And How Dev Tooling Can Benefit The End User

Where Your Wallet Fetches Transactions

Quick shout-out to @LagginTimes !

Who Am I?

• Orange-pilled during COVID
• Open Source Contributor to BDK
• Currently funded by BDKF

@evanlinjin (GitHub, Twitter)

What is BDK

• Bitcoin Wallet Library (On-Chain Transaction)
• Free & Open Source
• Modular & Flexible
• Cross-platform

https://bitcoindevkit.org

Who Uses BDK?

Agenda

• The Need For Light Clients
• What is SPV (Simplified Payment Verification)
• Electrum
• Connection Bloom Filtering (BIP-37)
• Client Side Block Filtering (BIP-157)
• How BDK Can Help

The Need For Light Clients

Bitcoin-Qt

MyBitcoin.com Fiasco

2009 - 2011 Era

Mt. Gox Hack

What is SPV?

• Mentioned in whitepaper
• Simplified Payment Verification
• Prove relevant transaction is committed to blockchain
• Trusting the proof-of-work
• Earliest SPV wallets are still high-bandwidth

https://bitcoin.org/bitcoin.pdf

Electrum

• Brain-child of Thomas Voegtlin
• Easy-to-use wallet with stronger security guarantees
• Other innovations

Electrum - Thomas Voegtlin 7th September 2016

https://youtu.be/hjYCXOyDy7Y

Electrum Protocol

• How Electrum client and server communicate
• Electrum Client
  • Non-custodian
  • Connects to multiple Electrum servers
  • Verifies data from servers with SPV
• Electrum Server
  • Serves methods
  • Multiple implementations: ElectrumX, Electrs, Electrum Personal Server, etc.
• Many wallets use the Electrum protocol

https://electrum.readthedocs.io

Electrum Pros

• Fast syncing, low-bandwidth
• Does SPV checks

Electrum Cons

• Server can omit data
• Client gives addresses to server (privacy)

https://electrum.readthedocs.io

Bloom Filters (BIP-37)

• An attempt at doing SPV privately
• Client gives "bloom filter" to server
• Configurable false-positive rate
• Bitcoin P2P network

https://github.com/bitcoin/bips/blob/master/bip-0037.mediawiki

Problems with BIP-37

• Hard to get privacy right
• Servers can still omit data
• Heavy on servers (DoS attack vector)

https://eprint.iacr.org/2014/763.pdf

Client Side Block Filtering (BIP-157)

• Server creates filters
• One filter per block
• Client downloads block if filter matches interested data
• Filter headers - verify authenticity

https://github.com/bitcoin/bips/blob/master/bip-0157.mediawiki

CBF Pros

• Better privacy guarantees
• Servers cannot omit data*
• Filters generated once

CBF Cons

• More bandwidth
• More client-side processing

*assuming client is connected to at least one honest server

Bitcoin Wallets Today

• Most wallets get transactions via Electrum servers
• Most wallets do not do SPV
• Most users do not run their own nodes
• We need better defaults
• We need better tooling for developers

How Does BDK Help?

Modular chain-data source

• bdk_electrum

• bdk_esplora

• bdk_bitcoind_rpc

• bdk_electrum (with SPV) ?

• bdk_cbf ?

• bdk_floresta ?

• bdk_neutrum ?

https://github.com/bitcoindevkit/bdk

When BDK v1.0?

When BDK v1.0?

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