an introduction to abstract syntax notation 1 (asn.1)
DESCRIPTION
An Introduction to Abstract Syntax Notation 1 (ASN.1). Steinar Andresen/Rolv Bræk/Finn Arve Aagesen Norwegian University of Science and Technology, Trondheim. The need of a “common language” In order to cooperate the following needs arise. - PowerPoint PPT PresentationTRANSCRIPT
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An Introduction to Abstract Syntax Notation 1 (ASN.1)
Steinar Andresen/Rolv Bræk/Finn Arve Aagesen
Norwegian University of Science and Technology, Trondheim
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The need of a “common language”In order to cooperate the following needs arise
A shared interpretation of what the data means and a common protocol for interchange
•A shared view on data structure The ASN.1 Notation
•Transfer coding rulesThe ASN.1 Encoding schemes: BER, PER, ..
A shared interpretation of what the data means and a common protocol for interchange
•A shared view on data structure The ASN.1 Notation
•Transfer coding rulesThe ASN.1 Encoding schemes: BER, PER, ..
LAN - Org A
LAN Org C
LAN Org B
PUBLIC
WAN
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The history of ASN.1
General purpose notation and encoding scheme: • Developed to be applied to the MHS protocols (X.400) (“born”
in 1982)
• Generalised as general tools ISO 8824 Notation and ISO 8825 Encoding rules in 1990, Revised in 1995
• General use in many application fields today
General purpose notation and encoding scheme: • Developed to be applied to the MHS protocols (X.400) (“born”
in 1982)
• Generalised as general tools ISO 8824 Notation and ISO 8825 Encoding rules in 1990, Revised in 1995
• General use in many application fields today
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The original “realm” of ASN
• Applied first to the Presentation layer in the “Open Systems Interconnection”.
• Soon used to define the protocols of the Applications layer:FTAM, ROSE, MHS, etc.
• Also used for lower layers
• Applied first to the Presentation layer in the “Open Systems Interconnection”.
• Soon used to define the protocols of the Applications layer:FTAM, ROSE, MHS, etc.
• Also used for lower layers
Application
Presentation
Session
Transport
Network
Datalink
Physical
OSI Protocol Stack
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Why ASN.1 and BER?
Applicat ion
Presentation
Session
Transport
Network
Datalink
Physical
OSI Protocol Stack
on
s
Applicat ion
Presentation
Session
Transport
Network
Datalink
Physical
OSI Protocol Stack
ASN.1for the data syntax
BERfor the (sequential)transfer syntax
PDU PDU
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ASN.1 Use
ASN.1
BER
PDU PDU
Encode Decode
ASN.1
A PDU can be a complex element (letter, document, …) and:
• specified using datatypes of SDL, LOTOS, UML, ...
• implemented using datatypes of CHILL, C++, Java, ...
ASN.1 provides a language independent syntax and ASN.1 compilers take care of the mapping
A PDU can be a complex element (letter, document, …) and:
• specified using datatypes of SDL, LOTOS, UML, ...
• implemented using datatypes of CHILL, C++, Java, ...
ASN.1 provides a language independent syntax and ASN.1 compilers take care of the mapping
0 1 | 0 | 1 | 0 | 0 | 1 | 1
C++, Java, SDL...
C++, Java,...
C++, Java, SDL...
C++, Java,...
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ASN.1 Module
• A module is a set of ASN.1 definitions assembled for a specific purpose.
• The structure of a module is:
ModuleDefinition::= ModuleIdentifier DEFINITIONSDEFINITIONS::= BEGIN
ModuleBodyEND
• A module is a set of ASN.1 definitions assembled for a specific purpose.
• The structure of a module is:
ModuleDefinition::= ModuleIdentifier DEFINITIONSDEFINITIONS::= BEGIN
ModuleBodyEND
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ASN.1 Module Identifier
• ModuleIdentifer is an element of type Object Identifiers
• Object Identifiers are adminstrered by ISO, ITU-T, etc. A Module Identifier represents an official reference to the Module.
• ModuleIdentifer is an element of type Object Identifiers
• Object Identifiers are adminstrered by ISO, ITU-T, etc. A Module Identifier represents an official reference to the Module.
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Module Body
ModuleBody::= Exports -- definitions that may be exported to other modules Imports -- definitions that are imported from other modules AssignmentList --this modules definitions
| -- “|” means “or”
empty
ModuleBody::= Exports -- definitions that may be exported to other modules Imports -- definitions that are imported from other modules AssignmentList --this modules definitions
| -- “|” means “or”
empty
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Assignments
WheatherReport ::= SEQUENCE{ ......}
Name of a type reference to defined type
sampleWReport WheatherReport::= { ......}
Name of a value The type of this value Actual value spec.
Type assignment
Value assignment
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Type assignment
A type assignment has three syntactic elements:
• the type reference (the name allocated to it),
• the symbol “::=“ (means defined as) and
• the appropriate type notation
A type assignment has three syntactic elements:
• the type reference (the name allocated to it),
• the symbol “::=“ (means defined as) and
• the appropriate type notation
WheatherReport ::= SEQUENCE
{
stationNumber INTEGER {1..99999}
timeOfReport UTCTime
.........
}
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Value assignment
A value assignment has four syntactic elements: • the value reference (the name allocated),
• the type to which the value belongs
• the symbol “::=“ (means defined as) and
• the appropriate value notation
A value assignment has four syntactic elements: • the value reference (the name allocated),
• the type to which the value belongs
• the symbol “::=“ (means defined as) and
• the appropriate value notation
Sample value assignment:
sampleReport WheatherReport ::=
{
stationNumber 73290
timeOfReport “900102125703Z”
.........
}
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Sequence
Letter ::= SEQUENCE {
opening OCTETSTRING,
body OCTETSTRING,
closing OCTETSTRING,
address AddressType
}
AddressType ::= SEQUENCE {
name OCTETSTRING,
number INTEGER,
street OCTETSTRING,
postOffice OCTETSTRING,
state OCTETSTRING,
zipCode INTEGER
}
Letter ::= SEQUENCE {
opening OCTETSTRING,
body OCTETSTRING,
closing OCTETSTRING,
address AddressType
}
AddressType ::= SEQUENCE {
name OCTETSTRING,
number INTEGER,
street OCTETSTRING,
postOffice OCTETSTRING,
state OCTETSTRING,
zipCode INTEGER
}
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Optional
AddressType ::= SEQUENCE {
name OCTETSTRING,
number INTEGER,
street OCTETSTRING,
apartNumber INTEGER OPTIONAL,
postOffice OCTETSTRING,
state OCTETSTRING,
zipCode INTEGER
}
AddressType ::= SEQUENCE {
name OCTETSTRING,
number INTEGER,
street OCTETSTRING,
apartNumber INTEGER OPTIONAL,
postOffice OCTETSTRING,
state OCTETSTRING,
zipCode INTEGER
}
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Tags
Letter ::= SEQUENCE {
opening OCTETSTRING,
body OCTETSTRING,
closing OCTETSTRING,
receiverAddr AddressType OPTIONAL,
senderAddr AddressType OPTIONAL
}
Letter ::= SEQUENCE {
opening OCTETSTRING,
body OCTETSTRING,
closing OCTETSTRING,
receiverAddr [0] AddressType OPTIONAL,
senderAddr [1] AddressType OPTIONAL
}
Letter ::= SEQUENCE {
opening OCTETSTRING,
body OCTETSTRING,
closing OCTETSTRING,
receiverAddr AddressType OPTIONAL,
senderAddr AddressType OPTIONAL
}
Letter ::= SEQUENCE {
opening OCTETSTRING,
body OCTETSTRING,
closing OCTETSTRING,
receiverAddr [0] AddressType OPTIONAL,
senderAddr [1] AddressType OPTIONAL
}
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Spelling Conventions
• Reserved words: only CAPITAL letters (INTEGER, CHOICE,…)
• Types: first letter Capital (TransactionID)
• Value reference: first letter Lowercase (application(0))
• Identifier: first letter Lowercase (destination, responder)
• Macro: only CAPITAL letters
• Reserved words: only CAPITAL letters (INTEGER, CHOICE,…)
• Types: first letter Capital (TransactionID)
• Value reference: first letter Lowercase (application(0))
• Identifier: first letter Lowercase (destination, responder)
• Macro: only CAPITAL letters
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ASN.1 Tagged Types
Four classes:
1. UNIVERSAL (ASN.1 In-build types)
2. Application specific types (non-ambiguous within module)
3. Context specific types (non-ambiguous within construct)
3. Private (non-ambiguous within some ”enterprise”)
UNIVERSAL:
• Simple types (BOOLEAN, INTEGER, ENUMERATED, …)
• Constructor types (SEQUENCE, SEQUENCE OF, SET, SETOF)
• Additional predefined (NumericString, Teletxstring, GeneralizedTime, …)
• OBJECT IDENTIFIER
• Tagging is needed to recognise the types in the transfer syntaxt (when decoding a received PDU)
Four classes:
1. UNIVERSAL (ASN.1 In-build types)
2. Application specific types (non-ambiguous within module)
3. Context specific types (non-ambiguous within construct)
3. Private (non-ambiguous within some ”enterprise”)
UNIVERSAL:
• Simple types (BOOLEAN, INTEGER, ENUMERATED, …)
• Constructor types (SEQUENCE, SEQUENCE OF, SET, SETOF)
• Additional predefined (NumericString, Teletxstring, GeneralizedTime, …)
• OBJECT IDENTIFIER
• Tagging is needed to recognise the types in the transfer syntaxt (when decoding a received PDU)
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Universal Types
Universal Tag ASN.1 Type
• 1 BOOLEAN
• 2 INTEGER
• 3 BITSTRING
• 4 OCTETSTRING
• 5 NULL
• 6 OBJECTIDENTIFIER
• 7 ObjectDescriptor
• 8 EXTERNAL
• 9 REAL
• 10 ENUMERATED
• 11-15 reserved for addenda
• 16 SEQUENCE, SEQUENCE OF
• 17 SET, SET OF
• … ...
Universal Tag ASN.1 Type
• 1 BOOLEAN
• 2 INTEGER
• 3 BITSTRING
• 4 OCTETSTRING
• 5 NULL
• 6 OBJECTIDENTIFIER
• 7 ObjectDescriptor
• 8 EXTERNAL
• 9 REAL
• 10 ENUMERATED
• 11-15 reserved for addenda
• 16 SEQUENCE, SEQUENCE OF
• 17 SET, SET OF
• … ...
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ExampleExample DEFINITIONS::= BEGIN
TransactionID ::= INTEGER
Component ::= INTEGER {application(0), networkManager(1),systemManager(2)}
Request ::= PrintableString
EntityIdentifier ::= [PRIVATE 1] IMPLICIT OCTETSTRING
RequestPDU ::= SEQUENCE {responseRequired BOOLEAN, TransactionID, requestor EntityIdentifier,request CHOICE {
command [0] IMPLICIT SET {destination Component, Request}
shutdown [1] IMPLICIT NULL}}
ResponsePDU ::= SEQUENCE {TransactionID, responder EntityIdentifier OPTIONAL, result INTEGER {success(0), failure(1)}}
END
Example DEFINITIONS::= BEGIN
TransactionID ::= INTEGER
Component ::= INTEGER {application(0), networkManager(1),systemManager(2)}
Request ::= PrintableString
EntityIdentifier ::= [PRIVATE 1] IMPLICIT OCTETSTRING
RequestPDU ::= SEQUENCE {responseRequired BOOLEAN, TransactionID, requestor EntityIdentifier,request CHOICE {
command [0] IMPLICIT SET {destination Component, Request}
shutdown [1] IMPLICIT NULL}}
ResponsePDU ::= SEQUENCE {TransactionID, responder EntityIdentifier OPTIONAL, result INTEGER {success(0), failure(1)}}
END
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A Value assignment example
aRequestPDU RequestPDU ::= {ResponseRequired TRUE, 45, requestor “MySystem”,request {
command {destination systemManager, ‘status’}
}}
aResponsePDU ResponsePDU::= {45, result INTEGER {success}}
aRequestPDU RequestPDU ::= {ResponseRequired TRUE, 45, requestor “MySystem”,request {
command {destination systemManager, ‘status’}
}}
aResponsePDU ResponsePDU::= {45, result INTEGER {success}}
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ASN.1 Transfer Syntax
• Basic Encoding Rules BER
• Packed Encoding Rules PER
• Canonical Encoding Rules CER
• Disting. Encoding Rules DER
• Basic Encoding Rules BER
• Packed Encoding Rules PER
• Canonical Encoding Rules CER
• Disting. Encoding Rules DER
• Defines how to encode the values before sending over the line
• Basically it is a Type, Length, Value encoding scheme with one or more octets for each of the fields.
• Defines how to encode the values before sending over the line
• Basically it is a Type, Length, Value encoding scheme with one or more octets for each of the fields.
Type Length Value
identified by tagging
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TLV encoding scheme
Octet 1 Octet 2 Octet 3 Octet n...
bit8 bit 7 ...bit1
TypeLengthTypeLengthValueTypeLengthValue…
DataElement
DataElement
DataElement
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ASN.1 Transfer Syntax
T A G F I E L D (=Type identifier field)
| 8 | 7 | 6 | 5 | 4 | 3 | 2 | 1 |
f numberclass
Class:
• 00 UNIVERSAL
• 01 APPLICATION
• 10 Context specific
• 11 Private
f:
• 0 primitive encoding
• 1 constructed encoding
Class:
• 00 UNIVERSAL
• 01 APPLICATION
• 10 Context specific
• 11 Private
f:
• 0 primitive encoding
• 1 constructed encoding
number:
• <31 directly
• >=31 as below:
number:
• <31 directly
• >=31 as below:
class f 11111 1 … 1 … 0 …
last
...
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Examples
• BOOLEAN: UNIVERSAL 1 = 00000001 hex
• INTEGER: UNIVERSAL 2 = 00000002 hex
• SEQUENCE: UNIVERSAL 16 constructed = 00110000 = 30 hex
• [PRIVATE 35] IMPLICIT INTEGER = 11011111 00100011
• BOOLEAN: UNIVERSAL 1 = 00000001 hex
• INTEGER: UNIVERSAL 2 = 00000002 hex
• SEQUENCE: UNIVERSAL 16 constructed = 00110000 = 30 hex
• [PRIVATE 35] IMPLICIT INTEGER = 11011111 00100011
|c la s s | f | n u m b e r |
0 | 0 0 0 | 0 | 0 | 0 | 1
B O O L E A N
|c la s s | f | n u m b e r |
0 | 0 0 0 | 0 | 0 | 1 | 0
I N T E G E R
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Length field
Definite form
• short: length < 128
• long: length > 128
Indefinite form: only for
constructed types
Definite form
• short: length < 128
• long: length > 128
Indefinite form: only for
constructed types
0 <length>
1 <length of length field>
<length field> <length field>...
10000000 <value> 00000000 00000000... <value>
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VALUE FIELDS
| contents |
0 | 0 | 0 | 0 | 0 |0 | 0 | 0
| length |
0 | 0 | 0 | 0 |0 | 0 | 0 | 1
|class| f | number |
0 | 0 0 0 | 0 | 0 | 0 | 1
BOOLEAN
Ex. FALSE
(TRUE with content value different from 0)
| contents |
0 | 1 | 1 | 0 | 0 |1 | 0 | 0
| length |
0 | 0 | 0 | 0 |0 | 0 | 0 | 1
|class| f | number |
0 | 0 0 0 | 0 | 0 | 1 | 0
INTEGER
Ex. 100 (decimal)
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How to encode
RequestPDU ::= SEQUENCE {responseRequired BOOLEAN, TransactionID, requestor EntityIdentifier,request CHOICE {
command [0] IMPLICIT SET {destination Component, Request}
shutdown [1] IMPLICIT NULL}}
where:
ResponseRequired = FALSE, TransactionID = 10, requestor = “MySystem”,request = command {
destination = networkManager,
Request = ‘status’}
??
RequestPDU ::= SEQUENCE {responseRequired BOOLEAN, TransactionID, requestor EntityIdentifier,request CHOICE {
command [0] IMPLICIT SET {destination Component, Request}
shutdown [1] IMPLICIT NULL}}
where:
ResponseRequired = FALSE, TransactionID = 10, requestor = “MySystem”,request = command {
destination = networkManager,
Request = ‘status’}
??
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Encoding summary
Universal Tag ASN.1 Type
• 1 BOOLEAN
• 2 INTEGER
• 3 BITSTRING
• 4 OCTETSTRING
• 5 NULL
• 6OBJECTIDENTIIER
• 7 ObjectDescriptor
• 8 EXTERNAL
• 9 REAL
• 10 ENUMERATED
• 11-15 reserved for addenda
• 16 SEQUENCE, SEQUENCE OF
• 17 SET, SET OF
• … ...
Universal Tag ASN.1 Type
• 1 BOOLEAN
• 2 INTEGER
• 3 BITSTRING
• 4 OCTETSTRING
• 5 NULL
• 6OBJECTIDENTIIER
• 7 ObjectDescriptor
• 8 EXTERNAL
• 9 REAL
• 10 ENUMERATED
• 11-15 reserved for addenda
• 16 SEQUENCE, SEQUENCE OF
• 17 SET, SET OF
• … ...
Class:
• 00 UNIVERSAL
• 01 APPLICATION
• 10 Context specific
• 11 Private
f:
• 0 primitive encoding
• 1 constructed encoding
Class:
• 00 UNIVERSAL
• 01 APPLICATION
• 10 Context specific
• 11 Private
f:
• 0 primitive encoding
• 1 constructed encoding
| 8 | 7 | 6 | 5 | 4 | 3 | 2 | 1 |
f numberclass
number:
• <31 directly
• >=31 as below:
number:
• <31 directly
• >=31 as below:
class f 11111 1 … 1 … 0 … ...