Class: Scl::SecretShare

Inherits:
Object
  • Object
show all
Defined in:
lib/scl/secret_share.rb

Class Method Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(minimum, shares, encoder: Format::BASE64) ⇒ SecretShare

Returns a new instance of SecretShare.



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# File 'lib/scl/secret_share.rb', line 9

def initialize(minimum, shares, encoder: Format::BASE64)
  raise "Minimum must be larger than zero and less than shares" unless (0..shares) === minimum
  @encoder = encoder
  @minimum = minimum
  @shares  = shares
end

Class Method Details

.combine(shares, encoder: nil) ⇒ Object 



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# File 'lib/scl/secret_share.rb', line 35

def self.combine(shares, encoder: nil)
  decoded = shares.map do |share|
    share = encoder && encoder != Format::BASE64 ? encoder.decode(share) : share
    share.chars.each_slice(ENCODED_CHUNK_SIZE).map(&:join).each_slice(2).map do |random, polynomial|
      OpenStruct.new({
        x: base64_decode(random),
        y: base64_decode(polynomial)
      })
    end
  end

  chunks = decoded[0].length.times.map do |chunk|
    secret = OpenSSL::BN.new(0)
    decoded.each do |share|
      point = share[chunk]
      numerator, denominator = OpenSSL::BN.new(1), OpenSSL::BN.new(1)
      decoded.each do |peer|
        if peer != share
          current = peer[chunk].x
          numerator =  OpenSSL::BN.new((numerator * -current).to_i % PRIME)
          denominator = OpenSSL::BN.new((denominator * (point.x - current)).to_i  % PRIME)
        end
      end
      working = (point.y * numerator) * mod_inverse(denominator) + PRIME
      secret = ((secret + working) + 1000 * PRIME) % PRIME
    end
    secret
  end

  hex_data = chunks.map{|chunk| chunk.to_s(16).rjust(64, "0") }.join
  hex_data.chars.each_slice(64).map(&:join).map do |chunk|
    chunk.gsub(/(?:00)+$/,'').chars.each_slice(2).map{|pair|
      pair.join.to_i(16).chr
    }
  end.join
end

Instance Method Details

#generate(secret) ⇒ Object 



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# File 'lib/scl/secret_share.rb', line 16

def generate(secret)
  polynomials = chunks(secret).map do |chunk|
    [chunk] + (@minimum - 1).times.map do |i|
      random
    end
  end

  @shares.times.map do |i|
    result = ''
    polynomials.map do |polynomial|
      x = random
      y = evaluate_polynomial(polynomial, x)
      result << base64_encode(x)
      result << base64_encode(y)
    end
    @encoder == Format::BASE64 ? result : @encoder.encode(result)
  end
end