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Introduction

A blind signature based rate limiting tokens, or their keyed verification analogues (e.g. privacy pass) can be used to rate limit requests, but presents challenges with regards to stockpiling and interaction requirements (credential requests can be batched and done ahead of time subject to anti-stockpiling mitigations, but are still fundamentall O(N)).

The somewhat obvious idea (probably not novel, but I couldn't find a description) presented here uses the unlinkable multi-show property of anonymous credentials to construct token bucket filters with a one time setup, permitting non-interactive self-issuance of usage tokens whose honest usage is anonymous (tokens of a single credential or different credentials are indistinguishable).

One time set up

A client wishes to make repeated anonymous requests to a rate limited server.

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# This script lives in my home manager home.packages. I also have:
#
#   programs.direnv.enable = true;
#   programs.direnv.nix-direnv.enable = true;
#
# To enable a language, I use e.g.:
#
#    nix registry add rust-direnv ~/code/dev-templates/rust
#
# where the directory is my local fork of https://github.com/the-nix-way/dev-templates

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Summary

Since Taproot (more generally any kind of MAST) spends have variable size which depends on the path being used, the last such input to be signed in a multiparty transaction can always use a larger than estimated witness to unfairly extract a fee contribution from the other parties to the transaction (keeping the absolute fees the same and reducing the feerate for the transaction).

Attack Scenario

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Bitcoin Privacy Introduction

Why privacy matters in Bitcoin

Celsius recent court filings provided a terrible and arguably avoidable loss of privacy for many of its customers, and will likely have chilling ripple effects for a long time to come. The goal of this presentation-turned-writeup is to give some context so that the reader can understand the consequences of such incidents and where to find more detailed information in order to mitigate such risks, and the tradeoffs that entails.

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moved to https://github.com/zkSNACKs/WabiSabi/blob/master/explainer.md

WabiSabi by Analogy

WabiSabi is a protocol (work in progress) for constructing CoinJoin transactions with the aid of a centralized coordinator. It utilizes keyed-verification anonymous credentials, homomorphic value commitments, and zero knowledge proofs to achieve privacy and flexibility.

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CAVEAT LECTOR

this notes have been largely superseded by discussions in the https://github.com/zkSNACKs/WabiSabi repository.

secondly, this describes a general framework which may be instantiated in different ways, a point that was not made clearly (the specific types described are more like independent examples of possible designs, not a specific proposal)

Overview

Modifications to the zerolink Chaumian coinjoin scheme to support:

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bitcoin privacy related bookmarks

protocols

• CoinShuffle: Practical Decentralized Coin Mixing for Bitcoin | SpringerLink
• Blindcoin: Blinded, Accountable Mixes for Bitcoin | SpringerLink
• P2P Mixing and Unlinkable P2P Transactions
• P2P Mixing and Unlinkable Transactions
• Anonymous CoinJoin Transactions with Arbitrary Values
• Sci-Hub | Sybil-Resistant Mixing for Bitcoin | 10.1145/2665943.2665955

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// PoC for 2-of-3 multisig where one of the keys is an opendime (sealed at time of scriptPubKey creation)
// see on https://ivy-lang.org/bitcoin
// the script ivy generates seems sub-optimal (some unconditional rotation and rolling of stack elements)
// but this is just a yucky PoC, and the ivy source is arguably easier to understand anyway

contract LockWithKeyHashMultisig(
  pubKey1: PublicKey,
  pubKey2: PublicKey,
  pubKey3hash: Ripemd160(Sha256(PublicKey)), // opendime address
  dummyKey: PublicKey, // should be a curve point with no known discrete log

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guix hash	dependency source file	guix revision	package file	line
1wl1x93b5w457ddsdgj0lh7yjq4q6l7wfbgwhagkc8fm2qkkrd0p	expat-2.2.6.tar.bz2	HEAD	gnu/packages/xml.scm	75
1wm4pv12f36cwzhldpp7vy3lhm3xdcnp4f184xkxsp7b18r7gm7x	libXau-1.0.8.tar.bz2	HEAD	gnu/packages/xorg.scm	4821
0dbfn5bznnrhqzvkrcmw4c44yvvpwdcsrvzxf4rk27r36b9x865m	libXext-1.3.3.tar.bz2	HEAD	gnu/packages/xorg.scm	4547
040rcs9fpv4bslhiy43v7dcrzakz4vwwpyqg4jp8bn24sl95ci7f	protobuf-2.6.1.tar.bz2	HEAD	gnu/packages/protobuf.scm	139
1c2vma9gqgc2v06rfxdiqgwhxmzk2cbmknwf1ng3m76vr0xb5x7k	xextproto-7.3.0.tar.bz2	HEAD	gnu/packages/xorg.scm	2369
18dighcs333gsvajvvgqp8l4cx7h1x7yx9gd5xacnk80spyykrf3	zlib-1.2.11.tar.gz	HEAD	gnu/packages/compression.scm	81
0jjirhw6xwz2ffmbg5kr79108l8i1bdaw7szc67n3qpkygaxsjb0	dbus-1.10.18.tar.gz	d8048a1212e880ce360aaf1b32f4bf3c84e51028	gnu/packages/glib.scm	78
1wy7svvp7df6bjpg1m5vizb3ngd7rhb20vpclv3x3qa71khs6jdl	fontconfig-2.12.1.tar.bz2	ab4e939c50b579eaee634c7c90c600f9c9f3aa3f	gnu/packages/fontutils.scm	233
121gm15ayfg3rglby8ifh8384

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#!/bin/bash

set -e

echo "Pinging peers..."
bitcoin-cli ping

sleep 2

# loop until all but 2 slowest peers have responded