Method: ExtID::Type#decode

Defined in:
lib/extid.rb

#decode(s) ⇒ Object

Raises:



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# File 'lib/extid.rb', line 35

def decode(s)
  raise ArgumentError, "invalid prefix" unless s.start_with?(@prefix)
  hex_ciphertext = s[@prefix.size..]
  ciphertext = [hex_ciphertext].pack("H*")

  cipher = OpenSSL::Cipher.new('AES-128-ECB')
  cipher.decrypt
  cipher.key = @key
  cipher.padding = 0

  plaintext = cipher.update(ciphertext) + cipher.final
  plaintext[0, 8].unpack("q>").first
end