Bug #8439

closed

test_aes_gcm_wrong_tag(OpenSSL::TestCipher) fails randomly

Added by vo.x (Vit Ondruch) about 12 years ago. Updated over 11 years ago.

Status:

Closed

Assignee:

MartinBosslet (Martin Bosslet)

Target version:

2.1.0

ruby -v:

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

Backport:

1.9.3: DONTNEED, 2.0.0: DONE

[ruby-core:55143]

Description

=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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#1 [ruby-core:55149]

Updated by zzak (zzak _) about 12 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?

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#2 [ruby-core:55737]

Updated by vo.x (Vit Ondruch) about 12 years ago

Might be related/duplicate to #8221

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#3 [ruby-core:55812]

Updated by MartinBosslet (Martin Bosslet) about 12 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.

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#4 [ruby-core:58204]

Updated by akr (Akira Tanaka) over 11 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.

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Updated by akr (Akira Tanaka) over 11 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.