OpenSSL is a software library for applications that secure communications over computer networks against eavesdropping or need to identify the party at the other end. It is widely used by Internet servers, including the majority of HTTPS websites.
OpenSSL contains an open-source implementation of the SSL and TLS protocols. The core library, written in the C programming language, implements basic cryptographic functions and provides various utility functions. Wrappers allowing the use of the OpenSSL library in a variety of computer languages are available.
General OpenSSL Commands
These commands allow you to generate CSRs, Certificates, Private Keys, and do other miscellaneous tasks.
- Generate a new private key and Certificate Signing Request (CSR):
$ 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 (
$ openssl pkcs12 -info -in keyStore.p12
Debugging Using OpenSSL
If you are receiving an error that the private key does not 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:
$ openssl s_client -connect www.paypal.com:443 #~OR~ $ openssl s_client -showcerts -connect www.example.com:443
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 (
$ openssl pkcs12 -export -out certificate.pfx -inkey privateKey.key -in certificate.crt -certfile CACert.crt