Sapio Programming 101

Stateful Smart Contracts for Bitcoin with OP_CTV

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Who what where why

Jeremy Rubin: bitcoin researcher & developer

Judica: a new org devoted to bitcoin r&d

Sapio: a new paradigm for bitcoin smart contracts

Where: VR

Why: so that bitcoin fixes this

Background

BIP-119 OP_CTV:

Simple Covenants for Bitcoin

BIP-119 CheckTemplateVerify Summary

• Proposed Op using a hash to specify exact transaction(s) that can spend a coin when the coin is created
• Scripts can recursively commit to transactions which contain many outputs that also commit to transactions
• Many Uses:
• Enables a congestion control functionality
• CTV + if/else branches → powerful smart contracts!
• & more!

This talk is only on Sapio, a CTV contracting language.

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What if No CTV?

We have a CTV Emulation Oracle!

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CTV is just this but no trusted servers.

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This Talk is All About Concrete Examples

My Goals:

Get you excited to use Sapio.

Get feedback on how you’d use it.

Teach you the very basics.

Non Goals:

Cover everything exciting.

This is your 101 class.

Liquid: A Contract Parable

Federation Managed Funds Script

11 <watchman keys> 15 CHECKMULTISIG NOTIF 4032 CSV <backup keys> CHECKMULTISIG ENDIF

Federation Managed Funds MiniScript

11 <watchman keys> 15 CHECKMULTISIG NOTIF 4032 CSV <backup keys> CHECKMULTISIG ENDIF

or_c(multi(11, <15 watchman keys>), and_v(multi(2, <3 backup keys>), older(4032)))

Federation Managed Funds MiniScript Policy

11 <watchman keys> 15 CHECKMULTISIG NOTIF 4032 CSV <backup keys> CHECKMULTISIG ENDIF

or_c(multi(11, <15 watchman keys>), and_v(multi(2, <3 backup keys>), older(4032)))

or(thresh(11, <15 watchman keys>), and(thresh(2, <3 backup keys>), older(4032)))

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Federation Managed Funds MiniScript Policy Sapio

Sapio → Policy → Miniscript → Script

Sapio:

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Policy: or(thresh(3,pk(A),pk(B),pk(C),pk(D)),and(thresh(2,pk(E),pk(F),pk(G)),older(4199029)))

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MiniScript: andor(multi(2,E,F,G),older(7672384),multi(3,A,B,C,D))

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Script: 2 x('E') x('F') x('G') 3 OP_CHECKMULTISIG

OP_NOTIF

3 x('A') x('B') x('C') x('D') 4 OP_CHECKMULTISIG

OP_ELSE

x('751240') OP_CHECKSEQUENCEVERIFY

OP_ENDIF

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Backup Recovery .

Federation Spend .

Federation Spend

Backup Recovery .

Backup Recovery ,

Federation Spend .

Backup Recovery .

Recap:

• You can write Scripts in Bitcoin
• Miniscript + Policy make that easier
• Sapio adds another layer

Recent Liquid Bug

I

A

M

A

B

L

O

C

K

C

H

A

I

N

S

H

O

R

T

CTV to the Rescue

G

same as before

Backup Operator (Looks Familiar)

Policy: or(thresh(3,pk(A),pk(B),pk(C),pk(D)),and(thresh(2,pk(E),pk(F),pk(G)),older(4199029)))

MiniScript: andor(thresh_m(2,E,F,G),older(7672384),thresh_m(3,A,B,C,D))

Script:

2 x('E') x('F') x('G') 3 OP_CHECKMULTISIG

OP_NOTIF 3 x('A') x('B') x('C') x('D') 4 OP_CHECKMULTISIG

OP_ELSE x('751240') OP_CHECKSEQUENCEVERIFY OP_ENDIF

FederatedPegIn

Policy:

or( and( thresh(2,pk(E),pk(F),pk(G)), txtmpl(H(BackupOperator))),

thresh(3,pk(A),pk(B),pk(C),pk(D)))

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MiniScript:

or_i(and_v(txtmpl(H(BackupOperator)),thresh_m(2,E,F,G)),thresh_m(3,A,B,C,D))

Script:

OP_IF

x(H(BackupOperator)) OP_CHECKTEMPLATEVERIFY OP_DROP

2 x('E') x('F') x('G') 3 OP_CHECKMULTISIG

OP_ELSE

3 x('A') x('B') x('C') x('D') 4 OP_CHECKMULTISIG

OP_ENDIF

11/15

2/3

Peg In

UTXO

Peg Out

UTXO

Backup

2/3

& 4 weeks

11/15

Peg Out

UTXO

Backup

UTXO

11/15

2/3

Peg In

UTXO

Peg Out

UTXO

Backup

2/3

& 4 weeks

11/15

Peg Out

UTXO

Backup

UTXO

D.R.Y. a little harder

don’t repeat yourself,

don’t repeat yourself,

don’t repeat yourself,

don’t repeat yourself...

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Why DRY?

Helper Function

Class

Factory

State

Machine

What else...

can we do?

TIC

TAC

TOE

What else...

can we do?

should

CANCELED

CANCELED

CANCELED

CANCELED

CANCELED

CANCELED

CANCELED

CANCELED

CANCELED

CANCELED

CANCELED

CANCELED

CANCELED

CANCELED

CANCELED

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CANCELED

CANCELED

CANCELED

CANCELED

C

​

​

​

CANCELED

CANCELED

CANCELED

CANCELED

CANCELED

CANCELED

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Options Contracts, CoinJoins,

Wallet Vaults, Fundraisers,

Lightning Network, Games,

Payment Pools, Wills,

Escrows, BMM Chains,

Congestion Control,

Subscriptions, and more….

So much to do…

so little time

Instead lets go deep!

Boring is the new Exciting:

Fees

Estimation

We can estimate how much fees are needed presently.

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But fee rates may change by the time our contract goes out!

Simple Contract

ctv(h)

utxo

1 BTC

Tx h

Simple Contract: CPFP

ctv(h)

utxo

1 BTC

Tx h

Some TX

0.001 fee

0.999 BTC

Simple Contract: CPFP

ctv(h)

utxo

1 BTC

Tx h

Some TX

0.001 fee

2.001 BTC

3 BTC

Simple Contract: Gas/Anchor Output

ctv(h)

utxo

0 BTC

Tx h

1 BTC

Simple Contract: Gas/Anchor Output

ctv(h)

utxo

0

BTC

Tx h

1 BTC

Some TX

0.001 fee

2.001 BTC

2 BTC

Simple Contract: Conditionalizing

ctv(h)

utxo

0

BTC

Tx h

1 BTC

ctv(h)

utxo

1

BTC

Tx h

Simple Contract: Gas/Anchor Input

ctv(h)

utxo

1 BTC

Tx h

0.001 BTC

Simple Contract: Conditionalizing

ctv(h)

utxo

1 BTC

Tx h

0.001 BTC

ctv(h)

utxo

1 BTC

Tx h

How to Pick a Fee Method

• Does your contract have nodes with relative timelocks?
• You’ll need an Gas/Anchor In/Out for mempool; or
• Pay high enough fees
• Do you need TXID Non-Malleability (e.g., for HTLCS)?
• Prefer Unconditional Gas/Anchor outputs
• Don’t care about Malleability?
• Conditional Gas/Anchor Inputs are Nice!
• Jeremy’s Favorite?
• Gas/Anchor outputs

Composability

Sapio is a lot like React

signal

Refundable

UTXO

1 day

refund

UTXO

receive

UTXO

0

0

11/15

2/3

Peg In

UTXO

Peg Out

UTXO

Backup

2/3

& 4 weeks

11/15

Peg Out

UTXO

Backup

UTXO

11/15

Refundable

UTXO

1 day

refund

UTXO

0

0

0

Fees (Again)

11/15

2/3

Peg In

UTXO

Peg Out

UTXO

Backup

2/3

& 4 weeks

11/15

Peg Out

UTXO

Backup

UTXO

11/15

Refundable

UTXO

1 day

refund

UTXO

0

0

11/15

2/3

Peg In

UTXO

Peg Out

UTXO

Backup

2/3

& 4 weeks

11/15

Peg Out

UTXO

Backup

UTXO

11/15

Refundable

UTXO

1 day

refund

UTXO

0

0

0

2/3

Peg In

UTXO

Backup

2/3

& 4 weeks

11/15

Peg Out

UTXO

Backup

UTXO

11/15

Refundable

UTXO

0

0

11/15

2/3

Peg In

UTXO

Peg Out

UTXO

Backup

2/3

& 4 weeks

11/15

Peg Out

UTXO

Backup

UTXO

11/15

Refundable

UTXO

1 day

refund

UTXO

0

0

0

Fee TX

fee

change

2/3

Peg In

UTXO

Backup

2/3

& 4 weeks

11/15

Peg Out

UTXO

Backup

UTXO

11/15

Refundable

UTXO

0

0

Fee TX

fee

change

⚠ ATOMIC ⚠

⚠ ATOMIC ⚠

2/3

Peg In

UTXO

Backup

2/3

& 4 weeks

11/15

Peg Out

UTXO

Backup

UTXO

11/15

Refundable

UTXO

0

0

Fee TX

fee

change

Fee TX

fee

change

⚠ ATOMIC ⚠

2/3

Peg In

UTXO

Backup

2/3

& 4 weeks

11/15

Peg Out

UTXO

Backup

UTXO

11/15

Refundable

UTXO

0

0

Fee TX

fee

change

Fee TX

fee

change

⚠ ATOMIC ⚠

2/3

Peg In

UTXO

Backup

2/3

& 4 weeks

11/15

Peg Out

UTXO

Backup

UTXO

11/15

Refundable

UTXO

0

0

Fee TX

fee

change

Fee TX

fee

change

Fee TX

fee

more

change

Traits & Composability

Sapio is a lot like React

1000+ Slides on Sapio Contract Design

Left Intentionally Missing

Sapio Programming 102 Syllabus

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• Using the Sapio-UX to develop, debug, & use contracts
• Contracts
• Secure Wallet Vaults
• Congestion Control Contracts
• Integrating Sapio in Applications, APIs & ABIs
• Advanced Sapio Programming & Safety Analysis
• Sapio Compiler Architecture
• Managing Sapio contract state & Watchtowers

What’s Next for Sapio?

What’s Next for Sapio?

• Improve Language & Polish for Open Sourcing
• Developing Library of High Quality Contract Components
• Improving Developer & Ecosystem Tools
• Work on CTV Deployment
• Looking for funding/grants :)

Tweet @JeremyRubin for Alpha access to Sapio!

Interested getting paid to work on it? DM for details...

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Sapio Q&A