CVE-2012-2417

Advisory

Pycrypto version 2.6 includes a fix for CVE-2012-2417: PyCrypto before 2.6 does not produce appropriate prime numbers when using an ElGamal scheme to generate a key, which reduces the signature space or public key space and makes it easier for attackers to conduct brute force attacks to obtain the private key.
https://github.com/Legrandin/pycrypto/commit/9f912f13df99ad3421eff360d6a62d7dbec755c2

Affected package

Affected versions

Fixed versions

Vulnerability changelog

===
* [CVE-2012-2417] Fix LP985164: insecure ElGamal key generation.
(thanks: Legrandin)

In the ElGamal schemes (for both encryption and signatures), g is
supposed to be the generator of the entire Z^*_p group. However, in
PyCrypto 2.5 and earlier, g is more simply the generator of a random
sub-group of Z^*_p.

The result is that the signature space (when the key is used for
signing) or the public key space (when the key is used for encryption)
may be greatly reduced from its expected size of log(p) bits, possibly
down to 1 bit (the worst case if the order of g is 2).

While it has not been confirmed, it has also been suggested that an
attacker might be able to use this fact to determine the private key.

Anyone using ElGamal keys should generate new keys as soon as practical.

Any additional information about this bug will be tracked at
https://bugs.launchpad.net/pycrypto/+bug/985164

* Huge documentation cleanup (thanks: Legrandin).

* Added more tests, including test vectors from NIST 800-38A
(thanks: Legrandin)

* Remove broken MODE_PGP, which never actually worked properly.
A new mode, MODE_OPENPGP, has been added for people wishing to write
OpenPGP implementations. Note that this does not implement the full
OpenPGP specification, only the "OpenPGP CFB mode" part of that
specification.
https://bugs.launchpad.net/pycrypto/+bug/996814

* Fix: getPrime with invalid input causes Python to abort with fatal error
https://bugs.launchpad.net/pycrypto/+bug/988431

* Fix: Segfaults within error-handling paths
(thanks: Paul Howarth & Dave Malcolm)
https://bugs.launchpad.net/pycrypto/+bug/934294

* Fix: Block ciphers allow empty string as IV
https://bugs.launchpad.net/pycrypto/+bug/997464

* Fix DevURandomRNG to work with Python3's new I/O stack.
(thanks: Sebastian Ramacher)

* Remove automagic dependencies on libgmp and libmpir, let the caller
disable them using args.

* Many other minor bug fixes and improvements (mostly thanks to Legrandin)

Resources

• https://pypi.org/project/pycrypto
• https://pyup.io/changelogs/pycrypto/
• https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2012-2417
• https://github.com/Legrandin/pycrypto/commit/9f912f13df99ad3421eff360d6a62d7dbec755c2
• https://bugs.launchpad.net/pycrypto/+bug/985164
• http://www.openwall.com/lists/oss-security/2012/05/25/1
• http://lists.fedoraproject.org/pipermail/package-announce/2012-June/081789.html
• https://github.com/dlitz/pycrypto/blob/373ea760f21701b162e8c4912a66928ee30d401a/ChangeLog
• http://secunia.com/advisories/49263
• http://lists.fedoraproject.org/pipermail/package-announce/2012-June/081759.html
• http://lists.fedoraproject.org/pipermail/package-announce/2012-June/081713.html
• http://www.osvdb.org/82279
• http://www.securityfocus.com/bid/53687
• https://hermes.opensuse.org/messages/15083589
• http://www.debian.org/security/2012/dsa-2502
• http://www.mandriva.com/security/advisories?name=MDVSA-2012:117
• https://exchange.xforce.ibmcloud.com/vulnerabilities/75871