libcacard: improve documentation

Using the file-backed smartcard backend is black magic, but it can
be useful if your only smartcard bricks itself if it is accessed
the wrong way too many times.

Complete the documentation to include the art of creating certificates
and using them with QEMU, based on Ray Strode's useful tutorial at
https://blogs.gnome.org/halfline/2013/09/08/another-smartcard-post/
but with ccid-card-emulated or vscclient instead of SPICE.

Cc: Ray Strode <rstrode@redhat.com>
Reviewed-by: Alon Levy <alevy@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

docs/ccid.txt

@@ -47,6 +47,7 @@ In ubuntu/debian:
 Configuring and building:
     ./configure --enable-smartcard && make
 
+
 3. Using ccid-card-emulated with hardware
 
 Assuming you have a working smartcard on the host with the current
@@ -54,19 +55,55 @@ user, using NSS, qemu acts as another NSS client using ccid-card-emulated:
 
     qemu -usb -device usb-ccid -device ccid-card-emulated
 
-4. Using ccid-card-emulated with certificates
 
-You must create the certificates. This is a one time process. We use NSS
+4. Using ccid-card-emulated with certificates stored in files
-certificates:
 
-    certutil -d /etc/pki/nssdb -x -t "CT,CT,CT" -S -s "CN=cert1" -n cert1
+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.
 
-Assuming the current user can access the certificates (use certutil -L to
+You can use the emulated card type with the certificates backend:
-verify), 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/libcoolkeypk11.so
+    modutil -dbdir /etc/pki/nssdb -list
 
-    qemu -usb -device usb-ccid -device ccid-card-emulated,backend=certificates,cert1=cert1,cert2=cert2,cert3=cert3
 
 5. Using ccid-card-passthru with client side hardware
 
@@ -74,15 +111,23 @@ on the host specify the ccid-card-passthru device with a suitable chardev:
 
     qemu -chardev socket,server,host=0.0.0.0,port=2001,id=ccid,nowait -usb -device usb-ccid -device ccid-card-passthru,chardev=ccid
 
-on the client run vscclient, built when you built the libcacard library:
+on the client run vscclient, built when you built QEMU:
-    libcacard/vscclient <qemu-host> 2001
+
+    vscclient <qemu-host> 2001
+
 
 6. Using ccid-card-passthru with client side certificates
 
-Run qemu as per #5, and run vscclient as follows:
+This case is not particularly useful, but you can use it to debug
-(Note: vscclient command line interface is in a state of change)
+your setup if #4 works but #5 does not.
+
+Follow instructions as per #4, except run QEMU and vscclient as follows:
+Run qemu as per #5, and run vscclient from the "fake-smartcard"
+directory as follows:
+
+    qemu -chardev socket,server,host=0.0.0.0,port=2001,id=ccid,nowait -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
 
-    libcacard/vscclient -e "db=\"/etc/pki/nssdb\" use_hw=no soft=(,Test,CAC,,cert1,cert2,cert3)" <qemu-host> 2001
 
 7. Passthrough protocol scenario
 
@@ -126,10 +171,11 @@ kill/quit         |                          |                |               |
 
 8. libcacard
 
-ccid-card-passthru and vscclient use libcacard as the card emulator.
+Both ccid-card-emulated and vscclient use libcacard as the card emulator.
-libcacard implements a completely virtual CAC (DoD standard for smart cards)
+libcacard implements a completely virtual CAC (DoD standard for smart
-compliant card and uses NSS to actually retrive certificates and do any
+cards) compliant card and uses NSS to retrieve certificates and do
-encryption using the backend (real reader + card or file backed certificates).
+any encryption.  The backend can then be a real reader and card, or
+certificates stored in files.
 
-For documentation of cac_card see README in libcacard subdirectory.
+For documentation of the library see docs/libcacard.txt.