Hashes are mathematical formulas that convert variable-length data into fixed-length numeric values. They are used in databases for faster searches and in cryptography for password security and digital signature authentication. Hash functions simplify searches by transforming text strings into numbers, with a fixed length to make the computer’s job more efficient. Hash keys are unique numbers assigned to each entry in a database. Hash functions must minimize collisions and be one-way, meaning they cannot be reverse-engineered.
Hashes are mathematical formulas that take a string of variable-length data, usually in the form of text, and convert it into shorter, fixed-length numeric values. Hashes are frequently used in computer databases to make searches faster and more efficient. They are also used in cryptography to ensure passwords are not compromised and to authenticate digital signatures, among other uses. Hashes are also referred to as hash functions and can also be considered algorithms.
Hashes play an important role in facilitating database searches. In a database composed of names, for example, if a user searches for “John Doe,” the computer would have to match all characters in the search to those in each database entry. Each character in the name would have 26 different possibilities — the letters of the English alphabet — while also varying the length of the entries would slow down the search.
Conversely, applying a hash function would make computer life much easier. Transforming each text string into a series of numbers would simplify the search, because the computer would have only ten possibilities to check each character: digits from “0” to “9”. The fixed length of the number series also helps the computer do its job more efficiently.
In a database to which a hash function is applied, all entries have a corresponding unique number. This is called a hash key. In this case, when you do a search, the computer first hashes the input you typed, such as “John Doe.” This translates into a numeric value, such as “456789”. The computer can then quickly match this result to the pound key corresponding to the correct entry.
Hashes also work like digital signatures. For example, a sender, Robert, wants to send a document to someone, and the recipient, Mary, wants to make sure the document hasn’t been tampered with en route. The sender, Robert, just needs to run the document through a hash function, which results in a numeric value. Robert then encrypts the hash key and sends the document along with the encrypted key.
Mary receives both items and decrypts the hash key. You can now see the numerical value resulting from the document before it was sent. To verify that the document in your hands is exactly the same, you run the document through a hash function on your computer. Finally, she compares both keys. If they are the same, the document has not been altered in transit to the recipient.
There are many different hash functions, each with their own mathematical formulas. For a hash function to work, it must minimize any collisions, which occur when two database entries have the same hash key. Hash functions must also be one-way. This means that you can produce a key from a database entry or document, but not the other way around. In other words, you cannot reverse-engineer the original document from its hash key.
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