introduction to security system, Essays (university) of Computer Security

Download introduction to security system and more Essays (university) Computer Security in PDF only on Docsity! Chapter 1 - Introduction What is a “Secure” Computer System?  To decide whether a computer system is “secure”, you must first decide what “secure” means to you, then identify the threats you care about. You Will Never Own a Perfectly Secure System!  Threats - examples  Viruses, trojan horses, etc.  Denial of Service  Stolen Customer Data  Modified Databases  Identity Theft and other threats to personal privacy  Equipment Theft  Espionage in cyberspace  Hack-tivism  Cyberterrorism  … Computer Security Goals 5 Confidentiality AvailabilityIntegrity • To prevent the weakness from being exploited while preserving three very important aspects s S= secure Confidentiality, Integrity, Availability (CIA)  CIA  Confidentiality: Who is authorized to use data?  Integrity: Is data „good?”  Availability: Can access data whenever need it? C I A S S = Secure  CIA or CIAAAN…  (other security components added to CIA)  Authentication  Authorization  Non-repudiation  … Need to Balance CIA  Example 1: C vs. I+A  Disconnect computer from Internet to increase confidentiality  Availability suffers, integrity suffers due to lost updates  Example 2: I vs. C+A  Have extensive data checks by different people/systems to increase integrity  Confidentiality suffers as more people see data, availability suffers due to locks on data under verification)  Encryption: the transformation of information using a secret, called an encryption key, so that the transformed information can only be read using another secret, called the decryption key (which may, in some cases, be the same as the encryption key). Tools for Confidentiality  Authentication: the determination of the identity or role that someone has. This determination can be done in a number of different ways, but it is usually based on a combination of  –something the person has (like a smart card or a radio key fob storing secret keys),  –something the person knows (like a password),  –something the person is (like a human with a fingerprint). Tools for Confidentiality  Access control: rules and policies that limit access to confidential information to those people and/or systems with a “need to know.”  –This need to know may be determined by identity, such as a person’s name or a computer’s serial number, or by a role that a person has, such as being a manager or a computer security specialist. Tools for Confidentiality  Availability: the property that information is accessible and modifiable in a timely fashion by those authorized to do so.  •Tools:  –Physical protections: infrastructure meant to keep information available even in the event of physical challenges.  –Computational redundancies: computers and storage devices that serve as fallbacks in the case of failures. Availability Definitions  Intruder : is the one who exploit any available mean of hacking to hack a system.  Vulnerability: is a weakness in the security system (i.e, design, implementation..etc. any point can be exploited to cause loss or harm to the system)  Threat: is a set of circumstances that has the potential to cause harm or loss Vulnerabilities, Threats, and Controls  Vulnerability = a weakness in a security system  Threat = circumstances that have a potential to cause harm  Controls = means and ways to block a threat, which tries to exploit one or more vulnerabilities  Threats are blocked by control of Vulnerability  Attack (materialization of a vulnerability/threat combination)  = exploitation of one or more vulnerabilities by a threat; tries to defeat controls  Attack may be:  Successful (a.k.a. an exploit)  resulting in a breach of security, a system penetration, etc.  Unsuccessful  when controls block a threat trying to exploit a vulnerability  Eavesdropping: the interception of information intended for someone else during its transmission over a communication channel. Threats and Attacks Alteration: unauthorized modification of information. – Example: the man-in-the-middle attack, where a network stream is intercepted, modified, and retransmitted. Threats and Attacks  Denial-of-service: the interruption or degradation of a data service or information access.  –Example: email spam, to the degree that it is meant to simply fill up a mail queue and slow down an email server. Threats and Attacks  Correlation and traceback: the integration of multiple data sources and information flows to determine the source of a particular data stream or piece of information. Threats and Attacks The message M is called the plaintext. • Alice will convert plaintext M to an encrypted form using an encryption algorithm E that outputs a ciphertext C for M. Encryption and Decryption Symmetric Encryption  Or conventional / private-key / single-key  Sender and recipient share a common key  All traditional schemes are symmetric / single key / private-key encryption algorithms, with a single key, used for both encryption and decryption. Since both sender and receiver are equivalent, either can encrypt or decrypt messages using that common key. Requirements  Two requirements for secure use of symmetric encryption:  A strong encryption algorithm  A secret key known only to sender / receiver  Mathematically have: Y = EK(X) X = DK(Y)  Plaintext X, ciphertext Y, key K, encryption algorithm EK, decryption algorithm DK. Cryptography  characterize cryptographic system by:  Type of encryption operations used  Substitution  Transposition  Number of keys used  Single-key or private  Two-key or public  Way in which plaintext is processed  Block  Stream Cryptanalysis  Typically objective is to recover the key in use rather then simply to recover the plaintext of a single ciphertext.  There are two general approaches:  Cryptanalytic attacks rely on the nature of the algorithm plus perhaps some knowledge of the general characteristics of the plaintext or even some sample plaintext-ciphertext pairs.  Brute-force attacks  try every possible key on a piece of ciphertext until an intelligible translation into plaintext is obtained. On average,half of all possible keys must be tried to achieve success.  Replace each letter with the one “three over”  in the alphabet Caesar Cipher  Bob has two keys: a private key, SB, which Bob  keeps secret, and a public key, PB, which Bob  broadcasts widely.  – In order for Alice to send an encrypted message to  Bob, she need only obtain his public key, PB, use  that to encrypt her message, M, and send the  result, C = EPB (M), to Bob. Bob then uses his  secret key to decrypt the message as M = DSB (C). Public-Key Cryptography  Separate keys are used for encryption and decryption. Public-Key Cryptography