Skip to content

Instantly share code, notes, and snippets.

spreading tribal knowledge

Yash Bhutwala yashbhutwala

spreading tribal knowledge
View GitHub Profile
laanwj /
Last active Aug 10, 2020
tools to write (block) data to png files and vice versa
#!/usr/bin/env python3
# Distributed under the MIT software license
import binascii, struct, sys, io, argparse
from PIL import Image
IMG_WIDTH = 512 # could be made adaptive...
MIN_HEIGHT = 4 # minimum height of image; twitter won't let us upload anything smaller
def div_roundup(x,y):
achow101 /
Last active Mar 21, 2021
How to Use Bitcoin Core with Hardware Wallets

Using Bitcoin Core with Hardware Wallets

This approach is fairly manual, requires the command line, and requires a patched version of Bitcoin Core.

Note: For this guide, code lines prefixed with $ means that the command is typed in the terminal. Lines without $ are output of the commands.


I am not liable for any coins that may be lost through this method. The software mentioned may have bugs. Use at your own risk.

sipa /
Last active Apr 30, 2021
Covert ECDH over secp256k1

Covert ECDH over secp256k1

If ECDH is used to establish a shared session secret for an encrypted connection, two elliptic curve points need to be transmitted (one in each direction) before encryption starts. In order to avoid being identifiable as a (specific) ECDH negotiation, ideally those two points are sent in a way that is indistinguishable from random.

This problem is easily addressed by using curves that support Elligator-style encodings: functions that encode a (subset of) elliptic curve points as sequences of bytes with no observable bias: (almost) every byte sequence corresponds to exactly one point, and the others correspond to none.

Unfortunately, no Elligator-style encoding is known for secp256k1.


I'll first give some thoughts on the design of the wallet in general, before explaining current and future SegWit wallet support.

Current design

Conceptually, a wallet currently contains mapKeys, mapScripts, and setWatchOnly, which together determine which outputs are considered "ours" (IsMine), and how to solve and sign for them. Then the wallet further contains key metadata, key chains, and key pool at the wallet level that feed into this.

We determine whether outputs are ours using ad-hoc logic that mostly answers the question "Could we sign this?", but with some notable exceptions:

bobrik /
Last active Jul 28, 2021
CFS hiccups

A description of known problems in Satoshi Nakamoto's paper, "Bitcoin: A Peer-to-Peer Electronic Cash System", as well as notes on terminology changes and how Bitcoin's implementation differs from that described in the paper.


The longest chain not only serves as proof of the sequence of events witnessed, but proof that it came from the largest pool of CPU power.

karpathy /
Created May 30, 2016
Training a Neural Network ATARI Pong agent with Policy Gradients from raw pixels
""" Trains an agent with (stochastic) Policy Gradients on Pong. Uses OpenAI Gym. """
import numpy as np
import cPickle as pickle
import gym
# hyperparameters
H = 200 # number of hidden layer neurons
batch_size = 10 # every how many episodes to do a param update?
learning_rate = 1e-4
gamma = 0.99 # discount factor for reward
bastman /
Created Mar 31, 2016
docker cleanup guide: containers, images, volumes, networks

Docker - How to cleanup (unused) resources

Once in a while, you may need to cleanup resources (containers, volumes, images, networks) ...

delete volumes

// see:

$ docker volume rm $(docker volume ls -qf dangling=true)
$ docker volume ls -qf dangling=true | xargs -r docker volume rm