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AUSCERT External Security Bulletin Redistribution
Side-channel attack fixed in libgcrypt
14 June 2018
AusCERT Security Bulletin Summary
Operating System: Windows
UNIX variants (UNIX, Linux, OSX)
Impact/Access: Access Privileged Data -- Existing Account
CVE Names: CVE-2018-0495
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The GnuPG Project is pleased to announce the availability of Libgcrypt
versions 1.8.3 and 1.7.10. These releases mitigate a novel side-channel
attack on ECDSA signatures and also bring fixes for a few other bugs.
Libgcrypt is a general purpose library of cryptographic building blocks.
It is originally based on code used by GnuPG. It does not provide any
implementation of OpenPGP or other protocols. Thorough understanding of
applied cryptography is required to use Libgcrypt.
Noteworthy changes in version 1.8.3
- Use blinding for ECDSA signing to mitigate a novel side-channel
- Fix incorrect counter overflow handling for GCM when using an IV
size other than 96 bit. [#3764]
- Fix incorrect output of AES-keywrap mode for in-place encryption
on some platforms.
- Fix the gcry_mpi_ec_curve_point point validation function.
- Fix rare assertion failure in gcry_prime_check.
Release info at <https://dev.gnupg.org/T4016>.
We also released a new version of the older 1.7 branch with similar
Comments on the attack
Details on CVE-2018-0495 can be found in the paper "Return of the Hidden
Number Problem" which can be downloaded from the advisory page
See <https://dev.gnupg.org/T4011> for a timeline.
One user of Libgcrypt is GnuPG, thus a quick comment: GnuPG does not use
the vulenrable ECDSA signatures by default. Further, it is much harder
to mount such an attack against an offline protocol like OpenPGP than
against online protocols like TLS. Anyway, we also released a new
Windows installer for GnuPG 2.2.8 featuring the fixed Libgcrypt version.
That installer is linked from the usual download page and a new Gpg4win
version will be released soon.
Source code is hosted at the GnuPG FTP server and its mirrors as listed
at <https://gnupg.org/download/mirrors.html>. On the primary server
the source tarball and its digital signature are:
or gzip compressed:
The URLs for the older 1.7 branch are:
In order to check that the version of Libgcrypt you downloaded is an
original and unmodified file please follow the instructions found at
<https://gnupg.org/download/integrity_check.html>. In short, you may
use one of the following methods:
- Check the supplied OpenPGP signature. For example to check the
signature of the file libgcrypt-1.8.3.tar.bz2 you would use this
gpg --verify libgcrypt-1.8.3.tar.bz2.sig libgcrypt-1.8.3.tar.bz2
This checks whether the signature file matches the source file.
You should see a message indicating that the signature is good and
made by one or more of the release signing keys. Make sure that
this is a valid key, either by matching the shown fingerprint
against a trustworthy list of valid release signing keys or by
checking that the key has been signed by trustworthy other keys.
See the end of this mail for information on the signing keys.
- If you are not able to use an existing version of GnuPG, you have
to verify the SHA-1 checksum. On Unix systems the command to do
this is either "sha1sum" or "shasum". Assuming you downloaded the
file libgcrypt-1.8.3.tar.bz2, you run the command like this:
and check that the output matches the first line from the
You should also verify that the checksums above are authentic by
matching them with copies of this announcement. Those copies can be
found at other mailing lists, web sites, and search engines.
Libgcrypt is distributed under the terms of the GNU Lesser General
Public License (LGPLv2.1+). The helper programs as well as the
documentation are distributed under the terms of the GNU General Public
License (GPLv2+). The file LICENSES has notices about contributions
that require that these additional notices are distributed.
For help on developing with Libgcrypt you should read the included
manual and optional ask on the gcrypt-devel mailing list . A
listing with commercial support offers for Libgcrypt and related
software is available at the GnuPG web site .
If you are a developer and you may need a certain feature for your
project, please do not hesitate to bring it to the gcrypt-devel
mailing list for discussion.
Maintenance and development of GnuPG is mostly financed by donations.
The GnuPG project currently employs one full-time developer and two
contractors. They all work exclusively on GnuPG and closely related
software like Libgcrypt, GPGME, and GPA.
We have to thank all the people who helped the GnuPG project, be it
testing, coding, translating, suggesting, auditing, administering the
servers, spreading the word, and answering questions on the mailing
lists. Special thanks to Keegan Ryan of NCC Group for his proper
handling of the disclosure.
Many thanks to our numerous financial supporters, both corporate and
individuals. Without you it would not be possible to keep GnuPG in a
good shape and address all the small and larger requests made by our
Your GnuPG hackers
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