Case4,Case5

CASE 4 A hash function takes an item of a given type and generates an integer hash value within a given range. The input items can be anything: strings, compiled shader programs, files, even directories. The same input always generates the same hash value, and a good hash function tends to generate different hash values when given different inputs. A hash function has no awareness of “other” items in the set of inputs. It just performs some arithmetic and/or bit-magic operations on the input item passed to it. Therefore, there’s always a chance that two different inputs will generate the same hash value. Take the well-known hash function CRC32, for example. If you feed this function the two strings “plumless” and “buckeroo”, it generates the same value. This is known as a hash collision. 2) For an ideal hash function, the fastest way to compute a first or second preimage is through a brute force attack.[citation needed] For an n-bit hash, this attack has a time complexity 2n, which is considered too high for a typical output size of n=160 bits. If such complexity is the best that can be achieved by an adversary, then the hash function is considered Preimage resistant. Faster Preimage attacks can be found by cryptanalysing certain hash functions, and are specific to that function. Some significant Preimage attacks have already been discovered, but they are not yet practical. If a practical preimage attack is discovered, it would drastically affect many Internet protocols. In this case, "practical" means that it could be executed by an attacker in a meaningful amount of time for a meaningful amount of money. A preimaging attack that costs trillions of dollars and takes decades to preimage one desired hash value or one message is not practical; one that costs a few thousand dollars and takes a few weeks might be very practical. 3). Open addressing: The simplest way to resolve a collision is to start with the hash address and do a sequential search through the table for an empty location. The idea is to place the record in the next available position in the array. This method is called linear probing. An empty record is indicated by a special value called null. The major drawback of the linear probe method is clustering. CASE 5 Secret Key Cryptography (SKC): Uses a single key for both encryption and decryption Public Key Cryptography (PKC): Uses one key for encryption and another for decryption Hash Functions: Uses a mathematical transformation to irreversibly "encrypt" information

Estudyanteng hectic

The Conficker worm may have failed to cause the digital pandemonium that some may have feared, but that
doesn't mean we are in the clear. Just because the worm failed to create much of a stir on the day it was set to activate doesn't mean it won't wake up and act later.
Today, as on any day, PC users should make sure their systems are patched and running the latest security software. People should patch their systems to close the hole in Windows that Conficker exploits and should update their antivirus software. The major antivirus vendors all have free Conficker removal tools.

                                                                 Case 2.

A Romanian hacker was charged, after a joint operation of the Romanian police and the FBI, with hacking 
 into NASA computers. The US space agency notified in July the Romanian police that its servers had been breached by unidentified people who accessed secure networks from computers based in Romania.
Victor faur, 26, from Arad, was charged with breaking into NASA servers and even disrupting communication with spacecraft, which forced the