Simple Root CA and Intermediate CA

The following example shows how to use OpenSSL to create a self singed root certificate for a root certificate authority (CA). Use the root certificate to create a certificate for an intermediate CA and finally issue a server certificate.

danger

The OpenSSL commands and configurations are examples to demonstrate the possibility of using OpenSSL in combination with a Securosys HSM for PKI applications. Some of the tools are not considered to have "production quality" by OpenSSL itself:

This command was originally meant as an example of how to do things in a CA. Its code does not have production quality. It was not supposed to be used as a full blown CA itself -- openssl-ca man page

Preparation

1. Create the directories and initial files

   mkdir -p myCA/{rootCA,intermediateCA}/{certs,crl,newcerts,private,csr}
   
   touch myCA/rootCA/index.txt
   echo 1000 > myCA/rootCA/serial
   echo 1000 > myCA/rootCA/crlnumber
   
   touch myCA/intermediateCA/index.txt
   echo 1000 > myCA/intermediateCA/serial
   echo 1000 > myCA/intermediateCA/crlnumber

2. Download the configuration for the root CA openssl_root.cnf, and the intermediate CA openssl_intermediate.cnf. These two configurations specify constraints, policies and extensions that are applied to the certificates they create and sign.

Root CA certificate

1. Create a key.

   openssl genpkey -propquery "provider=pkcs11" \
       -algorithm rsa -pkeyopt rsa_keygen_bits:4096 \
       -pkeyopt pkcs11_uri:"pkcs11:object=MyRootCA"
   note

   If your pkcs11-provider is configured to access to multiple partitions on the HSM the pkcs11-uris used in these examples are ambiguous. Additionally specify the partition by adding the token attribute to the URI. E.g.: Use pkcs11:object=MyRootCA;token=<USER_PARTITION_NAME> instead of pkcs11:object=MyRootCA.

2. Create a self-signed certificate. The v3_ca extensions defined in the openssl_root.cnf configuration are applied which enable the "CA:true" property.

   openssl req -config openssl_root.cnf \
       -key "pkcs11:object=MyRootCA" \
       -new -x509 -days 7300 -sha256 -extensions v3_ca \
       -out myCA/rootCA/certs/ca.cert.pem \
       -subj "/C=CH/ST=Zurich/L=Zurich/O=My Example Organisation/OU=IT Department/CN=Root CA"

Intermediate CA certificate

1. Create a key.

   openssl genpkey -propquery "provider=pkcs11" \
       -algorithm rsa -pkeyopt rsa_keygen_bits:4096 \
       -pkeyopt pkcs11_uri:"pkcs11:object=MyIntermediateCA"

2. Create a certificate signing request (CSR).

   openssl req -config openssl_intermediate.cnf \
       -key "pkcs11:object=MyIntermediateCA" \
       -new -sha256 \
       -out myCA/intermediateCA/certs/intermediate.csr.pem \
       -subj "/C=CH/ST=Zurich/L=Zurich/O=My Example Organisation/OU=IT Department/CN=Intermediate CA"

3. As root CA, sign the CSR for the intermediate CA with the root CA key.The v3_intermediate_ca extensions defined in the openssl_root.cnf configuration are applied.

   openssl ca -batch -config openssl_root.cnf \
       -keyfile "pkcs11:object=MyRootCA" \
       -extensions v3_intermediate_ca -days 750 -notext -md sha256 \
       -in myCA/intermediateCA/certs/intermediate.csr.pem \
       -out myCA/intermediateCA/certs/intermediate.cert.pem

4. Verify the signature on the intermediate certificate

   openssl verify -CAfile myCA/rootCA/certs/ca.cert.pem \
       myCA/intermediateCA/certs/intermediate.cert.pem

Server certificate

1. Create a key.

   openssl genpkey -propquery "provider=pkcs11" \
       -algorithm rsa -pkeyopt rsa_keygen_bits:4096 \
       -pkeyopt pkcs11_uri:"pkcs11:object=server-www.example.com"

2. Create a certificate signing request (CSR).

   openssl req -copy_extensions=copyall \
       -key "pkcs11:object=server-www.example.com" \
       -new -sha256 \
       -out server-www.example.com.csr.pem \
       -subj "/C=CH/ST=Bern/L=Bern/O=My Example Organisation/OU=IT Department/CN=www.example.com" \
       -addext "subjectAltName = DNS:www.example.com, DNS:*.www.example.com"

3. As intermediate CA, sign the server CSR with the intermediate CA key.

   openssl ca -batch -config openssl_intermediate.cnf \
       -extensions v3_server_cert \
       -keyfile "pkcs11:object=MyIntermediateCA" \
       -days 40 -notext -md sha256 \
       -in server-www.example.com.csr.pem \
       -out server-www.example.com.cert.pem

4. Verify the certificate by checking the signatures using OpenSSL.

   cat myCA/intermediateCA/certs/intermediate.cert.pem \
       myCA/rootCA/certs/ca.cert.pem \
       > chain.pem
   
   openssl verify -show_chain \
       -trusted myCA/rootCA/certs/ca.cert.pem \
       --untrusted chain.pem \
       server-www.example.com.cert.pem

   Additionally test the certificate by starting a https server

   openssl s_server \
       -cert server-www.example.com.cert.pem \
       -key 'pkcs11:object=server-www.example.com' \
       -chainCAfile chain.pem -naccept +1

   and connecting to it

   curl -v --cacert myCA/rootCA/certs/ca.cert.pem \
       --connect-to www.example.com:443:localhost:4433 \
       https://www.example.com