OpenSSL is a powerful Linux command for managing certificates. These are some common operations I frequently use.
Generate RSA Key Pair
This command generates a 2048 bits private key.
openssl genrsa -out example.key 2048
Verify private and public key by comparing the output of the following 2 commands.
ssh-keygen -yef id_rsa ssh-keygen -yef id_rsa.pub
Generate Certificate Signing Request (CSR) With Existing Key
CSR is generated from existing private key. Make sure you keep your private key well.
openssl req -out example.csr -key example.key -new
Generate New Key And Certificate Signing Request (CSR)
Generate a new private key and new CSR using that key.
openssl req -new -newkey rsa:2048 -nodes -keyout example.key -out example.csr
Check Certificate Signing Request (CSR) Info
openssl req -in example.csr -noout -text
Generate Self-signed SSL Cert
Both private key and CSR are needed to generate SSL cert. Choose an appropriate expiry date for your cert.
openssl x509 -req -days 3650 -in example.csr -signkey example.key -out example.crt
Generate PKCS12 Cert From PEM Cert And Private Key
Note that the CA bundle file is needed for the
certfile switch is optional.
openssl pkcs12 -export -out example.pfx -inkey example.key -in example.crt -certfile CACert.crt
Generate PKCS7 Cert To PEM Cert
openssl pkcs7 -print_certs -in certificate.p7b -out certificate.pem
Check Cert Information
This is referring to x509 certs, which is used by Apache for SSL.
openssl x509 -in example.crt -text
View a certificate encoded in PKCS#7 format
openssl pkcs7 -print_certs -in example.p7b
View a certificate and key pair encoded in PKCS#12 format
openssl pkcs12 -info -in example.pfx
RSA private key is used to generate CSR and cert. Verification can be performed by matching modulus that is embedded in key, CSR, and cert.
Get hashed modulus of key
openssl rsa -in example.key -noout -modulus | md5sum
"unable to load private key" Issue
If you are getting "unable to load private key" issue, and the first line in key file is
-----BEGIN OPENSSH PRIVATE KEY----- instead of
-----BEGIN RSA PRIVATE KEY-----, there is a workaround. Use the following command to convert it to regular REM format.
ssh-keygen -p -m PEM -f example.key
Get hashed modulus of CSR
openssl req -in example.csr -noout -modulus | md5sum
Get hashed modulus of cert
openssl x509 -in example.crt -noout -modulus | md5sum