SignedConfig

Cryptograpically sign a configuration hash. A way to (lightly) enforce configuration / licensing of an installed Ruby application.

---

SignedConfig has two modes:

Writer mode : intended to be used by a sort of "licensing console", takes a config hash and a private key and generates signed "license text." The licensed text contains a YML serialized "human readable" version of the config hash and a matching signature.

Reader mode: intended to be used by the "licensed application" takes a public key (which should be distributed with the application) and the "license text." It confirms the signature matches the config hash, and deserializes the license text from YML back into a Ruby hash.

This gem was extracted from an enterprise Rails webapp. It's unusual for a Rails application in that, it's installed onsite on clients' servers. (This is not unusual for an "enterprise application," however.)

Writing licenses

config_hash = {
  :client_name: "Acme Inc."
  :license_level: "high"
  :licensed_features: ["widget_management", "foobar_creation"],
  :expiration_date: 2099-01-01 00:00:00 UTC
  :num_superusers: 1
  :num_users: 20
}
org_name = "BRANDED"

writer = SignedConfig::Writer.new(SIGNED_CONFIG_PRIVATE_KEY, config_hash, org_name)
self.signed_config = writer.signed_config

Reading licenses

def verify
  begin
    reader = SignedConfig::Reader.new(SIGNED_CONFIG_PUBLIC_KEY, params[:license])
    @config = reader.config
    flash[:success] = 'License is valid.'
  rescue SignedConfig::SignatureDoesNotMatch
    flash[:error] = 'License is invalid.'
    flash.discard
    render :new
  end
end

Example of generated license:

=========================BEGIN BRANDED LICENSE=========================
---
:config: |
  ---
  :client_name: Acme Inc.
  :license_level: high
  :licensed_features:
  - widget_management
  - foobar_creation
  :expiration_date: 2099-01-01 00:00:00 UTC
  :num_superusers: 1
  :num_users: 20
:signature: |
  VUiNY22N9cIs+RUJ1+w+T7pXEkBwOhGx2heeo3ekxybWjm+gEBXkt8n3Y8+s
  pUyK0RfLM6NK9LMP6/Ke5IXL199hDLKXJnfy/nuZ+uIkNmoL1Bd7FhMqXCmd
  HyRuuSkHTsQG4hk1VCS/mn/KaZWn1P+dyng4HWYWCAJYt2dtJqf/ZbLmIXdI
  xX9GplIG5wCto7Dss7ksBR2x97QFe5P3OGQAjX0qw/jFWY8pOy+JCaJqB4b4
  U/xy9p/+VWPhdmQPY8/hIowx9WC2UqbV5QKTEJzqWebG7xbvwmJfywE60+qO
  rhEqh8fza8jagTbmzBtpsXyyTd4ZAusXuwc7uMTtFQ==

=========================END BRANDED LICENSE=========================

How "secure" is this?

Since Ruby is not compiled and trivially easy to modify, it's very unsuited for being "hacker proof." Normally this doesn't matter as, enforcing license compliance is trivial for a classic consumer webapp where users only interact with the app via their web browsers.

However, for enterprise clients, it makes sense to just make it "slightly difficult" to modify the license to add users, enable additional features, or extend the expiration date. The security that this gem provides raises the bar just from the point where anyone could read and alter a plain text configuration file, to the point where any "programmer" type could figure out modifications in an hour or two.

However, I believe this is sufficient to enforce 95% of business agreements.

Additionally SignedConfig only uses a SHA1 hashing algorithm which is not hacker-proof anymore.

Development

Running the tests

rake