Cryptography series: certificate format representation of PKI X.509

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Catalog * brief introduction

• An example of a certificate
• X.509 The suffix of the certificate
  • .pem
  • .cer, .crt, .der
  • .p7b, .p7c
  • .p12
  • .pfx
• Certificate hierarchy and cross certification
• x.509 Scope of use of certificate
• summary

brief introduction

stay PKI(public key infrastructure) Public key infrastructure , All operations are around certificates and keys , It provides the creation of 、 management 、 distribution 、 Use 、 A set of roles required to store and revoke digital certificates and manage public key encryption 、 Strategy 、 Hardware 、 Software and programs .

With the key , You can create a certificate based on the key . If you want certificates to be widely used , A common standard must be indispensable , stay PKI In the system , It's called this standard X.509.

X.509 The standard defines the most commonly used format for public key certificates .

An example of a certificate

The most important part of the certificate is the public key information , Extract the public key from the certificate , The public key can be used to decrypt the data encrypted by the sender with the private key . Public key information is the core of certificate .

In addition to the public key , The certificate contains a lot of other information , For example, it contains identity information ( Host name 、 Organizations or individuals, etc ）.

Creating a certificate is very simple , Let's take a look at the use openssl Command to create a certificate .

Before creating a certificate , First, you need to create the public and private keys that the certificate depends on ,x.509 Certificates can support a variety of public and private key algorithms , such as RSA, DSA, ECDSA, ed25519 etc. .

Here we choose to use RSA Algorithm , The generated key pair is as follows ：

openssl genrsa -des3 -out ca.key 1024
Generating RSA private key, 1024 bit long modulus
...............++++++
.............................................++++++
e is 65537 (0x10001)
Enter pass phrase for ca.key:
Verifying - Enter pass phrase for ca.key:

Input pass, We can get ca.key, This is a RSA PRIVATE KEY.

And then you can use this ca.key To create a certificate .

openssl req -new -x509 -days 20 -key ca.key -out ca.crt
Enter pass phrase for ca.key:
You are about to be asked to enter information that will be incorporated
into your certificate request.
What you are about to enter is what is called a Distinguished Name or a DN.
There are quite a few fields but you can leave some blank
For some fields there will be a default value,
If you enter '.', the field will be left blank.
-----
Country Name (2 letter code) []:SH
State or Province Name (full name) []:SH
Locality Name (eg, city) []:SH
Organization Name (eg, company) []:HW
Organizational Unit Name (eg, section) []:HW
Common Name (eg, fully qualified host name) []:caserver
Email Address []:[email protected]

You can see , Based on the key , Certificates also need to be provided, such as Country Name,Province Name,Organization Name Extra information .

Last , We can get one CA certificate ca.crt.

If you want to view the status of the certificate , You can use the following command ：

openssl x509 -noout -text -in ca.crt
Certificate:
    Data:
        Version: 1 (0x0)
        Serial Number: 9511149647544559472 (0x83fe64365379a770)
    Signature Algorithm: sha256WithRSAEncryption
        Issuer: C=SH, ST=SH, L=SH, O=HW, OU=HW, CN=caserver/[email protected]
        Validity
            Not Before: Apr 27 06:33:16 2022 GMT
            Not After : May 17 06:33:16 2022 GMT
        Subject: C=SH, ST=SH, L=SH, O=HW, OU=HW, CN=caserver/[email protected]
        Subject Public Key Info:
            Public Key Algorithm: rsaEncryption
                Public-Key: (1024 bit)
                Modulus:
                    00:9f:b4:ff:16:15:51:2a:de:2f:23:cd:7d:27:41:
                    3c:30:1f:f3:cb:bf:3f:7c:96:ba:c3:81:a8:eb:88:
                    be:11:31:03:6f:c3:1d:f1:dc:4c:ea:3d:da:15:24:
                    59:32:8b:7e:87:a0:0b:57:b9:79:e4:72:2f:4b:50:
                    9d:00:eb:ee:52:24:f3:e8:e9:92:1c:ec:47:d9:98:
                    8c:f9:0f:71:a6:91:b2:5b:c1:59:bf:1f:27:47:6b:
                    9c:ce:22:e7:9d:2c:4a:3a:83:72:43:47:5d:ee:9e:
                    64:78:cb:3c:48:af:27:08:c1:08:41:c0:e0:92:e9:
                    13:81:1c:c7:72:3c:2f:5f:f3
                Exponent: 65537 (0x10001)
    Signature Algorithm: sha256WithRSAEncryption
         68:09:be:cb:89:c0:0d:27:d2:bb:b2:f0:fb:6e:e2:0a:19:86:
         92:cf:e5:90:48:b7:99:02:f1:75:6a:6d:79:1e:18:c7:95:7c:
         89:92:ed:a1:bf:ad:91:76:c6:63:59:bb:6d:31:1e:11:5a:5e:
         32:86:12:89:00:69:d0:77:c6:d6:69:11:0a:f7:7b:61:6e:95:
         f8:d6:6b:89:c0:6c:49:eb:38:d9:f5:82:43:32:6e:14:fb:a0:
         fb:be:12:a5:dc:69:66:b8:1b:22:cb:0f:9f:56:52:40:6d:48:
         b6:78:29:dc:67:aa:79:c5:00:e3:68:9a:65:9a:94:99:be:ce:
         b0:d2

You can see CA The certificate contains the date , Serial number , Signature algorithm , publisher , Additional information such as effectiveness .

The certificate generated above is actually a root certificate , This root certificate can sign other certificate requests , So as to generate sub certificates , Thus, a cascade structure of certificates is generated .

If a client wants to send a message to CA server What should I do to request a new certificate ？

First, the client also needs to generate its own key pair . If the client is CA server own , So this request CA The process of signing a certificate is called self signing .

To request a certificate , First you have to generate a request csr, It can also be used openssl Order to proceed ：

openssl req -new -key ca.key -out server.csr
Enter pass phrase for ca.key:
You are about to be asked to enter information that will be incorporated
into your certificate request.
What you are about to enter is what is called a Distinguished Name or a DN.
There are quite a few fields but you can leave some blank
For some fields there will be a default value,
If you enter '.', the field will be left blank.
-----
Country Name (2 letter code) []:CN
State or Province Name (full name) []:SH
Locality Name (eg, city) []:SH
Organization Name (eg, company) []:citi
Organizational Unit Name (eg, section) []:org
Common Name (eg, fully qualified host name) []:client
Email Address []:[email protected]

Please enter the following 'extra' attributes
to be sent with your certificate request
A challenge password []:

csr Because the request also needs to generate a CA certificate , So you need to enter similar information .

Finally, we generate a server.csr file .

Next use this csr File to request a certificate ：

openssl x509 -req -days 20 -in server.csr -CA ca.crt -CAkey ca.key -CAcreateserial -out server.crt
Signature ok
subject=/C=CN/ST=SH/L=SH/O=citi/OU=org/CN=client/[email protected]
Getting CA Private Key
Enter pass phrase for ca.key:

The meaning of the above command is CA server Upper private key, Root certificate and just generated certificate request server.csr, Build use CA server Signed self signed certificate .

Finally, we get a self signature server.csr Certificate file .

Also use openssl Command to view the status of the certificate ：

openssl x509 -noout -text -in server.crt

Certificate:
    Data:
        Version: 1 (0x0)
        Serial Number: 14663444799761243679 (0xcb7f055ae9515e1f)
    Signature Algorithm: sha1WithRSAEncryption
        Issuer: C=SH, ST=SH, L=SH, O=HW, OU=HW, CN=caserver/[email protected]
        Validity
            Not Before: Apr 27 07:28:08 2022 GMT
            Not After : May 17 07:28:08 2022 GMT
        Subject: C=CN, ST=SH, L=SH, O=citi, OU=org, CN=client/[email protected]
        Subject Public Key Info:
            Public Key Algorithm: rsaEncryption
                Public-Key: (1024 bit)
                Modulus:
                    00:9f:b4:ff:16:15:51:2a:de:2f:23:cd:7d:27:41:
                    3c:30:1f:f3:cb:bf:3f:7c:96:ba:c3:81:a8:eb:88:
                    be:11:31:03:6f:c3:1d:f1:dc:4c:ea:3d:da:15:24:
                    59:32:8b:7e:87:a0:0b:57:b9:79:e4:72:2f:4b:50:
                    9d:00:eb:ee:52:24:f3:e8:e9:92:1c:ec:47:d9:98:
                    8c:f9:0f:71:a6:91:b2:5b:c1:59:bf:1f:27:47:6b:
                    9c:ce:22:e7:9d:2c:4a:3a:83:72:43:47:5d:ee:9e:
                    64:78:cb:3c:48:af:27:08:c1:08:41:c0:e0:92:e9:
                    13:81:1c:c7:72:3c:2f:5f:f3
                Exponent: 65537 (0x10001)
    Signature Algorithm: sha1WithRSAEncryption
         31:2e:b6:d7:3e:2d:ae:f1:2e:44:b5:5e:73:42:91:39:80:9f:
         a8:ed:9c:60:78:35:21:df:4a:45:b0:b1:d1:80:c1:ee:cb:30:
         75:34:66:61:43:6c:0a:85:4f:a3:e5:09:9f:2b:07:62:6a:3a:
         60:22:78:f0:7d:32:ef:2f:46:95:34:60:22:03:47:78:6f:0c:
         7e:f1:85:ea:d6:4b:1e:45:b5:56:a1:d7:52:9c:19:ae:24:26:
         3d:a7:0b:f2:94:c1:d3:e3:04:25:f8:ce:b8:cb:84:6a:d1:b4:
         63:7c:df:87:f8:44:86:49:b5:96:dc:43:c7:7a:17:d3:82:c6:
         6a:af

You can see the structure and structure root ca The certificate is the same , there Subject Is to create server.csr Information entered in .

X.509 The suffix of the certificate

The certificate suffix we used above is crt, That is to say certificate Abbreviation .

in fact X.509 Certificates also support several other types of suffixes .

.pem

pem The full name is Privacy-enhanced Electronic Mail, You can tell by the name ,pem Originally prepared for encrypted mail .

It is a kind of DER+Base64 Certificate to encode .PEM Certificates are usually in text format , With "-----BEGIN CERTIFICATE-----“ start , And ”-----END CERTIFICATE-----" end .

.cer, .crt, .der

All three are based on DER Binary certificate for encoding , But sometimes you use Base64 Encoding , such as .pem.

.p7b, .p7c

Yes, it is PKCS#7 Signed data .

PKCS The full name is Public-Key Cryptography Standards , By RSA A series of standards developed by laboratories and other security system developers to promote the development of public key cryptography .

PKCS#7 The full name of is called Cryptographic Message Syntax Standard.

.p12

Yes, it is PKCS#12 Signed data , Can contain both certificate and private key .

.pfx

PKCS#12 The forerunner of , Usually contains PKCS#12 Formatted data .

Certificate hierarchy and cross certification

The hierarchy of certificates should be well understood , The hierarchy of certificates is also called certificate chain .

From the final certificate we received , It can be followed by one or more CA certificate , The last certificate is the root certificate .

For example, the chain structure of certificates is A->B->C.

To verify A Validity of certificate , Then we need to use B To verify , that B The effectiveness of the , Also needed C To verify , In this way, the level of verification is up to the root certificate .

What is cross certification ？

If there is now A->B and D->E These two certificate chains . But now the two chains are independent , If A Certificates also want to use E How should we handle the authentication ？

Let's think about it first A->B The meaning of ,A->B intend A Certificate use B Certificate to sign . More precisely, it is A Certificate is used B The public key in the certificate is used to sign .

If we use E Yes B Sign the public key in to get a certificate C, that B and C Have the same public key , So for A Come on ,A->B and A->C->E Are valid certificate chains .

If you use B Yes E The public key of , Get a certificate F, So for D->E and D->F->B There are also two valid certificate chains .

Such a structure is called cross authentication .

Cross certification is used in different root systems CA The scenario of chain mutual authentication , Very useful .

x.509 Scope of use of certificate

x.509 Certificates are widely used , such as web The most common way to visit TLS/SSL and HTTPS It's all about x.509 certificate .

in addition SMTP, POP, IMAP, LDAP, XMPP Provide for the right to x.509 Certificate support .

summary

That's all x.509 Introduction to the use of certificates and related principles .

Please refer to http://www.flydean.com/42-pki-x509/

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