Elia Battiston | 4750d3c | 2022-07-14 13:24:56 +0000 | [diff] [blame] | 1 | package messages |
| 2 | |
| 3 | import ( |
| 4 | "fmt" |
| 5 | "time" |
| 6 | |
| 7 | "github.com/jcmturner/gofork/encoding/asn1" |
| 8 | "github.com/jcmturner/gokrb5/v8/asn1tools" |
| 9 | "github.com/jcmturner/gokrb5/v8/crypto" |
| 10 | "github.com/jcmturner/gokrb5/v8/iana" |
| 11 | "github.com/jcmturner/gokrb5/v8/iana/asnAppTag" |
| 12 | "github.com/jcmturner/gokrb5/v8/iana/errorcode" |
| 13 | "github.com/jcmturner/gokrb5/v8/iana/keyusage" |
| 14 | "github.com/jcmturner/gokrb5/v8/iana/msgtype" |
| 15 | "github.com/jcmturner/gokrb5/v8/keytab" |
| 16 | "github.com/jcmturner/gokrb5/v8/krberror" |
| 17 | "github.com/jcmturner/gokrb5/v8/types" |
| 18 | ) |
| 19 | |
| 20 | type marshalAPReq struct { |
| 21 | PVNO int `asn1:"explicit,tag:0"` |
| 22 | MsgType int `asn1:"explicit,tag:1"` |
| 23 | APOptions asn1.BitString `asn1:"explicit,tag:2"` |
| 24 | // Ticket needs to be a raw value as it is wrapped in an APPLICATION tag |
| 25 | Ticket asn1.RawValue `asn1:"explicit,tag:3"` |
| 26 | EncryptedAuthenticator types.EncryptedData `asn1:"explicit,tag:4"` |
| 27 | } |
| 28 | |
| 29 | // APReq implements RFC 4120 KRB_AP_REQ: https://tools.ietf.org/html/rfc4120#section-5.5.1. |
| 30 | type APReq struct { |
| 31 | PVNO int `asn1:"explicit,tag:0"` |
| 32 | MsgType int `asn1:"explicit,tag:1"` |
| 33 | APOptions asn1.BitString `asn1:"explicit,tag:2"` |
| 34 | Ticket Ticket `asn1:"explicit,tag:3"` |
| 35 | EncryptedAuthenticator types.EncryptedData `asn1:"explicit,tag:4"` |
| 36 | Authenticator types.Authenticator `asn1:"optional"` |
| 37 | } |
| 38 | |
| 39 | // NewAPReq generates a new KRB_AP_REQ struct. |
| 40 | func NewAPReq(tkt Ticket, sessionKey types.EncryptionKey, auth types.Authenticator) (APReq, error) { |
| 41 | var a APReq |
| 42 | ed, err := encryptAuthenticator(auth, sessionKey, tkt) |
| 43 | if err != nil { |
| 44 | return a, krberror.Errorf(err, krberror.KRBMsgError, "error creating Authenticator for AP_REQ") |
| 45 | } |
| 46 | a = APReq{ |
| 47 | PVNO: iana.PVNO, |
| 48 | MsgType: msgtype.KRB_AP_REQ, |
| 49 | APOptions: types.NewKrbFlags(), |
| 50 | Ticket: tkt, |
| 51 | EncryptedAuthenticator: ed, |
| 52 | } |
| 53 | return a, nil |
| 54 | } |
| 55 | |
| 56 | // Encrypt Authenticator |
| 57 | func encryptAuthenticator(a types.Authenticator, sessionKey types.EncryptionKey, tkt Ticket) (types.EncryptedData, error) { |
| 58 | var ed types.EncryptedData |
| 59 | m, err := a.Marshal() |
| 60 | if err != nil { |
| 61 | return ed, krberror.Errorf(err, krberror.EncodingError, "marshaling error of EncryptedData form of Authenticator") |
| 62 | } |
| 63 | usage := authenticatorKeyUsage(tkt.SName) |
| 64 | ed, err = crypto.GetEncryptedData(m, sessionKey, uint32(usage), tkt.EncPart.KVNO) |
| 65 | if err != nil { |
| 66 | return ed, krberror.Errorf(err, krberror.EncryptingError, "error encrypting Authenticator") |
| 67 | } |
| 68 | return ed, nil |
| 69 | } |
| 70 | |
| 71 | // DecryptAuthenticator decrypts the Authenticator within the AP_REQ. |
| 72 | // sessionKey may simply be the key within the decrypted EncPart of the ticket within the AP_REQ. |
| 73 | func (a *APReq) DecryptAuthenticator(sessionKey types.EncryptionKey) error { |
| 74 | usage := authenticatorKeyUsage(a.Ticket.SName) |
| 75 | ab, e := crypto.DecryptEncPart(a.EncryptedAuthenticator, sessionKey, uint32(usage)) |
| 76 | if e != nil { |
| 77 | return fmt.Errorf("error decrypting authenticator: %v", e) |
| 78 | } |
| 79 | err := a.Authenticator.Unmarshal(ab) |
| 80 | if err != nil { |
| 81 | return fmt.Errorf("error unmarshaling authenticator: %v", err) |
| 82 | } |
| 83 | return nil |
| 84 | } |
| 85 | |
| 86 | func authenticatorKeyUsage(pn types.PrincipalName) int { |
| 87 | if pn.NameString[0] == "krbtgt" { |
| 88 | return keyusage.TGS_REQ_PA_TGS_REQ_AP_REQ_AUTHENTICATOR |
| 89 | } |
| 90 | return keyusage.AP_REQ_AUTHENTICATOR |
| 91 | } |
| 92 | |
| 93 | // Unmarshal bytes b into the APReq struct. |
| 94 | func (a *APReq) Unmarshal(b []byte) error { |
| 95 | var m marshalAPReq |
| 96 | _, err := asn1.UnmarshalWithParams(b, &m, fmt.Sprintf("application,explicit,tag:%v", asnAppTag.APREQ)) |
| 97 | if err != nil { |
| 98 | return krberror.Errorf(err, krberror.EncodingError, "unmarshal error of AP_REQ") |
| 99 | } |
| 100 | if m.MsgType != msgtype.KRB_AP_REQ { |
| 101 | return NewKRBError(types.PrincipalName{}, "", errorcode.KRB_AP_ERR_MSG_TYPE, errorcode.Lookup(errorcode.KRB_AP_ERR_MSG_TYPE)) |
| 102 | } |
| 103 | a.PVNO = m.PVNO |
| 104 | a.MsgType = m.MsgType |
| 105 | a.APOptions = m.APOptions |
| 106 | a.EncryptedAuthenticator = m.EncryptedAuthenticator |
| 107 | a.Ticket, err = unmarshalTicket(m.Ticket.Bytes) |
| 108 | if err != nil { |
| 109 | return krberror.Errorf(err, krberror.EncodingError, "unmarshaling error of Ticket within AP_REQ") |
| 110 | } |
| 111 | return nil |
| 112 | } |
| 113 | |
| 114 | // Marshal APReq struct. |
| 115 | func (a *APReq) Marshal() ([]byte, error) { |
| 116 | m := marshalAPReq{ |
| 117 | PVNO: a.PVNO, |
| 118 | MsgType: a.MsgType, |
| 119 | APOptions: a.APOptions, |
| 120 | EncryptedAuthenticator: a.EncryptedAuthenticator, |
| 121 | } |
| 122 | var b []byte |
| 123 | b, err := a.Ticket.Marshal() |
| 124 | if err != nil { |
| 125 | return b, err |
| 126 | } |
| 127 | m.Ticket = asn1.RawValue{ |
| 128 | Class: asn1.ClassContextSpecific, |
| 129 | IsCompound: true, |
| 130 | Tag: 3, |
| 131 | Bytes: b, |
| 132 | } |
| 133 | mk, err := asn1.Marshal(m) |
| 134 | if err != nil { |
| 135 | return mk, krberror.Errorf(err, krberror.EncodingError, "marshaling error of AP_REQ") |
| 136 | } |
| 137 | mk = asn1tools.AddASNAppTag(mk, asnAppTag.APREQ) |
| 138 | return mk, nil |
| 139 | } |
| 140 | |
| 141 | // Verify an AP_REQ using service's keytab, spn and max acceptable clock skew duration. |
| 142 | // The service ticket encrypted part and authenticator will be decrypted as part of this operation. |
| 143 | func (a *APReq) Verify(kt *keytab.Keytab, d time.Duration, cAddr types.HostAddress, snameOverride *types.PrincipalName) (bool, error) { |
| 144 | // Decrypt ticket's encrypted part with service key |
| 145 | //TODO decrypt with service's session key from its TGT is use-to-user. Need to figure out how to get TGT. |
| 146 | //if types.IsFlagSet(&a.APOptions, flags.APOptionUseSessionKey) { |
| 147 | // err := a.Ticket.Decrypt(tgt.DecryptedEncPart.Key) |
| 148 | // if err != nil { |
| 149 | // return false, krberror.Errorf(err, krberror.DecryptingError, "error decrypting encpart of ticket provided using session key") |
| 150 | // } |
| 151 | //} else { |
| 152 | // err := a.Ticket.DecryptEncPart(*kt, &a.Ticket.SName) |
| 153 | // if err != nil { |
| 154 | // return false, krberror.Errorf(err, krberror.DecryptingError, "error decrypting encpart of service ticket provided") |
| 155 | // } |
| 156 | //} |
| 157 | sname := &a.Ticket.SName |
| 158 | if snameOverride != nil { |
| 159 | sname = snameOverride |
| 160 | } |
| 161 | err := a.Ticket.DecryptEncPart(kt, sname) |
| 162 | if err != nil { |
| 163 | return false, krberror.Errorf(err, krberror.DecryptingError, "error decrypting encpart of service ticket provided") |
| 164 | } |
| 165 | |
| 166 | // Check time validity of ticket |
| 167 | ok, err := a.Ticket.Valid(d) |
| 168 | if err != nil || !ok { |
| 169 | return ok, err |
| 170 | } |
| 171 | |
| 172 | // Check client's address is listed in the client addresses in the ticket |
| 173 | if len(a.Ticket.DecryptedEncPart.CAddr) > 0 { |
| 174 | //If client addresses are present check if any of them match the source IP that sent the APReq |
| 175 | //If there is no match return KRB_AP_ERR_BADADDR error. |
| 176 | if !types.HostAddressesContains(a.Ticket.DecryptedEncPart.CAddr, cAddr) { |
| 177 | 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") |
| 178 | } |
| 179 | } |
| 180 | |
| 181 | // Decrypt authenticator with session key from ticket's encrypted part |
| 182 | err = a.DecryptAuthenticator(a.Ticket.DecryptedEncPart.Key) |
| 183 | if err != nil { |
| 184 | return false, NewKRBError(a.Ticket.SName, a.Ticket.Realm, errorcode.KRB_AP_ERR_BAD_INTEGRITY, "could not decrypt authenticator") |
| 185 | } |
| 186 | |
| 187 | // Check CName in authenticator is the same as that in the ticket |
| 188 | if !a.Authenticator.CName.Equal(a.Ticket.DecryptedEncPart.CName) { |
| 189 | return false, NewKRBError(a.Ticket.SName, a.Ticket.Realm, errorcode.KRB_AP_ERR_BADMATCH, "CName in Authenticator does not match that in service ticket") |
| 190 | } |
| 191 | |
| 192 | // Check the clock skew between the client and the service server |
| 193 | ct := a.Authenticator.CTime.Add(time.Duration(a.Authenticator.Cusec) * time.Microsecond) |
| 194 | t := time.Now().UTC() |
| 195 | if t.Sub(ct) > d || ct.Sub(t) > d { |
| 196 | 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)) |
| 197 | } |
| 198 | return true, nil |
| 199 | } |