wdiff draft-ietf-kink-kink-01.txt draft-ietf-kink-kink-02.txt

INTERNET-DRAFT KINK M. Thomas
Editor
M. Froh
Cybersafe
M. Hur
D. McGrew
J. Vilhuber
Cisco
S Medvinsky
Motorola
July 19,
October 20, 2001

Kerberized Internet Negotiation of Keys (KINK)
draft-ietf-kink-kink-01.txt
draft-ietf-kink-kink-02.txt

Status of this Memo

This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026. Internet-Drafts are working
documents of the Internet Engineering Task Force (IETF), its areas,
and its working groups. Note that other groups may also distribute
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Abstract

The

KINK Working Group will create a standards track protocol to
facilitate centralized key exchange in an application independent
fashion. Participating systems will use the Kerberos architecture as
defined in RFC 1510 for key management and the KINK protocol between
applications. The goal of KINK is to produce defines a low-latency, computationally inexpensive, easily
managed, and cryptographically sound protocol that is flexible enough to be able to be extended for
many applications.

The initial focus of the protocol will be keying IPsec set up and maintain
[IPSEC] security associations as defined in RFC 2401. Future version of the using [KERBEROS] authentication. KINK
protocol may define new objects and Domains of Interpretation
reuses many [ISAKMP] Quick Mode payloads to
extend KINK create, delete and
maintain IPsec security associations which should lead to be suitable for keying other kinds substantial
reuse of applications. existing [IKE] implementations.

Conventions used in this document

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC-2119.

Action Items:

o Which Diffie Hellman group for PFS?

o Word the KINK_ENCRYPT IV use description better

o Better discussion of error scenarios; more specific error codes?

o Should we register the KINK payloads with IANA as ISAKMP types?
This would avoid potential name space collisions.

o Still need to talk about when to use U-U vs. normal mode (aka
Discovery).

o Need a port from IANA

Changes from -00

o Numerous editorial changes

o Change CREATE SA to reflect ACK reliability guidelines. Mention
grace timer for ACK.

o Make final ACK optional in DELETE flow. This seems like it was a
mistake. Clarify the grace timer.

o Add STATUS verb to reflect the ability of Quick mode to send
mid-SA notifications.

o Reorganize the KINK header to not have a short paylaod and
reserve all of the flags.

o Clarify the method of applying the keyed hash over the message.
Also remove redundant checksum type in checksum field (it's
defined to be the etype of the ticket).

o Clarify the padding rules.

o Clarify in GETTGT/TGTREP that you supply a realm to GETTGT and
TGTREP returns the principal name of to do the UU with.

o List all of the appropriate Kerberos Errors that can be
returned. Mention which ones must be handled.

o Add IKE major/minor version in ISAKMP payload header.

o Clarify how to produce the KINK encrypt header.

o Add an INTERNAL ERROR error code.

o Modify the various headers/payloads of section 6 and 8 to more
accurately reflect that we are using IKE Quick Mode directly;
remove text describing ISAKMP headers, refer to 240x.

o Add section for PFS support.

o Change key derivation section to reflect the use of quick mode
method.

o Reflect ACK handling in Transport Considerations

o Add Security Considerations.

1. Introduction

KINK is designed to provide a secure, scalable mechanism for estab-
lishing keys between communicating entities within a centrally
managed environment in which it is important to maintain consistent
security policy. The security goals of KINK are to provide privacy,
authentication, and replay protection of key management messages, and
to avoid denial of service vulnerabilities whenever possible. The
performance goals of the protocol are to incur a low computational
cost, to have a low latency, to have a small footprint, and to avoid or
minimize the use of public key operations. In particular, the
protocol should provide proto-
col provides the capability to establish SAs security associations in two mes-
sages
messages with minimal computational effort.

Kerberos [KERB] and [RFC1510] [KERBEROS] provides an efficient mechanism for
trusted third party authentication for clients and servers. (Kerberos (Ker-
beros also provides an efficient mechanism mechanisms for inter-realm authentication
natively and with [PKCROSS].) Clients obtain tickets (a ticket is a symmetric key cer-
tificate) from an online
authentication server (the Key Distribution Center or KDC). Tickets
are then used to construct credentials for authen-
ticating authenticating the client
to the server. As a result of this authentica-
tion, authentication operation, the
client and the server will also share a secret (a key, generated by
the KDC, that is encrypted within secret. KINK uses this pro-
perty as the ticket). basis of distributing keys for IPsec.

The central key management provided by Kerberos is efficient, efficient because
it limits computational cost and limits complexity. complexity versus IKE's
necessity of using public key cryptography. Initial authenti-
cation authentication
to the KDC may be performed using either symmetric keys or asym-
metric asymmetric
keys using [PKINIT]; however, subsequent requests for tickets util-
ize tickets, as
well as authenticated exchanges between client and server always
utilize symmetric cryptography, which is much more efficient than public
key cryptography. Therefore, public key operations (if
any) are limited and are amortized over the lifetime of the initial
authentication operation to the Kerberos tickets. KDC. For exam-
ple, example, a server client
may use a single public key exchange with the KDC to efficiently
establish multiple security associations with many other
servers. Since servers in
the extended realm of the KDC. Kerberos principal also scales better than
direct peer to peer keying when symmetric keys are used. The reason
is that since the keys (used for initial asymmetric
authentication) are stored in the KDC, the number of principal
keys is order of magnitude O(n) rather than O(n^2), as would be required
for a pre-shared key type O(n*m), where "n" is the number of clients
and "m" is the number of solution. servers.

This document specifies the Kerberized Internet Negotiation of Keys
Protocol and its use to establish and maintain IPsec Security Associ-
ations [RFC2401]. KINK could be used to maintain Security Associa-
tions defined in other Domains of Interpretation, though such use is
outside of the scope of this document. It should be noted that KINK
is a complement to and not a replacement for the Internet Key
Exchange [IKE], as KINK requires the use of an online authentication
server and cannot provide identity protection nor perfect forward
secrecy (as described in [RFC2412]). There are many situations in
which centralized key management is desirable.

While Kerberos specifies a standard protocol between the client and
the KDC to get tickets, the actual ticket exchange between client and
server is application specific. KINK is intended to be an alterna-
tive to requiring each application having its own method of tran-
sporting and validating service tickets using a protocol which is
efficient and tailored to the specific needs of Kerberos and the
applications for which it provides keying and parameter negotiation.

KINK defines the "on the wire" protocol for establishing keys based
on Kerberos authentication. This is a general protocol that may be
used to securely establish keys for any purpose. This protocol is
ideally suited for environment in which efficiency, scalability, and
central management are important. This document defines the KINK pro-
tocol and also defines a domain of interpretation to establish (DOI) for establishing and
maintain
maintaining IPsec security associations. Any Security Associations [IPSEC]. No other domains of interpre-
tation must be
interpretation are defined separately. The protocol takes full advantage
of the features of RFC 2401 but in the context of a centralized key-
ing authority. this document.

2. Terminology

Ticket
A Kerberos term for a record that helps a client authenticate
itself to a server; it contains the client's identity, a session
key, a lifetime, and other information, all sealed using the
server's secret key. The combination of a ticket and an authentica-
tor (which proves freshness and knowledge of the key within the
ticket) creates an authentication credential.

KDC
Key Distribution Center, a network service that supplies tickets
and temporary session keys; or an instance of that service or the
host on which it runs. The KDC services both initial ticket and
Ticket-Granting Ticket (TGT) requests. The initial ticket portion
is referred to as the Authentication Server (or service). The
Ticket-Granting Ticket portion is referred to as the Ticket-
Granting Server (or service).

Realm
A Kerberos administrative domain. A single KDC may be responsible
for one or more realms. A fully qualified principal name includes
a realm name along with a principal name unique within that realm.

3. Protocol Overview

This document specifies

TGT
A ticket granting ticket is a protocol (KINK) that allows two peers to
directly establish symmetric keys, where one peer has already
obtained an authentication credential normal Kerberos ticket which the KDC
issues for the other peer from Kerberos service. The main purpose of a
trusted third party known as TGT is to
capture the Kerberos KDC (Key Distribution
Center). An results of initial authentication credential for subsequent ticket
granting requests, thus providing a server obtained from single sign-on service.

User-User
Kerberos normally divides the
KDC is known as world into clients and servers where
the Kerberos service ticket.

The use server maintains a table of keys (keytab) which is used to
encrypt/decrypt service tickets. In situations where a principal
may not have a keytab (ex. a human/client principal rather than a
service principal), Kerberos tickets minimizes provides the amount means of state that is
required for this key management protocol. It issuing what is possible for only
one of
known as a User-User ticket. To produce the peers to save Kerberos tickets, while User-User ticket, the other peer can
remain completely stateless. KINK uses this property to allow mes-
sage exchanges to be stateless. That is,
KDC requires the ticket granting tickets from both client princi-
pals. Kerberos does not specify a secure session means obtaining a client's
ticket granting ticket, and is not
required to exchange KINK messages thus application specific.

Principal
Kerberos named entities are known as each message contains all of
the information required principals, and are roughly
equivalent to authenticate the message. This X.509 distinguished names. Principals are either
client or service principals. A principal is an entity that
engages in
contrast to IKE [IKE] which requires a phase 1 security association
to be created and maintained in order to create subsequent security
associations. relationship. A Kerberos tickets utilize only symmetric key cryptography with rela-
tively small overhead required to process them (as compared principal name is
roughly equivalent to public
key-based protocols). However, an authentication mechanism that X.509 distinguished name (it associates
the principal with an adminsitrative domain). Principals may be
client or servers. A server principal is
utilized between generally distinguished
by a flag in a KDC client principal database and the KDC can be either symmetric key
based (as specified by the base Kerberos protocol [RFC1510]) or pub-
lic key based (as specified a keytab maintained by PKINIT [PKINIT]).

KINK hosts are peers in
the IPsec sense server.

DER
ASN.1 Distinguished Encoding Rules; Kerberos version 5 uses this
encoding format of the meaning that a KINK
host can initiate ASN.1.

Quick-Mode
IKE defines two phases: an authentication phase (phase 1, or respond to KINK commands. Messages come in three
varieties: commands, replies, Main
Mode) and acknowledgments. In most cir-
cumstances, a KINK security association can be installed in two mes-
sages: a command maintenance phase (phase 2, or
Quick Mode). KINK reuses IKE Quick Mode.

AP-REQ/AP-REP
Kerberos defines an standardized message format and transport for
contacting a reply. The method here is KDC to use an "optimis-
tic" algorithm where negotiation proposals are prioritized perform initial authentication, and the
top choice is installed in the security association database. If for
some reason grant-
ing subsequent service tickets. When a client needs to authenticate
to a server, Kerberos provides a standardized message format, but
leaves the respondent does not choose transport as application specific. The messages which
perform this function are AP-REQ between the first proposal, client and the
respondent may choose another but at server,
and AP-REP between the cost of server and client if mutual authentication
is needed.

3. Protocol Overview

KINK is a ACK message so
that it command/response protocol which can be guaranteed create, delete and
maintain IPsec security associations. Each command or response con-
tains a common header along with a set of delivery.

Since type-length-value payloads
which are constrained according to the KDC type of command or response.
KINK itself is a stateless protocol in that each command or response
does not possess a symmetric key PKINIT principals KINK
defines an unauthenticated request require storage of hard state for getting a peer's ticket grant-
ing ticket. This allows KINK peers itself. This is in
contrast to request a User IKE's use of Main Mode to User service
ticket. Upon receipt first establish an ISAKMP secu-
rity association followed by subsequent Quick Mode exchanges.

KINK uses Kerberos mechanisms to provide mutual authentication,
replay protection. For security association establishment. KINK pro-
vides privacy of the User to User payloads which follow the Kerberos authentica-
tor. KINK's design mitigates denial of service ticket, all messages attacks by requiring
authenticated exchanges are identical. Discovery issues are discussed in section
XXX. before the use of any public key operations
and the installation of any state. KINK is intended as also provides the means of
using Kerberos User-User mechanisms when there isn't a generic key management protocol based on Ker-
beros tickets. It can be used shared
between the server and the KDC. This is typically -- but not limited
to provide key management -- the case with IPsec peers using [PKINIT] for any
security layer above level 2 in initial authenti-
cation.

KINK directly reuses [ISAKMP] Quick Mode payloads, with some minor
changes and omissions. In most cases, KINK exchanges are a single
command and its response. The lone exception is the Internet protocol stack, includ-
ing application-layer security. CREATE command
which allows a final acknowledgment message when the respondent needs
a full three-way handshake. This document includes an IPSec DOI
(Domain of Interpretation) is only needed when the optimistic
keying route is not taken, though it is expected that enables KINK to be used directly as
an IPSec key management protocol. Other DOI specifications may that will not
be
used to apply the norm. KINK to other security protocols. also provides rekeying and dead peer detection as
basic features.

4. Message Flows

KINK message flows all follow the same pattern between the two peers:
a command, a response and an optional acknowledgement. a possible acknowledgment with CREATE's.
The actual Kerberos KDC traffic here is for illustrative purposes
only. In prac-
tice, practice, when a principal obtains various tickets is a subject sub-
ject of Ker-
beros Kerberos and local policy consideration. In these flows, we
assume that A and B both have TGT's from their KDC.

4.1. Standard KINK Message Flow

A B KDC
------ ------ ---
1 COMMAND------------------->

2 <------------------REPLY

3 [ ACK---------------------> ]

Figure 1: KINK Message Flow

4.2. GETTGT Message Flow

If the initiator determines that it will not be able to directly get a normal
service ticket for the respondent (ie, (eg, B is a PKINIT client principal), it
must
MUST first fetch the TGT from the respondent first in order to get a User-
User service ticket:

A B KDC
------ ------ ---
1 GETTGT+KRB_TGT_REQ------->

2 <-------REPLY+KRB_TGT_REP

3 TGS-REQ+TGT(B)------------------------------------->

4 <--------------------------------------------TGS-REP

Figure 2: GETTGT Message Flow

4.3. CREATE Security Association

This flow instantiates a security association. The CREATE command
takes an "optimistic" approach where security associations are
initially created on the expectation that the respondent will chose
the initial proposed payload. The optimistic payload is defined as
the first transform of the first proposal of the first conjugate.
The initiator MUST checks to see if the optimistic payload was
selected by comparing all transforms and attributes which MUST be
identical from the initiator's optimistic proposal with the lone
exception of LIFE_KILOBYTES and LIFE_SECONDS. Both of these
attributes MAY be set to a lower value by the respondent and still
expect optimistic keying, but MUST NOT be set to a higher value which
MUST generate an error.

CREATE'ing a security association on an existing SPI is an error in
KINK and MUST be rejected with an ISAKMP notification of INVALID-SPI.

A B KDC
------ ------ ---

A creates initial inbound SA (B->A)

1 CREATE+ISAKMP------------>

B creates inbound SA to A (A->B). If B chooses A's first optimistic
proposal, it creates the outbound SA as well (B->A).

2 <------------REPLY+ISAKMP

A creates outbound SA and modifies inbound SA if it first
proposal wasn't acceptible. acceptable.

3 [ ACK--------------------> ]

[ B creates the outbound SA to A (B-A). ]

Figure 3: CREATE Message Flow

The security associations are instantiated as follows: In step one
host A creates an inbound security association in its security asso-
ciation database from B->A using the first optimistic proposal in the
ISAKMP SA proposal. It is then ready to receive any messages from B.
A then sends the CREATE message to B. If B agrees to A's initial proposal and does not desire to con-
tribute entropy to the session key, optimistic
proposal, B instantiates a security associ-
ation association in its database from
A->B. B then instantiates the security association from B->A. It then
sends a REPLY to A without a NONCE payload and without requesting an
ACK. If B does not choose the first proposal, it sends the actual
choice in the REPLY, a NONCE payload and requests that the REPLY be
acknowledged. Upon receipt of the REPLY, A modifies the inbound security secu-
rity association as necessary, instantiates the security association
from A->B, If B requested an ACK, A now sends the ACK message. Upon
receipt of the ACK, B installs the final security association from
B->A.

Note: if B adds a nonce, or does not choose the first proposal, it SHOULD
MUST request an ACK so that it can install the final outbound security secu-
rity association. Since ACK's are not reliable [see section on Transport
Considerations], The initiator MUST always generate an ACK if the requestor SHOULD implement a grace timer to
install
ACKREQ bit is set in the outbound security association. KINK header, even if it believes that the
respondent was in error.

4.3.1. CREATE Key Derivation Considerations

The CREATE command's optimistic approach allows a security associa-
tion to be created in two messages rather than three. The implication
of a two message exchange is that B will not contribute to the key
since A must set up the inbound security association before it
receives any additional keying material from B. Under normal cir-
cumstances this may be suspect, however KINK takes advantage of the
fact that the KDC provides a reliable source of randomness which is
used in key derivation. In many cases, this will provide an adequate
session key so that B will not require an acknowledgment. Since B is
always at liberty to contribute to the keying material, this is
strictly a key strength versus number of messages tradeoff which KINK
implementations may decide as a matter of policy.

4.4. DELETE Security Association

The DELETE command deletes an existing security association. The DOI
specific payloads describe the actual security association to be
deleted. For the IPSEC DOI, those payloads will include an ISAKMP
payload contains the SPI to be deleted in each direction.

A B KDC
------ ------ ---

A deletes outbound SA to B

1 DELETE+ISAKMP------------>

B deletes inbound and outbound SA to A

2 <-------------REPLY+ISAKMP

A deletes inbound SA to B

[3 ACK--------------------> ]

[ B deletes inbound SA to A]

Figure 4: DELETE Message Flow

The DELETE command takes a "pessimistic approach" which does not
delete incoming security associations until it receives acknowledg-
ment that the other host has received the DELETE. The exception to
the pessimistic approach is if the initiator wants to immediately
cease all activity on an incoming SA. In this case, it MAY delete the
incoming SA as well in step one. The respondent If the receiver cannot find an
appropriate SPI to delete, it MUST NOT return an ISAKMP INVALID_SPI
notification which also serves to inform the initiator that it can
delete its the incoming SA until it either receives SA. For simplicity, KINK does not allow half open
security associations; thus upon receiving a DELETE, the final ACK, or responder
MUST delete its security associations, and MUST reply with ISAKMP
delete notification messages if the transac-
tion times out. SPI is found.

A final race condition with DELETE exists. Packets in flight while the
DELETE operation is taking place may, due to network reording, reordering, etc,
arrive after the diagrams above recommend deleting the incoming
security secu-
rity association. A KINK implementation MUST SHOULD implement a grace
timer which SHOULD be set to a period of at least two times the aver-
age round trip time, or to a configurable value. A KINK implementa-
tion MAY chose to set the grace period to zero at appropriate times
to ungracefully delete a security association. The behavior described
here loosely mimics the behavior of the TCP [RFC793] flags FIN and
RST.

4.4.1. Rekeying Security Associations

KINK requires the initiator of a security association to be responsi-
ble for rekeying a security association. The reason is twofold: the
first is to prevent needless duplication of security associations as
the result of collisions due to an initiator and respondent both try-
ing to renew an existing security association. The second reason is
due to the client/server nature of Kerberos exchanges which expects
the client to get and maintain tickets. While KINK requires that a
KINK host be able to get and maintain tickets, in practice it is
often advantageous for servers to wait for clients to initiate sessions ses-
sions so that they do not need to maintain a large ticket cache.

There are no special semantics for rekeying security associations in
KINK. That is, in order to rekey an existing security association,
the initiator must CREATE a new security association followed by
either DELETE'ing the old security association or letting it just time
out. When identical flow selectors are available on different
security secu-
rity associations, KINK implementations SHOULD chose choose the security
association most recently created. It should be noted that KINK
avoids most of the problems of [IKE] rekeying by having a reliable
delete mechanism.

Normally a KINK implementation which rekeys existing security associ-
ations will try to rekey the security association ahead of a hard SA
expiration. We call this time the rekey time Trekey. In order to
avoid synchronization with similar implementations, KINK initiators
MUST randomly pick a rekeying time between Trekey and the SA expira-
tion time minus the amount of time it would take to go through a full
retransmission time cycle, Tretrans. Trk SHOULD be set at least twice
as high as Tretrans.

4.4.2. Dead Peer Detection

In order to determine that a KINK peer has lost its security database
information, KINK peers MUST record the current epoch for which they
have valid SADB information and reflect that epoch in each AP-REQ and
AP-REP message. When a KINK peer creates state for a given security
association, it MUST also record the principal's epoch as well. If it
discovers on a subsequent message that the principal's epoch has
changed, it MUST consider all security associations created by that
principal as invalid, and take some action such as tearing those SA's
down.

It should be noted that KINK alone cannot provide a complete solution
for dead peer detection since in many situations a KINK peer would
have no reason to send subsequent KINK messages from whence it could
determine the epoch mismatch. The larger picture may require some
assistance from the IP layer itself to inform IPsec peers that they
are sending SA protected data into a black hole. Assuming this
mechanism is eventually defined, KINK peers SHOULD use this informa-
tion as a hint that something is amiss and perform a dead peer detec-
tion operation by using the STATUS message to elicit a response which
contains the peer's current epoch. Since the STATUS message is
integrity protected, it in combination with network layer messaging
should provide a secure means of recovery from dead peers.

4.5. STATUS Message Flow

At any point, a sender may send status, normally in the form of DOI
specific payloads to its peer. In the case of the IPsec DOI, these
are generally in the form of ISAKMP Notification Payloads.

A B KDC
------ ------ ---

1 STATUS+ISAKMP------------>

2 <-------------REPLY+ISAKMP

Figure 4: 5: STATUS Message Flow

5. KINK Message Format

All values in KINK are formatted in the network byte order: Most
Significant Byte first.

0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | MjVer | MnVer | Length |
+---------------+---------------+---------------+---------------+
| Domain of Interpretation (DOI) |
+-------------------------------+-------------------------------+
| Transaction ID (XID) |
+---------------+---------------+-+-----------------------------+
| CksumLen | NextPayload |A| Reserved |
+---------------+---------------+-+-----------------------------+
| |
~ Cksum ~
| |
+-------------------------------+-------------------------------+
| |
~ A series of payloads ~
| |
+-------------------------------+-------------------------------+

Figure 5: 6: Format of a KINK message

Fields:

o Type (1 octet) - The type of message of this packet

Type Value
----- -----
RESERVED 0
CREATE 1
DELETE 2
REPLY 3
GETTGT 4
ACK 5
STATUS 6

o MjVer (4 bits) - Major protocol version number. This MUST be set
to 1.

o MnVer (4 bits) - Minor protocol version number. This MUST be set
to 0.

o Length (16 bits) (2 octets) - Length of the message in octets. Note that it
is legal within KINK to omit the last bytes of padding in the last
payload in the overall length.

o DOI (4 octets) - The domain of interpretation. All DOI's must be
registered with the IANA in the "Assigned Numbers" RFC [STD-2].

The IANA Assigned Number for the Internet IP Security DOI (IPSEC
DOI) is one (1). This field defines the context of all other sub-
payloads in this payloads. If other sub-payloads have a DOI field
(example: Security Association Payload), then the DOI in that
sub-payload MUST be checked against the DOI in this header, and
the values MUST be the same.

o XID (4 octets) - The transaction ID. A KINK transaction is bound
together by a transaction ID which is created by the command ini-
tiator and replicated in subsequent messages in the transaction. A
transaction is defined as a command, a reply, and an optional ack-
nowledgment. Transaction ID's are used by the initiator to
discriminate between multiple outstanding requests to a respon-
dent. It is not used for replay protection because that func-
tionality is provided by Kerberos. The value of XID is chosen by
the initiator and MUST be unique with all outstanding transac-
tions. XID's MAY be constructed by using a monotonic counter, or
random number generator.

o CksumLen (2 octets) -- CksumLen is the length in octets of the
keyed hash of the message. A CksumLen of zero implies that the
message is unauthenticated. Note that as with payload padding, the
length here denotes the actual number of octets of the checksum
structure not including any padding required.

o NextPayload (1 octet) -- Indicates the type of the first payload
after the message header

o A (1 bit) -- ACK Request. Set to one if the responder desires requires an
explicit acknowledgement acknowledgment that a REPLY was received. An initiator
MUST NOT set this flag. flag, nor should any other command other than
CREATE request an ACK and then only when the optimistic SA is not
chosen.

o Reserved (15 bits) -- Reserved and must be zero

o Cksum (variable) - Keyed checksum over the entire message. This
field MUST always be present whenever a key is available via an
AP-REQ or AP-REP payload. The key used MUST be the session key in
the ticket. When a key is not available, this field is not
present, and the CksumLen field is set to zero. The hash algorithm
used is the same as specified in the etype for the Kerberos ses-
sion key in the Kerberos ticket. If the etype does not specify a
hash algorithm, SHA1 with a 20 byte checksum MUST be used. The
format of the Cksum field is as follows:

0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+---------------+---------------+
| checksum (variable) | ~ padding (variable) |
+---------------+---------------+---------------+---------------+

Figure 6: 7: KINK Checksum
To compute the checksum, the checksum field is zeroed out and the
appropriate algorithm is run over the entire message (as given by
the Length field in the KINK header), and placed in the Checksum
field. To verify the checksum, the checksum is saved, and the
checksum field is zeroed out. The checksum algorithm is run over
the message, and the result is compared with the saved version. If
they do not match, the message MUST be dropped.

The KINK header is followed immediately by a series of
Type/Length/Value fields, defined in the next section.

5.1. KINK Payloads

Immediately following the header, there is a list of
Type/Length/Value (TLV) payloads. There can be any number of payloads
following the header. Each payload MUST begin with a payload header.
Each payload header is built on the generic payload header. Any data
immediately follows the generic header. Payloads are all implicitly
padded to longword 4 octet boundaries, though the payload length field MUST
accurately reflect the actual number of octets in the payload.

Figure 7: 8: Format of a KINK payload

Fields:

o NextPayload (2 octets) - The type of the next payload

NextPayload Number
---- ------
KINK_DONE 0 (same as ISAKMP_NEXT_NONE)
KINK_AP_REQ 1 14
KINK_AP_REP 2 15
KINK_KRB_ERROR 3 16
KINK_TGT_REQ 4 17
KINK_TGT_REP 5 18
KINK_ISAKMP 6 19
KINK_ENCRYPT 7 20
KINK_ERROR 8 21

NextPayload type KINK_DONE denotes that the current payload is the
final payload in the message.

Note: the payload types are taken from the ISAKMP registry for
payload types. As such, payloads 0-13 are used for ISAKMP, and
22-127 are reserved to IANA.

o RESERVED (1 octet) - Unused, MUST be set to 0.

o Length (2 octets) - The length of this payload, including the Type
and Length fields.

o Value (variable) - This value of this field is depends on the Type.

5.1.1. KINK Padding Rules

KINK has the following rules regarding alignment and padding:

o All length fields MUST reflect the actual number of octets in the
structure; ie they do not account for padding bytes

o Between KINK payloads, checksums, headers or any other other vari-
able length data, the adjacent fields MUST be longword aligned. aligned on 4 octet
boundaries.

o Variable length fields MUST always start immediately after the
last octet of the previous field. Ie, they are not padded to a
longword 4
octet boundary.

5.1.2. 5.1.1 KINK_AP_REQ Payload

The KINK_AP_REQ payload relays a kerberos Kerberos AP-REQ to the respondent.
The AP-REQ MUST request mutual authetication. authentication. The service that the
KINK peer SHOULD request is "ipsec/fqdn@REALM" "kink/fqdn@REALM" where "ipsec" "kink" is the
KINK IPsec service, "fqdn" is the fully qualified domain name of the
service host, and REALM is the Kerberos realm of the service. The
exception to this rule is when User-User service is requested in
which case the service name MUST be the service returned in the
GetTGT response payload.

The value field of this payload has the following format:

Figure 8: 9: KINK_AP_REQ Payload
Fields:

o EPOCH - the absolute time at which the creator of the AP-REQ has
valid security database (SADB) information. Typically this is when
the KINK keying daemon started if it does not retain SADB informa-
tion across different restarts. The format of this fields is net-
work order encoding of the standard posix four octet time stamp.

o KRB_AP_REQ - The value field of this payload contains a raw Ker-
beros KRB_AP_REQ.

5.1.3. KINK_AP_REP Payload

The KINK_AP_REP payload relays a kerberos AP-REP to the initiator.
The AP-REP MUST be checked for freshness as described in [1510]. [KERBEROS].

The value field of this payload has the following format:

Figure 9: 10: KINK_AP_REP Payload
Fields:

o EPOCH - the absolute time at which the creator of the AP-REP has
valid security database (SADB) information. Typically this is when
the KINK keying daemon started if it does not retain SADB informa-
tion across different restarts. The format of this fields is net-
work order encoding of the standard posix four octet time stamp.

o KRB_AP_REP - The value field of this payload contains a raw Ker-
beros KRB_AP_REP.

5.1.4. KINK_KRB_ERROR Payload

The KINK_KRB_ERROR payload relays kerberos Kerberos type errors back to the
initiator. The receiver MUST be prepared to receive any valid [1510]
[KERBEROS] error type, but the sender SHOULD only send only the following
errors:

KRB5KRB_AP_ERR_BAD_INTEGRITY
KRB5KRB_AP_ERR_TKT_EXPIRED
KRB5KRB_AP_ERR_TKT_NYV
KRB5KRB_AP_ERR_REPEAT
KRB5KRB_AP_ERR_NOT_US
KRB5KRB_AP_ERR_BADMATCH
KRB5KRB_AP_ERR_SKEW
KRB5KRB_AP_ERR_BADADDR
KRB5KRB_AP_ERR_BADVERSION
KRB5KRB_AP_ERR_MSG_TYPE
KRB5KRB_AP_ERR_MODIFIED
KRB5KRB_AP_ERR_BADORDER
KRB5KRB_AP_ERR_ILL_CR_TKT
KRB5KRB_AP_ERR_BADKEYVER
KRB5KRB_AP_ERR_NOKEY
KRB5KRB_AP_ERR_MUT_FAIL
KRB5KRB_AP_ERR_BADDIRECTION
KRB5KRB_AP_ERR_METHOD
KRB5KRB_AP_ERR_BADSEQ
KRB5KRB_AP_ERR_INAPP_CKSUM
KRB5KRB_AP_WRONG_PRINC
KRB5KRB_AP_ERR_TKT_INVALID

A compliant
KRB5KRB_AP_ERR_BADKEYVER

KINK implementation implementations MUST take make use of keyed Kerberos errors when the
appropriate action for:

KRB5KRB_AP_ERR_BAD_INTEGRITY
KRB5KRB_AP_ERR_TKT_EXPIRED
KRB5KRB_AP_ERR_REPEAT
KRB5KRB_AP_ERR_SKEW
KRB5KRB_AP_ERR_MUT_FAIL service key is available as specified in [KRBREVS]. In
particular, clock skew errors MUST be integrity protected. For
unauthenticated Kerberos errors, the receiver MAY choose to act on
them, but SHOULD take precautions against make-work kinds of attacks.

Note that KINK does not make use of the text or e_data field of the
Kerberos error message, though a compliant KINK implementation MUST
be prepared to receive them and MAY log them.

The value field of this payload has the following format:

Figure 10: 11: KINK_KRB_ERROR Payload

Fields:

o KRB_ERROR - The value field of this payload contains a raw
Kerberos KRB_ERROR.

5.1.5. KINK_TGT_REQ Payload

The KINK_TGT_REQ payload provides a means to get a TGT from the peer
in order to obtain a User to User service ticket from the KDC

The value field of this payload has the following format:

Figure 11: 12: KINK_TGT_REQ Payload

Fields:

o RealmNameLen - The length of the realm name that follows

o RealmName - The realm name that the responder should return a TGT
for.

o RESERVED - reserved and must be zero

If the responder is unable to get a TGT for the domain, it must
reply with a KRB_ERROR payload type.

5.1.6. KINK_TGT_REP Payload

The value field of this payload contains the TGT requested in a
previous KINK_TGT_REP command.

Figure 12: 13: KINK_TGT_REQ Payload

Fields:

o PrincNameLen - The length of the principal name that immediately
follows

o PrincName - The client principal that the initiator should request
a User to User service ticket for.

o TGTlength - The length of TGT that immediately follows

o TGT - the DER encoded TGT of the responder

5.1.7. KINK_ISAKMP Payload

The value field of this payload has the following format:

Figure 13: 14: KINK_ISAKMP Payload

Fields:

o InnerNextPload - First payload type of the inner series of ISAKMP
payloads.

o IkeMj QMMaj - The ISAKMP major version of the inner payloads. MUST be set to 1.

o IkeMn QMMin - The IKE minor version of the inner payloads payloads. MUST be set to 0.

o RESERVED - reserved and must be zero

The KINK_ISAKMP payload encapsulates the IKE Quick Mode (phase
two) payloads to take the appropriate action dependent on the KINK
command. There may be any number of KINK_ISAKMP payloads within a
single KINK message. While IKE is somewhat fuzzy about whether
multiple different SA's may be created within a single IKE mes-
sage, KINK explicitly requires that a new ISAKMP header be used
for each discrete SA operation. In other words, a KINK sender MUST
NOT send multiple quick mode transactions within a single
KINK_ISAKMP payload.

The purpose of the ISAKMP Quick Mode version is to allow backward compati-
bilty compa-
tibility with IKE and ISAKMP if there are subsequent revisions. At
the present time, the ISAKMP Quick Mode major and minor versions are set
to one and one (1.1) zero (1.0) respectively. While strictly speaking These versions do not
correspond to the ISAKMP version is not the same as in the IKE version, that is how it is com-
monly construed, and KINK explicitly makes that linkage. ISAKMP header. A com-
plient compliant
KINK implementation MUST support receipt of ISAKMP version
1.1 1.0 payloads. It MAY
support subsequent versions (both sending and receiving), and
SHOULD provide a means to resort back to ISAKMP Quick Mode version 1.1 1.0 if
the KINK peer is unable to process future versions. A complient compliant
KINK implementation MUST NOT mix ISAKMP Quick Mode versions in any given
transaction.

5.1.8. KINK_ENCRYPT Payload

The KINK_ENCRYPT payload encapsulates other payloads and is encrypted
using the encyption encryption algorithm specified by the etype of the session
key. This payload MUST be the final payload in the message. KINK
encrypt payloads MUST be encrypted before the final KINK checksum is
applied.

Figure 14: 15: KINK_ENCRYPT Payload
Fields:

o InnerNextPload (variable) - First payload type of the inner series
of encrypted KINK payloads.

o RESERVED - reserved and must be zero

Note: the coverage of the encrypted data begins at InnerNextPload
so that first payload's type is kept confidential. Thus, the
number of encrypted octets is PayloadLength - 4.

[XXX/mat: I'm trying to say use krb5_c_encrypt()
without IV set to NULL. I may be on crack here, so somebody
say something if this is wrong.]

The format of the encryption payload uses the normal [RFC1510] [KERBEROS]
semantics of prepending a crypto-specific initialization vector
and padding the entire message out to the crypto-specfic crypto-specific number
of bytes. For example, with DES-CBC, the initialization vector
will be 8 octets long, and the entire message will be padded to an
8 octet boundary. Note that KINK Encrypt payload MUST NOT include
a checksum since this is redundant with the message integrity check-
sum
checksum in the KINK header.

5.1.9. KINK_ERROR Payload

The KINK_ERROR payload type provides a protocol level mechanism of
returning an error condition. This payload should not be used for
either Kerberos generated errors, or DOI specific errors which have
their own payloads defined. The error code is a an in network order
integer. order.

Figure 15: 16: KINK_ERROR Payload

ErrorCode Number Purpose
--------- ------ -------------------
KINK_OK 0
KINK_PROTOERR 1
KINK_INVDOI 2
KINK_INVMAJ 3
KINK_INVMIN 4
KINK_INTERR 5
RESERVED 6 - 8191
Private Use 8192 - 16383

o KINK_OK - No error detected
o
KINK_PROTOERR 1 - The message was malformed
o
KINK_INVDOI 2 - Invalid DOI
o
KINK_INVMAJ 3 - Invalid Major Version
o
KINK_INVMIN 4 - Invalid Minor Version
o
KINK_INTERR 5 - An unrecoverable internal error was
detected
RESERVED 6 - 8191
Private Use 8192 - 16383

6. KINK Messages

KINK messages are either commands, replies, or acknowledgments. A
command is sent by an initiator to the respondent. A reply is sent
by the respondent to the initator. If the respondent desires confir-
mation of the reply, it sets the ACKREQ bit in the message header.
The initiator will then respond with an ACK messages. All commands,
responses and acknowledgements are bound together by the XID field of
the message header. The XID is normally a monotonically incrementing
field, and is used by the initiator to differentiate between out-
standing requests to a responder. The XID field does not provide
replay protection as that functionality is provided by Kerberos
mechanisms. In addition, commands and responses MUST use a
cryptographic hash over the entire message if the two peers share a
symmetric key via a ticket exchange.

6.1. CREATE

This message initiates an establishment of new Security
Association(s). The CREATE message must contain an AP-REQ payload and
any DOI specific payloads. The valid ISAKMP-CREATE payloads are
described in section 7.

CREATE contains the following payloads:
KINK Header
KINK_AP_REQ Payload
[KINK_ENCRYPT]
[ISAKMP-CREATE-PAYLOADS]

6.2. DELETE

This message indicates that the sending peer has deleted or will
shortly delete Security Association(s) with the other peer. The
valid ISAKMP-DELETE payloads are described in section 7.
DELETE contains the following payloads:
KINK Header (with DOI)
KINK_AP_REQ Quick Mode Payload
[KINK_ENCRYPT]
[ISAKMP-DELETE-PAYLOADS]

6.3. REPLY

The REPLY message is a generic reply which must contain either a
KINK_AP_REP or a KRB-ERROR payload. REPLY's may contain additional
DOI specific payloads such as ISAKMP payloads defined in this docu-
ment. The valid ISAKMP-REPLY payloads are described in section 7.

REPLY
KINK Header
KINK_AP_REP | KINK_KRB_ERROR Payload
[KINK_ENCRYPT]
[ KINK_ERROR ]
[ISAKMP-REPLY-PAYLOADS]

All REPLY messages must contain either a KINK_AP_REP or
KINK_KRB_ERROR. It may optionally contain a KINK_ERROR. The checksum
in the KRB-ERROR message is not used, since the KINK header already
contains a checksum field.

The server MUST return a KRB_AP_ERR_SKEW if the server clock and the
client clock are off by more than the policy-determined clock skew
limit (usually 5 minutes). The optional client's time in the KRB-
ERROR MUST be filled out, and the client MUST compute the difference
(in seconds) between the two clocks based upon the client and server
time contained in the KRB-ERROR message. The client SHOULD store
this clock difference and use it to adjust its clock in subsequent
messages.

6.4. ACK

This is an acknowledgment returned to the originator of a REPLY mes-
sage. This message MUST NOT contain any payloads beside a lone AP-REQ
header. If the initiator detects an error in the AP-REP or any other
KINK or Kerberos error, it SHOULD take remedial action by reinitiat-
ing the initial command with the appropriate error to instruct the
KINK receiver how to correct its original problem.

ACK
KINK Header
[KINK_AP_REQ]

6.5. STATUS

This is an acknowledgment returned to the originator of a REPLY mes-
sage. This message MUST NOT contain any DOI specific payloads. ACK
MAY contain both KINK_ERROR's and KRB_ERROR's. In particular, if a
command initiator found an error in the AP_REP, it MUST send an ACK
with the proper Kerberos error regardless of the state of the ACKREQ
flag of the respondent. The respondent SHOULD be prepared to receive
an unexpected ACK from the initiator. The valid ISAKMP-STATUS pay-
loads are described in section 7.

STATUS
KINK Header
[KINK_AP_REQ]
[KINK_ENCRYPT]
[ KINK_ERROR ]
[ISAKMP-STATUS-PAYLOADS]

7. IPSEC DOI-specific ISAKMP Payloads Profile

KINK directly uses IKE/ISAKMP ISAKMP payloads to negotiate security associa-
tions. In particular, KINK uses IKE phase II payload types (aka Quick
Mode). In general, there should be very few changes necessary to for an
IKE implemenation implementation to establish the security associations, and unless
there is a note to the contrary in the memo, all capabilities and
requirements in [IKE] MUST be supported. IKE Phase I payloads MUST
NOT be sent.

Unlike IKE, KINK defines specific commands for creation, deletion,
and status of security associations, mainly to facilitate predictable
SA creation/deletion (see section 4.3 and 4.4). As such, KINK places
certain restrictions on what payloads may be sent with which com-
mands, and some additional restrictions and semantics of some of the
payloads. Implementors should refer to [IKE] and [ISAKMP] for the
actual format and semantics. If a particular IKE phase II payload is
not mentioned here, it means that there are no differences in its
use.

7.1. IKE Phase II (Quick Mode) Differences

The following sections detail the differences to standard IKE phase
II payloads which must be incorporated for a complient KINK impleme-
nation.

7.1.1. Security Association Payload

6.1. General Quick Mode Differences

o The Security Association Payload header for IP is defined in
[IPDOI] section 4.6.1. For this memo, the Domain of Interpreta-
tion MUST be set to 1 (IPSec) and the Situation bitmap MUST be
set to 1 (SIT_IDENTITY_ONLY). All other fields are omitted
(because SIT_IDENTITY_ONLY is set).

o KINK also expands the semantics of IKE in that the first propo-
sal MUST be the it defines an optmis-
tic proposal which the sender of a for CREATE command is
prepared commands to receive incoming IPsec datagrams. allow SA creation to com-
plete in two messages.

o IKE quick mode Quick Mode (phase 2) uses the hash algorithm used in main
mode (phase 1) to generate the keying material. KINK MUST use
the hashing algorithm specified in the session ticket's etype.

o PFS uses the Diffie Hellman group used in KINK does not use the phase 1 exchange. HASH payload at all.

o KINK uses XXX.

7.1.2. allows the NONCE payload Nr to be optional to facilitate
optimistic keying.

6.2. Security Association Attributes Supported Payloads

KINK supports the following security association attributes from
[IPDOI]:

class value type
-------------------------------------------------
SA Life Type 1 B
SA Life Duration 2 V
Encapsulation Mode 4 B
Authentication Algorithm 5 B
Key Length 6 B
Key Rounds 7 B

Refer to [IPDOI] for the actual definitions for these attributes.

7.1.3.

6.3. Proposal and Transform Payloads

KINK directly uses the Proposal and Transform payloads with no
differences. KINK, however, places additional relevance to the first
proposal and first transform of each conjugate for optimistic keying.

6.4. Identification Payload Differences Payloads

The Identification payload carries information that is used to iden-
tify the traffic that is to be protected using the keys exchanges in
this memo. (NB: The payload name is misleading, and should really be
called the selector payload). KINK only restricts the selector ID types to the following: following values:

ID Type Value
------- -----
ID_IPV4_ADDR 1
ID_IPV4_ADDR_SUBNET 4
ID_IPV6_ADDR 5
ID_IPV6_ADDR_SUBNET 6
ID_IPV4_ADDR_RANGE 7
ID_IPV6_ADDR_RANGE 8

7.1.4.

6.5. Nonce Payloads

The Nonce payload contains random data that MUST be used in key
generation by the initiating KINK peer, and MAY be used by the
responding KINK peer. In IKE, the nonce payload also provides proof
of freshness of the exchange, but this functionality is already
provided by Kerberos' use of timestamps for liveliness. A receiving
KINK peer MUST NOT use the nonce payload as the primary freshness
indicator, though it MAY use it as an additional check.

7.1.5.

6.6. Notify Payloads

Notification information can be error messages specifying why an SA
could not be established. It can also be status data that a process
managing an SA database wishes to communicate with a peer process.
For example, a secure front end or security gateway may use the
Notify message to synchronize SA communication. The table below
lists the Notification messages and their corresponding values that
are supported in KINK.

NOTIFY MESSAGES - ERROR TYPES

Errors Value
INVALID-PAYLOAD-TYPE 1
SITUATION-NOT-SUPPORTED 3 [?]
INVALID-MAJOR-VERSION 5
INVALID-MINOR-VERSION 6
INVALID-EXCHANGE-TYPE 7
INVALID-FLAGS 8
INVALID-MESSAGE-ID 9
INVALID-PROTOCOL-ID 10
INVALID-SPI 11
INVALID-TRANSFORM-ID 12
ATTRIBUTES-NOT-SUPPORTED 13
NO-PROPOSAL-CHOSEN 14
BAD-PROPOSAL-SYNTAX 15
PAYLOAD-MALFORMED 16
INVALID-KEY-INFORMATION 17
INVALID-ID-INFORMATION 18
ADDRESS-NOTIFICATION 26
NOTIFY-SA-LIFETIME 27
UNEQUAL-PAYLOAD-LENGTHS 30
RESERVED (Future Use) 31 - 8191
Private Use 8192 - 16383

NOTIFY MESSAGES - STATUS TYPES

Status Value
CONNECTED 16384
RESERVED (Future Use) 16385 - 24575
DOI-specific codes 24576 - 32767
Private Use 32768 - 40959
RESERVED (Future Use) 40960 - 65535

7.1.6. PFS Support

6.7. Delete Payloads

KINK directly uses ISAKMP delete payloads with no changes.

6.8. KE Payloads

IKE requires that perfect forward secrecy be supported through the
use of the KE payload. However, Kerberos in general does not provide
PFS so it is somewhat questionable whether a system which is heavily
relying on Kerberos benefits from PFS. KINK retains the ability to
use PFS, but relaxes the requirement from must implement to SHOULD
implement.

7.2.

7. IPsec DOI Message Formats

7.2.1.

KINK messages are either commands, replies, or acknowledgments. A
command is sent by an initiator to the respondent. A reply is sent
by the respondent to the initiator. If the respondent desires confir-
mation of the reply, it sets the ACKREQ bit in the message header.
The ACKREQ bit MUST NOT be set by the respondent except in the lone
case of a CREATE message for which one of the security associations
did not use the optimistic payload. In that case, the ACKREQ bit MUST
be set. All commands, responses and acknowledgments are bound
together by the XID field of the message header. The XID is normally
a monotonically incrementing field, and is used by the initiator to
differentiate between outstanding requests to a responder. The XID
field does not provide replay protection as that functionality is
provided by Kerberos mechanisms. In addition, commands and responses
MUST use a cryptographic hash over the entire message if the two
peers share a symmetric key via a ticket exchange.

7.1. REPLY Message Considerations

The REPLY message is a generic reply which MUST contain either a
KINK_AP_REP, a KRB-ERROR, or KINK_ERROR payload. REPLY's MAY contain
additional DOI specific payloads such as ISAKMP payloads which are
defined in the following sections. The checksum in the KRB-ERROR
message is not used, since the KINK header already contains a check-
sum field.

7.2. ACK Message Considerations
ACK's are sent only when the ACKREQ bit is set in a REPLY message.
ACK's MUST NOT contain any payloads beside a lone AP-REQ header. If
the initiator detects an error in the AP-REP or any other KINK or
Kerberos error, it SHOULD take remedial action by reinitiating the
initial command with the appropriate error to instruct the KINK
receiver how to correct its original problem.

7.3. CREATE

This message initiates an establishment of new Security
Association(s). The CREATE message must contain an AP-REQ payload and
any DOI specific payloads.

CREATE contains the following payloads: KINK Header
KINK_AP_REQ payload
[KINK_ENCRYPT]
KINK_ISAKMP payload
SA Payload[s]
Proposal Payloads
Transform Payloads
Nonce Payload (Ni)
[KE]
[IDci, IDcr]
[Notification Payloads]

Note: KINK, like IKE allows the creation of many security
associations in one create command. If any of the optimistic creation
mode proposals is not chosen by the respondent, it MUST request an
ACK.

Replies are of the following forms:

REPLY KINK Header
KINK_AP_REP payload
[KINK_ENCRYPT]
KINK_ISAKMP payload
SA Payload[s]
Proposal Payload
Transform Payload
[ Nonce Payload (Nr)]
[IDci, IDcr]
[Notification Payloads]

Note that there MUST be at least a single proposal payload and a
single transform payload in REPLY messages. Also: unlike IKE, the
Nonce Payload Nr is not required, and its absense absence means that the
optimistic mode SA's installed by the initiator are valid. If any of
the first proposals are not chosen by the recipient, it MUST include
the nonce payload as well to indicate that the initiator's outgoing
SA's must be modified.

KINK, like IKE allows the creation of many security associations in
one create command. If any of the optimistic creation mode proposals
is not chosen by the respondent, it MUST request an ACK.

If an IPspec DOI specific error is encountered, the respondent must
reply with a Notify payload describing the error:

REPLY KINK Header
KINK_AP_REP payload
[KINK_ENCRYPT]
[ KINK_ERROR payload ]
[KINK_ERROR]
KINK_ISAKMP payload
[Notification Payloads]

If the respondent finds a Kerberos error for which it can produce a
valid authenticator, the REPLY takes the following form:

REPLY KINK Header
KINK_AP_REP
[KINK_ENCRYPT]
KINK_KRB_ERROR

Finally, if the respondent finds an a Kerberos or KINK type of error it
which it cannot create a AP-REP for, MUST reply with a lone
KINK_KRB_ERROR or KINK_ERROR payload:

REPLY KINK Header
KINK_KRB_ERROR|KINK_ERROR payload

7.2.2.
[KINK_KRB_ERROR]
[KINK_ERROR]

7.4. DELETE

This message indicates that the sending peer has deleted or will
shortly delete Security Association(s) with the other peer.

DELETE contains the following payloads: KINK Header
KINK_AP_REQ payload
[KINK_ENCRYPT]
[ KINK_ERROR payload ]
KINK_ISAKMP payload
Delete Payload[s]
[Notification Payloads]

There are three forms of replies for a DELETE. The normal form is:

REPLY KINK Header
KINK_AP_REP payload
[KINK_ENCRYPT]
[ KINK_ERROR payload ]
KINK_ISAKMP payload
Delete Payload[s]
[Notification Payloads]

If an IPspec IPsec DOI specific error is encountered, the respondent must
reply with a Notify payload describing the error:

REPLY KINK Header
KINK_AP_REP payload
[ KINK_ENCRYPT payload ]
[ KINK_ERROR payload ]
KINK_ISAKMP payload
[Notification Payloads]

If the respondent finds a Kerberos error for which it can produce a
valid authenticator, the REPLY takes the following form:

REPLY KINK Header
KINK_AP_REP
[KINK_ENCRYPT]
KINK_KRB_ERROR

If the respondent finds a KINK or Kerberos type of error it MUST
reply with a lone KINK_KRB_ERROR or KINK_ERROR payload:

REPLY KINK Header
KRB_ERROR | KINK_KRB_ERROR payload

7.2.3.
[KRB_ERROR]
[KINK_KRB_ERROR]

7.5. STATUS

This

The STATUS command is used in two ways:

1) As a means to relay an ISAKMP Notification message indicates that the sending

2) As a means of probing a peer whether its epoch has deleted or will
shortly delete Security Association(s) with the other peer. changed for
dead peer detection.

STATUS contains the following payloads:
KINK Header
KINK_AP_REQ payload
[ [KINK_ENCRYPT]
[ KINK_ERROR payload ]
KINK_ISAKMP payload
[Notification Payloads] ]

There are three two forms of replies for a STATUS. The normal form is:

REPLY KINK Header
KINK_AP_REP payload
[KINK_ENCRYPT]
[ KINK_ERROR payload ] [KINK_ENCRYPT]
[KINK_ERROR]
KINK_ISAKMP payload
[Notification Payloads] ]

If an IPspec DOI specific error is encountered, the respondent must
reply with finds a Notify payload describing Kerberos error for which it can produce a
valid authenticator, the error: REPLY takes the following form:

REPLY KINK Header
KINK_AP_REP payload
[ KINK_ENCRYPT payload ]
[ KINK_ERROR payload ]
KINK_ISAKMP payload [Notification Payloads]
[KINK_ENCRYPT]
KINK_KRB_ERROR

If the respondent finds a KINK or Kerberos type of error it MUST
reply with a lone KINK_KRB_ERROR or KINK_ERROR payload:

REPLY
KINK Header
KRB_ERROR | KINK_KRB_ERROR payload
[KRB_ERROR]
[KINK_KRB_ERROR]

8. Key Derivation

KINK uses the same key derivation mechanisms that [IKE] uses in sec-
tion 5.5, which is:

KEYMAT = prf(SKEYID_d, protocol | SPI | Ni_b [ | Nr_b])

The following differences apply:

o SKEYID_d is the session key in the Kerberos service ticket from
the AP-REQ.

o Nr_b is optional

By optional, it is meant that the equivalent of a zero length
nonce was supplied.

9. Transport Considerations

KINK uses UDP on port XXX [XXX -- TBA by IANA] to transport its messages.
There is one timer T which SHOULD take into consideration round trip considera-
tions
considerations and MUST implement a truncated exponential backoff
mechanism. The state machines machine is simple: any message which expects a
response
must MUST retransmit the request using timer T. Since Kerberos
requires that messages be retransmitted with new times for replay
protection, the message must MUST be recreated each time including the
checksum of the message.

Note that in KINK delivery of Both commands and replies with the ACKREQ
bit set are kept on retransmit timers. When a final ACK is not reliable. A KINK
implementation that asks for initiator receives
a final ACK REPLY with the ACKREQ bit set, it MUST be prepared for retain the ACK
not being delivered. Two mechanisms are possible ability to work around regen-
erate the
need ACK message for the transaction for a final ACK:

1) A timer minimum of the average round trip time between the two KINK
peers times some comfort margin can be started. If the ACK is
not received within that time period, the requestor can assume
that either its response was lost by the initiator, a full
retransmission timeout cycle or until it notices that packets have
arrived on the
ACK was lost. In the first case, the initiator will usually
retransmit the initial request within the timeout period. In the
second case, the final cleanup should be performed as if the
initiator sent the ACK.

2) If reliability is required, the respondent could initiate newly constructed SA, whichever comes first.

When a
security association in KINK peer retransmits a message, it MUST create a new Kerberos
authenticator for the opposite direction with AP-REQ so that the same
characteristics. peer can differentiate
between replays and dropped packets. This has results in a potential race
condition when a retransmission occurs before an in-flight reply is
received/processed. To counter this race condition, the downside retransmit-
ting party SHOULD keep a list of instantiating two
security associations simultaneously and is not recommended. valid authenticators which are out-
standing for any particular transaction.

10. Security Considerations

KINK cobbles together and reuses many parts of both Kerberos and IKE,
the latter which in turn is cobbled together from many other memos.
As such, KINK inherits many of the weaknesses and considerations of
each of its components. However, KINK only uses only IKE Phase II payload payloads
to create and delete security association, associations, the security considera-
tions which pertain to IKE Phase I can may be safely ignored.

KINK's use of Kerberos presents a couple of considerations. First,
KINK explicitly expects that the KDC will provide adequate entropy
when it generates session keys. Second, Kerberos normally being is used as a user
authentication vehicle allows for potentially weak user and key-
tab keys which in turn can be protocol with the weak link in subsequently generated
IPsec security associations. possibility of dictionary attacks on
user passwords. This memo does not describe a particular method to
avoid these pitfalls, but recommends that suitable randomly generated
keys be used for the service principals and client princi-
pals such as using the -randomkey
option with MIT's "kadmin addprinc"
command. command as well as for clients
when that is practical.

Kerberos itself does not provide for perfect forward secrecy which
makes KINK's reliance on the IKE ability to do PFS somewhat suspect
from an overall system's standpoint. In isolation KINK itself should
be secure from offline analysis from compromised principal
passphrases if PFS is used, but the existence of other Kerberized
service which do not provide PFS makes this a less than optimal
situation on the whole.

11. IANA Considerations

KINK requires that a new well known port UDP be created. Since KINK
uses standard message types from [IKE], KINK does not require any new
registries. Any new DOI's, ISAKMP types, etc for future versions of
KINK MUST use the registries defined for [IKE].

12. Protocol Considerations

12.1.

10.1. Security Policy Database Considerations

KINK leaves the population of the IPsec security policy database out
of scope. There are, however, considerations which should be pointed
out. Firstly, First, even though when and when not to initiate a user to user
flow is left to the discretion of the KINK implemention, implementation, a Ker-
beros Kerberos
client which initially authenticated using a symmetric key SHOULD NOT
use a user-user flow if the respondent is also in the same realm.

Likewise, a KINK initiator which authenticated in a public key realm
SHOULD use a user-user flow if the respondent is in the same realm.

KINK does not define the cross realm behavior.

At a minimum a the security policy database for a KINK implementation
SHOULD contain a logical record of the KDC to contact, principal name
for the respon-
dent, respondent, and whether the KINK implementation should use a
direct AP-
REQ/AP-REP AP-REQ/AP-REP flow, or a User-User flow to CREATE/DELETE the
security association.

That said, there is considerable room for improvement on how a KINK
initiator could auto-discover how a respondent in a different realm
initially authenticated. This is left as an implementation detail as
well as the subject of possible future standardization efforts which
are outside of the scope of the KINK working group.

13.

11. IANA Considerations

KINK requires that a new well known system port for UDP be created.
Since KINK uses standard message types from [IKE], KINK does not
require any new registries. Any new DOI's, ISAKMP types, etc for
future versions of KINK MUST use the registries defined for [IKE].

12. Related Work

The IPsec working group has defined a number of protocols that pro-
vide the ability to create and maintain cryptographically secure
security associations at layer three (ie, the IP layer). This effort
has produced two distinct protocols:

o a mechanism for encrypting and authenticating IP datagram
payloads which assumes a shared secret between the sender and
receiver

o a mechanism for IPsec peers to perform mutual authentication
and exchange keying material

The IPsec working group has defined a peer to peer authentication and
keying mechanism, IKE (RFC 2409). One of the drawbacks of a peer to
peer protocol is that each peer must know and implement a site's
security policy which in practice can be quite complex. In addition,
the peer to peer nature of IKE requires the use of Diffie Hellman
(DH) to establish a shared secret. DH, unfortunately, is computation-
ally quite expensive and prone to denial of service attacks. IKE also
relies on X.509 certificates to realize scalable authentication of
peers. Digital signatures are also computationally expensive and cer-
tificate based trust models are difficult to deploy in practice.
While IKE does allow for pre-shared symmetric keys, key distribution
is required between all peers -- an O(n2) problem -- which is prob-
lematic for large deployments.

14.

13. References

[RFC1510]

[KERBEROS]
J. Kohl, C. Neuman. The Kerberos Network Authentication Service
(V5). Request for Comments 1510.

[KERB]B.C. Neuman, Theodore Ts'o. Kerberos: An Authentication Service
for Computer Networks, IEEE Communications, 32(9):33-38. Sep-
tember 1994.

[PKINIT]
B. Tung, C. Neuman, M. Hur, A. Medvinsky, S.Medvinsky, J. Wray,
J. Trostle. Public Key Cryptography for Initial Authentication
in Kerberos. draft-ietf-cat-kerberos-pk-init-11.txt

[PKCROSS]
M.Hur, B. Tung, T. Ryutov, C. Neuman, G. Tsudik, A. Medvinsky,
B. Sommerfeld. Public Key Cryptography for Cross-Realm Authen-
tication in Kerberos. draft-ietf-cat-kerberos-pk-cross-06.txt

[RFC2401]

[IPSEC]
S. Kent, R. Atkinson. Security Architecture for the Internet
Protocol. Request for Comments 2401.

[IKE]D. Harkins, D. Carrel. The Internet Key Exchange (IKE).
Request for Comments 2409.

[ISAKMP]
Maughhan, D., Schertler, M., Schneider, M., and J. Turner,
"Internet Security Association and Key Management Protocol
(ISAKMP)", RFC 2408, November 1998.

[IPDOI]
Piper, D., "The Internet IP Security Domain Of Interpretation
for ISAKMP", RFC 2407, November 1998.

15.

[RFC2412]
Orman, H., "The OAKLEY Key Determination Protocol", RFC 2412,
November 1998.

[RFC793]
Postel, J., "Transmission Control Protocol", RFC 793, Sep-01-
1981

14. Mailing List

Please send comments to the KINK mailing list (ietf-kink@vpnc.org).
You can subscribe by sending mail to ietf-kink-request@vpnc.org with
a line in the body of the mail with the word SUBSCRIBE in it.

16.

15. Author's Addresses

Mike Froh
CyberSafe Corporation
180 Elgin Street
Ottawa, Ontario K2P 2K3
Phone: +1 613 234 7300
E-mail: mike.froh@cybersafe.com

Matthew Hur
David McGrew
Mike
Michael Thomas
Jan Vilhuber
Matthew Hur
Cisco Systems
170 West Tasman Drive
San Jose, CA 95134
E-mail: {mcgrew,mat,mhur,vilhuber}@cisco.com

Sasha Medvinsky
Motorola
6450 Sequence Drive
San Diego, CA 92121
+1 858 404 2367
E-mail: smedvinsky@gi.com

17. Acknowledgements

16. Acknowledgments

Many have contributed to the KINK effort, including our working group
chairs Derek Atkins and Jonathan Trostle. The original inspiration
came from Cablelab's Packetcable effort which defined a simplifed
version of Kerberized IPsec. The inspiration for wholly reusing IKE
Phase II is the result of the Tero Kivinen's initial draft suggesting
the obvious.