Class: CcipherFactory::ShamirSharing

Inherits:
Object
  • Object
show all
Defined in:
lib/ccipher_factory/shamir/shamir_sharing.rb

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(threshold, secretdata = nil) ⇒ ShamirSharing

Returns a new instance of ShamirSharing.



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# File 'lib/ccipher_factory/shamir/shamir_sharing.rb', line 15

def initialize(threshold, secretdata=nil)
  @threshold = threshold
  @secretdata = secretdata
  @_coefficients = []

  if secretdata
    secretdata.each_char do |secretbyte|
      rand = Ccrypto::AlgoFactory.engine(Ccrypto::SecureRandomConfig)
      randVal = rand.random_bytes(@threshold-1)
      thesecoefficients = secretbyte+randVal
      #thesecoefficients = secretbyte+OpenSSL::Random.random_bytes(@threshold-1)
      @_coefficients << thesecoefficients
    end
  end
end

Instance Attribute Details

#_coefficients ⇒ Object (readonly)

Returns the value of attribute _coefficients.



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# File 'lib/ccipher_factory/shamir/shamir_sharing.rb', line 12

def _coefficients
  @_coefficients
end

#secretdata ⇒ Object (readonly)

Returns the value of attribute secretdata.



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# File 'lib/ccipher_factory/shamir/shamir_sharing.rb', line 13

def secretdata
  @secretdata
end

Instance Method Details

#compute_share(x) ⇒ Object 



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# File 'lib/ccipher_factory/shamir/shamir_sharing.rb', line 44

def compute_share(x)
  raise "x should be integer" unless x.class == Fixnum
  raise "x must be between 1 and 255" if x <= 0 || x  >256
  raise "@_coefficient must be initialized" if @_coefficients.empty?

  sharebytes = []

  @_coefficients.each do |thiscoefficient|
    thisshare = _f(x,thiscoefficient)
    sharebytes << thisshare
  end

  return x, sharebytes
end

#is_valid_share?(share) ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/ccipher_factory/shamir/shamir_sharing.rb', line 31

def is_valid_share?(share)
  raise "Share is of incorrect length: #{share.size}" if share.size !=2
  raise "Must initialize coefficient before checking is_valid_share?" unless @_coefficients
  raise "Must initialize coefficient before checking is_valid_share?" if @_coefficients.size != share[1].size

  x  = share[0]
  fx = share[1]

  correctshare = compute_share(x)

  correctshare == share
end

#recover_secretdata(shares) ⇒ Object 



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# File 'lib/ccipher_factory/shamir/shamir_sharing.rb', line 59

def recover_secretdata(shares)
  newshares = []

  shares.each do |share|
    newshares << share unless newshares.include?(share)
  end

  shares = newshares

  if @threshold > shares.size
    raise "Threshold: #{@threshold} is smaller than the number of uniquie shares: #{shares.size}"
  end

  if @secretdata
    raise "Recovoring secretdata when some is stored. Use check_share instead"
  end

  xs = []

  shares.each do |share|
    if xs.include?(share[0])
      raise "Different shares with the same first byte: #{share[0]}"
    end

    if share[1].size != shares[0][1].size
      raise "Shares have different lengths!"
    end

    xs << share[0]
  end

  mycoefficients = []
  mysecretdata = ''

  shares[0][1].size.times.each do |byte_to_use|
    fxs = []
    shares.each do |share|
      fxs << share[1][byte_to_use]
    end

    resulting_poly = _full_lagrange(xs,fxs)

    if resulting_poly[0..@threshold-1] + [0]*(shares.size - @threshold) != resulting_poly
      raise "Share do not match. Cannot decode"
    end

    mycoefficients << resulting_poly.map{|p| p.chr}.join

    mysecretdata += resulting_poly[0].chr
  end

  @_coefficients = mycoefficients
  @secretdata = mysecretdata
end