The key needs to be 24 words long in order to achieve 256-bit encryption. Some systems, like some cryptocurrency wallets, only employ 12 words, or a 128-bit key. Because we take the security of our customers’ data and privacy seriously, we choose for a 256-bit encryption key size.
These 24 words are not a pass-phrase, they constitute a randomly generated 256bit key where each word is a digit with 2048 possible values – so 2048^24 combinations = 2.9642775e+79. We followed the BIP0039 crypto standard in our implementation of the recovery words.