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Abstract Syntax Notation One ASN.1

Abstract Syntax Notation One ASN.1. These slides are based in parts upon slides of Prof. Dssouli (Concordia university ). Abstract Syntax Notation One. Both the information and communications models need to be specified syntactically and semantically .

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Abstract Syntax Notation One ASN.1

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  1. Abstract Syntax Notation OneASN.1 These slides are based in parts upon slides of Prof. Dssouli (Concordia university)

  2. Abstract Syntax Notation One • Both the information and communications models need to be specified syntactically and semantically. • This requires a language that specifies the management protocol in the application layer. • This is where Abstract Syntax Notation One (ASN.1) plays a role. • ASN.1 is actually more than a syntax; it’s a language that addresses both syntax and semantics • Two type of syntax • Abstract syntax: set of rules that specify data type and structure for information storage • Transfer syntax: set of rules for communicating information between systems • Can generate machine-readable code: Basic Encoding Rules (BER) • ASN.1 is based on the Backus system and uses the formal syntax and grammar of the Backus-Nauer Form (BNF)

  3. Definition: <name> ::= <definition> where <name> denotes “entity” and the symbol “::=“ represents “defined as” primitive definitions: <digit> ::= 0|1|2|3|4|5|6|7|8|9 <op> ::= +|-|x|/ similarly, an entity number can be constructed from primitives: <number> ::= <digit> | <digit> <number> Example: 9 is primitive 9 19 is construct of 1 and 9 619 is construct of 6 and 19 Backus-Nauer Form (BNF)

  4. Assignments <BooleanType> ::= BOOLEAN data type assignment (or name of the entity) <BooleanValue> ::= TRUE | FALSE value assignment (assigned value to the data type) Group of assignments: Modules Start with capital letters Usually modules are built from primitive (atomic) data types (e.g., INTEGER, REAL, etc..) May use ASN.1 constructs (e.g., SET, SEQUENCE, etc.) Constructors are used to build structured data types Backward and forward references, and inline definition ASN.1 Assignments

  5. Constructs: “list makers” A module PersonnelRecord (a set of data types) Primitives data types Construct: alternatives ASN.1 Modules Three construction mechanisms (develop structured data types): Alternatives: CHOICE List: SET and SEQUENCE Repetition: SET OF and SEQUENCE OF

  6. Lists built with “SEQUENCE” maintains the correct order PersonnelRecord is a set of different data types, each uniquely associated with a name and can be encoded and transmitted in any order. ASN.1 Modules Example: “Smith”, “Manager”, {“North”, “Chile”} “Manager”, “Smith”, {“North”, “Chile”} {“North”, “Chile”}, “Smith”, “Manager”

  7. ASN.1 Symbols Symbol Meaning ::= Defined as | or, alternative, options of a list - Signed number -- Following the symbol are comments {} Start and end of a list [] Start and end of a tag () Start and end of subtype .. Range

  8. Data Types Data types are generally defined based on a structure and a tag: • Structure: simple (or atomic), structured, etc.. • Tag: class and a tag

  9. Data Type: • Structure & Tag • Structure defines how data type is built • Tag uniquely identifies the data type

  10. ASN.1 simple types • Basic Types • BOOLEAN • INTEGER • ENUMERATED • REAL • BIT STRING • OCTET STRING • Character String Types (various subsets of ISO 10646-1) • NumericString (0-9,<space>) • PrintableString (0-9,A-Z,a z,<space>,<special>) • VisibleString • GraphicString • TeletexString • UTF8String • IA5String

  11. ASN.1 simple types • Syntax:<type name> ::=type • Example:counter ::= INTEGER IpAddress ::= OCTET STRING PageNumber ::= INTEGER ChapterNumber::= INTEGER Months::=ENUMERATED {january (1), february (2), march (3), april (4), may (5), june (6), july (7 august (8), september (9), october (10), november (11), december (12)}

  12. ASN.1 simple types • A subtype is derived from a parent type • Syntax:<subtype name> ::= <type> ( <constraint> ) Examples: Counter ::= INTEGER ( 0..4294967295 ) IpAddress ::= OCTET STRING ( SIZE(4) ) Spring ::= Months ( march | april | may ) Summer ::= Months ( june | july | august ) SmallPrime ::= INTEGER ( 2 | 3 | 5 | 7 | 11 )

  13. Structure • Simple PageNumber ::= INTEGER ChapterNumber ::= INTEGER • Structured / Construct BookPageNumber ::= SEQUENCE {ChapterNumber, Separator, PageNumber} • Tagged • Derived from another type; given a new ID • In Fig. 3-14, INTEGER is either universal or application specific • Other • CHOICE, ANY

  14. Structured Type • SEQUENCE • Ordered list maker • SEQUENCE OF • Ordered array of repetitive data • SET • Unordered list maker • SET OF • Unordered list of repetitive data

  15. ASN.1 structured types • A data type isstructured typewhen it contains other types (i.e., have components) BookPageNumber ::= SEQUENCE {ChapterNumber, Separator, PageNumber} separator is a VisibleString data type with value “-” Example: {1-1, 2-3, 3-39} BookPages ::= SEQUENCE OF { BookPageNumber } BookPages ::= SEQUENCE OF { SEQUENCE {ChapterNumber, Separator, PageNumber}} Example: {1-1, 1-2,..,2-1, 2-2,…..}

  16. ASN.1 structured types • The pages of a book could also be specified as a collection of individual pages in random order BookPages ::= SET OF { SEQUENCE {ChapterNumber, Separator, PageNumber} }

  17. ASN.1 Tagged Types • Tag uniquely identifies a data type and is required for encoding the data types for communication • Comprises class and tag number • Class: • Universal - similar to global variables • Application - only in the application used • Context-specific - specific context in application • Private - used extensively by commercial vendors Example: BOOLEAN Universal 1 INTEGER Universal 2 research Application [1] product-based Context-specific under research [0]

  18. UNIVERSAL 1 BOOLEAN UNIVERSAL 2 INTEGER UNIVERSAL 3 BIT STRING UNIVERSAL 4 OCTET STRING UNIVERSAL 9 REAL UNIVERSAL 10 ENUMERATED UNIVERSAL 6 OBJECT IDENTIFIER UNIVERSAL 7 ObjectDescriptor UNIVERSAL 26 VisibleString . . . UNIVERSAL 5 NULL UNIVERSAL 23 UTCTime UNIVERSAL 24 GeneralizedTime UNIVERSAL 16 SEQUENCE [OF] UNIVERSAL 17 SET [OF] ASN.1 Tagged Types - basic types - object types - character string types - miscellaneous types - structured types

  19. Tag nb is 1 (overrides that of BOOLEAN) Application specific Context specific (subset of an application, and limited to the application) ASN.1 Tagged Types

  20. ASN.1 Object Types • Used to name and describe information objects • Such as standard documents, data structures, managed objects • In general, an information object is a class of information, e.g., file format, rather than an instance of such a class (i.e., individual file) • Object identifier is a unique identifier for a particular object and its value consist of a set of integers • Object descriptor is a human readable description of an information object

  21. ASN.1 Object Types root internet OBJECT IDENTIFIER ::= {iso(1) org(3) dod(6) 1 } ccitt(0) iso(1) joint-iso-ccitt(2) org(3) dod(6) internet(1) mgmt(2) private(4) experimental(3) mib-2(1) enterprise(1) private OBJECT IDENTIFIER ::= {internet 4 }

  22. ASN.1 Object Types • Private type is used extensively by vendors of network products • A vendor is assigned a node on the MIT, all branches and leaves under that node will be assigned private data types by the vendor ibm OBJECT IDENTIFIER ::= {iso(1) org(3) dod(6) internet(1) private(4) enterprize(1) 2}

  23. ASN.1 syntax containing management information is encoded using the Basic Encoding Rules (BER) that is defined for the transfer syntax BER is a specification developed and standardized by CCITT and OSI ASCII data is converted to bit-oriented data TLV, Type-Length-Value: is a specific encoding structure Type: indicates the ASN.1 type, class of the type Length: length of the actual value representation Value: the value of the ASN.1 type as a string of octets Encoding Structure

  24. P/C (1-bit) specifies whether the structure is simple or a construct 0 for simple 1 for construct Encoding Structure 1 byte

  25. Encoding Structure • Class (2 bits): specifies the class being used 1 byte

  26. Encoding Structure • Tag Number: designates the tag value in binary • Example: 00 0 00010 for encoding INTEGER 1 byte Universal class Primitive Tag value = 2

  27. Identifier Octet Bits 8 7 6 5 4 3 2 1 0 = Primitive 1 = Constructed 0 0 = Universal 0 1 = Application 1 0 = Context-specific 1 1 = Private Tag number < 31 Class P/C Tag number

  28. Leading octet 2nd octet Last octet Class P/C 1 1 1 1 1 1 1 0 + + + . . . = Tag number Tag number >= 31 . . .

  29. one octet L octets 0 Length L Contents (or Value) field first octet K octets L octets 1 K Length L Contents field Binary equivalent of 128 Encoding of Length Field • Short form ( L < 128 octets) • Long form ( 128  L < 21008 octets) Example, L = 128: 10000001 10000000

  30. Type Length Value 02 01 1B 0 00010 00 UNIVERSAL P 2 Length is 2 to indicate 2 octets for Value 02 02 00 81 today INTEGER ::= 129 00 81 51 02 0 10001 01 P 17 APPLICATION BER, Examples distance INTEGER ::= 27 DayOfYear ::= [APPLICATION 17] IMPLICIT INTEGER today DayOfYear ::= 129

  31. Birthday ::= SEQUENCE { name VisibleString, day DayOfYear} Type Definition UNIVERSAL 16 00 1 10000 myBirthday Birthday ::= { name "Jane", day 129} Value Assignment BER Encoding BER, Examples Birthday Length Contents 30?? VisibleString Length Contents 1A 04 "Jane" DayOfYear Length Contents 51 02 00 81 0A

  32. Example: SNMP Message Tag Message ::= SEQUENCE { version INTEGER { version-1(0) }, community OCTET STRING, data ANY } 30 02 04

  33. Example: SNMP Message Type  30: SEQUENCE Length  82 01 c0: 448 octets 82: 10000010

  34. Type  30: SEQUENCE Length  32: 50 octets

  35. Macros <macroname> MACRO ::= BEGIN TYPE NOTATION ::= <syntaxOfNewType> VALUE NOTATION ::= <syntaxOfNewValue> <auxiliaryAssignments> END

  36. Macro Example OBJECT-TYPE MACRO ::= BEGIN TYPE NOTATION ::= "SYNTAX" type (TYPE ObjectSyntax) “ACCESS" Access "STATUS" Status VALUE NOTATION ::= value (VALUE ObjectName) Access ::= "read-only" | "read-write“ | "write-only | "not-accessible" Status ::= "mandatory” | "optional“ | "obsolete" END

  37. Object-Type Example sysName OBJECT-TYPE SYNTAX DisplayString (SIZE (0..255)) ACCESS read-write STATUS mandatory ::= { system 5 }

  38. Marco Example 2 CAR MACRO::= BEGIN TYPE NOTATION ::= Brand Engine CarType Year VALUE NOTATION ::= value (VALUE OBJECT IDENTIFIER) Brand ::= “BRAND” value (PrintableString) Engine ::= “CC” Ccs Ccs ::= Cc | Ccs”,” Cc Cc ::= value (INTEGER (600..5000)) CarType ::= “STYLE” CType CType ::= “Sedan” | “Liftback” | “SUV” | “Other” Year ::= “YEAR” value (INTEGER) END

  39. Camry CAR BRAND Toyota CC 2000, 2400, 3000 STYLE Sedan YEAR 2006 ::= {toyota 3}

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