Can someone explain how secure the deterministic wallet implementations of Electrum and Armory are? As far as I know, Electrum uses a 128-bit seed to generate all the addresses. I don't get this because since even a single bitcoin address consists of 256-bits. why not make this seed something much larger? And electrum uses something called "root key" and "chain code" which I can't find any explanations about.
Any ideas on how secure these implementations are?