PackageMaintainers/PKCS11

Testing PKCS#11 support

The proposed packaging guidelines say that any program which can accept SSL certificates from a file should also allow them to come from a PKCS#11 token. This page exists to help packagers understand those guidelines and test their packages.

But I don't have any PKCS#11 hardware

You don't need hardware. There are plenty of PKCS#11 providers which are purely software. These include

• NSS Certificate Database (Firefox, Evolution, Chrome)
• GNOME keyring
• SoftHSM

The simplest one to test with is probably GNOME keyring. Obviously not everyone will be running GNOME for their day-to-day usage but it shouldn't be too hard to use GNOME keyring just for a simple test.

Import certificate

The seahorse GUI tool allows you to browse the contents of PKCS#11 tokens and import certificates and keys. If you simply run seahorse under GNOME you should see a 'Gnome2 Key Storage' token listed under the 'Certificates' heading. You can select the 'File'... 'Import' menu item to import a certificate from a file into the GNOME keyring (or indeed any other provider you choose to use).

Determine the PKCS#11 URI of your certificate

Unfortunately, seahorse doesn't show the PKCS#11 URI of the objects when you're browsing (bug #749071). So you'll want to use p11tool to list them and find the URI:

$ p11tool --list-certs --login pkcs11:token=Gnome2%20Key%20Storage
Object 0:
	URL: pkcs11:model=1.0;manufacturer=Gnome%20Keyring;serial=1%3aUSER%3aDEFAULT;token=Gnome2%20Key%20Storage;id=%59%ae%17%70%af%e8%af%9f%5b%94%fb%c6%89%f6%f1%4c%11%5c%36%0e;object=Woodhouse%2c%20David;type=cert
	Type: X.509 Certificate
	Label: Woodhouse, David
	ID: 59:ae:17:70:af:e8:af:9f:5b:94:fb:c6:89:f6:f1:4c:11:5c:36:0e

The interesting part there is the URL. In fact a lot of the information there is redundant; all you probably need is the token and id parts:

pkcs11:token=Gnome2%20Key%20Storage;id=%59%ae%17%70%af%e8%af%9f%5b%94%fb%c6%89%f6%f1%4c%11%5c%36%0e

See if you can use it

Now let's pretend I'm packaging the OpenConnect VPN client. It has fairly reasonable documentation (if I do say so myself) on how to use it with PKCS#11. It looks like it should comply with the Fedora guidelines and just accept a PKCS#11 URI on the command line with the -c option, in place of a filename.

Let's test...

$ openconnect -c 'pkcs11:token=Gnome2%20Key%20Storage;id=%59%ae%17%70%af%e8%af%9f%5b%94%fb%c6%89%f6%f1%4c%11%5c%36%0e'  https://auth.startssl.comPOST https://auth.startssl.com/
Attempting to connect to server 192.116.242.27:443
Using client certificate 'Woodhouse\, David'
SSL negotiation with auth.startssl.com
SSL connection failure: A TLS fatal alert has been received.
Failed to open HTTPS connection to auth.startssl.com
Failed to obtain WebVPN cookie

Yes, it failed to actually make a VPN connection, but that's expected — that server isn't running an AnyConnect VPN service. The important part is that the VPN client was attempting to use the correct client certificate.

Now let's pretend that I'm packaging curl. Curl uses a colon to separate the certificate and the password so we'll need to escape the colon in the URI...

$ curl -E 'pkcs11\:token=Gnome2%20Key%20Storage;id=%59%ae%17%70%af%e8%af%9f%5b%94%fb%c6%89%f6%f1%4c%11%5c%36%0e' -I -v https://auth.startssl.com* Rebuilt URL to: https://auth.startssl.com/
*   Trying 192.116.242.27...
* Connected to auth.startssl.com (192.116.242.27) port 443 (#0)
* Initializing NSS with certpath: sql:/etc/pki/nssdb
*   CAfile: /etc/pki/tls/certs/ca-bundle.crt
  CApath: none
* NSS: client certificate not found: pkcs11:token=Gnome2%20Key%20Storage;id=%e6%34%78%b5%fd%86%77%ba%b9%86%95%c3%19%02%74%d1%f5%33%9a%97
* NSS error -12227 (SSL_ERROR_HANDSHAKE_FAILURE_ALERT)
* SSL peer was unable to negotiate an acceptable set of security parameters.
* Closing connection 0
curl: (35) NSS: client certificate not found: pkcs11:token=Gnome2%20Key%20Storage;id=%e6%34%78%b5%fd%86%77%ba%b9%86%95%c3%19%02%74%d1%f5%33%9a%97

Oops, that 'client certificate not found' doesn't look good. If curl was built with GnuTLS instead of NSS that probably would have worked fine. As it is, let's file bug 1219544 against curl...

Crypto library support

GnuTLS

If your package builds against GnuTLS, then in most cases it should Just Work. The common GnuTLS APIs for handling certificates and keys will support do the right thing.

OpenSSL

OpenSSL has no native support for PKCS#11, but there are a number of external tools which can make it work with PKCS#11. There are pkcs11-helper and libp11 helper libraries which can be used to add PKCs#11 support to an application which uses OpenSSL, but the simplest option is probably to use engine_pkcs11.

NSS

Although NSS is entirely based around PKCS#11, NSS is ironically the most problematic of the major crypto libraries. It does not integrate properly with the platform and load the correct PKCS#11 providers (Mozilla bug 1161219), and it does not facilitate the use of RFC7512 PKCS#11 URIs (Mozilla bug 1162897).

These deficiencies in NSS can be worked around by manually loading the p11-kit-proxy.so module, and by using libp11-kit to parse URIs and manually iterate over the available tokens and search for objects.

Or it might be easier just to build against GnuTLS if your package has that option!