On Mon, Nov 20, 2017 at 9:00 PM, R0b0t1 <r03...@gmail.com> wrote:
> Hello friends!
>
> On Wed, Nov 15, 2017 at 3:02 PM, Robin H. Johnson <robb...@gentoo.org> wrote:
>> Replying to your original question here, to repeat the answer I emphasised
>> before, along with significantly more detail in the history of Portage hashes
>> (pulled from my notes back to GLEP57 and some minor updates).
>>
>> On Wed, Nov 08, 2017 at 12:57:49PM -0600, R0b0t1 wrote:
>>> These posts are concerning because it looks like someone became stir
>>> crazy and invented a problem to solve. The changes proposed to date
>>> have remained poorly justified, and no one has addressed the concern
>>> that multiple hashes *is* actually more secure.
>>>
>>> If it was deemed necessary at one point, what justification was used?
>>> I.e. https://en.wikipedia.org/wiki/Wikipedia:Chesterton's_fence.
>> On Wed, Nov 15, 2017 at 11:47:41AM -0600, R0b0t1 wrote:
>>> Does the existence of a decision mean I would need to contact the trustees
>>> if I feel the changes have not been adequately justified?
>>
>> In GLEP59, I referenced a paper by Joux [J04], in which it was shown that a
>> concatenation of multiple hashes is NOT much more secure against collisions
>> than the strongest of the individual hashes.
>>
>> That was cited as original logic in GLEP59 for the removal of SHA256 (that
>> removal was never implemented). WHIRLPOOL & SHA512 were kept out of an
>> abundance of caution at the time, mostly to implementation bugs in hashes
>> (as I
>> have referenced in the related threads since).
>>
>> Your logic regarding removing something you think I don't understand is wrong
>> (Chesterton's Fence):
>>
>> If you dig in the history of Portage, you will see that it's always been
>> valid,
>> to have just a SINGLE hash for each file in a Manifest. Required hashes has
>> NEVER contained more than one hash.
>>
>> If multiple hashes are present, then Portage will validate all of them, but a
>> potential attacker can still modify the Manifest and have only a single hash
>> listed. Exactly which hash MUST be present has changed over time.
>>
>> Manifest1 is very old, and was stored in $CAT/$PN/files/digest-$P
>> Manifest2 is the current $CAT/$PN/Manifest (and soon in more locations per
>> MetaManifest).
>>
>> 1999/xx/xx: Portage starts with Manifest1 format, MD5-only (CVS)
>> 2004/08/25: Portage gets SHA1 support in Manifest1, but is problematic, SHA1
>> generation manual only.
>> https://sources.gentoo.org/cgi-bin/viewvc.cgi/gentoo-src/portage/pym/portage_checksum.py?revision=1.1&view=markup
>> https://sources.gentoo.org/cgi-bin/viewvc.cgi/gentoo-src/portage/pym/portage.py?r1=1.485&r2=1.486
>> 2005/12/19: Portage Manifest1 supports MD5,SHA1,SHA256,RMD160, but still
>> requires only a single hash present. Generates MD5+SHA256+RMD160.
>> https://gitweb.gentoo.org/proj/portage.git/commit/?id=cd3e3775966a9f58aebb91f58cbdb5903faad3de
>> 2006/03/24: Manifest2 introduced.
>> https://gitweb.gentoo.org/proj/portage.git/commit/?id=f993747ca501e8a70d6f6174711149a172cfc3c2
>> 2007/01/20: MANIFEST2_REQUIRED_HASH introduced, SHA1, it must be present &
>> pass
>> https://gitweb.gentoo.org/proj/portage.git/commit/?id=e768571187d1655fbb558c23d61fa2983e48e411
>> 2007/12/18: MANIFEST1_REQUIRED_HASH introduced, MD5, it must be present &
>> pass
>> https://gitweb.gentoo.org/proj/portage.git/commit/?id=d9b10deaa03ce174d5ccc3b59c477549ad87e884
>> 2008/02/28: Manifest1 support dropped.
>> https://gitweb.gentoo.org/proj/portage.git/commit/?id=66940e1f2f0549ee8f01dad59016e168105e193d
>> 2011/10/02: GLEP59 implemented, MANIFEST2_REQUIRED_HASH changes to SHA256
>> https://gitweb.gentoo.org/proj/portage.git/commit/?id=c8cd3a985cc529299411d7343a11004b7d1330ef
>> 2017/06/15: MANIFEST2_REQUIRED_HASH changes to SHA512
>> https://gitweb.gentoo.org/proj/portage.git/commit/?id=e6abcc0b7cbdca481862a5c7cca946c01c471ffb
>>
>> [J04] Joux, Antoie. (2004). "Multicollisions in Iterated Hash Functions -
>> Application to Cascaded Constructions;"
>> Proceedings of CRYPTO 2004, Franklin, M. (Ed); Lecture Notes in Computer
>> Science 3152, pp. 306-316.
>> Available online from:
>> http://web.cecs.pdx.edu/~teshrim/spring06/papers/general-attacks/multi-joux.pdf
>>
>
> This is the information I was looking for, thank you. I feel that the
> matter has been adequately explained. I apologize for missing your
> response.
>
> The paper gives a counter intuitive result, so I suspect I will have
> to spend more time with it.
>
I appreciate the thought that robbat2 gave to his response, but I
would like to clarify that it is beyond and above what I expected.
What I wanted to avoid was something I encountered on the GCC mailing
list: When I asked why GCJ was removed, I was told that it was hard to
maintain. When I asked for an example of past maintenance issues (and
made it clear I had no interest in disputing whether the issues were
valid or not) I received no reply from the maintainer except his
original answer, leaving me to wonder whether GCJ was actually hard to
maintain.
I have seen similar exchanges associated with other projects.
Cheers,
R0b0t1
