You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: des_cbc_md5.rb
    path of file: ./repos/metasploit-framework/lib/rex/proto/kerberos/crypto
    
    the code of the file until where you have to start completion: # -*- coding: binary -*-

require 'rex/text'

module Rex
  module Proto
    module Kerberos
      module Crypto
        class DesCbcMd5 < BlockC
    
          def encrypt(plaintext, key, msg_type, confounder: nil)
            confounder = Rex::Text::rand_text(BLOCK_SIZE) if confounder == nil
            padded_data = pad_with_zeroes(plaintext, PADDING_SIZE)
            hashed_data = confounder + "\x00" * HASH_LENGTH + padded_data
            hash_fn = OpenSSL::Digest.new('MD5')
            checksum = hash_fn.digest(hashed_data)

            raise Rex::Proto::Kerberos::Model::Error::KerberosError, 'Invalid checksum size' unless checksum.length == HASH_LENGTH

            plaintext = confounder + checksum + padded_data

            cipher = OpenSSL::Cipher.new('des-cbc')
            if key.length != cipher.key_len
              raise Rex::Proto::Kerberos::Model::Error::KerberosError, "Encryption key length must be #{cipher.key_len} for des-cbc"
            end