This is the archived Spring 2015 version of the course. For the most recent version, see

Class 16: Alternate Cryptocurrencies

Posted: Sun 15 March 2015

Project Proposals

Project Proposals are due Thursday, 19 March (11:59pm). Send your proposal by email to with subject line Project Proposal. Your email should contain at least:

  1. Title of your Proposal - a short title that should get across what you are doing.

  2. Team members list - a list of everyone on your team. You should cc: all the team members in the email so I have one email to reply-all to that will reach your full tem.

  3. Motivation - explanation of why your project topic is worthwhile.

  4. Project Plan - what you plan to do.

  5. First deliverable - description of what you will have ready to submit for the first deadline, Sunday, 5 April (note that you will be presenting about your project in class on Wednesday, 1 April).

If you are looking for teammates for your project, or searching for a project idea, come to my office hours after class today if possible.

Note: due to a bug in slideshare's updated player, ink markings no longer appear in the viewer.
If you download the slides, they are present though. Hopefully, the player will be fixed someday.

Alternate Cryptocurrencies

How can decentralized cryptocurrencies be different from bitcoin?


  • Economics: deflationary vs. inflationary
  • Proof-of-work: possible advantages of other proof-of-work mechanisms
  • Consensus mechanism: majority of computing power vs. alternatives
  • Scripting language for transactions: simpler vs. more powerful and expressive
  • Parameters: speed of blocks, size of transactions


What is a key derivation function?

Why is SHA-256 is horrible key derivation function today?

Colin Percival, Stronger Key Derivation via Sequential Memory-Hard Functions, 2009. presentation slides including XKCD 538.

What is a memory-hard algorithm?

Is a memory-hard algorithm better for a cryptocurrency proof-of-work than a compute-intensive one like SHA-256?

Andrew Miller, Ari Juels, Elaine Shi, Bryan Parno, and Jonathan Katz. Permacoin: Repurposing Bitcoin Work for Data Preservation. IEEE Security and Privacy ("Oakland") 2014.

Interesting Video

If you're still looking for ideas for your project still, this video may give you some good ideas: What Satoshi Didn't Know, Gavin Anderson, DevCore Boston 2015. (This talk gets into the history of bitcoin and lots of issues with flaws in its design, and raises some interesting possibilities for future work - e.g., are there ways to use old unspent transactions to solve network problems without spending them?)