Chris McCormick

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Aug. 3, 2018

Live-code 8-bit algorave music in the browser with Clojurescript

Speccy is a small utililty I built for live-coding chiptune music in the browser with Clojurescript.

You can copy sounds from sfxr.me and paste them in as synth definitions, using code to modify any parameter over time, or start from scratch by building a synth up from basic parameters.

You can paste the following examples into the online editor to try it out:

; blippy synth
(sfxr {:wave :square :env/decay 0.1 :note #(at % 32 {0 24 3 29 7 60 12 52 19 29 28 52})})

; donk bass
(sfxr "1111128F2i1nMgXwxZ1HMniZX45ZzoZaM9WBtcQMiZDBbD7rvq6mBCATySSmW7xJabfyy9xfh2aeeB1JPr4b7vKfXcZDbWJ7aMPbg45gBKUxMijaTNnvb2pw"
      {:note #(or
        (at % 57
          {5 35
           27 34})
        (at % 32
           {0 24
            6 29
            18 21
            26 12}))})

; hi hat
(sfxr {:wave :noise
       :env/sustain 0.05
       :env/decay 0.05
       :vol #(sq % [0.3 0.1 0.2 0.1])})

; snare
(sfxr "7BMHBGCKUHWi1mbucW62sVAYvTeotkd4qSZKy91kof8rASWsAx1ioV4EjrXb9AHhuKEprWr2D4u4YHJpYEzWrJd8iitvr23br2DCGu7zMqFmPyoSFtUEqiM64"
      {:note 36
       :vol #(at % 16
         {4 0.5
          12 0.5})})

The full source code and documentation is available at GitHub.

Enjoy!

July 30, 2018

Hash Function Attacks Illustrated

Here are some illustrated explanations of the main ways in which cryptographic hash functions can be attacked, and be resistant to those attacks.

Zooko Wilcox's blog post Lessons From The History Of Attacks On Secure Hash Functions gives us a nice overview of these and I've quoted his concise explanations below. Check out his great post for more detail and history on this topic.

A cryptographic hash function is an important building block in the cryptographic systems that keep us safe in our communications on the internet.

A hash function takes some input data and generates a hopefully unique string of bits for each different input. The same input always generates the same result.

Diagram of an ideal hash function

The input to a secure hash function is called the pre-image and the output is called the image.

I use the following key below:

A red square

Red for inputs which can be varied by an attacker.

A green square

Green for inputs which can't be varied under the attack model.

To attack a hash function the variable inputs are generally iterated on in a random or semi-random brute-force manner.

Collision attack

Diagram of a collision attack on a hash function

A hash function collision is two different inputs (pre-images) which result in the same output. A hash function is collision-resistant if an adversary can't find any collision.