Transcript Trends and Challenges in Computer Security and Cryptography

Trends and Challenges in
Computer Security and
Cryptography
Bernard Menezes
Department of Computer Science
IIT Bombay
Goals
• To put cryptography, network security,
system security and application security in
perspective
• To sample trends and/or challenges in
cryptography and network security
Computer Security in perspective
•
•
•
•
•
•
•
Information Security
Network Security
System Security
Application Security
Operating System Security
Database Security
Language Security
Cryptography
• Generally considered part of Network Security
• Vast and intense subject and has emerged as a
course/research area in its own right
• Requires mathematical prerequisites –
Number Theory, Discrete math (groups,
rings, fields, etc.)
Pursuit of Mathematics
• One may develop mathematical theory with no
apparent goal in mind (math for math sake)
• Decades/centuries later, scientists and engineers
may stumble upon some excellent applications of
mathematical theories
• Examples – the use of differential equations in
the analysis of electrical circuits, the use of
number theory and discrete math in
cryptography
Useful math background for
cryptography
•
•
•
•
•
•
Modulo arithmetic and the gcd
Euclid’s algorithm
Euler’s Theorem and Fermat’s Little Theorem
Lagrange’s Theorem
Chinese Remainder Theorem
Theorems related to subgroups, generators,
etc.
Security, Mathematics, Security
• Is Cryptography = Security?
• Is Cryptography a subset of Applied
Mathematics?
But, a word of caution!
“ Whoever thinks his problem can be solved
using cryptography, doesn’t understand his
problem
and
doesn’t
understand
cryptography ”
- Source unknown
What is Security about (in the
technical sense)
• (Goals of the hacker/attacker/adversary)
• Attacks
• Vulnerabilities
• Defences
Some Attack Goals
• Theft of sensitive information (example, credit
card information)
• Disruption of service (rendering a service
inaccessible or unavailable)
• Information Warfare (attacking infrastructure
of an “enemy” country)
• Illegal access to or use of resources
(circumventing controls so as to gain
unauthorized access)
Attacks, Attacks, Attacks!
Who commits what?
“ Once we know our weaknesses, they cease to
do us any harm”
- Georg Christoph Lichtenberg
Vulnerabilities
• A vulnerability is a weakness or lacuna in a
policy, procedure, protocol, hardware or
software within an organization that has the
potential to cause it damage or loss.
Vulnerability Types
• Human Vulnerabilities
– Induced by careless/unthinking human behaviour
– Ex. clicking on a link in an e-mail message from a
questionable source
– Related to phishing and cross-site scripting attacks
Vulnerability Types (contd.)
• Protocol Vulnerabilities
– Attacks on commonly used networking protocols such as
TCP, IP, ARP, ICMP and DNS
– Ex. Connection hijacking caused by ARP spoofing, etc.
– Denial of Service Attacks (DoS) which exploit the 3-way
TCP handshake
– Pharming attacks exploit vulnerabilities in DNS
Vulnerability Types (contd.)
• Software Vulnerabilities
– Caused by sloppy software
– Software may perform as expected under normal
conditions but when provided with a specific input, it turns
malicious
– Examples include Buffer Overflow vulnerability, Cross-site
Scripting (XSS) vulnerability and SQL Injection vulnerability
Vulnerability Types (contd.)
• Configuration Vulnerabilities
– relate to settings on system/application software, on files,
etc.
– Read-write-execute (and other) permissions on files (and
other objects) may be too generous.
– Privilege level assigned to a process may be higher than
what it should be to carry out a task.
– Often lead to “privilege escalation” attacks.
Advice to a Security Designer
“ You can’t make something secure if you don’t
know how to break it”
- Marc Weber Tobias
Defence Strategies
 Prevention
 Detection
 Recovery
 Forensics/Traceback
Examples of Preventive Strategies
• Code Auditing and Testing (against software flaws)
– Blackbox
– Whitebox
• Access Control (against unauthorized access)
– Authentication
– Authorization
• Encryption (against eavesdropping)
Examples of Detection
• Integrity checks on messages, files
– Simple CRC-type checksums not effective for security
applications
– Use of the Message Authentication Code (MAC)
• Intrusion detection systems based on
– Anomaly detection
– Signature detection
Trends and Challenges in Cryptography
– Identity-based Cryptography
– Secure Group Communication
– Green Cryptography
– Quantum Cryptography
Trends and Challenges in Security
• Defense against botnets
• Application software security
• Web services security
• Electronic payment
• Electronic passports
Web Services Security
Web apps versus web services
• Many of the earlier web applications (such as
internet banking) involved human-to-program
interaction. However, applications such as supply
chain management differ from traditional web
applications in several significant respects:
• Programs communicate with each other over the
web with little or no human intervention.
Web apps versus web services (contd.)
• Services might have a composite nature. Such
“composite services” necessitate the
involvement of multiple providers, each
providing an “atomic service”.
• There are potentially a large number of
“atomic service” providers offering a given
service. So clients have a choice and can
dynamically change providers.
Web Services
The World-wide Web Consortium, W3C, defines a
web service as
“a software system identified by a URI whose public
interfaces and bindings are defined and described
using XML. Its definition can be discovered by other
software systems. These systems may then interact
with the web service in a manner prescribed by its
definition using XML-based messages conveyed by
internet protocols”.
Entities involved in a web service
Security Challenges Specific to Web Services
• SSL/TLS, IPSec are some of the common ways
of securing web communication
• However, these are point-to-point protocols.
• Web services require fine-grained security
• SSL does not support non-repudiation
• SSL operates at the transport level. What we
need is a protocol that understands a
message.
Standards for Web Services Security
•
•
•
•
•
XML Digital Signature
XML Encryption
WS-Sec
SAML (Secure Assertion Markup Language)
XACML (eXtensible Access Control Markup
Language)
Standards for Web Services Security
(contd.)
•
•
•
•
WS-Policy
XKMS (XML Key Management Specification)
WS-Trust
WS-Federation
XML Digital Signature
• Provides authentication, data integrity
(tamperproofing) and non-repudiation
• Very flexible
– Can sign one or more items within an XML document
– Supports multiple signers (ex. business partners)
– Can sign both local and remote objects, XML and non-XML
content
– Support for multiple signing algos + digest algos +
canonicalization methods.
WS-Sec
 Defines XML elements that are used to communicate
security tokens in the header of a SOAP message
within the <Security> header.
 A security claim is a statement made about a
subject’s identity, signing key, etc.
 One or more claims is/are represented by a security
token.
 Common examples of security tokens are a
username + password, an X.509 certificate, a
Kerberos ticket or a SAML assertion.
WS-Sec Token Example
< UsernameToken >
< Username > Shivani < /Username >
< Password Type = “PasswordDigest” >
4u%h&+q:L
< /Password >
< Nonce > . . . < /Nonce >
< Created > . . . < Created >
< /UsernameToken >
WS-Sec Binary Token
< BinarySecurityToken
ValueType = “ . . . X509v3”
EncodingType = “ . . . Base64Binary” >
Lp9tba4Pc7G . . .
< / BinarySecurityToken >
Security Assertion Markup Language
(SAML)
• designed to support single sign-on and propagate
authorization information
• SAML defines three basic components:
• Assertions
– Authentication
– Attribute
– Authorization
SAML Authenticating Assertion
<saml:Assertion . . .
<saml:AuthenticationStatement
AuthMethod=“password”
AuthInstant=“2008- . . .
<saml:Subject>
<saml:NameID
SecurityDomain=“iitb.ac.in”
Name=“Rajesh” />
…
…
WS-Security Specifications
Application Security
Attacks that exploit software
vulnerabilities
•
•
•
•
Buffer Overflow
Cross-site Scripting
SQL Injection
Format String . . .
Some of these are on the Top-10 list of risks
brought out by OWASP
What about malware attacks?
Buffer Overflow (BOF)
• The BOF vulnerability is one of the oldest and, by far,
the most common of software vulnerabilities.
• As early as 1988, the Morris worm was one of the
first to exploit this vulnerability.
• Since then, many creative ways of converting such a
vulnerability into an exploit have been devised.
Buffer Overflow (BOF) contd.
• A buffer overflow (BOF) occurs when the space allocated to a
variable (typically an array or string variable) is insufficient to
accommodate the variable in its entirety.
• For example, a certain amount of buffer space is allocated for
an array. If array bounds are not checked while populating it,
the array may overflow into contiguous memory and corrupt
it.
• Interestingly, this could cause an attacker to subvert the
normal flow of a program. Malicious code supplied by the
attacker in the buffer could be executed.
Exploiting Stack Overflows
• Provide input to a buffer on the stack which includes
malicious code (often called shellcode)
• Overflow the buffer so that the return address to the
calling program is overwritten with the address of
the malicious code
• That way, when the called function terminates, it will
not return to the calling program. Instead, the
malicious code will be executed
Buffer Overflow Defences
There are many defences against BOF.
Some of the best known are
– Make the stack non-executable. This prevents malicious
code on the stack from being executed. However, exploits
like return into LibC are still possible
– Compiler-based option: Place a “canary variable” on the
stack between the local variables and the return address. If
a BOF modifies the return address, the canary will be
corrupted. This will be detected by the compiler and the
program will be aborted.
Related Attacks
• Heap Overflow: A program’s dynamically allocated variable
are stored on the heap. Buffers in this area may also be
overflown leading to Heap buffer overflow attacks.
• Format String Attacks:
C language printf( ), for example, uses a format string as
function parameter. An attacker may pass a malicious string as
input parameter enabling the attacker to read or write
arbitrary locations in memory.
Cross-site Scripting Attacks
• A web site is said to have a cross-site scripting vulnerability if
it inadvertently includes malicious scripts crafted by an
attacker in pages returned by it.
• For example,
<SCRIPT> Malicious Code </SCRIPT>
• The malicious code may, for example, read browser cookies
on the victim’s machine and ship these off to an attacker’s
web server
Persistent XSS Attack
• The malicious code (scripts) on a web page is saved on the
web server.
• When an innocent user downloads the web page, the
malicious scripts execute on that user’s browser.
• Example: Users update their profile on a social networking
site. These profiles may be read (downloaded) by other users
through their browsers
Non-persistent XSS Attack
• Exploits the fact that some servers echo back certain user
input back to the client without validating it
• For example, a user may be asked for personal details in an
HTML form. Suppose he enters his name as “Prashant”. The
server then responds with “Hello Prashant”
• Note that the server has echoed back his name
• Now, what would happen if, instead of Prashant, the user
enters
<SCRIPT>alert(‘Fire!’)</SCRIPT>
Overcoming XSS
• Validate and filter all user input. (Should this be done at the
client or server?)
• One strategy is to make a blacklist of all user input that should
be filtered out. For example, single/double quotes, angular
brackets, etc. should not appear in an e-mail address input
from the user.
• A better solution in most cases is the equivalent of a whitelist
approach - specify precisely what user input is expected. This
is often accomplished by the use of a regular expression.
SQL Injection (Background)
• Form parameters may be passed as a query string in
an extended URL to the server as in
www.iitb.ac.in?s_ID=08935710&passwd=4ep*NdF
• The server application retrieves the form parameters
and uses them to build an SQL query such as
select s_ID, gpa
from students09
where s_ID = 08935710 and passwd = ‘4ep*NdF’
Constructing an SQL query directly from
user input (Example 1)
select s_ID, gpa
from students09
where s_ID = 123 and passwd = ‘abc’ or ‘x’ = ‘x’
Constructing an SQL query directly from
user input (Example 2)
select s_ID, gpa
from students09
where s_ID = 123 or 1=1 - - and passwd = ‘ abc ’
Constructing an SQL query directly from
user input (Example 3)
select s_ID, gpa
from students09
where s_ID = 123; DROP TABLE students09; - - and passwd =
‘ abc ’
“ There are two things I am sure after all these
years: there is a growing societal need for high
assurance software, and market forces are
never going to provide it”
- Earl Boebert
Electronic Payment
E-Payment
• Obviates the need to transport, handle, store
and dispense physical cash
• Results in enormous savings to banks and
merchants.
• Offers unprecedented convenience to the
customer who does not need to carry
currency notes and coins.
E-Payment – Distinguishing Features
• Real-time, pre-paid, post-paid
• Remote versus proximity
• E-payment enabling device (cellphone, PC,
smart card)
• Communication medium (bluetooth, NFC,
internet, etc.)
• On-line versus off-line
CardHolder Present E-Transactions
• Considerable credit card fraud has motivated the use of “Chip
N Pin” cards
• Basically a smart card (with an on-card processor)
• Cardholder authenticated using a PIN
• PIN is also securely stored on the card and is securely
communicated to the terminal
• Based on the EMV protocol
Mobile Payment Facilities
• Account-related enquiries (for example,
account balance)
• Cheque Book Request
• SMS alerts
• Utility Bill Payment
• Purchase of movie tickets, etc.
• Funds Transfer
Botnets
Botnets
• A botnet is an army of compromised computers or
bots connected to the internet and remotely
controlled by a “botmaster”.
• The earliest botnets were a collection of zombies
that participated in Distributed Denial of Service
(DDoS) attacks.
• Today’s botnets may comprise tens of thousands or
even millions of bots.
Botnets (contd.)
• The emergence of botnets is closely linked to the motive of
financial gain
• Often used to send spam mail on behalf of third parties.
• Bot programs may contain keyloggers and other forms of
spyware that capture sensitive personal information such as
passwords and credit card numbers and send these to the
botmaster.
• Botnets have also been used as an extortion tool – “Pay up or
your web site will be bombarded by a DDoS attack”.
Botnets (contd.)
• One important difference between a bot and a
computer infected by a traditional worm/virus or
Trojan is that a bot needs to communicate with
specific nodes in the botnet to receive fresh
commands.
• Early botnets used an IRC server as a Command &
Control Server. A channel on such a server was used
to convey the botmaster’s commands.
Recent Bots
• A more recent trend has been distributed and decentralized
botnet architectures which leverage existing highly scalable
and robust P2P networks.
• The connectivity of P2P networks ensures that even if a large
number of bots are disabled, the rest of the bots continue to
stay connected.
•
Moreover, there are no fixed C&C servers making it hard to
detect and incapacitate a P2P-based botnet.
The Storm Botnet
• First detected in January 2007. Its other names are Peacomm,
Nuwar and Zhelatin.
• Storm bots are infected in stages. The most common vectors
for propagating the primary infection appear to be e-mail or
infected web sites.
• E-mail was sent with sensational subject lines like “230 die as
Storm batters Europe”. Likewise, users were lured into
downloading free but infected files from web sites containing
music of various pop artists.
A Generic Botnet
Advice to a wannabe Security Analyst
“Security engineering, especially in this third
wave, requires you to think differently. You
need to figure out not how something works,
but how something can be made not to work.
You need to imagine an intelligent and
malicious adversary inside your system
(remember Satan’s computer) constantly
trying new ways to subvert it . . .
Advice to a wannabe Security Analyst
(contd.)
. . . You have to consider all ways your
system can fail, most of them having nothing
to do with the design itself. You have to look
at everything backwards, upside down, and
sideways. You have to think like an alien.”
- Bruce Schneier