A lightweight and fast pure Swift ECDSA

Overview

This is a pure Swift implementation of the Elliptic Curve Digital Signature Algorithm. It is compatible with Swift 5.3. It is also compatible with OpenSSL. It uses some elegant math such as Jacobian Coordinates to speed up the ECDSA on pure Swift.

Curves

We currently support secp256k1, but it's super easy to add more curves to the project. Just add them on Curve.swift

Speed

We ran a test on a MAC Pro i5 2017. The libraries were run 100 times and the averages displayed bellow were obtained:

Library	sign	verify
starkbank-ecdsa	0.3ms	1.1ms

Sample Code

How to sign a json message for Stark Bank:

import starkbank

// Generate privateKey from PEM string
let privateKey = try PrivateKey.fromPem("""
-----BEGIN EC PARAMETERS-----
BgUrgQQACg==
-----END EC PARAMETERS-----
-----BEGIN EC PRIVATE KEY-----
MHQCAQEEIODvZuS34wFbt0X53+P5EnSj6tMjfVK01dD1dgDH02RzoAcGBSuBBAAK
oUQDQgAE/nvHu/SQQaos9TUljQsUuKI15Zr5SabPrbwtbfT/408rkVVzq8vAisbB
RmpeRREXj5aog/Mq8RrdYy75W9q/Ig==
-----END EC PRIVATE KEY-----
""")

// Create message from json
let message = "This is a text message"

let signature = Ecdsa.sign(message: message, privateKey: privateKey)

// Generate Signature in base64. This result can be sent to Stark Bank in the request header as the Digital-Signature parameter.
print(signature.toBase64())

// To double check if the message matches the signature, do this:
let publicKey = privateKey.publicKey()

print(Ecdsa.verify(message: message, signature: signature, publicKey: publicKey))

Simple use:

import starkbank

// Generate new Keys
let privateKey = PrivateKey()
let publicKey = privateKey.publicKey()

let message = "My test message"

// Generate Signature
let signature = Ecdsa.sign(message: message, privateKey: privateKey)

// To verify if the signature is valid
print(Ecdsa.verify(message: message, signature: signature, publicKey: publicKey))

OpenSSL

This library is compatible with OpenSSL, so you can use it to generate keys:

openssl ecparam -name secp256k1 -genkey -out privateKey.pem
openssl ec -in privateKey.pem -pubout -out publicKey.pem

Create a message.txt file and sign it:

openssl dgst -sha256 -sign privateKey.pem -out signatureDer.txt message.txt

To verify, do this:

import starkbank

let publicKeyPem = try? NSString(contentsOfFile: NSString(string:"/path/to/your/public-key/publicKey.pem").expandingTildeInPath, encoding: String.Encoding.utf8.rawValue)
let signatureDer = try? NSString(contentsOfFile: NSString(string:"/path/to/your/signature/signatureDer.txt").expandingTildeInPath, encoding: String.Encoding.utf8.rawValue)
let message = try? NSString(contentsOfFile: NSString(string:"/path/to/your/message/message.txt").expandingTildeInPath, encoding: String.Encoding.utf8.rawValue)

let publicKey = try PrivateKey.fromPem(privateKeyPem! as String)
let signature = try Signature.fromDer(signatureDer)

print(Ecdsa.verify(message: message! as String, signature: signature, publicKey: publicKey))

You can also verify it on terminal:

openssl dgst -sha256 -verify publicKey.pem -signature signatureDer.txt message.txt

NOTE: If you want to create a Digital Signature to use with Stark Bank, you need to convert the binary signature to base64.

openssl base64 -in signatureDer.txt -out signatureBase64.txt

You can do the same with this library:

import starkbank

let signatureDer = try? NSString(contentsOfFile: NSString(string:"/path/to/your/signature/signatureDer.txt").expandingTildeInPath, encoding: String.Encoding.utf8.rawValue)

let signature = try Signature.fromDer(signatureDer)

print(signature.toBase64())