Add ActiveSupport::KeyGenerator as a simple wrapper around PBKDF2

This will be used to derive keys from the secret and a salt, in order to allow us to
do things like encrypted cookie stores without using the secret for multiple
purposes directly.

1 files changed, 23 insertions, 0 deletions

diff --git a/activesupport/lib/active_support/key_generator.rb b/activesupport/lib/active_support/key_generator.rb
new file mode 100644
index 0000000000..04d170f801
--- /dev/null
+++ b/activesupport/lib/active_support/key_generator.rb
@@ -0,0 +1,23 @@
+require 'openssl'
+
+module ActiveSupport
+  # KeyGenerator is a simple wrapper around OpenSSL's implementation of PBKDF2
+  # It can be used to derive a number of keys for various purposes from a given secret.
+  # This lets rails applications have a single secure secret, but avoid reusing that
+  # key in multiple incompatible contexts.
+  class KeyGenerator
+    def initialize(secret, options = {})
+      @secret = secret
+      # The default iterations are higher than required for our key derivation uses
+      # on the off chance someone uses this for password storage
+      @iterations = options[:iterations] || 2**16
+    end
+
+    # Returns a derived key suitable for use.  The default key_size is chosen
+    # to be compatible with the default settings of ActiveSupport::MessageVerifier.
+    # i.e. OpenSSL::Digest::SHA1#block_length
+    def generate_key(salt, key_size=64)
+      OpenSSL::PKCS5.pbkdf2_hmac_sha1(@secret, salt, @iterations, key_size)
+    end
+  end
+end