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CRYPTOGRAPHY AND NETWORK. SECURITY LECTURE NOTES for. Bachelor of Technology in. Computer Science and Engineering. &. Information. To access the Cryptography and Network Security: Principles and Practice, Sixth Edition, .. PDF files: Reproductions of all figures and tables from the book. Network Security: Private Communication in a Public W orld [Chap]. Charles Kaufman, Mike Prentice-Hall. Cryptography and Network Security, W illiam Stallings, Prentice Hall Lai and Hongbo Yu n kipentoriber.tk pdf.
Nonetheless, good modern ciphers have stayed ahead of cryptanalysis; it is typically the case that use of a quality cipher is very efficient i.
Cryptography and Network Security Seminar PPT and PDF Report
Advent of modern cryptography Cryptanalysis of the new mechanical devices proved to be both difficult and laborious. In the United Kingdom, cryptanalytic efforts at Bletchley Park during WWII spurred the development of more efficient means for carrying out repetitious tasks.
Extensive open academic research into cryptography is relatively recent; it began only in the mid's. In recent times, IBM personnel designed the algorithm that became the Federal i. Following their work in , it became popular to consider cryptography systems based on mathematical problems that are easy to state but have been found difficult to solve.
Some modern cryptographic techniques can only keep their keys secret if certain mathematical problems are intractable , such as the integer factorization or the discrete logarithm problems, so there are deep connections with abstract mathematics. There are very few cryptosystems that are proven to be unconditionally secure. The one-time pad is one, and was proven to be so by Claude Shannon.
There are a few important algorithms that have been proven secure under certain assumptions. For example, the infeasibility of factoring extremely large integers is the basis for believing that RSA is secure, and some other systems, but even so proof of unbreakability is unavailable since the underlying mathematical problem remains open. In practice, these are widely used, and are believed unbreakable in practice by most competent observers.
The discrete logarithm problem is the basis for believing some other cryptosystems are secure, and again, there are related, less practical systems that are provably secure relative to the solvability or insolvability discrete log problem.
For instance, continuous improvements in computer processing power have increased the scope of brute-force attacks , so when specifying key lengths , the required key lengths are similarly advancing. The chief ones are discussed here; see Topics in Cryptography for more. Symmetric-key cryptography Main article: Symmetric-key algorithm Symmetric-key cryptography, where a single key is used for encryption and decryption Symmetric-key cryptography refers to encryption methods in which both the sender and receiver share the same key or, less commonly, in which their keys are different, but related in an easily computable way.
This was the only kind of encryption publicly known until June A block cipher enciphers input in blocks of plaintext as opposed to individual characters, the input form used by a stream cipher. Many, even some designed by capable practitioners, have been thoroughly broken, such as FEAL. In a stream cipher, the output stream is created based on a hidden internal state that changes as the cipher operates.
That internal state is initially set up using the secret key material. RC4 is a widely used stream cipher; see Category:Stream ciphers. Cryptographic hash functions are a third type of cryptographic algorithm. They take a message of any length as input, and output a short, fixed length hash , which can be used in for example a digital signature.
For good hash functions, an attacker cannot find two messages that produce the same hash. MD4 is a long-used hash function that is now broken; MD5 , a strengthened variant of MD4, is also widely used but broken in practice. The US National Security Agency developed the Secure Hash Algorithm series of MD5-like hash functions: SHA-0 was a flawed algorithm that the agency withdrew; SHA-1 is widely deployed and more secure than MD5, but cryptanalysts have identified attacks against it; the SHA-2 family improves on SHA-1, but is vulnerable to clashes as of ; and the US standards authority thought it "prudent" from a security perspective to develop a new standard to "significantly improve the robustness of NIST 's overall hash algorithm toolkit.
Cryptographic hash functions are used to verify the authenticity of data retrieved from an untrusted source or to add a layer of security. Message authentication codes MACs are much like cryptographic hash functions, except that a secret key can be used to authenticate the hash value upon receipt;  this additional complication blocks an attack scheme against bare digest algorithms , and so has been thought worth the effort.
Public-key cryptography Main article: Public-key cryptography Public-key cryptography, where different keys are used for encryption and decryption. Padlock icon from the Firefox Web browser , which indicates that TLS , a public-key cryptography system, is in use. Symmetric-key cryptosystems use the same key for encryption and decryption of a message, although a message or group of messages can have a different key than others. A significant disadvantage of symmetric ciphers is the key management necessary to use them securely.
Each distinct pair of communicating parties must, ideally, share a different key, and perhaps for each ciphertext exchanged as well. The number of keys required increases as the square of the number of network members, which very quickly requires complex key management schemes to keep them all consistent and secret.
Whitfield Diffie and Martin Hellman , authors of the first published paper on public-key cryptography. In a groundbreaking paper, Whitfield Diffie and Martin Hellman proposed the notion of public-key also, more generally, called asymmetric key cryptography in which two different but mathematically related keys are used—a public key and a private key.
Instead, both keys are generated secretly, as an interrelated pair. In a public-key encryption system, the public key is used for encryption, while the private or secret key is used for decryption. While Diffie and Hellman could not find such a system, they showed that public-key cryptography was indeed possible by presenting the Diffie—Hellman key exchange protocol, a solution that is now widely used in secure communications to allow two parties to secretly agree on a shared encryption key.
Other asymmetric-key algorithms include the Cramer—Shoup cryptosystem , ElGamal encryption , and various elliptic curve techniques. Ellis had conceived the principles of asymmetric key cryptography. Williamson is claimed to have developed the Diffie—Hellman key exchange. Public-key cryptography is also used for implementing digital signature schemes. A digital signature is reminiscent of an ordinary signature ; they both have the characteristic of being easy for a user to produce, but difficult for anyone else to forge.
Digital signatures can also be permanently tied to the content of the message being signed; they cannot then be 'moved' from one document to another, for any attempt will be detectable. In digital signature schemes, there are two algorithms: one for signing, in which a secret key is used to process the message or a hash of the message, or both , and one for verification, in which the matching public key is used with the message to check the validity of the signature.
Digital signatures are central to the operation of public key infrastructures and many network security schemes e. For example, the hardness of RSA is related to the integer factorization problem, while Diffie—Hellman and DSA are related to the discrete logarithm problem.
The security of elliptic curve cryptography is based on number theoretic problems involving elliptic curves.
Chapter 7: The Role of Cryptography in Information Security
Because of the difficulty of the underlying problems, most public-key algorithms involve operations such as modular multiplication and exponentiation, which are much more computationally expensive than the techniques used in most block ciphers, especially with typical key sizes.
As a result, public-key cryptosystems are commonly hybrid cryptosystems , in which a fast high-quality symmetric-key encryption algorithm is used for the message itself, while the relevant symmetric key is sent with the message, but encrypted using a public-key algorithm. Similarly, hybrid signature schemes are often used, in which a cryptographic hash function is computed, and only the resulting hash is digitally signed.
Breaking and reading of the Enigma cipher at Poland's Cipher Bureau , for 7 years before the war, and subsequent decryption at Bletchley Park , was important to Allied victory. It is a common misconception that every encryption method can be broken. In connection with his WWII work at Bell Labs , Claude Shannon proved that the one-time pad cipher is unbreakable, provided the key material is truly random , never reused, kept secret from all possible attackers, and of equal or greater length than the message.
Cryptography and Network Security
In such cases, effective security could be achieved if it is proven that the effort required i. This means it must be shown that no efficient method as opposed to the time-consuming brute force method can be found to break the cipher. Since no such proof has been found to date, the one-time-pad remains the only theoretically unbreakable cipher. There are a wide variety of cryptanalytic attacks, and they can be classified in any of several ways.
A common distinction turns on what Eve an attacker knows and what capabilities are available. In a ciphertext-only attack , Eve has access only to the ciphertext good modern cryptosystems are usually effectively immune to ciphertext-only attacks.
In a known-plaintext attack , Eve has access to a ciphertext and its corresponding plaintext or to many such pairs. In a chosen-plaintext attack , Eve may choose a plaintext and learn its corresponding ciphertext perhaps many times ; an example is gardening , used by the British during WWII. In a chosen-ciphertext attack , Eve may be able to choose ciphertexts and learn their corresponding plaintexts.
For example, a simple brute force attack against DES requires one known plaintext and decryptions, trying approximately half of the possible keys, to reach a point at which chances are better than even that the key sought will have been found.
But this may not be enough assurance; a linear cryptanalysis attack against DES requires known plaintexts with their corresponding ciphertexts and approximately DES operations. Public-key algorithms are based on the computational difficulty of various problems.
The most famous of these are the difficulty of integer factorization of semiprimes and the difficulty of calculating discrete logarithms , both of which are not yet proven to be solvable in polynomial time using only a classical Turing-complete computer.
Much public-key cryptanalysis concerns designing algorithms in P that can solve these problems, or using other technologies, such as quantum computers.
For instance, the best known algorithms for solving the elliptic curve-based version of discrete logarithm are much more time-consuming than the best known algorithms for factoring, at least for problems of more or less equivalent size. Thus, other things being equal, to achieve an equivalent strength of attack resistance, factoring-based encryption techniques must use larger keys than elliptic curve techniques. For this reason, public-key cryptosystems based on elliptic curves have become popular since their invention in the mids.
While pure cryptanalysis uses weaknesses in the algorithms themselves, other attacks on cryptosystems are based on actual use of the algorithms in real devices, and are called side-channel attacks. If a cryptanalyst has access to, for example, the amount of time the device took to encrypt a number of plaintexts or report an error in a password or PIN character, he may be able to use a timing attack to break a cipher that is otherwise resistant to analysis.
An attacker might also study the pattern and length of messages to derive valuable information; this is known as traffic analysis  and can be quite useful to an alert adversary. Poor administration of a cryptosystem, such as permitting too short keys, will make any system vulnerable, regardless of other virtues. Social engineering and other attacks against humans e. Cryptographic primitives Much of the theoretical work in cryptography concerns cryptographic primitives —algorithms with basic cryptographic properties—and their relationship to other cryptographic problems.
More complicated cryptographic tools are then built from these basic primitives. These primitives provide fundamental properties, which are used to develop more complex tools called cryptosystems or cryptographic protocols, which guarantee one or more high-level security properties. Note however, that the distinction between cryptographic primitives and cryptosystems, is quite arbitrary; for example, the RSA algorithm is sometimes considered a cryptosystem, and sometimes a primitive.
Typical examples of cryptographic primitives include pseudorandom functions , one-way functions , etc. Please go to here if you wanna read it directly from there. Bernard menezes network pdf Direct Link 1 It is also known to be a nocturnal species. PC Added ability to rotate character models with the mouse in UI s that show character models That is simply unacceptable for such a high-end printer, especially one that is geared towards small offices.
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If you get some good team synergy going though, it can make for an awesome and visceral experience. Doubt it is first come first serve. The macro close up setting on this camera is great Check the update from the following link and download. The range for this field is 2 to 4, Just uninstall WhatsApp and install it again. It is the right time to take stock of the situation.But this may not be enough assurance; a linear cryptanalysis attack against DES requires known plaintexts with their corresponding ciphertexts and approximately DES operations.
In some countries, even the domestic use of cryptography is, or has been, restricted. Digital Signatures Verifiable Encryption of Digital Signatures PDF : This scholarly essay reports on the current methods of digital signature verification and offers one new potential alternative.
This provided the cryptanalysts with a finger hold from which to begin breaking a code. And I don t think they really could have rushed out a quality device sooner, or they would have. Symmetric-key cryptosystems use the same key for encryption and decryption of a message, although a message or group of messages can have a different key than others.
For example, data is decrypted on servers and end-user devices when processed.
A root CA is at the top of the certificate signing hierarchy. Revocation Certificates are sometimes revoked for cause.