Perl DES PCBC as protection against decryption/crypt analysis
This is actually a good question, about how a mode of operation will affect analysis of a data stream.

In regards to an implementation of AES-PCBC, if you have AES-ECB you can build a wrapper for PCBC around it with the appropriate block size. It is not too difficult, but unnecessary...

In regards to security analysis, PCBC is no more resistant than CBC with an unknown Initialization Vector, since upon decryption the only difference between the modes is that the previous block input is only 1 value.



This will make decryption slower since it can not be decoded in parallel, but brute forcing the key space CAN be done in parallel. Once the correct combination of mode input and key are found, the entire remaining data stream will be correctly decrypted. The brute force of the IV/prior block is faster than the key, since no key change is required. DES is a 64-bit block, which means it has a small IV, and that makes your Key/IV search combination theoretically feasible with appropriate hardware (not now, but in the future yes).

The error propagation aspect of the mode was desired before widespread use of message authentication codes, modern cryptography sees error propagation through a mode as unnecessary. There are other applications that may prefer error propagation, but data at rest is not one of them. The downsides of error propagating modes (mostly performance) do not make up for any perceived advantage in security.

A bad mode is bad, but a good mode does not make a good cipher any better, and DES just isn't good enough anymore.