How to use OpenSSL?

OpenSSL is the true Swiss Army knife of certificate management, and just like with the real McCoy, you spend more time extracting the nail file when what you really want is the inflatable hacksaw. You'll find an overview of the most commonly used commands below.

Certificate requests and key generation

Typically, when you ordered a new SSL certificate you must generate a CSR or certificate signing request, with a new private key:

openssl req -sha256 -nodes -newkey rsa:2048 -keyout www.server.com.key -out www.server.com.csr

Alternatively, use the Kinamo CSR Generator for easy CSR creation.

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

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 -keyout www.server.com.key -out www.server.com.crt -days 365

View and verify certificates

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

openssl x509 -noout -modulus -in www.server.com.crt | openssl sha256
openssl req -noout -modulus -in www.server.com.csr | openssl sha256
openssl rsa -noout -modulus -in 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

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

Checking SSL Connections

This will output the website's certificate, including any intermediate certificates

openssl s_client -connect https://www.server.com:443