[PeterBarrett]

A 6 letter alphanumeric password, do they think people use old laptops to generate the possible passwords?! It should be at least 128 or 256 if they're being serious about security and preferably much much longer than that.

[wcoenen]

128 bits of entropy should suffice to make brute forcing impossible.

That corresponds to a 22 character mixed-case alphanumeric password. (62 choices per character, 62^22 > 2^128). But only if the characters are chosen randomly by a password generator; characters chosen by a human will have patterns and therefore lower entropy.

80 bits of entropy should still be enough to occupy a large amount of specialized hardware for a long time. That would correspond to 14 characters.

[ghshephard]

Depends on whether the decoding can be done offline, or requires the actual iPhone that the data is encrypted on.

[ionwake]

Is it possible to brute force this? Using quantum computers?

[higherpurpose]

I don't think you need quantum computers to bruteforce a 6-letter password.