ITU-T X 690-2015 Information technology C ASN 1 encoding rules Specification of Basic Encoding Rules (BER) Canonical Encoding Rules (CER) and Distinguished Encoding Rules (DER) (St.pdf

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1、 I n t e r n a t i o n a l T e l e c o m m u n i c a t i o n U n i o n ITU-T X.690 TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU (08/2015) SERIES X: DATA NETWORKS, OPEN SYSTEM COMMUNICATIONS AND SECURITY OSI networking and system aspects Abstract Syntax Notation One (ASN.1) Information technology

2、ASN.1 encoding rules: Specification of Basic Encoding Rules (BER), Canonical Encoding Rules (CER) and Distinguished Encoding Rules (DER) Recommendation ITU-T X.690 ITU-T X-SERIES RECOMMENDATIONS DATA NETWORKS, OPEN SYSTEM COMMUNICATIONS AND SECURITY PUBLIC DATA NETWORKS Services and facilities X.1X.

3、19 Interfaces X.20X.49 Transmission, signalling and switching X.50X.89 Network aspects X.90X.149 Maintenance X.150X.179 Administrative arrangements X.180X.199 OPEN SYSTEMS INTERCONNECTION Model and notation X.200X.209 Service definitions X.210X.219 Connection-mode protocol specifications X.220X.229

4、Connectionless-mode protocol specifications X.230X.239 PICS proformas X.240X.259 Protocol Identification X.260X.269 Security Protocols X.270X.279 Layer Managed Objects X.280X.289 Conformance testing X.290X.299 INTERWORKING BETWEEN NETWORKS General X.300X.349 Satellite data transmission systems X.350

5、X.369 IP-based networks X.370X.379 MESSAGE HANDLING SYSTEMS X.400X.499 DIRECTORY X.500X.599 OSI NETWORKING AND SYSTEM ASPECTS Networking X.600X.629 Efficiency X.630X.639 Quality of service X.640X.649 Naming, Addressing and Registration X.650X.679 Abstract Syntax Notation One (ASN.1) X.680X.699 OSI M

6、ANAGEMENT Systems management framework and architecture X.700X.709 Management communication service and protocol X.710X.719 Structure of management information X.720X.729 Management functions and ODMA functions X.730X.799 SECURITY X.800X.849 OSI APPLICATIONS Commitment, concurrency and recovery X.85

7、0X.859 Transaction processing X.860X.879 Remote operations X.880X.889 Generic applications of ASN.1 X.890X.899 OPEN DISTRIBUTED PROCESSING X.900X.999 INFORMATION AND NETWORK SECURITY X.1000X.1099 SECURE APPLICATIONS AND SERVICES X.1100X.1199 CYBERSPACE SECURITY X.1200X.1299 SECURE APPLICATIONS AND S

8、ERVICES X.1300X.1399 CYBERSECURITY INFORMATION EXCHANGE X.1500X.1599 CLOUD COMPUTING SECURITY X.1600X.1699 For further details, please refer to the list of ITU-T Recommendations. Rec. ITU-T X.690 (08/2015) i INTERNATIONAL STANDARD ISO/IEC 8825-1 RECOMMENDATION ITU-T X.690 Information technology ASN.

9、1 encoding rules: Specification of Basic Encoding Rules (BER), Canonical Encoding Rules (CER) and Distinguished Encoding Rules (DER) Summary Recommendation ITU-T X.690 | ISO/IEC 8825-1 defines a set of Basic Encoding Rules (BER) that may be applied to values of types defined using the ASN.1 notation

10、. Application of these encoding rules produces a transfer syntax for such values. It is implicit in the specification of these encoding rules that they are also used for decoding. This Recommendation | International Standard defines also a set of Distinguished Encoding Rules (DER) and a set of Canon

11、ical Encoding Rules (CER) both of which provide constraints on the Basic Encoding Rules (BER). The key difference between them is that DER uses the definite length form of encoding while CER uses the indefinite length form. DER is more suitable for the small encoded values, while CER is more suitabl

12、e for the large ones. It is implicit in the specification of these encoding rules that they are also used for decoding. History Edition Recommendation Approval Study Group Unique ID* 1.0 ITU-T X.690 1994-07-01 7 11.1002/1000/3046 1.1 ITU-T X.690 (1994) Technical Cor. 1 1995-11-21 7 11.1002/1000/3283

13、 1.2 ITU-T X.690 (1994) Technical Cor. 2 1997-12-12 7 11.1002/1000/4182 1.3 ITU-T X.690 (1994) Technical Cor. 3 1997-12-12 7 11.1002/1000/4183 2.0 ITU-T X.690 1997-12-12 7 11.1002/1000/4447 2.1 ITU-T X.690 (1997) Technical Cor. 1 1999-06-18 7 11.1002/1000/4705 2.2 ITU-T X.690 (1997) Amd. 1 1999-06-1

14、8 7 11.1002/1000/4704 2.3 ITU-T X.690 (1997) Technical Cor. 2 2001-02-02 7 11.1002/1000/5335 3.0 ITU-T X.690 2002-07-14 17 11.1002/1000/6089 3.1 ITU-T X.690 (2002) Amd. 1 2003-10-29 17 11.1002/1000/7021 3.2 ITU-T X.690 (2002) Amd. 2 2006-06-13 17 11.1002/1000/8838 3.3 ITU-T X.690 (2002) Technical Co

15、r. 1 2007-05-29 17 11.1002/1000/9108 4.0 ITU-T X.690 2008-11-13 17 11.1002/1000/9608 4.1 ITU-T X.690 (2008) Cor. 1 2011-10-14 17 11.1002/1000/11378 4.2 ITU-T X.690 (2008) Cor. 2 2014-03-01 17 11.1002/1000/12147 5.0 ITU-T X.690 2015-08-13 17 11.1002/1000/12483 * To access the Recommendation, type the

16、 URL http:/handle.itu.int/ in the address field of your web browser, followed by the Recommendations unique ID. For example, http:/handle.itu.int/11.1002/1000/11830-en. ii Rec. ITU-T X.690 (11/2015) FOREWORD The International Telecommunication Union (ITU) is the United Nations specialized agency in

17、the field of telecommunications, information and communication technologies (ICTs). The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ of ITU. ITU-T is responsible for studying technical, operating and tariff questions and issuing Recommendations on them with a view to sta

18、ndardizing telecommunications on a worldwide basis. The World Telecommunication Standardization Assembly (WTSA), which meets every four years, establishes the topics for study by the ITU-T study groups which, in turn, produce Recommendations on these topics. The approval of ITU-T Recommendations is

19、covered by the procedure laid down in WTSA Resolution 1. In some areas of information technology which fall within ITU-Ts purview, the necessary standards are prepared on a collaborative basis with ISO and IEC. NOTE In this Recommendation, the expression “Administration“ is used for conciseness to i

20、ndicate both a telecommunication administration and a recognized operating agency. Compliance with this Recommendation is voluntary. However, the Recommendation may contain certain mandatory provisions (to ensure, e.g., interoperability or applicability) and compliance with the Recommendation is ach

21、ieved when all of these mandatory provisions are met. The words “shall“ or some other obligatory language such as “must“ and the negative equivalents are used to express requirements. The use of such words does not suggest that compliance with the Recommendation is required of any party. INTELLECTUA

22、L PROPERTY RIGHTSITU draws attention to the possibility that the practice or implementation of this Recommendation may involve the use of a claimed Intellectual Property Right. ITU takes no position concerning the evidence, validity or applicability of claimed Intellectual Property Rights, whether a

23、sserted by ITU members or others outside of the Recommendation development process. As of the date of approval of this Recommendation, ITU had not received notice of intellectual property, protected by patents, which may be required to implement this Recommendation. However, implementers are caution

24、ed that this may not represent the latest information and are therefore strongly urged to consult the TSB patent database at http:/www.itu.int/ITU-T/ipr/. ITU 2015 All rights reserved. No part of this publication may be reproduced, by any means whatsoever, without the prior written permission of ITU

25、. Rec. ITU-T X.690 (08/2015) iii CONTENTS Page Introduction . v 1 Scope 1 2 Normative references 1 2.1 Identical Recommendations | International Standards 1 2.2 Additional references 1 3 Definitions 1 4 Abbreviations . 2 5 Notation 2 6 Convention . 2 7 Conformance 3 8 Basic encoding rules . 3 8.1 Ge

26、neral rules for encoding 3 8.2 Encoding of a boolean value . 6 8.3 Encoding of an integer value . 6 8.4 Encoding of an enumerated value . 7 8.5 Encoding of a real value 7 8.6 Encoding of a bitstring value. 8 8.7 Encoding of an octetstring value . 9 8.8 Encoding of a null value 10 8.9 Encoding of a s

27、equence value . 10 8.10 Encoding of a sequence-of value. 10 8.11 Encoding of a set value . 10 8.12 Encoding of a set-of value . 11 8.13 Encoding of a choice value . 11 8.14 Encoding of a value of a prefixed type 11 8.15 Encoding of an open type 12 8.16 Encoding of an instance-of value 12 8.17 Encodi

28、ng of a value of the embedded-pdv type 12 8.18 Encoding of a value of the external type . 12 8.19 Encoding of an object identifier value. 13 8.20 Encoding of a relative object identifier value 14 8.21 Encoding of an OID internationalized resource identifier value . 14 8.22 Encoding of a relative OID

29、 internationalized resource identifier value 15 8.23 Encoding for values of the restricted character string types 15 8.24 Encoding for values of the unrestricted character string type . 17 8.25 Encoding for values of the useful types 17 8.26 Encoding for values of the TIME type and the useful time t

30、ypes 17 9 Canonical encoding rules . 17 9.1 Length forms . 18 9.2 String encoding forms . 18 9.3 Set components . 18 10 Distinguished encoding rules 18 10.1 Length forms . 18 10.2 String encoding forms . 18 10.3 Set components . 19 11 Restrictions on BER employed by both CER and DER . 19 11.1 Boolea

31、n values 19 11.2 Unused bits 19 11.3 Real values 19 iv Rec. ITU-T X.690 (11/2015) 11.4 GeneralString values . 19 11.5 Set and sequence components with default value . 20 11.6 Set-of components . 20 11.7 GeneralizedTime . 20 11.8 UTCTime 20 11.9 The TIME type and the useful time types 21 12 Use of BE

32、R, CER and DER in transfer syntax definition 21 Annex A Example of encodings . 23 A.1 ASN.1 description of the record structure . 23 A.2 ASN.1 description of a record value . 23 A.3 Representation of this record value . 23 Annex B Identification of Encoding Rules . 25 Annex C Illustration of real va

33、lue encoding . 26 Rec. ITU-T X.690 (08/2015) v Introduction Rec. ITU-T X.680 | ISO/IEC 8824-1, Rec. ITU-T X.681 | ISO/IEC 8824-2, Rec. ITU-T X.682 | ISO/IEC 8824-3, Rec. ITU-T X.683 | ISO/IEC 8824-4 (Abstract Syntax Notation One or ASN.1) together specify a notation for the definition of abstract sy

34、ntaxes, enabling application standards to define the types of information they need to transfer. It also specifies a notation for the specification of values of a defined type. This Recommendation | International Standard defines encoding rules that may be applied to values of types defined using th

35、e ASN.1 notation. Application of these encoding rules produces a transfer syntax for such values. It is implicit in the specification of these encoding rules that they are also to be used for decoding. There may be more than one set of encoding rules that can be applied to values of types that are d

36、efined using the ASN.1 notation. This Recommendation | International Standard defines three sets of encoding rules, called basic encoding rules, canonical encoding rules and distinguished encoding rules. Whereas the basic encoding rules give the sender of an encoding various choices as to how data v

37、alues may be encoded, the canonical and distinguished encoding rules select just one encoding from those allowed by the basic encoding rules, eliminating all of the senders options. The canonical and distinguished encoding rules differ from each other in the set of restrictions that they place on th

38、e basic encoding rules. The distinguished encoding rules is more suitable than the canonical encoding rules if the encoded value is small enough to fit into the available memory and there is a need to rapidly skip over some nested values. The canonical encoding rules is more suitable than the distin

39、guished encoding rules if there is a need to encode values that are so large that they cannot readily fit into the available memory or it is necessary to encode and transmit a part of a value before the entire value is available. The basic encoding rules is more suitable than the canonical or distin

40、guished encoding rules if the encoding contains a set value or set-of value and there is no need for the restrictions that the canonical and distinguished encoding rules impose. This is due to the memory and CPU overhead that the latter encoding rules exact in order to guarantee that set values and

41、set-of values have just one possible encoding. Annex A gives an example of the application of the basic encoding rules. It does not form an integral part of this Recommendation | International Standard. Annex B summarizes the assignment of object identifier and OID internationalized resource identif

42、ier values made in this Recommendation | International Standard. It does not form an integral part of this Recommendation | International Standard. Annex C gives examples of applying the basic encoding rules for encoding reals. It does not form an integral part of this Recommendation | International

43、 Standard. ISO/IEC 8825-1:2015 (E) Rec. ITU-T X.690 (08/2015) 1 INTERNATIONAL STANDARD ITU-T RECOMMENDATION Information technology ASN.1 encoding rules: Specification of Basic Encoding Rules (BER), Canonical Encoding Rules (CER) and Distinguished Encoding Rules (DER) 1 Scope This Recommendation | In

44、ternational Standard specifies a set of basic encoding rules that may be used to derive the specification of a transfer syntax for values of types defined using the notation specified in Rec. ITU-T X.680 | ISO/IEC 8824-1, Rec. ITU-T X.681 | ISO/IEC 8824-2, Rec. ITU-T X.682 | ISO/IEC 8824-3, and Rec.

45、 ITU-T X.683 | ISO/IEC 8824-4, collectively referred to as Abstract Syntax Notation One or ASN.1. These basic encoding rules are also to be applied for decoding such a transfer syntax in order to identify the data values being transferred. It also specifies a set of canonical and distinguished encod

46、ing rules that restrict the encoding of values to just one of the alternatives provided by the basic encoding rules. 2 Normative references The following Recommendations and International Standards contain provisions which, through reference in this text, constitute provisions of this Recommendation

47、 | International Standard. At the time of publication, the editions indicated were valid. All Recommendations and Standards are subject to revision, and parties to agreements based on this Recommendation | International Standard are encouraged to investigate the possibility of applying the most rece

48、nt edition of the Recommendations and Standards listed below. Members of IEC and ISO maintain registers of currently valid International Standards. The Telecommunication Standardization Bureau of the ITU maintains a list of currently valid ITU-T Recommendations. NOTE This Recommendation | Internatio

49、nal Standard is based on ISO/IEC 10646:2003. It cannot be applied using later versions of this standard. 2.1 Identical Recommendations | International Standards Recommendation ITU-T X.680 (2015) | ISO/IEC 8824-1:2015, Information technology Abstract Syntax Notation One (ASN.1): Specification of basic notation. Recommendation ITU-T X.681 (2015) | ISO/IEC 8824-2:2015, Information technology Abstract Syntax Notation One (ASN.1): Information object specification. Recommendation ITU-T X.682 (2015) |