[ruby-core:58204] [ruby-trunk - Bug #8439] test_aes_gcm_wrong_tag(OpenSSL::TestCipher) fails randomly

Issue #8439 has been updated by akr (Akira Tanaka).


I tracked down the random failure.

It seems that the failure occur when tag[-1].succ is 2byte.
I.e. it fails when tag[-1] is "9", "Z", "z" or "\xFF".

I modified test_aes_gcm_wrong_tag as follows:

Index: test_cipher.rb
===================================================================
--- test_cipher.rb      (revision 43555)
+++ test_cipher.rb      (working copy)
@@ -187,6 +187,7 @@ class OpenSSL::TestCipher < Test::Unit::
       tag = cipher.auth_tag
 
       decipher = new_decryptor('aes-128-gcm', key, iv)
+      p [tag[-1], tag[-1].succ]
       decipher.auth_tag = tag[0..-2] << tag[-1].succ
       decipher.auth_data = "aad"
 
When the test fails, ["9", "10"], ["Z", "AA"], ["z", "aa"] or ["\xFF", "\x01\x00"] are shown.
Assuming tag[-1] is a random byte, I guess the test fails once per 64 times on average because 4/256=1/64.

I'm not sure the intent of tag[-1].succ, though.

----------------------------------------
Bug #8439: test_aes_gcm_wrong_tag(OpenSSL::TestCipher) fails randomly
https://bugs.ruby-lang.org/issues/8439#change-42785

Author: vo.x (Vit Ondruch)
Status: Assigned
Priority: Normal
Assignee: MartinBosslet (Martin Bosslet)
Category: ext
Target version: current: 2.1.0
ruby -v: ruby -v: ruby 2.0.0p195 (2013-05-14 revision 40734) [x86_64-linux]
Backport: 1.9.3: UNKNOWN, 2.0.0: UNKNOWN


=begin
 7) Error:
 test_aes_gcm_wrong_tag(OpenSSL::TestCipher):
 OpenSSL::Cipher::CipherError: unable to set GCM tag
     /builddir/build/BUILD/ruby-2.0.0-p195/test/openssl/test_cipher.rb:190:in `auth_tag='
     /builddir/build/BUILD/ruby-2.0.0-p195/test/openssl/test_cipher.rb:190:in `test_aes_gcm_wrong_tag'

I am building ruby against openssl-1.0.1e-8.el7.x86_64
=end



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