scute/README

Scute
=====

This is a PKCS #11 implementation for the GnuPG Agent using the GnuPG
Smart Card Daemon.  Currently, only the OpenPGP card is supported.

TOC
===

* Purpose
* Prerequisites
* Installation
* Client Authentication
* Features and Limitations
* Development
* Mozilla Bugs
* Copyright and License


Purpose
=======

Scute enables you to use your OpenPGP smart card for client
authentication with SSL in Mozilla.  See below for more details on how
to get this working.

In the future, Scute will enable you to use your OpenPGP smart card
for email decryption and signing with Thunderbird, using the X.509
protocol.


Prerequisites
=============

For the compilation:
* libgpg-error 0.7
* libassuan 0.6.10

At runtime:
* Mozilla (or any other supported application using PKCS #11).
* GnuPG 2.0, in particular: gpg-agent, scdaemon
* Pinentry


Installation
============

To install the PKCS #11 Module, follow the generic installation
instructions in the file INSTALL that accompanies this software.  You
also need to install the Mozilla Personal Security Manager (PSM),
which may come with your GNU/Linux distribution in a package named
mozilla-psm or similar.

After installation, you can configure Mozilla to use Scute by
visiting the preferences dialog in the "advanced" category, under
"Security Devices".  There you can "load" the module from its
installed path, e.g. "/usr/lib/libscute.so".

Note that for the module load to complete successfully, the GPG Agent
must be running and available.  This means that Mozilla needs to have
the GPG_AGENT_INFO variable set correctly in its environment.


Client Authentication
=====================

For client authentication to work, several steps need to be completed.
Depending on your situation, some of these steps may be performed by
third parties, like service providers.  However, they can also all be
performed locally, if use of client authentication with a local
service is desired.

For this introduction, we assume an Apache web server with SSL at the
server side, and a connecting client running Firefox.  As a
certification authority (CA) we use OpenSSL.  Scute provides a PKCS #11
compatible security device to Firefox for client authentication.  This
security device gives Firefox access to the client's OpenPGP smart
card.

The Client Perspective
----------------------

To get things started, we have to prepare an initialised OpenPGP smart
card by uploading an off-card key or generating a key on the card.
The card you got may already have been initialised.  Otherwise, you
can find more information on this step in the smartcard HowTo, which
also documents other basic card operations:
http://www.gnupg.org/(en)/howtos/card-howto/en/smartcard-howto.html

Once the card is initialised, we have to generate a certificate
signing request (CSR) to get the authentication key of the card
(OPENPGP.3, the third key on the card) certified by the CA.  This can
be done with the script "gpgsm-gencert.sh".  For the CSR, a
distinguished name (DN) is required.  Your CA will have more
information about what this DN should contain.  Below we use an
example for a test-employee "Floppy Head" of the test-CA that ships
with OpenSSL ("Snake Oil, Ltd.").

Generating the CSR is then just a matter of answering a few questions:

$ gpgsm-gencert.sh > /tmp/floppy.csr
Key type
 [1] RSA
 [2] existing key
 [3] OPENPGP.1
 [4] OPENPGP.3
Your selection: 4
You selected: OPENPGP.3
Key usage
 [1] sign, encrypt
 [2] sign
 [3] encrypt
Your selection: 2
You selected: sign
Name (DN)
> CN=Floppy Head,OU=Webserver Team,O="Snake Oil, Ltd",L=Snake Town,ST=Snake Desert,C=XY
E-Mail addresses (end with an empty line)
> floppy@head.com
E-Mail addresses (end with an empty line)
>
DNS Names (optional; end with an empty line)
>
URIs (optional; end with an empty line)
>
Parameters for certificate request to create:
     1  Key-Type: card:OPENPGP.3
     2  Key-Length: 
     3  Key-Usage: sign
     4  Name-DN: CN=Floppy Head,OU=Webserver Team,O="Snake Oil, Ltd",L=Snake Town,ST=Snake Desert,C=XY
     5  Name-Email: floppy@head.com

Really create such a CSR?
 [1] yes
 [2] no
Your selection: 1
You selected: yes
gpgsm: certificate request created

It is required to enter the signing PIN of the card to complete this
step.  The certificate can then be found in the file "/tmp/floppy.csr".
This file should then be sent to the CA for certification (see below).

The CA will return to the client a certificate "/tmp/floppy.crt", who
can then the issuer certificate of the CA (in this example, we access
directly the local server certificate) and its own certificate with
gpgsm:

$ gpgsm --import /etc/apache/ssl.crt/snakeoil-ca-rsa.crt
gpgsm: total number processed: 1
gpgsm:               imported: 1
marcus@ulysses:~/g10/projects/pkcs11-for-scdaemon/ca/usercert/card3$ gpgsm --import /tmp/floppy.crt
gpgsm: total number processed: 1
gpgsm:              unchanged: 1

$ gpgsm --list-keys Floppy
Serial number: 08
       Issuer: /CN=Snake Oil CA/OU=Certificate Authority/O=Snake Oil, Ltd/L=Snake Town/ST=Snake Desert/C=XY/EMail=ca@snakeoil.dom
      Subject: /CN=Floppy Head/OU=Webserver Team/O=Snake Oil, Ltd/ST=Snake Desert/C=XY
     validity: 2006-10-11 13:17:08 through 2007-10-11 13:17:08
     key type: 1024 bit RSA
  fingerprint: C9:08:0E:86:92:6C:7B:4B:8C:23:1C:9D:D7:15:BF:D4:A4:00:54:11

Now the client can configure his web browser.  If desired, the client
can install the web servers certificate (alternatively, Firefox will
ask when establishing the initial connection).

To actually perform the client authentication, the client needs to set
up the web browser for use with Scute.  The Scute PKCS #11 module,
installed under /usr/lib/libscute.so by default, needs to be loaded as
a security device in Firefox under
Preferences->Advanced->Security->Certificates->Security Devices->Load
When the security device is loaded, card insertion should cause the
security device list be updated with the inserted token (the card), and the certificate that has been imported into gpgsm should be visible under 
Preferences->Advanced->Security->Certificates->View Certificates
automatically.

Firefox will by default select the certificate to be used for client
authentication automatically from the list of available certificates.
This setting can be changed if desired in
Preferences->Advanced->Security->Certificates ("Select one
automatically" vs. "Ask me every time")

When the client then attempts to open the URL "https://localhost/" in
this example, the web server will require SSL authentication, which
causes Firefox to look (or ask) for a client certificate.  If the
certificate on the card is suitable (or selected), the user will have
to enter the PIN number on the card to sign into the web site.


The CA Perspective
------------------

The CA will have to process the CSR submitted by the client.  After
verifying the identity of the submitter by some external means, the CA
may use for example this OpenSSL command to create a certificate (we
use the example CA shipping with the Apache SSL module on Ubuntu):

# cd /etc/apache/ssl.crt/
# openssl ca -in /tmp/floppy.csr -cert /etc/apache/ssl.crt/snakeoil-ca-rsa.crt -keyfile /etc/apache/ssl.key/snakeoil-ca-rsa.key -out /tmp/floppy.crt
Using configuration from /usr/lib/ssl/openssl.cnf
Check that the request matches the signature
Signature ok
Certificate Details:
        Serial Number: 8 (0x8)
        Validity
            Not Before: Oct 11 13:17:08 2006 GMT
            Not After : Oct 11 13:17:08 2007 GMT
        Subject:
            countryName               = XY
            stateOrProvinceName       = Snake Desert
            organizationName          = Snake Oil, Ltd
            organizationalUnitName    = Webserver Team
            commonName                = Floppy Head
        X509v3 extensions:
            X509v3 Basic Constraints:
                CA:FALSE
            Netscape Comment:
                OpenSSL Generated Certificate
            X509v3 Subject Key Identifier:
                72:AF:B8:13:3D:3D:9D:02:93:E4:D4:56:0C:06:90:4C:26:85:85:5D
            X509v3 Authority Key Identifier:
                DirName:/C=XY/ST=Snake Desert/L=Snake Town/O=Snake Oil, Ltd/OU=Certificate Authority/CN=Snake Oil CA/emailAddress=ca@snakeoil.dom
                serial:00

Certificate is to be certified until Oct 11 13:17:08 2007 GMT (365 days)
Sign the certificate? [y/n]:y


1 out of 1 certificate requests certified, commit? [y/n]y
Write out database with 1 new entries
Data Base Updated

The resulting file, "/tmp/floppy.crt" is sent back from the CA to the
client along with the issuer certificate.

For more information how to set up and work with a CA using OpenSSL,
please see the OpenSSL documentation.

The Server Perspective
----------------------

The service provider will set up an Apache web server with SSL
support, and configure it to accept certificates from the CA.  This
step is quite involved.  Garex has a concise HowTo online at
http://www.garex.net/apache/ about how to do this.  Beside the
creation of a certificate that has its own fully qualified domain name
(FQDN) as common name (CN part of the DN), this involves installing
the Apache SSL module and configuration for it, for example in
httpd.conf:

SSLEngine on
SSLCertificateFile /etc/apache/ssl.crt/server.crt
SSLCertificateKeyFile /etc/apache/ssl.key/server.key

SSLVerifyClient require
SSLVerifyDepth 1
SSLCACertificateFile /etc/apache/ssl.crt/snakeoil-ca-rsa.crt

The file server.key is not protected by a passphrase (if it is, this
passphrase needs to be provided when starting up Apache), and
server.crt has "CN=localhost" as part of its DN for this example.


Features and Limitations
========================

Scute implements version 2.20 of the PKCS #11 specification.

The OpenPGP smart card application is supported in read-only mode.

The following functions are not supported:

* C_Initialize: No support for native thread package.  Locking
  callbacks must be provided if multi-threaded operation is desired.

* C_WaitForSlotEvent: Not implemented.  The interface as specified by
  PKCS #11 is broken anyway, as the function can not safely be
  canceled.  Thus, we require polling.

* C_GetOperationState, C_SetOperationState: Not supported.

* C_InitToken, C_InitPIN, C_SetPIN: Not supported.  No write
  operations are allowed.  To configure the token, please use the
  tools accompanying the GnuPG software suite.

* C_Login, C_Logout: Not supported.  No login into the token by the
  software is required.  Passphrase queries are implemented by the use
  of GPG Agent and Pinentry.

* C_EncryptInit, C_Encrypt, C_EncryptUpdate, C_EncryptFinal,
  C_DigestInit, C_Digest, C_DigestUpdate, C_DigestKey, C_DigestFinal,
  C_VerifyInit, C_Verify, C_VerifyUpdate, C_VerifyFinal,
  C_VerifyRecoverInit, C_VerifyRec: Not supported.  Only secret key
  operations are supported.

* C_SignInit, C_Sign: Currently, only signing 36 bytes
  (MD5+SHA1) hashes is supported (used for client authentication).

* C_DecryptInit, C_Decrypt: Not yet supported, but will be in the
  future.

* C_SignUpdate, C_SignFinal, C_DecryptUpdate, C_DecryptFinal: No
  progressive crypto-operations are supported.

* C_SignRecoverInit, C_SignRecover: Not supported.

* C_DigestEncryptUpdate, C_DecryptDigestUpdate, C_SignEncryptUpdate,
  C_DecryptVerifyUpdate: Dual-purpose cryptographic functions are not
  supported.

* C_GenerateKey, C_GenerateKeyPair, C_WrapKey, C_UnwrapKey,
  C_DeriveKey: Key management functions are not supported.  Please use
  the tools accompanying the GnuPG software suite to generate and
  import keys for use with the token.

* C_SeedRandom, C_GenerateRandom: Not supported at this point.
  C_GenerateRandom may be supported in the future, though.

* C_CreateObject, C_CopyObject, C_DestroyObject, C_SetAttributeValue:
  Only read-only operations are supported on objects.

* C_GetObjectSize: Not supported.

* CKO_CERTIFICATE:
  The label specifies the key on the card used (e.g. OPENPGP.3).  The
  ID is the fingerprint.

* CKO_PRIVATE_KEY:
  The CKA_LOCAL attribute can not be supported by the OpenPGP card.
  It is always set to false (as the key on the card may be copied to
  the card from an external source).


Development
===========

Scute is single-threaded.  There is a global lock that is taken in all
entry points of Scute, except for C_Initialize, C_Finalize,
C_GetFunctionList, and stubs.


Here are a couple of hints on how to develop PKCS #11 modules for
Mozilla:

libopensc2 ships with a pkcs11-spy library that can be loaded as a
wrapper around the PKCS #11 library you want to use to log all
functions invoked by Mozilla.  Here is how to use it:

 Set the PKCS11SPY_OUTPUT environment variable to a filename.
 pkcs11-spy appends its log messages at the end of this file.  Set the
 PKCS11SPY environment variable to the filename of the PKCS #11 module
 you actually want to use.  Start Mozilla within this environment.

There is a different, probably more powerful way to debug Mozilla PKCS
#11 libraries.  However, to be able to use it, you need to configure
and compile the Mozilla NSS sources with --enable-debug.  Instructions
can be found at:
http://www.mozilla.org/projects/security/pki/nss/tech-notes/tn2.html

Here are a couple of links to more information about implementing a
PKCS #11 module for Mozilla:

Implementing PKCS #11 for the Netscape Security Library
(Caution: The content may be out of date)
http://docs.sun.com/source/816-6150-10/index.htm
http://docs.sun.com/source/816-6150-10/pkcs.htm

Common PKCS #11 Implementation Problems
http://www.mozilla.org/projects/security/pki/pkcs11/netscape/problems.html

PKCS #11 Conformance Testing
http://www.mozilla.org/projects/security/pki/pkcs11/

And of course the Mozilla NSS web page:
http://www.mozilla.org/projects/security/pki/nss/


Mozilla Bugs
============

Mozilla has a bug that causes the security devices list to become
corrupt when a security device is unloaded: The wrong entry is removed
from the list.  This is corrected by waiting for a refresh or closing
and reopening the security device manager.


Copyright and License
=====================

The majority of files are copyrighted by g10 Code GmbH and licensed
under the GPL with a special exception for Mozilla.

Some files in the include/ directory are copyrighted by RSA Security
Inc. and licensed under the conditions found in the file
include/disclaimer.txt.


g10 Code GmbH
marcus@g10code.com


 Copyright 2006 g10 Code GmbH

 This file is free software; as a special exception the author gives
 unlimited permission to copy and/or distribute it, with or without
 modifications, as long as this notice is preserved.

 This file is distributed in the hope that it will be useful, but
 WITHOUT ANY WARRANTY, to the extent permitted by law; without even the
 implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.