Since 9.12, BIND has undergone substantial code refactoring and cleanup, and some very old code has been removed that supported obsolete operating systems and operating systems for which ISC is no longer able to perform quality assurance testing. Specifically, workarounds for UnixWare, BSD/OS, AIX, Tru64, SunOS, TruCluster and IRIX have been removed. On UNIX-like systems, BIND now requires support for POSIX.1c threads (IEEE Std 1003.1c-1995), the Advanced Sockets API for IPv6 (RFC 3542), and standard atomic operations provided by the C compiler. More information can be found in the PLATFORM.md file that is included in the source distribution of BIND 9. If your platform compiler and system libraries provide the above features, BIND 9 should compile and run. If that isn't the case, the BIND development team will generally accept patches that add support for systems that are still supported by their respective vendors. As of BIND 9.14, the BIND development team has also made cryptography (i.e., TSIG and DNSSEC) an integral part of the DNS server. The OpenSSL cryptography library must be available for the target platform. A PKCS#11 provider can be used instead for Public Key cryptography (i.e., DNSSEC signing and validation), but OpenSSL is still required for general cryptography operations such as hashing and random number generation.