Often when downloading torrents or directly the files themselves, the description contains something like “ad33e486d0578a892b8vbd8b19e28754” (for example, in ex.ua), often with an “md5” note. This hash code is the result that the hash function produces after processing the incoming data. Translated from English, a hash means confusion, marijuana, weed or a dish of finely chopped meat and vegetables. Decrypting the hash is very, very difficult, it can be said that it is almost impossible. Then the question arises: “Why do we need all these hash functions in general if they produce an incomprehensible gibberish that still cannot be decrypted?” This will be discussed in this article.
What is a hash function and how does it work?
This function is designed to convert incoming data of arbitrarily large size into a result of a fixed length. The conversion process itself is called hashing, and the result is a hash or hash code. Sometimes they use the words “fingerprint” or “message digest”, but in practice they are much less common. There are many different algorithms on how you can turn any data array into a certain sequence of characters of a certain length. The most widely used algorithm called md5, which was developed back in 1991. Despite the fact that today md5 is somewhat outdated and is not recommended for use, it is still in use and often instead of the word "hash code", they simply write md5 on the sites and indicate the code itself.
Why do we need a hash function?
Knowing the result, it is almost impossible to determine the source data, but the same input data gives the same result. Therefore, the hash function (also called the convolution function) is often used to store very important information, such as password, login, identification number and other personal information. Instead of comparing the information entered by the user with that stored in the database, their hashes are compared. This ensures that in case of accidental leakage of information no one will be able to use important data for their own purposes. By comparing the hash code, it is also convenient to check the correctness of downloading files from the Internet, especially if there were communication interruptions during the download.
Hash Functions: What Are They?
Depending on its purpose, the hash function can be one of three types:
1. Function for checking the integrity of information
When data is transmitted over the network, the packet hash is calculated, and this result is also transmitted along with the file. Upon receipt, the hash code is calculated again and compared with the value received over the network. If the code does not match, then this indicates errors, and the damaged packet will be transmitted again. Such a function has a fast calculation speed, but a small number of hash values ​​and poor stability. An example of this type: CRC32, which has only 232 different values.
2. Cryptographic function
This type is used to protect against unauthorized access (NI). They allow you to check whether data distortion as a result of ND occurred during file transfer over the network. The true hash in this case is publicly available, and the hash of the resulting file can be calculated using many different programs. Such functions have a long and stable life, and the search for collisions (possible matches of the result from different source data) is very complicated. It is these functions that are used to store passwords (SH1, SH2, MD5) and other valuable information in the database.
3. Function designed to create an effective data structure
Its purpose is a compact and fairly ordered organization of information in a special structure, which is called a hash table. Such a table allows you to add new information, delete information and search for the necessary data at a very high speed.