"hf mf nested" gets stuck with some cards

[uzlonewolf]

When you run hf mf nested against a card that does not respond at all to a bad key (instead of NACKing it like it should), the pm3 gets stuck in a loop and requires you to pull the USB cable.

Adding a if(BUTTON_PRESS() || usb_poll_validate_length()) inside the inner while(target_nt[i] == 0) loop in void MifareNested() fixes it; I'll create a pull request for this in a bit.

[uzlonewolf]

Upon further reflection, I think the loop is from what seems to be a static nonce and is not the lack of a NACK. Either way #900 fixes it. The card I'm working on does not NACK, appears to have a static nonce, and seems to be invulnerable to nested, hardnested, and darkside.

[iceman1001]

The infamous 01 20 01 45 nonce?

[uzlonewolf]

Seems to be.

#db# Nonce#2: Testing nt1=01200145 nt2enc=11358b4c nt2par=b0
#db# Nonce#2: dismissed (= nonce#1), ntdist=160

[iceman1001]

Yup, darkside, nested or hardnested will not work on it as you noticed.

Should add blacklisting or somehow identify when nonce is fixed and abort correctly

[uzlonewolf]

That's not a bad idea, I'll see if I can implement it later. I guess a more generic approach than blacklisting would be to keep a count and break if we get the same nonce more than X times. This also seems to be a dupe of RfidResearchGroup/proxmark3#408

[iceman1001]

yup, we have ran into that fixed nonce tag for some time now. If you try darkside etc on that repo it should detect a fixed nonce and quite.

[uzlonewolf]

I didn't want to hardcode that nonce since it is possible to get it from a RNG and doesn't help if cards start using different static values, so I added a counter and it now bails out with a new error code (-4) if it doesn't get a different value after 50 tries.

[iceman1001]

Sounds about like the solution in place, 50tries is way more lenient than needed. If you get the same nonce twice in a row something is fishy. Well, not for darkside but nested. I think if we have 10 times in a row without sync, is a no-show.

[uzlonewolf]

True, but 50 is still finished in almost 1/2 the timeout value, so I didn't see a reason to reduce it more. Gives the card a few more chances in case it has a really bad PRNG.

[pwpiwi]

but 50 is still finished in almost 1/2 the timeout value

That is with standard timing or with 's' or 'ss' slow timing options? I would agree with @iceman1001 that 50 is way too much. A weak PRNG still produces 65535 different nonces, therefore the chances for a duplicate nonce is quite low.

[pwpiwi]

Are you going to crack it as well? Or do we leave it with the message because you can get the keys with 'hf mf cgetblk' anyway?

[uzlonewolf]

Huh? Why do you think cgetblk would work?

proxmark3> hf mf cgetblk 4
No chinese magic backdoor command detected          
--block number: 4           
#db# wupC1 error          
Can't read block. error=2