KERBEROS V5 ASN.1 Codec
Kerberos v5 grammar
Here is the ASN.1 grammar for SPNEGO V5 as define din RFC 4220 :
KerberosV5Spec2 {
iso(1) identified-organization(3) dod(6) internet(1)
security(5) kerberosV5(2) modules(4) krb5spec2(2)
} DEFINITIONS EXPLICIT TAGS ::= BEGIN
-- OID arc for KerberosV5
--
-- This OID may be used to identify Kerberos protocol messages
-- encapsulated in other protocols.
--
-- This OID also designates the OID arc for KerberosV5-related OIDs.
--
-- NOTE: RFC 1510 had an incorrect value (5) for "dod" in its OID.
id-krb5 OBJECT IDENTIFIER ::= {
iso(1) identified-organization(3) dod(6) internet(1)
security(5) kerberosV5(2)
}
Int32 ::= INTEGER (-2147483648..2147483647)
-- signed values representable in 32 bits
UInt32 ::= INTEGER (0..4294967295)
-- unsigned 32 bit values
Microseconds ::= INTEGER (0..999999)
-- microseconds
KerberosString ::= GeneralString (IA5String)
Realm ::= KerberosString
PrincipalName ::= SEQUENCE {
name-type [0] Int32,
name-string [1] SEQUENCE OF KerberosString
}
KerberosTime ::= GeneralizedTime -- with no fractional seconds
HostAddress ::= SEQUENCE {
addr-type [0] Int32,
address [1] OCTET STRING
}
-- NOTE: HostAddresses is always used as an OPTIONAL field and
-- should not be empty.
HostAddresses -- NOTE: subtly different from rfc1510,
-- but has a value mapping and encodes the same
::= SEQUENCE OF HostAddress
-- NOTE: AuthorizationData is always used as an OPTIONAL field and
-- should not be empty.
AuthorizationData ::= SEQUENCE OF SEQUENCE {
ad-type [0] Int32,
ad-data [1] OCTET STRING
}
PA-DATA ::= SEQUENCE {
-- NOTE: first tag is [1], not [0]
padata-type [1] Int32,
padata-value [2] OCTET STRING -- might be encoded AP-REQ
}
KerberosFlags ::= BIT STRING (SIZE (32..MAX))
-- minimum number of bits shall be sent,
-- but no fewer than 32
EncryptedData ::= SEQUENCE {
etype [0] Int32 -- EncryptionType --,
kvno [1] UInt32 OPTIONAL,
cipher [2] OCTET STRING -- ciphertext
}
EncryptionKey ::= SEQUENCE {
keytype [0] Int32 -- actually encryption type --,
keyvalue [1] OCTET STRING
}
Checksum ::= SEQUENCE {
cksumtype [0] Int32,
checksum [1] OCTET STRING
}
Ticket ::= [APPLICATION 1] SEQUENCE {
tkt-vno [0] INTEGER (5),
realm [1] Realm,
sname [2] PrincipalName,
enc-part [3] EncryptedData -- EncTicketPart
}
-- Encrypted part of ticket
EncTicketPart ::= [APPLICATION 3] SEQUENCE {
flags [0] TicketFlags,
key [1] EncryptionKey,
crealm [2] Realm,
cname [3] PrincipalName,
transited [4] TransitedEncoding,
authtime [5] KerberosTime,
starttime [6] KerberosTime OPTIONAL,
endtime [7] KerberosTime,
renew-till [8] KerberosTime OPTIONAL,
caddr [9] HostAddresses OPTIONAL,
authorization-data [10] AuthorizationData OPTIONAL
}
-- encoded Transited field
TransitedEncoding ::= SEQUENCE {
tr-type [0] Int32 -- must be registered --,
contents [1] OCTET STRING
}
TicketFlags ::= KerberosFlags
-- reserved(0),
-- forwardable(1),
-- forwarded(2),
-- proxiable(3),
-- proxy(4),
-- may-postdate(5),
-- postdated(6),
-- invalid(7),
-- renewable(8),
-- initial(9),
-- pre-authent(10),
-- hw-authent(11),
-- the following are new since 1510
-- transited-policy-checked(12),
-- ok-as-delegate(13)
AS-REQ ::= [APPLICATION 10] KDC-REQ
TGS-REQ ::= [APPLICATION 12] KDC-REQ
KDC-REQ ::= SEQUENCE {
-- NOTE: first tag is [1], not [0]
pvno [1] INTEGER (5) ,
msg-type [2] INTEGER (10 -- AS -- | 12 -- TGS --),
padata [3] SEQUENCE OF PA-DATA OPTIONAL
-- NOTE: not empty --,
req-body [4] KDC-REQ-BODY
}
KDC-REQ-BODY ::= SEQUENCE {
kdc-options [0] KDCOptions,
cname [1] PrincipalName OPTIONAL
-- Used only in AS-REQ --,
realm [2] Realm
-- Server's realm
-- Also client's in AS-REQ --,
sname [3] PrincipalName OPTIONAL,
from [4] KerberosTime OPTIONAL,
till [5] KerberosTime,
rtime [6] KerberosTime OPTIONAL,
nonce [7] UInt32,
etype [8] SEQUENCE OF Int32 -- EncryptionType
-- in preference order --,
addresses [9] HostAddresses OPTIONAL,
enc-authorization-data [10] EncryptedData OPTIONAL
-- AuthorizationData --,
additional-tickets [11] SEQUENCE OF Ticket OPTIONAL
-- NOTE: not empty
}
KDCOptions ::= KerberosFlags
-- reserved(0),
-- forwardable(1),
-- forwarded(2),
-- proxiable(3),
-- proxy(4),
-- allow-postdate(5),
-- postdated(6),
-- unused7(7),
-- renewable(8),
-- unused9(9),
-- unused10(10),
-- opt-hardware-auth(11),
-- unused12(12),
-- unused13(13),
-- 15 is reserved for canonicalize
-- unused15(15),
-- 26 was unused in 1510
-- disable-transited-check(26),
--
-- renewable-ok(27),
-- enc-tkt-in-skey(28),
-- renew(30),
-- validate(31)
AS-REP ::= [APPLICATION 11] KDC-REP
TGS-REP ::= [APPLICATION 13] KDC-REP
KDC-REP ::= SEQUENCE {
pvno [0] INTEGER (5),
msg-type [1] INTEGER (11 -- AS -- | 13 -- TGS --),
padata [2] SEQUENCE OF PA-DATA OPTIONAL
-- NOTE: not empty --,
crealm [3] Realm,
cname [4] PrincipalName,
ticket [5] Ticket,
enc-part [6] EncryptedData
-- EncASRepPart or EncTGSRepPart,
-- as appropriate
}
EncASRepPart ::= [APPLICATION 25] EncKDCRepPart
EncTGSRepPart ::= [APPLICATION 26] EncKDCRepPart
EncKDCRepPart ::= SEQUENCE {
key [0] EncryptionKey,
last-req [1] LastReq,
nonce [2] UInt32,
key-expiration [3] KerberosTime OPTIONAL,
flags [4] TicketFlags,
authtime [5] KerberosTime,
starttime [6] KerberosTime OPTIONAL,
endtime [7] KerberosTime,
renew-till [8] KerberosTime OPTIONAL,
srealm [9] Realm,
sname [10] PrincipalName,
caddr [11] HostAddresses OPTIONAL
}
LastReq ::= SEQUENCE OF SEQUENCE {
lr-type [0] Int32,
lr-value [1] KerberosTime
}
AP-REQ ::= [APPLICATION 14] SEQUENCE {
pvno [0] INTEGER (5),
msg-type [1] INTEGER (14),
ap-options [2] APOptions,
ticket [3] Ticket,
authenticator [4] EncryptedData -- Authenticator
}
APOptions ::= KerberosFlags
-- reserved(0),
-- use-session-key(1),
-- mutual-required(2)
-- Unencrypted authenticator
Authenticator ::= [APPLICATION 2] SEQUENCE {
authenticator-vno [0] INTEGER (5),
crealm [1] Realm,
cname [2] PrincipalName,
cksum [3] Checksum OPTIONAL,
cusec [4] Microseconds,
ctime [5] KerberosTime,
subkey [6] EncryptionKey OPTIONAL,
seq-number [7] UInt32 OPTIONAL,
authorization-data [8] AuthorizationData OPTIONAL
}
AP-REP ::= [APPLICATION 15] SEQUENCE {
pvno [0] INTEGER (5),
msg-type [1] INTEGER (15),
enc-part [2] EncryptedData -- EncAPRepPart
}
EncAPRepPart ::= [APPLICATION 27] SEQUENCE {
ctime [0] KerberosTime,
cusec [1] Microseconds,
subkey [2] EncryptionKey OPTIONAL,
seq-number [3] UInt32 OPTIONAL
}
KRB-SAFE ::= [APPLICATION 20] SEQUENCE {
pvno [0] INTEGER (5),
msg-type [1] INTEGER (20),
safe-body [2] KRB-SAFE-BODY,
cksum [3] Checksum
}
KRB-SAFE-BODY ::= SEQUENCE {
user-data [0] OCTET STRING,
timestamp [1] KerberosTime OPTIONAL,
usec [2] Microseconds OPTIONAL,
seq-number [3] UInt32 OPTIONAL,
s-address [4] HostAddress,
r-address [5] HostAddress OPTIONAL
}
KRB-PRIV ::= [APPLICATION 21] SEQUENCE {
pvno [0] INTEGER (5),
msg-type [1] INTEGER (21),
-- NOTE: there is no [2] tag
enc-part [3] EncryptedData -- EncKrbPrivPart
}
EncKrbPrivPart ::= [APPLICATION 28] SEQUENCE {
user-data [0] OCTET STRING,
timestamp [1] KerberosTime OPTIONAL,
usec [2] Microseconds OPTIONAL,
seq-number [3] UInt32 OPTIONAL,
s-address [4] HostAddress -- sender's addr --,
r-address [5] HostAddress OPTIONAL -- recip's addr
}
KRB-CRED ::= [APPLICATION 22] SEQUENCE {
pvno [0] INTEGER (5),
msg-type [1] INTEGER (22),
tickets [2] SEQUENCE OF Ticket,
enc-part [3] EncryptedData -- EncKrbCredPart
}
EncKrbCredPart ::= [APPLICATION 29] SEQUENCE {
ticket-info [0] SEQUENCE OF KrbCredInfo,
nonce [1] UInt32 OPTIONAL,
timestamp [2] KerberosTime OPTIONAL,
usec [3] Microseconds OPTIONAL,
s-address [4] HostAddress OPTIONAL,
r-address [5] HostAddress OPTIONAL
}
KrbCredInfo ::= SEQUENCE {
key [0] EncryptionKey,
prealm [1] Realm OPTIONAL,
pname [2] PrincipalName OPTIONAL,
flags [3] TicketFlags OPTIONAL,
authtime [4] KerberosTime OPTIONAL,
starttime [5] KerberosTime OPTIONAL,
endtime [6] KerberosTime OPTIONAL,
renew-till [7] KerberosTime OPTIONAL,
srealm [8] Realm OPTIONAL,
sname [9] PrincipalName OPTIONAL,
caddr [10] HostAddresses OPTIONAL
}
KRB-ERROR ::= [APPLICATION 30] SEQUENCE {
pvno [0] INTEGER (5),
msg-type [1] INTEGER (30),
ctime [2] KerberosTime OPTIONAL,
cusec [3] Microseconds OPTIONAL,
stime [4] KerberosTime,
susec [5] Microseconds,
error-code [6] Int32,
crealm [7] Realm OPTIONAL,
cname [8] PrincipalName OPTIONAL,
realm [9] Realm -- service realm --,
sname [10] PrincipalName -- service name --,
e-text [11] KerberosString OPTIONAL,
e-data [12] OCTET STRING OPTIONAL
}
METHOD-DATA ::= SEQUENCE OF PA-DATA
TYPED-DATA ::= SEQUENCE SIZE (1..MAX) OF SEQUENCE {
data-type [0] Int32,
data-value [1] OCTET STRING OPTIONAL
}
-- preauth stuff follows
PA-ENC-TIMESTAMP ::= EncryptedData -- PA-ENC-TS-ENC
PA-ENC-TS-ENC ::= SEQUENCE {
patimestamp [0] KerberosTime -- client's time --,
pausec [1] Microseconds OPTIONAL
}
ETYPE-INFO-ENTRY ::= SEQUENCE {
etype [0] Int32,
salt [1] OCTET STRING OPTIONAL
}
ETYPE-INFO ::= SEQUENCE OF ETYPE-INFO-ENTRY
ETYPE-INFO2-ENTRY ::= SEQUENCE {
etype [0] Int32,
salt [1] KerberosString OPTIONAL,
s2kparams [2] OCTET STRING OPTIONAL
}
ETYPE-INFO2 ::= SEQUENCE SIZE (1..MAX) OF ETYPE-INFO2-ENTRY
AD-IF-RELEVANT ::= AuthorizationData
AD-KDCIssued ::= SEQUENCE {
ad-checksum [0] Checksum,
i-realm [1] Realm OPTIONAL,
i-sname [2] PrincipalName OPTIONAL,
elements [3] AuthorizationData
}
AD-AND-OR ::= SEQUENCE {
condition-count [0] Int32,
elements [1] AuthorizationData
}
AD-MANDATORY-FOR-KDC ::= AuthorizationData
END
Decoding Kerberos messages
The Kerberos protocol define many standalone messages. We will define the state machine for each of those messages.
AS-REQ
This is a message sent to the Authentication Service by a client.
It's a KDC-REQ message with a specific type. Here is its grammar :
AS-REQ ::= [APPLICATION 10] KDC-REQ
KDC-REQ ::= SEQUENCE {
-- NOTE: first tag is [1], not [0]
pvno [1] INTEGER (5) ,
msg-type [2] INTEGER (10 -- AS -- | 12 -- TGS --), -- Here, 10
padata [3] SEQUENCE OF PA-DATA OPTIONAL
-- NOTE: not empty --,
req-body [4] KDC-REQ-BODY
}
A typical PDU for this message will be something like :
0x6A L1 // APPLICATION 10
0x30 L2 // SEQUENCE
0xA1 0x03
0x02 0x01 NN // pvno
0xA2 0x03
0x02 0x01 0x0A // msg-type, 10
[0xA3 L3 abcd] // SEQUENCE OF PA-DATA OPTIONAL
0xA4 L4 abcd // KDC-REQ-BODY
If the PA-DATA is not absent, then t can be empty.
TGS-REQ
This is a message sent to the Ticket Granting Service by a client.
It's a KDC-REQ message with a specific type. Here is its grammar :
TGS-REQ ::= [APPLICATION 12] KDC-REQ
KDC-REQ ::= SEQUENCE {
-- NOTE: first tag is [1], not [0]
pvno [1] INTEGER (5) ,
msg-type [2] INTEGER (10 -- AS -- | 12 -- TGS --), -- Here, 12
padata [3] SEQUENCE OF PA-DATA OPTIONAL
-- NOTE: not empty --,
req-body [4] KDC-REQ-BODY
}
A typical PDU for this message will be something like :
0x6C L1 // APPLICATION 12
0x30 L2 // SEQUENCE
0xA1 0x03
0x02 0x01 NN // pvno
0xA2 0x03
0x02 0x01 0x0C // msg-type, 12
[0xA3 L3 abcd] // SEQUENCE OF PA-DATA OPTIONAL
0xA4 L4 abcd // KDC-REQ-BODY