Method: HenselCode::Tools#random_prime

Defined in:
lib/hensel_code/tools.rb

#random_prime(bits) ⇒ Object 



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# File 'lib/hensel_code/tools.rb', line 19

def random_prime(bits)
  # The OpenSSL library only generates random primes from 16 bits on
  # The 3513 is the first 16-bit number
  # which means there are 3512 primes under 16 bits in length
  # Therefore for allowing values for the parameter 'bits' between 2 and 15,
  # we generate all primes from 2 to 15 bits using Ruby's Prime library
  # and select only those with bit length equal to the value of 'bits'
  # so we sample one element
  # We only do this if the value of 'bits' is less than 16, otherwise we
  # use OpenSSL to generate the prime
  if bits >= 2 && bits < 16
    primes = Prime.first(3512)
    primes.select { |p| p.bit_length == bits }.sample
  elsif bits >= 16
    OpenSSL::BN.generate_prime(bits).to_i
  else
    raise BadBitRangeForRandomPrime, "The bit length must be greater than or equal to 2"
  end
end