# MD4

MD4 is a message digest algorithm (the fourth in a series) designed by Professor Ronald Rivest of MIT in 1990. It implements a cryptographic hash function for use in message integrity checks. The digest length is 128 bits. The algorithm has influenced later designs, such as the MD5, SHA and RIPEMD algorithms.

Weaknesses in MD4 were demonstrated by Den Boer and Bosselaers in a paper published in 1991. In August 2004, researchers reported generating collisions in MD4 using "hand calculation" [1], alongside attacks on later hash function designs in the MD4/MD5/SHA/RIPEMD family.

## MD4 hashes

The 128-bit (16-byte) MD4 hashes (also termed message digests) are typically represented as 32-digit hexadecimal numbers. The following demonstrates a 43-byte ASCII input and the corresponding MD4 hash:

```MD4("The quick brown fox jumps over the lazy dog") = 1bee69a46ba811185c194762abaeae90
```

Even a small change in the message will (with overwhelming probability) result in a completely different hash, e.g. changing d to c:

```MD4("The quick brown fox jumps over the lazy cog") = b86e130ce7028da59e672d56ad0113df
```

The hash of the zero-length string is:

```MD4("") = 31d6cfe0d16ae931b73c59d7e0c089c0
```