ASN.1

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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.
PKI2001 (TIFR, Mumbai)
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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Why Care about Technical
Architecture & Standards?
If you want
Application
Portability
You must standardize
APIs
Implementation
Interoperability
Protocols
Implementation
Replaceability
All
PKI2001 (TIFR, Mumbai)
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ASN.1 Encoding
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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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Encoding Abstract
Values
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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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ASN.1 data types
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PKI2001 (TIFR, Mumbai)
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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Arbitrarily complex structures can
be built up from these data types
using constructors such as :
 SET{
} - order not significant
 SEQUENCE { } -fixed order
one example,
PKI2001 (TIFR, Mumbai)
WeatherReport
{
stationNumber
timeOfReport
pressure
temperature
humidity
windVelocity
windDirection
}
::=SEQUENCE
INTEGER(1..99999)
UTCTime
INTEGER(850..1100)
INTEGER(-100..60)
INTEGER(0..100)
INTEGER(0..500)
INTEGER(0..48)
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TLV
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PKI2001 (TIFR, Mumbai)
(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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Basic Encoding Rules
A Schematic Representation
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The use of ASN.1
Compilers
PKI2001 (TIFR, Mumbai)
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