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PKI2001 (TIFR, Mumbai)

ASN.1 Abstract Syntax Notation OneAbstract Syntax Notation One

ASN.1 is a standard way to describea message(a unit application data) that can be sent or received in a network.

ASN.1 is divided into two parts:1. The rules of syntax for describing the contents of a message in terms of data type and content sequence or structure.2. How you actually encode each data item in a message.

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PKI2001 (TIFR, Mumbai)

Why Care about Technical Architecture & Standards?

If you want You must standardize

Application APIs

Portability

Implementation Interoperability Protocols

Implementation Replaceability All

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PKI2001 (TIFR, Mumbai)

ASN.1 Encoding

Given any ASN.1 description of a message, a representation can be derived mechanically by applying a set of encoding rules.

Initially only a single set, the Basic Encoding Rules(BER), were standardized.

Later Canonical and Distinguished Encoding Rules were standardized

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PKI2001 (TIFR, Mumbai)

Encoding Abstract Values When any (correct) set of encoding

rules are applied to the abstract values in any given ASN.1 type, they will produce bit-patterns (actually octet strings) for each value such that any given octet string corresponds to precisely one abstract value.

The reverse is not necessarily true.

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PKI2001 (TIFR, Mumbai)

ASN.1 data types

ASN.1 notation is recognizable as a high level definition language.

It is constructed in modules with unique identifiers.

There are over 20 built-in identifiers e.g. BOOLEAN, INTEGER, ENUMERATED, REAL, BIT STRING, UTCTime, EXTERNAL, OCTET STRING, NULL etc.

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PKI2001 (TIFR, Mumbai)

Arbitrarily complex structures can be built up from these data types using constructors such as : SET{ } - order not significant SEQUENCE { } -fixed order

one example,WeatherReport ::=SEQUENCE

{

stationNumber INTEGER(1..99999)

timeOfReport UTCTime

pressure INTEGER(850..1100)

temperature INTEGER(-100..60)

humidity INTEGER(0..100)

windVelocity INTEGER(0..500)

windDirection INTEGER(0..48)

}

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PKI2001 (TIFR, Mumbai)

TLV(type-length-value), ILC(identifier - length - contents)

BER generate encodings which are of a class known as type - length - value.

Now in ASN.1 they are called as identifier - length - contents.

The structure is therefore recursive such that the contents can be a series of ILCs

This bottoms out with genuine contents such as a text string or an integer.

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PKI2001 (TIFR, Mumbai)

Basic Encoding RulesA Schematic RepresentationA Schematic Representation

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PKI2001 (TIFR, Mumbai)

The use of ASN.1 Compilers