MD5 In Java

Hashing is the transformation of a string of characters into a usually shorter fixed-length value or key that represents the original string. Hashing is used to index and retrieve items in a database because it is faster to find the item using the shorter hashed key than to find it using the original value. It is also used in many encryption algorithms.

ALGORITHM

MD5 processes a variable-length message into a fixed-length output of 128 bits. The input message is broken up into chunks of 512-bit blocks (sixteen 32-bit words); the message is padded so that its length is divisible by 512. The padding works as follows: first a single bit, 1, is appended to the end of the message. This is followed by as many zeros as are required to bring the length of the message up to 64 bits fewer than a multiple of 512. The remaining bits are filled up with 64 bits representing the length of the original message, modulo 2⁶⁴.

The main MD5 algorithm operates on a 128-bit state, divided into four 32-bit words, denoted A, B, C, and D. These are initialized to certain fixed constants. The main algorithm then uses each 512-bit message block in turn to modify the state. The processing of a message block consists of four similar stages, termedrounds; each round is composed of 16 similar operations based on a non-linear function F, modular addition, and left rotation. Figure 1 illustrates one operation within a round. There are four possible functions F; a different one is used in each round:

${\displaystyle {\begin{aligned}F(B,C,D)&=(B\wedge {C})\vee (\neg {B}\wedge {D})\\G(B,C,D)&=(B\wedge {D})\vee (C\wedge \neg {D})\\H(B,C,D)&=B\oplus C\oplus D\\I(B,C,D)&=C\oplus (B\vee \neg {D})\end{aligned}}}$

${\displaystyle \oplus ,\wedge ,\vee ,\neg }$ denote the XOR, AND, OR and NOT operations respectively.

IMPLEMENTATION IN JAVA

import java.security.*;
import java.math.*;

public class MD5 {
    public static void main(String args[]) throws Exception{
        String s="This is a wCodes";
        MessageDigest m=MessageDigest.getInstance("MD5");
        m.update(s.getBytes(),0,s.length());
        System.out.println("MD5: "+new BigInteger(1,m.digest()).toString(16));
    }
}

2.Another WORKING Sample of Code:

MessageDigest md5 = MessageDigest.getInstance("MD5");
md5.update(StandardCharsets.UTF_8.encode(string));
return String.format("%032x", new BigInteger(1, md5.digest()));

3.The Other Way Is By Using The Guava Hashing Method

Hasher hasher = Hashing.md5().newHasher();
hasher.putString("my string");
byte[] md5 = hasher.hash().asBytes();

FUTURE OF MD5

As MD5 and SHA-1 have significant (theoretical) weaknesses, they evidently should be withdrawn from applications. However, practice shows that the industry responds slowly in replacing them with secure hash function standards. To alleviate possible damage by collision attacks, we have introduced a technique that efficiently detects both identical-prefix and chosen-prefix collision attacks against both MD5 and SHA-1 given only one of the two documents in a collision. Such an indication can be used to abort further processing or communications, before sensitive information can be accessed or transmitted.

The future de facto hash function standard SHA-3 is currently being selected in an international competition by the National Institute of Standards and Technology (NIST) in the U.S. Nevertheless, due to the continued usage of SHA-1 in the foreseeable future, more research is needed on the real-world security of SHA-1 and on whether our ideas can be extended to other important hash function standards such as the future SHA-3.