🔐 secp256k1.swift

Swift package with elliptic curve public key cryptography, ECDSA, Schnorr Signatures for Bitcoin and C bindings from libsecp256k1.

Objectives

Long-term goals are:

• Lightweight ECDSA & Schnorr Signatures functionality
• Built for simple or advance usage with things like BIP340
• Exposed C bindings to take full control of the secp256k1 implementation
• Familiar API design by modeling after Swift Crypto
• Automatic updates for Swift and libsecp256k1
• Availability for Linux and Apple platform ecosystems

Example Usage

ECDSA

import secp256k1

//  Private key
let privateBytes = try! "14E4A74438858920D8A35FB2D88677580B6A2EE9BE4E711AE34EC6B396D87B5C".bytes
let privateKey = try! secp256k1.Signing.PrivateKey(rawRepresentation: privateBytes)

//  Public key
print(String(bytes: privateKey.publicKey.rawRepresentation))

// ECDSA
let messageData = "We're all Satoshi.".data(using: .utf8)!
let signature = try! privateKey.ecdsa.signature(for: messageData)

//  DER signature
print(try! signature.derRepresentation.base64EncodedString())

Schnorr

let privateBytes = try! "C90FDAA22168C234C4C6628B80DC1CD129024E088A67CC74020BBEA63B14E5C9".bytes
let privateKey = try! secp256k1.Signing.PrivateKey(rawRepresentation: privateBytes)

// Extra params for custom signing
var auxRand = try! "C87AA53824B4D7AE2EB035A2B5BBBCCC080E76CDC6D1692C4B0B62D798E6D906".bytes
var messageDigest = try! "7E2D58D8B3BCDF1ABADEC7829054F90DDA9805AAB56C77333024B9D0A508B75C".bytes

// API allows for signing variable length messages
let signature = try! privateKey.schnorr.signature(message: &messageDigest, auxiliaryRand: &auxRand)

Tweak

let privateBytes = try! "C90FDAA22168C234C4C6628B80DC1CD129024E088A67CC74020BBEA63B14E5C9".bytes
let privateKey = try! secp256k1.Signing.PrivateKey(rawRepresentation: privateBytes)

// Adding a tweak to the private key and public key
let tweak = try! "5f0da318c6e02f653a789950e55756ade9f194e1ec228d7f368de1bd821322b6".bytes
let tweakedPrivateKey = try! privateKey.tweak(tweak)
let tweakedPublicKeyKey = try! privateKey.publicKey.tweak(tweak)

Elliptic Curve Diffie Hellman

let privateKey = try! secp256k1.KeyAgreement.PrivateKey()
let publicKey = try! secp256k1.KeyAgreement.PrivateKey().publicKey

// Create a shared secret with a private key from only a public key
let sharedSecret = try! privateKey.sharedSecretFromKeyAgreement(with: publicKey)

Silent Payments

let privateSign1 = try! secp256k1.Signing.PrivateKey()
let privateSign2 = try! secp256k1.Signing.PrivateKey()

let privateKey1 = try! secp256k1.KeyAgreement.PrivateKey(rawRepresentation: privateSign1.rawRepresentation)
let privateKey2 = try! secp256k1.KeyAgreement.PrivateKey(rawRepresentation: privateSign2.rawRepresentation)

let sharedSecret1 = try! privateKey1.sharedSecretFromKeyAgreement(with: privateKey2.publicKey)
let sharedSecret2 = try! privateKey2.sharedSecretFromKeyAgreement(with: privateKey1.publicKey)

let sharedSecretSign1 = try! secp256k1.Signing.PrivateKey(rawRepresentation: sharedSecret1.bytes)
let sharedSecretSign2 = try! secp256k1.Signing.PrivateKey(rawRepresentation: sharedSecret2.bytes)

// Payable Silent Payment public key
let xonlyTweak2 = try! sharedSecretSign2.publicKey.xonly.add(privateSign1.publicKey.xonly.bytes)

// Spendable Silent Payment private key
let privateTweak1 = try! sharedSecretSign1.add(xonly: privateSign1.publicKey.xonly.bytes)

Getting Started

This repository primarily uses Swift package manager as its build tool, so we recommend using that as well. If you want to depend on secp256k1.swift in your own project, simply add it as a dependencies' clause in your Package.swift:

.package(url: "https://github.com/GigaBitcoin/secp256k1.swift.git", .upToNextMajor(from: "0.6.0"))

Try in a playground using the SPI Playgrounds app or 🏟 Arena

arena GigaBitcoin/secp256k1.swift

Danger

These APIs should not be considered stable and may change at any time, libsecp256k1 is still experimental and has not been formally released.