MD4 is a cryptographic hash function that was developed by Ronald Rivest in 1990. It was widely used in the past for a variety of purposes, including digital signatures, password protection, and message authentication. However, due to several vulnerabilities that have been discovered in the algorithm over the years, it is no longer considered secure and should not be used for new applications.
The MD4 algorithm takes as input a message of arbitrary length and produces a fixed-length hash value as output. The hash value is typically a 128-bit value represented as a hexadecimal string.
The algorithm operates on the message in 512-bit blocks and uses a series of logical and bitwise operations to transform the input data into the output hash.
One of the main weaknesses of MD4 is its susceptibility to collision attacks. A collision occurs when two different messages produce the same hash value, which can be exploited by an attacker to create forged digital signatures or to impersonate a legitimate user.
As a result of these vulnerabilities, modern cryptographic applications typically use stronger hash functions such as SHA-256 or SHA-3 instead of MD4. If you need to use a hash function for a new application, it's important to choose a hash function that has been widely studied and is considered secure by the cryptographic community.