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YubiHSM PKCS#11 Module

The YubiHSM PKCS#11 Module is a native library to interact with a YubiHSM 2 device using the PKCS#11 interface.

This library works as a translation layer between libyubihsm and software using PKCS#11. For example, a function in this implementation takes the input as specified by PKCS#11, translates it into the input expected by the corresponding function in libyubihsm, calls that function and then translates the result into the return value expected by PKCS#11.

Connector Configuration

The Connector is a component required by a YubiHSM 2 device that performs the communication between the device and applications using it.

A connector can be either an external process communicating over HTTP (by default http://localhost:12345), or directly linked in by libyubihsm in the case of direct USB access.

The PKCS#11 module requires a configuration file containing the URL of the Connector and other configuration options. The default location for that file is the current directory and its default name is yubihsm_pkcs11.conf. However, using the environment variable YUBIHSM_PKCS11_CONF, one can point to a custom location and name.

Below is an example of a yubihsm_pkcs11.conf file:

connector=http://localhost:12345
debug
libdebug
dinout

This file will turn on debug messages for the PKCS#11 module (debug), libyubihsm (libdebug) and functions call tracing (dinout)

A full list of the configuration options can be found on the developers website.

Initialization Arguments

One of the possible parameters given to the PKCS#11 C_Initialize function, pReserved, can also be used to provide configuration options to the module. While this is technically in violation of the PKCS#11 specifications which requires that field to be set to NULL, some application such as OpenSSL support this behavior.

An example of using this technique can be found on the developers website.

Logging In

All interesting operations available through the PKCS#11 interface require a logged-in session. One peculiarity of the YubiHSM PKCS#11 module is that the user PIN MUST be prefixed with the ID (16 bits, in hexadecimal, zero padded if required) of the Authentication Key that should be used to perform the login operation.

For example, to use the default Authentication Key with ID 1 and password password, the user PIN would then be 0001password. To be compliant with PKCS#11 standards, the Authentication Key password MUST be at least 8 characters long.

PKCS#11 Attributes

There are a number of settable attributes defined by PKCS#11 that do not accurately translate to YubiHSM 2 Capabilities and are therefore treated as always having a fixed value. A list of those attributes and their values can be found on the developers website.

Capabilities and Domains

Objects created via the PKCS#11 module inherit the Domains of the Authentication Key used to establish the session. The Domains can not be changed or modified via the PKCS#11 module.

A table mapping PKCS#11 objects to YubiHSM 2 Capabilities can be found on the developers website.

PKCS#11 Objects

Not all PKCS#11 Object Types are implemented. A list of what is implemented is available here.

Examples

C Code Example

Code examples of how to use the PKCS#11 module from C programs can be found in the test link:tests/ecdh_derive_test.c

Pkcs11-tool Example

To derive an ECDH key using a public key in the file peer.key and a private key in the YubiHSM 2 with OpenSC pkcs11-tool, the following command can be used:

pkcs11-tool -vvv --module yubihsm_pkcs11.so --derive -i peer.key --id 64 --login --pin 0001password

The private key in YubiHSM 2 has Object ID 0x0064 and the public key in peer.key is expected to be in DER format. By default, this command will expect to find a yubihsm_pkcs11.conf file in the current directory.