AdaStream - Decentralized File Hosting Incentivised via Cardano Ada Payments

Introduction

This project is a Cardano implementation of the BitStream protocol by Robin Linus.

Original paper: BitStream: Decentralized File Hosting Incentivised via Bitcoin Payments

TL;DR

Alice wants to buy a file from Bob.
Bob encrypts the file with a random key and sends it to Alice.
Bob creates a bond contract on Cardano with a collateral and a commitment to the key and the file.
Alice pays Bob for the file via a HTLC (Hash Time Lock Contract), using Cardano or Bitcoin Lightning Network.
Alice decrypts the file with the key from the HTLC or takes the money back after the timeout.
If Bob cheats, Alice can prove it and get the collateral from the bond contract.
Bob can withdraw the collateral by revealing the key.

Abstract from the original paper

An atomic swap of coins for files would enable an open market for content hosting, in which anyone can monetize their excess bandwidth and data storage capacities, by serving decentralized multimedia services. Verifiable encryption provides a theoretical solution, but the computational overhead is too expensive in practice. We propose a solution to the fair exchange problem, which is highly efficient such that servers can handle large files and manage many clients simultanously. Compatible payment methods include Lightning, Ecash, and every other system that supports hash-timelock contracts. The server encrypts the file such that if there’s any mismatch during decryption the client can derive a compact fraud proof. A bond contract guarantees the client receives the exact file or they can punish the server. The transfer happens fully off-chain. An on-chain transaction is required only in case a server cheated.

Implementation

I use Scala and Scalus to compile a bond and HTLC contracts, encrypt and decrypt the files, and create the transactions.

How to run

Prerequisites

Java
scala-cli
Cardano uplc command line tool is needed for testing

If you use Nix, you can run nix develop to get a shell with all the dependencies.

Export your preview wallet mnemonic and BlockFrost API key

I use PrivateKey and Public Key from the first address of the wallet create from a mnemonic phrase. Here's a random mnemonic phrase for testing purposes. Do not use it in production.

export MNEMONIC="accident cluster album vacuum witness rather right clown liquid shallow liar myself now okay toy potato toe achieve sphere piano crush drum vivid jungle"
export BLOCKFROST_API_KEY="your blockfrost api key"

If you don't have BlockFrost API key it still can work, but you will not be able to create transactions.

Build the project

scala-cli --power package . -o adastream --assembly

Get the keys

./adastream keys
export pubKeyHex="640441A18DCD46E08EF74B7E3B038B11355F9BBC58B60ADEC3E8165771E51E00"

Encrypt a file

export preimage=$(head -c 32 /dev/urandom | xxd -p -c 64)
cat bitcoin.pdf | ./adastream encrypt $preimage  > bitcoin.pdf.encrypted

If you want to test the fraud proof, you can produce a wrongly encrypted file.

export preimage=$(head -c 32 /dev/urandom | xxd -p -c 64)
cat bitcoin.pdf | ./adastream encrypt-wrong $preimage  > bitcoin.pdf.encrypted-wrong

Verify a file

  cat bitcoin.pdf.encrypted | ./adastream verify $pubKeyHex

Create a bond contract transaction on Cardano Preview network

  cat bitcoin.pdf.encrypted | ./adastream bond

Create a bond withdraw transaction on Cardano Preview network

  cat bitcoin.pdf.encrypted | ./adastream withdraw $preimage $encId

Decrypt a file

  cat bitcoin.pdf.encrypted | ./adastream decrypt $preimage $pubKeyHex > bitcoin.decrypted.pdf

Create a fraud proof transaction on Cardano Preview network

  cat bitcoin.pdf.encrypted-wrong | ./adastream spend-bond $preimage $pubKeyHex > /dev/null

Run an API server

  ./adastream server

Web API

Open http://localhost:8080/docs in your browser to access the Swagger UI.

On-Chain example

Withdraw Transation

On Cardano Preview network TxId – 10fea052e27e335a5addac89adc16460970b4b46ae86b8072377b9951d675404

Fraud Proof Transaction

On Cardano Preview network 8faeadb75252c67475e1e1ddacde75d629b47938d70c082c07630955d46c8fae

nau/adastream