> For the complete documentation index, see [llms.txt](https://alham-rizvi.gitbook.io/alhamrizvi/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://alham-rizvi.gitbook.io/alhamrizvi/cryptography/hashing/15.-murmurhash.md).

# 13\_murmurhash.md — MurmurHash

***

## 1. What MurmurHash Is

MurmurHash is a **non-cryptographic hash function** designed for:

* speed
* uniform distribution

It is commonly used in:

* hash tables
* databases
* distributed systems

***

## 2. Key Characteristics

* Very fast
* Deterministic
* Not cryptographically secure
* Good distribution (low collisions in normal use)

***

## 3. Variants

Common versions:

| Version     | Notes            |
| ----------- | ---------------- |
| MurmurHash2 | Older version    |
| MurmurHash3 | Most widely used |

***

## 4. Example

```
Input  → hello  
MurmurHash3 → 613153351  (example integer output)
```

Unlike SHA, output is often:

* integer
* not always hex string

***

## 5. How It Works (Simple Idea)

MurmurHash uses:

* multiplication
* XOR operations
* bit rotations

***

### High-level flow:

1. Split input into blocks
2. Mix each block with constants
3. Combine using XOR and rotation
4. Finalize hash

***

## 6. Why It Is Fast

* Uses simple CPU operations
* No heavy cryptographic structure
* Optimized for performance

***

## 7. Why It Is NOT Secure

### 1. No collision resistance

Attackers can easily find:

```
m1 ≠ m2 but hash(m1) = hash(m2)
```

***

### 2. Predictable structure

Given input/output patterns:

* easier to reverse or manipulate

***

### 3. No cryptographic guarantees

* not one-way
* not resistant to attacks

***

## 8. Practical Usage

MurmurHash is used in:

* hash maps
* database indexing
* Bloom filters
* caching systems
* load balancing

***

## 9. Tools and Code

### Python (via library)

```python
import mmh3

print(mmh3.hash("hello"))
```

***

### Install library

```bash
pip install mmh3
```

***

## 10. CTF Mindset

When you see MurmurHash:

* Assume it is weak
* Do NOT treat it like SHA

***

### Try:

* reversing logic
* brute force (small inputs)
* collision crafting
* exploiting predictable behavior

***

## 11. MurmurHash vs Cryptographic Hash

| Feature              | MurmurHash      | SHA-256      |
| -------------------- | --------------- | ------------ |
| Purpose              | Speed           | Security     |
| Collision resistance | Weak            | Strong       |
| Reversible           | Sometimes       | No           |
| Use case             | Data structures | Cryptography |

***

## 12. Real-World Status

MurmurHash is:

* Widely used in systems
* Trusted for performance
* Not used for security

***

## 13. Final Summary

MurmurHash is:

* Fast
* Efficient
* Non-cryptographic
* Unsafe for security use

***

### Core Idea

MurmurHash shows that:

> some hash functions are designed for performance, not security — and using them in security contexts leads to vulnerabilities.


---

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