Sign server and client certificates
We will be signing certificates using our intermediate CA. You can use these signed certificates in a variety of situations, such as to secure connections to a web server or to authenticate clients connecting to a service.
The steps below are from your perspective as the certificate authority. A third-party, however, can instead create their own private key and certificate signing request (CSR) without revealing their private key to you. They give you their CSR, and you give back a signed certificate. In that scenario, skip the genrsa and req commands.
Create a key
Our root and intermediate pairs are 4096 bits. Server and client certificates normally expire after one year, so we can safely use 2048 bits instead.
Although 4096 bits is slightly more secure than 2048 bits, it slows down TLS handshakes and significantly increases processor load during handshakes. For this reason, most websites use 2048-bit pairs.
If you’re creating a cryptographic pair for use with a web server (eg, Apache), you’ll need to enter this password every time you restart the web server. You may want to omit the -aes256 option to create a key without a password.
➜ CA openssl genrsa -aes256 -out intermediate/private/www.example.com.key.pem 2048 Generating RSA private key, 2048 bit long modulus ...+++ ................................................+++ e is 65537 (0x10001) Enter pass phrase for intermediate/private/www.example.com.key.pem: Verifying - Enter pass phrase for intermediate/private/www.example.com.key.pem: ➜ CA chmod 400 intermediate/private/www.example.com.key.pem
Create a certificate
Use the private key to create a certificate signing request (CSR). The CSR details don’t need to match the intermediate CA. For server certificates, the Common Name must be a fully qualified domain name (eg, www.example.com), whereas for client certificates it can be any unique identifier (eg, an e-mail address). Note that the Common Name cannot be the same as either your root or intermediate certificate.
➜ CA openssl req -config intermediate/openssl.cnf -key intermediate/private/www.example.com.key.pem -new -sha256 -out intermediate/csr/www.example.com.csr.pem Enter pass phrase for intermediate/private/www.example.com.key.pem: 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]:CN State or Province Name [Beijing]:Beijing Locality Name :Haidian Organization Name [Usoft Ltd]:Usoft Ltd Organizational Unit Name :Usoft Ltd gRPC services Common Name :www.example.com Email Address :email@example.com
To create a certificate, use the intermediate CA to sign the CSR. If the certificate is going to be used on a server, use the server_cert extension. If the certificate is going to be used for user authentication, use the usr_cert extension. Certificates are usually given a validity of one year, though a CA will typically give a few days extra for convenience.
➜ CA openssl ca -config intermediate/openssl.cnf -extensions server_cert -days 375 -notext -md sha256 -in intermediate/csr/www.example.com.csr.pem -out intermediate/certs/www.example.com.cert.pem Using configuration from intermediate/openssl.cnf Enter pass phrase for /Users/xinxingegeya/CA/intermediate/private/intermediate.key.pem: Check that the request matches the signature Signature ok Certificate Details: Serial Number: 4096 (0x1000) Validity Not Before: Jan 3 07:45:47 2016 GMT Not After : Jan 12 07:45:47 2017 GMT Subject: countryName = CN stateOrProvinceName = Beijing localityName = Haidian organizationName = Usoft Ltd organizationalUnitName = Usoft Ltd gRPC services commonName = www.example.com emailAddress = firstname.lastname@example.org X509v3 extensions: X509v3 Basic Constraints: CA:FALSE Netscape Cert Type: SSL Server Netscape Comment: OpenSSL Generated Server Certificate X509v3 Subject Key Identifier: 98:F0:98:CC:DF:DA:FF:F5:2B:FE:B0:95:6F:E8:1F:FA:55:53:A0:45 X509v3 Authority Key Identifier: keyid:1A:29:51:6C:66:90:9D:57:8E:41:5E:19:2A:74:E1:D9:B0:8E:9D:8B DirName:/C=CN/ST=Beijing/L=Beijing/O=Usoft Ltd/OU=dev/CN=usoft.com/emailAddressemail@example.com serial:10:01 X509v3 Key Usage: critical Digital Signature, Key Encipherment X509v3 Extended Key Usage: TLS Web Server Authentication Certificate is to be certified until Jan 12 07:45:47 2017 GMT (375 days) Sign the certificate? [y/n]:y 1 out of 1 certificate requests certified, commit? [y/n]y Write out database with 1 new entries Data Base Updated
The intermediate/index.txt file should contain a line referring to this new certificate.
V 170112074547Z 1000 unknown /C=CN/ST=Beijing/L=Haidian/O=Usoft Ltd/OU=Usoft Ltd gRPC services/CN=www.example.com/emailAddressfirstname.lastname@example.org
Verify the certificate
➜ CA openssl x509 -noout -text -in intermediate/certs/www.example.com.cert.pem
The output will also show the X509v3 extensions. When creating the certificate, you used either the server_cert or usr_cert extension. The options from the corresponding configuration section will be reflected in the output.
Use the CA certificate chain file we created earlier (ca-chain.cert.pem) to verify that the new certificate has a valid chain of trust.
➜ CA openssl verify -CAfile intermediate/certs/ca-chain.cert.pem intermediate/certs/www.example.com.cert.pem intermediate/certs/www.example.com.cert.pem: OK
Deploy the certificate
You can now either deploy your new certificate to a server, or distribute the certificate to a client. When deploying to a server application (eg, Apache), you need to make the following files available:
If you’re signing a CSR from a third-party, you don’t have access to their private key so you only need to give them back the chain file (ca-chain.cert.pem) and the certificate (www.example.com.cert.pem).