After logstash restart, it takes about 10 minutes to encrypt the first message

Problems: As title. Cipher is as follow:  
cipher {
    mode => "encrypt"
    algorithm => "des-cbc"  
    iv_random_length => 8
    key => "@CIPHER_KEY_TOKEN@"
    source => "data"
    target => "data"
    #enable_metric => false
  }
