[marshray]

When you said "something like that" I began imagining the type of liberties a well-meaning developer might take with that advice. For example, he might use the same key for all algorithms. He might use two block ciphers with two keys. The effective security you get from these constructions is notoriously counterintuitive.

We obviously use three independent keys. The security of the composition is then at least as good as the security of the best of these algorithms.

That's not obvious at all to an implementer. For example, there are NIST standards for 1-, 2-, and 3-key variations on triple-DES. http://en.wikipedia.org/wiki/Triple_DES#Keying_options