This is Crypt::ECB, a Perl-only implementation of the ECB mode. In combination with a block cipher such as DES, IDEA or Blowfish, you can encrypt and decrypt messages of arbitrarily long length. Though for security reasons other modes than ECB such as CBC should be preferred. See textbooks on cryptography if you want to know why. In addition to this module you will need to install one or more of the Crypt::DES, Crypt::IDEA, or Crypt::Blowfish modules.