README.md

bip-schnorrrb

This is a Ruby implementation of the Schnorr signature scheme over the elliptic curve. This implementation relies on the ecdsa gem for operate elliptic curves.

The code is based upon the BIP340.

Installation

Add this line to your application's Gemfile:

gem 'bip-schnorr', require: 'schnorr'

And then execute:

$ bundle

Or install it yourself as:

$ gem install bip-schnorr

Usage

Signing

require 'schnorr'

private_key = ['B7E151628AED2A6ABF7158809CF4F3C762E7160F38B4DA56A784D9045190CFEF'].pack("H*")

message = ['5E2D58D8B3BCDF1ABADEC7829054F90DDA9805AAB56C77333024B9D0A508B75C'].pack('H*')

# create signature
signature = Schnorr.sign(message, private_key)
# if use auxiliary random data, specify it to the 3rd arguments.
aux_rand = SecureRandom.bytes(32) # aux_rand must be a 32-byte binary.
signature = Schnorr.sign(message, private_key, aux_rand)

# signature r value
signature.r 

# signature s value
signature.s 

# convert signature to binary

signature.encode

Verification

require 'schnorr'

# public key does not start with 02 or 03.
public_key = ['DFF1D77F2A671C5F36183726DB2341BE58FEAE1DA2DECED843240F7B502BA659'].pack('H*')

signature = ['6896BD60EEAE296DB48A229FF71DFE071BDE413E6D43F917DC8DCF8C78DE33418906D11AC976ABCCB20B091292BFF4EA897EFCB639EA871CFA95F6DE339E4B0A'].pack('H*')

message = ['243F6A8885A308D313198A2E03707344A4093822299F31D0082EFA98EC4E6C89'].pack('H*')

# verify signature.(result is true or false)
result = Schnorr.valid_sig?(message, public_key, signature) 

# signature convert to Signature object
sig = Schnorr::Signature.decode(signature) 

MuSig2*

This library support MuSig2* as defined BIP-327.

require 'schnorr'

sk1 = 1 + SecureRandom.random_number(Schnorr::GROUP.order - 1)
pk1 = (Schnorr::GROUP.generator.to_jacobian * sk1).to_affine.encode

sk2 = 1 + SecureRandom.random_number(Schnorr::GROUP.order - 1)
pk2 = (Schnorr::GROUP.generator.to_jacobian * sk2).to_affine.encode

pubkeys = [pk1, pk2]

# Key aggregation.
agg_ctx = Schnorr::MuSig2.aggregate(pubkeys)
# if you have tweak value.
agg_ctx = Schnorr::MuSig2.aggregate_with_tweaks(pubkeys, tweaks, modes)

## Aggregated pubkey is
### Return point:
agg_ctx.q
### Return x-only pubkey string
agg_ctx.x_only_pubkey

msg = SecureRandom.bytes(32)

# Generate secret nonce and public nonce.
sec_nonce1, pub_nonce1 = Schnorr::MuSig2.gen_nonce(
        pk: pk1,
        sk: sk1,  # optional
        agg_pubkey: agg_ctx.x_only_pubkey,  # optional
        msg: msg, # optional
        extra_in: SecureRandom.bytes(4),  # optional
        rand: SecureRandom.bytes(32)  # optional
)

## for stateless signer.
agg_other_nonce = described_class.aggregate_nonce([pub_nonce1])
pub_nonce2, sig2 = described_class.deterministic_sign(
        sk2, agg_other_nonce, pubkeys, msg, 
        tweaks: tweaks, # optional
        modes: modes, # optional
        rand: SecureRandom.bytes(32)  # optional
)

# Nonce aggregation
agg_nonce = Schnorr::MuSig2.aggregate_nonce([pub_nonce1, pub_nonce2])

# Generate partial signature.
session_ctx = Schnorr::MuSig2::SessionContext.new(
        agg_nonce, pubkeys, msg, 
        tweaks, # optional
        modes # optional
)
sig1 = session_ctx.sign(sec_nonce1, sk1)

# Verify partial signature.
signer_index = 0
session_ctx.valid_partial_sig?(sig1, pub_nonce1, signer_index)

# Signature aggregation.
sig = session_ctx.aggregate_partial_sigs([sig1, sig2])

# Verify signature.
Schnorr.valid_sig?(msg, agg_ctx.x_only_pubkey, sig.encode)

Note

This library changes the following functions of ecdsa gem in lib/schnorr/ec_point_ext.rb.

• ECDSA::Point class has following two instance methods.
  • #has_even_y? check the y-coordinate of this point is an even.
  • #encode(only_x = false) encode this point into a binary string.
• ECDSA::Format::PointOctetString#decode:
  • supports decoding only from x coordinate.
  • decode 33 bytes of zeros as infinity points.