Security

1. Security

2. Reported Security Incidents 1995 – 2003Source: http://www.cert.org/present/cert-overview-trends/module-1.pdf

3. Imperative Need for Secure CommunicationCost of downtime

4. Secure Communication • Characteristics of a secure communication • Confidentiality • Authentication • Message Integrity and non-repudiation • Availability and Access Control

5. Confidentiality • The communicator wants the following to be confidential: • The fact that the communication is occurring • Timing of communication • Frequency of communication • Confidentiality often relies on cryptographic techniques for encrypting/ decrypting data using one or more keys to encrypt/decrypt data

6. Authentication • Both sender and receiver should be able to confirm identity of other party involved in communication • Confirm that the other party is indeed who/what they claim to be • Authentication relies on authentication techniques, several of which rely on cryptographic techniques

7. Message Integrity and Non-Repudiation • Message integrity • Content of communication is not altered maliciously or by accident • Relies on cryptographic techniques • Non-repudiation • Not denying what was communicated

8. Availability • Can communication occur in first place? • Hackers preventing infrastructure from being used by legitimate users – e.g., viruses, DoS attacks • Detect breaches and respond to attacks

9. Access Control • Entities allowed to gain access to resources only if they have the appropriate access rights (e.g., login ID, passwords, biometric devices) • Facilitated by firewalls, which provide access control based on a per-packet basis, and on a per-service basis. • Provide a degree of isolation and protection from those outside of one’s network

10. Cryptography • Symmetric Key Cryptography • Public Key Cryptography

11. Symmetric Key Cryptography • Symmetric Key Cryptography • Caesar Cipher • Monoalphabetic Cipher • Polyalphabetic Cipher • Data Encryption Standard (DES) • Triple DES (3DES) • Advanced Encryption Standard (AES) • Trusted Intermediaries for symmetric key distribution • Key Distribution Center (KDC) • Kerberos

12. Basic Terminology • Plain Text • Original data – not disguised • Cipher (Encrypted) Text • Disguised data – looks unintelligible to intruder • Data disguised using encryption algorithm • Key • A string of #s or characters used as input to encryption algorithm to disguise plain text • Symmetric Key: Both parties use same key to encrypt and decrypt text

13. Symmetric Key Cryptography • Caesar Cipher • Each letter in plaintext is substituted with letter that is K letters later • Wrap around is allowed (i.e., z followed by letter a) • If K = 3, a in plaintext becomes d in cipher text b in plaintext becomes e in cipher text • Example: Decrypt the following using a Caesar Cipher of K =3; Assume ‘wrap around’ is allowed. “L JP J JHHN”

14. Symmetric Key Cryptography • Data Encryption Standard (DES) • Published in 1977, and updated in 1993 • For commercial and non-classified U.S. Govt. use • Encodes plaintext using 56-bit key • Objective: Scramble data and key so that every bit of the cipher text depends on every bit of the data and every bit of the key • Algorithm: Complex (beyond the scope of the course); Decryption works by reversing the algorithm’s operations.

15. How well does DES work? • DES challenge contest • Launched in 1997 by RSA Data Security Inc. -- A network security company • Encrypted “strong cryptography makes the world a safer place” using a 56-bit DES. • Winning team took 4 months to decode. • Used volunteers throughout the Internet to systematically explore key space. • Claimed $10K cash prize after testing only a quarter of the key space (about 18 quadrillion keys)

16. How well does DES work? • In 1999, RSA launched another DES challenge. • Message was decrypted in little over 22 hours by a network of volunteers and a special purpose computer called “Deep Crack”. • Claimed $250 K cash prize.

17. Symmetric Key Cryptography • Triple DES (3 DES) • If 56-bit DES is considered to be insecure, one can simply run the algorithm multiple times, using a different key each time • DES run three times (with a different 56-bit key each time DES is run).

18. Symmetric Key Cryptography • Advanced Encryption Standard (AES) • NIST – in Nov 2001 announced successor to DES. • AES is also a symmetric key algorithm that processes data in 128-bit blocks • AES can operate with 128-bit keys, 192-bit keys, and 256-bit keys

19. Trusted Intermediaries • Disadvantage of Symmetric Key Cryptography: • 2 communicating parties have to agree upon their secret key ahead of time in a secure manner. • Since sender and receiver do not meet face to face in the networking world , they need a trusted intermediary • Trusted Intermediaries: • Key Distribution Center • Kerberos

20. Key Distribution Center (KDC) • A server that shares a different secret symmetric key with each registered user. • KDC knows the secret key of each user, and each user can communicate securely with KDC using this key.

21. Example: Using KDC • Assume Sender (S) and Recipient (R) use KDC for their communication. • Assume S’s secret key known to S and KDC is KS-KDC • Assume R’s secret key known to R and KDC is KR-KDC.

22. Example: Using KDC • Using key, S sends a message to KDC saying that S wants to communicate with R. We denote this message as MS-KDC(S, R). • KDC decrypts MS-KDC(S, R) • KDC generates a random number key KSR, which is to be used as symmetric key by S and R during their communication.

23. Example: Using KDC – cont’d • KDC sends S the key KSR, and a pair of values X and KSR encrypted using R’s key. We denote this message sent back to S by KDC as: • MKDC-S(KSR, MKDC-R(X, KSR)). • S decrypts message and extracts symmetric key KSR. S extracts and forwards MKDC-R(X, KSR) to R • Note that S cannot decrypt MKDC-R(X, KSR) • R decrypts MKDC-R(X, KSR) and uses KSR as symmetric key to converse with S • R and S communicate using symmetric key KSR

24. Kerberos • Developed by MIT • Very similar to KDC • Has additional functions such as: • Time stamp for validity of “nonce” KSR. • Has information about which users have access privileges to which services on which network servers.

25. Public Key CryptographyOverview • Define concept of Public and Private keys • Demonstrate RSA Algorithm • Review Authentication Protocols (ap) • Exchanging Public Keys • Person in the middle-attack

26. Introduction - Public Key Cryptography • Use public key cryptography so that two parties can communicate using encryption/decryption without using a shared secret key. • Key maintenance is difficult • Public key cryptography: • A radically different and marvelously elegant approach towards encryption/decryption • Also used for authentication and digital signatures

27. Basic Idea of Public Key Cryptography • Each participant has a private key (known only to the participant) and a public key. • Public key is made available to others • Could be posted even on a website which is accessible by the rest of the world. • Public key of recipient is used by sender to encrypt message. • Recipient decrypts message using recipient’s private key.

28. Public Key Cryptography • Example: • Sender (S) wishes to send a message to Recipient (R) • S fetches R’s public key. • S uses R’s public key to encrypt message • S sends encrypted message to R. • R decrypts cipher text with R’s private key.

29. RSA Algorithm • Named after its founders, Ron Rivest, Adi Shamir, and Leonard Adleman • Has become almost synonymous with public key cryptography

30. Using the RSA Algorithm • R’s public key is denoted as KR+ and the private key is denoted as KR-. • These keys are chosen such that: KR- (KR+ (m)) = KR+ (KR- (m)) = m • S will encrypt a plain text message, m, using public key KR+ and send it to R

31. Using the RSA Algorithm • To encrypt the message, S uses R’s public key and determines the cipher text, c as: • c = me mod n • To decrypt the message, R uses R’s private key and determines the plain text, m as: • m = cd mod n

32. Using the RSA AlgorithmCreate R’s Keys • Choose two large prime numbers, p and q. • The larger the values, the more difficult it is to break RSA, and the longer it takes to encode/decode. • It is recommended that the product of p and q be on the order of 1024 bits for corporate use and 768 bits for use with “less valuable information”. • For a discussion on how to find large prime numbers, see http://www.utm.edu/research/primes/prove/). • For example, choose p = 5 and q = 7

33. Using the RSA AlgorithmCreate R’s Keys • Compute n = pq =35 • Compute z = (p-1)(q-1) = (4)(6) = 24 • Choose a number, e, less than n, which has no common factors (other than 1) with z. • R chooses e = 5 • Find a number, d, such that ed-1 is exactly divisible (that is, with no remainder) by z. • d = 29; • Note (ed-1) = (5x29 -1) = (145-1) = 144 • 144 is exactly divisible by z = 24

34. Using the RSA AlgorithmCreate R’s Keys • Recap: p = 5, q = 7, n = 35, z = 24, e = 5, d = 29 • R’s public key is given by • KR+ = (n, e) = (35, 5); • R’s private key is given by • KR- = (n, d) = (35, 29) • Example • Interpret each letter in the English alphabet as a number between 1 and 26. That is, a = 1, b = 2, …, z = 26. • S will send message “love” to R

35. Using the RSA AlgorithmEncrypt Message using KR+ = (n, e) = (35, 5); • S will send 17152210 to R

36. Using the RSA AlgorithmEncrypt Message using KR- = (n, d) = (35, 29);

37. RSA and DES/AES • RSA is a complex algorithm and uses concepts from number theory. • DES is at least 100 times faster than RSA. • In practice, RSA is often used in combination with DES or AES. • Message is encrypted using DES key • S encrypts DES key with R’s public key • R decrypts and obtains DES key with R’s private key. • Message is decrypted using DES key

38. Authentication • ap 4.0 (symmetric) • S announces to R, “I am S” • R sends a plaintext nonce (= n) to S. • Note nonce is a one time value that is specific to that communication session • S resends same nonce back to R but this time nonce is encrypted with symmetric key used by S and R. • R decrypts nonce using symmetric key. If decrypted nonce equals the nonce sent to S earlier (i.e. decrypted nonce = n) , then S is authenticated. • However, this implies that S and R must have decided upon and exchanged their symmetric key.

39. Authentication • ap 5.0 (public/private) • S announces to R, “I am S” • R sends a plaintext nonce (= n) to S • S resends same nonce back to R but this time nonce is encrypted with S’s private key. • R decrypts nonce using S’s public key. If decrypted nonce equals the nonce sent to S earlier (i.e. decrypted nonce = n) , then S is authenticated.

40. Exchanging Public Keys • Why should public key be publicly available? • Wouldn’t it be better for S and R to exchange their respective public keys via e-mail, after authenticating each other? • Possibility of “person in the middle attack.”

41. S transmits, “I am S” T eavesdrops. R sends a nonce = n. T intercepts nonce, and sends R encrypted nonce (encrypted using T’s private key). R sends a message to S asking for S’s public key. T intercepts message, and sends T’s public key to R. R decrypts nonce with T’s public key (thinking that he is using S’s public key), and inadvertently authenticates T. While R is encrypting new data using T’s public key, T is busy posing as R to S. In particular: T transmits R’s nonce to S S transmits encrypted nonce (encrypted using S’s private key). T intercepts encrypted nonce, and asks S for her public key. S sends her public key Person in the Middle Attack

42. Person in the Middle Attack – cont’d • R sends encrypted data (encrypted using T’s public key) • T decrypts using her private key, and finds out R’s plain text. • T encrypts R’s plain text using S’s public key. • T transmits encrypted text to S. • S decrypts using her private key, and finds out R’s plain text. • S and R presume that they have had a secure communication. They are ignorant of the fact that T has intercepted and decrypted all messages.

43. Availability and Access Control • Examples of common attacks • Firewalls

44. Examples of some attacks • Denial of Service attacks • Hacker attempts to disrupt the network by flooding the network with messages so that the network cannot process messages from legitimate users • Examples • “Ping” attacks • Smurf attack • SYN flood attack • Distributed Denial of Service attacks

45. Ping Packets • Packets that ask a computer to respond with an acknowledgement • Used to see if a computer is still operational in a network • Ping by computer name • Ping bus.orst.edu • Ping by IP address • Ping 128.193.76.73

47. TCP header: Packet #s (Sequence #s) • Assume a file has 500,000 bytes • Assume TCP breaks this file into packets, where each packet size is 1000 bytes • Each packet is given a packet # • The packet # for a packet is the number of the first byte in that packet. • The packet # of first packet would be 1 • The packet # of next packet would be 1001 • The packet # of third packet would be 2002 and so on

48. TCP: Acknowledgement # • Assume S transmits to R • R acknowledges receipt of S’s message, by specifying an acknowledgment #. • The ACK # sent by R is the packet # of the next packet that R is expecting from S. • Example: • After S sends first packet, R sends an acknowledgment to S by specifying ACK# 1001. • After S sends second packet, R acknowledges by specifying ACK# 2001.

49. SYN Flood Attack • Nature of attack • Attacker (client) sends a TCP SYN (Synchronize Sequence/Packet Number) request to server. • The server responds by sending a TCP SYN/ACK packet. • The attacker does not respond – resulting in half-open session using up server resources. • The attacker sends a flood of such TCP SYN requests without responding. • Requests from other legitimate clients are unable to reach the server due to multiple half-open sessions

50. Distributed DoS (DDos) attack • In a DDoS attack, a hacker first gains control of hundreds/thousands of computers (slaves). • Plants software referred to as DDoS agent on each of the slaves • Hacker then uses software referred to as DDoS handler (master) to control the agents (slaves) • Attacker launches attacks from all the slaves and it is difficult to trace hacker