require 'pwn'

def repeated_block?(bytes)
  blocks = bytes.each_slice(16).to_a
  blocks != blocks.uniq
end

s = Sock.new('crypto.chal.csaw.io', 5001)
s.recvline # greeting
i = 1
loop do
  puts "Round #{i}"
  s.recvline
  s.sendline('A' * 32)
  s.recvline
  ciphertext = line[/: *([0-9a-f]+)/] && $1
  s.recvline # ECB or CBC?
  if repeated_block?(ciphertext.chars)
    s.sendline('ECB')
    STDERR.write(0)
  else
    s.sendline('CBC')
    STDERR.write(1)
  end
  i += 1
end