class Net::IMAP::SASL::CramMD5Authenticator

def hmac_md5(text, key)
  if key.length > 64
    key = Digest::MD5.digest(key)
  end
  k_ipad = key + "\0" * (64 - key.length)
  k_opad = key + "\0" * (64 - key.length)
  for i in 0..63
    k_ipad[i] = (k_ipad[i].ord ^ 0x36).chr
    k_opad[i] = (k_opad[i].ord ^ 0x5c).chr
  end
  digest = Digest::MD5.digest(k_ipad + text)
  return Digest::MD5.hexdigest(k_opad + digest)
end