CompSci 461/661

General

Instructor: G. Andrew Stone (gastone@umass.edu): Office Hours on Tues by appointment (send a message on Piazza) or via Zoom (813 149 9032) any day most times (PM me on Piazza).

Syllabus

TAs:
David Thibodeau dpthibodeau@umass.edu
Juan Altmayer Pizzorno jpizzorno@umass.edu

Graders:

Classroom:
461: Tues 2:30PM - 3:45PM: Computer Sciences Building 140
661: Tues 4:00PM - 5:15PM: Computer Sciences Building 140 (remote students use Zoom meeting: https://umass-amherst.zoom.us/j/92771831987)

Discussion: Piazza
Assignment Submission: Gradescope Course Entry Code: 7XJYPJ
Midterm: In class Oct 21
Final: BOTH SECTIONS: 12/16/2025, Tuesday 3:30PM - 5:30PM CompSci room 142
For the Midterm and final you may bring a 8.5x11" doublesided HANDWRITTEN by yourself, NOT PRINTED, cheat sheet. If it is too big I will make it smaller. If it is not handwritten I will take it before the exam.

General Reference Materials:

Bitcoin (UTXO) blockchain Concepts
Math
Ethereum

In Class Notes and Recordings

Week N notes
461 Recordings
661 Recordings

Weekly Process

Each week we’ll follow the same pattern:

1. Skim the written materials.
2. Watch the video, which is an overview of the written material. It does not replace them!
3. Read through the written materials in detail.
4. Come to class prepared for discussion with questions remaining from what you read, and ready to answer questions from your instructor. Discussion is not a repeat of the videos. It moves deeper on the video topics, and new material will be introduced! Attendance is mandatory!

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Week 13: Nov 25 Bitcoin Scripting

• Bitcoin Script Virtual Machine Description: https://github.com/bitcoinbook/bitcoinbook/blob/develop/ch07_authorization-authentication.adoc

• Bitcoin (actually Nexa) instruction set (opcode) Reference. Yes, actually READ through these! (so you get a sense of what can and can’t be done)

• Lightning Video Lecture

Week 12: Nov 18 Class meets! Tokens and Scripting

Reading material

• Bitcoin Tokens (Ordinals and Inscriptions)
  • https://docs.ordinals.com/overview.html and/or https://github.com/ordinals/ord/blob/master/bip.mediawiki Skim to understand that one can assign each Satoshi an order by mining – this is the Nth satoshi mined, and that that number can be carried forward through transactions to assign a number to every satoshi in the UTXO set.

Tools

• Bitcoin Scripting online: https://siminchen.github.io/bitcoinIDE/build/editor.html
• Nexa script debugger: https://debug.nexa.org/

Week 11: Nov 5 - 11: No class on Tuesday (Veteran’s day) CryptoZombies Week 2

• Familiarize yourself with the Ethereum online IDE: https://remix.ethereum.org

• There will be an open Zoom on Wednesday during class time where we can hack on Remix together.

• Ethereum Tokens (look at this code, should take you 10 min)
  • Contract-implemented and enforced tokens (similar to what you did in cryptozombies). Follow the link into the EIPs to see the Solidity interface.
  • ERC-20 Token Standard
  • ERC-721 Non-fungible Tokens

(check back here during this week for additional ethereum content)

Week 10: Oct 29 - Nov 4: No class (Election Day) CryptoZombies Week 1

• Go to https://cryptozombies.io/en/solidity and work through the first 5 “lessons”.
  • From Making the Zombie Factory to ERC721 & Crypto-Collectibles

• Read selections from: Native Blockchain Tokens (Group Tokenization Proposal)
  • Miner validated tokens on bitcoin-like blockchains.
  • Skip the intro, read “Functional Description”, up to “Contract Encumbered Groups”.
  • Read the use cases (at the end) to understand general token use cases for any token technology on any blockchain.

Week 9: Byzantine Generals Problem (not on midterm)

Byzantine Generals Video Lecture
Byzantine Fault Tolerance vs Proof Of Work Video Lecture

Vukolic paper: Proof-of-work vs. BFT Replication

Week 8: Oct 21 Midterm

Week 7: Oct 8-14

Midterm topics review in class Notes

Reference

Byzantine Generals Video Lecture Notes
FLP, CAP, BFT Comparison lecture notes

(optional) Impossibility Of Distributed Consensus (original FLP paper)

Week 6: Oct 1-7 Block Propagation

Efficient Block Propagation Lecture Video
Bloom Filter Lecture Notes
Invertible Bloom Lookup Table (IBLT)
(661) Graphene Paper
(461) Graphene short paper

Week 5: Sept 24-30 Bitcoin Networking, Eclipse Attacks, and Distributed Clock Synchronization

• Networking and Eclipse Attack Video Lecture

• Single transaction block analysis

• Clock Synchronization

We are going to use short excerpts from “Distributed Systems: Principles and Paradigms” by Andrew S. Tanenbaum and Maarten Van Steen. Fortunately, the entire text is available for free! Just give any email address to the author’s web site and they’ll send you a PDF.

Please read:

• Section 6.1: Clock Synchronization (no need to read the Berkeley algorithm or about wireless networks)
• Section 6.2: Logical clocks

Later in the semester, we’ll use the text for another topic.

• Logical Clock Conditions - Georgia Tech
• Real World Scenario (clocks) - Georgia Tech

Reference

• Eclipse Attacks on Bitcoin’s Peer-to-Peer Network

Purely optional reading for the course, but if you are interested, here is the original Lamport paper:

• Time, clocks, and the ordering of events in a distributed system, by Leslie Lamport, Communications of the ACM; 21(7): 558–565. (1978)

Week 4: (Sept 17-23) Elliptic Curve Crypto

• ECC Video Lecture part 1
• ECC Video Lecture part 2

elliptic-curve-cryptography-a-gentle-introduction
ECC part 2

661 only
Review this paper Attacks against Autofinalization and Parking.
Understand:

• That a variety of “tweaks” can be invented to modify Satoshi’s algorithm to choose the “main chain”
• What two proposed tweaks: “autofinalization” and “parking” actually do
• There seems to be no description of this consensus change, except for the source code located in this function (reading just the comments may be helpful).

Reference

These notes are from a different year than the video was recorded, but are similar enough to use for reference: ECC Video Lecture part 1 notes

(Optional) Chapter 8, Paar and Pelzl
(Optional) Chapter 9, Paar and Pelzl

Week 3: (Sep 9 - 16) Selfish Mining, Sybil Attack

Please skim the papers, watch the videos, and then read the papers carefully.

• Selfish Mining paper

• Sybil Attack paper

• Sybil Attack Lecture

• Selfish Mining Lecture

Reference

• Sybil Attack Lecture Notes
• Selfish Mining Lecture Notes

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Week 2: (Sep 3-9) Cryptography Overview, Doublespend Attacks

We continue our investigation into basic blockchain architecture.

• Overview of Applied Cryptography Video Lecture
• Doublespend Attack Video Lecture (1/2)
• Doublespend Attack (2/2) – note the final equation in this video has some typos although the derivation is correct in essence. Use the equation in Satoshi’s white paper to calculate the likelihood of matching the main chain. And to calculate the probability of exceeding the main chain:

$$\lambda = \frac{zq}{p}$$
$$1- \sum_{k=0}^{z+1} (\frac{\lambda^ke^{-\lambda}}{k!})(1-(q/p)^{z+1-k}), if q < p$$

Reference

• Overview of Applied Cryptography Notes
• Doublespend Analysis Notes – with correct doublespend derivation

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Week 1: Introduction

These are the materials for our first week.

• The Bitcoin Whitepaper
• Introduction and Class Logistics Video Lecture
• Blockchains Part 1 Video Lecture
• Blockchains Part 2 Video Lecture

Reference

• Introduction and Class Logistics Video Notes
• Blockchains Video Notes
• blockchain in one diagram

Course Possibilities