OpenSSL command to include "basicConstraints" extension - ssl

Question

A certificate is generated using the following openssl command :
openssl req -new -x509 -keyout server.key.pem -out server.crt.pem -config /etc/ssl/openssl.cnf -extensions cust_const
The corresponding CSR is generated using the command:
openssl x509 -x509toreq -in server.crt.pem -signkey server.key.pem -out server.csr -extensions cust_const
The conf file (openssl.cnf) has the below mentioned entry.
[ cust_const ]
basicConstraints = CA:FALSE
The problem is that the generated CSR doesn't include basicConstraints extension.
How can basicConstraints be included into the CSR when we already have a certificate with basicConstraints in it?

Answer 1

when you want to create a CSR to be signed by other CA he will "make" you CA as well ( e.g. root will sign intermediate as CA with depthLen=1 , where intermediate will sign endPoint as CA=FALSE ... )
first you need to understand what do you want to do (root / intermediate / Endpoint)
if you are root create extensions file (look for openssl default for help...)
below short list command to help you get started :
create root ca certificate
openssl genrsa -des3 -out rootca.key 2048
openssl rsa -in rootca.key -out rootca.key.insecure
openssl req -key rootca.key.insecure -new -x509 -days 3650 -extensions v3_ca -out rootca.crt
openssl x509 -text -in rootca.crt
NOTE:
it uses the default extensions file: /usr/lib/ssl/openssl.cnf (or /etc/ssl/openssl.cnf)
create intermediate certificate
openssl genrsa -des3 -out intermediate.key 2048
openssl rsa -in intermediate.key -out intermediate.key.insecure
openssl req -new -key intermediate.key.insecure -out intermediate.csr
NOTE: you might need these commands before the next command 'openssl ca'.
mkdir demoCA
touch demoCA/index.txt
echo 1122334455667788 > demoCA/serial
openssl ca -extensions v3_ca -days 3650 -outdir . -batch -cert rootca.crt -keyfile rootca.key.insecure -in intermediate.csr -out intermediate.crt
NOTE: after run 'openssl ca' you can remove the demoCA folder
rm -rf demoCA
openssl x509 -text -in intermediate.crt
openssl verify -CAfile rootca.crt intermediate.crt
create server/client certificate
openssl genrsa -des3 -out server.key 2048
openssl rsa -in server.key -out server.key.insecure
openssl req -new -key server.key.insecure -out server.csr
openssl x509 -req -days 3650 -CAcreateserial -CA intermediate.crt -CAkey intermediate.key.insecure -in server.csr -out server.crt
openssl x509 -text -in server.crt