[OT] passphrases Was: Re: Allowing paste into pinentry-gtk-2?

[David Shaw]

On Apr 18, 2011, at 6:56 PM, Robert J. Hansen wrote:

>> Yes, well, that would mean that a 32-character English passphrase will
>> average about 64 bits of randomness. Is that really enough to protect
>> a key from an offline brute force attack? I think not, but am open to
>> being persuaded. :)
> 
> As I've said a few times now, no question about "is X really sufficient to protect a passphrase from being broken?" can be answered without a lot of context.  Who are you worried about breaking it?  How hard will they try?
> 
> To give you an example, RC5-64 was a giant distributed network of computers run by hobbyists using spare CPU cycles, trying to brute-force a 64-bit key.  Their volunteer network was much larger than anyone outside of megacorporations or First World intelligence agencies or major crime syndicates have.
> 
> It took them eighteen months.

Actually around 58 months: just under 5 years.

> 64-bit crypto isn't good for long-term storage, but if you want to foil someone who doesn't have megacorporation-level resources for a period of months or years, it'll do just fine.  Against First World intelligence agencies it might take a few seconds.

Are you asserting that there exists a group that can brute-force a 64-bit key in a few seconds?

David