Changing PINs of German bank card

[Binarus]

On 11.07.2017 10:14, NdK wrote:
> Il 11/07/2017 09:44, Binarus ha scritto:
> 
>> - If somebody tries to brute force the pin (or online banking password),
>> the access will be permanently denied if there are more than 3 failures
>> (the exact number may vary). That means that the length of the pin /
>> password is not as important as one might think, because it is
>> practically impossible to brute force a 4 digit pin with only 3 tries.

> If you routinely use your card twice a day, they can make two or four
> guesses each day: every correct PIN you insert resets the counter.

I am not completely sure if I got you right. Wouldn't that mean that I
have to lose my card, the bad person then makes two guesses, then I get
back my card and enter my correct pin, then I lose my card again, and
the same bad person finds it again and makes another two guesses, then I
get my card back again and so on?

This is practically impossible (unless I have missed something obvious).
How could the correct pin be entered and the counter be reset if I
didn't get the card back?

Or did you refer to an adversary who copied the card? In that case, he
still would have to know when I actually have entered the correct pin
(which would mean that he permanently had to observe me) to start his
next two tries.

Furthermore, people usually call their bank to make their card invalid
as soon as they notice they have lost it. This means that they usually
won't enter the correct pin again after having lost the card.

The only way to abuse the fail counter reset feature would be to steal
the card, to copy it and to return it to its owner, and to do this in a
way that the owner would not notice it. But again, the adversary would
then still have to observe the card owner to see when the counter is
reset and to start his next tries.

> The probability to guess the correct code during the 5-years life of the
> card is definitely non-negligible.>
>> And there is one more very important thing most people don't think of:
>> What happens if you have an accident or if you die? Your heirs will have
>> all sorts of troubles if something happens to you and they can't access
>> your electronic accounts because they don't have the passwords.

> Usually there are other, non-technical ways. For example they just go to
> the bank with a death certificate.

I already have seen cases where it was not that easy in Germany.
Usually, presenting a death certificate to the bank is not enough. I
have seen that the bank had to make sure that the people presenting the
death certificate actually were the legal heirs. That meant that those
people had to acquire all sorts of documents from all sorts of
authorities which has been very expensive (several hundreds of EUR), but
more important, was very unpleasant and time consuming, especially in
the situation they were.

AFAIK, there is only one thing you could do to avoid that hassle: The
testator and the heirs should make a contract of inheritance. Such a
contract must be made by a notary, so this will also have its cost, but
when you present such a contract to the bank (in addition to the death
certificate), you will have no problems.

But now, being a German citizen, try the same thing with eBay, Facebook,
LinkedIn, PayPal and so on ... no thanks.

>> So I tend to write down at least my master password on a sheet of paper,
>> put that in a sealed envelope and give it to a relative who I highly
>> trust. In case I die, they open the envelope, have the master password
>> for my password safe and can use that to open the access to all my
>> accounts. Alternatively, you could have some relative you trust memorize
>> your master password. But since he won't use it regularly (hopefully),
>> he probably will forget it after short time ...

> Better use shamir's secret sharing, or just use LCD-segments characters
> printed on two acetate sheets that need to be combined to be read.
> Obviously the two sheets are to be given to two different people, in
> sealed envelopes...

Nice ideas :-) My own security needs are not that high, though (hoping
that life won't punish me for that optimism).

> BTW the method you use is the same that was used for our mainframe's
> master password. :)

To add to it, if you mistrust your relatives, you could put the password
on paper into some sort of lock box and carry the key to that lock box
with you. But then what would happen if you lost that key?

Regards,

Binarus