ALaymansGuidetoaSubsetofASN1BERandDER资源-CSDN文库

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### ASN.1、BER与DER基础知识详解 #### 引言随着软件开发复杂度的不断提高，抽象成为管理软件设计过程中的关键原则之一。通过抽象，设计师可以在不关心具体实现细节的情况下定义系统的一部分，从而简化了整体的设计过程并提高了模块间的独立性。这种做法不仅为后续的实现留出了灵活性，还能在实施时验证各部分是否符合预先设定的“公理”条件，进而确保整个系统的稳定性和可维护性。开放系统互连（OSI）模型是当前最复杂的系统之一，它涉及大量的抽象层次。OSI是一种国际标准化组织制定的体系结构，用于规范从物理层到应用层的计算机之间的互联方式。在OSI模型中，较高层次的对象通常被抽象定义，并期望通过较低层次的对象来实现。例如，某一层的服务可能需要在两台计算机之间传输某些抽象对象；而较低的一层则可能提供字符串的传输服务，使用编码规则将这些抽象对象转换为由一串二进制数字组成的字符串。本文将详细介绍OSI模型中的抽象语法表示法（Abstract Syntax Notation One, ASN.1）、基本编码规则（Basic Encoding Rules, BER）以及特定编码规则（Distinguished Encoding Rules, DER）的基础知识。 #### ASN.1概述 **ASN.1** 是一种用于定义数据结构的表示方法。它允许用户以一种标准化的方式定义数据类型及其结构，从而使不同平台或系统之间的数据交换成为可能。ASN.1标准不仅定义了一组符号语言，还规定了如何将抽象数据类型编码为字节序列，即BER和DER编码规则。 ##### ASN.1特点 - **标准化**: ASN.1是ISO/ITU-T国际标准。 - **跨平台**: 定义的数据类型可以跨多种编程语言和操作系统进行解析。 - **可扩展性**: 支持自定义数据类型，便于扩展。 - **清晰性**: 采用明确且简洁的语法来描述数据结构。 - **兼容性**: 可与其他通信协议（如HTTP、XML等）结合使用。 #### BER与DER编码规则 ##### 基本编码规则（BER） BER是一种通用的编码规则，旨在将ASN.1定义的数据类型转换为二进制格式。BER的特点在于其灵活性，允许相同的数据以不同的方式进行编码，这取决于编码时的具体参数设置。BER适用于多种情况，特别是在数据需要在不同的系统之间进行交换时特别有用。 - **通用性**: 可用于编码所有ASN.1数据类型。 - **灵活性**: 编码结果可能因为参数的不同而有所不同。 - **可读性**: 编码过程中保留了原始数据的结构信息，有助于调试和追踪问题。 ##### 特定编码规则（DER） DER是BER的一个子集，它提供了一种确定性的编码方法，这意味着相同的输入数据总是会产生相同的输出编码。DER的主要优势在于它的确定性和唯一性，非常适合于需要验证数据完整性的场景，比如数字签名和证书管理。 - **确定性**: 相同的输入数据总能产生相同的编码结果。 - **唯一性**: 消除了BER中的模糊性，使得数据验证更为简单可靠。 - **高效性**: 由于编码结果固定，减少了不必要的编码差异导致的处理负担。 #### 结论通过理解ASN.1、BER与DER的基础概念，我们能够更好地把握OSI模型中数据表示和传输的核心原理。这些编码规则不仅在理论上有重要意义，在实际的应用场景中也扮演着至关重要的角色，尤其是在网络安全、数字证书管理等领域。希望本文能够帮助读者建立起对这些概念的基本认知，并为进一步学习相关技术奠定坚实的基础。

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A Layman's Guide to a

Subset of ASN.1, BER, and

DER

An RSA Laboratories Technical Note

Burton S. Kaliski Jr.

Revised November 1, 1993

Abstract. This note gives a layman's introduction to a subset of OSI's Abstract Syntax Notation One

(ASN.1), Basic Encoding Rules (BER), and Distinguished Encoding Rules (DER). The particular

purpose of this note is to provide background material sufficient for understanding and implementing the

PKCS family of standards.

1. Introduction

It is a generally accepted design principle that abstraction is a key to managing

software development. With abstraction, a designer can specify a part of a

system without concern for how the part is actually implemented or represented.

Such a practice leaves the implementation open; it simplifies the specification;

and it makes it possible to state "axioms" about the part that can be proved when

the part is implemented, and assumed when the part is employed in another,

higher-level part. Abstraction is the hallmark of most modern software

specifications.

One of the most complex systems today, and one that also involves a great deal

of abstraction, is Open Systems Interconnection (OSI, described in X.200). OSI is

an internationally standardized architecture that governs the interconnection of

computers from the physical layer up to the user application layer. Objects at

higher layers are defined abstractly and intended to be implemented with

objects at lower layers. For instance, a service at one layer may require transfer

of certain abstract objects between computers; a lower layer may provide

Supersedes June 3, 1991 version, which was also published as NIST/OSI Implementors' Workshop

document SEC-SIG-91-17. PKCS documents are available by electronic mail to <pkcs@rsa.com>.



1991–

1993 RSA Laboratories, a division of RSA Data Security, Inc. License to copy

this document is granted provided that it is identified as "RSA Data Security, Inc. Public-Key

Cryptography Standards (PKCS)" in all material mentioning or referencing this document.

003-903015-110-000-000

Page 2 A LAYMAN'S GUIDE TO A SUBSET OF ASN.1, BER, AND DER

transfer services for strings of ones and zeroes, using encoding rules to

transform the abstract objects into such strings. OSI is called an open system

because it supports many different implementations of the services at each layer.

OSI's method of specifying abstract objects is called ASN.1 (Abstract Syntax

Notation One, defined in X.208), and one set of rules for representing such

objects as strings of ones and zeros is called the BER (Basic Encoding Rules,

defined in X.209). ASN.1 is a flexible notation that allows one to define a variety

data types, from simple types such as integers and bit strings to structured types

such as sets and sequences, as well as complex types defined in terms of others.

BER describes how to represent or encode values of each ASN.1 type as a string

of eight-bit octets. There is generally more than one way to BER-encode a given

value. Another set of rules, called the Distinguished Encoding Rules (DER),

which is a subset of BER, gives a unique encoding to each ASN.1 value.

The purpose of this note is to describe a subset of ASN.1, BER and DER

sufficient to understand and implement one OSI-based application, RSA Data

Security, Inc.'s Public-Key Cryptography Standards. The features described

include an overview of ASN.1, BER, and DER and an abridged list of ASN.1

types and their BER and DER encodings. Sections 2—

4 give an overview of

ASN.1, BER, and DER, in that order. Section 5 lists some ASN.1 types, giving

their notation, specific encoding rules, examples, and comments about their

application to PKCS. Section 6 concludes with an example, X.500 distinguished

names.

Advanced features of ASN.1, such as macros, are not described in this note, as

they are not needed to implement PKCS. For information on the other features,

and for more detail generally, the reader is referred to CCITT Recommendations

X.208 and X.209, which define ASN.1 and BER.

Terminology and notation. In this note, an octet is an eight-bit unsigned integer.

Bit 8 of the octet is the most significant and bit 1 is the least significant.

The following meta-syntax is used for in describing ASN.1 notation:

BIT monospace denotes literal characters in the type and value

notation; in examples, it generally denotes an octet value in

hexadecimal

bold italics denotes a variable

[] bold square brackets indicate that a term is optional

{} bold braces group related terms

| bold vertical bar delimits alternatives with a group

2. ABSTRACT SYNTAX NOTATION ONE Page 3

…… bold ellipsis indicates repeated occurrences

= bold equals sign expresses terms as subterms

2. Abstract Syntax Notation One

Abstract Syntax Notation One, abbreviated ASN.1, is a notation for describing

abstract types and values.

In ASN.1, a type is a set of values. For some types, there are a finite number of

values, and for other types there are an infinite number. A value of a given

ASN.1 type is an element of the type's set. ASN.1 has four kinds of type: simple

types, which are "atomic" and have no components; structured types, which

have components; tagged types, which are derived from other types; and other

types, which include the CHOICE type and the ANY type. Types and values can

be given names with the ASN.1 assignment operator (::=) , and those names

can be used in defining other types and values.

Every ASN.1 type other than CHOICE and ANY has a tag, which consists of a

class and a nonnegative tag number. ASN.1 types are abstractly the same if and

only if their tag numbers are the same. In other words, the name of an ASN.1

type does not affect its abstract meaning, only the tag does. There are four

classes of tag:

Universal, for types whose meaning is the same in all applications; these

types are only defined in X.208.

Application, for types whose meaning is specific to an application, such as

X.500 directory services; types in two different applications may

have the same application-specific tag and different meanings.

Private, for types whose meaning is specific to a given enterprise.

Context-specific, for types whose meaning is specific to a given structured

type; context-specific tags are used to distinguish between

component types with the same underlying tag within the context

of a given structured type, and component types in two different

structured types may have the same tag and different meanings.

The types with universal tags are defined in X.208, which also gives the types'

universal tag numbers. Types with other tags are defined in many places, and

are always obtained by implicit or explicit tagging (see Section 2.3). Table 1 lists

some ASN.1 types and their universal-class tags.

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