INTERNET-DRAFT KINK M. Froh Cybersafe M. Hur Cybersafe D. McGrew Cisco S. Medvinsky Motorola M. Thomas Cisco J. Vilhuber Cisco September 2000 Kerberized Internet Negotiation of Keys (KINK) draft-ietf-kink-kink-00.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 working documents as Internet-Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. Action Items: Need to come to agreement on whether ACK is a MUST when respondent changes cipher suite, keys, etc. Need to determine whether a "stateful" mode is useful. Better discussion of error scenarios Copyright Notice Copyright (C) The Internet Society (2000). All Rights Reserved. Abstract The KINK Working Group will create a standards track protocol to Froh, Hur, McGrew, Medvinsky, Thomas, Vilhuber [Page 1] INTERNET DRAFT KINK September 2000 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 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 security associations as defined in RFC 2401. Future version of the KINK protocol may define new objects and Domains of Interpretation to extend KINK to be suitable for keying other kinds of applications. 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. 1 Introduction KINK is designed to provide a secure, scalable mechanism for establishing 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 the capability to establish SAs in two messages with minimal computational effort. Kerberos [KERB] and [RFC1510] provides an efficient mechanism for trusted third party authentication for clients and servers. (Kerberos also provides an efficient mechanism for inter-realm authentication [PKCROSS].) Clients obtain tickets (a ticket is a symmetric key certificate) from an online authentication server (the Key Distribution Center or KDC). Tickets are used to construct credentials for authenticating the client to the server. As a result of this authentication, the client and the server share a secret (a key, generated by the KDC, that is encrypted within the ticket). The central key management provided by Kerberos is efficient, because it limits computational cost and limits complexity. Initial authentication to the KDC may be performed using either symmetric or asymmetric keys [PKINIT]; however, subsequent requests for tickets utilize symmetric cryptography, which is much more efficient than public key cryptography. Therefore, public key operations are limited and are amortized over the lifetime of the Kerberos tickets. For example, a server may use a single public key exchange with the KDC to efficiently establish multiple security associations with other servers. Since Kerberos principal keys (used for initial asymmetric authentication) are stored in the KDC, the number of Froh, Hur, McGrew, Medvinsky, Thomas, Vilhuber [Page 2] INTERNET DRAFT KINK September 2000 principal keys is order of magnitude O(n) rather than O(n^2), as would be required for a pre-shared key type of solution. This document specifies the Kerberized Internet Negotiation of Keys Protocol and its use to establish and maintain IPsec Security Associations [RFC2401]. KINK could be used to maintain Security Associations 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 alternative to requiring each application having its own method of transporting 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 protocol and also defines a domain of interpretation to establish and maintain IPsec security associations. Any other domains of interpretation must be defined separately. The protocol takes full advantage of the features of RFC 2401 but in the context of a centralized keying authority. 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 authenticator (which proves freshness and knowledge of the key within the ticket) creates an authentication credential. Key Distribution Center (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 Froh, Hur, McGrew, Medvinsky, Thomas, Vilhuber [Page 3] INTERNET DRAFT KINK September 2000 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 a protocol (KINK) that allows two peers to directly establish symmetric keys, where one peer has already obtained an authentication credential for the other peer from a trusted third party known as the Kerberos KDC (Key Distribution Center). An authentication credential for a server obtained from the KDC is known as the Kerberos service ticket. The use of Kerberos tickets minimizes the amount of state that is required for this key management protocol. It is possible for only one of the peers to save Kerberos tickets, while the other peer can remain completely stateless. KINK uses this property to allow message exchanges to be stateless. That is, a secure session is not required to exchange KINK messages as each message contains all of the information required to authenticate the message. This is in contrast to IKE [IKE] which requires a phase 1 security association to be created and maintained in order to create subsequent security associations. Kerberos tickets utilize only symmetric key cryptography with relatively small overhead required to process them (as compared to public key-based protocols). However, an authentication mechanism that is utilized between a KDC client and the KDC can be either symmetric key based (as specified by the base Kerberos protocol [RFC1510]) or public key based (as specified by PKINIT [PKINIT]). KINK hosts are peers in the IPsec sense of the meaning that a KINK host can initiate or respond to KINK commands. Messages come in three varieties: commands, replies, and acknowledgments. In most circumstances, a KINK security association can be installed in two messages: a command and a reply. The method here is to use an "optimistic" algorithm where negotiation proposals are prioritized and the top choice is installed in the security association database. If for some reason the respondent does not choose the first proposal, the respondent may choose another but at the cost of a ACK message so that it can be guaranteed of delivery. Since the KDC does not possess a symmetric key PKINIT principals KINK defines an unauthenticated request for getting a peer's ticket granting ticket. This allows KINK peers to request a User to User service ticket. Upon receipt of the User to User service ticket, all messages exchanges are identical. Discovery issues are discussed in section KINK is intended as a generic key management protocol based on Kerberos tickets. It can be used to provide key management for any security layer above level 2 in the Internet protocol stack, including application-layer security. This document includes an IPSec DOI (Domain of Interpretation) that enables KINK to be used directly as an IPSec key management protocol. Other DOI Froh, Hur, McGrew, Medvinsky, Thomas, Vilhuber [Page 4] INTERNET DRAFT KINK September 2000 specifications may be used to apply KINK to other security protocols. 4 Message Flows KINK message flows all follow the same pattern between the two peers: a command, a response and an optional acknowledgement. The actual Kerberos KDC traffic here is for illustrative purposes only. In practice, when a principal obtains various tickets is a subject of 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 service ticket for the respondent (ie, B is a PKINIT principal), it must 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 Froh, Hur, McGrew, Medvinsky, Thomas, Vilhuber [Page 5] INTERNET DRAFT KINK September 2000 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. A B KDC ------ ------ --- A creates initial inbound SA 1 CREATE+ISAKMP------------> B creates inbound SA to A. If it chooses A's first proposal, it creates the outbound SA as well. 2 <------------REPLY+ISAKMP A creates outbound SA and modifies inbound SA if first choice wasn't acceptible. 3 [ ACK--------------------> ] [ B creates the outbound SA to 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 database from B->A with the first proposal in the ISAKMP proposal. It is then ready to receive any messages from B. A then sends the CREATE message to B. B instantiates a security association in its database from A->B. If it agreed to A's initial proposal sends a REPLY to A without requesting an ACK and also instantiates the security association from B->A. If B does not choose the first proposal, it sends the actual choice in the REPLY and requests that the REPLY be acknowledged. Upon receipt of the REPLY, A modifies the inbound security 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. 4.3.1 CREATE Key Derivation Considerations The CREATE command's optimistic approach allows a security association 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 circumstances 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 Froh, Hur, McGrew, Medvinsky, Thomas, Vilhuber [Page 6] INTERNET DRAFT KINK September 2000 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 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 acknowledgment 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 MUST NOT delete its incoming SA until it either receives the final ACK, or the transaction times out. A final race condition with DELETE exists. Packets in flight while the DELETE operation is taking place may, due to network reording, etc, arrive after the diagrams above recommend deleting the incoming security association. A KINK implementation MUST implement a grace timer which SHOULD be set to a period of two times the average round trip time, or to a configurable value. A KINK implementation 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. Froh, Hur, McGrew, Medvinsky, Thomas, Vilhuber [Page 7] INTERNET DRAFT KINK September 2000 4.4.1 Rekeying Security Associations KINK requires the initiator of a security association to be responsible for rekeying a security association. The reason is twofold: we would like to prevent needless duplication of security associations as the result of collisions due to an initiator and respondent both trying 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 probably advantageous for servers to wait for clients to initiate sessions so that they do not need 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 DETETE'ing the old security association or letting it just time out. When identical flow selectors are available on different security associations, KINK implementations SHOULD chose the security association most recently created. 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 | Flags | NextPayload | +---------------+---------------+-------------------------------+ | | ~ Cksum ~ | | +-------------------------------+-------------------------------+ | | ~ A series of payloads ~ | | +-------------------------------+-------------------------------+ Figure 5: Format of a KINK message Fields: o Type (1 octet) - The type of message of this packet Froh, Hur, McGrew, Medvinsky, Thomas, Vilhuber [Page 8] INTERNET DRAFT KINK September 2000 Type Value ----- ----- RESERVED 0 CREATE 1 DELETE 2 REPLY 3 GETTGT 4 ACK 5 o MjVer (4 bits) - Major protocol version number. This MUST be set to 1. PacketCable IPSec key management MUST set this to 0. o MnVer (4 bits) - Minor protocol version number. This MUST be set to 0. o Length (16 bits) - Length of the message in octets 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. 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. o Flags (8 bits) bit 1: ACKREQ - ACK Request. Set to one if the responder desires an explicit acknowledgement that a REPLY was received. An initiator MUST NOT set this flag. bits 2-8: RSV - Reserved o NextPayload (1 octet)- Indicates the type of the first payload after the message header o Cksum (variable) - Keyed checksum (HMAC) over the entire message. This field MUST always be present whenever a key is available. 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 Froh, Hur, McGrew, Medvinsky, Thomas, Vilhuber [Page 9] INTERNET DRAFT KINK September 2000 as specified in the etype for the Kerberos session key in the Ker- beros ticket. If the etype does not specify a hash algorithm, the SHA1 MUST be used. The format of the Cksum field MUST mimic the Kerberos checksum structure (without the ASN.1 encoding) as fol- lows: 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 +---------------+---------------+---------------+---------------+ | Kerberos cksumtype | checksum (variable) | +---------------+---------------+---------------+---------------+ Figure 6: KINK Checksum 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. 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 +---------------+---------------+---------------+---------------+ | Next Payload | RESERVED | Payload Length | +---------------+---------------+---------------+---------------+ | value (variable) | +---------------+---------------+---------------+---------------+ Figure 7: Format of a KINK payload Fields: o NextPayload (2 octets) - The type of the next payload NextPayload Number ---- ------ KINK_DONE 0 KRB_AP_REQ 1 KRB_AP_REP 2 KRB_ERROR 3 KRB_TGT_REQ 4 KRB_TGT_REP 5 ISAKMP_PAYLOAD 6 KINK_ENCRYPT 7 KINK_ERROR 8 Froh, Hur, McGrew, Medvinsky, Thomas, Vilhuber [Page 10] INTERNET DRAFT KINK September 2000 NextPayload type KINK_DONE denotes that the current payload is the final payload in the message. 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 field is depends on the Type. 5.1.1 KRB_AP_REQ Payload The value field of this payload contains a raw Kerberos KRB_AP_REQ. 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 +---------------+---------------+---------------+---------------+ | Next Payload | RESERVED | Payload Length | +---------------+---------------+---------------+---------------+ | | ~ AP_REQ ~ | | +---------------------------------------------------------------+ Figure 8: KRB_AP_REQ Payload 5.1.2 KRB_AP_REP Payload The value field of this payload contains a raw Kerberos KRB_AP_REP. 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 +---------------+---------------+---------------+---------------+ | Next Payload | RESERVED | Payload Length | +---------------+---------------+---------------+---------------+ | | ~ AP_REP ~ | | +---------------------------------------------------------------+ Figure 9: KRB_AP_REP Payload Froh, Hur, McGrew, Medvinsky, Thomas, Vilhuber [Page 11] INTERNET DRAFT KINK September 2000 5.1.3 KRB_ERROR Payload The value field of this payload contains a raw Kerberos KRB_ERROR. 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 +---------------+---------------+---------------+---------------+ | Next Payload | RESERVED | Payload Length | +---------------+---------------+---------------+---------------+ | | ~ KRB_ERROR ~ | | +---------------------------------------------------------------+ Figure 10: KRB_ERROR Payload 5.1.4 KRB_TGT_REQ Payload The value field of this payload has the following format: 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 +---------------+---------------+---------------+---------------+ | Next Payload | RESERVED | Payload Length | +---------------+---------------+---------------+---------------+ | RealmNameLen | RealmName (variable) ~ +---------------+---------------+---------------+---------------+ | | ~ RealmName(variable) ~ | | +---------------------------------------------------------------+ Figure 11: KRB_TGT_REQ Payload Fields: o PrincipalNameLen - The length of the realm name that follows o RealmName - The realm name that the responder should return a TGT for. If the responder is unable to get a TGT for the domain, it must reply with a KRB_ERROR payload type. Froh, Hur, McGrew, Medvinsky, Thomas, Vilhuber [Page 12] INTERNET DRAFT KINK September 2000 5.1.5 KRB_TGT_REP Payload The value field of this payload contains the TGT requested in a previous KRB_TGT_REP command. 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 +---------------+---------------+---------------+---------------+ | Next Payload | RESERVED | Payload Length | +---------------+---------------+---------------+---------------+ | RealmNameLen | RealmName (variable) ~ +---------------+---------------+---------------+---------------+ | | ~ RealmName(variable) ~ | | +---------------------------------------------------------------+ | | ~ TGT ~ | | +---------------------------------------------------------------+ Figure 12: KRB_TGT_REQ Payload Fields: o RealmNameLen - The length of the realm name that follows o RealmName - The realm that the initiator requested a TGT for. o TGT - the DER encoded TGT of the responder 5.1.6 ISAKMP_PAYLOAD The value field of this payload has the following format: 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 +---------------+---------------+---------------+---------------+ | Next Payload | RESERVED | Payload Length | +---------------+---------------+---------------+---------------+ | InnerNextPload| RESERVED | +---------------+---------------+---------------+---------------+ | Payload (variable) | +---------------+---------------+---------------+---------------+ Figure 13: ISAKMP_PAYLOAD Payload Fields: o InnerNextPload (variable) - First payload type of the inner series of Froh, Hur, McGrew, Medvinsky, Thomas, Vilhuber [Page 13] INTERNET DRAFT KINK September 2000 ISAKMP payloads. 5.1.7 KINK_ENCRYPT The KINK_ENCRYPT payload encapsulates other payloads and is encrypted using the encyption algorithm specified by the etype of the session key. This payload MUST be the final payload in the message. 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 +---------------+---------------+---------------+---------------+ | Next Payload | RESERVED | Payload Length | +---------------+---------------+---------------+---------------+ | InnerNextPload| RESERVED | +---------------+---------------+---------------+---------------+ | Payload (variable) | +---------------+---------------+---------------+---------------+ Figure 14: KINK_ENCRYPT Payload Fields: o InnerNextPload (variable) - First payload type of the inner series of encrypted KINK payloads. 5.1.8 KINK_ERROR 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 network order integer. 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 +---------------+---------------+---------------+---------------+ | Next Payload | RESERVED | Payload Length | +---------------+---------------+---------------+---------------+ | ErrorCode | +---------------+---------------+---------------+---------------+ Figure 15: KINK_ERROR Payload ErrorCode Number --------- ------ KINK_OK 0 KINK_PROTOERR 1 KINK_INVDOI 2 KINK_INVMAJ 3 KINK_INVMIN 4 Froh, Hur, McGrew, Medvinsky, Thomas, Vilhuber [Page 14] INTERNET DRAFT KINK September 2000 RESERVED 5 - 8191 Private Use 8192 - 16383 o KINK_OK - No error detected o KINK_PROTOERR - The message was malformed o KINK_INVDOI - Invalid DOI o KINK_INVMAJ - Invalid Major Version o KINK_INVMIN - Invalid Minor Version 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 crypto- graphic hash over the entire message if the two peers share a sym- metric 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. CREATE contains the following payloads: KINK Header KRB_AP_REQ Payload [KINK_ENCRYPT] [CREATE-PAYLOADS] 6.3 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 (with DOI) KRB_AP_REQ Payload [KINK_ENCRYPT] [DELETE-PAYLOADS] 6.4 REPLY The REPLY message is a generic reply which must contain either a KRB_AP_REP or a KRB-ERROR payload. REPLY's may contain additional DOI specific payloads such as ISAKMP payloads defined in this document. Froh, Hur, McGrew, Medvinsky, Thomas, Vilhuber [Page 15] INTERNET DRAFT KINK September 2000 REPLY KINK Header KRB_AP_REP | KRB_ERROR Payload [KINK_ENCRYPT] [ KINK_ERROR ] [REPLY-PAYLOADS] All REPLY messages must contain either a KRB_AP_REP or 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 check- sum 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. 6.5 ACK 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. ACK KINK Header [KRB_AP_REQ] [KINK_ERROR] [KRB_ERROR] 7 IPSEC DOI-specific Payload Formats These payloads follow the conventions and values established by [ISAKMP]. In other words, each payload has a generic, well- established header. Only certain payloads will be reused from [ISAKMP], however. The rest of ISAKMP will not be used, since Ker- beros provides the equivalent functionality. Only the payloads listed in this document will be valid for KINK. Froh, Hur, McGrew, Medvinsky, Thomas, Vilhuber [Page 16] INTERNET DRAFT KINK September 2000 7.1 Security Association Payload When using the IP Domain of Interpretation, the protocol, transform identifiers, and Security association Identifiers from section 4.4 in [IPDOI] MUST be used. 7.1.1 Security Association Payload Format The Security Association Payload header for IP is defined in [IPDOI] section 4.6.1. For this memo, the Domain of Interpretation 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). Given this restriction, the Security Association Payload looks like this: 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 +---------------+---------------+---------------+---------------+ ! Next Payload ! RESERVED ! Payload Length ! +---------------+---------------+---------------+---------------+ ! Domain of Interpretation (IPSec) | +---------------+---------------+---------------+---------------+ ! Situation ! +---------------+---------------+---------------+---------------+ ! ! ~ List of Proposal Payloads ~ ! ! +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 16: Security Association Payload Format Froh, Hur, McGrew, Medvinsky, Thomas, Vilhuber [Page 17] INTERNET DRAFT KINK September 2000 7.1.2 Proposal Payload Format Immediately following the Security Association payload header is a proposal payload header, as defined in [ISAKMP], section 3.6 (which in turn contains transform payloads, which contains a set of attributes as defined in [ISAKMP], section 3.3. 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 +---------------+---------------+---------------+---------------+ ! Next Payload ! RESERVED ! Payload Length ! +---------------+---------------+---------------+---------------+ ! Proposal # ! Protocol-Id ! SPI Size !# of Transforms! +---------------+---------------+---------------+---------------+ ! SPI (variable) ! +---------------+---------------+---------------+---------------+ ! ! ~ List of Transform Payloads ~ ! ! +---------------+---------------+---------------+---------------+ Figure 17: Proposal Payload Format 7.1.3 Transform Payload Format 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 +---------------+---------------+---------------+---------------+ ! Next Payload ! RESERVED ! Payload Length ! +---------------+---------------+---------------+---------------+ ! Transform # ! Transform-Id ! RESERVED2 ! +---------------+---------------+---------------+---------------+ ! ! ~ List of SA Attributes ~ ! ! +---------------+---------------+---------------+---------------+ Figure 18: Transform Payload Format Froh, Hur, McGrew, Medvinsky, Thomas, Vilhuber [Page 18] INTERNET DRAFT KINK September 2000 7.1.4 Security Association Attributes 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. 7.2 Identification Payloads The Identification payload carries information that is used to identify 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). 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ! Next Payload ! RESERVED ! Payload Length ! +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ! ID Type ! DOI Specific ID Data ! +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~ Identification Data ~ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 19: Identification Payload Format The Identification Payload fields are defined as follows: o Next Payload (1 octet) - Identifier for the payload type of the next payload in the message. If the current payload is the last in the message, then this field will be 0. o RESERVED (1 octet) - Unused, set to 0. o Payload Length (2 octets) - Length in octets of the current payload, including the generic payload header. o ID Type (1 octet) - Specifies the type of Identification being used. This field is DOI-dependent. o DOI Specific ID Data (3 octets) - Contains DOI specific Identifica- tion data. If unused, then this field MUST be set to 0. Froh, Hur, McGrew, Medvinsky, Thomas, Vilhuber [Page 19] INTERNET DRAFT KINK September 2000 or IP DOI, this field has the following format: +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ! Protocol ID ! Port ! +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ o Identification Data (variable length) - Contains identity informa- tion. The values for this field are DOI-specific and the format is specified by the ID Type field. Specific details for the IETF IP Security DOI Identification Data are detailed in [IPDOI]. Valid ID-types for KINK are: ID TypeValue ------------ 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 Traffic selection is very Domain of Interpretation specific, so the contents of ID's MUST depend on the DOI present in SA. 7.3 Nonce Payloads The Nonce payload contains random data that SHOULD be used in key generation by both sides. It also provides freshness of the exchange, in addition to whatever freshness/replay-protection mechanisms the transport mechanism may provide. 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ! Next Payload ! RESERVED ! Payload Length ! +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ! ! ~ Nonce Data ~ ! ! +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 20: Nonce Payload Format The Nonce Payload fields are defined as follows: o Next Payload (1 octet) - Identifier for the payload type of the next payload in the message. If the current payload is the last in the message, then this field will be 0. o RESERVED (1 octet) - Unused, set to 0. Froh, Hur, McGrew, Medvinsky, Thomas, Vilhuber [Page 20] INTERNET DRAFT KINK September 2000 o Payload Length (2 octets) - Length in octets of the current payload, including the generic payload header. o Nonce Data (variable length) - Contains the random data generated by the transmitting entity. 7.4 Delete Payloads 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ! Next Payload ! RESERVED ! Payload Length ! +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ! Domain of Interpretation (DOI) ! +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ! Protocol-Id ! SPI Size ! # of SPIs ! +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ! ! ~ Security Parameter Index(es) (SPI) ~ ! ! +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 21: Delete Payload Format For IPSec, the Delete will always refer to a specific connection, and therefore a specific SPI. The DOI field must therefore always be set to 1 (IP DOI), and the protocol and SPI fields will be set to the protocol and SPI this deletion pertains to. Froh, Hur, McGrew, Medvinsky, Thomas, Vilhuber [Page 21] INTERNET DRAFT KINK September 2000 7.4 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. Values in the Private Use range are expected to be DOI-specific values. 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ! Next Payload ! RESERVED ! Payload Length ! +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ! Domain of Interpretation (DOI) ! +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ! Protocol-ID ! SPI Size ! Notify Message Type ! +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ! ! ~ Security Parameter Index (SPI) ~ ! ! +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ! ! ~ Notification Data ~ ! ! +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 22: Notification Payload Format The Notification Payload fields are defined as follows: o Next Payload (1 octet) - Identifier for the payload type of the next payload in the message. If the current payload is the last in the message, then this field will be 0. o RESERVED (1 octet) - Unused, set to 0. o Payload Length (2 octets) - Length in octets of the current payload, including the generic payload header. o Domain of Interpretation (4 octets) - Identifies the DOI (as described in Section 2.1) under which this notification is taking place. For ISAKMP this value is zero (0) and for the IPSEC DOI it is one (1). Other DOI's can be defined using the description in appen- dix B. o Protocol-Id (1 octet) - Specifies the protocol identifier for the current notification. Examples might include ISAKMP, IPSEC ESP, IPSEC AH, OSPF, TLS, etc. o SPI Size (1 octet) - Length in octets of the SPI as defined by the Froh, Hur, McGrew, Medvinsky, Thomas, Vilhuber [Page 22] INTERNET DRAFT KINK September 2000 Protocol-Id. In the case of ISAKMP, the Initiator and Responder cookie pair from the ISAKMP Header is the ISAKMP SPI, therefore, the SPI Size is irrelevant and MAY be from zero (0) to sixteen (16). If the SPI Size is non-zero, the content of the SPI field MUST be ignored. The Domain of Interpretation (DOI) will dictate the SPI Size for other protocols. o Notify Message Type (2 octets) - Specifies the type of notification message (see section 3.14.1). Additional text, if specified by the DOI, is placed in the Notification Data field. o SPI (variable length) - Security Parameter Index. The receiving entity's SPI. The use of the SPI field is described in section 2.4 of [ISAKMP]. The length of this field is determined by the SPI Size field and is not necessarily aligned to a 4 octet boundary. o Notification Data (variable length) - Informational or error data transmitted in addition to the Notify Message Type. Values for this field are DOI-specific. The following Notify Types are taken directly from [ISAKMP] with unsupported values removed. 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 Froh, Hur, McGrew, Medvinsky, Thomas, Vilhuber [Page 23] INTERNET DRAFT KINK September 2000 Private Use 32768 - 40959 RESERVED (Future Use) 40960 - 65535 8 IPsec DOI Message Formats 8.1 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. CREATE contains the following payloads: KINK Header KRB_AP_REQ payload [KINK_ENCRYPT] ISAKMP_PAYLOAD payload SA Payload Proposal Payloads Transform Payloads Nonce Payload [ ID Payloads ] Replies are of the following forms: REPLY KINK Header KRB_AP_REP payload [KINK_ENCRYPT] ISAKMP_PAYLOAD payload SA Payload Proposal Payload Transform Payload [ Nonce Payload ] [ ID Payload ] Note that there MUST be a single proposal payload and a single transform payload in REPLY messages. If an IPspec DOI specific error is encountered, the respondent must reply with a Notify payload describing the error: REPLY KINK Header KRB_AP_REP payload [KINK_ENCRYPT] [ KINK_ERROR payload ] ISAKMP_PAYLOAD payload Notify payload Froh, Hur, McGrew, Medvinsky, Thomas, Vilhuber [Page 24] INTERNET DRAFT KINK September 2000 If the respondent finds an Kerberos type of error it MUST reply with a lone KRB_ERROR payload: REPLY KINK Header KRB_ERROR payload [KINK_ENCRYPT] [ KINK_ERROR payload ] 8.2 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 (with DOI) KRB_AP_REQ payload [KINK_ENCRYPT] [ KINK_ERROR payload ] ISAKMP_PAYLOAD payload Delete Payload There are three forms of replies for a DELETE The normal form is: REPLY KINK Header KRB_AP_REP | KRB_ERROR payload [KINK_ENCRYPT] [ KINK_ERROR payload ] ISAKMP_PAYLOAD payload Delete Payload If an IPspec DOI specific error is encountered, the respondent must reply with a Notify payload describing the error: REPLY KINK Header KRB_AP_REP payload [ KINK_ENCRYPT payload ] [ KINK_ERROR payload ] ISAKMP_PAYLOAD payload Notify payload If the respondent finds an Kerberos type of error it MUST reply with a lone KRB_ERROR payload: REPLY KINK Header KRB_ERROR payload [ KINK_ENCRYPT payload ] [ KINK_ERROR payload ] Froh, Hur, McGrew, Medvinsky, Thomas, Vilhuber [Page 25] INTERNET DRAFT KINK September 2000 9 Key Derivation During the establishment of SAs the initiator and responder each pro- vide random nonces that add entropy to the KDC supplied session key in order to derive the SA keying material (KEYMAT). KEYMAT = HMAC(Secret, Ni [ | Nr ]) The function is initially called with the session key found in the service ticket used for Secret and is called recursively with the resulting KEYMAT until it has generated proper number of bits. The initator MUST add entropy in the form of a random nonce to the ticket session key when it instantiates the optimistic security asso- ciation. The HMAC algorithm used is the same as specified in the etype for the Kerberos session key in the Kerberos ticket. If the etype does not specify a hash algorithm, the SHA1 MUST be used. The results are placed in the subkey field of the AP-REQ. The number of subkey bits MUST be large enough to generate keying material for the largest encryption and integrity algorithms proposed. Bits for the security association keys are taken from the generated key in network order starting with the key for the initiator's inbound security association with the integrity algorithm key first followed by the encryption algorithm, and repeated for for the initiator's outbound security association. There is no implied pad- ding between the encryption and integrity keying material. The respondent MAY choose to add more entropy to the key, but if it does, it SHOULD request an ACK message before it sends data on the newly created security association. It MUST place the concatenation of the two nonces it choses in the subkey field of the AP-REP. The nonce sizes MUST be the same size that the initiator chose. Upon receipt of the AP-REP, the initiator MUST compare the second nonce to determine if the respondent added entropy to the keying material. If it has, the initiator MUST modify the keys for the initial security association using the rules described above. The following flow illustrates the derivation of keys: A B ----- ----- K0=HMAC(SessKey, Nonce1, 0) AP-REP(subkey=Nonce1)----------------> K1=HMAC(SessKey, Nonce1, Nonce2) K2=HMAC(SessKey, Nonce1, Nonce3) [where Nonce3 MAY be null] <-------------------------------- AP-REQ(subkey=Nonce2|Nonce3) Figure 23: Key Derivation K0 is used to instantiate the optimistic incoming security associa- tion from B->A. K1 is always the key that is used for the security Froh, Hur, McGrew, Medvinsky, Thomas, Vilhuber [Page 26] INTERNET DRAFT KINK September 2000 association between A->B. The value of the subkey in the AP-REQ is always Nonce1. The value of the subkey in the AP-REP is the concate- nation of Nonce2 and Nonce3 where Nonce3 is equal to zero if B does not desire to add entropy to the optimistic security association B- >A. 10 Transport Considerations KINK uses UDP on port XXX to transport its messages. There is one timer T which SHOULD take into consideration round trip considera- tions and MUST implement a truncated exponential backoff mechanism. The state machines is simple: any message which expects a response must retransmit the request using timer T. Since Kerberos requires that messages be retransmitted with new times for replay protection, the message must be recreated each time including the checksum of the message. 11 Security Considerations 12 Protocol Considerations 12.1 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, even though when and when not to initiate a user to user flow is left to the discretion of the KINK implemention, a Ker- beros 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, and whether the KINK implementation should use a direct 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. Froh, Hur, McGrew, Medvinsky, Thomas, Vilhuber [Page 27] INTERNET DRAFT KINK September 2000 13 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 References [RFC1510] 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. September 1994. [PKINIT] B. Tung, C. Neuman, M. Hur, A. Medvinsky, S.Medvinsky, J. Wray, J. Trostle. Public Key Cryptography for Initial Authentication in Ker- beros. 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 Authentication in Kerberos. draft-ietf-cat-kerberos-pk-cross-06.txt Froh, Hur, McGrew, Medvinsky, Thomas, Vilhuber [Page 28] INTERNET DRAFT KINK September 2000 [RFC2401] S. Kent, R. Atkinson. Security Architecture for the Internet Proto- col. 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 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 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 CyberSafe Corporation 1605 NW Sammamish Road Issaquah WA 98027-5378 Phone: +1 425 391 6000 E-mail: matt.hur@cybersafe.com David McGrew Mike Thomas Jan Vilhuber Cisco Systems 170 West Tasman Drive San Jose, CA 95134 E-mail: {mcgrew,mat,vilhuber}@cisco.com Froh, Hur, McGrew, Medvinsky, Thomas, Vilhuber [Page 29] INTERNET DRAFT KINK September 2000 Sasha Medvinsky Motorola 6450 Sequence Drive San Diego, CA 92121 +1 858 404 2367 E-mail: smedvinsky@gi.com 17 Expiration This memo is filed as , and expires February, 2001. Froh, Hur, McGrew, Medvinsky, Thomas, Vilhuber [Page 30]