Issue #5741 has been updated by MartinBosslet (Martin Bosslet). mame (Yusuke Endoh) wrote: > I think that adding a method to String requires matz's approval. > If you propose to add a method to others, such as openssl, you > can do it at your discretion. > Sure - I would appreciate to have more opinions on how this can be done best. I haven't really had the time to think it through yet, but unfortunately I see two major obstacles for either approach. 1. I'm having doubts if this could be handled reliably within String itself due to copy on write behavior. So when we finally call something like String#clear, we would also need to clear any proliferated instances, too. I haven't analyzed it yet, maybe someone could tell me if that's possible at all? 2. If we implement the feature separately (SecureByteBuffer), there is a serious chicken & egg problem: how can we feed the password to the implementation without using a String first? It's not as easy as it may sound and it would require massive changes in existing code - I fear this could be too invasive for anyone to adopt it... Any thoughts? ---------------------------------------- Feature #5741: Secure Erasure of Passwords https://bugs.ruby-lang.org/issues/5741#change-25316 Author: MartinBosslet (Martin Bosslet) Status: Assigned Priority: Normal Assignee: matz (Yukihiro Matsumoto) Category: Target version: 2.0.0 In other languages it is considered good practice to securely erase passwords immediately after they were used. Imagine authentication in a web app - ultimately a String containing the password arrives at the server, where it will be processed and compared to some previously stored value. After this is done, there is no need to store these password Strings any longer, so they should be discarded right away (more on why later). In C, you would simply overwrite the array of bytes with zeroes or random values. In Java, Strings are immutable, that's why there it is common practice to use char[] for all things password and overwrite them when done. Currently, there is no way in Ruby to overwrite the memory that was used by a String. String#clear and String#replace both use str_discard internally, which only frees the underlying pointer without overwriting it. The problem with not erasing passwords is this: the contents of the String stay in memory until they are finally GC'ed. But even then only the pointer will be freed, leaving the contents mostly intact until the memory is reclaimed and overwritten later on. This could be exploited if an attacker had access to the memory of the server. This could happen in many ways: a core dump after a crash, access to the host if the server runs in a VM, or even by deep-freezing the DRAM :) [1] It could be argued that given the examples above, much more devastating attacks would be possible since in all of those cases you more or less have physical access to the machine. But I would still consider this to be a valid concern, if not only for the reason of never opening additional attack surfaces if they can be avoided relatively easily. I also found [2], which seems to show that Python deals with similar problems and it also contains more background info. Eric Hodel and I discussed this yesterday and Eric came up with a C extension that can be used to illustrate the problem (attached). If you inspect the resulting core dump, you will find the following: - the untouched String remains in memory fully intact - the String#clear'ed String remains to a large extent, typically the first character is missing - so if you typed "PASSWORD", search for "ASSWORD" (unintentional pun) instead - The String#clear_secure'ed will have been completely erased, no traces remain My questions: 1. Would you agree that we need this functionality? 2. Where would we ideally place it? I'm not sure whether String is the perfect place, but on the other hand, String is the only place where we have access to the implementation details. 3. Are there better alternative ways how we could achieve this? [1] http://www.schneier.com/blog/archives/2008/02/cold_boot_attac.html [2] http://stackoverflow.com/questions/728164/securely-erasing-password-in-memory-python -- http://bugs.ruby-lang.org/