Is MD4 even less secure than MD5?

Yes, considerably. MD4 (1990) is MD5's direct predecessor, and it's cryptographically shattered: full collisions can be found by hand on ordinary hardware in a fraction of a second using known attacks published in the early 2000s. Where MD5 collisions took real computational effort to first demonstrate, MD4 collisions are essentially instant. It should never be used anywhere security matters.

Why would anyone still need MD4 in 2026?

Mostly for interoperability with legacy systems that baked MD4 in decades ago and never changed it. The best-known example is NTLM, Windows' authentication protocol, which still uses MD4 internally to hash passwords for compatibility reasons. If you're debugging or reimplementing something that touches NTLM, old rsync/librsync checksums, or a handful of other legacy protocols, you may need to reproduce an MD4 digest even though nobody would design it in today.

How is MD4 related to MD5?

Ronald Rivest designed MD5 in 1992 as a direct, more conservative successor to his own MD4 (1990), after early cryptanalysis suggested MD4 was weaker than intended. Both share the same overall Merkle–Damgård structure and similar bitwise round functions, MD5 just adds a fourth round and more mixing per round. That shared lineage is also why both eventually fell to similar categories of collision attacks, just years apart and at very different difficulty levels.

Does this tool send my text to a server?

No. The MD4 computation runs entirely in your browser using a pure JavaScript implementation of RFC 1320, so nothing you type is sent anywhere or logged.

MD4 Hash Calculator - Calculate MD4 Checksum Online

Overview

Introduction

MD4 is the oldest hash function in this category, dating to 1990, and it's almost never the right choice for anything new. It survives today mostly because a handful of legacy protocols, NTLM chief among them, still depend on it internally.

This tool computes MD4's 128-bit digest of your input text entirely in your browser, useful for reproducing a known value while working with or reverse-engineering one of those legacy systems.

What Is MD4 Hash Calculator?

MD4 (Message-Digest Algorithm 4) is a cryptographic hash function designed by Ronald Rivest and published in RFC 1320, producing a 128-bit digest shown here as 32 hexadecimal characters.

It predates MD5 by two years and uses a simpler, three-round structure. Full collisions were demonstrated in the early 2000s and can now be found essentially instantly, making it one of the weakest widely-known hash functions still in any active use.

How MD4 Hash Calculator Works

The input is UTF-8 encoded, padded to a multiple of 512 bits per the Merkle–Damgård construction, and processed in 64-byte blocks through three rounds of 16 operations each, using bitwise functions and per-round additive constants distinct from MD5's four rounds.

The resulting four 32-bit words form the 128-bit digest, hex-encoded into the 32-character string this tool returns.

When To Use MD4 Hash Calculator

Use this when you specifically need an MD4 digest to match against a legacy system, reproducing part of an NTLM hash calculation, debugging old rsync-family checksums, or working with software that hard-coded MD4 decades ago.

There's essentially no reason to choose MD4 for anything new; if you just want a fast, non-adversarial checksum, MD5 or a checksum like CRC32 is a better, more standard choice, and if security matters at all, use SHA-256 or BLAKE3 instead.

Often used alongside MD5 Hash Calculator and SHA-1 Hash Calculator.

Features

Advantages

Very fast to compute, even simpler than MD5.
Small, fixed 32-character hex output.
Matches the exact algorithm still embedded in a handful of legacy protocols like NTLM.

Limitations

Collisions can be generated almost instantly with well-known attacks; offers essentially no cryptographic security.
Not preimage-resistant enough to trust for any adversarial context.
Rarely useful outside of legacy interoperability work.

Examples

Hashing a short greeting

Input

Hello, world!

Output

0abe9ee1f376caa1bcecad9042f16e73

13 bytes of UTF-8 text produce the standard 32-character MD4 hex digest.

Hashing the RFC 1320 test string "abc"

Input

abc

Output

a448017aaf21d8525fc10ae87aa6729d

This exact value appears in RFC 1320's own published test vectors, useful for confirming any MD4 implementation is correct.

Best Practices & Notes

Best Practices

Only use MD4 to match or reproduce a value from a legacy system that already requires it.
Never use MD4 for any new security-sensitive design, not even as a starting point.
If you just need a fast non-cryptographic checksum, prefer CRC32 or Adler-32 instead, they're simpler and equally unsuitable for security, but purpose-built for integrity checking rather than pretending to be cryptographic.

Developer Notes

This tool implements MD4 by hand in TypeScript following RFC 1320's exact specification (three rounds of 16 operations, distinct round functions F/G/H, and per-round left-rotation amounts), since MD4 isn't included in most modern hash libraries. It's verified against every test vector published in RFC 1320 section A.5, including the empty string, single characters, and the 80-character digit-repetition vector.

MD4 Hash Calculator Use Cases

Reproducing part of an NTLM hash while debugging Windows authentication
Verifying an old file checksum published using MD4
Reimplementing or auditing legacy software that hard-codes MD4
Confirming a hash library's MD4 implementation against known test vectors

Common Mistakes

Assuming MD4 provides any meaningful security margin at all, even compared to MD5.
Using MD4 in new code out of habit or copy-paste from old examples.
Confusing MD4 output with MD5 output since both are 32 hex characters; they are not interchangeable and will not match for the same input.

Tips

If a value doesn't match what you expect, double-check you're not comparing it against an MD5 digest of the same input, both are 32 hex characters and easy to mix up.
Use the MD5 tool alongside this one to see how the two related-but-different algorithms diverge on identical input.

MD4 Hash Calculator