Bug #8439

test_aes_gcm_wrong_tag(OpenSSL::TestCipher) fails randomly

Added by vo.x (Vit Ondruch) about 7 years ago. Updated over 6 years ago.

Target version:
ruby -v:
ruby -v: ruby 2.0.0p195 (2013-05-14 revision 40734) [x86_64-linux]


7) Error:
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='

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

Updated by zzak (Zachary Scott) about 7 years ago

  • Category set to ext
  • Status changed from Open to Assigned
  • Assignee set to MartinBosslet (Martin Bosslet)
  • Target version set to 2.1.0

Can you reproduce this with trunk?

Updated by vo.x (Vit Ondruch) about 7 years ago

Might be related/duplicate to #8221

Updated by MartinBosslet (Martin Bosslet) about 7 years ago

vo.x (Vit Ondruch) wrote:

Might be related/duplicate to #8221

Yes, very much sounds like it. I need to take a deeper look at what happens in the OpenSSL implementation that might explain the random failures.

Updated by akr (Akira Tanaka) over 6 years ago

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.


Updated by akr (Akira Tanaka) over 6 years ago

  • Status changed from Assigned to Closed
  • % Done changed from 0 to 100

This issue was solved with changeset r43676.
Vit, thank you for reporting this issue.
Your contribution to Ruby is greatly appreciated.
May Ruby be with you.

  • test/openssl/test_cipher.rb (test_aes_gcm_wrong_tag): Don't use String#succ because it can make modified (wrong) auth_tag longer than 16 bytes. The longer auth_tag makes that EVP_CIPHER_CTX_ctrl (and internally aes_gcm_ctrl) fail. [ruby-core:55143] [Bug #8439] reported by Vit Ondruch.

Updated by vo.x (Vit Ondruch) over 6 years ago

  • Backport changed from 1.9.3: UNKNOWN, 2.0.0: UNKNOWN to 1.9.3: UNKNOWN, 2.0.0: REQUIRED

Updated by nagachika (Tomoyuki Chikanaga) over 6 years ago

  • Backport changed from 1.9.3: UNKNOWN, 2.0.0: REQUIRED to 1.9.3: UNKNOWN, 2.0.0: DONE

r43676 was backported to ruby_2_0_0 at r44566.

Updated by usa (Usaku NAKAMURA) over 6 years ago

  • Backport changed from 1.9.3: UNKNOWN, 2.0.0: DONE to 1.9.3: DONTNEED, 2.0.0: DONE

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