A simple FileHandler which allows to inspect binary files containing ASN.1 data that has been encoded using the Basic Encoding Rules (BER). As the Canonical and Distinguished Encoding Rules (CER & DER) are just restricted subsets of BER, data encoded with these can be analyzed just as well.
As such binary data is often encoded in the Base64 format to simplify transfer through email systems, this viewer will automatically detect such an additional encoding and decode it prior to decoding the binary BER contents.
ASN.1 stands for Abstract Syntax Notation One, which is an international standard describing the abstract definition of arbitrary data structures (ITU-T X.680). It provides a syntax for defining complex structures which are built from a set of well defined basic data types and other structured types.
An extension standard (ITU-T X.690) provides the specification of a set of encoding rules, which can be used to represent ASN.1 data in binary form. This standard first defines Basic Encoding Rules (BER) which specify how basic and structured types are to be represented in binary form. On top of this two more set of rules, namely the Canonical Encoding Rules (CER) and the Distinguished Encoding Rules (DER), define a set of constraints for the BER, which allow applications to process data in a more efficient manner.
As CER and DER are both subsets of BER, this FileHandler can be used to analyze the contents of ASN.1 data files containing the binary form of any of these encodings.
Although from todays point of view the BER don't represent a very efficient way of encoding the represented data, data thus encoded is in wide use in the areas of security/cryptography (e.g. certificates, cryptographic key material, etc.) and network communication protocols. There the main units of communication are called PDUs (for Protocol Data Unit).