Blooming Sidechains!

Cryptocurrency CaféUVa cs4501 Spring 2015David Evans

Class 23:Blooming

Sidechains!

Plan

• Bloom Filters

– Design and Analysis

– Use in Bitcoin

• Merged Mining

• Sidechains

1

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

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

Project Presentations will be April 20, 22 and 27.

2

32 GB

3

SPV Nodes

4

Simplified Payment Verification

SPV Wallet

Full Node

filter

blocks matching filter

5

6

Bloom Filters

7

8

Conventional Hash Table

9

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

H is pseudorandom functionH(x) [0, k)

Conventional Hash Table

10

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

H is pseudorandom functionH(x) [0, k)

11

12

How does Bloom’s application compare to use by bitcoin SPV nodes?

Bloom Filter Design

13

14

15

16

Probability of false match:

(1 – (1 – 1/m)kn)k

m: bits in arrayk: number of hashesn: number of elements

17

Probability of false match:

(1 – (1 – 1/m)kn)k

m: bits in arrayk: number of hashesn: number of elements

18

Do Bloom filters really provide privacy?

Merged Mining

19

20

Pointcoin 0 Pointcoin 1Pointcoin

6764…

Bitcoin 0 Bitcoin 1Bitcoin351247

…

Difficulty: 8,324,713Hash rate: ~0 TH/s

Difficulty: 49,446,390,688Hash rate: 310K TH/s

Should PointCoin Pizza be worried?

21

http://blockexplorer.bitcoin-class.org/

SHA-256 Proof-of-Work Cryptocurrency

22

Merged Mining

23

Goal: Enable using same hashing power to mine both Bitcoin and Namecoin (with different difficulty)

24

25

https://explorer.namecoin.info/blocks/block_225529.txt

26

27

Pointcoin 0 Pointcoin 1Pointcoin

6764…

Bitcoin 0 Bitcoin 1Bitcoin351247

…

Difficulty: 8,324,713Hash rate: ~0 TH/s

Difficulty: 49,446,390,688Hash rate: 310K TH/s

Namecoin 0 Namecoin 1Namecoin

225529…

Difficulty: 16,527,985,062Hash rate: 110K TH/s

Namecoin Bug

28

29https://github.com/namecoin/namecoin/commit/d70d01ff77310d3755891cb43cb2700b553019f4

Charge

Projects should be making good progress now!

30

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

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

Project Presentations will be April 20, 22 and 27.