Sym — Light Weight Symmetric Encryption for Humans

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Description

sym is a command line utility and a Ruby API that makes it trivial to encrypt and decrypt sensitive data. Unlike many other existing encryption tools, sym focuses on usability and streamlined interface (CLI), with the goal of making encryption easy and transparent. The result? There is no excuse for keeping your application secrets unencrypted :)

Motivation

The primary goal of this tool is to streamline and simplify handling of relatively sensitive data in the most trasparent and easy to use way as possible, without sacrificing security.

Most common use-cases include:

  • Encrypting/decrypting of application secrets, so that the encrypted secrets can be safely checked into the git repository and distributed, and yet without much of the added headache that this often requires
  • Secure message transfer between any number of receipients
  • General purpose encryption/decryption with a single encryption key, optionally itself re-encrypted with a password.

Sym is a layer built on top of the OpenSSL library, and, hopefully, makes encryption more accessible to every-day developers, QA, and dev-ops folks, engaged in deploying applications.

What's Included

This gem includes two primary components:

  • Ruby API for enabling encryption/decryption of any data within any Ruby class, with extremely easy-to-use methods
  • Rich command line interface CLI with many additional features to streamline handling of encrypted data.

Symmetric Encryption simply means that we are using the same private key to encrypt and decrypt. In addition to the private key, the encryption uses an IV vector. The library completely hides iv generation from the user, and automatically generates a random iv per encryption.

Massive Time Savers

So how does sym substantiate its claim that it streamlines the encryption process? I thought about it, and turns out there are quite a few reasons:

  • By using Mac OS-X Keychain, sym offers a simple yet secure way of storing the key on a local machine, much more secure then storing it on a file system.
  • By using a password cache (-c) via an in-memory provider such as memcached or drb, sym invocations take advantage of password cache, and only ask for a password once per a configurable time period.
  • By using SYM_ARGS environment variable, where common flags can be saved.
  • By reading a key from the default key source file ~/.sym.key which requires no flags at all.
  • By utilizing the --negate option to quickly encrypt a regular file, or decrypt an encrypted file with extension .enc.
  • By using the -t (edit) mode, that opens an encrypted file in your $EDITOR, and replaces the encrypted version upon save & exit.

As you can see, we really tried to build a tool that provides good security for application secrets, including password-based encryption, but does not annoyingly ask for password every time. With --edit option, and --negate options you can treat encrypted files like regular files.

Encrypting application secrets had never been easier! –– Socrates [LOL, -ed.]

How It Works

  1. You generate a new encryption key, that will be used to both encrypt and decrypt the data. The key is 256 bits, or 32 bytes, or 45 bytes when base64-encoded, and can be generated with sym -g.
    • You can optionally password protect the key with sym -gp
    • You can save the key into a file with sym -gpo key-file
    • Or you can save it into the OS-X Keychain, with sym -gpx keychain-name
    • You can also cache the password, with sym -gpcx keychain-name
    • Normally, sym will also print the resulting key to STDOUT.
    • You can prevent the key from being printed to STDOUT with -q/--quiet.
  2. You then take a piece of sensitive data that you want to encrypt. This can be a file or a string.
  3. You can then use the key to encrypt sensitive data, with sym -e [key-spec] [data-spec], passing it the key in several accepted ways. Smart flag -k automatically interpretes the source of the key, by trying:
    • a file with a pathname.
    • or environment variable
    • or OS-X Keychain password entry
    • or you can paste the key interactively with -i
  4. Input data can be read from a file with -f file, or read from STDIN, or a passed on the command line with -s string
  5. Output is the encrypted data, which is printed to STDOUT by the default, or it can be saved to a file with -o <file>
  6. Encrypted file can be later decrypted with sym -d [key-spec] [data-spec]

Sample session that uses Mac OS-X Keychain to store the password-protected key.

# Gen a new key, password-encrypt it, cache the password, save
# result in the key chain entry 'my-new-key' (but don't print it '-q')
❯ sym -gpqcx my-new-key
New Password     :  •••••••••
Confirm Password :  •••••••••

❯ sym -eck my-new-key -s 'My secret data' -o secret.enc
Coin::Vault listening at: druby://127.0.0.1:24924
Password: •••••••••

❯ cat secret.enc
BAhTOh1TeW06OkRhdGE6OldyYXBFefDFFD.....

❯ sym -dck my-new-key -f secret.enc
My secret data

# Now, let's save our keychain key in the default key file:
❯ sym -ck my-new-key -o ~/.sym.key
# Now we can decrypt/encrypt with this key at will
❯ sym -n secret.enc
# created a decrypted file `secret` 

# Lets now save common flags in the SYM_ARGS bash variable:
❯ export SYM_ARGS="-ck my-new-key"
❯ sym -df secret.enc 
My secret data

The line that says Coin::Vault listening at: druby://127.0.0.1:24924 is the indication that the local dRB server used for caching passwords has been started. Password caching is off by default, but is enabled with -c flag. In the example above, the decryption step fetched the password from the cache, and so the user was not required to re-enter the password.

Direct Editing Encrypted Files

Instead of decrypting data anytime you need to change it, you can use the shortcut flag -t (for "edi*t*"), which decrypts your data into a temporary file, automatically opening it with an $EDITOR.

Example:

sym -t -f config/application/secrets.yml.enc -k ~/.key

This is one of those time-saving features that can make a difference in making encryption feel easy and transparent.

For more information see the section on inline editing.

Installation

If you plan on using the library in your Ruby project with Bundler managing its dependencies, just include the following line in your Gemfile:

gem 'sym'

And then run bundle.

Or install it into the global namespace with gem install command:

$ gem install sym
$ sym -h
$ sym -E # see examples

BASH Completion

Optionally, after gem installation, you can also install bash-completion of gem's command line options, but running the following command (and feel free to use any of the "dot" files you prefer):

sym -B/--bash-support ~/.bashrc

Should you choose to install it (this part is optional), you will be able to use "tab-tab" after typing sym, and you'll be able to choose from all of the supported flags.

Using sym with the Command Line

Private Keys

The private key is the cornerstone of the symmetric encryption. Using sym, the key can be:

  • generated and printed to STDOUT, or saved to Mac OS-X KeyChain or a file
  • fetched from the Keychain in subsequent operations
  • password-protected during generation (or import) with the -p flag.
  • password can be cached using either memcached or dRB server, if the -c flag is provided.
  • must be kept very well protected and secure from attackers.

The unencrypted private key will be in the form of a base64-encoded string, 45 characters long.

Encrypted (with password) private key will be considerably longer, perhaps 200-300 characters long.

Generating Private Keys

Let's generate a new key, and copy it to the clipboard (using pbcopy command on Mac OS-X):

sym -g | pbcopy

Or save a new key into a bash variable

KEY=$(sym -g)

Or save it to a file:

sym -go ~/.key

Or create a password-protected key (-p), and save it to a file (-o), cache the password (-c), and don't print the new key to STDOUT (-q for quiet):

sym -gpcqo ~/.secret
New Password:     ••••••••••
Confirm Password: ••••••••••
Key Sources

You can subsequently use the private key by passing either of these options to the -k flag (sym attempts to resolve the key automatically, by trying each option and moving to the next until the key is found):

  1. the -k value flag, where the value is one of:
    • a file path
    • an environment variable name
    • an actual base64-encoded key (not recommended for security reasons)
    • a keychain name
  2. pasting or typing the key with the -i (interactive) flag
  3. a default key file, in your home folder, ~/.sym.key, used only when no other flags were passed in.

Using KeyChain Access on Mac OS-X

KeyChain storage is a huge time saver. It allows you to securely store the key the keychain, meaning the key can not be easily extracted by an attacker without a login to your account. Just having access to the disk is not enough.

Apple had released a security command line tool, which this library uses to securely store a key/value pair of the key name and the actual private key in your OS-X KeyChain. The advantages of this method are numerous:

  • The private key won't be lying around your file system unencrypted, so if your Mac is ever stolen, you don't need to worry about the keys running wild.
  • If you sync your keychain with the iCloud you will have access to it on other machines

As mentioned previously, to add the key to the KeyChain on the Mac, use -x <key-name> flag with -g flag when generating a key. The key name is what you call this particular key, based on how you plan to use it. For example, you may call it staging, etc.

The following command generates the private key and immediately stores it in the KeyChain access under the name provided:

sym -gx staging   # the key is passwordless
sym -gpcx staging # this key is password protected, with the password cached

Next, whenever you need to use this key, you can specify the key with -k staging.

Finally, you can delete a key from KeyChain access by running:

keychain <name> delete

Below we describe the purpose of the executable keychain shipped with sym.

KeyChain Key Management

keychain is an additional executable installed with the gem, which can be used to read (find), update (add), and delete keychain entries used by sym.

It's help message is self-explanatory:

Usage: keychain <name> [ add <contents> | find | delete ]

Moving a Key to the Keychain

You can easily move an existing key from a file or a string to a keychain by combining -k or -k to read the key, with -x to write it.

sym -k $keysource -x mykey

Adding Password to Existing Key

You can add a password to a key by combining one of the key description flags (-k, -i) and then also -p. Use -q to hide new key from the STDOUT, and c to cache the password.

sym -k $mykey -pqcx moo

The above example will take an unencrypted key passed in $mykey, ask for a password and save password protected key into the keychain with name "moo."

Password Caching

Nobody likes to re-type passwords over and over again, and for this reason Sym supports password caching via either a locally running memcached instance (the default, if available), or a locally started dRB (distributed Ruby) server based on the Coin gem.

Specifics of configuring both Cache Providers is left to the Configuration class, an example of which is shown below in the Ruby API section.

In order to control password caching, the following flags are available:

  • -c turns on caching
  • -u seconds sets the expiration for cached passwords
  • -r memcached | drb controls which of the providers is used. Without this flag, sym auto-detects caching provider by first checking for memcached, and then starting the dRB server.

Saving Common Flags in an Environment Variable

You can optionally store frequently used flags for sym in the SYM_ARGS environment variable. For example, to always cache passwords, and to always use the same encryption key from the keychain named "production", set the following in your ~/.bashrc:

export SYM_ARGS="-cx production"

This will be automatically appended to the command line if the -A/--sym-args flag is provided, and so to encrypt/decrypt anything with password caching enabled and using that particular key, you would simply type:

# -cx production are added from SYM_ARGS
sym -Aef file -o file.enc

# And to decrypt:
sym -Adf file.enc -o file.original

# Or edit the encrypted file:
sym -Atf file.enc

Complete CLI Usage

This may be a good time to take a look at the full help message for the sym tool, shown naturally with a -h or --help option.

Sym (2.5.1)

CLI Usage Examples

Generating the Key:

Generate a new private key into an environment variable:

export KEY=$(sym -g)
echo $KEY
# => 75ngenJpB6zL47/8Wo7Ne6JN1pnOsqNEcIqblItpfg4=

Generate a new password-protected key & save to a file:

sym -gpqo ~/.key
New Password     : ••••••••••
Confirm Password : ••••••••••

Encrypt a plain text string with a key, and save the output to a file:

sym -e -s "secret string" -k $KEY -o file.enc
cat file.enc
# => Y09MNDUyczU1S0UvelgrLzV0RTYxZz09CkBDMEw4Q0R0TmpnTm9md1QwNUNy%T013PT0K

Decrypt a previously encrypted string:

sym -d -s $(cat file.enc) -k $KEY
# => secret string

Encrypt a file and save it to sym.enc:

sym -e -f app-sym.yml -o app-sym.enc -k $KEY

Decrypt an encrypted file and print it to STDOUT:

sym -df app-sym.enc -k $KEY

Inline Editing

The sym CLI tool supports one particularly interesting mode, that streamlines handling of encrypted files. The mode is called edit mode, and is activated with the -t flag.

In this mode sym can decrypt the file, and open the result in an $EDITOR. Once you make any changes, and save it (exiting the editor), sym will automatically diff the new and old content, and if different – will save encrypt it and overwrite the original file.

NOTE: this mode does not seem to work with GUI editors such as Atom or TextMate. Since sym waits for the editor process to complete, GUI editors "complete" immediately upon starting a windowed application. In this mode several flags are of importance:

-b (--backup)

Here is a full command that opens a file specified by -f | --file, using the key specified in -k | --keyfile, in the editor defined by the $EDITOR environment variable (or if not set – defaults to /bin/vi)".

To edit an encrypted file in $EDITOR, while asking to paste the key (-i | --interactive), while creating a backup file (-b | --backup):

sym -tibf data.enc
# => Private Key: ••••••••••••••••••••••••••••••••••••••••••••
#
# => Diff:
# 3c3
# # (c) 2015 Konstantin Gredeskoul.  All rights reserved.
# ---
# # (c) 2016 Konstantin Gredeskoul.  All rights reserved.

Ruby API

To use this library, you must include the main Sym module into your library.

Any class including Sym will be decorated with new class methods #private_key and #create_private_key, as well as instance methods #encr, and #decr.

#create_private_key will generate a new key each time it's called, while #private_key will either assign an existing key (if a value is passed) or generate and save a new key in the class instance variable. Therefore each class including Sym will use its key (unless the key is assigned).

The following example illustrates this point:

require 'sym'

class TestClass
  include Sym
end
@key = TestClass.create_private_key
@key.eql?(TestClass.private_key)  # => false
# A new key was created and saved in #private_key accessor.

class SomeClass
  include Sym
  private_key TestClass.private_key
end

@key.eql?(SomeClass.private_key)  # => true (it was assigned)

Encryption and Decryption Operations

So how would we use this library from another Ruby project to encrypt and decrypt values?

After including the Sym module in a ruby class, the class will now have the #encr and #decr instance methods, as well as #secret and `#create_private_key class methods.

Therefore you could write something like this below, protecting a sensitive string using a class-level secret.

require 'sym'
class TestClass
  include Sym
  private_key ENV['SECRET']

  def sensitive_value=(value)
    @sensitive_value = encr(value, self.class.private_key)
  end
  def sensitive_value
    decr(@sensitive_value, self.class.private_key)
  end
end

Full Application API

Since the command line interface offers more than just encryption/decryption, it is available via Sym::Application class.

The class is instantiated with a hash that would be otherwise generated by Slop.parse(argv) – ie, typical options.

Here is an example:

require 'sym/application'

key  = Sym::Application.new(generate: true).execute
# => returns a new private key

Configuration

The library offers a typical Sym::Configuration class which can be used to tweak some of the internals of the gem. Its meant for an advanced user who knows what he or she is doing. The code snippet shown below is an actual part of the Configuration class, but you can override it by including it in your code that uses and initializes this library, right after the require. The Configuration class is a Singleton, so changes to it will propagate to any subsequent calls to the gem.

require 'zlib'
require 'sym'
Sym::Configuration.configure do |config|
  config.password_cipher          = 'AES-128-CBC'
  config.data_cipher              = 'AES-256-CBC'
  config.private_key_cipher       = config.data_cipher
  config.compression_enabled      = true
  config.compression_level        = Zlib::BEST_COMPRESSION
  config.encrypted_file_extension = 'enc'
  config.default_key_file         = "#{ENV['HOME']}/.sym.key"

  config.password_cache_timeout          = 300

  # When nil is selected, providers are auto-detected.
  config.password_cache_default_provider = nil
  config.password_cache_arguments        = {
    drb:       {
      opts: {
        uri: 'druby://127.0.0.1:24924'
      }
    },
    memcached: {
      args: %w(127.0.0.1:11211),
      opts: { namespace:  'sym',
              compress:   true,
              expires_in: config.password_cache_timeout
      }

    }
  }
end

As you can see, it's possible to change the default cipher type, although not all ciphers will be code-compatible with the current algorithm, and may require additional code changes.

Encryption Features & Cipher Used

The sym executable as well as the Ruby API provide:

  • Symmetric data encryption with:
    • the Cipher AES-256-cBC used by the US Government
    • 256-bit private key, that
      • can be generated and is a base64-encoded string about 45 characters long. The decoded key is always 32 characters (or 256 bytes) long.
      • can be optionally password-encrypted using the 128-bit key, and then be automatically detected (and password requested) when the key is used
      • can optionally have its password cached for 15 minutes locally on the machine using memcached or using a dRB server
  • Rich command line interface with some innovative features, such as inline editing of an encrypted file, using your favorite $EDITOR.
  • Data handling:
    • Automatic compression of the data upon encryption
    • Automatic base64 encryption to make all encrypted strings fit onto a single line.
    • This makes the format suitable for YAML or JSON configuration files, where only the values are encrypted.
  • Rich Ruby API
  • (OS-X Only): Ability to create, add and delete generic password entries from the Mac OS-X KeyChain, and to leverage the KeyChain to store sensitive private keys.

Development

After checking out the repo, run bin/setup to install dependencies. Then, run rake spec to run the tests. You can also run bin/console for an interactive prompt that will allow you to experiment.

To install this gem onto your local machine, run bundle exec rake install.

To release a new version, update the version number in version.rb, and then run bundle exec rake release, which will create a git tag for the version, push git commits and tags, and push the .gem file to rubygems.org.

Contributing

Bug reports and pull requests are welcome on GitHub at https://github.com/kigster/sym.

License

Sym library is © 2016-2017 Konstantin Gredeskoul.

The gem is available as open source under the terms of the MIT License.

The library is designed to be a layer on top of OpenSSL, distributed under the Apache Style license.

Acknowledgements

Konstantin Gredeskoul is the primary developer of this library. Contributions from others are strongly encouraged and very welcome. Any pull requests will be reviewed promptly.

Contributors:

  • Wissam Jarjoui (Shippo)
  • Megan Mathews
  • Barry Anderson