This guide will demonstrate the steps required to encrypt and decrypt files using OpenSSL on Mac OS X. The working assumption is that by demonstrating how to encrypt a file with your own public key, you'll also be able to encrypt a file you plan to send to somebody else using their private key, though you may wish to use this approach to keep archived data safe from prying eyes.
Jun 22, 2012 The private key (identification) is now located in /home/ demo /.ssh/idrsa. Step Three—Copy the Public Key. Once the key pair is generated, it’s time to place the public key on the server that we want to use. You can copy the public key into the new machine’s authorizedkeys file with the ssh-copy-id command.
Assuming you've already done the setup described later in this document, that id_rsa.pub.pcks8 is the public key you want to use, that id_rsa is the private key the recipient will use, and secret.txt is the data you want to transmit…
OpenSSL makes it easy to encrypt/decrypt files using a passphrase. Unfortunately, pass phrases are usually 'terrible' and difficult to manage and distribute securely.
You can add -base64 if you expect the context of the text may be subject to being 'visible' to people (e.g., you're printing the message on a pbulic forum). If you do, you'll need to add it to the decoding step as well. You can choose from several cypers but aes-256-cbc is reasonably fast, strong, and widely supported. Base64 will increase the size of the encrypted file by approximately 30%
You will need to provide the same password used to encrypt the file. All that changes between the encrypt and decrypt phases is the input/output file and the addition of the -d flag. If you pass an incorrect password or cypher then an error will be displayed.
RSA encryption can only work with very short sections of data (e.g. an SHA1 hash of a file, or a password) and cannot be used to encrypt a large file. The solution is to generate a strong random password, use that password to encrypt the file with AES-256 in CBC mode (as above), then encrypt that password with a public RSA key. The encrypted password will only decrypt with a matching public key, and the encrypted file will require the unique password encrypted in the by the RSA key.
The copy of OpenSSL bundled with Mac OS X has several issues. Mac OS X 10.7 and earlier are not PCI compliant. It is best to replace it. See here for details: http://www.dctrwatson.com/2013/07/how-to-update-openssh-on-mac-os-x/
By default your private key will be stored in
The default format of id_rsa.pub isn't particularly friendly. If you are going to public your key (for example) on your website so that other people can verify the authorship of files attributed to you then you'll want to distribute it in another format. I find it useful to keep a copy in my .ssh folder so I don't have to re-generate it, but you can store it anywhere you like.
The passwords used to encrypt files should be reasonably long 32+ characters, random, and never used twice. To do this we'll generate a random password which we will use to encrypt the file.
This will generate 192 bytes of random data which we will use as a key. If you think a person may need to view the contents of the key (e.g., they're going to display it on a terminal or copy/paste it between computers) then you should consider base-64 encoding it, however:
There is a limit to the maximum length of a message that can be encrypted using RSA public key encryption. If you want to use very long keys then you'll have to split it into several short messages, encrypt them independently, and then concatinate them into a single long string. Decrypting the password will require reversing the technique: splitting the file into smaller chuncks, decrypting them independently, and then concatinating those into the original password key file.
Now that you have a good random password, you can use that to AES encrypt a file as seen in the 'with passwords' section
Decrypting the file works the same way as the 'with passwords' section, except you'll have to pass the key.
We used fast symetric encryption with a very strong password to encrypt the file to avoid limitations in how we can use asymetric encryption. Finally, we'll use asymetric encryption to encrypt the password. This solves the problem of 'how do I safely transmit the password for the encrypted file' problem. You can encrypt is using the recipients public key and they can decode it using their private key. Encrypt the password using a public key:
The recipient can decode the password using a matching private key:
There are a number of ways to do this step, but typically you'll want just a single file you can send to the recipent to make transfer less of a pain. I'd recommend just making a tarball and delivering it through normal methods (email, sftp, dropbox, whatever). Though a secure method of exchange is obviously preferable, if you have to make the data public it should still be resistent to attempts to recover the information.
The file can be extracted in the usual way:
You may want to securely delete the unecrypted keyfile as the recipient will be able to decode it using their private key and you already have the unencrypted data.
Last updated 29 February 2012.
This will step you through the process of generating a SSH keypair on Mac OS X. Begin by opening your Terminal, generally found in the 'Utilities' subdirectory of your 'Applications' directory.
Before you generate your keypair, come up with a passphrase. The rules for good passwords also apply here: mix of upper and lower case, numbers, spaces and punctuation. Limit it to less than 31 characters.
Now, generate your keypair! Enter the following:
$ ssh-keygen -t rsa -C '[email protected]'
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Note: Do not type the dollar sign above; it is an example of the default command prompt shown by Mac OS X. Your actual prompt may be different. In the example above and below, the actual part you should type is the part that follows the dollar sign.
Your terminal should respond:
Press Return to accept the default value. Your terminal should respond:
Enter passphrase (empty for no passphrase):
Enter the passphrase you decided on above. The response will be:
Enter same passphrase again:
Enter the passphrase again and press Return. The program will think a bit, and respond with something like this. Note that many of the details in the example below are just for example purposes; much of the actual output you see will differ from the below.
You can use the pbcopy
utility to easily insert your public key (or other text files) into your Mac's clipboard so that you can add it to your Drupal.org profile, GitHub, or other places. The filename should be yourfilename.pub
- with yourfilename being the filename you entered when you first created this file. If you just hit enter, the default is id_rsa.pub
.
$ pbcopy < ~/.ssh/id_rsa.pub
You won't see any output in the terminal, but the contents of your public key will now be in your clipboard and can be easily pasted anywhere where you can normally paste text.
In case you're curious, the pbpaste
utility works the other way, allowing you to easily grab the contents of the clipboard for use in the terminal. For example, the following command will write the contents of the clipboard to a file:
$ pbpaste > ~/clipboard.text