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Abstract Syntax Notation One (ASN.1)
is standard for describing data structures in telecommunication and
computer networking world.
ASN.1
provides a set of formal rules for describing the structure of
objects.
Specification describe abstract objects, that are independent
of machine-specific encoding techniques.
ASN
defined data can be encoded using on of encoding rules:
Basic Encoding Rules (BER)
Canonical Encoding Rules (CER)
Distinguished Encoding Rules (DER)
XML Encoding Rules (XER)
Packed Encoding Rules (PER)
Generic String Encoding Rules (GSER)
ASN.1 together with specific ASN.1 encoding rules facilitates the exchange of structured data especially between application programs over networks by describing data structures in a way that is independent of machine architecture and implementation language.
ASN
encoded data looks logicaly as follows:
Encoded data structure contains three elements:
Tag - unique value, which identifies type of data. Tag carries some additional info - like complexity indicator and context indicator. Actual tag value is unique for single ASN definition(aside some basic tag values which are defined in ASN specification)
Length - indicates length of current data structure
Payload - depending on definition this can be simple value - like integer or it can carry another ASN encoded data structure.