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<?xml version="1.0" encoding="ISO-8859-1" ?>
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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
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<html xmlns="http://www.w3.org/1999/xhtml">
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<head>
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<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1" />
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<title>Eclipse Distribution License - Version 1.0</title>
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<style type="text/css">
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body {
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margin-top: 0.05em;
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margin-bottom: 0.05em;
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}
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SHA-1: collision detection support
Update SHA1 class to include a Java port of sha1dc[1]'s ubc_check,
which can detect the attack pattern used by the SHAttered[2] authors.
Given the shattered example files that have the same SHA-1, this
modified implementation can identify there is risk of collision given
only one file in the pair:
$ jgit ...
[main] WARN org.eclipse.jgit.util.sha1.SHA1 - SHA-1 collision 38762cf7f55934b34d179ae6a4c80cadccbb7f0a
When JGit detects probability of a collision the SHA1 class now warns
on the logger, reporting the object's SHA-1 hash, and then throws a
Sha1CollisionException to the caller.
From the paper[3] by Marc Stevens, the probability of a false positive
identification of a collision is about 14 * 2^(-160), sufficiently low
enough for any detected collision to likely be a real collision.
git-core[4] may adopt sha1dc before the system migrates to an entirely
new hash function. This commit enables JGit to remain compatible with
that move to sha1dc, and help protect users by warning if similar
attacks as SHAttered are identified.
Performance declined about 8% (detection off), now:
MessageDigest 238.41 MiB/s
MessageDigest 244.52 MiB/s
MessageDigest 244.06 MiB/s
MessageDigest 242.58 MiB/s
SHA1 216.77 MiB/s (was ~240.83 MiB/s)
SHA1 220.98 MiB/s
SHA1 221.76 MiB/s
SHA1 221.34 MiB/s
This decline in throughput is attributed to the step loop unrolling in
compress(), which was necessary to easily fit the UbcCheck logic into
the hash function. Using helper functions s1-s4 reduces the code
explosion, providing acceptable throughput.
With detection enabled (default):
SHA1 detectCollision 180.12 MiB/s
SHA1 detectCollision 181.59 MiB/s
SHA1 detectCollision 181.64 MiB/s
SHA1 detectCollision 182.24 MiB/s
sha1dc (native C) ~206.28 MiB/s
sha1dc (native C) ~204.47 MiB/s
sha1dc (native C) ~203.74 MiB/s
Average time across 100,000 calls to hash 4100 bytes (such as a commit
or tree) for the various algorithms available to JGit also shows SHA1
is slower than MessageDigest, but by an acceptable margin:
MessageDigest 17 usec
SHA1 18 usec
SHA1 detectCollision 22 usec
Time to index-pack for git.git (217982 objects, 69 MiB) has increased:
MessageDigest SHA1 w/ detectCollision
------------- -----------------------
20.12s 25.25s
19.87s 25.48s
20.04s 25.26s
avg 20.01s 25.33s +26%
Being implemented in Java with these additional safety checks is
clearly a penalty, but throughput is still acceptable given the
increased security against object name collisions.
[1] https://github.com/cr-marcstevens/sha1collisiondetection
[2] https://shattered.it/
[3] https://marc-stevens.nl/research/papers/C13-S.pdf
[4] https://public-inbox.org/git/20170223230621.43anex65ndoqbgnf@sigill.intra.peff.net/
Change-Id: I9fe4c6d8fc5e5a661af72cd3246c9e67b1b9fee6
8 years ago
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.ubc-name {
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margin-left: 0.5in;
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white-space: pre;
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}
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</style>
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</head>
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<body lang="EN-US">
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<p><b>Eclipse Distribution License - v 1.0</b></p>
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<p>Copyright (c) 2007, Eclipse Foundation, Inc. and its licensors. </p>
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<p>All rights reserved.</p>
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<p>Redistribution and use in source and binary forms, with or without modification,
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are permitted provided that the following conditions are met:
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<ul><li>Redistributions of source code must retain the above copyright notice,
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this list of conditions and the following disclaimer. </li>
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<li>Redistributions in binary form must reproduce the above copyright notice,
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this list of conditions and the following disclaimer in the documentation
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and/or other materials provided with the distribution. </li>
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<li>Neither the name of the Eclipse Foundation, Inc. nor the names of its
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contributors may be used to endorse or promote products derived from
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this software without specific prior written permission. </li></ul>
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<p>THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
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AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
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WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
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IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT,
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INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
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NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
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PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
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ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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POSSIBILITY OF SUCH DAMAGE.</p>
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SHA-1: collision detection support
Update SHA1 class to include a Java port of sha1dc[1]'s ubc_check,
which can detect the attack pattern used by the SHAttered[2] authors.
Given the shattered example files that have the same SHA-1, this
modified implementation can identify there is risk of collision given
only one file in the pair:
$ jgit ...
[main] WARN org.eclipse.jgit.util.sha1.SHA1 - SHA-1 collision 38762cf7f55934b34d179ae6a4c80cadccbb7f0a
When JGit detects probability of a collision the SHA1 class now warns
on the logger, reporting the object's SHA-1 hash, and then throws a
Sha1CollisionException to the caller.
From the paper[3] by Marc Stevens, the probability of a false positive
identification of a collision is about 14 * 2^(-160), sufficiently low
enough for any detected collision to likely be a real collision.
git-core[4] may adopt sha1dc before the system migrates to an entirely
new hash function. This commit enables JGit to remain compatible with
that move to sha1dc, and help protect users by warning if similar
attacks as SHAttered are identified.
Performance declined about 8% (detection off), now:
MessageDigest 238.41 MiB/s
MessageDigest 244.52 MiB/s
MessageDigest 244.06 MiB/s
MessageDigest 242.58 MiB/s
SHA1 216.77 MiB/s (was ~240.83 MiB/s)
SHA1 220.98 MiB/s
SHA1 221.76 MiB/s
SHA1 221.34 MiB/s
This decline in throughput is attributed to the step loop unrolling in
compress(), which was necessary to easily fit the UbcCheck logic into
the hash function. Using helper functions s1-s4 reduces the code
explosion, providing acceptable throughput.
With detection enabled (default):
SHA1 detectCollision 180.12 MiB/s
SHA1 detectCollision 181.59 MiB/s
SHA1 detectCollision 181.64 MiB/s
SHA1 detectCollision 182.24 MiB/s
sha1dc (native C) ~206.28 MiB/s
sha1dc (native C) ~204.47 MiB/s
sha1dc (native C) ~203.74 MiB/s
Average time across 100,000 calls to hash 4100 bytes (such as a commit
or tree) for the various algorithms available to JGit also shows SHA1
is slower than MessageDigest, but by an acceptable margin:
MessageDigest 17 usec
SHA1 18 usec
SHA1 detectCollision 22 usec
Time to index-pack for git.git (217982 objects, 69 MiB) has increased:
MessageDigest SHA1 w/ detectCollision
------------- -----------------------
20.12s 25.25s
19.87s 25.48s
20.04s 25.26s
avg 20.01s 25.33s +26%
Being implemented in Java with these additional safety checks is
clearly a penalty, but throughput is still acceptable given the
increased security against object name collisions.
[1] https://github.com/cr-marcstevens/sha1collisiondetection
[2] https://shattered.it/
[3] https://marc-stevens.nl/research/papers/C13-S.pdf
[4] https://public-inbox.org/git/20170223230621.43anex65ndoqbgnf@sigill.intra.peff.net/
Change-Id: I9fe4c6d8fc5e5a661af72cd3246c9e67b1b9fee6
8 years ago
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<hr>
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<p><b>SHA-1 UbcCheck - MIT</b></p>
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<p>Copyright (c) 2017:</p>
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<div class="ubc-name">
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Marc Stevens
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Cryptology Group
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Centrum Wiskunde & Informatica
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P.O. Box 94079, 1090 GB Amsterdam, Netherlands
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marc@marc-stevens.nl
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</div>
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<div class="ubc-name">
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Dan Shumow
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Microsoft Research
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danshu@microsoft.com
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</div>
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<p>Permission is hereby granted, free of charge, to any person obtaining a copy
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of this software and associated documentation files (the "Software"), to deal
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in the Software without restriction, including without limitation the rights
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to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
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copies of the Software, and to permit persons to whom the Software is
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furnished to do so, subject to the following conditions:
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</p>
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<ul><li>The above copyright notice and this permission notice shall be included
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in all copies or substantial portions of the Software.</li></ul>
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<p>THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
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SOFTWARE.</p>
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</body>
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</html>
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