This is the archived Spring 2015 version of the course. For the most recent version, see http://bitcoin-class.org.

# Class 23: Sidechains

Posted: Wed 08 April 2015

## Schedule

Each team will have an opportunity to present their project the last three classes (April 20, 22 and 27). Teams will sign up for presentation slots at Monday's class. Final projects are due by 11:59pm on Sunday, 3 May.

Thursday, 6pm Commerce School 223. Entrepreneurial and Career Ventures in the world of Digital Currency Panel.

Friday, 10:45am Rice 242. Suman Jana, Rise of the Planet of the Apps: Security and Privacy in the Age of Bad Code.

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.

# Bloom Filters

Burton Bloom, Space/Time Trade-offs in Hash Coding with Allowable Errors, Communications of the ACM, July 1970.

### Conventional Hash Table

Store collection of N b-bit elements, using k > N cells.

H is pseudorandom function, H(x) ← [0, k).

### Bloom Filter

Tradeoff: shrink size of array to store, accept false matches.

m = number of bits in array
k = number of hash functions
n = number of elements

What is the probability a given element of the array is not selected by a particular hash function?

What is the probability a given element of the array is not selected for a particular element by any of the k hash functions?

After n elements, what is the probability that an array bit is 0?

Probability of false match: (1 - (1 - 1/m)kn)k

How big should m be to have less than 0.01% false positive rate for a block with 1000 addresses?

How much privacy does using a bloom filter provide to an SPV wallet?

# Merged Mining

Merged Mining Specification

How can Namecoin leverage Bitcoin mining power while maintaining its own blockchain and difficulty level?

What are the advantages of enabing bitcoin miners to also mine namecoin?

# Side Chains

Why is it so hard to evolve bitcoin?

Adam Back, Matt Corallo, Luke Dashjr, Mark Friedenbach, Gregory Maxwell, Andrew Miller, Andrew Poelstra, Jorge TimÃ³n, and Pieter Wuille. Enabling Blockchain Innovations with Pegged Sidechains.

Blockstream