Question

How would you go about hiding sensitive information from going into log files? Yes, you can consciously choose not to log sensitive bits of information in the first place, but there can be general cases where you blindly log error messages upon failures or trace messages while investigating a problem etc. and end up with sensitive information landing in your log files.

For example, you could be trying to insert an order record that contains the credit card number of a customer into the database. Upon a database failure, you may want to log the SQL statement that was just executed. You would then end up with the credit card number of the customer in a log file.

Is there a design paradigm that can be employed to “tag” certain bits of information as sensitive so that a generic logging pipeline can filter them out?

Answer 1

My current practice for the case in question is to log a hash of such sensitive information. This enables us to identify log records that belong to a specific claim (for example a specific credit-card number) but does not give anybody the power to just grab the logs and use the sensitive information for their evil purposes.

Of course, doing this consistently involves good coding practices. I usually choose to log all objects using their toString overloads (in Java or .NET) which serializes the hash of the values for fields marked with a Sensitive attribute applied to them.

Of course, SQL strings are more problematic, but we rely more on our ORM for data persistence and log the state of the system at various stages then log SQL queries, thus it is becomes a non-issue.