Skip to content

OpenSSL is an open source software system that provides the following:

  • Forensic-grade implementations of the most widely used hash functions.
  • Symmetric cryptographic functions
  • Asymmetric cryptographic function
  • Certificate management functions
  • A complete S/MIME implementation
  • A complete SSL/TLS implementation

OpenSSL is interesting for forensic practitioners and developers because it provides a basic toolkit for building software, and because the higher-level certificate management functions give you an easy way to decode the contents of certificates that are used to secure computer systems.

This web page contains step-by-step instructions on using OpenSSL from the command line to perform specific tasks. There are a lot of online OpenSSL guides and we'll try to link to some of them from here. But this page is a handy reference just the same.

File Extensions

OpenSSL doesn't care what you use for file extensions. However, the following extensions to seem to be commonly used:

File Extension Meaning
.pem can contain a private key, public key, or certificate signing request.
.crt Windows file extension for a .pem file.
.p12 a PKCS12 file, which contains a private key and a certificate, encrypted for transport with a passphrase. This is the format that Windows and MacOS like to import


  • convert pem to pkcs12:

% openssl pkcs12 -export -in mpage.crt -inkey mpage.key -out mpage.p12 -name 'MPage Signing Key'

  • convert pkcs12 to pem, putting both private key and certificate in the same file

% openssl pkcs12 -in mpage.p12 -out mpage.pem

  • The same, but with no encryption of file

% openssl pkcs12 -in mpage.p12 -out mpage.pem -nodes

  • Decrypt a PEM file private key:

% openssl rsa -in newreq.pem -out key.pem

  • Print the contents of a certificate

% openssl x509 -in mpage.pem -text

  • Input the PKCS12 file and output a key file and a cert file:

openssl pkcs12 -in slg.p12 -out slg.key -nocerts -nodes openssl pkcs12 -in slg.p12 -out slg.pem -nokeys -nodes

Making Certificates

To make certificates all in one step:

openssl req -new -x509 -nodes -out imapd.pem -keyout imapd.pem -days 3650

Make a certificate request for a CA to sign:

openssl req -newkey rsa:1024 -keyout mycert.key -out mycert.csr -nodes

To make an RSA key and then use the key to make the certificate signing request:

openssl genrsa -out myfile.key 1024 openssl req -new -key myfile.key -out myfile.csr

Get a certificate from an SSL server

openssl s_client -connect

Viewing Certificates

openssl x509 -in ssl.crt-text


  • to sign an outgoing mail:

from_email = `openssl x509 -email -in certfile.pem -noout` x509_subject = `openssl x509 -subject -in certfile.pem -noout` openssl smime -from %s  -to %s  -subject %s -sign -inkey file -signer %s -in tempfile.txt extra

See Also