X.690 ASN.1规范：BER、CER与DER编码规则详解

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X.690-ASN.1是国际电信联盟电信标准化部门(ITU-T)和国际标准化组织/国际电工委员会(ISO/IEC)联合发布的标准，它是Abstract Syntax Notation One (ASN.1)的一部分，专注于开放系统互连(OSI)网络和通信的抽象语法表示。该标准文档详细规定了三种基本的编码规则：Basic Encoding Rules (BER), Canonical Encoding Rules (CER)，以及Distinguished Encoding Rules (DER)。 Ber (Basic Encoding Rules) 是一种普遍使用的编码方式，它适用于大部分的数据传输场景。它允许将复杂的数据结构转换为二进制形式，以便在网络中高效且可靠地传输。BER使用了编码标记、长度、值和检查位等元素，确保数据的完整性和一致性，即使在可能出现错误的环境中也能正确解析。 CER (Canonical Encoding Rules)，又称规范编码规则，它提供了一种更紧凑的编码形式，通过去除不必要的结构细节来优化空间效率。CER编码通常用于那些对数据格式有严格要求或者需要最小化传输开销的场景。然而，CER不保证唯一性，可能产生多个等效的编码。 DER (Distinguished Encoding Rules)，是一种更为严格且唯一的编码方式，主要用于证书、公钥基础设施(PKI)和安全相关应用。DER确保每个数据结构都有一个确定的、无歧义的二进制表示，这对于数字签名、证书链验证等安全操作至关重要。由于其强制唯一性，DER通常比BER和CER占用更多的存储空间，但提供了更好的可读性和审计跟踪。 X.690标准被广泛应用于网络协议设计、数据交换、安全协议和管理系统中，尤其是在 OSI 的第7层及以上，涉及服务定义、协议规格、安全协议以及管理对象等方面。它不仅定义了数据结构的编码规则，还提供了标准化的方式来描述和交换这些结构，对于保证跨平台的互操作性和一致性起着关键作用。在实际应用中，开发者会根据具体需求选择合适的编码规则，如在需要快速传输且对数据完整性要求较高的情况下，可能会倾向于使用BER；而对于存储空间有限或对数据格式有严格要求的情况，CER可能是更好的选择；而在安全性要求极高的场景，如数字签名和证书交换，DER则是不可或缺的。X.690-ASN.1是IT行业中不可或缺的基础工具，对于理解和实现复杂数据结构的标准化编码至关重要。

Introduction

ITU-T Rec. X.680 | ISO/IEC 8824-1, ITU-T Rec. X.681 | ISO/IEC 8824-2, ITU-T Rec. X.682 | ISO/IEC 8824-3,

ITU-T Rec. X.683 | ISO/IEC 8824-4 (Abstract Syntax Notation One or ASN.1) together specify a notation for the

definition of abstract syntaxes, 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 the 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 defined 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 values 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 sender's options.

The canonical and distinguished encoding rules differ from each other in the set of restrictions that they place on the

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 distinguished 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 distinguished 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 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 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 Standard.

ITU-T Rec. X.690 (07/2002) v

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ASN.1（抽象语法表示） 规范之X.690

在有限带宽的环境下，如何利用ASN.1的Packed Encoding Rules (PER)进行高效的数据编码，并且它的优势相对于BER、DER等编码规则有哪些特点？

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在有限带宽的环境下，如何利用ASN.1的Packed Encoding Rules (PER)进行高效的数据编码？请解释PER编码规则相较于BER、DER等其他编码规则的优势。

如何根据ITU-T X.691标准实现ASN.1数据结构的PER编码和解码？请提供一个具体实现的示例。

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ASN.1（抽象语法表示）规范之X.690