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authorCy Schubert <cy@FreeBSD.org>2023-06-26 22:56:52 +0000
committerCy Schubert <cy@FreeBSD.org>2023-06-26 22:56:52 +0000
commitb6a943f7197af1a5eb6bb028b9b808ec5016e30c (patch)
treecfbb91e940dd89d0e1d46095f43c228d7d079fa0 /doc/standardisation/draft-foo3
parent6f4e10db3298f6d65e1e646fe52aaafc3682b788 (diff)
Heimdal 7.8.0 does not support OpenSSL 3.0. 7.9.0 will but it hasn't been released yet. We are importing f62e2f278 for its OpenSSL 3.0 support.
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+Network Working Group Assar Westerlund
+<draft-ietf-cat-krb5-firewalls.txt> SICS
+Internet-Draft Johan Danielsson
+November, 1997 PDC, KTH
+Expire in six months
+
+ Kerberos vs firewalls
+
+Status of this Memo
+
+ This document is an Internet-Draft. 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."
+
+ To view the entire list of current Internet-Drafts, please check the
+ "1id-abstracts.txt" listing contained in the Internet-Drafts Shadow
+ Directories on ftp.is.co.za (Africa), ftp.nordu.net (Europe),
+ munnari.oz.au (Pacific Rim), ds.internic.net (US East Coast), or
+ ftp.isi.edu (US West Coast).
+
+ Distribution of this memo is unlimited. Please send comments to the
+ <cat-ietf@mit.edu> mailing list.
+
+Abstract
+
+Introduction
+
+ Kerberos[RFC1510] is a protocol for authenticating parties
+ communicating over insecure networks.
+
+ Firewalling is a technique for achieving an illusion of security by
+ putting restrictions on what kinds of packets and how these are sent
+ between the internal (so called "secure") network and the global (or
+ "insecure") Internet.
+
+Definitions
+
+ client: the user, process, and host acquiring tickets from the KDC
+ and authenticating itself to the kerberised server.
+
+ KDC: the Kerberos Key Distribution Center
+
+
+
+
+Westerlund, Danielsson [Page 1]
+
+Internet Draft Kerberos vs firewalls November, 1997
+
+
+ Kerberised server: the server using Kerberos to authenticate the
+ client, for example telnetd.
+
+Firewalls
+
+ A firewall is usually placed between the "inside" and the "outside"
+ networks, and is supposed to protect the inside from the evils on the
+ outside. There are different kinds of firewalls. The main
+ differences are in the way they forward packets.
+
+ o+ The most straight forward type is the one that just imposes
+ restrictions on incoming packets. Such a firewall could be
+ described as a router that filters packets that match some
+ criteria.
+
+ o+ They may also "hide" some or all addresses on the inside of the
+ firewall, replacing the addresses in the outgoing packets with the
+ address of the firewall (aka network address translation, or NAT).
+ NAT can also be used without any packet filtering, for instance
+ when you have more than one host sharing a single address (for
+ example, with a dialed-in PPP connection).
+
+ There are also firewalls that does NAT both on the inside and the
+ outside (a server on the inside will see this as a connection from
+ the firewall).
+
+ o+ A third type is the proxy type firewall, that parses the contents
+ of the packets, basically acting as a server to the client, and as
+ a client to the server (man-in-the-middle). If Kerberos is to be
+ used with this kind of firewall, a protocol module that handles
+ KDC requests has to be written.
+
+ This type of firewall might also cause extra trouble when used with
+ kerberised versions of protocols that the proxy understands, in
+ addition to the ones mentioned below. This is the case with the FTP
+ Security Extensions [RFC2228], that adds a new set of commands to the
+ FTP protocol [RFC959], for integrity, confidentiality, and privacy
+ protecting commands. When transferring data, the FTP protocol uses a
+ separate data channel, and an FTP proxy will have to look out for
+ commands that start a data transfer. If all commands are encrypted,
+ this is impossible. A protocol that doesn't suffer from this is the
+ Telnet Authentication Option [RFC1416] that does all authentication
+ and encryption in-bound.
+
+Scenarios
+
+ Here the different scenarios we have considered are described, the
+ problems they introduce and the proposed ways of solving them.
+
+
+
+Westerlund, Danielsson [Page 2]
+
+Internet Draft Kerberos vs firewalls November, 1997
+
+
+ Combinations of these can also occur.
+
+ Client behind firewall
+
+ This is the most typical and common scenario. First of all the
+ client needs some way of communicating with the KDC. This can be
+ done with whatever means and is usually much simpler when the KDC is
+ able to communicate over TCP.
+
+ Apart from that, the client needs to be sure that the ticket it will
+ acquire from the KDC can be used to authenticate to a server outside
+ its firewall. For this, it needs to add the address(es) of potential
+ firewalls between itself and the KDC/server, to the list of its own
+ addresses when requesting the ticket. We are not aware of any
+ protocol for determining this set of addresses, thus this will have
+ to be manually configured in the client.
+
+ The client could also request a ticket with no addresses, but some
+ KDCs and servers might not accept such a ticket.
+
+ With the ticket in possession, communication with the kerberised
+ server will not need to be any different from communicating between a
+ non-kerberised client and server.
+
+ Kerberised server behind firewall
+
+ The kerberised server does not talk to the KDC at all so nothing
+ beyond normal firewall-traversal techniques for reaching the server
+ itself needs to be applied.
+
+ The kerberised server needs to be able to retrieve the original
+ address (before its firewall) that the request was sent for. If this
+ is done via some out-of-band mechanism or it's directly able to see
+ it doesn't matter.
+
+ KDC behind firewall
+
+ The same restrictions applies for a KDC as for any other server.
+
+Specification
+
+Security considerations
+
+ This memo does not introduce any known security considerations in
+ addition to those mentioned in [RFC1510].
+
+References
+
+
+
+
+Westerlund, Danielsson [Page 3]
+
+Internet Draft Kerberos vs firewalls November, 1997
+
+
+ [RFC959] Postel, J. and Reynolds, J., "File Transfer Protocol (FTP)",
+ RFC 969, October 1985
+
+ [RFC1416] Borman, D., "Telnet Authentication Option", RFC 1416,
+ February 1993.
+
+ [RFC1510] Kohl, J. and Neuman, C., "The Kerberos Network
+ Authentication Service (V5)", RFC 1510, September 1993.
+
+ [RFC2228] Horowitz, M. and Lunt, S., "FTP Security Extensions",
+ RFC2228, October 1997.
+
+Authors' Addresses
+
+ Assar Westerlund
+ Swedish Institute of Computer Science
+ Box 1263
+ S-164 29 KISTA
+ Sweden
+
+ Phone: +46-8-7521526
+ Fax: +46-8-7517230
+ EMail: assar@sics.se
+
+ Johan Danielsson
+ PDC, KTH
+ S-100 44 STOCKHOLM
+ Sweden
+
+ Phone: +46-8-7907885
+ Fax: +46-8-247784
+ EMail: joda@pdc.kth.se
+
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+Westerlund, Danielsson [Page 4]
+