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Gentoo: GLSA-202303-02 Normal: GnuPG Randomness Generation Vulnerability

gentoo
Calendar Grey December 2, 2016
Dist Gentoo Esm H88
Investigate the GnuPG RNG output reliability concern detailed in Gentoo's security notice. Users are advised to perform an upgrade.
Due to a design flaw, the output of GnuPG's Random Number Generator (RNG) is predictable.

Summary

A long standing bug (since 1998) in Libgcrypt (see "GLSA 201610-04" below) and GnuPG allows an attacker to predict the output from the standard RNG. Please review the "Entropy Loss and Output Predictability in the Libgcrypt PRNG" paper below for a deep technical analysis.

Topics%20covered

Topics Covered

security advisory gentoo GnuPG design flaw normal severity RNG predictability

Resolution

All GnuPG 1 users should upgrade to the latest version: # emerge --sync # emerge --ask --oneshot --verbose ">=app-crypt/gnupg-1.4.21"

References

[ 1 ] CVE-2016-6313 http://nvd.nist.gov/nvd.cfm?cvename=CVE-2016-6313 [ 2 ] Entropy Loss and Output Predictability in the Libgcrypt PRNG https://formal.kastel.kit.edu/~klebanov/pubs/libgcrypt-cve-2016-6313.pdf [ 3 ] GLSA 201610-04 https://security.gentoo.org/glsa/201610-04

Availability

This GLSA and any updates to it are available for viewing at the Gentoo Security Website: https://security.gentoo.org/glsa/201612-01
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Concerns

Security is a primary focus of Gentoo Linux and ensuring the confidentiality and security of our users' machines is of utmost importance to us. Any security concerns should be addressed to security@gentoo.org or alternatively, you may file a bug at https://bugs.gentoo.org.

Severity: Normal
Title: GnuPG: RNG output is predictable
Date: December 02, 2016
Bugs: #591536
ID: 201612-01

Topics%20covered

Topics Covered

security advisory gentoo GnuPG design flaw normal severity RNG predictability

Synopsis

Due to a design flaw, the output of GnuPG's Random Number Generator (RNG) is predictable.

Background

The GNU Privacy Guard, GnuPG, is a free replacement for the PGP suite of cryptographic software.

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Affected Packages

------------------------------------------------------------------- Package / Vulnerable / Unaffected ------------------------------------------------------------------- 1 app-crypt/gnupg < 1.4.21 >= 1.4.21

Impact

===== An attacker who obtains 580 bytes of the random number from the standard RNG can trivially predict the next 20 bytes of output. This flaw does not affect the default generation of keys, because running gpg for key creation creates at most 2 keys from the pool. For a single 4096 bit RSA key, 512 bytes of random are required and thus for the second key (encryption subkey), 20 bytes could be predicted from the the first key.
However, the security of an OpenPGP key depends on the primary key (which was generated first) and thus the 20 predictable bytes should not be a problem. For the default key length of 2048 bit nothing will be predictable.

Workaround

There is no known workaround at this time.

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