About STPPA: The “Special Topics on Privacy and Public Auditability” (STPPA) series is organized by the NIST Privacy Enhancing Cryptography (PEC) program in the Cryptographic Technology Group (Computer Security Division, Information Technology Laboratory). A main goal of the series is to gather reference material about "PEC tools", which may facilitate reflections on aspects related to development of recommendations/guidelines about advanced cryptography, namely for uses related to privacy and public auditability.