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Revise GLEP59 per Calchan questions: Python 2.5 is widely deployed now and provides SHA512. RIPEMD160 is broken. WHIRLPOOL added. Migration plan detail added.

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8 cardoe 1.1 <title>GLEP 59 -- Manifest2 hash policies and security implications</title>
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26     <tr class="field"><th class="field-name">GLEP:</th><td class="field-body">59</td>
27     </tr>
28     <tr class="field"><th class="field-name">Title:</th><td class="field-body">Manifest2 hash policies and security implications</td>
29     </tr>
30 robbat2 1.4 <tr class="field"><th class="field-name">Version:</th><td class="field-body">1.4</td>
31 cardoe 1.1 </tr>
32 robbat2 1.4 <tr class="field"><th class="field-name">Last-Modified:</th><td class="field-body"><a class="reference external" href="http://www.gentoo.org/cgi-bin/viewcvs.cgi/xml/htdocs/proj/en/glep/glep-0059.txt?cvsroot=gentoo">2010/01/13 03:26:53</a></td>
33 cardoe 1.1 </tr>
34     <tr class="field"><th class="field-name">Author:</th><td class="field-body">Robin Hugh Johnson &lt;robbat2&#32;&#97;t&#32;gentoo.org&gt;,</td>
35     </tr>
36     <tr class="field"><th class="field-name">Status:</th><td class="field-body">Draft</td>
37     </tr>
38     <tr class="field"><th class="field-name">Type:</th><td class="field-body">Standards Track</td>
39     </tr>
40     <tr class="field"><th class="field-name">Content-Type:</th><td class="field-body"><a class="reference external" href="glep-0002.html">text/x-rst</a></td>
41     </tr>
42     <tr class="field"><th class="field-name">Requires:</th><td class="field-body"><a class="reference external" href="http://www.gentoo.org/proj/en/glepglep-0044.html">44</a></td>
43     </tr>
44     <tr class="field"><th class="field-name">Created:</th><td class="field-body">October 2006</td>
45     </tr>
46 robbat2 1.4 <tr class="field"><th class="field-name">Updated:</th><td class="field-body">November 2007, June 2008, July 2008, October 2008, January 2010</td>
47 cardoe 1.1 </tr>
48     <tr class="field"><th class="field-name">Updates:</th><td class="field-body">44</td>
49     </tr>
50 robbat2 1.5 <tr class="field"><th class="field-name">Post-History:</th><td class="field-body">December 2009, January 2010</td>
51 robbat2 1.3 </tr>
52 cardoe 1.1 </tbody>
53     </table>
54     <hr />
55     <div class="contents topic" id="contents">
56     <p class="topic-title first">Contents</p>
57     <ul class="simple">
58     <li><a class="reference internal" href="#abstract" id="id1">Abstract</a></li>
59     <li><a class="reference internal" href="#motivation" id="id2">Motivation</a></li>
60     <li><a class="reference internal" href="#specification" id="id3">Specification</a><ul>
61     <li><a class="reference internal" href="#the-bad-news" id="id4">The bad news</a></li>
62     <li><a class="reference internal" href="#how-fast-can-md5-be-broken" id="id5">How fast can MD5 be broken?</a></li>
63     <li><a class="reference internal" href="#the-good-news" id="id6">The good news</a></li>
64 robbat2 1.5 <li><a class="reference internal" href="#what-should-be-done" id="id7">What should be done</a></li>
65     <li><a class="reference internal" href="#checksum-depreciation-timing" id="id8">Checksum depreciation timing</a></li>
66 cardoe 1.1 </ul>
67     </li>
68     <li><a class="reference internal" href="#backwards-compatibility" id="id9">Backwards Compatibility</a></li>
69     <li><a class="reference internal" href="#references" id="id10">References</a></li>
70     <li><a class="reference internal" href="#thanks-to" id="id11">Thanks to</a></li>
71     <li><a class="reference internal" href="#copyright" id="id12">Copyright</a></li>
72     </ul>
73     </div>
74     <div class="section" id="abstract">
75     <h1><a class="toc-backref" href="#id1">Abstract</a></h1>
76     <p>While Manifest2 format allows multiple hashes, the question of which
77     checksums should be present, why, and the security implications of such
78     have never been resolved. This GLEP covers all of these issues, and
79     makes recommendations as to how to handle checksums both now, and in
80     future.</p>
81     </div>
82     <div class="section" id="motivation">
83     <h1><a class="toc-backref" href="#id2">Motivation</a></h1>
84     <p>This GLEP is being written as part of the work on signing the Portage
85     tree, but is only tangentially related to the actual signing of
86     Manifests. Checksums present one possible weak point in the overall
87     security of the tree - and a comprehensive security plan is needed.</p>
88     </div>
89     <div class="section" id="specification">
90     <h1><a class="toc-backref" href="#id3">Specification</a></h1>
91     <div class="section" id="the-bad-news">
92     <h2><a class="toc-backref" href="#id4">The bad news</a></h2>
93     <p>First of all, I'd like to cover the bad news in checksum security.
94     A much discussed point, as been the simple question: What is the
95     security of multiple independent checksums on the same data?
96     The most common position (and indeed the one previously held by myself),
97     is that multiple checksums would be an increase in security, but we
98     could not provably quantify the amount of security this added.
99     The really bad news, is that this position is completely and utterly
100     wrong. Many of you will be aghast at this. There is extremely little
101 robbat2 1.5 added security in multiple checksums as noted by Joux [J04]. For any set
102     of checksums, the actual strength lies in that of the strongest
103     checksum.</p>
104     <p>Wang et al [W04] extended Joux's [J04] work on SHA-0 to cover MD4, MD5,
105     HAVAL-128 and RIPEMD families of hashes.</p>
106 cardoe 1.1 </div>
107     <div class="section" id="how-fast-can-md5-be-broken">
108     <h2><a class="toc-backref" href="#id5">How fast can MD5 be broken?</a></h2>
109 robbat2 1.5 <p>For a general collision, not a pre-image attack, since the announcement
110     by Wang et al [W04], the time required to break MD5 has been massively
111     reduced. Originally at 1 hour on a near-supercomputer (IBM P690) and
112     estimated at 64 hours with a Pentium-3 1.7Ghz. This has gone down to
113     less than in two years, to 17 seconds [K06a].</p>
114 cardoe 1.1 <p>08/2004 - 1 hour, IBM pSeries 690 (32x 1.7Ghz POWER4+) = 54.4 GHz-Hours
115     03/2005 - 8 hours, Pentium-M 1.6Ghz = 12.8 Ghz-Hours
116     11/2005 - 5 hours, Pentium-4 1.7Ghz = 8.5 Ghz-Hours
117     03/2006 - 1 minute, Pentium-4 3.2Ghz = .05 Ghz-Hours
118     04/2006 - 17 seconds, Pentium-4 3.2Ghz = .01 Ghz-Hours</p>
119     <p>If we accept a factor of 800x as a sample of how much faster a checksum
120     may be broken over the course of 2 years (MD5 using the above data is
121     &gt;2000x), then existing checksums do not stand a significant chance of
122     survival in the future. We should thus accept that whatever checksums we
123     are using today, will be broken in the near future, and plan as best as
124 robbat2 1.5 possible. (A brief review [H04] of the SHA1 attacks indicates an
125 cardoe 1.1 improvement of ~600x in the same timespan).</p>
126     <p>And for those that claim implementation of these procedures is not yet
127     feasible, see [K06b] for an application that can produce two
128 robbat2 1.5 self-extracting EXE files, with identical MD5s, and whatever payload you
129     want.</p>
130 cardoe 1.1 </div>
131     <div class="section" id="the-good-news">
132     <h2><a class="toc-backref" href="#id6">The good news</a></h2>
133 robbat2 1.5 <p>Of the checksums presently used by Manifest2 (SHA1, SHA256, RIPEMD160),
134     one stands close to being completely broken: SHA1; and another is
135     significantly weakened: RIPEMD160. The SHA2 series has suffered some
136     attacks, but still remains reasonably solid [G07],[K08].</p>
137 cardoe 1.1 <p>To reduce the potential for future problems and any single checksum
138     break leading to a rapid decrease in security, we should incorporate the
139     strongest hash available from each family of checksums, and be prepared
140     to retire old checksums actively, unless there is a overriding reason to
141 robbat2 1.5 keep a specific checksum, such as part of a migration plan.</p>
142 cardoe 1.1 </div>
143     <div class="section" id="what-should-be-done">
144     <h2><a class="toc-backref" href="#id7">What should be done</a></h2>
145     <p>Portage should always try to verify all supported hashes that are
146     available in a Manifest2, starting with the strongest ones as maintained
147     by a preference list. Over time, the weaker checksums should be removed
148     from Manifest2 files, once all old Portage installations have had
149     sufficient time to upgrade. We should be prepared to add stronger
150     checksums wherever possible, and to remove those that have been
151     defeated.</p>
152 robbat2 1.5 <p>As soon as feasible, we should add the SHA512 and WHIRLPOOL algorithms.
153     In future, as stream-based checksums are developed (in response to the
154     development by NIST [AHS]), they should be considered and used.</p>
155     <p>The SHA512 algorithm is available in Python 2.5, which has been a
156     dependency of Portage since approximately Python</p>
157     <p>The WHIRLPOOL checksum is not available within the PyCrypto library or
158     hashlib that is part of Python 2.5, but there are multiple alternative
159     Python implementations available, ranging from pure Python to C-based
160     (python-mhash).</p>
161     <p>The existence unsupported hash is not considered to be a failure unless
162     no supported hashes are available for a given Manifest entry.</p>
163     </div>
164     <div class="section" id="checksum-depreciation-timing">
165     <h2><a class="toc-backref" href="#id8">Checksum depreciation timing</a></h2>
166     <p>For the current Portage, both SHA1 and RIPEMD160 should be immediately
167     removed, as they present no advantages over the already present SHA256.
168     SHA256 cannot be replaced immediately with SHA512, as existing Portage
169     versions need at least one supported algorithm present (SHA256 support
170     was added in June 2006), so it must be retained for some while.</p>
171     <p>Immediately:
172     - Add WHIRLPOOL and SHA512.
173     - Remove SHA1 and RIPEMD160.</p>
174     <p>After the majority of Portage installations include SHA512 support:
175     - Remove SHA256.</p>
176 cardoe 1.1 </div>
177     </div>
178     <div class="section" id="backwards-compatibility">
179     <h1><a class="toc-backref" href="#id9">Backwards Compatibility</a></h1>
180     <p>Old versions of Portage may support and expect only specific checksums.
181     This is accounted for in the checksum depreciation discussion.</p>
182     </div>
183     <div class="section" id="references">
184     <h1><a class="toc-backref" href="#id10">References</a></h1>
185     <dl class="docutils">
186     <dt>[AHS] NIST (2007). &quot;NIST's Plan for New Cryptographic Hash Functions&quot;,</dt>
187     <dd>(Advanced Hash Standard). <a class="reference external" href="http://csrc.nist.gov/pki/HashWorkshop/">http://csrc.nist.gov/pki/HashWorkshop/</a></dd>
188     <dt>[BOBO06] Boneh, D. and Boyen, X. (2006). &quot;On the Impossibility of</dt>
189     <dd>Efficiently Combining Collision Resistant Hash Functions&quot;; Proceedings
190     of CRYPTO 2006, Dwork, C. (Ed.); Lecture Notes in Computer Science
191     4117, pp. 570-583. Available online from:
192     <a class="reference external" href="http://crypto.stanford.edu/~dabo/abstracts/hashing.html">http://crypto.stanford.edu/~dabo/abstracts/hashing.html</a></dd>
193     <dt>[H04] Hawkes, P. and Paddon, M. and Rose, G. (2004). &quot;On Corrective</dt>
194     <dd>Patterns for the SHA-2 Family&quot;. CRYPTO 2004 Cryptology ePrint Archive,
195     Report 2004/204. Available online from:
196     <a class="reference external" href="http://eprint.iacr.org/2004/207.pdf">http://eprint.iacr.org/2004/207.pdf</a></dd>
197 robbat2 1.2 <dt>[J04] Joux, Antoie. (2004). &quot;Multicollisions in Iterated Hash</dt>
198     <dd>Functions - Application to Cascaded Constructions;&quot; Proceedings of
199     CRYPTO 2004, Franklin, M. (Ed); Lecture Notes in Computer Science
200     3152, pp. 306-316. Available online from:
201     <a class="reference external" href="http://web.cecs.pdx.edu/~teshrim/spring06/papers/general-attacks/multi-joux.pdf">http://web.cecs.pdx.edu/~teshrim/spring06/papers/general-attacks/multi-joux.pdf</a></dd>
202 cardoe 1.1 <dt>[K06a] Klima, V. (2006). &quot;Tunnels in Hash Functions: MD5 Collisions</dt>
203     <dd>Within a Minute&quot;. Cryptology ePrint Archive, Report 2006/105.
204     Available online from: <a class="reference external" href="http://eprint.iacr.org/2006/105.pdf">http://eprint.iacr.org/2006/105.pdf</a></dd>
205     <dt>[K06b] Klima, V. (2006). &quot;Note and links to high-speed MD5 collision</dt>
206     <dd>proof of concept tools&quot;. Available online from:
207     <a class="reference external" href="http://cryptography.hyperlink.cz/2006/trick.txt">http://cryptography.hyperlink.cz/2006/trick.txt</a></dd>
208     <dt>[K08] Klima, V. (2008). &quot;On Collisions of Hash Functions Turbo SHA-2&quot;.</dt>
209     <dd>Cryptology ePrint Archive, Report 2008/003. Available online from:
210     <a class="reference external" href="http://eprint.iacr.org/2008/003.pdf">http://eprint.iacr.org/2008/003.pdf</a></dd>
211     <dt>[G07] Gligoroski, D. and Knapskog, S.J. (2007). &quot;Turbo SHA-2&quot;.</dt>
212     <dd>Cryptology ePrint Archive, Report 2007/403. Available online from:
213     <a class="reference external" href="http://eprint.iacr.org/2007/403.pdf">http://eprint.iacr.org/2007/403.pdf</a></dd>
214     <dt>[W04] Wang, X. et al: &quot;Collisions for Hash Functions MD4, MD5,</dt>
215     <dd>HAVAL-128 and RIPEMD&quot;, rump session, CRYPTO 2004, Cryptology ePrint
216     Archive, Report 2004/199, first version (August 16, 2004), second
217     version (August 17, 2004). Available online from:
218     <a class="reference external" href="http://eprint.iacr.org/2004/199.pdf">http://eprint.iacr.org/2004/199.pdf</a></dd>
219     </dl>
220     </div>
221     <div class="section" id="thanks-to">
222     <h1><a class="toc-backref" href="#id11">Thanks to</a></h1>
223     <dl class="docutils">
224     <dt>I'd like to thank the following folks, in no specific order:</dt>
225     <dd><ul class="first last simple">
226     <li>Ciaran McCreesh (ciaranm) - for pointing out the Joux (2004) paper,
227     and also being stubborn enough in not accepting a partial solution.</li>
228     <li>Marius Mauch (genone), Zac Medico (zmedico) and Brian Harring
229     (ferringb): for being knowledgeable about the Portage Manifest2
230     codebase.</li>
231     </ul>
232     </dd>
233     </dl>
234     </div>
235     <div class="section" id="copyright">
236     <h1><a class="toc-backref" href="#id12">Copyright</a></h1>
237 robbat2 1.4 <p>Copyright (c) 2006-2010 by Robin Hugh Johnson. This material may be
238 cardoe 1.1 distributed only subject to the terms and conditions set forth in the
239     Open Publication License, v1.0.</p>
240     <p>vim: tw=72 ts=2 expandtab:</p>
241     </div>
243     </div>
244     <div class="footer">
245     <hr class="footer" />
246     <a class="reference external" href="glep-0059.txt">View document source</a>.
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