HOWTO – use openssl on linux – a bunch of useful openssl commands to use

Generate CSRs, Certificates, Private Keys and do other miscellaneous tasks:

Generate a new private key and Certificate Signing Request

  • openssl req -out CSR.csr -new -newkey rsa:2048 -nodes -keyout privateKey.key


Generate a self-signed certificate

  • openssl req -x509 -sha256 -nodes -days 365 -newkey rsa:2048 -keyout privateKey.key -out certificate.crt


Generate a certificate signing request (CSR) for an existing private key

  • openssl req -out CSR.csr -key privateKey.key -new


Generate a certificate signing request based on an existing certificate

  • openssl x509 -x509toreq -in certificate.crt -out CSR.csr -signkey privateKey.key


Remove a passphrase from a private key

  • openssl rsa -in privateKey.pem -out newPrivateKey.pem

Checking Using OpenSSL:

If you need to check the information within a Certificate, CSR or Private Key, use these commands.


Check a Certificate Signing Request (CSR)

  • openssl req -text -noout -verify -in CSR.csr


Check a private key

  • openssl rsa -in privateKey.key -check


Check a certificate

  • openssl x509 -in certificate.crt -text -noout


Check a PKCS#12 file (.pfx or .p12)

  • openssl pkcs12 -info -in keyStore.p12

Debugging Using OpenSSL:
If you are receiving an error that the private doesn’t match the certificate or that a certificate that you installed to a site is not trusted, try one of these commands.


Check an MD5 hash of the public key to ensure that it matches with what is in a CSR or private key

  • openssl x509 -noout -modulus -in certificate.crt | openssl md5
  • openssl rsa -noout -modulus -in privateKey.key | openssl md5
  • openssl req -noout -modulus -in CSR.csr | openssl md5


Check an SSL connection. All the certificates (including Intermediates) should be displayed

Converting Using OpenSSL:

These commands allow you to convert certificates and keys to different formats to make them compatible with specific types of servers or software. For example, you can convert a normal PEM file that would work with Apache to a PFX (PKCS#12) file and use it with Tomcat or IIS.

Convert a DER file (.crt .cer .der) to PEM

  • openssl x509 -inform der -in certificate.cer -out certificate.pem


Convert a PEM file to DER

  • openssl x509 -outform der -in certificate.pem -out certificate.der


Convert a PKCS#12 file (.pfx .p12) containing a private key and certificates to PEM

  • openssl pkcs12 -in keyStore.pfx -out keyStore.pem -nodes


You can add -nocerts to only output the private key or add -nokeys to only output the certificates.
Convert a PEM certificate file and a private key to PKCS#12 (.pfx .p12)

  • openssl pkcs12 -export -out certificate.pfx -inkey privateKey.key -in certificate.crt -certfile CACert.crt

Published by

Ronny Van den Broeck

I'm a network and system engineer for more than 20 years now. During this period I became a pro in hunting down one's and zero's, with an eager mindset to help people accomplish the same or abstract them away from the matrix.

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