なんちゃってRSA暗号実装

rsa.rb

require "inline"
require "prime"

class RSA
  class << self
    def generate
      p, q = generate_unique_primes
      n = p * q
      e = (p - 1) * (q - 1) - 1
      d = generate_secret_key(e, (p - 1) * (q - 1))
      puts "Public Key: '#{n}:#{e}'"
      puts "Secret Key: '#{d}'" # TODO 1: eとdの値が一緒になってしまう
    end

    def encrypt(message, public_key)
      m = message # TODO 2: 文字列を数値に変換できるようにする
      n = public_key.split(":").first.to_i
      e = public_key.split(":").last.to_i
      puts "Code: '#{(m ** e) % n}'"
      # TODO 3: 数が大きいとべき乗で warning: in a**b, b may be too big のエラーが出る
    end

    def decrypt(code, public_key, secret_key)
      c = code
      n = public_key.split(":").first.to_i
      d = secret_key.to_i
      puts "Message: '#{(c ** d) % n}'"
    end

    private

    def generate_unique_primes
      p, q = 0, 0
      loop do
        p = Random.new.rand(100...1000)
        break if p.prime?
      end
      loop do
        q = Random.new.rand(100...1000)
        break if q.prime? && p != q
      end
      [p, q]
    end

    def generate_secret_key(e, _i)
      # TODO 4: 秘密鍵生成のもっとスマートなやりかたがあるはず
      ::GenerateSecretKey.new.execute(e, _i)
    end
  end
end

class GenerateSecretKey
  inline do |builder|
    builder.include "<math.h>"
    builder.c %q{
      long execute(long e, long _i) {
        long d = 0;
        while (d * e % _i != 1 % _i) { d++; }
        return d;
      }
    }
  end
end