What is MD5 algorithm & Steps for MD5 algorithm

In simpler words, the MD5(Mesage Digest 5) algorithm takes an input string and scrambles it using various functions, operations, and swapping techniques. This process produces a fixed-size 128-bit hexadecimal output. The output, known as a hash, is unique to each unique input. MD5 is often used to verify data integrity. For example, if you download a file, you can use MD5 to generate a hash of the downloaded file and compare it to the hash provided by the source. If the hashes match, the file is intact; if they don't, the file has been altered or corrupted.

In this article, we are going to learn about the functions, operations, and swapping techniques used in the MD5 algorithm.

MD5 was designed by Ronald Rivest in 1991 to replace an earlier hash function MD4,[3] and was specified in 1992 as RFC 1321.MD5 can be used as a checksum to verify data integrity against unintentional corruption. Historically it was widely used as a cryptographic hash function;

Hash Function - A hash function takes an input (or 'message') and returns a fixed-size string of bytes. The output, typically called the hash value or digest, is unique to each unique input. The key properties of a cryptographic hash function are:
→ Deterministic: The same input (or 'message') will always produce the same output.
→ Quick Computation: The hash value should be quick to compute.
→ Pre-Image Resistance: It should be difficult to generate the original input (or 'message') given the hash output.
→ Even a minor change in input should produce a vastly different hash.
→ Collision Resistance: It should be difficult to find two different inputs that produce the same output.

Steps in MD5 algorithm:

Suppose we have an input (or 'message') string for hashing using MD5, and the size of that string is 1000 bits. Now let's see the steps for hashing the input string using the MD5 algorithm.

Append Padding Bits and Length Bits: In this step, we ensure that the size of our input (or 'message') string is a multiple of 512. Currently, the length of our input (or 'message') string is 1000 bits that not divisible by 512. To address this, we add padding bits to the string. We start by adding a '1' bit, followed by '0's until the length becomes a multiple of 512. It's important to note that the padding should leave 64 bits remaining before the multiple of 512. These last 64 bits are reserved for adding the length of the original input (or 'message') string.
Initialalize MD Buffer: Here, the entire input (or 'message') is broken dowin into blocks of 512 bits each. Also, 4 Buffers are used of 32 bits each to store intermediate and final hash(4 Buffer * 32 bits = 128 bits) values during the hashing process.These buffers, typically denoted as A, B, C, and D.

The initial default values of 4 buffers A, B, C and D can be anything:(In this case)
A = 0x67452301
B = 0xefcdab89
C = 0x98badcfe
D = 0x10325476
Process Each 512-bit Block: Each 512-bit block is divided into 16 sub-blocks of 32 bits each, denoted as M[0] → M[15].
For each 512-bit block, we perform 4 rounds of operations, processing each of the 16 sub-blocks in each round.
In each round, $m_i$ values range from 0 to 15, representing the 16 sub-blocks, while the $k_i$ values range from 0 to 63 across all four rounds.
In each round, the function F is defined as follows:
- Round 1: (b AND c) OR (NOT b AND d)
- Round 2: (b AND d) OR (c AND NOT d)
- Round 3: b XOR c XOR d
- Round 4: c XOR (b OR NOT d)
After each round, the value of Buffer A changes to $A = (F(B, C, D) + M[i] + K[i]) \lll s) + B$ . Additionally, after each operation, the roles of A, B, C, and D rotate as illustrated in the diagram: the value of A feeds B, B feeds C, C feeds D, and D feeds A.
After all rounds are completed, the buffers A, B, C, and D contain the MD5 output, starting with the lower bit J and ending with the higher bits M.

Advantages of MD5 algorithm.

Simplicity: The MD5 algorithm is straightforward and easy to understand, making it a useful teaching tool for understanding hash functions.
Efficiency: MD5 is relatively fast and efficient in terms of computation, which is why it has been widely adopted in various applications.
Legacy Systems: MD5 has been widely implemented in many systems and protocols, so there is a significant amount of existing software and infrastructure that uses MD5.
Standardization: MD5 has been standardized in various protocols and applications, making it easy to integrate into systems that require hashing functionality.
Checksum: MD5 is commonly used as a checksum to verify data integrity. When downloading files, MD5 hashes are often provided so users can verify that the file has not been corrupted or altered during transmission.
Cross-Platform: MD5 is supported across many platforms and programming languages, making it versatile and easy to implement in different environments.

Disadvatages of MD5 algorithm.

Collision Attacks: MD5 is vulnerable to collision attacks, where two different inputs produce the same hash value. This vulnerability makes MD5 unsuitable for cryptographic security purposes.
Pre-Image Attacks: MD5 is also vulnerable to pre-image attacks, where an attacker can find an input that hashes to a specific output, although this is more difficult than a collision attack.
Obsolete: Due to its vulnerabilities, MD5 is considered obsolete for security-sensitive applications. Modern systems are encouraged to use more secure hash functions like SHA-256 or SHA-3.
Compliance Issues: Using MD5 in security contexts can lead to compliance issues with modern security standards and regulations.
128-Bit Output: MD5 produces a 128-bit (16-byte) hash value, which is shorter than the 256-bit or 512-bit outputs produced by more secure hash functions. This shorter length contributes to its vulnerability to attacks.
Scalability: In environments where large-scale data integrity is crucial, MD5’s weaknesses become more pronounced, making it unsuitable for verifying large datasets or securing large volumes of transactions.