This is triple-DES encryption where an encrypt operation is encrypt-decrypt-encrypt, and decrypt is decrypt-encrypt-decrypt.
This implementation uses Crypt::DES to do its dirty DES work, and simply provides a wrapper around that module: setting up the individual DES ciphers, initializing the keys, and performing the encryption/decryption steps.
DES-EDE3 encryption requires a key size of 24 bytes.
You're probably best off not using this module directly, as the encrypt and decrypt methods expect 8-octet blocks.
You might want to use the module in conjunction with Crypt::CBC, for example.
This would be DES-EDE3-CBC, or triple-DES in outer CBC mode.