Most Common OpenSSL Commands

One of the most versatile SSL tools (the default toolkit installed in Linux distributions) is OpenSSL which is an open source implementation of the SSL protocol. OpenSSL is commonly used to create the CSR and private key for many different platforms.

OpenSSL has hundreds of different functions to, for example, view the details of a CSR or certificate, compare an MD5 hash of the certificate and private key (to ensure they match), convert the certificate to a different format and so on.

Here the most common OpenSSL commands and their synthetic usage.

 

General OpenSSL Commands
 
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 (see How to Create and Install an Apache Self Signed Certificate for more info)

openssl req -x509 -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

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

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

openssl s_client -connect blog.bravi.org:443

 

Converting Using OpenSSL

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

Add option -nocerts to only output the private key or -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

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