Improve poor security recommendation in docs

As reported in #9960, the current documentation recommends an insecure practice for
key generation from a password (a single round of SHA-256). The modified documentation
uses ActiveSupport::KeyGenerator to perform proper key stretching.

1 files changed, 5 insertions, 4 deletions

diff --git a/activesupport/lib/active_support/message_encryptor.rb b/activesupport/lib/active_support/message_encryptor.rb
index ce40a7d689..0109a108be 100644
--- a/activesupport/lib/active_support/message_encryptor.rb
+++ b/activesupport/lib/active_support/message_encryptor.rb
@@ -12,10 +12,11 @@ module ActiveSupport
   # This can be used in situations similar to the <tt>MessageVerifier</tt>, but
   # where you don't want users to be able to determine the value of the payload.
   #
-  #   key = OpenSSL::Digest::SHA256.new('password').digest        # => "\x89\xE0\x156\xAC..."
-  #   crypt = ActiveSupport::MessageEncryptor.new(key)            # => #<ActiveSupport::MessageEncryptor ...>
-  #   encrypted_data = crypt.encrypt_and_sign('my secret data')   # => "NlFBTTMwOUV5UlA1QlNEN2xkY2d6eThYWWh..."
-  #   crypt.decrypt_and_verify(encrypted_data)                    # => "my secret data"
+  #   salt  = SecureRandom.random_bytes(64) 
+  #   key   = ActiveSupport::KeyGenerator.new('password').generate_key(salt) # => "\x89\xE0\x156\xAC..."
+  #   crypt = ActiveSupport::MessageEncryptor.new(key)                       # => #<ActiveSupport::MessageEncryptor ...>
+  #   encrypted_data = crypt.encrypt_and_sign('my secret data')              # => "NlFBTTMwOUV5UlA1QlNEN2xkY2d6eThYWWh..."
+  #   crypt.decrypt_and_verify(encrypted_data)                               # => "my secret data"
   class MessageEncryptor
     module NullSerializer #:nodoc:
       def self.load(value)