Computer Security Computer Security title Computer Security figure conclusion This section introduced security techniques. text Computer security is the effort to create a secure computing platform, designed so that agents (users or programs) cannot perform actions that they are not allowed to perform, but can perform the actions that they are allowed to. This involves specifying and implementing a security policy. The actions in question can be reduced to operations of access, modification and deletion. Computer security can be seen as a subfield of security engineering, which looks at broader security issues in addition to computer security. It is important to understand that in a secure system, the legitimate users of that system are still able to do what they should be able to do. In the case of a computer system sequestered in a vault without any means of power or communication, the term 'secure' is applied in a pejorative sense only. It is also important to distinguish the techniques employed to increase a system's security from the issue of that system's security status. In particular, systems which contain fundamental flaws in their security designs cannot be made secure without compromising their utility. Consequently, most computer systems cannot be made secure even after the application of extensive "computer security" measures. TECHNIQUES FOR CREATING SECURE SYSTEMS The following techniques can be used in engineering secure systems. Note that these techniques, whilst useful, do not of themselves ensure security -- a security system is no stronger than its weakest link. 1. Cryptographic 2. Authentication 3. Secure cryptoprocessors 4. Access control introduction This is the computer security course for beginners. It is based on the material for 3rd year students at the Computer Science Faculty, Department of Information Science, Technical University of Eindhoven. For this course, the students need basic knowledge of telematics service and data communication. keywords security; communication; computer security; cryptographic; secure; techniques; authentication; cryptoprocessors; access control additional text Various solutions against spam have been proposed and used. Some of them focus on text classification analysis such as authentication, while others focus on building new mechanisms that work together within an existing infrastructure such as cryptography or even refine the existing protocols. There are no perfect solutions yet. Each solution has its benefits and drawbacks. QuestionsForBeginner 1. What is computer security? 2. What is the purpose of computer security? 3. List some techniques for creating secure systems. Secure Cryptoprocessor title Secure Cryptoprocessor keywords secure cryptoprocessor; computer; cryptographic; physical security; Smartcards; ATM; cryptoprocessor; security introduction This section describes secure cryptoprocessor technique in a computer security. text A secure cryptoprocessor is a dedicated computer for carrying out cryptographic operations, embedded in a packaging with multiple physical security measures, which give it a degree of tamper resistance. The purpose of a secure cryptoprocessor is to act as the keystone of a security sub-system, eliminating the need to protect the rest of the sub-system with physical security measures. Smartcards are probably the most widely deployed form of secure cryptoprocessor, although more complex and versatile secure cryptoprocessors are widely deployed in systems such as ATMs. Some secure cryptoprocessors can even run general-purpose operating systems such as Linux inside their security boundary. Fritz is a secure cryptoprocessor that is under development and brings trusted computing to ordinary PCs by enabling a secure environment. The Fritz chip is designed to make it much harder to illegally copy copyrighted software. Fritz will do this using four different "methods". All four methods make use of extensive cryptography. Security measures used in secure cryptoprocessors: tamper-detecting and tamper-evident containment automatic zeroization of secrets in the event of tampering internal battery backup chain of trust boot-loader which authenticates the operating system before loading it chain of trust operating system which authenticates application software before loading it hardware-based capability registers, implementing a one-way privilege separation model Secure cryptoprocessors, whilst useful, are not invulnerable. The most famous secure cryptoprocessor is the IBM 4758. A team at the University of Cambridge reported the successful extraction of secret information from an IBM 4758, using a combination of guile, trickery, mathematics, and special-purpose codebreaking hardware. conclusion This section described secure cryptoprocessor technique in a computer security. figure QuestionsForIntermediate 1. What is secure cryptoprocessor? 2. What is the purpose of secure cryptoprocessor? 3. List some security measures used in secure cryptoprocessors. Access Control title Access Control keywords access control; secure computing; identity; list; program; networking; server; hosts introduction This section introduces access control technique in computer security. text The access control list (ACL) is a concept in secure computing, used to enforce privilege separation. It is a means of determining the appropriate access rights to a given object given certain aspects of the user process that is requesting them, principally the process's user identity (in POSIX, uid). The list is a data structure, usually a table, containing entries that specify individual user or group rights to specific system objects, such as a program, a process, or a file. These entries are known as access control entries (ACE) in the Microsoft Windows and OpenVMS operating systems. Each accessible object contains an identifier to its ACL. The privileges or permissions determine specific access rights, such as whether a user can read from, write to or execute an object. In some implementations an ACE can control whether or not a user, or group of users, may alter the ACL on an object. The ACL is a concept, with several different implementations in various operating systems, although there is a POSIX standard. In networking, the term Access Control List (ACL) refers to a list of the computing services available on a server, each with a list of hosts permitted to use the service. conclusion This section introduced access control technique in computer security. figure QuestionsForIntermediate 1. What is access control? 2. How does access control work? 3. What is important is access control? Authentication title Authentication keywords computer security; computer; authorization; protocols; access control; email; computer program introduction This section introduces authentication process in the computer system. text In computer security, authentication is the process by which a computer, computer program, or another user attempts to confirm that the computer, computer program, or user from whom the second party has received some communication is, or is not, the claimed first party. A blind credential, in contrast, does not establish identity at all, but only a narrow right or status of the user or program. The problem of authorization is often thought to be identical to that of authentication; many widely adopted standard security protocols, obligatory regulations, and even statutes are based on this assumption. However, there are many cases in which these two problems are different. One familiar example is access control. A computer system supposed to be used only by those authorized must attempt to detect and exclude the unauthorized. Access to it is therefore usually controlled by insisting on an authentication procedure before access is granted. A few examples are given below. However, note that much of the discussion on these topics is misleading because terms are used without precision. Part of this confusion may be due to the 'law enforcement' tone of much of the discussion. No computer, computer program, or computer user can 'confirm the identity' of another party. It is not possible to 'establish' or 'prove' an identity, either. There are tricky issues lurking under what appears to be a straightforward surface. It is only possible to apply one or more tests which, if passed, have been previously declared to be sufficient to proceed. The problem is to determine which tests are sufficient, and many such are inadequate. There have been many instances of such tests having been spoofed successfully; they have by their failure shown themselves, inescapably, to be inadequate. Many people continue to regard the test(s) -- and the decision to regard success in passing them -- as acceptable, and blame their failure on 'sloppiness' or 'incompetence' on the part of someone. The problem is that the test was supposed to work in practice -- not under ideal conditions of no sloppiness or incompetence -- and did not. It is the test which has failed in such cases. Consider the very common case of a confirmation email which must be replied to in order to activate an online account of some kind. Since email can easily be arranged to go to or come from bogus and untraceable addresses, this is just about the least authentication possible. Success in passing this test means little, without regard to sloppiness or incompetence. conclusion This section introduced authentication process in the computer system. figure additional text A Challenge/Response mechanism is one way to solve spam problem using authentication method. It is defined as a programmed attempt to authenticate messages from unknown addresses of recipients by sending them a challenge message, which must be correctly replied in order in order to differentiate humans from automated message originators . Messages from humans will pass and messages generated by spammers will be rejected. QuestionsForIntermediate 1. What is authentication? 2. What is the difference between authentication and authorization? Show examples to explain their difference. Examples of authentication title Examples of authentication keywords This section gave common examples of access control involving authentication. introduction This section gives examples of system uses authentication method. text Common examples of access control involving authentication include: withdrawing cash from an ATM. controlling a remote computer over the Internet. using an Internet banking system. The methods by which a human can authenticate themselves are generally classified into three cases: Something the user is (e.g., fingerprint or retinal pattern, DNA sequence (there are assorted definitions of what is sufficient), voice pattern (again several definitions), signature recognition or other biometric identifier) Something the user has (e.g., ID card) Something the user knows (e.g., a password, a pass phrase or a personal_identification_number (PIN)) Sometimes a combination of methods is used, e.g., a bank card and a PIN, in which case the term 'two-factor authentication' is used. conclusion This section gave examples of system uses authentication method. figure QuestionsForAdvanced Think about some examples in the daily life of access control involving authentication. Cryptography figure title Cryptography keywords confidentiality; integrity; authentication; non-repudiation; cryptography; digital signatures; network; conclusion This sections introduced the cryptography technique in computer security. text Cryptography is commonly used for securing communications. Four desirable properties are: 1. Confidentiality, also known as secrecy: only an authorised recipient should be able to extract the contents of the message from its encrypted form. Otherwise, it should not be possible to obtain any significant information about the message contents. 2. Integrity: the recipient should be able to determine if the message has been altered during transmission. 3. Authentication: the recipient should be able to identify the sender, and verify that the purported sender actually did send the message. 4. Non-repudiation: the sender should not be able to deny sending the message. Cryptography can provide mechanisms to help achieve all of the above. However, some goals aren't always necessary, practical or even desirable in some contexts. For example, the sender of a message may wish to remain anonymous; clearly non-repudiation would be inappropriate in that case. An example is Asymmetric cryptography also provides mechanisms for digital signatures, which are way to establish with high confidence (under the assumption that the relevant private key has not been compromised in any way) that the message received was sent by the claimed sender. Such signatures are often, in law / by implicit inference, as the digital equivalent of physical signatures on paper documents. In a technical sense, they are not as there is no physical contact nor connection between the 'signer' and the 'signed'. Properly used high quality designs and implementations are capable of a very high degree of assurance, likely exceeding any but the most careful physical signature. Examples of digital signature protocols include DSA and ElGamal. Digital signatures are central to the operation of public key infrastructure and many network security schemes (eg, Kerberos, most VPNs, etc). introduction This sections introduces the cryptography technique in computer security. additional text Examples of digital signature applied in anti spam system are digital signatures build by Earthlink, Inc, and Yahoo!. In November 2004, Earthlink, Inc, and Yahoo!. start testing encoding digital signatures into emails in order to differentiate spam from legitimate messages. The technology will be unnoticeable to end users, but will be utilized by ISPs to block unsolicited messages. The DomainKeys technology, developed by Yahoo, will embed a digital signature into outgoing messages. This signature matches a signature on the server which sends the message. ISPs will be able to check the signatures on incoming messages, and block any emails where the signatures do not correspond. Although DomainKeys is believed to provide more efficient protection than other technologies, it is more difficult to deploy, and requires more computing power to support. It is likely to be used in addition to other anti-spam tools. Google's Gmail and an Indian Internet provider, Sify, have already begun using this technology in a bid to keep end-user mailboxes free of spam. QuestionsForIntermediate 1. What are the properties of cryptography? What does each mean? How does each work? Give examples of each techniques. Symmetric key cryptography title Symmetric key cryptography keywords Symmetric key ciphers; key; encryption;decryption;private-key;one-key;single-key; cryptography. introduction Symmetric key ciphers use the same key for encryption and decryption, or a little more precisely, the key used for decryption is "easy" to calculate from the key used for encryption. Other terms include "private-key", "one-key" and "single-key" cryptography. text Symmetric key ciphers can be broadly grouped into block ciphers and stream ciphers. Stream ciphers encrypt one bit at a time, in contrast to a block cipher, which operates on a group of bits (a "block") of a certain length all in one go. Depending on the mode of operation, block ciphers can be implemented as self-synchronizing stream ciphers (CFB mode). Likewise, stream ciphers can be made to work on individual blocks of plaintext at a time. Thus, there is some duality between the two. The block ciphers DES, IDEA and AES, and the stream cipher RC4, are among the most well-known symmetric key ciphers. Other cryptographic primitives are sometimes classified as symmetric cryptography: Cryptographic hash functions produce a hash of a message. While it should be easy to compute, it must be very difficult to invert (one-way), though other properties are usually needed as well. MD5 and SHA-1 are well-known hash functions. Message authentication codes (MACs), also known as keyed-hash functions, are similar to hash functions, except that a key is needed to compute the hash. As the name suggests, they are commonly used for message authentication. They are often constructed from other primitives, such as block ciphers, unkeyed-hash functions or stream ciphers. conclusion This section introduced symmetric key cryptography figure QuestionsForAdvanced 1. What can be Symmetric key ciphers divided into? What does each mean? 2. What is Cryptographic hash functions and what is keyed-hash functions? Public key cryptography title Public key cryptography keywords Public key algorithms;Symmetric key encryption;Asymmetric cryptography; public key infrastructure;cryptography introduction Public key algorithm is one cryptography method based on hard mathematical problems. text Symmetric key encryption has a troublesome drawback ? two people who wish to exchange confidential messages must share a secret key. The key must be exchanged in a secure way, and not by the means they would normally communicate. This is usually inconvenient, and public-key (or asymmetric) cryptography provides an alternative. In public key encryption there are two keys used, a public and a private key, for encryption and decryption respectively. It must be "difficult" to derive the private key from the public key. This means that someone can freely send their public key out over an insecure channel and yet be sure that only they can decrypt messages encrypted with it. Public key algorithms are usually based on hard mathematical problems. RSA, for example, relies on the (conjectured) difficulty of factorisation. For efficiency reasons, hybrid encryption systems are used in practice; a key is exchanged using a public-key cipher, and the rest of the communication is encrypted using a symmetric-key algorithm (which is typically much faster). Elliptic curve cryptography is a type of public-key algorithm that may offer efficiency gains over other schemes. Asymmetric cryptography also provides mechanisms for digital signatures, which are way to establish with high confidence (under the assumption that the relevant private key has not been compromised in any way) that the message received was sent by the claimed sender. Such signatures are often, in law / by implicit inference, as the digital equivalent of physical signatures on paper documents. In a technical sense, they are not as there is no physical contact nor connection between the 'signer' and the 'signed'. Properly used high quality designs and implementations are capable of a very high degree of assurance, likely exceeding any but the most careful physical signature. Examples of digital signature protocols include DSA and ElGamal. Digital signatures are central to the operation of public key infrastructure and many network security schemes (eg, Kerberos, most VPNs, etc). conclusion This section introuduced public key cryptography system. figure QuestionsForAdvanced 1. Why is the public key cryptography needed? What is the drawback of symmetric key cryptography? 2. How does the public key cryptography work? 3. Explain the mechanism "digital signatures" in the asymmetric cryptography. 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