1. CSCE 201 Introduction to Information Security Fall 2010 Data Protection

2. CSCE 201 - Farkas22 Reading assignments Required for this class: – D. Cross, Data Protection and Recovery in Windows XP, http://technet.microsoft.com/en-us/library/bb457020.aspx http://technet.microsoft.com/en-us/library/bb457020.aspx – M. Horowitz The Safest Way to Protect Sensitive Computing Files, August 24, 2009, http://www.esecurityplanet.com/views/article.php/38358 61/article.htm http://www.esecurityplanet.com/views/article.php/38358 61/article.htm – Wikipedia, Encryption, http://en.wikipedia.org/wiki/Encryption http://en.wikipedia.org/wiki/Encryption

3. CSCE 201 - Farkas3 Sensitive Files Must be protected from – Hackers – Other users What to protect and at what level  security policy How to protect  security policy

4. CSCE 201 - Farkas4 Security Mechanism Several alternatives Which one to choose? – Level of assurance – User’s preferences (familiarity, ease of use, recommendations, etc.) – User’s technical knowledge – Availability – Financial considerations – Etc.

5. CSCE 201 - Farkas5 Data Protection via Operating System Microsoft® Windows® XP provides many enhancements in the area of data protection – Encrypting File System (EFS) – Data Recovery Agents (DRA) Best Practices Note: EFS is only available on Windows XP Professional; it is not supported on Windows XP Home Edition

6. What is Encryption? How secure it is? Can you decrypt the followings? HAY?OROWEU How are you? Hello

7. CSCE 201 - Farkas7 Insecure communications Sender Snooper Recipient Insecure channel Confidential

8. CSCE 201 - Farkas8 Terminology  Plaintext (cleartext): a message in its original form  Ciphertext (cyphertext): an encrypted message  Encryption: transformation of a message to hide its meaning  Cipher: cryptographic algorithm. A mathematical function used for encryption (encryption algorithm) and decryption (decryption algorithm).

9. CSCE 201 - Farkas9 Terminology  Decryption: recovering meaning from ciphertext  Cryptography: art and science of keeping messages secure  Cryptanalysis: art and science of breaking ciphertext  Cryptology: study of both cryptography and cryptanalysis

10. CSCE 201 - Farkas10 Lecture 4 Encryption and Decryption Plaintext EncryptionDecryption Ciphertext Additional requirements : Authentication Between communicating parties Third-party authentication Non-repudiation Integrity verification Key distribution Secret key (secure distribution) Public key (reliable distribution)

11. CSCE 201 - Farkas11 Lecture 4 Cryptanalysis Cryptanalyst’s goal: – Break message – Break key – Break algorithm

12. Secret Key Encryption (Symmetric key, Traditional)

13. CSCE 201 - Farkas13 Lecture 4 Secret Key Cryptosystem Encryption Decryption Plaintext Ciphertext K SenderRecipient C=E(K,M) M=D(K,C) K needs secure channel

14. CSCE 201 - Farkas14 Lecture 4 Basic Encryption Techniques Substitution (confusion) Permutation (diffusion) Combinations and iterations of these

15. CSCE 201 - Farkas15 Lecture 4 Simple Alphabetic Substitution Assign a new symbol to each plain text symbol randomly or by key, e.g., C  k, A  h, B  l M=CAB C =k h l  Advantages: large key space 26!  Disadvantages: trivially broken for known plaintext attack, repeated pattern, letter frequency distributions unchanged

16. CSCE 201 - Farkas16 Lecture 4 Transposition Letters of the message are rearranged Break patterns, e.g., columnar transposition Plaintext: this is a test t h i s i s a ttiehssiatst! e s t ! Advantages: easy to implement Disadvantages:  Trivially broken for known plaintext attack  Easily broken for cipher only attack

17. CSCE 201 - Farkas17 Symmetric Key Encryption Algorithms Data Encryption Standard (DES) Advanced Encryption Standard (AES)

18. CSCE 201 - Farkas18 Public-Key Encryption Two keys – one is private one is public Solves the key distribution problem (but need reliable channel) Provides electronic signatures Slower than secret-key encryption

19. CSCE 201 - Farkas19 Public-Key Encryption Needed for security: – One of the keys must be kept secret – Impossible (at least impractical) to decipher message if no other information is available – Knowledge of algorithm, one of the keys, and samples of ciphertext must be insufficient to determine the other key

20. CSCE 201 - Farkas20 Confidentiality A Sender B Recipient Insecure channel Plaintext Ciphertext Encryption Alg. Decryption Alg. B’s public key B’s private key (need reliable channel)

21. CSCE 201 - Farkas21 Public Key Cryptosystem Concept conceived by Diffie and Hellman in 1976 Rivest, Shamir, and Adleman (RSA) describe a public key system in 1978 Many proposals have been broken e.g., Merkle-Hellman proposal broken by Shamir Serious candidates (public domain) – RSA – El Gamal

22. CSCE 201 - Farkas22 Digital Signatures in RSA A B Insecure channel Plaintext Signed plaintext Encryption Alg. Decryption Alg. A’s public keyA’s private key (need reliable channel) SignVerify

23. CSCE 201 - Farkas23 Signature and Encryption D EDE A B Plaintext Signed Plaintext Signed Plaintext Encrypted Signed Plaintext A’s private key B’s public key B’s private key A’s public key

24. CSCE 201 - Farkas24 Hash Functions Hash function h maps an input x of arbitrary length to a fixed length output h(x) (compression) Accidental or intentional change to the data will change the hash value Given h and x, h(x) is easy to compute (ease of computation)

25. CSCE 201 - Farkas25 Hash functions Preimage resistant (one-way): if for all specified outputs, it is computationally infeasible to find any input that hashes to that output Second-preimage resistent (weak collision resistant): if it is computationally infeasible to find any second input which has the same output as any specified input Collision resistant (strong collision resistant): if it is computationally infeasible to find any two distinct inputs that has the same output

26. CSCE 201 - Farkas26 Attacks First preimage attack: given a hash h, find a message m such that hash(m) = h Second preimage attack: given a fixed message m1, find a different message m2 such that hash(m2) = hash(m1) Attack complexity: 2 n (considered too high for a typical output size of n=160 bits) Practical attacks: Collision attack

27. Use of Encryption for Data Protection

28. CSCE 201 - Farkas28 Data Recovery A process by which individual data elements such as files or folders are encrypted for more than one person or entity Windows XP operating system: symmetrically encrypted data blocks The symmetric key being protected by one or more public keys of a public/private key pair

29. CSCE 201 - Farkas29 Encrypting File System (EFS) Provides file system-level encryption Enables files to be transparently encrypted on NTFS file systems Protects confidential data from attackers with physical access to the computer While the operating system is running: User authentication and access control lists Attacker gains physical access to the computer: need protection of harddrive

30. CSCE 201 - Farkas30 File system-level encryption Individual files or directories are encrypted by the file system itself Advantages: – Flexible file-based key management – Individual management of encrypted files – Access control can be enforced through the use of public-key cryptography – Cryptographic keys are only held in memory while the file that is decrypted by them is held open

31. CSCE 201 - Farkas31 Next Class Malicious code