OPENSSL ASN. 1, DER, PEM, X509

ASN.1

It's a language standard , It can be done with C Language analogy ,ASN.1 The main purpose of is to describe the data structure , and C The main purpose of the language is to control the direction of the program . Use ASN.1 Can describe complex data objects . such as ： In a piece of data , Where is the length , Where is the content , Where is the sign, etc （ similar C Linguistic struct）.

Use ASN.1 Data structure of description , Need visualization , That's coding .ASN.1 There are many different coding implementations ,BER,CER,DER etc. , among DER It is the most common kind , You can actually use XML To code , Can also be converted to C Data structure of language .

DER

yes ASN.1 A coding implementation of , It's binary based .

PEM

yes 64 Base number , This is an information encoding format , Be similar to HEX Format .

If you will DER And PEM Documents for comparison ,DER Files are similar to binary BIN file ,PEM Files are similar to hexadecimal HEX Format file .

Illustrate with examples ：

You can use it. 0x01 To represent numbers 1, This is binary coding .

You can also use it ASCII The code '1' Representation number 1, This is it. HEX code .

PEM code （BASE64） Is to specify a series of symbols , Use these symbols to represent specific numbers .

X509

This is a data format standard , It defines the data structure of the digital certificate , There are many elements in digital certificates , Such as ： Version number 、 Public key 、 Owner information 、 Digital signature, etc . These elements must be organized in a fixed and unified data structure , Can be passed directly between different entities , If there is no standard , The certificate format defined by an organization can only be used by itself , No one else can use it , Finally, there may be thousands of certificate formats around the world . and X509 Is such a standard , To tell you , Where the version number should exist , Where does the public key exist ... With this unified format , Everyone abides by it , All organizations only need to support this certificate format .

X509 How to describe the data structure of a certificate ？ The answer is ASN.1, It has been used. ASN.1 To describe the data structure of digital certificate .X509 Certificate in format , There are many specific codes , Such as DER Coding format , Directly stored DER Coded X509 certificate , Usually the suffix is called x509.der perhaps der, Use PEM Format coded X509 The certificate suffix is usually called x509.pem or pem.

Digression

PKCS#1 The standard defines RSA Public private key data structure , This standard also uses ASN.1 To describe the data structure .

In fact, many computers 、 data 、 All the standards related to the algorithm use ASN.1 To describe the data structure .

We don't have to learn ASN.1 The grammar of , But it is necessary to understand its function and importance .

Last , The file suffix cannot represent its encoding format , The suffix is human , Just know the encoding format , You can use any suffix , Just for convenience , It is generally agreed to use the corresponding code as the suffix .