1. Jump to first page PKI2001 (TIFR, Mumbai) ASN.1 Abstract Syntax Notation One ASN.1 is a standard way to describe a 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.

2. Jump to first page PKI2001 (TIFR, Mumbai) Why Care about Technical Architecture & Standards? If you want You must standardize Application APIs Portability Implementation Interoperability Protocols Implementation Replaceability All

3. Jump to first page PKI2001 (TIFR, Mumbai) ASN.1 Encoding n Given any ASN.1 description of a message, a representation can be derived mechanically by applying a set of encoding rules. n Initially only a single set, the Basic Encoding Rules(BER), were standardized. n Later Canonical and Distinguished Encoding Rules were standardized

4. Jump to first page PKI2001 (TIFR, Mumbai) Encoding Abstract Values n 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. n The reverse is not necessarily true.

5. Jump to first page PKI2001 (TIFR, Mumbai) ASN.1 data types n ASN.1 notation is recognizable as a high level definition language. n It is constructed in modules with unique identifiers. n There are over 20 built-in identifiers e.g. BOOLEAN, INTEGER, ENUMERATED, REAL, BIT STRING, UTCTime, EXTERNAL, OCTET STRING, NULL etc.

6. Jump to first page PKI2001 (TIFR, Mumbai) n Arbitrarily complex structures can be built up from these data types using constructors such as : u SET{ } - order not significant u 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) }

7. Jump to first page PKI2001 (TIFR, Mumbai) TLV (type-length-value), ILC (identifier - length - contents) n BER generate encodings which are of a class known as type - length - value. n Now in ASN.1 they are called as identifier - length - contents. n The structure is therefore recursive such that the contents can be a series of ILCs n This bottoms out with genuine contents such as a text string or an integer.

8. Jump to first page PKI2001 (TIFR, Mumbai) Basic Encoding Rules A Schematic Representation

9. Jump to first page PKI2001 (TIFR, Mumbai) The use of ASN.1 Compilers