1 Introduction

This document describes the Libtasn1 library that provides Abstract Syntax Notation One (ASN.1, as specified by the X.680 ITU-T recommendation) parsing and structures management, and Distinguished Encoding Rules (DER, as per X.690) encoding and decoding functions.

The main features of this library are:

• On-line ASN.1 structure management that doesn’t require any C code file generation.
• Off-line ASN.1 structure management with C code file generation containing an array.
• Distinguished Encoding Rules (DER) encoding support.
• No limits for INTEGER and ENUMERATED values.
• It’s Free Software. Anybody can use, modify, and redistribute the library under the terms of the GNU Lesser General Public License version 2.1 or later. The command line tools, self-tests and build infrastructure are licensed under the GNU General Public License version 3.0 or later.
• Thread-safety. No global variables are used and multiple library handles and session handles may be used in parallel.
• Portability. The code should work on all Unix like operating systems, and Windows. The library itself should be portable to any C89 system, not even POSIX is required.