How to do it...

Let's see how to use tools such as crypt, gpg, and base64:

The crypt command is not commonly installed on Linux systems. It's a simple and relatively insecure cryptographic utility that accepts input from stdin, requests a passphrase, and sends encrypted output to stdout:

        $ crypt <input_file >output_file
        Enter passphrase:

We can provide a passphrase on the command line:

        $ crypt PASSPHRASE <input_file >encrypted_file

In order to decrypt the file, use this:

        $ crypt PASSPHRASE -d <encrypted_file >output_file

gpg (GNU privacy guard) is a widely used tool for protecting files to ensure that data is not read until it reaches its intended destination.

gpg signatures are also widely used in e-mail communications to "sign" e-mail messages, proving the authenticity of the sender.

In order to encrypt a file with gpg, use this:

          $ gpg -c filename

This command reads the passphrase interactively and generates filename.gpg. In order to decrypt a gpg file, use the following command:

          $ gpg filename.gpg

This command reads a passphrase and decrypts the file.

We are not covering gpg in much detail in this book. For more information, refer to http://en.wikipedia.org/wiki/GNU_Privacy_Guard.

Base64 is a group of similar encoding schemes that represent binary data in an ASCII string format by translating it into a radix-64 representation. These programs are used to transmit binary data via e-mail. The base64 command encodes and decodes the Base64 string. To encode a binary file into the Base64 format, use this:

        $ base64 filename > outputfile

Alternatively, use this command:

        $ cat file | base64 > outputfile

It can read from stdin.

Decode Base64 data as follows:

        $ base64 -d file > outputfile

Alternatively, use this:

        $ cat base64_file | base64 -d > outputfile