Issue #10098 has been updated by Shyouhei Urabe.


(Just to be clear) what is bad about the word "memcmp" is that the "cmp" part implies returning integers, rather than true/false.  One of such example that returns integer is String#casecmp.  But almost nobody wants integers for timing-safe comparisons, meseems at least.  We should provide a method that returns true/false, and in doing so "memcmp" is inappropriate.

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Feature #10098: [PATCH] Timing-safe string comparison for OpenSSL::HMAC
https://bugs.ruby-lang.org/issues/10098#change-60680

* Author: Matt U
* Status: Feedback
* Priority: Normal
* Assignee: Yukihiro Matsumoto
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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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