Information Systems Security

1. Information Systems Security Cryptography Domain #3

2. Cryptography Now and Before • In the past – mainly used for confidentiality • Today • Still used for confidentiality • Data integrity • Source authentication • Non-repudiation

3. Definitions • Cryptography • Hiding the meaning of communication • Cipher • Transforms characters or bits into an unreadable format • Cryptographic Algorithm • Procedure that turns readable data into an unreadable format (usually through mathematical formulas

4. More Definitions • Cryptanalysis • Science of studying and breaking encryption mechanisms • Cryptology • Study of cryptography and cryptanalysis • Key Clustering • When two keys generate the same ciphertext from the same plaintext

5. MORE Definitions • Cryptosystem • Encompasses all of the components for encryption and decryption • Plaintext • Readable format / decrypted • Ciphertext • Unreadable format / encrypted • Work Factor • Time, effort, and resources necessary to break a cryptosystem (should be too high for compromise)

6. Symmetric Cryptography • Two instances of the same key • One key used for encryption and decryption • Sender/receiver use same key (public/shared) • Key distribution a problem • Secure 2nd channel needed or offline • Does not implement non-repudiation

7. Historical Symmetric Keys • Hieroglyphics • Recorded in use in 2000 B.C. • 1st known type of cryptography • Only certain people knew the symbols • Used to glorify the life of deceased

8. Scytale Cipher • Paper or leather was wrapped around a rod • Message was written on paper and delivered by messenger • Sender and receiver had to have rod of same diameter • Was used around 400 B.C. • Transposition Cipher

9. Caesar Cipher • Symmetric cipher • Keys shifted ‘n’ number of letters • Also referred to as a shift cipher • If one alphabet is used – monoalphabetic substitution • If two alphabets are used – polyalphabetic substitution

10. Example • Decode the following messages: • UIJT POF JT FBTA

11. Vigenere Cipher • Polyalphabetic substitution cipher • Proposed by court of King Henry III • An extension of the Caesar Cipher • Strength is no frequency analysis can be performed

12. Enigma Machine • Rotor cipher used polyalphabetic substitution • Employed in WWII • Symmetric – original setting of rotors and how rotors moved must be the same • Sender entered characters and the rotors moved

13. Vernam Cipher • One-time pad • Only method that is completely secure • Still used today for backups encryption method • Senders uses one-time pad to encrypt and receiver uses twin to decrypt

14. Vernam • Deemed unbreakable if: • Pad is truly random values • Used only once • Securely distributed • Securely stored • Pad is at least as long as message

15. Key & Algorithm Relationship • Key – long string of values • Algorithm – group of mathematical equations that can be used for the encryption process • Used together – key values are used by the algorithm to indicate which equations to use, in what order, and with what values

16. Breaking Cryptosystems • Brute Force • Attempts all possible combinations of a given key space to derive the key • Takes ciphertext, applies key, and sees if understandable plaintext is derived • How many possible keys? • 40-bit key = 1 trillion • 56-bit key = 72 quadrillion • Easily breakable due to Moore’s Law • In 1998, broke DES in three days with 1536 PCs running at 40 MHz

17. Frequency Analysis • Patterns in ciphertext are identified and matched back to plaintext • For example, the most common letters in the English language are “iron seat” • Allows attackers to reverse-engineer encryption process

18. Characteristics of Strong Algorithms • Confusion • Complexity of the process to increase the workfactor of reverse engineering • Interceptor should not be able to predict what changing one character will do to ciphertext • Diffusion • Component going through an encryption should have MANY things take place • Change should affect many part of the ciphertext

19. Kerckhoff’s Principle • Only secrecy involved with cryptography should be the key • Should not base security on figuring out the algorithm • Algorithms should be publicly known • Government does NOT agree

20. Type of Ciphers Used Today • Substitution Methods • Transposition Methods • Symmetric Ciphers • Block • Stream • Asymmetric Ciphers

21. Encryption/Decryption • Substitution • Substitute one bit for another • Destination has to have the correct key to indicate how to substitute • Transposition • Bits are moved to new place in stream • No new bits are introduced • Destination must have correct key to unscramble

22. Symmetric – Block Cipher • Message is divided into blocks and put through mathematical function • Each block is encrypted separately • While message is not encrypted as one entity • Best used in software implementation

23. S-Box • Substitution box is common component • Table where a lookup using a few bits as an index yields some other bits • For example, in an 8 by 32 s-box, you enter with 8 bits and come out with 32 • DES uses 6 by 4 boxes • Blowfish uses 8 by 32 boxes

24. Symmetric Stream Cipher • Encrypts individual bits of the message • Bits are X-ORed with a bit from message • Stream algorithms have keystroke generators • Best used in hardware implementations • Caesar cipher is an example

25. Message Authentication Code (MAC) • MACs are computed and verified with same key • Four types • Unconditionally secure • One time pad • Has function-based MAC (HMAC) • Uses key with hash function (MD5) • Stream – broken into two substreams • Block – encrypt message and output final block of ciphertext as checksum (DES)

26. Digital Signatures • Provide Authenticity and Non-Repudiation • After hashed, MD value is encrypted with sender’s private key • Receiver validates the digital signature by decrypting it with the sender’s public key • Provides data integrity, authenticity, and non-repudiation

27. Digital Signature vs. MAC • Symmetric Cryptography • MAC = hash + symmetric key • Asymmetric Cryptography • DS = hash + asymmetric key

28. US Government Standard • Digital Signature Standard (DSS) • Secure hashing algorithm (SHA) must be used for message digest creation. • DSA, RSA, and ECDSA asymmetric algorithms can be used for digital signature creation • ECDSA = elliptic curve digital signature algorithm

29. Symmetric Algorithms • Data Encryption Standard (DES) – Break work in half and XOR several times. Became standard in 1977. • Triple DES – Encrypted/decrypted with 3 separate keys. Strength of 2 112. • Advanced Encryption Standard (AES) - Adopted in 1997 by NIST. Had larger block size then DES

30. Advantages of Symmetric • Very fast and secure method for confidentiality • Implemented in either hardware or software • Usually available at no cost to user

31. Disadvantages • Not able to provide non-repudiation • Can not provide access control or digital signatures • Need to share key

32. Security in Hashing • Strength of Hashing Algorithm • The hash should be computed over the entire message • Messages cannot be disclosed by MD value • Different messages should generate different MD values • Collision free • Resistant to birthday attacks

33. Hashing Issue • It is easier to find 2 messages that have the same MD than looking for one particular MD value on a message • Hashing value (n) Brute force to find hash value (2n) Brute force to find any 2 matching hash values 2(n/2) • Crux – A hashing algorithm that generates a larger MD value is less vulnerable to a bday attack than one that creates a smaller one

34. Key Management • Responsibilities • Secure key creation and distribution • Secure key recovery • Secure key storage and destruction • Characteristics • Split knowledge and control • Length of key • Never available in clear text

35. Asymmetric Key AlgorithmsPublic Key Cryptography • No key exchange needed • Users can generate their own public/private key pairs and exchange them • If you receive a public key from Bob, how do you know it is really Bob? • Need a trusted third party to vouch for the identity of the owner of a public key

36. Asymmetric Keys • Allows non-repudiation and access control • Extremely slow • Output may be much larger than the plaintext • Hashing • Integrity • Digital Signatures

37. CA and RA Roles • Registration Authority • Accepts registration requests from users • Validates users identities • Passes request to CA • Certificate Authority • Creates digital signature • Binds identity to signature • Maintains certificate during lifetime • Verisign, Thawte, IP, Belsign, etc.

38. Example • Bob wants to participate in a PKI • Bob send request to RA • RA validates Bob’s identity • RA sends request to CA • CA generates certificate and sends to Bob • Bob’s identity is now bound to the public key that is embedded in the digital certificate

39. Components of PKI • Certificate Revocation Lists (CRL) • Certificates can become revoked • CRL is list of revoked certificates signed by CA • Method to tell others not to trust (compromised) • Certificate Directory • Storage of certificates • Usually publicly accessible • Each certificate is digitally signed

40. Steganography • Hiding information in media • No algorithm, key or encryption required • Hides data • Digital watermarks are used to detect • Messages can be sent without knowledge • Specialized tools to carry this out • Hide and Seek • Steg Detect

41. Email Standards • Pretty Good Privacy (PGP) • Free email client that provides security • Uses passphrases instead of passwords • Web of trust instead of hierarchy of CAs • PGP provides confidentiality via IDEA • Integrity via MD5

42. Secure Protocols • Secure Hypertext (SHTTP) • Protects each message • Older less used • HTTPS • HTTP runs on top of SSL • Provides secure communication channel • All messages are protected • Secure Socket Layer (SSL) • Netscape developed; requies PKI • Works at transport layer

43. Secure email Standard • Secure MIME (SMIME) • Secure Multipurpose Internet Mail Extension • Allows for encryption, hashing, and digital signatures to take place in a uniform manner • Email client vendors follow this standard • Transparent between different email clients

44. Secure Electronic Transaction • SET • Developed by Visa and Mastercard for more secure monetary transactions over the Internet • Uses PKI to protect sensitive data and authenticates each ‘hop’ in the transaction • Slow in acceptance and deployment • Goal to replace SSL • Slow the throughput of the transaction

45. Network Layer Protection • IPSec • Developed because IPv4 has no security • Sets up a secure channel between computers instead of between applications • Application secure channels provided by SSL • Network layer security • Provides host-to-host, host-to-subnet, and subnet-to-subnet connections

46. Key Issues with IPSec • Internet Key Exchange (IKE) • Used to negotiate the key exchange between two entities • Suite of ISAKMP and Oakley protocols • Internet Security Association and Key Management Protocol (ISAKMP) • Framework for key negotiation • Oakley Protocol • Negotiates key information using Diffie-Hellman algorithm

47. IPSec Modes of Operation • Transport Mode • Offers payload protection • Protects header up to the network layer • Tunnel Mode • Protects the whole packet • Includes payload and all headers • Creates a new IP header`

48. Attacks on Crypto • Ciphertext-only Attack • Attacker only has ciphertext • Goal to reverse the encryption process • Known plaintext attack • Attacker has ciphertext and plaintext • Chosen-plaintext attack • Attacker can choose what plaintext is encrypted • Chosen-ciphertext attack • Attacker can choose ciphertext to be decrypted

49. More Attacks • Replay Attack • Attacker obtains a set of credentials and sends them to authentication source • Timestamps and sequence numbers protect against this attack • Man in Middle Attack • Attacker injects itself between two users and reads messages • Sequence numbers and digital signatures protect against this attack