Modes 0–2 use a custom DES variant that retains the standard 16-round Feistel network structure but differs from FIPS 46-3 in its permutation tables, S-boxes, and key rotation direction.
Why would you need a custom DES variant? Did Cadence have a cryptographer on staff? Or did they license this DES-variant? Or was a three-letter US government agency involved?
Looks like the DES-related modes were developed back before crypto code export restrictions were relaxed.
Looks like the DES-related modes were developed back before crypto code export restrictions were relaxed.