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A lightweight and fast pure Ruby ECDSA

Overview

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

Security

starkbank-ecdsa includes the following security features:

  • RFC 6979 deterministic nonces: Eliminates the catastrophic risk of nonce reuse that leaks private keys
  • Low-S signature normalization: Prevents signature malleability (BIP-62)
  • Public key on-curve validation: Blocks invalid-curve attacks during verification
  • Montgomery ladder scalar multiplication: Constant-operation point multiplication to mitigate timing side channels
  • Hash truncation: Correctly handles hash functions larger than the curve order (e.g. SHA-512 with secp256k1)
  • Fermat's little theorem for modular inverse: More uniform execution time than the extended Euclidean algorithm

Installation

To install StarkBank`s ECDSA-Ruby, run:

gem install starkbank-ecdsa

Curves

We currently support secp256k1 and prime256v1 (P-256), but you can add more curves to the project. You just need to use the EllipticCurve::Curve.add() method.

Speed

We ran a test on Ruby 2.6.10 on a MAC Pro. The library was run 100 times and the averages displayed below were obtained:

Library sign verify
starkbank-ecdsa 1.5ms 3.6ms

Performance is driven by Jacobian coordinates, a branch-balanced Montgomery ladder for variable-base scalar multiplication, a precomputed affine table of powers-of-two multiples of the generator ([G, 2G, 4G, ..., 2^n*G]) combined with a width-2 NAF of the scalar to eliminate doublings during signing, a mixed affine+Jacobian addition fast path, curve-specific shortcuts in point doubling (A=0 for secp256k1, A=-3 for prime256v1), the secp256k1 GLV endomorphism to split 256-bit scalars into two ~128-bit halves for a 4-scalar simultaneous multi-exponentiation during verification, Shamir's trick with Joint Sparse Form as the fallback path for curves without an efficient endomorphism, and the extended Euclidean algorithm for modular inversion.

Sample Code

How to sign a json message for Stark Bank:

require 'starkbank-ecdsa'
require "json"

# Generate privateKey from PEM string
privateKey = EllipticCurve::PrivateKey.fromPem("-----BEGIN EC PARAMETERS-----\nBgUrgQQACg==\n-----END EC PARAMETERS-----\n-----BEGIN EC PRIVATE KEY-----\nMHQCAQEEIODvZuS34wFbt0X53+P5EnSj6tMjfVK01dD1dgDH02RzoAcGBSuBBAAK\noUQDQgAE/nvHu/SQQaos9TUljQsUuKI15Zr5SabPrbwtbfT/408rkVVzq8vAisbB\nRmpeRREXj5aog/Mq8RrdYy75W9q/Ig==\n-----END EC PRIVATE KEY-----\n")

# Create message from json
message = {
    "transfers": [
        {
            "amount": 100000000,
            "taxId": "594.739.480-42",
            "name": "Daenerys Targaryen Stormborn",
            "bankCode": "341",
            "branchCode": "2201",
            "accountNumber": "76543-8",
            "tags": ["daenerys", "targaryen", "transfer-1-external-id"]
        }
    ]
}.to_json

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

# Generate Signature in base64. This result can be sent to Stark Bank in header as Digital-Signature parameter
puts signature.toBase64()

# To double check if message matches the signature
publicKey = privateKey.publicKey()

puts EllipticCurve::Ecdsa.verify(message, signature, publicKey)

Simple use:

require 'starkbank-ecdsa'

# Generate new Keys
privateKey = EllipticCurve::PrivateKey.new()
publicKey = privateKey.publicKey()

message = "My test message"

# Generate Signature
signature = EllipticCurve::Ecdsa.sign(message, privateKey)

# Verify if signature is valid
puts EllipticCurve::Ecdsa.verify(message, signature, publicKey)

How to add more curves:

require 'starkbank-ecdsa'

newCurve = EllipticCurve::Curve::CurveFp.new(
    0xf1fd178c0b3ad58f10126de8ce42435b3961adbcabc8ca6de8fcf353d86e9c00,
    0xee353fca5428a9300d4aba754a44c00fdfec0c9ae4b1a1803075ed967b7bb73f,
    0xf1fd178c0b3ad58f10126de8ce42435b3961adbcabc8ca6de8fcf353d86e9c03,
    0xf1fd178c0b3ad58f10126de8ce42435b53dc67e140d2bf941ffdd459c6d655e1,
    0xb6b3d4c356c139eb31183d4749d423958c27d2dcaf98b70164c97a2dd98f5cff,
    0x6142e0f7c8b204911f9271f0f3ecef8c2701c307e8e4c9e183115a1554062cfb,
    "frp256v1",
    [1, 2, 250, 1, 223, 101, 256, 1]
)

EllipticCurve::Curve.add(newCurve)

publicKeyPem = "-----BEGIN PUBLIC KEY-----\nMFswFQYHKoZIzj0CAQYKKoF6AYFfZYIAAQNCAATeEFFYiQL+HmDYTf+QDmvQmWGD\ndRJPqLj11do8okvkSxq2lwB6Ct4aITMlCyg3f1msafc/ROSN/Vgj69bDhZK6\n-----END PUBLIC KEY-----"

publicKey = EllipticCurve::PublicKey.fromPem(publicKeyPem)

puts publicKey.toPem

How to generate a compressed public key:

require 'starkbank-ecdsa'

privateKey = EllipticCurve::PrivateKey.new()
publicKey = privateKey.publicKey()
compressedPublicKey = publicKey.toCompressed()

puts compressedPublicKey

How to recover a compressed public key:

require 'starkbank-ecdsa'

compressedPublicKey = "0252972572d465d016d4c501887b8df303eee3ed602c056b1eb09260dfa0da0ab2"
publicKey = EllipticCurve::PublicKey.fromCompressed(compressedPublicKey)

puts publicKey.toPem()

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

It's time to verify:

require 'starkbank-ecdsa'

publicKeyPem = EllipticCurve::Utils::File.read("publicKey.pem")
signatureDer = EllipticCurve::Utils::File.read("signatureDer.txt", "binary")
message = EllipticCurve::Utils::File.read("message.txt")

publicKey = EllipticCurve::PublicKey.fromPem(publicKeyPem)
signature = EllipticCurve::Signature.fromDer(signatureDer)

puts EllipticCurve::Ecdsa.verify(message, signature, 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 in the Stark Bank, you need to convert the binary signature to base64.

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

With this library, you can do it:

require 'starkbank-ecdsa'

signatureDer = EllipticCurve::Utils::File.read("test/signatureDer.txt", "binary")

signature = EllipticCurve::Signature.fromDer(signatureDer)

puts signature.toBase64()

Developing the gem

Clone the repository and install the dependencies:

git clone https://github.com/starkbank/ecdsa-ruby.git
bundle install

Run all unit tests

rake test

Run benchmark

ruby benchmark.rb