OpenPGP card
Table of Contents
The OpenPGP card is an ISO/IEC 7816-4/-8 compatible smart card implementation that is integrated with many GnuPG functions. Using this smart card, various cryptographic tasks (encryption, decryption, digital signing/verification, authentication etc.) can be performed.
The cards come in various form factors ranging from the standard size ID-1, over ID-1 with cut-outs for ID-000 (i.e. SIM card size), which together with an USB card reader allows to build a do-it-yourself crypto stick, to the GPF Crypto Stick.
They implement the OpenPGP card specification which evolved compatibly from v1.0 in 2003, via v1.1 in 2004, to v2.0 which was released in 2009.
Version 1.0 of the specification is mostly of theoretical interest, as most - if not all - cards adhere to version 1.1 or version 2.0.
All versions allow storing card holder details as well as generating and storing up to three RSA key pairs on the card.
While the 1.x version only supported 1024-bit RSA keys and no certificates, version 2.0 allows for RSA keys up to 4096 bits (requires GnuPG 2.0.18+) and optionally an X.509 card holder certificate for the AUT key on the card.
Other changes were:
- V1.1 brought 4 optional DOs for private use with different access conditions
- V2.0 brought optional support for
- card reset functionality (life cycle management)
- SecureMessaging
- changeable algorithm attributes
- other algorithms than RSA (not specified)
- Removal of PW2 ("Encryption PIN") present in v1.1. In v2.0 only "Admin PIN" and "User PIN" are specified. Furthermore, v2.0 spec defines "user consent" capabilities for signature key.
Where/How to get one?
OpenPGP cards / CryptoSticks can be obtained from vendors like e.g.
or by becoming a fellow in the Free Software Foundation Europe which uses the OpenPGP card specification on the Fellowship Smart Cards it hands out to its fellows.
State of OpenSC support
OpenPGP card v1.0/ 1.1 should work since OpenSC 0.9.1. Starting with OpenSC 0.12.2, OpenSC supports OpenPGP card v2.0 too.
However the cards can only be modified with GnuPG. So you need to use GnuPG to create/store keys etc.
OpenSC driver details
OpenPGP cards only implement a small subset of the ISO/IEC 7816-4/-8 standard. Most importantly, they do not use a file system to store the application specific data. Instead the data stored for the application is accessible via Data Objects (DO) only.
These DOs come in two variants:
- simple DOs that do not have a meaningful internal structure
- complex DOs that have a well-known internal structure which is encoded according to ASN.1 BER rules
In order to make OpenPGP cards accessible for OpenSC's PKCS15 functions, the OpenPGP card driver in OpenSC simulates a file system.
It does so by reading the well-known DOs on the card and converting them according to this logic:
- simple DOs are treated as wEFs
- complex DOs are treated as DFs with their elements as children.
As complex DOs can also contain complex DOs as elements, this conversion is done recursively, leading to a multi-level hierarchy.
This file-system is currently read-only, hence any operation writing to the card, i.e. personalization and key generation, needs to be done via GnuPG.
Examples
Here's an example of a card as seen via gnupg:
$ gpg --card-edit
Application ID ...: D2760001240101010001000004D50000
Version ..........: 1.1
Manufacturer .....: PPC Card Systems
Serial number ....: 000004D5
Name of cardholder: John Doe
Language prefs ...: en
Sex ..............: male
URL of public key : [not set]
Login data .......: johndoe
Private DO 1 .....: [not set]
Private DO 2 .....: [not set]
Signature PIN ....: forced
Key attributes ...: 1024R 1024R 1024R
Max. PIN lengths .: 254 254 254
PIN retry counter : 0 0 0
Signature counter : 5
Signature key ....: 6B71 349B 27F0 370A A964 9BD4 967C B116 BDFA 3CDD
created ....: 2010-03-07 09:17:36
Encryption key....: 3A2F 8637 C325 AAEE 18DD 88F1 AC40 47D4 2764 F212
created ....: 2010-03-07 09:18:25
Authentication key: F49C 7334 2AEC B098 60C9 04C7 9BFC 9789 DF31 19A9
created ....: 2010-03-07 09:18:25
General key info..:
pub 1024R/BDFA3CDD 2010-03-07 John Doe <john.doe@example.org>
sec> 1024R/BDFA3CDD created: 2010-03-07 expires: never
card-no: 0001 000004D5
ssb> 1024R/DF3119A9 created: 2010-03-07 expires: never
card-no: 0001 000004D5
ssb> 1024R/2764F212 created: 2010-03-07 expires: never
card-no: 0001 000004D5
In opensc-explorer the very same card looks like
$ opensc-explorer OpenSC Explorer version 0.12.1-svn Using reader with a card: SCM SCR 335 [CCID Interface] (60600adc) 00 00 OpenSC [3F00]> ls FileID Type Size 004F wEF 16 [005E] DF 8 [0065] DF 20 [006E] DF 202 [0073] DF 157 [007A] DF 5 5F50 wEF 0 [B600] DF 141 [B800] DF 141 [A400] DF 141 B601 wEF 142 B801 wEF 141 A401 wEF 142 OpenSC [3F00]> cd 0065 OpenSC [3F00/0065]> ls FileID Type Size 005B wEF 9 5F2D wEF 2 5F35 wEF 1 OpenSC [3F00/0065]> cat 005B 00000000: 44 6F 65 3C 3C 4A 6F 68 Doe<<John OpenSC [3F00/0065]>
Tips
General
- Minimum PIN length is 6 (you get a generic "Bad PIN" error if trying to use a shorter one) and Admin PIN must be at least 8 digits.
- OpenPGP v2.0 card can be erased with the following command (ATTENTION! ONLY USE IT ON A V2 CARD LIKE CRYPTOSTICK! WILL BRICK OTHERS!)
$ opensc-tool -s 00:20:00:81:08:40:40:40:40:40:40:40:40 \ -s 00:20:00:81:08:40:40:40:40:40:40:40:40 \ -s 00:20:00:81:08:40:40:40:40:40:40:40:40 \ -s 00:20:00:81:08:40:40:40:40:40:40:40:40 \ -s 00:20:00:83:08:40:40:40:40:40:40:40:40 \ -s 00:20:00:83:08:40:40:40:40:40:40:40:40 \ -s 00:20:00:83:08:40:40:40:40:40:40:40:40 \ -s 00:20:00:83:08:40:40:40:40:40:40:40:40 \ -s 00:e6:00:00 \ -s 00:44:00:00
Mac OS X
- Use http://www.gpgtools.org/ to get GnuPG2 for Mac OS X
- Remove OpenSC.tokend from /System/Library/Security/tokend when personalizing your token. scdaemon requires exclusive access which can not be shared with OpenSC.tokend, which is started when OpenPGP card/token is inserted.
- kill scdaemon and re-insert your reader if you still see this:
gpg: selecting openpgp failed: Card error gpg: OpenPGP card not available: Card error
Linux (and Gnome)
GnomeKeyring gpg-agent confusion
Under Gnome, gnome-keyring sets up GPG_AGENT_INFO:
$ env | grep GPG_AGENT GPG_AGENT_INFO=/tmp/keyring-cKD5KN/gpg:0:1
This agent is not capable of talking to smart cards (--card-status & --card-edit):
$ gpg2 --card-status gpg: selecting openpgp failed: Unsupported certificate gpg: OpenPGP card not available: Unsupported certificate
Solution: use gpg2 from a console or unset GPG_AGENT_INFO to use smart card related functions:
$ GPG_AGENT_INFO= gpg2 --card-status scdaemon[11344]: enabled debug flags: command cardio Application ID ...: D2760001240102000005000005460000 Version ..........: 2.0 Manufacturer .....: ZeitControl ...
Or permanently disable the gnome-keyring agent:
$ gnome-session-properties
And then uncheck 'GPG Password Agent', log out and log back in.
gpg2 and multiple readers
gpg2 only works if the OpenPGP compatible card is in the first listed reader:
$ opensc-tool -l # Detected readers (pcsc) Nr. Card Features Name 0 No Sitecom USB simcard reader MD-010 00 00 1 Yes German Privacy Foundation Crypto Stick v1.2 01 00 $ GPG_AGENT_INFO= gpg2 --card-status scdaemon[10980]: enabled debug flags: command cardio gpg: selecting openpgp failed: Card not present gpg: OpenPGP card not available: Card not present
versus
$ opensc-tool -l # Detected readers (pcsc) Nr. Card Features Name 0 Yes German Privacy Foundation Crypto Stick v1.2 00 00 1 No Sitecom USB simcard reader MD-010 01 00 $ GPG_AGENT_INFO= gpg2 --card-status scdaemon[11344]: enabled debug flags: command cardio Application ID ...: D2760001240102000005000005460000 Version ..........: 2.0 Manufacturer .....: ZeitControl ...
Solution: remove other smart card readers. If all readers are USB, killing pcscd and inserting readers in the "right order" (CryptoStick? first) helps. If this is not possible (for example, a reader integrated into the keyboard) editing the CCID driver Info.plist file and removing entries related to the "other" smart card readers can help. Alternatively look up the name of the reader you are using and add it to ~/.gnupg/scdaemon.conf (or --reader-port command line option if using GnuPG 1.X):
reader-port "German Privacy Foundation Crypto Stick v1.2 01 00"
After this a reader other than the first reader can be used. Be sure to change the configuration file if your reader setup changes (like more readers are added before the right one) as the numbering at the end of the name changes.
No readers error
If there are no readers connected, gpg2 gives a "generic" error message:
$ opensc-tool -l No smart card readers found. $ GPG_AGENT_INFO= gpg2 --card-status scdaemon[11033]: enabled debug flags: command cardio gpg: selecting openpgp failed: Card error gpg: OpenPGP card not available: Card error
This is jut FYI
