Security

Objectives

· To discuss security threats and attacks

· To explain the fundamentals of encryption & authentication.

· To examine the uses of cryptography in computing

· To describe the various countermeasures to security attacks

Security Violations

§ Categories

ü Breach of confidentiality

ü Breach of integrity

ü Breach of availability

ü Theft of service

ü Denial of service

§ Methods

ü Masquerading (breach authentication)

ü Replay attack

ü Message modification

ü Man-in-the-middle attack

Standard Security Attacks

Security Measure Levels

§ Security must occur at four levels to be effective:

ü Physical

ü Human: Avoid social engineering, phishing.

ü Operating System

ü Network

§ Security is as weak as the weakest link in the chain

Program Threats

Trojan Horse

Code segment that misuses its environment:

Spyware, pop-up browser windows, covert channels

Trap Door

Specific user identifier or password that circumvents normal security procedures

Logic Bomb

Program that initiates a security incident under certain circumstances

Stack & Buffer Overflow

Exploits a bug in a program (overflow either the stack or memory buffers)

C Program with Buffer-overflow Condition

Bufferoverflow.c

#define MemSize 10

int
main(int argc, char *argv[])
{

char buf1[10];
char buf2[10];
char *buf3 = malloc(MemSize);
char *buf4 = malloc(MemSize);

strncpy(buf1, argv[1], sizeof(buf1));
printf("stack buf1 ncpy: %s\n", buf1);

strcpy(buf2, argv[1]);
printf("stack buf2: %s\n", buf2);

strncpy(buf3, argv[1], MemSize);
printf("heap buf3 ncpy:%s\n", buf3);

strcpy(buf4, argv[1]);
printf("heap buf4: %s\n", buf4);

}

To Run:

% bufferoverflow 0123456789abdelwahab

stack buf1 ncpy: 0123456789

stack buf2: 0123456789abdelwahab

heap buf3 ncpy:0123456789

heap buf4: 0123456789abdelwahab

% bufferoverflow 0123456789abdelwahab0123456789

stack buf1 ncpy: 0123456789

stack buf2: 0123456789abdelwahab0123456789

Segmentation fault (core dumped)

System and Network Threats

Internet worm

Exploited UNIX networking features (remote access) and bugs in finger and sendmail programs

Port scanning

Automated attempt to connect to a range of ports on one or a range of IP addresses

Denial of Service

ü Overload the targeted computer to prevent it from doing any useful work

ü Distributed denial-of-service (DDOS) come from multiple sites at once

Secure Communication over Insecure Medium

Symmetric Encryption

(encryption)
plaintext >>>>>>>>> ciphertext
|
key
                            |
ciphertext >>>>>>>> plaintext
(decryption)

ü Same key used to encrypt and decrypt

ü DES is most commonly used symmetric block-encryption algorithm (created by US Govt)

ü Triple-DES considered more secure

ü Advanced Encryption Standard (AES)

Example: XOR encryption/decryption

Message M = 7 (111)

Key K = 4 (100)

C = E(K, M) = M XOR K = 111 XOR 100 = 011 = 3

M = D(K, C) = C XOR K = 011 XOR 100 = 111 = 7

Asymmetric Encryption

Each individual has two keys:

ü private key (not revealed to anyone)

ü public key (make it known to everyone)

(encryption)
plaintext >>>>>>>>>> ciphertext
                             |
public key

private key
|
ciphertext >>>>>>>>> plaintext
(decryption)

Example:

Public Key (5, 91) &

Private Key (29, 91)

M = 69.

C = 69 ** 5 mod 91 = 62

M = 62 ** 29 mod 91 = 69

Authentication – Hash Functions

Also known as: message digest, fingerprint, one-way function

The hash of a message m, h=H(m) has the following properties:

ü Given m, it is easy to compute h.

ü Given h, it is hard to compute m.

ü Given m, it is hard to find another m' such that H(m) = H(m').

ü It is hard to find m1 and m2 such that H(m1) = H(m2).

Common message-digest functions include MD5, which produces a 128-bit hash,

and SHA-1, which outputs a 160-bit hash

Authentication

MAC message-authentication code

Send (m,h) where h = H(m|K)     >>>>>     Got (m,h) is OK if h = H (m|K)

K is the shared secret

Digital Signature

(signing)
plaintext >>>>>>>>> ciphertext
|
private key

public key
                          |
ciphertext >>>>>>>> plaintext
(verification)

Key Distribution

Digital Certificates: Proof of who owns a public key

ü It is a Public key digitally signed by a trusted party

ü Trusted party receives proof of identification from entity and certifies that public key belongs to entity

ü Certificate authority (CA) are trusted party – their public keys included with web browser distributions

Example – SSL

ü SSL – Secure Socket Layer.

ü Used between web servers and browsers for secure communication (credit card numbers)

ü The server is verified with a certificate assuring the client that it is talking to the correct server

ü Asymmetric cryptography used to establish a secure session key (symmetric encryption)

for bulk of communication during session

User Authentication

· User identity most often established through passwords,

· Passwords must be kept secret

ü Frequent change of passwords

ü Use of “non-guessable” passwords