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Cryptographic Protocols and Network Security G. Sivakumar Computer - - PowerPoint PPT Presentation

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Some Puzzles Security Connection Cryptography Need For Formal Methods Cryptographic Protocols and Network Security G. Sivakumar Computer Science and Engineering IIT Bombay siva@iitb.ac.in Oct 14, 2004 G. Sivakumar Computer Science and

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Some Puzzles Security Connection Cryptography Need For Formal Methods

Cryptographic Protocols and Network Security

  • G. Sivakumar

Computer Science and Engineering IIT Bombay siva@iitb.ac.in

Oct 14, 2004

  • G. Sivakumar

Computer Science and Engineering IIT Bombay siva@iitb.ac.in Cryptographic Protocols and Network Security

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Some Puzzles Security Connection Cryptography Need For Formal Methods

Exchanging Secrets

Goal A and B to agree on a secret number. But, C can listen to all their conversation. Solution? A tells B: I’ll send you 3 numbers. Let’s use their LCM as the key.

  • G. Sivakumar

Computer Science and Engineering IIT Bombay siva@iitb.ac.in Cryptographic Protocols and Network Security

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SLIDE 3

Some Puzzles Security Connection Cryptography Need For Formal Methods

Exchanging Secrets

Goal A and B to agree on a secret number. But, C can listen to all their conversation. Solution? A tells B: I’ll send you 3 numbers. Let’s use their LCM as the key.

  • G. Sivakumar

Computer Science and Engineering IIT Bombay siva@iitb.ac.in Cryptographic Protocols and Network Security

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Some Puzzles Security Connection Cryptography Need For Formal Methods

Mutual Authentication

Goal A and B to verify that both know the same secret number. No third party (intruder or umpire!) Solution? A tells B: I’ll tell you first 2 digits, you tell me the last two...

  • G. Sivakumar

Computer Science and Engineering IIT Bombay siva@iitb.ac.in Cryptographic Protocols and Network Security

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SLIDE 5

Some Puzzles Security Connection Cryptography Need For Formal Methods

Mutual Authentication

Goal A and B to verify that both know the same secret number. No third party (intruder or umpire!) Solution? A tells B: I’ll tell you first 2 digits, you tell me the last two...

  • G. Sivakumar

Computer Science and Engineering IIT Bombay siva@iitb.ac.in Cryptographic Protocols and Network Security

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Some Puzzles Security Connection Cryptography Need For Formal Methods

Zero-Knowledge Proofs

Goal A to prove to B that she knows how to solve the cube. Without actually revealing the solution! Solution? A tells B: Close your eyes, let me solve it...

  • G. Sivakumar

Computer Science and Engineering IIT Bombay siva@iitb.ac.in Cryptographic Protocols and Network Security

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SLIDE 7

Some Puzzles Security Connection Cryptography Need For Formal Methods

Zero-Knowledge Proofs

Goal A to prove to B that she knows how to solve the cube. Without actually revealing the solution! Solution? A tells B: Close your eyes, let me solve it...

  • G. Sivakumar

Computer Science and Engineering IIT Bombay siva@iitb.ac.in Cryptographic Protocols and Network Security

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Some Puzzles Security Connection Cryptography Need For Formal Methods

Paper, Scissors, Rock Game

Goal How to play over Internet? Using email, say? Solution? You mail me your choice. I’ll reply with mine.

  • G. Sivakumar

Computer Science and Engineering IIT Bombay siva@iitb.ac.in Cryptographic Protocols and Network Security

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SLIDE 9

Some Puzzles Security Connection Cryptography Need For Formal Methods

Paper, Scissors, Rock Game

Goal How to play over Internet? Using email, say? Solution? You mail me your choice. I’ll reply with mine.

  • G. Sivakumar

Computer Science and Engineering IIT Bombay siva@iitb.ac.in Cryptographic Protocols and Network Security

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Some Puzzles Security Connection Cryptography Need For Formal Methods

  • Mr. Sum and Mr. Product

Someone thinks of two numbers between 2 and 500 inclusive. He then adds them up and whispers the sum to Mr. Sum. He also multiplies them together and whispers the product to Mr. Product. The following conversation then ensues. Mr Product: I don’t know what the two original numbers were. Mr Sum: I already knew that you didn’t know. Mr Product: Well now I know. Mr Sum: Aha! So do I. What were the original two numbers?

  • G. Sivakumar

Computer Science and Engineering IIT Bombay siva@iitb.ac.in Cryptographic Protocols and Network Security

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Some Puzzles Security Connection Cryptography Need For Formal Methods

  • Mr. Sum and Mr. Product

Someone thinks of two numbers between 2 and 500 inclusive. He then adds them up and whispers the sum to Mr. Sum. He also multiplies them together and whispers the product to Mr. Product. The following conversation then ensues. Mr Product: I don’t know what the two original numbers were. Mr Sum: I already knew that you didn’t know. Mr Product: Well now I know. Mr Sum: Aha! So do I. What were the original two numbers?

  • G. Sivakumar

Computer Science and Engineering IIT Bombay siva@iitb.ac.in Cryptographic Protocols and Network Security

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Some Puzzles Security Connection Cryptography Need For Formal Methods

  • Mr. Sum and Mr. Product

Someone thinks of two numbers between 2 and 500 inclusive. He then adds them up and whispers the sum to Mr. Sum. He also multiplies them together and whispers the product to Mr. Product. The following conversation then ensues. Mr Product: I don’t know what the two original numbers were. Mr Sum: I already knew that you didn’t know. Mr Product: Well now I know. Mr Sum: Aha! So do I. What were the original two numbers?

  • G. Sivakumar

Computer Science and Engineering IIT Bombay siva@iitb.ac.in Cryptographic Protocols and Network Security

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SLIDE 13

Some Puzzles Security Connection Cryptography Need For Formal Methods

  • Mr. Sum and Mr. Product

Someone thinks of two numbers between 2 and 500 inclusive. He then adds them up and whispers the sum to Mr. Sum. He also multiplies them together and whispers the product to Mr. Product. The following conversation then ensues. Mr Product: I don’t know what the two original numbers were. Mr Sum: I already knew that you didn’t know. Mr Product: Well now I know. Mr Sum: Aha! So do I. What were the original two numbers?

  • G. Sivakumar

Computer Science and Engineering IIT Bombay siva@iitb.ac.in Cryptographic Protocols and Network Security

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Some Puzzles Security Connection Cryptography Need For Formal Methods

Sharing a Dosa

Goal All should get equal share of dosa. No envy factor. No trusted umpire. Solution? 2 people case is easy- you cut, i choose!

  • G. Sivakumar

Computer Science and Engineering IIT Bombay siva@iitb.ac.in Cryptographic Protocols and Network Security

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SLIDE 15

Some Puzzles Security Connection Cryptography Need For Formal Methods

Sharing a Dosa

Goal All should get equal share of dosa. No envy factor. No trusted umpire. Solution? 2 people case is easy- you cut, i choose!

  • G. Sivakumar

Computer Science and Engineering IIT Bombay siva@iitb.ac.in Cryptographic Protocols and Network Security

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Some Puzzles Security Connection Cryptography Need For Formal Methods

Internet’s Growth and Charter

Information AnyTime, AnyWhere, AnyForm, AnyDevice, ... WebTone like DialTone

  • G. Sivakumar

Computer Science and Engineering IIT Bombay siva@iitb.ac.in Cryptographic Protocols and Network Security

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Some Puzzles Security Connection Cryptography Need For Formal Methods

Internet’s Dream

Why should a fridge be on Internet? Will security considerations make this a nightmare?

  • G. Sivakumar

Computer Science and Engineering IIT Bombay siva@iitb.ac.in Cryptographic Protocols and Network Security

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Some Puzzles Security Connection Cryptography Need For Formal Methods

Security Concerns

Match the following! Problems Attackers Highly contagious viruses Unintended blunders Defacing web pages Disgruntled employees or customers Credit card number theft Organized crime On-line scams Foreign espionage agents Intellectual property theft Hackers driven by technical challenge Wiping out data Petty criminals Denial of service Organized terror groups Spam E-mails Information warfare Reading private files ... Surveillance ... Crackers vs. Hackers Note how much resources available to attackers.

  • G. Sivakumar

Computer Science and Engineering IIT Bombay siva@iitb.ac.in Cryptographic Protocols and Network Security

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Some Puzzles Security Connection Cryptography Need For Formal Methods

Vulnerabilities

Application Security Buggy code Buffer Overflows Host Security Server side (multi-user/application) Client side (virus)

Transmission Security

  • G. Sivakumar

Computer Science and Engineering IIT Bombay siva@iitb.ac.in Cryptographic Protocols and Network Security

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Some Puzzles Security Connection Cryptography Need For Formal Methods

Denial of Service

Small shop-owner versus Supermarket

What can the attacker do? What has he gained or compromised? What defence mechanisms are possible? Screening visitors using guards (who looks respectable?) VVIP security, but do you want to be isolated? what is the Internet equivalent?

  • G. Sivakumar

Computer Science and Engineering IIT Bombay siva@iitb.ac.in Cryptographic Protocols and Network Security

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Some Puzzles Security Connection Cryptography Need For Formal Methods

Yahoo DDoS attack

A real example of network insecurity. Caused traffic to Yahoo to zoom to 100s of Mbps Broke the capacity of machines at Yahoo and its ISPs Internet Control Message Protocol (ICMP) normally used for good purposes. Ping used to check “are you alive?”

  • G. Sivakumar

Computer Science and Engineering IIT Bombay siva@iitb.ac.in Cryptographic Protocols and Network Security

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Some Puzzles Security Connection Cryptography Need For Formal Methods

Yahoo DDoS attack

  • G. Sivakumar

Computer Science and Engineering IIT Bombay siva@iitb.ac.in Cryptographic Protocols and Network Security

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Some Puzzles Security Connection Cryptography Need For Formal Methods

Security Requirements

Informal statements (formal is much harder)

Confidentiality Protection from disclosure to unauthorized persons Integrity Assurance that information has not been modified unauthorizedly. Authentication Assurance of identity of originator of information. Non-Repudiation Originator cannot deny sending the message. Availability Not able to use system or communicate when desired. Anonymity/Pseudonomity For applications like voting, instructor evaluation. Traffic Analysis Should not even know who is communicating with

  • whom. Why?

Emerging Applications Online Voting, Auctions (more later)

And all this with postcards (IP datagrams)!

  • G. Sivakumar

Computer Science and Engineering IIT Bombay siva@iitb.ac.in Cryptographic Protocols and Network Security

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Some Puzzles Security Connection Cryptography Need For Formal Methods

Security Mechanisms

System Security: “Nothing bad happens to my computers and equipment” virus, trojan-horse, logic/time-bombs, ... Network Security:

Authentication Mechanisms “you are who you say you are” Access Control Firewalls, Proxies “who can do what”

Data Security: “for your eyes only”

Encryption, Digests, Signatures, ...

  • G. Sivakumar

Computer Science and Engineering IIT Bombay siva@iitb.ac.in Cryptographic Protocols and Network Security

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Some Puzzles Security Connection Cryptography Need For Formal Methods

Security Mechanisms

System Security: “Nothing bad happens to my computers and equipment” virus, trojan-horse, logic/time-bombs, ... Network Security:

Authentication Mechanisms “you are who you say you are” Access Control Firewalls, Proxies “who can do what”

Data Security: “for your eyes only”

Encryption, Digests, Signatures, ...

  • G. Sivakumar

Computer Science and Engineering IIT Bombay siva@iitb.ac.in Cryptographic Protocols and Network Security

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Some Puzzles Security Connection Cryptography Need For Formal Methods

Security Mechanisms

System Security: “Nothing bad happens to my computers and equipment” virus, trojan-horse, logic/time-bombs, ... Network Security:

Authentication Mechanisms “you are who you say you are” Access Control Firewalls, Proxies “who can do what”

Data Security: “for your eyes only”

Encryption, Digests, Signatures, ...

  • G. Sivakumar

Computer Science and Engineering IIT Bombay siva@iitb.ac.in Cryptographic Protocols and Network Security

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Some Puzzles Security Connection Cryptography Need For Formal Methods

Network Security Mechanism Layers

Cryptograhphic Protocols underly all security mechanisms. Real Challenge to design good ones for key establishment, mutual authentication etc.

  • G. Sivakumar

Computer Science and Engineering IIT Bombay siva@iitb.ac.in Cryptographic Protocols and Network Security

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Some Puzzles Security Connection Cryptography Need For Formal Methods

Cryptography and Data Security

sine qua non [without this nothing :-] Historically who used first? (L & M) Code Language in joint families!

  • G. Sivakumar

Computer Science and Engineering IIT Bombay siva@iitb.ac.in Cryptographic Protocols and Network Security

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Some Puzzles Security Connection Cryptography Need For Formal Methods

Symmetric/Private-Key Algorithms

  • G. Sivakumar

Computer Science and Engineering IIT Bombay siva@iitb.ac.in Cryptographic Protocols and Network Security

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Some Puzzles Security Connection Cryptography Need For Formal Methods

Asymmetric/Public-Key Algorithms

Keys are duals (lock with one, unlock with other) Cannot infer one from other easily How to encrypt? How to sign?

  • G. Sivakumar

Computer Science and Engineering IIT Bombay siva@iitb.ac.in Cryptographic Protocols and Network Security

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Some Puzzles Security Connection Cryptography Need For Formal Methods

One way Functions

Mathematical Equivalents

Factoring large numbers (product of 2 large primes) Discrete Logarithms

  • G. Sivakumar

Computer Science and Engineering IIT Bombay siva@iitb.ac.in Cryptographic Protocols and Network Security

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Some Puzzles Security Connection Cryptography Need For Formal Methods

One-way Functions

Computing f(x) = y is easy.

  • Eg. y = 4x mod 13 (If x is 3, y is —?)

n 4n mod 13 10n mod 13 1 4 10 2 3 9 3 12 12 4 9 3 5 10 4 6 1 1 7 4 10 . . . . . . . . .

Note: need not work with numbers bigger than 13 at all! But given y = 11, finding suitable x is not easy! Can do by brute-force (try all possibilities!) No method that is much better known yet!

  • G. Sivakumar

Computer Science and Engineering IIT Bombay siva@iitb.ac.in Cryptographic Protocols and Network Security

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Some Puzzles Security Connection Cryptography Need For Formal Methods

RSA Encryption Example

Pick 2 primes (p = 251, q = 269). Let n = p ∗ q = 67519 and φ(n) = (p − 1) ∗ (q − 1) = 67000. Pick e = 50253 (relatively prime to φ(n)). Compute d = e−1 mod φ(n) = 27917 (only one such d exists, with (e ∗ d) mod φ(n) = 1. Interesting number-theoretic property for any m < n is the following ((me) mod n)d mod n = m = ((md) mod n)e mod n Therefore to encrypt a message m take it 2 chars at a time (16 bits, so less than 65536) and compute E(m) = me mod n. This is the public key (the numbers e, n). Decrypting is done by m = D(E(m)) = E(m)d mod n and is easy

  • nly if d (private key) is known.
  • G. Sivakumar

Computer Science and Engineering IIT Bombay siva@iitb.ac.in Cryptographic Protocols and Network Security

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Some Puzzles Security Connection Cryptography Need For Formal Methods

Digital Signatures

  • G. Sivakumar

Computer Science and Engineering IIT Bombay siva@iitb.ac.in Cryptographic Protocols and Network Security

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Some Puzzles Security Connection Cryptography Need For Formal Methods

Verifying Signatures

Digital Signatures provide three important security services Integrity, Source Non-Repudiation, Authentication

  • G. Sivakumar

Computer Science and Engineering IIT Bombay siva@iitb.ac.in Cryptographic Protocols and Network Security

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Some Puzzles Security Connection Cryptography Need For Formal Methods

Diffie-Hellman Key Establishment Protocol

  • G. Sivakumar

Computer Science and Engineering IIT Bombay siva@iitb.ac.in Cryptographic Protocols and Network Security

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Some Puzzles Security Connection Cryptography Need For Formal Methods

Man-in-the-middle attack

Authentication was missing! Can be solved if Kasparov and Anand know each other’s public key (Needham-Schroeder). Yes, but different attack possible.

  • G. Sivakumar

Computer Science and Engineering IIT Bombay siva@iitb.ac.in Cryptographic Protocols and Network Security

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Some Puzzles Security Connection Cryptography Need For Formal Methods

Needham-Schroeder Protocol

  • G. Sivakumar

Computer Science and Engineering IIT Bombay siva@iitb.ac.in Cryptographic Protocols and Network Security

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Some Puzzles Security Connection Cryptography Need For Formal Methods

Attack by Lowe (1995)

  • G. Sivakumar

Computer Science and Engineering IIT Bombay siva@iitb.ac.in Cryptographic Protocols and Network Security

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Some Puzzles Security Connection Cryptography Need For Formal Methods

Why Are Security Protocols Often Wrong?

They are trivial programs built from simple primitives, BUT, they are complicated by concurrency a hostile environment

a bad user controls the network Concern: active attacks masquerading, replay, man-in-middle, etc.

vague specifications

we have to guess what is wanted

Ill-defined concepts Protocol flaws rather than cryptosystem weaknesses Formal Methods needed!

  • G. Sivakumar

Computer Science and Engineering IIT Bombay siva@iitb.ac.in Cryptographic Protocols and Network Security

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Some Puzzles Security Connection Cryptography Need For Formal Methods

Online Voting Protocols

Are we ready for elections via Internet? George Bush (Nov 2000, dimpled chads) Pervez Musharaf (April 2002) Maharashtra (Oct 13, 2004) E-Voting Protocols Requirements

No loss of votes already cast (reliability) No forging of votes (authentication) No modification of votes cast (integrity) No multiple voting No vote secrecy violation (privacy) No vulnerability to vote coercion No vulnerability to vote selling or trading protocols (voter is an adversary) No loss of ability to cast and accept more votes (availability, no denial of service)

  • G. Sivakumar

Computer Science and Engineering IIT Bombay siva@iitb.ac.in Cryptographic Protocols and Network Security

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Some Puzzles Security Connection Cryptography Need For Formal Methods

Other Desirable Properties

Must not only be correct and secure, but also be seen to be so by skeptical (but educated and honest) outsiders. Auditability: Failure or procedural error can be detected and corrected, especially the loss of votes. Verifiability: Should be able to prove

My vote was counted All boothes were counted The number of votes in each booth is the same as the number

  • f people who voted

No one I know who is ineligible to vote did so No one voted twice ...

without violating anonymity, privacy etc. Zero Knowledge Proofs

  • G. Sivakumar

Computer Science and Engineering IIT Bombay siva@iitb.ac.in Cryptographic Protocols and Network Security

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Some Puzzles Security Connection Cryptography Need For Formal Methods

References

Books TCP/IP Illustrated by Richard Stevens, Vols 1-3, Addison-Wesley. Applied Cryptography - Protocols, Algorithms, and Source Code in C by Bruce Schneier, Jon Wiley & Sons, Inc. 1996 Cryptography and Network Security: Principles and Practice by William Stallings (2nd Edition), Prentice Hall Press; 1998. Practical Unix and Internet Security, Simson Garfinkel and Gene Spafford, O’Reilly and Associates, ISBN 1-56592-148-8. Web sites www.cerias.purdue.edu (Centre for Education and Research in Information Assurance and Security) www.sans.org (System Administration, Audit, Network Security) cve.mitre.org (Common Vulnerabilities and Exposures) csrc.nist.gov (Computer Security Resources Clearinghouse) www.vtcif.telstra.com.au/info/security.html

  • G. Sivakumar

Computer Science and Engineering IIT Bombay siva@iitb.ac.in Cryptographic Protocols and Network Security