In Ruby, the
& operator is commonly known as a bitwise AND operator used for binary operations. However, it can also be used as a logical operator and be very useful in certain applications, such as security. Here’s an exploration of why using
& might be useful in preventing timing attacks, contrasting it with the more typical logical
& as a bitwise operator
& operator is usually used to perform bitwise AND operations between two integers. For example:
a = 5 # binary 101 b = 3 # binary 011 puts a & b # binary 001, output: 1
& as a logical operator
When dealing with boolean values,
& can also be used as a logical AND operator, without the short-circuiting behavior of
&&. This makes it useful in contexts like preventing timing attacks.
What is short-circuiting?
Short-circuiting occurs when, for instance, in a boolean condition like
true || something, the interpreter can immediately cease evaluation after the first part because the final result is already determined.
What is a timing attack?
A timing attack is a side-channel attack where an attacker attempts to compromise a system by analyzing the time taken to execute cryptographic algorithms. Even a tiny difference in execution time can provide clues to the attacker.
&& in security context?
& ensures that all the comparisons are made, regardless of whether the previous ones were
&& short-circuits if any comparison returns
false. By not short-circuiting, the
& operator ensures that the comparison takes a consistent amount of time, regardless of the input.
Here’s an example of how to protect the sidekiq web admin with basic auth:
Sidekiq::Web.use(Rack::Auth::Basic) do |username, password| ActiveSupport::SecurityUtils.secure_compare(username, Settings.sidekiq.admin_username) & ActiveSupport::SecurityUtils.secure_compare(password, Settings.sidekiq.admin_password) end
This code takes the same amount of time to run, regardless of where the credentails start to differ, making it more resistant to timing attacks.