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Introduction to Information Security. Mark Stamp Department of Computer Science San Jose State University stamp@cs.sjsu.edu. The Cast of Characters. Alice and Bob are the good guys. Trudy is the bad guy. Trudy is our generic “intruder”. Alice’s Online Bank.
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Introduction toInformation Security Mark StampDepartment of Computer ScienceSan Jose State Universitystamp@cs.sjsu.edu Intro to Information Security 1
The Cast of Characters • Alice and Bob are the good guys • Trudy is the bad guy • Trudy is our generic “intruder” Intro to Information Security 2
Alice’s Online Bank • Alice opens Alice’s Online Bank (AOB) • What are Alice’s security concerns? • If Bob is a customer of AOB, what are his security concerns? • How are Alice and Bob concerns similar? How are they different? • How does Trudy view the situation? Intro to Information Security 3
CIA • Confidentiality, Integrity and Availability • AOB must prevent Trudy from learning Bob’s account balance • Confidentiality: prevent unauthorized reading of information Intro to Information Security 4
CIA • Trudy must not be able to change Bob’s account balance • Bob must not be able to improperly change his own account balance • Integrity: prevent unauthorized writing of information Intro to Information Security 5
CIA • AOB’s information must be available when needed • Alice must be able to make transaction • If not, she’ll take her business elsewhere • Availability: Data is available in a timely manner when needed • Availability is a “new” security concern • In response to denial of service (DoS) Intro to Information Security 6
Beyond CIA • How does Bob’s computer know that “Bob” is really Bob and not Trudy? • Bob’s password must be verified • This requires some clever cryptography • What are security concerns of pwds? • Are there alternatives to passwords? Intro to Information Security 7
Beyond CIA • When Bob logs into AOB, how does AOB know that “Bob” is really Bob? • As before, Bob’s password is verified • Unlike standalone computer case, network security issues arise • What are network security concerns? • Protocols are critically important • Crypto also important in protocols Intro to Information Security 8
Beyond CIA • Once Bob is authenticated by AOB, then AOB must restrict actions of Bob • Bob can’t view Charlie’s account info • Bob can’t install new software, etc. • Enforcing these restrictions is known as authorization • Access control includes both authentication and authorization Intro to Information Security 9
Beyond CIA • Cryptography, protocols and access control are implemented in software • What are security issues of software? • Most software is complex and buggy • Software flaws lead to security flaws • How to reduce flaws in software development? Intro to Information Security 10
Beyond CIA • Some software is intentionally evil • Malware: computer viruses, worms, etc. • What can Alice and Bob do to protect themselves from malware? • What can Trudy do to make malware more “effective”? Intro to Information Security 11
Beyond CIA • Operating systems enforce security • For example, authorization • OS: large and complex software • Win XP has 40,000,000 lines of code! • Subject to bugs and flaws like any other software • Many security issues specific to OSs • Can you trust an OS? Intro to Information Security 12
My Book • The text consists of four major parts • Cryptography • Access control • Protocols • Software Intro to Information Security 13
Cryptography • “Secret codes” • The book covers • Classic cryptography • Symmetric ciphers • Public key cryptography • Hash functions • Advanced cryptanalysis Intro to Information Security 14
Access Control • Authentication • Passwords • Biometrics and other • Authorization • Access Control Lists (ACLs) and Capabilities • Multilevel security (MLS), security modeling, covert channel, inference control • Firewalls and Intrusion Detection Systems Intro to Information Security 15
Protocols • Simple authentication protocols • “Butterfly effect” --- small change can have drastic effect on security • Cryptography used in protocols • Real-world security protocols • SSL, IPSec, Kerberos • GSM security Intro to Information Security 16
Software • Software security-critical flaws • Buffer overflow • Other common flaws • Malware • Specific viruses and worms • Prevention and detection • The future of malware Intro to Information Security 17
Software • Software reverse engineering (SRE) • How hackers “dissect” software • Digital rights management • Shows difficulty of security in software • Also raises OS security issues • Limits of testing • Open source vs closed source Intro to Information Security 18
Software • Operating systems • Basic OS security issues • “Trusted” OS requirements • NGSCB: Microsoft’s trusted OS for PC • Software is a big security topic • Lots of material to cover • Lots of security problems to consider Intro to Information Security 19
Think Like Trudy • In the past, no respectable sources talked about “hacking” in detail • It was argued that such info would help hackers • Very recently, this has changed • Books on network hacking, how to write evil software, how to hack software, etc. Intro to Information Security 20
Think Like Trudy • Good guys must think like bad guys! • A police detective • Must study and understand criminals • In information security • We want to understand Trudy’s motives • We must know Trudy’s methods • We’ll often pretend to be Trudy Intro to Information Security 21
Think Like Trudy • Is all of this security information a good idea? • “It’s about time somebody wrote a book to teach the good guys what the bad guys already know.” --- Bruce Schneier Intro to Information Security 22
Think Like Trudy • We must try to think like Trudy • We must study Trudy’s methods • We can admire Trudy’s cleverness • Often, we can’t help but laugh at Alice and Bob’s stupidity • But, we cannot act like Trudy Intro to Information Security 23
Security Books Intro to Information Security 24
Security Books • Security Engineering: A Guide to Building Dependable Distributed Systems, Anderson, John Wiley & Sons, Inc., 2001 • Plusses • Highly readable/entertaining • Case studies • Emphasis on human factors • Minuses • Glosses over technical issue • Not a textbook Intro to Information Security 25
Security Books • Network Security: Private Communication in a Public World, second edition, Kaufman, Perlman, and Speciner, Prentice Hall, 2002 • Plusses • Solid on protocols • Brief but good on crypto • Minuses • No software, access control • Too much RFC detail Intro to Information Security 26
Security Books • Security in Computing, third edition, Pfleeger and Pfleeger, Prentice Hall, 2003 • Plusses • Good on OS topics • OK on software topics • Minuses • Dated • Boring Intro to Information Security 27
Security Books • Applied Cryptography: Protocols, Algorithms and Source Code in C, Second Edition, Schneier, John Wiley & Sons, Inc., 1995 (2nd edition) • Plusses • Encyclopedic • Widely used • Minuses • Crypto only • Sloppy in places Intro to Information Security 28
Security Books • Computer Security, Gollmann, John Wiley & Sons, Inc., 1999 • Plusses • Chapter 8: How things go wrong • Good on security modeling • Minuses • Mostly theoretical • No software/limited topics Intro to Information Security 29
Security Books • Computer Security: Art and Science, Bishop, Addison Wesley, 2003 • Plusses • Security modeling • Theory • Minuses • Theory, theory, and more theory • As much fun to read as a calculus textbook Intro to Information Security 30
Security Books • Fundamentals of Secure Computer Systems, Tjaden, Franklin, Beedle, and Associates, 2003 • Plusses • Intrusion detection systems • Good general approach • Minuses • Weak crypto, software, protocols • Good approach, not well executed Intro to Information Security 31
Security Books • Cryptography and Network Security: Principles and Practice, 3rd edition, Stallings, Prentice Hall, 2002 • Plusses • Some OK protocols material • Minuses • Lots of pointless facts • Not coherent Intro to Information Security 32
“Hacker” Books • Counter Hack: A Step-by-Step Guide to Computer Attacks and Effective Defenses, Skoudis, Prentice Hall, 2001 • Shellcoder’s Handbook: Discovering and Exploiting Security Holes, Koziol et al, Wiley, 2004 • Hacker Disassembling Uncovered, Kaspersky, A-List, 2003 • Reversing: Secrets of Reverse Engineering, Eilam, Wiley, 2005 Intro to Information Security 33
My Book • Information Security: Principles and Practice, Stamp, John Wiley & Sons, Inc., 2005 • Plusses • Too many to list… • Minuses • Can’t think of any… Intro to Information Security 34
Crypto Intro to Information Security 35
Crypto Topics • Crypto Basics • Symmetric ciphers • Stream ciphers, Block ciphers • Public key crypto • Knapsack, RSA, DH, ECC, signatures, etc. • Hash functions • Advanced cryptanalysis Intro to Information Security 36
Crypto • Cryptology The art and science of making and breaking “secret codes” • Cryptography making “secret codes” • Cryptanalysis breaking “secret codes” • Crypto all of the above (and more) Intro to Information Security 37
How to Speak Crypto • A cipher or cryptosystem is used to encrypt the plaintext • The result of encryption is ciphertext • We decrypt ciphertext to recover plaintext • A keyis used to configure a cryptosystem • A symmetric key cryptosystem uses the same key to encrypt as to decrypt • A public key cryptosystem uses a public key to encrypt and a private key to decrypt (sign) Intro to Information Security 38
Crypto • Basis assumption • The system is completely known to the attacker • Only the key is secret • Also known as Kerckhoffs Principle • Crypto algorithms are not secret • Why do we make this assumption? • Experience has shown that secret algorithms are weak when exposed • Secret algorithms never remain secret • Better to find weaknesses beforehand Intro to Information Security 39
Crypto as Black Box key key encrypt plaintext plaintext decrypt ciphertext Intro to Information Security 40
Taxonomy of Cryptography • Symmetric Key • Same key for encryption as for decryption • Stream ciphers • Block ciphers • Public Key • Two keys, one for encryption (public), and one for decryption (private) • Digital signatures --- nothing comparable in symmetric key crypto • Hash algorithms Intro to Information Security 41
Taxonomy of Cryptanalysis • Ciphertext only • Known plaintext • Chosen plaintext • “Lunchtime attack” • Protocols might encrypt chosen text • Adaptively chosen plaintext • Related key • Forward search (public key crypto only) • Etc., etc. Intro to Information Security 42
Symmetric Key Crypto • Stream cipher --- like a one-time pad • Key is relatively short • Key is stretched into a long keystream • Keystream is then used like a one-time pad • Block cipher --- based on codebook concept • Block cipher key determines a codebook • Each key yields a different codebook • Employ both “confusion” and “diffusion” Intro to Information Security 43
Block Cipher Notation • P = plaintext block • C = ciphertext block • Encrypt P with key K to get ciphertext C • C = E(P, K) • Decrypt C with key K to get plaintext P • P = D(C, K) Intro to Information Security 44
Block Cipher Modes • Many modes of operation • We discuss two • Electronic Codebook (ECB) mode • Obvious thing to do • Encrypt each block independently • There is a serious weakness • Cipher Block Chaining (CBC) mode • Chain the blocks together • More secure than ECB, virtually no extra work Intro to Information Security 45
ECB Mode • Notation: C=E(P,K) • Given plaintext P0,P1,…,Pm,… • Obvious way to use a block cipher is EncryptDecrypt C0=E(P0,K), P0=D(C0,K), C1=E(P1,K), P1=D(C1,K), C2=E(P2,K),… P2=D(C2,K),… • For a fixed key K, this is an electronic version of a codebook cipher • A new codebook for each key Intro to Information Security 46
ECB Weaknesses • Suppose Pi=Pj • Then Ci=Cj and Trudy knows Pi=Pj • This gives Trudy some information, even if she does not know Pi or Pj • Trudy might know Pi • A “cut and paste” attack also possible Intro to Information Security 47
Alice Hates ECB Mode • Alice’s uncompressed image, Alice ECB encrypted (TEA) • Why does this happen? • Same plaintext block same ciphertext! Intro to Information Security 48
CBC Mode • Blocks are “chained” together • A random initialization vector, or IV, is required to initialize CBC mode • IV is random, but need not be secret EncryptionDecryption C0 = E(IVP0,K), P0 = IVD(C0,K), C1 = E(C0P1,K), P1 = C0D(C1,K), C2 = E(C1P2,K),… P2 = C1D(C2,K),… Intro to Information Security 49
CBC Mode • Identical plaintext blocks yield different ciphertext blocks • Cut and paste is still possible, but more complex (and will cause garbles) • If C1 is garbled to, say, G then P1 C0D(G,K), P2 GD(C2,K) • But, P3 = C2D(C3,K), P4 = C3D(C4,K), … • Automatically recovers from errors! Intro to Information Security 50