Re: Can’t set new PIN using Reset Code

[Kirill Elagin]

For anyone interested, I was able to get my card back in order. I am
85% confident that there is a bug in GnuPG that causes it to compute
the KDF in the reset command incorrectly.

Here is what I did.

Step 1 was to figure out how to tap into the communication with the
card. After a bit of searching I found out that `scdaemon` is
responsible for communicating with the card.
I ended up writing:

```
debug-level 8
debug-ccid-driver
debug-ccid-driver
log-file /tmp/scdaemon.log
```

into `$HOME/.gnupg/scdaemon.conf`. I did not really try any other
options, my understanding is that `debug-ccid-driver` (twice!) is what
makes it dump raw APDUs, but I have also thrown `debug-level` in just
for good measure.

Then I did `gpg --edit-card` and, as described in my previous email,
used the `unblock` command to set PIN to 123456789.
Immediately after that I used the `passwd` command entering both the
old and the new PIN as 123456789.

Then I inspected the log.
The first APDU of interest is RESET RETRY COUNTER (00 2C ...). I took
notice of the last 32 bytes, which are supposed to be the salted hash
of the PIN. I kinda inspected to find the unhashed PIN there, but,
not, the bytes looked pretty arbitrary.
The second APDU of interest is CHANGE REFERENCE DATA (00 24 ...). Its
payload is old hash followed by new hash. In my case they both were
the same, but they both were different from what I found in the
previous APDU.

I simply took the first APDU and replaced the hash of the new PIN with
the correct one from the second APDU. I sent it manually using
`gpg-connect-agent --hex`, and – tada! – my card works again.

I haven’t looked at the code yet, but my theory is that either a wrong
salt is used or the hash calculation is incorrect in some other way.

Cheers,
Kirill

On Fri, Apr 23, 2021 at 3:58 PM Kirill Elagin <kirelagin at gmail.com> wrote:
>
> Hello,
>
> Today gnupg suddenly refused to accept the PIN code of my YubiKey and
> it got blocked. I am not exactly sure what happened, but it does not
> matter now anyway.
>
> I am trying to unblock the PIN using a Reset Code.
>
> ```
> $ gpg --edit-card
>
> Reader ...........: Yubico YubiKey FIDO CCID 00 00
> Application ID ...: D2760001240103040006117659560000
> Application type .: OpenPGP
> Version ..........: 3.4
> Manufacturer .....: Yubico
> Serial number ....: 11765956
> Name of cardholder: Kirill Elagin
> Language prefs ...: en
> Salutation .......:
> URL of public key : https://bruna.kir.elagin.me/kirelagin.asc
> Login data .......: kirelagin
> Signature PIN ....: not forced
> Key attributes ...: rsa2048 rsa2048 rsa2048
> Max. PIN lengths .: 127 127 127
> PIN retry counter : 0 3 0
> Signature counter : 3
> KDF setting ......: on
> Signature key ....: CC5E B1EF E671 C418 33CC  318B FA66 ABF3 CFA3 569C
>       created ....: 2021-01-27 16:37:47
>       keygrip ....: AD296DDA5EB86005A83ABCCC57046D9E64007C10
> Encryption key....: 047A 7B2F B0E9 6F07 F9C2  16DC B3D9 F87D 907D C8B1
>       created ....: 2021-01-27 16:38:41
>       keygrip ....: B0960250674C237FF7D7979C8871684392B84F9C
> Authentication key: 8039 572F A015 0862 CB26  7A65 6D74 9968 B8E9 D1FE
>       created ....: 2021-01-27 16:39:33
>       keygrip ....: C9CAE2108556320815105E1D528B62D081965835
> General key info..:
> sub  rsa2048/FA66ABF3CFA3569C 2021-01-27 Kirill Elagin <kirelagin at gmail.com>
> sec>  rsa4096/90D516249B728BE6  created: 2017-11-30  expires: never
>                                 card-no: 0006 05764872
> ssb>  rsa2048/FA66ABF3CFA3569C  created: 2021-01-27  expires: 2022-01-01
>                                 card-no: 0006 11765956
> ssb>  rsa2048/B3D9F87D907DC8B1  created: 2021-01-27  expires: 2022-01-01
>                                 card-no: 0006 11765956
> ssb>  rsa2048/6D749968B8E9D1FE  created: 2021-01-27  expires: 2022-01-01
>                                 card-no: 0006 11765956
> ssb>  rsa4096/85D128E1B30E1931  created: 2017-11-30  expires: never
>                                 card-no: 0006 05764872
> ssb>  rsa4096/435BC889600C52F1  created: 2017-11-30  expires: never
>                                 card-no: 0006 05764872
>
> gpg/card> unblock
> gpg: OpenPGP card no. D2760001240103040006117659560000 detected
> PIN changed.
>
> gpg/card>
> ```
>
> It says that the PIN was changed, however when I try to use the card
> with the new PIN, it keeps saying that it’s wrong.
>
> Note that the admin pin is blocked (which, ugh, is a different story –
> I got it blocked months ago during the initial setup and I was so
> tired of that process that I decided not to start over). Also note
> that the first and the second retry counters are different (I have no
> idea why; I always assumed that gnupg was supposed to keep them in
> sync). And also note that KDF is enabled (which, I think, might be
> contributing to the issue – all my problems with e.g. the admin PIN
> getting blocked started after I enabled KDF).
>
> I’m pretty sure that at this point the easiest option is just to wipe
> the card and start over, but, I thought, I would still give it a try,
> so I’m looking for tips on how to debug this issue. And has anyone
> seen anything like that before?
>
> This all started with gnupg 2.2.23, I have now upgraded to 2.2.27 and
> it’s still the same.
>
> Cheers,
> Kirill