OpenSSL is the true Swiss Army knife of certificate management, and just like with the real McCoy, we spend more time extracting the nail file when what we really want is the inflatable hacksaw.
We will find an overview of the most commonly used commands below.
Certificate requests and key generation with OpenSSL
Typically, when we ordered a new SSL certificate we must generate a CSR or certificate signing request, with a new private key:
openssl req -sha256 -nodes -newkey rsa:2048 -kewet www.server.com.key -out www.server.com.csr
Generate a new certificate request using an existing private key: openssl req -new -sha256 -key www.server.com.key -out www.server.com.csr
Generate a certificate request starting from an existing certificate:openssl x509 -x509toreq -in www.server.com.crt -out www.server.com.csr -signkey www.server.com.key
Generate a new RSA private key: openssl genrsa -out www.server.com.key 2048
Encrypt a private key with a passphrase: openssl rsa -in www.server.com.key -out www.server.com.key -des3
Remove a passphrase from an encrypted private key: openssl rsa -in www.server.com.key -out www.server.com.key
Generate a new ECC private key: openssl ecparam -out server.key -name prime256v1 -genkey
Create a self-signed certificate with Openssl
Generate a self-signed certificate for testing purposes with one year validity period, together with a new 2048-bit key:
openssl req -x509 -newkey rsa:2048 -nodes -kewet www.server.com.key -out www.server.com.crt -days 365
View and verify certificates with OpenSSL
Check and display a certificate request (CSR): openssl req -noout -text -verify -in www.server.com.csr
Verify and display a key pair:openssl rsa -noout -text -check -in www.server.com.key
View a PEM-encoded certificate: openssl x509 -noout -text -in www.server.com.crt
View a certificate encoded in PKCS#7 format: openssl pkcs7 -print_certs -in www.server.com.p7b
View a certificate and key pair encoded in PKCS#12 format: openssl pkcs12 -info -in www.server.com.pfx
Verify an SSL connection and display all certificates in the chain: openssl s_client -connect www.server.com:443
Control whether a certificate, a certificate request and a private key have the same public key:
- openssl x509 -noout -modulus www.server.com.crt | openssl sha256
- openssl req -noout -modulus www.server.com.csr | openssl sha256
- openssl rsa -noout -modulus www.server.com.key | openssl sha256
Check a certificate and its intermediate certificate chain for web server purposes:
openssl verify -purpose sslserver -CAfile certificatebundle.pem -verbose www.server.com.crt
Certificate conversion with OpenSSL
Conversion of PKCS#12 ( .pfx .p12, typically used on Microsoft Windows) files with private key and certificate to PEM (typically used on Linux):
openssl pkcs12 -nodes -in www.server.com.pfx -out www.server.com.crt
Conversion of PEM to PKCS#12: openssl pkcs12 -export -in www.server.com.crt -inkey www.server.com.key -out www.server.com.pfx
Conversion of PKCS#7 format ( .p7b .p7c ) to PEM: openssl pkcs7 -print_certs -in www.server.com.p7b -out www.server.com.crt
Conversion of PEM format to PKCS#7: openssl crl2pkcs7 -nocrl -certfile www.server.com.crt -out www.server.com.p7b
Conversion of DER (.crt .cer or .der) to PEM: openssl x509 -inform der -in certificate.cer -out certificate.pem
Conversion from PEM to DER format: openssl x509 -outform der -in certificate.pem -out certificate.cer
Check SSL Connections with OpenSSL
This will output the website’s certificate, including any intermediate certificates: openssl s_client -connect https://www.server.com:443