Lecture 18:
Java™ Decaffeinated
CS551: Security and Privacy
University of Virginia
Computer Science
David Evans
http://www.cs.virginia.edu/~evans
Menu
• SSL Challenge Question
• Java
• Voting
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SSL Challenge Question
Are there skeletons in VeriSign’s closet?
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Secure Socket Layer (SSL)
141 Sextillion years;
Not going any where for awhile;
grab a snickers
SSL Background
• Two Kinds of SSL
– Low Encryption (40-bit; 1.1x1012 possible keys)
– High Encryption (128-bit; 3.8x1038 possible keys)
• SSL is a transport level technology for
authentication and data encryption between a
web server and a Web server (example).
• Applied at the socket interface from the
application to the network software.
Data Link
Header
Internet Transport Application
Header Header
Header
Plaintext
Data being sent
Cipher Text
SSL Handshake
Server
Client
• Tell me who you are;
• Here are the protocols I support.
• For your ID, I know who you are
and have your public key;
• Here is a secret key I created
with your protocols encrypted with
your key
• Here is my Digital ID to prove
who I am;
• Here is the protocols I have
decided we should use.
• Here is a copy of everything
we’ve said encrypted with our
secret key.
• Here is a copy of everything we’ve
said encrypted with our secret key.
SSL Data Exchange
Time to Break Specific Keys
Years
Key length
(bits)
40
1995
2000
2005
68 hours
8.6 minutes
56
7.4 weeks
6.5 days
1.07
minutes
19 hours
64
36.7 years
4.6 years
6.9 months
128
6.7x1017
millennia
8.4x1016
millennia
1.1x1016
millennia
[Erkomaa, 1998]
Brute Force Attacks
Remarks
DES
Challenge #1
DES
Challenge
Final
DES
Challenge on
128-bit
Single
Computer
Small
Network
VeriSigns
Assumption
Total Key
Space
Number of
Seconds
Number of
Years
Search Space
(keys/sec)
Key size
(bit)
7.50E+09
56
7.20576E+16 9607679.205
0.30
9.10E+11
56
7.20576E+16 79184.16927
**22 hours
2.45E+11
128
3.40282E+38 1.38891E+27
4.404E+19
650000
128
3.40282E+38 5.23511E+32
1.66E+25
1.00E+06
128
3.40282E+38 3.40282E+32
1.08E+25
76,400,000
128
3.40282E+38 4.45396E+30
1.412E+23
Target: 1.41E+23
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VeriSign’s Claim
N u m b e r o f Ye a rs
1E +27
1E +24
1E +21
Ye ars
1E +18
1E +15
N um b e r o f Ye a rs
1E +12
1E +09
100000
0
1000
1
650000
1000000
76400000
Se arch Sp ace Sp e e d
2 .4 5 E + 1 1
Moore’s Law
18 months
C racking 128-bit K eys
1 .0 0 0 E + 2 0
N u m b er o f Years to C rack
1 .0 0 0 E + 1 8
1 .0 0 0 E + 1 6
1 .0 0 0 E + 1 4
1 .0 0 0 E + 1 2
1 .0 0 0 E + 1 0
1 .0 0 0 E + 0 8
1 .0 0 0 E + 0 6
1 .0 0 0 E + 0 4
1 .0 0 0 E + 0 2
1 .0 0 0 E + 0 0
1998
2000
2002
2004
2006
2008
2010
2012
2014
2016
Ye a r
C o ns e rva tive E s tim a te
B o ld E s tim a te
M o o re 's L a w
2018
General Timeline
Not to scale
CS-551 Class
(1.25 hours)
Total Human Lifetime
Universe Lifetime
0
1010
1019 1020 1023
Quintillion years
Sextillion years
VeriSign’s Assumptions
• Hackers or key breakers have computers that
are extremely slow.
• We are using the processing speed of
computers that were built in the 1980’s era.
• Distributed networks and special hardware
are not authorized for key breaking schemes.
• We are not increasing our processing power
every 18-24 months (based on Moore’s Law).
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Java Security
Real or Decaf?
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Java
A.
B.
C.
D.
E.
Island in Indonesia
A Programming Language (Java)
A Portable Low-Level Language (JVML)
A Platform (JavaVM)
A successful marketing strategy
– JavaScript is not related to Java or Java
F. So you can have more time to work on
your projects
G. All of the above
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Java : Programming Language
“A simple, object-oriented,
distributed, interpreted, robust,
secure, architecture neutral,
portable, high-performance,
multithreaded, and dynamic
language.”
[Sun95]
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What is a secure language?
1. Language is designed so it cannot
express certain computations
considered insecure.
A few attempts to do this: PLAN, packet filters
2. Language is designed so that
(accidental) program bugs are likely
to be caught by the compiler or runtime environment instead of leading
to security vulnerabilities.
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Safe Programming Languages
• Type Safety
– Compiler and run-time environment ensure that
bits are treated as the type they represent
• Memory Safety
– Compiler and run-time environment ensure that
program cannot access memory outside defined
storage
• Control Flow Safety
– Can’t jump to arbitrary addresses
Which of these does C++ have?
Not a new idea: LISP had these in 1960!
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Java Safety
• Type Safety
– Most types checked statically
– Coercions, array assignments type checked at run
time
• Memory Safety
– No direct memory access (e.g., pointers)
– Primitive array type with mandatory run-time
bounds checking
• Control Flow Safety
– Structured control flow, no arbitrary jumps
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Malicious Code
Can a safe programming language
protect you from malcode?
1. Code your servers in it to protect from
buffer overflow bugs
2. Only allow programs from untrustworthy
origins to run if the are programmed in
the safe language
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Safe Languages?
• But how can you tell program was
written in the safe language?
– Get the source code and compile it (most
vendors, and all malicious attackers refuse
to provide source code)
– Special compilation service signs object
files generated from the safe language
(SPIN, [Bershad96])
– Verify object files preserve safety
properties of source language (Java)
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JVML
malcode.java

Java
Source
Code
javac
Compiler
malcode.class
JVML
Object
Code
JavaVM
Joe User
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Joe wants to know JVML code satisfies
Java’s safety properties.
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Does JVML satisfy Java’s
safety properties?
iconst_2
istore_0
aload_0
arraylength
push integer constant 2 on stack
store top of stack in variable 0 as int
load object reference from variable 0
replace array on top of stack with its
length
No! This code violates Java’s type rules.
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malcode.class
JVML
Object
Code
Bytecode Verifier
Trusted Computing Base
Java Bytecode Verifier
Invalid
“Okay”
STOP
JavaVM
Joe User
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Bytecode Verifier
• Checks JVML code satisfies Java’s
safety properties
• Type safe – stack and variable slots
must store and load as same type
• Memory safe (guaranteed by instruction
set)
• Control flow safe: jumps must be within
function, or call/return
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Are Java Bytecode Verifiers
Complicated?
• ~700 rules to enforce, JVML specification is
(not all clearly specified)
• Emin Gün Sirer found > 100 bugs in
commercial bytecode verifiers (using
automatic test generation)
– At least 15 of them were security vulnerabilities
• JVML includes jsr instruction (jump to
subroutine), can be called with different types
in variables and on stack
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Java
malcode.java
javac
Compiler
malcode.class
JVML
Trusted Computing Base
Java Bytecode Verifier
Invalid
“Okay”
STOP
JavaVM
Joe User
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JavaVM
• Virtual machine – interpreter for JVML
programs
• Has complete access to host machine
• Bytecode verifier ensures some safety
properties, JavaVM must ensure rest:
– Type safety of run-time casts, array
assignments
– Memory safety: array bounds checking
– Resource use policy
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JavaVM Policy Enforcment
[JDK 1.0 – JDK 1.1]
From java.io.File:
public boolean delete() {
SecurityManager security =
System.getSecurityManager();
if (security != null) {
security.checkDelete(path);
}
if (isDirectory()) return rmdir0();
else return delete0();
}
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java.lang.SecurityManager
/**
Throws a SecurityException if the calling
thread is not allowed to delete the specified
file.
This method is invoked for the current security
manager by the delete method of class File.
*/
(Some other comments deleted.)
public void checkDelete(String file) {
throw new SecurityException();
}
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Security Manager
• Reference monitor
– How well does it satisfy the requirements?
• Complete mediation
• Can stop execution/prevent action
• Limited effect on execution until policy violation
• User/host application creates a
subclass of SecurityManager to define a
policy
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HotJava’s Policy (JDK 1.1.7)
public class AppletSecurity
extends SecurityManager {
...
public synchronized void
checkDelete(String file) {
checkWrite(file);
}
...
}
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AppletSecurity.checkWrite
(some exception handling code removed)
public synchronized void checkWrite(String file) {
if (inApplet()) {
if (!initACL) initializeACLs();
String realPath =
(new File(file)).getCanonicalPath();
for (int i = writeACL.length ; i-- > 0 ;) {
if (realPath.startsWith(writeACL[i])) return;
}
throw new AppletSecurityException
("checkwrite", file, realPath);
}
}
Note: no checking if not inApplet!
Very important this does the right thing.
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inApplet
boolean inApplet() {
return inClassLoader();
}
Inherited from java.lang.SecurityManager:
protected boolean inClassLoader() {
return
currentClassLoader() != null;
}
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currentClassLoader
/**
Returns an object describing the most recent class
loader executing on the stack.
Returns the class loader of the most recent occurrence
on the stack of a method from a class defined using a
class loader; returns null if there is no occurrence on the
stack of a method from a class defined using a class
loader.
*/
protected native ClassLoader currentClassLoader();
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Recap
• java.io.File.delete
calls
before deleting
• HotJava overrides SecurityManager with
AppletSecurity to set policy
• AppletSecurity.checkDelete calls
SecurityManager.checkDelete
AppletSecurity.checkWrite
• AppletSecurity.checkWrite checks if
any method on stack has a ClassLoader
• If not no checks; if it does, checks ACL list
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JDK 1.0 Trust Model
• When JavaVM loads a class from the
CLASSPATH, it has no associated
ClassLoader (can do anything)
• When JavaVM loads a class from
elsewhere (e.g., the web), it has an
associated ClassLoader
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JDK Evolution
• JDK 1.1: Signed classes from
elsewhere and have no associated
ClassLoader
• JDK 1.2:
– Different classes can have different policies
based on ClassLoader
– Explict enable/disable/check privileges
– SecurityManager is now AccessController
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What can go wrong?
• Java API doesn’t call right SecurityManager
checks (63 calls in java.*)
– Font loading bug, synchronization
• ClassLoader is tricked into loading external
class as internal
• Bug in Bytecode Verifier can be exploited to
circumvent SecurityManager
• Policy is too weak and allows damaging
behavior
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Hostile Applets
• See http://java.sun.com/sfaq/chronology.html
(about 1 new vulnerability/month)
• Easy to write “annoying” applets (policy
is too imprecise; no way to constrain
many resource operations)
• http://www.cigital.com/hostileapplets/index.html
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Voting
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VA Absentee Voting: Ballot
1. Print out form from state web site
2. Fill in name and address, sign by voter
and a witness
3. Mail to local election official
4. Local election official mails ballot to
voter’s address (presumably: checks
voter is registered, verifies address,
marks on election rolls)
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VA Absentee Voting
1. Open Envelope A in presence of witness
(do not open without witness present)
2. Borrow No. 2 pencil and mark ballot.
3. Place ballot in Envelope B and seal. Do
not put anything else in that envelope.
4. Fill in identification and sign Envelope B.
Witness signs Envelope B.
5. Place Envelope B in return envelope preaddressed to Secretary of the Electoral
Board. Mail or hand deliver in person.
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Voting Challenges
• (50 points) Explain why VA absentee ballot
protocol uses Envelope A and requires voter
to open it in presence of a witness
• (50 points) Devise a good absentee voting
protocol (better than my baseline)
• (200 points) Exploit vulnerabilities in
electoral protocols so Harry Browne or Ralph
Nader wins election
– Remember getting me arrested is -10000
points!
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Charge
• Tomorrow: Vote
– Pay attention to security protocols: who are
you trusting?
– Don’t get arrested, but think about how a
malicious person might defeat the system
• Next time
– Guest Lecture: Chenxi Wang
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