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Your iPhone just got less secure. Blame the FBI

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Re: Your iPhone just got less secure. Blame the FBI

#201

Post by mettamage »

wrsh07 wrote: post #170
zodPod wrote: post #165

Earlier quoted context omitted.

This is a great clarification of how this problem works. I STILL can't grasp why you'd switch. Since you have no idea which door it is, couldn't the 2/3 probability be applied to either his door or your door? For all you know, the one that he removed was just one random one of the goat doors. Your chance of picking the car was 1/3 before, if you could have the car already, why would it be better to switch now that he…

I find it clearer if you have 100 doors. Pick one. The host eliminates 98 doors [with no prize behind them]. Do you switch? Or do you stick with your original guess? As the parent mentioned, switching gives you a 99/100 chance of being correct, staying gives you a mere 1/100 chance.

Thanks for clarifying a very counter intuitive problem. I always struggled with this one, not anymore :) Sometimes scaling things up is the best way to understand things. Who knew!

Re: Your iPhone just got less secure. Blame the FBI

#202

Post by School-Cotton »

ricardobeat wrote: post #178
wrsh07 wrote: post #170

Earlier quoted context omitted.

I find it clearer if you have 100 doors. Pick one. The host eliminates 98 doors [with no prize behind them]. Do you switch? Or do you stick with your original guess? As the parent mentioned, switching gives you a 99/100 chance of being correct, staying gives you a mere 1/100 chance.

I don't see why the other door has 99x more probability of being correct. It's still 50/50, original door or remaining door, the other 98 don't change the odds.

Let's play a game to make this more clear. I'm thinking of a number between 1 and 1000. First, guess what it is.

Re: Your iPhone just got less secure. Blame the FBI

#203

Post by [deleted] »

carleverett wrote: post #150
function_seven wrote: post #138

Earlier quoted context omitted.

If one of the doors is shown to not have the prize , the odds are now 1/2 when the choice of reveal door is made randomly. That's because 1/3 of the time, you're not even offered the chance to switch, since it's pointless. I'll run the trials here. Assume the first two doors have the goat, and the third door has the car. Pick Reveal Switch? Outcome ---- ------ ------- ------- 1 2 Y 3 Car 2 1 Y 3 Car 3 1 N 3 Car 3 2 N…

But in the actual game, you are always given the chance to switch. Here are the possible outcomes of the game, with the third column being what the contestant should do to win: You Pick Car Switch? ------- ----- ------ 1 1 N 2 1 Y 3 1 Y 1 2 Y 2 2 N 3 2 Y 1 3 Y 2 3 Y 3 3 N Without knowing anything else, switching means that you win 2/3 of the time.

[deleted]

Re: Your iPhone just got less secure. Blame the FBI

#204

Post by FireBeyond »

wyldfire wrote: post #148
exelius wrote: post #55

Earlier quoted context omitted.

I agree with you, and I think this will eventually lead to a world where governments are unable to exert meaningful influence on large corporations. We're already starting to get there; I have a feeling that if the supreme court had forced Apple to write a custom version of iOS that things could have gotten really messy very quickly -- there were rumors that Apple's entire iOS engineering team was ready to resign if…

> Fuck it, we're based in Ireland now Apple has an enormous investment in their design team in Cupertino. It would be an enormous impact to their product development capability to start over somewhere else. It's not enough to say "HQ is over here bro," court orders still work in California. Then again this whole All Writs effort to "build me a tool to help my investigation" seems to break new ground. Maybe it wouldn'…

"Maybe it wouldn't even be enough to pack up and move all R&D out of the US (e.g. injunction on US sales until the foreign Apple company complies)."

That'd be an interesting possibility. Government, to U.S. consumers: "YOU are not allowed to buy the products you chose, because a foreign company refused to perform work for the U.S. Government." ...

Re: Your iPhone just got less secure. Blame the FBI

#205

Post by chc »

wkandek wrote: post #176
mikeash wrote: post #104

Earlier quoted context omitted.

According to the article, the vulnerability was already known by a third party, and all the FBI did was ask/pay that third party to use it on this phone. I don't see how that act alters the security of iPhones. I agree that the FBI should inform Apple of the vulnerability they used. I just don't think that failing to do so makes iPhones less secure. Failing to do so leaves them as they are, and informing Apple would…

I do not believe the FBI can legally report the vulnerability. They did not find it, they do not "own" it. They have used a service to get to the phone's data. Even if they reverse engineered the exploit used, it would be a breach of contract to disclose the vulnerability.

I'm not sure what "ownership" is supposed to mean in this context. Legally speaking, how does one "own" a security vulnerability?

Re: Your iPhone just got less secure. Blame the FBI

#206

Post by tptacek »

wolf550e wrote: post #144
tptacek wrote: post #120

Earlier quoted context omitted.

There is no such thing as "responsible disclosure". That's a term invented by vendors to coerce independent researchers into doing free work for them. Semantic drift has somewhat legitimized the term, but I think it's important we remember why it was conjured in the first place.

How would you call Google Project Zero's 90 day policy?

A decision they had every right to make for themselves, but that they have no right to impose on anyone else. I'm pretty sure Tavis Ormandy agrees with me.

Re: Your iPhone just got less secure. Blame the FBI

#207

Post by Zigurd »

There are reasons to doubt the FBI is being honest about this matter: Firstly, they must have known they could desolder and copy the chip containing the PIN-protected key, replacing it if it were erased. This method was put forward by multiple security experts. So the FBI started from a dishonest position regarding Apple being the only source of assistance.

Now they claim that a mystery exploit emerged and was put to use between Sunday night and Tuesday. That's not enough time to crack the phone using a pile of chips and brute-forcing the PIN.

Since the FBI started from a dishonest position, and hasn't spent enough time to plausibly have used the know approach, and they have carefully avoided saying they actually got keys and/or encrypted data out of the phone - or that they did anything at all with the phone, there is a more than small chance that the FBI has simply moved their own vague goalposts and declared that they have everything they need.

Not honest or ethical.

Re: Your iPhone just got less secure. Blame the FBI

#208

Post by ustolemyname »

tyleraland wrote: post #118
adekok wrote: post #88

Earlier quoted context omitted.

> The probabilities change, even when a door you didn't pick [and doesn't hold the prize] is opened. That's the common misunderstanding of the problem. Most people think that the probabilities go fro 1/3, 1/3, 1/3 to 1/2, 1/2, after choosing a door and having Monty Hall open one of the others. The probabilities don't change. The probabilities are 1/3, 1/3, 1/3 at the start. After you choose a door, they're still 1/3,…

I only started to understand how to look at this problem once I realized the host was going to eliminate a bad door _no matter what was chosen_. Of course if you have already selected a bad door he won't eliminate it. Another useful exercise is to stretch the number of doors to some large N and suppose the choice was posed repeatedly with a decreasing number of doors. If you can have anywhere from 2 to N guesses and…

Not switching until the end should work out better than switching multiple times.

4 doors, in 8ths to simplify fractions.

  2/8,2/8,2/8,2/8 => initial conditions, choose leftmost
  2/8,3/8,3/8 => random bad door removed, choose a random 3/8
  3/8,5/8 => remove another door.
Next choice is only 5/8, whereas if we had waited it would have been 6/8.

Re: Your iPhone just got less secure. Blame the FBI

#209

Post by ikeboy »

woodman wrote: post #184
jfoster wrote: post #164

Earlier quoted context omitted.

It wouldn't set a legal precedent unless a court ruled on it. It would only have come to that if Apple continued to decline the FBI's request.

Again, victim blaming. How is that any different from the false choice "We can do this the hard way, or the easy way"? Have you considered what will happen to the number of such requests as devices continue to become more secure?

As devices become more secure, Apple will no longer be able to unlock them.

If you put a backdoor into your phones, you should expect to have to use it.

Re: Your iPhone just got less secure. Blame the FBI

#210

Post by logfromblammo »

pklausler wrote: post #186
pklausler wrote: post #180

Earlier quoted context omitted.

This is good reasoning. Unlike other probability puzzles, the new information isn't useful in this one. P(my first choice was right) = P(my first choice was right | given that I've been shown a goat in another door) It's my second-favorite probability puzzle; my favorite is the one in which the new information has no relevance at all but still changes the probabilities, the "not both daughters" problem.

I should have just given the other problem, sorry for the laziness. Your friend tells you that she has two children. They're not both boys, she adds. What are the odds that they're both girls? (Obviously 1/3). When she tells you that one child is named Mary, the odds that they're both girls change (to 1/2)! Even though you knew that at least one of the children was a girl, and the name might as well be arbitrary, and…

After first datum (there are two children):

  Presuming A and B to be independent events
  (first child is a girl, second child is a girl)
  P(A) = 1 - P(!A) = 1/2
  P(B) = 1 - P(!B) = 1/2

  P(A and B) = P(B|A) * P(A) = 1/2 * 1/2 = 1/4
  P(A and !B) = P(!B|A) * P(A) = 1/2 * 1/2 = 1/4
  P(!A and B) = P(B|!A) * P(!A) = 1/2 * 1/2 = 1/4
  P(!A and !B) = P(!B|!A) * P(!A) = 1/2 * 1/2 = 1/4
Good so far.

But the probability later on depends on how you find out that at least one of your friend's children is a girl. If your friend tells you a random fact about her whole family, the probability is 1/3. If she tells you a fact about a randomly chosen child, the probability is 1/2.

You can presume from "they're not both boys" that the statement is equivalent to "there is at least one girl". When she tells you the name, you now know "a specific child of mine is a girl".

"Not both boys" gives you the precondition "!(!A & !B)" which equates to "A or B".

  P(A or B) = P(A and B) + P(A and !B) + P(!A and B) = 3/4
  P(A and B|A or B) = P(A or B|A and B) * P(A and B) / P(A or B) = 1 * 1/4 / 3/4 = 1/3
"Mary is a girl" gives you either the precondition "A" or the precondition "B"

  P(A and B|A) = P(A|A and B) * P(A and B) / P(A) = 1 * 1/4 / 1/2 = 1/2
  P(A and B|B) = P(B|A and B) * P(A and B) / P(B) = 1 * 1/4 / 1/2 = 1/2
These are both the same number, so that works out fine.
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