Libp11 was orginaly written as part of OpenSC and later spun off as standalone project.
wrote libp11 or helped improving it.
Libp11 is released as Open Source software under the LGPL license and thus can be used in your software, too.
Libp11 uses the PKCS#11 header files and includes a copy of these header files.
License to copy and use this software is granted provided that it is identified as "RSA Security Inc. PKCS #11 Cryptographic Token Interface (Cryptoki)" in all material mentioning or referencing this software or this function.
License is also granted to make and use derivative works provided that such works are identified as "derived from the RSA Security Inc. PKCS #11 Cryptographic Token Interface (Cryptoki)" in all material mentioning or referencing the derived work.
This software is provided “AS IS” and RSA Security, Inc. disclaims all warranties including but not limited to the implied warranty of merchantability, fitness for a particular purpose, and noninfringement.
Strictly speaking Libp11 implements the "RSA Security Inc. PKCS #11 Cryptographic Token Interface (Cryptoki)" (with very small modification so it compiles on unix as well as on windows).
Authors of GPL software please note that libp11 uses OpenSSL library and those header files, and depending on the interpretation of the general public license it is necessary to grant exemptions to the GPL.
Only few implementations of PKCS#11 API are open source software (for example OpenSC, MuscleCard?, gpkcs11). Most other implementations are shipped binary only with proprietory licenses by the smart card / solution vendors. To allow any PKCS#11 API implementation to be used with your license you need an exemption as well.
Here is an example that would cover all of this:
In addition to the terms set out under the GPL, permission is granted to link the software against the openssl and libp11 libraries and use any plugin implementing PKCS!#11 API under any license.
Libp11 includes svn2cl by
Copyright (C) 2004, 2005 Arthur de Jong.
Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions
are met:
1. Redistributions of source code must retain the above copyright
notice, this list of conditions and the following disclaimer.
2. Redistributions in binary form must reproduce the above copyright
notice, this list of conditions and the following disclaimer in
the documentation and/or other materials provided with the
distribution.
3. The name of the author may not be used to endorse or promote
products derived from this software without specific prior
written permission.
THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE
GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER
IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR
OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN
IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.