Chip Card Interface Device (CCID)

USB CCID device

The USB CCID device is a USB device implementing the CCID specification, which lets one connect smart card readers that implement the same spec. For more information see the specification:

Universal Serial Bus
Device Class: Smart Card
Specification for
Integrated Circuit(s) Cards Interface Devices
Revision 1.1
April 22rd, 2005

Smartcards are used for authentication, single sign on, decryption in public/private schemes and digital signatures. A smartcard reader on the client cannot be used on a guest with simple usb passthrough since it will then not be available on the client, possibly locking the computer when it is “removed”. On the other hand this device can let you use the smartcard on both the client and the guest machine. It is also possible to have a completely virtual smart card reader and smart card (i.e. not backed by a physical device) using this device.


The cryptographic functions and access to the physical card is done via the libcacard library, whose development package must be installed prior to building QEMU:

In redhat/fedora:

yum install libcacard-devel

In ubuntu:

apt-get install libcacard-dev

Configuring and building:

./configure --enable-smartcard && make

Using ccid-card-emulated with hardware

Assuming you have a working smartcard on the host with the current user, using libcacard, QEMU acts as another client using ccid-card-emulated:

qemu -usb -device usb-ccid -device ccid-card-emulated

Using ccid-card-emulated with certificates stored in files

You must create the CA and card certificates. This is a one time process. We use NSS certificates:

mkdir fake-smartcard
cd fake-smartcard
certutil -N -d sql:$PWD
certutil -S -d sql:$PWD -s "CN=Fake Smart Card CA" -x -t TC,TC,TC -n fake-smartcard-ca
certutil -S -d sql:$PWD -t ,, -s "CN=John Doe" -n id-cert -c fake-smartcard-ca
certutil -S -d sql:$PWD -t ,, -s "CN=John Doe (signing)" --nsCertType smime -n signing-cert -c fake-smartcard-ca
certutil -S -d sql:$PWD -t ,, -s "CN=John Doe (encryption)" --nsCertType sslClient -n encryption-cert -c fake-smartcard-ca

Note: you must have exactly three certificates.

You can use the emulated card type with the certificates backend:

qemu -usb -device usb-ccid -device ccid-card-emulated,backend=certificates,db=sql:$PWD,cert1=id-cert,cert2=signing-cert,cert3=encryption-cert

To use the certificates in the guest, export the CA certificate:

certutil -L -r -d sql:$PWD -o fake-smartcard-ca.cer -n fake-smartcard-ca

and import it in the guest:

certutil -A -d /etc/pki/nssdb -i fake-smartcard-ca.cer -t TC,TC,TC -n fake-smartcard-ca

In a Linux guest you can then use the CoolKey PKCS #11 module to access the card:

certutil -d /etc/pki/nssdb -L -h all

It will prompt you for the PIN (which is the password you assigned to the certificate database early on), and then show you all three certificates together with the manually imported CA cert:

Certificate Nickname                        Trust Attributes
fake-smartcard-ca                           CT,C,C
John Doe:CAC ID Certificate                 u,u,u
John Doe:CAC Email Signature Certificate    u,u,u
John Doe:CAC Email Encryption Certificate   u,u,u

If this does not happen, CoolKey is not installed or not registered with NSS. Registration can be done from Firefox or the command line:

modutil -dbdir /etc/pki/nssdb -add "CAC Module" -libfile /usr/lib64/pkcs11/
modutil -dbdir /etc/pki/nssdb -list

Using ccid-card-passthru with client side hardware

On the host specify the ccid-card-passthru device with a suitable chardev:

qemu -chardev socket,server=on,host=,port=2001,id=ccid,wait=off \
     -usb -device usb-ccid -device ccid-card-passthru,chardev=ccid

On the client run vscclient, built when you built QEMU:

vscclient <qemu-host> 2001

Using ccid-card-passthru with client side certificates

This case is not particularly useful, but you can use it to debug your setup.

Follow instructions above, except run QEMU and vscclient as follows.

Run qemu as per above, and run vscclient from the “fake-smartcard” directory as follows:

qemu -chardev socket,server=on,host=,port=2001,id=ccid,wait=off \
     -usb -device usb-ccid -device ccid-card-passthru,chardev=ccid
vscclient -e "db=\"sql:$PWD\" use_hw=no soft=(,Test,CAC,,id-cert,signing-cert,encryption-cert)" <qemu-host> 2001

Passthrough protocol scenario

This is a typical interchange of messages when using the passthru card device. usb-ccid is a usb device. It defaults to an unattached usb device on startup. usb-ccid expects a chardev and expects the protocol defined in cac_card/vscard_common.h to be passed over that. The usb-ccid device can be in one of three modes:

  • detached

  • attached with no card

  • attached with card

A typical interchange is (the arrow shows who started each exchange, it can be client originated or guest originated):

client event        |    vscclient           |    passthru    |    usb-ccid  |  guest event
                    |    VSC_Init            |                |              |
                    |    VSC_ReaderAdd       |                |    attach    |
                    |                        |                |              |  sees new usb device.
  card inserted ->  |                        |                |              |
                    |    VSC_ATR             |   insert       |    insert    |  see new card
                    |                        |                |              |
                    |    VSC_APDU            |   VSC_APDU     |              | <- guest sends APDU
client <-> physical |                        |                |              |
 card APDU exchange |                        |                |              |
 client response -> |    VSC_APDU            |   VSC_APDU     |              |  receive APDU response
                                    [APDU<->APDU repeats several times]
   card removed  -> |                        |                |              |
                    |    VSC_CardRemove      |   remove       |   remove     |   card removed
                                    [(card insert, apdu's, card remove) repeat]
  kill/quit         |                        |                |              |
    vscclient       |                        |                |              |
                    |    VSC_ReaderRemove    |                |   detach     |
                    |                        |                |              |   usb device removed.


Both ccid-card-emulated and vscclient use libcacard as the card emulator. libcacard implements a completely virtual CAC (DoD standard for smart cards) compliant card and uses NSS to retrieve certificates and do any encryption. The backend can then be a real reader and card, or certificates stored in files.