MD4 Hash Generator: Early Merkle-Damgård Checksum Tool
MD4 hash calculator: MD5's direct predecessor with 128-bit output. Broken by collision attacks; use only for legacy interoperability, never for security.
Updated 2026-08-16
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Features
- Compute MD4 hashes online, the direct predecessor to MD5 with 128-bit output
- Real-time computation with 32 hex character digest
- One-click copy, save as .txt, and uppercase/lowercase toggle
- Explore the intermediate step between MD2 and MD5 in hash evolution
- Hash verification against known MD4 checksums
- Hash comparison tool: paste an expected 32-character MD4 hash alongside new output for instant verification
- Real-time input length display: shows character and byte counts alongside the hash for educational reference
- Cross-platform browser access: study MD4 on any device without installing cryptographic libraries
How to Use
- 1Type or paste your text into the input box above.
- 2Your hash digest appears instantly; no page reload needed.
- 3Toggle UPPERCASE / lowercase to change the hex output format.
- 4Click the copy icon to copy the hash to clipboard, or use Save to save as .txt.
- 5Paste an expected hash into the Verify field to check for a match.
- 6How to trace hash algorithm evolution: input the same text in MD2, MD4, and MD5 tools on this site and compare the 32-character outputs. Observe how the internal structure changed across the three generations.
- 7How to verify legacy NTLM hashes: Windows NTLM v1 internally uses MD4. Paste an NTLM hash into the Verify field after inputting the corresponding password to check legacy compatibility.
- 8How to study MD4's three-round structure: input a single byte and observe the output, then try longer inputs to understand how each of the three rounds processes data differently.
- 9How to compare collision resistance: while MD4 collisions are trivial to find today, input two different texts and observe how easy it is to see they're different: a property collision attacks break by finding two inputs with the same output.
- 10How to use MD4 for cryptanalysis education: vary the input and save several outputs as .txt files to build a dataset showing how small input changes propagate through the hash.
Frequently Asked Questions
What is MD4?
MD4 was designed by Ron Rivest in 1990 as a 128-bit hash function. It was the direct predecessor to MD5 and introduced design concepts that influenced all subsequent hash algorithms. (See: RFC 1320)
How is MD4 different from MD5?
MD5 added an extra round and improved the internal structure to fix MD4 weaknesses. MD4 uses three rounds; MD5 uses four. Both produce 128-bit output.
Is MD4 secure?
No. MD4 is severely compromised: collisions can be found in microseconds. It should never be used for any purpose, including checksums, as intentional collisions are trivial to create.
Why study MD4 today?
Only for legacy system interoperability and cryptanalysis education. Some very old NTLM variants in Windows used MD4 internally.
What came after MD4?
MD5 in 1992, then the SHA family. Both represent separate lineages but were influenced by MD4's pioneering Merkle-Damgard approach.
How was MD4 broken?
MD4 was broken in 1995 by Dobbertin who found collisions with high probability. Today, collisions can be found in microseconds on modern hardware using advanced differential cryptanalysis techniques.
What is the output length of MD4?
MD4 produces a 128-bit (16-byte) hash displayed as 32 hexadecimal characters, regardless of input size. (See: RFC 1320)
How does MD4's structure work?
MD4 uses three rounds of 16 operations each (48 total) on 32-bit words, with a Merkle-Damgard construction. Unlike MD5, it uses simpler non-linear functions and no final round.
Is MD4 related to NTLM v1?
Yes. Windows NTLM v1 (NT LAN Manager) uses MD4 to hash passwords. While Microsoft has deprecated NTLM v1, some legacy enterprise environments may still utilize this protocol and its MD4 dependency.
What lessons did cryptographers learn from MD4's failure?
MD4's collapse demonstrated that simple message expansion and insufficient rounds make a hash vulnerable to differential cryptanalysis. This directly led to MD5's additional round and more complex operations.
Can MD4 output be truncated?
Technically MD4 only produces full 128-bit output. For shorter hashes, cryptographers moved to SHA-1 (160-bit) and SHA-224 (224-bit) rather than truncating MD4 output.
What makes MD4 faster but less secure than modern hashes?
MD4 uses only 48 simple operations for 128-bit output. SHA-256 uses 64 more complex operations for double the output size. Modern hashes trade speed for security through more rounds and better diffusion properties.
Why can't a MD4 hash be reversed or decrypted?
MD4 is a one-way function: the digest is not an encryption of the input but a fixed-size fingerprint, and there is no mathematical inverse. Recovering the input is only possible by brute force or rainbow tables, which is why unsalted hashes of weak passwords can be cracked. That is also why it is used for integrity checks and password storage (with salt) rather than for hiding content.
Why can't I use an md4 hash generator to verify file downloads?
Nobody publishes MD4 checksums: MD4 is broken, and every distribution moved to SHA-256 (or MD5 historically). Even where MD4 checksums exist, they are useless against tampering because intentional collisions are trivial to create. For download verification use SHA-256: sha256sum file on Linux/macOS, or Get-FileHash file -Algorithm SHA256 in PowerShell.
Why does my NTLM hash look different from the md4 hash of the same password?
NTLM does not hash the plain UTF-8 text you type: it hashes the UTF-16LE encoding of the password, so MD4('password') differs from the NTLM hash even though NTLM v1 internally uses MD4. If you need to reproduce an NTLM hash, encode the password as UTF-16LE first, then hash. This is a good example of why comparing hash vs md5 outputs naively misleads: different digests often mean different input encodings, not a different algorithm family.