GPGME

This README is better viewed through the YARD formatted documentation: www.rubydoc.info/github/ueno/ruby-gpgme for latest github version, or www.rubydoc.info/gems/gpgme for latest gem release.

Requirements

Ruby 1.8 or later
GPGME 1.1.2 or later
gpg-agent (optional, but recommended)

Installation

$ gem install gpgme

API

GPGME provides three levels of API. The highest level API is as simple as it gets, the mid level API provides more functionality but might be less user-friendly, and the lowest level API is close to the C interface of GPGME.

The highest level API

For example, to create a cleartext signature of the plaintext from stdin and write the result to stdout can be written as follows.

crypto = GPGME::Crypto.new
crypto.clearsign $stdin, :output => $stdout

The mid level API

The same example can be rewritten in the mid level API as follows.

plain = GPGME::Data.new($stdin)
sig   = GPGME::Data.new($stdout)
GPGME::Ctx.new do |ctx|
  ctx.sign(plain, sig, GPGME::SIG_MODE_CLEAR)
end

The lowest level API

The same example can be rewritten in the lowest level API as follows.

ret = []
GPGME::gpgme_new(ret)
ctx = ret.shift
GPGME::gpgme_data_new_from_fd(ret, 0)
plain = ret.shift
GPGME::gpgme_data_new_from_fd(ret, 1)
sig = ret.shift
GPGME::gpgme_op_sign(ctx, plain, sig, GPGME::SIG_MODE_CLEAR)

As you see, it’s much harder to write a program in this API than the highest level API. However, if you are already familiar with the C interface of GPGME and want to control detailed behavior of GPGME, it might be useful.

Usage

All the high level methods attack the mid level GPGME::Ctx API. It is recommended to read through the GPGME::Ctx.new methods for common options.

Also, most of the input/output is done via GPGME::Data objects that create a common interface for reading/writing to normal strings, or other common objects like files. Read the GPGME::Data documentation to understand how it works. Every time the lib needs a GPGME::Data object, it will be automatically converted to it.

Crypto

The GPGME::Crypto class has the high level convenience methods to encrypt, decrypt, sign and verify signatures. Here are some examples, but it is recommended to read through the GPGME::Crypto class to see all the options.

Document encryption via GPGME::Crypto#encrypt:

crypto = GPGME::Crypto.new
crypto.encrypt "Hello world!", :recipients => "[email protected]"

Symmetric encryption:

crypto = GPGME::Crypto.new :password => "gpgme"
crypto.encrypt "Hello world!", :symmetric => true

Document decryption via GPGME::Crypto#decrypt (including signature verification):

crypto.decrypt File.open("text.gpg")

Document signing via GPGME::Crypto#sign. Also the clearsigning and detached signing.

crypto.sign "I hereby proclaim Github the beneficiary of all my money when I die"

Sign verification via GPGME::Crypto#verify

sign = crypto.sign "Some text"
data = crypto.verify(sign) { |signature| signature.valid? }

Key

The GPGME::Key object represents a key, and has the high level related methods to work with them and find them, export, import, deletetion and creation.

Key listing

GPGME::Key.find(:secret, "[email protected]")
# => Returns an array with all the secret keys available in the keychain.
#    that match "[email protected]"

Key exporting

GPGME::Key.export("[email protected]")
# => Returns a GPGME::Data object with the exported key.

key = GPGME::Key.find(:secret, "[email protected]").first
key.export
# => Returns a GPGME::Data object with the exported key.

Key importing

GPGME::Key.import(File.open("my.key"))

Key validation

GPGME::Key.valid?(public_key)
# => Returns wheter this key is valid or not

TODO: Key generation

Engine

Provides three convenience methods to obtain information about the gpg engine one is currently using. For example:

Getting current information

GPGME::Engine.info.first
     # => #<GPGME::EngineInfo:0x00000100d4fbd8
            @file_name="/usr/local/bin/gpg",
            @protocol=0,
            @req_version="1.3.0",
            @version="1.4.11">

Changing home directory to work with different settings:

GPGME::Engine.home_dir = '/tmp'

Round trip example using keychain keys

Rather than importing the keys it’s possible to specify the recipient when performing crypto functions. Here’s a roundtrip example, and note that as this is for a console, the conf.echo = false line is to stop IRB complaining when echoing binary data

# Stop IRB echoing everything, which errors with binary data.
# Not required for production code
conf.echo = false

class PassphraseCallback
  def initialize(passphrase)
    @passphrase = passphrase
  end

  def call(*args)
    fd = args.last
    io = IO.for_fd(fd, 'w')
    io.puts(@passphrase)
    io.flush
  end
end

# recipients can be found using $ gpg --list-keys --homedir ./keychain_location
# pub   2048R/A1B2C3D4 2014-01-17
# Use that line to substitute your own. 2048R is the key length and type (RSA in this case)

# If you want to substitute a non-default keychain into the engine do this:
# home_dir = Rails.root.join('keychain_location').to_s
# GPGME::Engine.set_info(GPGME::PROTOCOL_OpenPGP, '/usr/local/bin/gpg', home_dir)
# Note GPG executable location will change across platforms

crypto = GPGME::Crypto.new
options = {:recipients => 'A1B2C3D4'}

plaintext = GPGME::Data.new(File.open(Rails.root.join('Gemfile')))

data = crypto.encrypt plaintext, options

f = File.open(Rails.root.join('Gemfile.gpg'), 'wb')
bytes_written = f.write(data)
f.close

puts bytes_written

crypto = GPGME::Crypto.new
options = {:recipients => 'A1B2C3D4', :passphrase_callback => PassphraseCallback.new('my_passphrase')}

cipthertext = GPGME::Data.new(File.open(Rails.root.join('Gemfile.gpg')))

data = crypto.decrypt cipthertext, options
puts data

Contributing

To run the local test suite you need bundler and gpg:

bundle
rake compile   # simple rake task to compile the extension
rake           # runs the test suite

License

The library itself is licensed under LGPLv2.1+. See the file COPYING.LESSER and each file for copyright and warranty information.