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PKCS#11 (Cryptoki) support

PKCS#11 (Public Key Cryptography Standard #11) defines a platform-independent API for the control of hardware security modules (HSMs) and other cryptographic support devices.

BIND 9 is known to work with three HSMs: The AEP Keyper, which has been tested with Debian Linux, Solaris x86 and Windows Server 2003; the Thales nShield, tested with Debian Linux; and the Sun SCA 6000 cryptographic acceleration board, tested with Solaris x86. In addition, BIND can be used with all current versions of SoftHSM, a software-based HSM simulator library produced by the OpenDNSSEC project.

PKCS#11 makes use of a "provider library": a dynamically loadable library which provides a low-level PKCS#11 interface to drive the HSM hardware. The PKCS#11 provider library comes from the HSM vendor, and it is specific to the HSM to be controlled.

There are two available mechanisms for PKCS#11 support in BIND 9: OpenSSL-based PKCS#11 and native PKCS#11. When using the first mechanism, BIND uses a modified version of OpenSSL, which loads the provider library and operates the HSM indirectly; any cryptographic operations not supported by the HSM can be carried out by OpenSSL instead. The second mechanism enables BIND to bypass OpenSSL completely; BIND loads the provider library itself, and uses the PKCS#11 API to drive the HSM directly.

Prerequisites

See the documentation provided by your HSM vendor for information about installing, initializing, testing and troubleshooting the HSM.

Native PKCS#11

Native PKCS#11 mode will only work with an HSM capable of carrying out every cryptographic operation BIND 9 may need. The HSM's provider library must have a complete implementation of the PKCS#11 API, so that all these functions are accessible. As of this writing, only the Thales nShield HSM and SoftHSMv2 can be used in this fashion. For other HSMs, including the AEP Keyper, Sun SCA 6000 and older versions of SoftHSM, use OpenSSL-based PKCS#11. (Note: Eventually, when more HSMs become capable of supporting native PKCS#11, it is expected that OpenSSL-based PKCS#11 will be deprecated.)

To build BIND with native PKCS#11, configure as follows:

$ cd bind9
$ ./configure --enable-native-pkcs11 \
    --with-pkcs11=provider-library-path

This will cause all BIND tools, including named and the dnssec-* and pkcs11-* tools, to use the PKCS#11 provider library specified in provider-library-path for cryptography. (The provider library path can be overridden using the -E in named and the dnssec-* tools, or the -m in the pkcs11-* tools.)

Building SoftHSMv2

SoftHSMv2, the latest development version of SoftHSM, is available from https://github.com/opendnssec/SoftHSMv2. It is a software library developed by the OpenDNSSEC project (http://www.opendnssec.org) which provides a PKCS#11 interface to a virtual HSM, implemented in the form of a SQLite3 database on the local filesystem. It provides less security than a true HSM, but it allows you to experiment with native PKCS#11 when an HSM is not available. SoftHSMv2 can be configured to use either OpenSSL or the Botan library to perform cryptographic functions, but when using it for native PKCS#11 in BIND, OpenSSL is required.

By default, the SoftHSMv2 configuration file is prefix/etc/softhsm2.conf (where prefix is configured at compile time). This location can be overridden by the SOFTHSM2_CONF environment variable. The SoftHSMv2 cryptographic store must be installed and initialized before using it with BIND.

$  cd SoftHSMv2
$  configure --with-crypto-backend=openssl --prefix=/opt/pkcs11/usr
$  make
$  make install
$  /opt/pkcs11/usr/bin/softhsm-util --init-token 0 --slot 0 --label softhsmv2

OpenSSL-based PKCS#11

OpenSSL-based PKCS#11 mode uses a modified version of the OpenSSL library; stock OpenSSL does not fully support PKCS#11. ISC provides a patch to OpenSSL to correct this. This patch is based on work originally done by the OpenSolaris project; it has been modified by ISC to provide new features such as PIN management and key-by-reference.

There are two "flavors" of PKCS#11 support provided by the patched OpenSSL, one of which must be chosen at configuration time. The correct choice depends on the HSM hardware:

The modified OpenSSL code is included in the BIND 9 release, in the form of a context diff against the latest versions of OpenSSL. OpenSSL 0.9.8, 1.0.0, 1.0.1 and 1.0.2 are supported; there are separate diffs for each version. In the examples to follow, we use OpenSSL 0.9.8, but the same methods work with OpenSSL 1.0.0 through 1.0.2.

Note

The OpenSSL patches as of this writing (January 2016) support versions 0.9.8zh, 1.0.0t, 1.0.1q and 1.0.2f. ISC will provide updated patches as new versions of OpenSSL are released. The version number in the following examples is expected to change.

Before building BIND 9 with PKCS#11 support, it will be necessary to build OpenSSL with the patch in place, and configure it with the path to your HSM's PKCS#11 provider library.

Patching OpenSSL

$ wget http://www.openssl.org/source/openssl-0.9.8zc.tar.gz

Extract the tarball:

$ tar zxf openssl-0.9.8zc.tar.gz

Apply the patch from the BIND 9 release:

$ patch -p1 -d openssl-0.9.8zc \
          < bind9/bin/pkcs11/openssl-0.9.8zc-patch

Note

The patch file may not be compatible with the "patch" utility on all operating systems. You may need to install GNU patch.

When building OpenSSL, place it in a non-standard location so that it does not interfere with OpenSSL libraries elsewhere on the system. In the following examples, we choose to install into "/opt/pkcs11/usr". We will use this location when we configure BIND 9.

Later, when building BIND 9, the location of the custom-built OpenSSL library will need to be specified via configure.

Building OpenSSL for the AEP Keyper on Linux

The AEP Keyper is a highly secure key storage device, but does not provide hardware cryptographic acceleration. It can carry out cryptographic operations, but it is probably slower than your system's CPU. Therefore, we choose the 'sign-only' flavor when building OpenSSL.

The Keyper-specific PKCS#11 provider library is delivered with the Keyper software. In this example, we place it /opt/pkcs11/usr/lib:

$ cp pkcs11.GCC4.0.2.so.4.05 /opt/pkcs11/usr/lib/libpkcs11.so
$ cd openssl-0.9.8zc
$ ./Configure linux-x86_64 \
        --pk11-libname=/opt/pkcs11/usr/lib/libpkcs11.so \
        --pk11-flavor=sign-only \
        --prefix=/opt/pkcs11/usr

Building OpenSSL for the SCA 6000 on Solaris

The SCA-6000 PKCS#11 provider is installed as a system library, libpkcs11. It is a true crypto accelerator, up to 4 times faster than any CPU, so the flavor shall be 'crypto-accelerator'.

In this example, we are building on Solaris x86 on an AMD64 system.

$ cd openssl-0.9.8zc
$ ./Configure solaris64-x86_64-cc \
        --pk11-libname=/usr/lib/64/libpkcs11.so \
        --pk11-flavor=crypto-accelerator \
        --prefix=/opt/pkcs11/usr

(For a 32-bit build, use "solaris-x86-cc" and /usr/lib/libpkcs11.so.)

After configuring, run make and make test.

Building OpenSSL for SoftHSM

SoftHSM (version 1) is a software library developed by the OpenDNSSEC project (http://www.opendnssec.org) which provides a PKCS#11 interface to a virtual HSM, implemented in the form of a SQLite3 database on the local filesystem. SoftHSM uses the Botan library to perform cryptographic functions. Though less secure than a true HSM, it can allow you to experiment with PKCS#11 when an HSM is not available.

The SoftHSM cryptographic store must be installed and initialized before using it with OpenSSL, and the SOFTHSM_CONF environment variable must always point to the SoftHSM configuration file:

$  cd softhsm-1.3.7
$  configure --prefix=/opt/pkcs11/usr
$  make
$  make install
$  export SOFTHSM_CONF=/opt/pkcs11/softhsm.conf
$  echo "0:/opt/pkcs11/softhsm.db" > $SOFTHSM_CONF
$  /opt/pkcs11/usr/bin/softhsm --init-token 0 --slot 0 --label softhsm

SoftHSM can perform all cryptographic operations, but since it only uses your system CPU, there is no advantage to using it for anything but signing. Therefore, we choose the 'sign-only' flavor when building OpenSSL.

$ cd openssl-0.9.8zc
$ ./Configure linux-x86_64 \
        --pk11-libname=/opt/pkcs11/usr/lib/libsofthsm.so \
        --pk11-flavor=sign-only \
        --prefix=/opt/pkcs11/usr

After configuring, run "make" and "make test".

Once you have built OpenSSL, run "apps/openssl engine pkcs11" to confirm that PKCS#11 support was compiled in correctly. The output should be one of the following lines, depending on the flavor selected:

(pkcs11) PKCS #11 engine support (sign only)

Or:

(pkcs11) PKCS #11 engine support (crypto accelerator)

Next, run "apps/openssl engine pkcs11 -t". This will attempt to initialize the PKCS#11 engine. If it is able to do so successfully, it will report “[ available ]”.

If the output is correct, run "make install" which will install the modified OpenSSL suite to /opt/pkcs11/usr.

Configuring BIND 9 for Linux with the AEP Keyper

$ cd ../bind9
$ ./configure \
       --with-openssl=/opt/pkcs11/usr \
       --with-pkcs11=/opt/pkcs11/usr/lib/libpkcs11.so

Configuring BIND 9 for Solaris with the SCA 6000

$ cd ../bind9
$ ./configure CC="cc -xarch=amd64" \
        --with-openssl=/opt/pkcs11/usr \
        --with-pkcs11=/usr/lib/64/libpkcs11.so

(For a 32-bit build, omit CC="cc -xarch=amd64".)

If configure complains about OpenSSL not working, you may have a 32/64-bit architecture mismatch. Or, you may have incorrectly specified the path to OpenSSL (it should be the same as the --prefix argument to the OpenSSL Configure).

Configuring BIND 9 for SoftHSM

$ cd ../bind9
$ ./configure \
       --with-openssl=/opt/pkcs11/usr \
       --with-pkcs11=/opt/pkcs11/usr/lib/libsofthsm.so

After configuring, run "make", "make test" and "make install".

(Note: If "make test" fails in the "pkcs11" system test, you may have forgotten to set the SOFTHSM_CONF environment variable.)

PKCS#11 Tools

BIND 9 includes a minimal set of tools to operate the HSM, including pkcs11-keygen to generate a new key pair within the HSM, pkcs11-list to list objects currently available, pkcs11-destroy to remove objects, and pkcs11-tokens to list available tokens.

In UNIX/Linux builds, these tools are built only if BIND 9 is configured with the --with-pkcs11 option. (Note: If --with-pkcs11 is set to "yes", rather than to the path of the PKCS#11 provider, then the tools will be built but the provider will be left undefined. Use the -m option or the PKCS11_PROVIDER environment variable to specify the path to the provider.)

Using the HSM

For OpenSSL-based PKCS#11, we must first set up the runtime environment so the OpenSSL and PKCS#11 libraries can be loaded:

$ export LD_LIBRARY_PATH=/opt/pkcs11/usr/lib:${LD_LIBRARY_PATH}

This causes named and other binaries to load the OpenSSL library from /opt/pkcs11/usr/lib rather than from the default location. This step is not necessary when using native PKCS#11.

Some HSMs require other environment variables to be set. For example, when operating an AEP Keyper, it is necessary to specify the location of the "machine" file, which stores information about the Keyper for use by the provider library. If the machine file is in /opt/Keyper/PKCS11Provider/machine, use:

$ export KEYPER_LIBRARY_PATH=/opt/Keyper/PKCS11Provider

Such environment variables must be set whenever running any tool that uses the HSM, including pkcs11-keygen, pkcs11-list, pkcs11-destroy, dnssec-keyfromlabel, dnssec-signzone, dnssec-keygen, and named.

We can now create and use keys in the HSM. In this case, we will create a 2048 bit key and give it the label "sample-ksk":

$ pkcs11-keygen -b 2048 -l sample-ksk

To confirm that the key exists:

$ pkcs11-list
Enter PIN:
object[0]: handle 2147483658 class 3 label[8] 'sample-ksk' id[0]
object[1]: handle 2147483657 class 2 label[8] 'sample-ksk' id[0]

Before using this key to sign a zone, we must create a pair of BIND 9 key files. The "dnssec-keyfromlabel" utility does this. In this case, we will be using the HSM key "sample-ksk" as the key-signing key for "example.net":

$ dnssec-keyfromlabel -l sample-ksk -f KSK example.net

The resulting K*.key and K*.private files can now be used to sign the zone. Unlike normal K* files, which contain both public and private key data, these files will contain only the public key data, plus an identifier for the private key which remains stored within the HSM. Signing with the private key takes place inside the HSM.

If you wish to generate a second key in the HSM for use as a zone-signing key, follow the same procedure above, using a different keylabel, a smaller key size, and omitting "-f KSK" from the dnssec-keyfromlabel arguments:

(Note: When using OpenSSL-based PKCS#11 the label is an arbitrary string which identifies the key. With native PKCS#11, the label is a PKCS#11 URI string which may include other details about the key and the HSM, including its PIN. See man_dnssec-keyfromlabel for details.)

$ pkcs11-keygen -b 1024 -l sample-zsk
$ dnssec-keyfromlabel -l sample-zsk example.net

Alternatively, you may prefer to generate a conventional on-disk key, using dnssec-keygen:

$ dnssec-keygen example.net

This provides less security than an HSM key, but since HSMs can be slow or cumbersome to use for security reasons, it may be more efficient to reserve HSM keys for use in the less frequent key-signing operation. The zone-signing key can be rolled more frequently, if you wish, to compensate for a reduction in key security. (Note: When using native PKCS#11, there is no speed advantage to using on-disk keys, as cryptographic operations will be done by the HSM regardless.)

Now you can sign the zone. (Note: If not using the -S option to dnssec-signzone, it will be necessary to add the contents of both K*.key files to the zone master file before signing it.)

$ dnssec-signzone -S example.net
Enter PIN:
Verifying the zone using the following algorithms:
NSEC3RSASHA1.
Zone signing complete:
Algorithm: NSEC3RSASHA1: ZSKs: 1, KSKs: 1 active, 0 revoked, 0 stand-by
example.net.signed

Specifying the engine on the command line

When using OpenSSL-based PKCS#11, the "engine" to be used by OpenSSL can be specified in named and all of the BIND dnssec-* tools by using the "-E <engine>" command line option. If BIND 9 is built with the --with-pkcs11 option, this option defaults to "pkcs11". Specifying the engine will generally not be necessary unless for some reason you wish to use a different OpenSSL engine.

If you wish to disable use of the "pkcs11" engine MDASH for troubleshooting purposes, or because the HSM is unavailable MDASH set the engine to the empty string. For example:

$ dnssec-signzone -E '' -S example.net

This causes dnssec-signzone to run as if it were compiled without the --with-pkcs11 option.

When built with native PKCS#11 mode, the "engine" option has a different meaning: it specifies the path to the PKCS#11 provider library. This may be useful when testing a new provider library.

Running named with automatic zone re-signing

If you want named to dynamically re-sign zones using HSM keys, and/or to to sign new records inserted via nsupdate, then named must have access to the HSM PIN. In OpenSSL-based PKCS#11, this is accomplished by placing the PIN into the openssl.cnf file (in the above examples, /opt/pkcs11/usr/ssl/openssl.cnf).

The location of the openssl.cnf file can be overridden by setting the OPENSSL_CONF environment variable before running named.

Sample openssl.cnf:

openssl_conf = openssl_def
[ openssl_def ]
engines = engine_section
[ engine_section ]
pkcs11 = pkcs11_section
[ pkcs11_section ]
PIN = <PLACE PIN HERE>

This will also allow the dnssec-* tools to access the HSM without PIN entry. (The pkcs11-* tools access the HSM directly, not via OpenSSL, so a PIN will still be required to use them.)

In native PKCS#11 mode, the PIN can be provided in a file specified as an attribute of the key's label. For example, if a key had the label pkcs11:object=local-zsk;pin-source=/etc/hsmpin, then the PIN would be read from the file /etc/hsmpin.

Warning

Placing the HSM's PIN in a text file in this manner may reduce the security advantage of using an HSM. Be sure this is what you want to do before configuring the system in this way.