While Encrypting a File with a Password from the Command Line using OpenSSLis very useful in its own right, the real power of the OpenSSL library is itsability to support the use of public key cryptograph for encrypting orvalidating data in an unattended manner (where the password is not required toencrypt) is done with public keys.

The Commands to Run

Generate a 2048 bit RSA Key

Type the following command in an open terminal window on your computer to generate your private key using SSL: $ openssl genrsa -out /path/to/wwwservercom.key 2048. This will invoke OpenSSL, instruct it to generate an RSA private key using the DES3 cipher, and send it as an output to a file in the same directory where you ran the command. Jan 31, 2010  How to create a self signed ssl cert with no passphrase for your test server. Generate your key with openssl. Openssl genrsa -out server.key 1024 Output: Generating RSA private key, 1024 bit long modulus. Jul 30, 2015 An SSH key passphrase is a secondary form of security that gives you a little time when your keys are stolen. If your RSA key has a strong passphrase, it might take your attacker a few hours to guess by brute force. That extra time should be enough to log in to any computers you have an account on.

You can generate a public and private RSA key pair like this:

openssl genrsa -des3 -out private.pem 2048

That generates a 2048-bit RSA key pair, encrypts them with a password you provideand writes them to a file. You need to next extract the public key file. You willuse this, for instance, on your web server to encrypt content so that it canonly be read with the private key.

Export the RSA Public Key to a File

This is a command that is

openssl rsa -in private.pem -outform PEM -pubout -out public.pem

The -pubout flag is really important. Be sure to include it.

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Next open the public.pem and ensure that it starts with-----BEGIN PUBLIC KEY-----. This is how you know that this file is thepublic key of the pair and not a private key.

To check the file from the command line you can use the less command, like this:

less public.pem

Do Not Run This, it Exports the Private Key

A previous version of the post gave this example in error.

openssl rsa -in private.pem -out private_unencrypted.pem -outform PEM

The error is that the -pubout was dropped from the end of the command.That changes the meaning of the command from that of exporting the public keyto exporting the private key outside of its encrypted wrapper. Inspecting theoutput file, in this case private_unencrypted.pem clearly shows that the keyis a RSA private key as it starts with -----BEGIN RSA PRIVATE KEY-----.

Visually Inspect Your Key Files

It is important to visually inspect you private and public key files to makesure that they are what you expect. OpenSSL will clearly explain the nature ofthe key block with a -----BEGIN RSA PRIVATE KEY----- or -----BEGIN PUBLIC KEY-----.

Openssl Generate Rsa Key Pair Passphrase Chart

You can use less to inspect each of your two files in turn:

  • less private.pem to verify that it starts with a -----BEGIN RSA PRIVATE KEY-----
  • less public.pem to verify that it starts with a -----BEGIN PUBLIC KEY-----

The next section shows a full example of what each key file should look like.

The Generated Key Files

The generated files are base64-encoded encryption keys in plain text format.If you select a password for your private key, its file will be encrypted withyour password. Be sure to remember this password or the key pair becomes useless.

The private.pem file looks something like this:

The public key, public.pem, file looks like:

Protecting Your Keys

Depending on the nature of the information you will protect, it’s important tokeep the private key backed up and secret. The public key can be distributedanywhere or embedded in your web application scripts, such as in your PHP,Ruby, or other scripts. Again, backup your keys!

Remember, if the key goes away the data encrypted to it is gone. Keeping aprinted copy of the key material in a sealed envelope in a bank safety depositbox is a good way to protect important keys against loss due to fire or harddrive failure.

Oh, and one last thing.

If you, dear reader, were planning any funny business with the private key that I have just published here. Know that they were made especially for this series of blog posts. I do not use them for anything else.

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OpenSSL is a robust, commercial-grade, and full-featured toolkit for the Transport Layer Security (TLS) and Secure Sockets Layer (SSL) protocols. It’s useful but hard to remember so many commands, so I have listed some common usages below.

General OpenSSL Commands

  • Generate a new RSA private key

  • Generate a new ECC private key

  • Generate a new private key and Certificate Signing Request

  • Generate a self-signed certificate

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

  • Generate a multi-domain SSL certificate signing request (CSR) for an existing private key

  • Generate a certificate signing request based on an existing certificate

  • Remove a passphrase from a private key

Checking Using OpenSSL

  • Check a Certificate Signing Request (CSR)

  • Check a private key

  • Check a certificate

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

  • Check the chained certificates

Debugging Using OpenSSL

Openssl Generate Rsa Key Pair Passphrase

Openssl Generate Rsa Key Pair With Password

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

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

  • Check an SSL connection using specified CA

Converting Using OpenSSL

Openssl Generate Rsa Key Pair

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

  • Convert a PEM file to DER

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

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