFields |
| 50 | } |
| 51 | |
| 52 | // TGSRep implements RFC 4120 KRB_TGS_REP: https://tools.ietf.org/html/rfc4120#section-5.4.2. |
| 53 | type TGSRep struct { |
| 54 | KDCRepFields |
| 55 | } |
| 56 | |
| 57 | // EncKDCRepPart is the encrypted part of KRB_KDC_REP. |
| 58 | type EncKDCRepPart struct { |
| 59 | Key types.EncryptionKey `asn1:"explicit,tag:0"` |
| 60 | LastReqs []LastReq `asn1:"explicit,tag:1"` |
| 61 | Nonce int `asn1:"explicit,tag:2"` |
| 62 | KeyExpiration time.Time `asn1:"generalized,explicit,optional,tag:3"` |
| 63 | Flags asn1.BitString `asn1:"explicit,tag:4"` |
| 64 | AuthTime time.Time `asn1:"generalized,explicit,tag:5"` |
| 65 | StartTime time.Time `asn1:"generalized,explicit,optional,tag:6"` |
| 66 | EndTime time.Time `asn1:"generalized,explicit,tag:7"` |
| 67 | RenewTill time.Time `asn1:"generalized,explicit,optional,tag:8"` |
| 68 | SRealm string `asn1:"generalstring,explicit,tag:9"` |
| 69 | SName types.PrincipalName `asn1:"explicit,tag:10"` |
| 70 | CAddr []types.HostAddress `asn1:"explicit,optional,tag:11"` |
| 71 | EncPAData types.PADataSequence `asn1:"explicit,optional,tag:12"` |
| 72 | } |
| 73 | |
| 74 | // LastReq part of KRB_KDC_REP. |
| 75 | type LastReq struct { |
| 76 | LRType int32 `asn1:"explicit,tag:0"` |
| 77 | LRValue time.Time `asn1:"generalized,explicit,tag:1"` |
| 78 | } |
| 79 | |
| 80 | // Unmarshal bytes b into the ASRep struct. |
| 81 | func (k *ASRep) Unmarshal(b []byte) error { |
| 82 | var m marshalKDCRep |
| 83 | _, err := asn1.UnmarshalWithParams(b, &m, fmt.Sprintf("application,explicit,tag:%v", asnAppTag.ASREP)) |
| 84 | if err != nil { |
| 85 | return processUnmarshalReplyError(b, err) |
| 86 | } |
| 87 | if m.MsgType != msgtype.KRB_AS_REP { |
| 88 | return krberror.NewErrorf(krberror.KRBMsgError, "message ID does not indicate an AS_REP. Expected: %v; Actual: %v", msgtype.KRB_AS_REP, m.MsgType) |
| 89 | } |
| 90 | //Process the raw ticket within |
| 91 | tkt, err := unmarshalTicket(m.Ticket.Bytes) |
| 92 | if err != nil { |
| 93 | return krberror.Errorf(err, krberror.EncodingError, "error unmarshaling Ticket within AS_REP") |
| 94 | } |
| 95 | k.KDCRepFields = KDCRepFields{ |
| 96 | PVNO: m.PVNO, |
| 97 | MsgType: m.MsgType, |
| 98 | PAData: m.PAData, |
| 99 | CRealm: m.CRealm, |
| 100 | CName: m.CName, |
| 101 | Ticket: tkt, |
| 102 | EncPart: m.EncPart, |
| 103 | } |
| 104 | return nil |
| 105 | } |
| 106 | |
| 107 | // Marshal ASRep struct. |
| 108 | func (k *ASRep) Marshal() ([]byte, error) { |
| 109 | m := marshalKDCRep{ |
| 110 | PVNO: k.PVNO, |
| 111 | MsgType: k.MsgType, |
| 112 | PAData: k.PAData, |
| 113 | CRealm: k.CRealm, |
| 114 | CName: k.CName, |
| 115 | EncPart: k.EncPart, |
| 116 | } |
| 117 | b, err := k.Ticket.Marshal() |
| 118 | if err != nil { |
| 119 | return []byte{}, err |
| 120 | } |
| 121 | m.Ticket = asn1.RawValue{ |
| 122 | Class: asn1.ClassContextSpecific, |
| 123 | IsCompound: true, |
| 124 | Tag: 5, |
| 125 | Bytes: b, |
| 126 | } |
| 127 | mk, err := asn1.Marshal(m) |
| 128 | if err != nil { |
| 129 | return mk, krberror.Errorf(err, krberror.EncodingError, "error marshaling AS_REP") |
| 130 | } |
| 131 | mk = asn1tools.AddASNAppTag(mk, asnAppTag.ASREP) |
| 132 | return mk, nil |
| 133 | } |
| 134 | |
| 135 | // Unmarshal bytes b into the TGSRep struct. |
| 136 | func (k *TGSRep) Unmarshal(b []byte) error { |
| 137 | var m marshalKDCRep |
| 138 | _, err := asn1.UnmarshalWithParams(b, &m, fmt.Sprintf("application,explicit,tag:%v", asnAppTag.TGSREP)) |
| 139 | if err != nil { |
| 140 | return processUnmarshalReplyError(b, err) |
| 141 | } |
| 142 | if m.MsgType != msgtype.KRB_TGS_REP { |
| 143 | return krberror.NewErrorf(krberror.KRBMsgError, "message ID does not indicate an TGS_REP. Expected: %v; Actual: %v", msgtype.KRB_TGS_REP, m.MsgType) |
| 144 | } |
| 145 | //Process the raw ticket within |
| 146 | tkt, err := unmarshalTicket(m.Ticket.Bytes) |
| 147 | if err != nil { |
| 148 | return krberror.Errorf(err, krberror.EncodingError, "error unmarshaling Ticket within TGS_REP") |
| 149 | } |
| 150 | k.KDCRepFields = KDCRepFields{ |
| 151 | PVNO: m.PVNO, |
| 152 | MsgType: m.MsgType, |
| 153 | PAData: m.PAData, |
| 154 | CRealm: m.CRealm, |
| 155 | CName: m.CName, |
| 156 | Ticket: tkt, |
| 157 | EncPart: m.EncPart, |
| 158 | } |
| 159 | return nil |
| 160 | } |
| 161 | |
| 162 | // Marshal TGSRep struct. |
| 163 | func (k *TGSRep) Marshal() ([]byte, error) { |
| 164 | m := marshalKDCRep{ |
| 165 | PVNO: k.PVNO, |
| 166 | MsgType: k.MsgType, |
| 167 | PAData: k.PAData, |
| 168 | CRealm: k.CRealm, |
| 169 | CName: k.CName, |
| 170 | EncPart: k.EncPart, |
| 171 | } |
| 172 | b, err := k.Ticket.Marshal() |
| 173 | if err != nil { |
| 174 | return []byte{}, err |
| 175 | } |
| 176 | m.Ticket = asn1.RawValue{ |
| 177 | Class: asn1.ClassContextSpecific, |
| 178 | IsCompound: true, |
| 179 | Tag: 5, |
| 180 | Bytes: b, |
| 181 | } |
| 182 | mk, err := asn1.Marshal(m) |
| 183 | if err != nil { |
| 184 | return mk, krberror.Errorf(err, krberror.EncodingError, "error marshaling TGS_REP") |
| 185 | } |
| 186 | mk = asn1tools.AddASNAppTag(mk, asnAppTag.TGSREP) |
| 187 | return mk, nil |
| 188 | } |
| 189 | |
| 190 | // Unmarshal bytes b into encrypted part of KRB_KDC_REP. |
| 191 | func (e *EncKDCRepPart) Unmarshal(b []byte) error { |
| 192 | _, err := asn1.UnmarshalWithParams(b, e, fmt.Sprintf("application,explicit,tag:%v", asnAppTag.EncASRepPart)) |
| 193 | if err != nil { |
| 194 | // Try using tag 26 |
| 195 | // Ref: RFC 4120 - mentions that some implementations use application tag number 26 wether or not the reply is |
| 196 | // a AS-REP or a TGS-REP. |
| 197 | _, err = asn1.UnmarshalWithParams(b, e, fmt.Sprintf("application,explicit,tag:%v", asnAppTag.EncTGSRepPart)) |
| 198 | if err != nil { |
| 199 | return krberror.Errorf(err, krberror.EncodingError, "error unmarshaling encrypted part within KDC_REP") |
| 200 | } |
| 201 | } |
| 202 | return nil |
| 203 | } |
| 204 | |
| 205 | // Marshal encrypted part of KRB_KDC_REP. |
| 206 | func (e *EncKDCRepPart) Marshal() ([]byte, error) { |
| 207 | b, err := asn1.Marshal(*e) |
| 208 | if err != nil { |
| 209 | return b, krberror.Errorf(err, krberror.EncodingError, "marshaling error of AS_REP encpart") |
| 210 | } |
| 211 | b = asn1tools.AddASNAppTag(b, asnAppTag.EncASRepPart) |
| 212 | return b, nil |
| 213 | } |
| 214 | |
| 215 | // DecryptEncPart decrypts the encrypted part of an AS_REP. |
| 216 | func (k *ASRep) DecryptEncPart(c *credentials.Credentials) (types.EncryptionKey, error) { |
| 217 | var key types.EncryptionKey |
| 218 | var err error |
| 219 | if c.HasKeytab() { |
| 220 | key, _, err = c.Keytab().GetEncryptionKey(k.CName, k.CRealm, k.EncPart.KVNO, k.EncPart.EType) |
| 221 | if err != nil { |
| 222 | return key, krberror.Errorf(err, krberror.DecryptingError, "error decrypting AS_REP encrypted part") |
| 223 | } |
| 224 | } |
| 225 | if c.HasPassword() { |
| 226 | key, _, err = crypto.GetKeyFromPassword(c.Password(), k.CName, k.CRealm, k.EncPart.EType, k.PAData) |
| 227 | if err != nil { |
| 228 | return key, krberror.Errorf(err, krberror.DecryptingError, "error decrypting AS_REP encrypted part") |
| 229 | } |
| 230 | } |
| 231 | if !c.HasKeytab() && !c.HasPassword() { |
| 232 | return key, krberror.NewErrorf(krberror.DecryptingError, "no secret available in credentials to perform decryption of AS_REP encrypted part") |
| 233 | } |
| 234 | b, err := crypto.DecryptEncPart(k.EncPart, key, keyusage.AS_REP_ENCPART) |
| 235 | if err != nil { |
| 236 | return key, krberror.Errorf(err, krberror.DecryptingError, "error decrypting AS_REP encrypted part") |
| 237 | } |
| 238 | var denc EncKDCRepPart |
| 239 | err = denc.Unmarshal(b) |
| 240 | if err != nil { |
| 241 | return key, krberror.Errorf(err, krberror.EncodingError, "error unmarshaling decrypted encpart of AS_REP") |
| 242 | } |
| 243 | k.DecryptedEncPart = denc |
| 244 | return key, nil |
| 245 | } |
| 246 | |
| 247 | // Verify checks the validity of AS_REP message. |
| 248 | func (k *ASRep) Verify(cfg *config.Config, creds *credentials.Credentials, asReq ASReq) (bool, error) { |
| 249 | //Ref RFC 4120 Section 3.1.5 |
| 250 | if !k.CName.Equal(asReq.ReqBody.CName) { |
| 251 | return false, krberror.NewErrorf(krberror.KRBMsgError, "CName in response does not match what was requested. Requested: %+v; Reply: %+v", asReq.ReqBody.CName, k.CName) |
| 252 | } |
| 253 | if k.CRealm != asReq.ReqBody.Realm { |
| 254 | return false, krberror.NewErrorf(krberror.KRBMsgError, "CRealm in response does not match what was requested. Requested: %s; Reply: %s", asReq.ReqBody.Realm, k.CRealm) |
| 255 | } |
| 256 | key, err := k.DecryptEncPart(creds) |
| 257 | if err != nil { |
| 258 | return false, krberror.Errorf(err, krberror.DecryptingError, "error decrypting EncPart of AS_REP") |
| 259 | } |
| 260 | if k.DecryptedEncPart.Nonce != asReq.ReqBody.Nonce { |
| 261 | return false, krberror.NewErrorf(krberror.KRBMsgError, "possible replay attack, nonce in response does not match that in request") |
| 262 | } |
| 263 | if !k.DecryptedEncPart.SName.Equal(asReq.ReqBody.SName) { |
| 264 | 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) |
| 265 | } |
| 266 | if k.DecryptedEncPart.SRealm != asReq.ReqBody.Realm { |
| 267 | 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) |
| 268 | } |
| 269 | if len(asReq.ReqBody.Addresses) > 0 { |
| 270 | if !types.HostAddressesEqual(k.DecryptedEncPart.CAddr, asReq.ReqBody.Addresses) { |
| 271 | return false, krberror.NewErrorf(krberror.KRBMsgError, "addresses listed in the AS_REP does not match those listed in the AS_REQ") |
| 272 | } |
| 273 | } |
| 274 | t := time.Now().UTC() |
| 275 | if t.Sub(k.DecryptedEncPart.AuthTime) > cfg.LibDefaults.Clockskew || k.DecryptedEncPart.AuthTime.Sub(t) > cfg.LibDefaults.Clockskew { |
| 276 | return false, krberror.NewErrorf(krberror.KRBMsgError, "clock skew with KDC too large. Greater than %v seconds", cfg.LibDefaults.Clockskew.Seconds()) |
| 277 | } |
| 278 | // RFC 6806 https://tools.ietf.org/html/rfc6806.html#section-11 |
| 279 | if asReq.PAData.Contains(patype.PA_REQ_ENC_PA_REP) && types.IsFlagSet(&k.DecryptedEncPart.Flags, flags.EncPARep) { |
| 280 | if len(k.DecryptedEncPart.EncPAData) < 2 || !k.DecryptedEncPart.EncPAData.Contains(patype.PA_FX_FAST) { |
| 281 | return false, krberror.NewErrorf(krberror.KRBMsgError, "KDC did not respond appropriately to FAST negotiation") |
| 282 | } |
| 283 | for _, pa := range k.DecryptedEncPart.EncPAData { |
| 284 | if pa.PADataType == patype.PA_REQ_ENC_PA_REP { |
| 285 | var pafast types.PAReqEncPARep |
| 286 | err := pafast.Unmarshal(pa.PADataValue) |
| 287 | if err != nil { |
| 288 | return false, krberror.Errorf(err, krberror.EncodingError, "KDC FAST negotiation response error, could not unmarshal PA_REQ_ENC_PA_REP") |
| 289 | } |
| 290 | etype, err := crypto.GetChksumEtype(pafast.ChksumType) |
| 291 | if err != nil { |
| 292 | return false, krberror.Errorf(err, krberror.ChksumError, "KDC FAST negotiation response error") |
| 293 | } |
| 294 | ab, _ := asReq.Marshal() |
| 295 | if !etype.VerifyChecksum(key.KeyValue, ab, pafast.Chksum, keyusage.KEY_USAGE_AS_REQ) { |
| 296 | return false, krberror.Errorf(err, krberror.ChksumError, "KDC FAST negotiation response checksum invalid") |
| 297 | } |
| 298 | } |
| 299 | } |
| 300 | } |
| 301 | return true, nil |
| 302 | } |
| 303 | |
| 304 | // DecryptEncPart decrypts the encrypted part of an TGS_REP. |
| 305 | func (k *TGSRep) DecryptEncPart(key types.EncryptionKey) error { |
| 306 | b, err := crypto.DecryptEncPart(k.EncPart, key, keyusage.TGS_REP_ENCPART_SESSION_KEY) |
| 307 | if err != nil { |
| 308 | return krberror.Errorf(err, krberror.DecryptingError, "error decrypting TGS_REP EncPart") |
| 309 | } |
| 310 | var denc EncKDCRepPart |
| 311 | err = denc.Unmarshal(b) |
| 312 | if err != nil { |
| 313 | return krberror.Errorf(err, krberror.EncodingError, "error unmarshaling encrypted part") |
| 314 | } |
| 315 | k.DecryptedEncPart = denc |
| 316 | return nil |
| 317 | } |
| 318 | |
| 319 | // Verify checks the validity of the TGS_REP message. |
| 320 | func (k *TGSRep) Verify(cfg *config.Config, tgsReq TGSReq) (bool, error) { |
| 321 | if !k.CName.Equal(tgsReq.ReqBody.CName) { |
| 322 | return false, krberror.NewErrorf(krberror.KRBMsgError, "CName in response does not match what was requested. Requested: %+v; Reply: %+v", tgsReq.ReqBody.CName, k.CName) |
| 323 | } |
| 324 | if k.Ticket.Realm != tgsReq.ReqBody.Realm { |
| 325 | 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) |
| 326 | } |
| 327 | if k.DecryptedEncPart.Nonce != tgsReq.ReqBody.Nonce { |
| 328 | return false, krberror.NewErrorf(krberror.KRBMsgError, "possible replay attack, nonce in response does not match that in request") |
| 329 | } |
| 330 | //if k.Ticket.SName.NameType != tgsReq.ReqBody.SName.NameType || k.Ticket.SName.NameString == nil { |
| 331 | // 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) |
| 332 | //} |
| 333 | //for i := range k.Ticket.SName.NameString { |
| 334 | // if k.Ticket.SName.NameString[i] != tgsReq.ReqBody.SName.NameString[i] { |
| 335 | // 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) |
| 336 | // } |
| 337 | //} |
| 338 | //if k.DecryptedEncPart.SName.NameType != tgsReq.ReqBody.SName.NameType || k.DecryptedEncPart.SName.NameString == nil { |
| 339 | // 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) |
| 340 | //} |
| 341 | //for i := range k.DecryptedEncPart.SName.NameString { |
| 342 | // if k.DecryptedEncPart.SName.NameString[i] != tgsReq.ReqBody.SName.NameString[i] { |
| 343 | // 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) |
| 344 | // } |
| 345 | //} |
| 346 | if k.DecryptedEncPart.SRealm != tgsReq.ReqBody.Realm { |
| 347 | 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) |
| 348 | } |
| 349 | if len(k.DecryptedEncPart.CAddr) > 0 { |
| 350 | if !types.HostAddressesEqual(k.DecryptedEncPart.CAddr, tgsReq.ReqBody.Addresses) { |
| 351 | return false, krberror.NewErrorf(krberror.KRBMsgError, "addresses listed in the TGS_REP does not match those listed in the TGS_REQ") |
| 352 | } |
| 353 | } |
| 354 | if time.Since(k.DecryptedEncPart.StartTime) > cfg.LibDefaults.Clockskew || k.DecryptedEncPart.StartTime.Sub(time.Now().UTC()) > cfg.LibDefaults.Clockskew { |
| 355 | if time.Since(k.DecryptedEncPart.AuthTime) > cfg.LibDefaults.Clockskew || k.DecryptedEncPart.AuthTime.Sub(time.Now().UTC()) > cfg.LibDefaults.Clockskew { |
| 356 | return false, krberror.NewErrorf(krberror.KRBMsgError, "clock skew with KDC too large. Greater than %v seconds.", cfg.LibDefaults.Clockskew.Seconds()) |
| 357 | } |
| 358 | } |
| 359 | return true, nil |
| 360 | } |