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 :)
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Sym — Light Weight Symmetric Encryption for Humans

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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 :)


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.

How It Works

  1. You start with a piece of sensitive data you want to protect. This can be a file or a string.
  2. 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 sym -gp -o key-file
    • Or you can save it into the OS-X Keychain, with sym -gp -x keychain-name
    • or you can print it to STDOUT, which is the default.
  3. You can then use the key to encrypt sensitive data, with sym -e [key-option] [data-option], passing it the key in several accepted ways:
    • You can pass the key as a string (not recommended) via -k key
    • Or read the key from a file -K key-file
    • Or read the key from the OS-X Keychain with -x keychain-name
    • 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-option] [data-option]

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

❯ sym -gpx my-new-key
New Password     :  •••••••••
Confirm Password :  •••••••••

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

❯ cat secret.enc

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

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

The line that says Coin::Vault listening at: druby:// 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 "edit"), which decrypts your data into a temporary file, automatically opening it with an $EDITOR.


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.


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 --bash-completion ~/.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 -g -o ~/.key
sym -go ~/.key

Or create a password-protected key (-p), and save it to a file (-o), and skip printing the new key to STDOUT (-q for quiet):

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

You can subsequently use the private key by passing either:

  1. the -k key-string flag
  2. the -K key-file flag
  3. the -x key-keychain-name flag to read the key from Mac OS-X KeyChain
  4. pasting or typing the key with the -i (interactive) flag

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

To activate the KeyChain mode on the Mac, use -x <key-name> field instead of -k or -K, and add it to -g 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 -g -x staging

Now, whenever you need to encrypt something you can specify the key with -x 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 $mykey -x mykey

Adding Password to Existing Key

You can add a password to a key by combining one of the key description flags (-k, -K, -i) and then also -p.

sym -k $mykey -p -x 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
  • -T seconds sets the expiration for cached passwords
  • -P 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="-x production -C"

This will always be appended to the command line, and so to encrypt/decrypt anything with password caching enabled and using that particular key, you would simply type:

# -x production -C are added from SYM_ARGS
sym -ef file -o file.enc

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

# Or edit the encrypted file:
sym -tf 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 (2.2.1) – encrypt/decrypt data with a private key

   # Generate a new key...
   sym -g [ -p ] [ -x keychain | -o keyfile | -q | ]  

   # To specify a key for an operation use one of...
   <key-spec> = -k key | -K file | -x keychain | -i 

   # Encrypt/Decrypt to STDOUT or an output file 
   sym -e <key-spec> [-f <file> | -s <string>] [-o <file>] 
   sym -d <key-spec> [-f <file> | -s <string>] [-o <file>] 

   # Edit an encrypted file in $EDITOR 
   sym -t <key-spec>  -f <file> [ -b ]

   # Specify any common flags in the BASH variable:
   export SYM_ARGS="-x staging -C"

   # And now encrypt without having to specify key location:
   sym -e -f <file>
   # May need to disable SYM_ARGS with -M, eg for help:
   sym -h -M 

  -e, --encrypt                     encrypt mode
  -d, --decrypt                     decrypt mode
  -t, --edit                        edit encrypted file in an $EDITOR

Create a new private key:
  -g, --generate                    generate a new private key
  -p, --password                    encrypt the key with a password

Read existing private key from:
  -k, --private-key      [key]      private key (or key file)
  -K, --keyfile          [key-file] private key from a file
  -x, --keychain         [key-name] add to (or read from) the OS-X Keychain
  -i, --interactive                 Paste or type the key interactively

Password Cache:
  -C, --cache-password              enable the cache (off by default)
  -T, --cache-for        [seconds]  to cache the password for
  -P, --cache-provider   [provider] type of cache, one of memcached, drb

Data to Encrypt/Decrypt:
  -s, --string           [string]   specify a string to encrypt/decrypt
  -f, --file             [file]     filename to read from
  -o, --output           [file]     filename to write to

  -b, --backup                      create a backup file in the edit mode
  -v, --verbose                     show additional information
  -A, --trace                       print a backtrace of any errors
  -D, --debug                       print debugging information
  -q, --quiet                       do not print to STDOUT
  -V, --version                     print library version
  -N, --no-color                    disable color output
  -M, --no-environment              disable reading flags from SYM_ARGS

  -a, --bash-completion  [file]     append shell completion to a file

Help & Examples:
  -E, --examples                    show several examples
  -h, --help                        show help

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)   – will create a backup of the original file
-v (--verbose) - will show additional info about file sizes

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
@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

@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)
  def sensitive_value
    decr(@sensitive_value, self.class.private_key)

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  = true).execute
# => returns a new private key


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.private_key_cipher  = config.data_cipher
  config.compression_enabled = true
  config.compression_level   = Zlib::BEST_COMPRESSION

  config.password_cache_timeout = 300
  config.password_cache_arguments        = {
    drb:       {
      opts: {
        uri: 'druby://'
    memcached: {
      args: %w(,
      opts: { namespace:  'sym',
              compress:   true,
              expires_in: config.password_cache_timeout


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.


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


Bug reports and pull requests are welcome on GitHub at


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.


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.


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