Hmm, you seem to be awfully aware of the various methods, are you one of those hardened criminals the article was speaking about that this law will protect us from?
No. What I want to point out is they're wasting taxpayer's money to create law that is not technically enforcible.
Think of the safe example, what if the owner give the police the safe's key, but refuse to tell you where the safe is hiding in? Granted the safe could be found with the aid of trained dogs and enough manforce, they might eventally find the safe. But for encrypted documents, there are thousands different method to do encryption (including those low-tech tricks like throwing lots of meaningless characters in the passage then do ROT-whatever on extended-ASCII code bases after encrypting it). And for each known encryption methods, slightly tweaking/adding additional parameter would create different encryption/decryption result, so God knows how many ways exist for encrypting things. If the criminal/suspect remain silence about the encryption method, I don't think the police can find enough people/resources to find out how to decrypt it.
I don't think I can outsmart those people, if I can think of these, I bet they also can.