Class: SecretSharing::Shamir::Secret

Inherits:
Object
  • Object
show all
Includes:
SecretSharing::Shamir
Defined in:
lib/secretsharing/shamir/secret.rb

Overview

A SecretSharing::Shamir::Secret object represents a Secret in the Shamir secret sharing scheme. Secrets can be passed in as an input argument when creating a new SecretSharing::Shamir::Container or can be the output from a Container that has successfully decoded shares. A new Secret take 0 or 1 args. Zero args means the Secret will be initialized with a random Numeric object with the Secret::DEFAULT_BITLENGTH. If a single argument is passed it can be a String, or Integer. If its a String, its expected to be of a special encoding that was generated as the output of calling #to_s on another Secret object. If the object type is an Integer it can be up to 4096 bits in length.

All secrets are internally represented as a Numeric which can be retrieved in its raw form using #secret.

Constant Summary collapse

MAX_BITLENGTH =

FIXME : Is a MAX_BITLENGTH really needed? Can it be larger if so?

4096

Instance Attribute Summary collapse

Instance Method Summary collapse

Methods included from SecretSharing::Shamir

#evaluate_polynomial_at, #extended_gcd, #get_prime_number, #get_random_number, #get_random_number_with_bitlength, #invmod, #lagrange, #miller_rabin_prime?, #mod_exp

Constructor Details

#initialize(opts = {}) ⇒ Secret

rubocop:disable Metrics/PerceivedComplexity



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# File 'lib/secretsharing/shamir/secret.rb', line 46

def initialize(opts = {})
  opts = {
    :secret => get_random_number(32) # 32 Bytes, 256 Bits
  }.merge!(opts)

  # override with options
  opts.each_key do |k|
    if self.respond_to?("#{k}=")
      send("#{k}=", opts[k])
    else
      fail ArgumentError, "Argument '#{k}' is not allowed"
    end
  end

  # FIXME : Do we really need the ability for a String arg to re-instantiate a Secret?
  # FIXME : If its a String, shouldn't it be able to be an arbitrary String converted to/from a Number?

  if opts[:secret].is_a?(String)
    # Decode a Base64.urlsafe_encode64 String which contains a Base 36 encoded Bignum back into a Bignum
    # See : Secret#to_s for forward encoding method.
    stripped_secret = opts[:secret].strip
    fail ArgumentError, 'invalid secret (empty String)' if stripped_secret.empty?
    decoded_secret = Base64.urlsafe_decode64(stripped_secret)
    fail ArgumentError, 'invalid secret (base64 decode returned nil or empty String)' if decoded_secret.empty?
    int_secret = decoded_secret.to_i(36)
    fail ArgumentError, 'invalid secret (not an Integer)' unless int_secret.is_a?(Integer)
    fail ArgumentError, 'invalid secret (Integer bit length < 100)' unless int_secret.bit_length > 100
    @secret = int_secret
  end

  @secret = opts[:secret] if @secret.nil?
  fail ArgumentError, "Secret must be an Integer, not a '#{@secret.class}'" unless @secret.is_a?(Integer)

  # Get the number of binary bits in this secret's value.
  @bitlength = @secret.bit_length

  fail ArgumentError, "Secret must have a bitlength less than or equal to #{MAX_BITLENGTH}" if @bitlength > MAX_BITLENGTH

  generate_hmac
end

Instance Attribute Details

#bitlength ⇒ Object

Returns the value of attribute bitlength.



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# File 'lib/secretsharing/shamir/secret.rb', line 40

def bitlength
  @bitlength
end

#hmac ⇒ Object

Returns the value of attribute hmac.



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# File 'lib/secretsharing/shamir/secret.rb', line 40

def hmac
  @hmac
end

#secret ⇒ Object

Returns the value of attribute secret.



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# File 'lib/secretsharing/shamir/secret.rb', line 41

def secret
  @secret
end

Instance Method Details

#==(other) ⇒ Object

Secrets are equal if the Numeric in @secret is the same. Do secure constant-time comparison of the objects.



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# File 'lib/secretsharing/shamir/secret.rb', line 90

def ==(other)
  other_secret_hash = RbNaCl::Hash.blake2b(other.secret.to_s, digest_size: 32)
  own_secret_hash   = RbNaCl::Hash.blake2b(@secret.to_s, digest_size: 32)
  RbNaCl::Util.verify32(other_secret_hash, own_secret_hash)
end

#secret? ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/secretsharing/shamir/secret.rb', line 102

def secret?
  @secret.is_a?(Integer)
end

#to_s ⇒ Object 



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# File 'lib/secretsharing/shamir/secret.rb', line 106

def to_s
  # Convert the Bignum to a Base 36 encoded String
  # Wrap the Base 36 encoded String as a URL safe Base 64 encoded String
  # Combined this should result in a relatively compact and portable String
  Base64.urlsafe_encode64(@secret.to_s(36))
end

#valid_hmac? ⇒ Boolean

See : generate_hmac

Returns:

  • (Boolean) 


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# File 'lib/secretsharing/shamir/secret.rb', line 114

def valid_hmac?
  return false if !@secret.is_a?(Integer) || @hmac.to_s.empty? || @secret.to_s.empty?
  hash = RbNaCl::Hash.sha512(@secret.to_s)
  key = hash[0, 32]
  authenticator = RbNaCl::Util.hex2bin(@hmac)
  msg = hash[33, 64]
  begin
    RbNaCl::HMAC::SHA256.verify(key, authenticator, msg)
  rescue
    false
  end
end