SYNOPSIS

gnupg-pkcs11-scd [--server] [--multi-server] [--daemon] [--verbose] [--quiet] [--sh] [--csh] [--options file ] [--no-detach] [--log-file file ] [--help]

DESCRIPTION

gnupg-pkcs11-scd is a drop-in replacement for the smart-card daemon (scd) shipped with the next-generation GnuPG (gnupg-2). The daemon interfaces to smart-cards by using RSA Security Inc. PKCS#11 Cryptographic Token Interface (Cryptoki). The following options are available:

--server

Run in server mode (foreground). If not redirected, input and output are over stdin/stdout.

--multi-server

Run in multi-server mode (foreground). In addition to communicating over stdin/stdout, the server also opens an additional listening UNIX socket.

--daemon

Detach and run in background.

--verbose

Be verbose while running.

--quiet

Be as quiet as possible.

--sh

Output sh-style environment variable definition.

--csh

Output csh-style environment variable definition.

--options file

Read options from file Some of the configuration options can only be set in the configuration file (see the Sx CONFIGURATION section).

--no-detach

Do not detach from console (useful for debugging purposes).

--log-file file

Output log to file

--help

Print help information.

When the daemon receives any of the SIGHUP, SIGTERM and SIGINT signals, it cleans up and exits.

gnupg-pkcs11-scd works only with already personalized cards and supports (for the time being) only RSA keypairs. The following constraints must be satisfied:

1. For each private key object, a certificate object must exist on the card. The existence of the corresponding public key object is not important (since the certificate includes public key).
2. The certificate and the corresponding private key must have identical CKA_ID attribute.

The PKCS#11 implementation is not obliged to enforce any of the above rules. However, practice has shown that popular PKCS#11 implementations found "in the wild" seem to respect them.

NOTES

Unlike gpg-agent, gnupg-pkcs11-scd supports more than one token available at the same time. In order to make gpg-agent happy, gnupg-pkcs11-scd always returns the same card serial number to gpg-agent. When unavailable token is requested, gnupg-pkcs11-scd will use NEEDPIN callback in order to ask for the requested token. When and if gpg-agent will support more than one serial number or NEEDTOKEN callback, this behavior will be modified.

FILES

Files affecting the operation of gnupg-pkcs11-scd

~/.gnupg/gnupg-pkcs11-scd.conf

gnupg-pkcs11-scd uses this as a default configuration file.

/etc/gnupg-pkcs11-scd.conf

gnupg-pkcs11-scd uses this as a default system wide configuration file.

~/.gnupg/gpg-agent.conf

Default configuration file for gpg-agent.

CONFIGURATION

To tell gpg-agent to use another smart-card daemon, the following needs to be put in ~/.gnupg/gpg-agent.conf

scdaemon-program /usr/bin/gnupg-pkcs11-scd
pinentry-program /usr/bin/pinentry-qt

The first line is mandatory in order to use gnupg-pkcs11-scd With the second line you can set your preferred pinentry program (it has to be one compatible with GnuPG). Of course, you need to adjust the paths according to your system setup.

An example ~/.gnupg/gnupg-pkcs11-scd.conf file (lines beginning with # are comments):

# Log file.
#log-file log1
# Default is not verbose.
#verbose
# Default is no debugging.
#debug-all
# Pin cache period in seconds; default is infinite.
#pin-cache 20
# Comma-separated list of available provider names. Then set
# attributes for each provider using the provider-[name]-attribute
# syntax.
providers p1
# Provider attributes (see below for detailed description)
provider-p1-library /usr/lib/pkcs11/p1.so
#provider-p1-allow-protected-auth
#provider-p1-cert-private
#provider-p1-private-mask 0
#emulate-openpgpg
#openpgp-sign 5C661B8C07CFD957F7D98D5B9A0F31D236BFAC2A
#openpgp-encr D2DC0BD1EDD185969748B6025B452816F97CBA57
#openpgp-auth A7B8C1A3A8F71FCEC018886F8767927B9C8D871F

The following attributes can be set for each provider:

library

Full path to the PKCS#11 shared library (= provider).

allow-protected-auth

Allow protected authentication for provider. This needs to be supported by the provider and you should have appropriate reader hardware.

cert-private

Authentication is required before certificates can be accessed. Most configurations store certificates as public, so there is no need to use this option.

private-mask

Private key mask mode. Use this only when you have problem using private key operations. The value is hex encoded mask number.

0

Determine automatically.

1

Force sign.

2

Force sign with recovery.

4

Force decrypt.

8

Force decrypt with unwrap.

emulate-openpgp

Emulate OpenPGP card. Unfortunately, gnupg cannot handle the OpenPGP card with certificates. So you need to turn this on in order to learn card keys.

In OpenPGP card emulation we cannot guess which key should match a type, so you have to specify the SHA1 of the key explicitly.

In order to determine which key is which, use the following command:

gpg-agent --server gpg-connect-agent

Enter "SCD LEARN" and look for "KEY-FRIEDNLY" responses, the first field is the hash, the second is the subject name.

You still have to store a certificate (may be self-signed) that corresponds to the keypair.

openpgp-sign

Hex string (Upper letter, no space) SHA1 of signing public key.

openpgp-encr

Hex string (Upper letter, no space) SHA1 of encryption public key.

openpgp-auth

Hex string (Upper letter, no space) SHA1 of authentication public key.

GNUPG INTEGRATION

Typical steps to set up a card for gpgsm usage:

1. Import the CA certificate of your issuer:

   gpgsm --import < ca-certificate

   You should also manually import all self-signed certificates.
2. Instruct GnuPG to discover all useful certificates on the card:

   gpgsm --learn-card

Signing, verification, etc. work as usual with gpgsm.

Typical steps to set up a card for gpg usage:

1. Aquire key ids:

   gpg-agent --server gpg-connect-agent

   Enter "SCD LEARN" and look for "KEY-FRIEDNLY" responses, the first field is the hash, the second is the subject name.
2. Configure gnupg-pkcs11-scd for opengpg emulation, specify the public key hashes to be used for signature, encryption and authentication.
3. Instruct GnuPG to discover all useful information of card:

   gpg --card-status

   You should see valid card status.
4. Now, you should virtual generate keys, the keys are not actually generated, but returned to gpg to be registered.

   gpg --card-edit

   admin

   generate (DO NOT BACKUP KEYS)

5. Disable the opengpg emulation.

Now you can use the same card with your gpg and gpgsm keys. We don't know if this is a bug or feature in gnupg, but we glad that it works.

Signing, verification, etc. work as usual with gpg.

SECURITY CONSIDERATIONS

All communication between components is currently unprotected and in plain text (that's how the Assuan protocol operates). It is trivial to trace (using e.g. the strace(1) program) individual components (e.g. pinentry) and steal sensitive data (such as the smart-card PIN) or even change it (e.g. the hash to be signed).

When using the software in production scenario, be sure to turn off debugging/verbose options in configuration of all components. Otherwise, some sensitive data might be displayed on the screen (most notably, the PIN).

AUTHORS AND COPYRIGHT

Copyright (c) 2006-2007 Zeljko Vrba <[email protected]>

Copyright (c) 2006-2011 Alon Bar-Lev <[email protected]>

All rights reserved.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.