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wtf is siphash?

rui314/siphash — explained in plain English

Analysis updated 2026-08-04 · repo last pushed 2025-07-29

34C++Audience · developerComplexity · 2/5StaleSetup · easy

TL;DR

SipHash is a small C++ library that protects apps from hash-flooding attacks by providing a fast, attack-resistant hash function. It is header-only, so you drop the file into your project and start using it immediately.

Mindmap

mindmap
  root((repo))
    What it does
      Fast hash function
      Attack-resistant hashing
      Scrambles data securely
    Tech stack
      C++
      Header-only library
    Use cases
      Web server lookups
      Database indexing
      Untrusted data hashing
    Audience
      C++ developers
      Security-minded builders
    Setup
      Drop-in file
      No compile step

Code map

Detail Auto

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filefunction / class

Why would anyone build with this?

REASON 1

Protect a web server's hash tables from slowdown attacks when logging thousands of user requests.

REASON 2

Safely index external files in a C++ database without risking performance from malicious input.

REASON 3

Drop in attack-resistant hashing for any C++ app that processes untrusted user-supplied data.

What's in the stack?

C++

How it stacks up

rui314/siphash0xjbb/modulestompeddelphicchen/esp32_flight_radar
Stars343434
LanguageC++C++C++
Last pushed2025-07-29
MaintenanceStale
Setup difficultyeasymoderatehard
Complexity2/54/54/5
Audiencedeveloperdeveloperdeveloper

Figures from each repo's GitHub metadata at analysis time.

How do you spin it up?

Difficulty · easy Time to first run · 5min

Header-only library, just drop the file into your project, no compile or linking step needed, but documentation is sparse.

The README does not mention a license, so the usage rights for this code are unknown.

Wtf does this do

SipHash is a small C++ library that helps developers protect their software from a specific type of cyberattack. When apps store information in hash tables, a common way to quickly look up data, attackers can sometimes craft specific inputs that intentionally slow the system down, causing it to grind to a halt. This library provides a fast, reliable way to hash data that is resistant to those attacks, keeping applications running smoothly and securely. At a high level, hashing is the process of taking a piece of data, like a word or a file, and scrambling it into a fixed-length string of characters. A good hash function does this in a way that is fast and evenly distributed. The SipHash algorithm was specifically designed to be unpredictable enough that bad actors cannot easily guess how their inputs will be scrambled, which prevents them from deliberately creating software bottlenecks. Under the hood, this project applies a modern version of the C++ programming language to execute that mathematical scrambling process. A developer would use this when building applications in C++ that need to process untrusted, user-supplied data and store it efficiently for quick retrieval. For example, if you are building a web server that needs to quickly log and look up thousands of user requests, or a database that indexes external files, you want a hashing function that will not break down when faced with unusual or maliciously crafted input. It gives developers peace of mind that their data structures will remain performant. What is notable about this project is that it is built as a "header-only" library. In C++, using external code normally requires a complicated setup process to compile and link files together. A header-only library skips that friction entirely, a developer can simply drop the file into their project and start using it right away. However, the project's documentation is very sparse and does not go into further detail about specific setup instructions or advanced features.

Yoink these prompts

Prompt 1
I want to use SipHash in my C++ project to protect hash tables from flooding attacks. Show me how to include the header file and hash a simple string or byte array.
Prompt 2
Write a C++ example that uses SipHash as the hash function for a hash map storing user-supplied keys, so the map stays fast even with unusual or malicious input.
Prompt 3
Help me compare SipHash to a standard hash like std::hash for a C++ web server that logs thousands of untrusted requests, and explain when to prefer SipHash.

Frequently asked questions

wtf is siphash?

SipHash is a small C++ library that protects apps from hash-flooding attacks by providing a fast, attack-resistant hash function. It is header-only, so you drop the file into your project and start using it immediately.

What language is siphash written in?

Mainly C++. The stack also includes C++.

Is siphash actively maintained?

Stale — no commits in 1-2 years (last push 2025-07-29).

What license does siphash use?

The README does not mention a license, so the usage rights for this code are unknown.

How hard is siphash to set up?

Setup difficulty is rated easy, with roughly 5min to a first successful run.

Who is siphash for?

Mainly developer.

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