Hashing
Producing hash values for accessing data or for security. A hash value (or simply hash), also called a message digest, is a number generated from a string of text. The hash is substantially smaller than the text itself, and is generated by a formula in such a way that it is extremely unlikely that some other text will produce the same hash value.
Hashes play a role in security systems where they’re used to ensure that transmitted messages have not been tampered with. The sender generates a hash of the message, encrypts it, and sends it with the message itself. The recipient then decrypts both the message and the hash, produces another hash from the received message, and compares the two hashes. If they’re the same, there is a very high probability that the message was transmitted intact.
Hashing is also a common method of accessing data records. Consider, for example, a list of names:
John Smith
Sarah Jones
Roger Adams
To create an index, called a hash table,for these records, you would apply a formula to each name to produce a unique numeric value. So you might get something like:
1345873 John smith
3097905 Sarah Jones
4060964 Roger Adams
Then to search for the record containing Sarah Jones,you just need to reapply the formula, which directly yields the index key to the record. This is much more efficient than searching through all the records till the matching record is found.
Read Also:
- haxie
Formed from the combination of the words hack and Mac OS X, a haxie is a hack specifically designed for use with the Mac OS X operating system. The term was coined by software company Unsanity.
- head
(n.) The mechanism that reads data from or writes data to a magnetic disk or tape. If the head becomes dirty, it will not work properly. This is one of the first things to check if your disk drive or tape drive begins to malfunction. The head is sometimes called a read/write head. Double-sided floppy […]
- head crash
(n.) A serious disk drive malfunction. A head crash usually means that the head has scratched or burned the disk. In a hard disk drive, the head normally hovers a few microinches from the disk. If the head becomes misaligned or if dust particles come between it and the disk, it can touch the disk. […]
- Header
(1) In many disciplines of computer science, a header is a unit of information that precedes a data object. In a network transmission, a header is part of the data packet and contains transparent information about the file or the transmission. In file management, a header is a region at the beginning of each file […]
- attenuation crosstalk ratio
Also known as headroom, attenuation crosstalk ratio (ACR) is the difference between attenuation and crosstalk at a given frequency along a cable. Measured in decibels, ACR is a calculation used in networking transmission to assure that a signal transmitted across a twisted-pair cable is stronger at the receiving end than any interference signals imposed on […]