A sharp enough 3cm blade is more than enough to make someone bleed to death.
A 5cm screwdriver is more than enough to give brain damage to someone.
A flexible extension hose like the ones that go under the sink (with the nuts attached) is perfect for knocking someone out.
A titanium tipped pen is quite good if you aim for ears, temple or throat.
A tightly rolled newspaper makes a very good blunt weapon.
Breaking/banning encryption like would have minimal benefits while exposing the whole society. Don't think that only the gov't will have the secondary keys if they decide to "only" have back doors. Anyone motivated enough will have them.
If chat encryption is banned... let's say it's not hard to reintroduce it on top of existing layers for anyone motivated enough or with enough money.