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In this article:
- What is hashing?
- Characteristics of a hash function
- Uses of hashing
What is Hashing?
The process of creating a digital ‘fingerprint’ of data is known as hashing. Hashing may also be referred to as a hash function or hash algorithm. The hash value generated by such a function is the result of chopping and mixing or substituting and transposing of the data among itself. The hash value hence arrived at is in the form of a string of random letters and numbers. This is actually the writing of binary data in the form of a hexadecimal notation.
Characteristics of a hash function
There are certain characteristics of a hash function that may be identified. They have been explained below:
- Deterministic
Hash functions are essentially deterministic. This means that if two hash values coming from the same has function are different, then it means that the inputs given to the function were different. This usually signifies that hash functions yield unique outputs for their inputs.
- Non-Injective
Hash functions are non-injective. This means that if the values of two outputs, that is, hash values, are equal, it is possible to a very large extent that the inputs were the same. However, this may not be necessary in some cases. Usually, strong mixing in a hash function would result in a completely different hash value even if a single bit of the given data is changed in the input.
- Infinite Domain
Hash functions usually posses an infinite domain which means that the byte strings are of a random or different or variable length while there is a finite range of the bit sequences.
In order to reach the input from the hash value, that is, to perform reverse hashing, a set of reversible mixing operations are performed.
-Uses of Hashing
Hashing finds a variety of uses in the world of computers and software applications. Each use of a hash function usually would have a tailor-made variation of the hash function for that particular application. Following are some of the uses of a hash function
- Cryptography
Hashing is used for cryptographic purposes on a large scale. Cryptographic hash functions are very good randomization functions. They have been found to be very effective in this regard. A cryptographic hash function is said to be well-designed when it is completely one-way. This means that it is not possible for someone to find a data input which would lead into a desired hash value from the function. This way, it prevents forging.
- Hash tables
Another widespread usage of hash functions is in the form of hash tables. These are often used in databases and help in performing fast retrieval of data with the help of a key for the record. The ideal hash function for a hash table would be one that takes the least amount of time to retrieve data from the table. This is done by reducing the number of collisions to the minimum possible level. Also, a good hash function would be able to retrieve the data in one or two ‘tries’ or ‘probes’ into the table.
- Error detection
Hash functions are used to detect errors in the transmission of data. This is done through what is known as a redundancy check. The data to be sent is passed through a hash function and the resultant hash value is sent alongwith the data. When the data reaches the destination, the data is again passed through the hash function and the resultant hash value is compared to the one which came with the data. If there is a mismatch between the two, it means that some error has occurred while the data was being transferred.
- Audio identification
Hash functions are used to match audio data such as an MP3 file to a database of known files and find if there are any similar data. This is often beneficial when identifying a particular song through software. A software can hold a database of hash values of various songs or other audio information. When an audio piece is played by the user to be identified, it is hashed and a fingerprint is created. This fingerprint is then compared to each value in the existing database of the software and the use is informed if a match is found. Shazam, a paid service, makes use of this technique to identify songs for its customers.
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