[ruby-core:65104] [ruby-trunk - Feature #10098] [PATCH] Timing-safe string comparison for OpenSSL::HMAC

Issue #10098 has been updated by Matt U.


Keen to hear feedback if any. Completely understand there are many more important tickets than this one, but it would be great to see this feature in MRI soon!
 
Devise, one of the most popular frameworks currently implements a timing-safe string compare in Ruby manually: https://github.com/plataformatec/devise/blob/66db52ce31b5d8629f5813a1d7f03a8bc17e5d52/lib/devise.rb#L480-L488

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Feature #10098: [PATCH] Timing-safe string comparison for OpenSSL::HMAC
https://bugs.ruby-lang.org/issues/10098#change-48961

* Author: Matt U
* Status: Open
* Priority: Normal
* Assignee: 
* Category: ext/openssl
* Target version: next minor
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I could be totally wrong, but it seems the standard library doesn't provide a reliable way of comparing hashes in constant-time.

* The docs for `OpenSSL::HMAC` encourage the use of `Digest#to_s` (see: http://ruby-doc.org/stdlib-2.1.0/libdoc/openssl/rdoc/OpenSSL/HMAC.html#method-c-new )
* Ruby's string comparison uses memcmp, which isn't timing safe (see: http://rxr.whitequark.org/mri/source/string.c#2382 )

With this patch I propose to add an additional method, `OpenSSL::HMAC#verify`, which takes a binary string with a digest and compares it against the computed hash.


---Files--------------------------------
hmac-timing.patch (2.5 KB)
hmac-timing.patch (2.48 KB)
tsafe_eql.patch (2.48 KB)
tsafe_inline.patch (3.51 KB)
0001-add-timing-safe-string-compare-method.patch (4.31 KB)


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