MD5 was designed by American cryptographer Ronald Linn Rivest and made public in 1992 to replace the MD4 algorithm.

MD5 (Message Digest Algorithm 5) is a widely used hash function that maps input messages of arbitrary length to a fixed-length hash value of 128 bits (16 characters (BYTES)).

MD5 is often used to encrypt sensitive information such as passwords in one direction so that it can be stored in a database without having to store the original plaintext password.

The characteristics of the MD5 algorithm are:

• Fixed output length : Regardless of the length of the input message, MD5 always produces a 128-bit hash value.
• Irreversibility : Because it is a one-way hash function, the original message cannot be deduced from the hash value.
• Uniqueness : Different input messages are almost impossible to produce the same MD5 hash value.
• Speed : The calculation speed is relatively fast.

MD5 is an algorithm that takes variable-length input information and outputs a fixed-length 128-bit hash. After a program process, it generates four 32-bit data sets, which are then combined to form a 128-bit hash. The basic method involves modulo operations, length adjustments, and iterative operations with concatenation variables to obtain the result.

An MD5 operation consists of 64 similar loops, divided into 4 groups of 16 iterations each. F is a non-linear function; each function is executed once. Mi represents a 32-bit input data, and Ki represents a 32-bit constant used to perform different calculations each time.

However, due to some security issues, MD5 is no longer recommended for use in security fields such as password storage or digital signatures, as it is vulnerable to collision attacks, where two different input messages may produce the same hash value.

Here are some common implementations of MD5 encryption in several programming languages:

Python

In Python, you can use the built-in hashlib module to calculate MD5 hash values.

import hashlib

data = "Hello, MD5!"
md5_hash = hashlib.md5(data.encode()).hexdigest()
print(md5_hash)

Java

In Java, you can use the java.security.MessageDigest class to calculate MD5 hash values.

import java.security.MessageDigest;

public class MD5Example {
    public static void main(String[] args) throws Exception {
        String data = "Hello, MD5!";
        MessageDigest md = MessageDigest.getInstance("MD5");
        byte[] md5Bytes = md.digest(data.getBytes());

        StringBuilder result = new StringBuilder();
        for (byte b : md5Bytes) {
            result.append(String.format("%02x", b));
        }

        System.out.println(result.toString());
    }
}

JavaScript (Node.js)

In JavaScript, you can use the crypto module to calculate MD5 hash values.

const crypto = require('crypto');

const data = 'Hello, MD5!';
const md5_hash = crypto.createHash('md5').update(data).digest('hex');
console.log(md5_hash);

PHP

In PHP, you can use the md5 function to calculate the MD5 hash value.

$data = 'Hello, MD5!';
$md5_hash = md5($data);
echo $md5_hash;

These examples demonstrate how to compute MD5 hash values ​​in different programming languages. Note that MD5 is no longer the preferred algorithm for cryptographic security; therefore, for secure applications, more robust hash algorithms such as SHA-256 or SHA-3 should be considered.