My ASN.1 Notes
Resources
Python ASN.1 Resources
pyasn1 is a free and open source implementation of ASN.1 types and codecs as a Python package. It has been first written to support particular protocol (SNMP) but then generalized to be suitable for a wide range of protocols based on ASN.1 specification.
asn1ate is a Python library for translating ASN.1 into other forms. It is intended for code generation from formal ASN.1 definitions, and a code generator for pyasn1 is included.
Python-ASN1 is a simple ASN.1 encoder and decoder for Python 2.6+ and 3.3+.
asn1tinydecoder.py is a simple and fast ASN.1 decoder without external libraries designed to parse large files.
Nice examples
Example explaining CHOICE tagging
Example to understand IMPLICIT tagging
TBCD
Telephony Binary-Coded Decimal strings are not part of the ASN.1 standard, but their use is prevalent in many telephony-related ASN.1 specifications.
Conversion of these types into standard numeric text strings is supported by Objective Systems software.
In general, BCD strings pack two numeric digits into a single byte value by using a four-bit nibble to hold each digit. By convention, the digits are reversed in TBCD strings, but there are no official standards for this encoding.