/*	$Source: /machusr/jtkohl/krb-tut/RCS/V5.slides,v $
 *	$Author: jtkohl $
 *	$Id: V5.slides,v 1.13 91/03/27 13:49:30 jtkohl Exp $
 */
#include "common.h"

START_SECTION("Future Work",XI)

NS_TITLE(Outline)

@begin[format,spacing 1.25lines]
@tabset(.75inch)
@>0.@\ Introduction to Tutorial
@>I.@\Introduction to Authentication
@>II.@\ Network Security Issues
@>III.@\ Kerberos Model
@>IV.@\ Kerberos Applications
@>V.@\ Kerberos Implementation/API
@>VI.@\ Kerberos Administration
@>VII.@\ X.509 Certificate Model
@>VIII.@\ Kerberos and X.509 Comparison
@>IX.@\ Privacy Enhanced E-mail
@>X.@\ Authorization Issues
BOLD(@>XI.@\ Future Work)
@>XII.@\ Lessons of the Internet Virus 
@end[format]

NEWSLIDE()
TITLE(Future Work)

BI()
Kerberos Version 5

Open Issues

Subject to change as we gain implementation experience
EI()
 
/* -------------------------------------------------- */
NEWSLIDE()
TITLE(Data Representation)

BI()
V4 used byte order of sender

V5 uses ASN.1
EI()

/* -------------------------------------------------- */
NEWSLIDE()
TITLE(Dates and Times)

BI()
V4
BI()
timestamps were UNIX times (seconds since 1/1/70)

expiration times were limited to N 5-minute intervals

N was 8 bits (i.e. 0 LTE() N LTE() 255) 
EI()

V5
BI()
ASN.1 GeneralizedTime

expiration times given by a start and end timestamps
EI()
EI()

/* -------------------------------------------------- */
NEWSLIDE()
TITLE(Ticket Lifetimes)

BI()
starttime
	BI()
	current time on KDC or 

	requested start time (if realm allows postdating)
	EI()

endtime such that lifetime of a ticket is the minimum of:
	BI()
	requested lifetime

	max lifetime allowed for requesting principal

	max lifetime allowed for requested service

	max lifetime allowed by the realm

	max lifetime of TGT (if issued by TGS)
	EI()
EI()
/* -------------------------------------------------- */
NEWSLIDE()
TITLE(Renewable Tickets)

BI()
issued if computed lifetime is less than requested lifetime

ticket in renewable until the minimum of:
	BI()
	requested endtime

	starttime + requesting principal's max renewable lifetime

	starttime + requested service's max renewable lifetime

	starttime + max renewable lifetime allowed by realm
	EI()
EI()
/* -------------------------------------------------- */
NEWSLIDE()
TITLE(Host Addresses)
BI()
V4
	BI()
	ticket contained one 32bit IP address
	EI()

V5
	BI()
	array of variable length addresses

	known address families: IP, chaos, ISO, XNS, AppleTalk, DECnet (Phase IV)
	EI()
EI()

NEWSLIDE()
TITLE(Multiple Encryption Algorithms)

BI()
each request includes algorithm identifier

servers may require specific algorithm

initial algorithms include:
	BI()
	null (for export)

	Lucifer (with 32bit CRC)

	DES (CBC with 32bit CRC)

	PCBC is no longer supported
	EI()

checksum algorithms include:
	BI()
	CRC-32
	
	RSA's Message Digest 4
	
	DES CBC
	EI()
EI()

NEWSLIDE()
TITLE(Principal Names)

BI()
V4
	BI()
	name

	instance

	realm

	protocol specifies no length limit
	(MIT implementation limitation of 40 bytes each)
	EI()

V5
	BI()
	arbitrary length array 

	easy mapping into X.500 distinguished name
	EI()
EI()

NEWSLIDE()
TITLE(Inter-realm Authentication)

BI()
V4
	BI()
	must share key with remote realm

	n@+(2) scaling problem
	EI()

V5
	BI()
	request can traverse series of realms (@i(authentication path))

	each realm transited is sealed in ticket

	KDC fills in previous realm for security

	server can judge trustworthy-ness of intermediary realms

	allows hierarchies solving n@+(2) problem
	(e.g. from mit.edu to stanford.edu
 via edu realm)
	EI()
EI()

NEWSLIDE()
TITLE(Administrative Server)

BI()
addition of dictionary check

generation of srvtab's by less privileged users
EI()

NEWSLIDE()
TITLE(Proxy and Forwarding)

BI()
remote service can access other network services on behalf of requesting 
principal

ticket request for remote address

proxy may grant limited access

forwarding grants all access

proxy cannot be use for additional TGT
EI()

NEWSLIDE()
TITLE(Authorization Data)

BI()
opaque data sealed in ticket

interpreted by end service

limit power of proxies

authorization server as alternative keeping state in servers

see Cliff Neuman's paper
EI()

NEWSLIDE()
TITLE(Invalid Tickets)

BI()
bit in ticket

KDC must validate before use

used for post-dated tickets

allows hot-list revocation
EI()

NEWSLIDE()
TITLE(New Database Fields)

BI()
larger lifetime 

max renewable lifetime

attributes - control which features can be used (proxy
 postdating
 etc.)

frequently changing fields (optional)
 	BI()
	last request

	last use of TGT
	EI()

string-to-key permutation choice
EI()

NEWSLIDE()
TITLE(Subsession keys and
sequence numbers)


BI()
subsession keys
	BI()
	client and server can negotiate to use different key to protect session

	allows multiple servers to share a key easily

	might be use by routing protocols
	EI()
sequence numbers
	BI()
	can be used in SAFE, PRIV messages

	sometimes easier/better suited for use than replay detection
	EI()
EI()
NEWSLIDE()
TITLE(User to User Authentication)

BI()
V4 
	BI()
	server must be registered with KDC

	server must keep its secret around

	users destroy their secret key after getting TGT

	use for public workstations, X displays, etc.
	EI()
EI()

NEWSLIDE()
TITLE_CONT(User to User Authentication)

@blankspace (3 inches)

@comment{@begin(enumerate, leftmargin +3 inches)}

@blankspace(1inch)
BN()
        A -> B @ @ @ @ @ a,b 

        B -> A @ @ @ T @-{b,tgs} 

        A -> K @ @ @ @ @ T @-{a,tgs}, T @-{b,tgs}

        K -> A @ @ @ { T @-{a,b}}K @-{b,tgs} @ {K @-{a,b} }K @-{a,tgs}

        A -> B @ @ @ @ @ T @-{a,b},  A @-{a,b}

@end(enumerate)

@picture(size = .01 inches, ScaleableLaser=uuser.PS)

NEWSLIDE()
TITLE(Remove fields from ticket)

BI()
suggestion to remove service name from ticket

not needed for integrity

still included in in current spec

needed for inter-realm TGS
EI()

NEWSLIDE()
TITLE(Inter-realm Directional Keys)

BI()
have directional inter-realm keys

allows unidirectional trust

KDC implementation issue
EI()

NEWSLIDE()
TITLE(Better Ticket Caching Code)

BI()
V4 clients stored ticket in a file

not good enough for diskless machines

shared memory added later

interface must be generalized (e.g. for Macintosh)

EI()

NEWSLIDE()
TITLE(Library Improvements)

BI()
don't force synchronized clocks

isolate OS dependencies (file system
network) as much as possible

implement proper replay detection
EI()

NEWSLIDE()
TITLE(Slave Propagation)

BI()
some sites don't like delay

use replicated database technology

is extra complexity worth it?
EI()

NEWSLIDE()
TITLE(Better Random Number Generator)

BI()
Uses DES encryption

Since the KDC gives out most random numbers
(session keys) this is especially practical.

can be used use for sequence numbers
EI()

NEWSLIDE()
TITLE(V4 to V5 migration)

BI()
glue library emulation

GSSAPI

V5 KDC issuing V4 tickets

link both into server/client

try one, exec the other if failure
EI()

NEWSLIDE()
TITLE(Validation suites for protocol)

BI() Proposal to do one for the Kerberos library routines implementing
protocols.

Proposal to improve, i.e. make automatic,
the one already available for the DES
library.
EI()

NEWSLIDE()
TITLE(Des_string_to_key seed)

BI()
Seed the des_string_to_key algorithm by the realm name 
so that	if someone uses the same password in
two realms, disclosure of one realm's key
doesn't compromise the user in the other
realm.

Proposal to tag Kerberos database entries
with the version of the string_to_key algorithm
which was used to produce the key, and include
that in the reply to an initial ticket request.
EI()

NEWSLIDE()
TITLE(Finding the Realm of Servers)

BI()
Proposal for a common mechanism for securely
finding out the realm, or possibly even the
entire name, of a server given just its network
name or address.  Taking the server's word for
it is not sufficient.
EI()

NEWSLIDE()
TITLE(Automatic changing of service keys)

BI()
Proposal for tools to periodically generate
and install new versions of server keys.

Observation that having this done without
manual intervention would increase security.
EI()