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.

- fixes bnc#764127 CVE-2012-2417 insecure ElGamal key     generation

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.

Updated python-pycrypto package fixes security vulnerability :

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 (CVE-2012-2417).

Note: any ElGamal keys that have previously been generated by PyCrypto should be regenerated after installing this update.

A vulnerability has been discovered and corrected in python-pycrypto :

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 (CVE-2012-2417).

The updated packages have been patched to correct this issue.

It was discovered that PyCrypto produced inappropriate prime numbers when generating ElGamal keys. An attacker could use this flaw to facilitate brute-forcing of ElGamal encryption keys.

Note that Tenable Network Security has extracted the preceding description block directly from the Ubuntu security advisory. Tenable has attempted to automatically clean and format it as much as possible without introducing additional issues.

It was discovered that that the ElGamal code in PythonCrypto, a collection of cryptographic algorithms and protocols for Python used insecure insufficient prime numbers in key generation, which lead to a weakened signature or public key space, allowing easier brute-force attacks on such keys.

Dwayne C. Litzenberger of PyCrypto reports :

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

The remote host is affected by the vulnerability described in GLSA-201206-23 (PyCrypto: Weak key generation)

    An error in the generate() function in ElGamal.py causes PyCrypto to       generate weak ElGamal keys.
  Impact :

    A remote attacker might be able to derive private keys.
  Workaround :

    There is no known workaround at this time.

This update is a security fix for CVE-2012-2417 (insecure ElGamal key generation). 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).

Note that Tenable Network Security has extracted the preceding description block directly from the Fedora security advisory. Tenable has attempted to automatically clean and format it as much as possible without introducing additional issues.

This update, to the current upstream pycrypto release, includes a number of regular bug fixes plus a security fix for CVE-2012-2417 (insecure ElGamal key generation). 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).

Note that Tenable Network Security has extracted the preceding description block directly from the Fedora security advisory. Tenable has attempted to automatically clean and format it as much as possible without introducing additional issues.

ID	Name	Product	Family	Severity
74669	openSUSE Security Update : python-crypto (openSUSE-SU-2012:0830-1)	Nessus	SuSE Local Security Checks	medium
69693	Amazon Linux AMI : python-crypto (ALAS-2012-86)	Nessus	Amazon Linux Local Security Checks	medium
66132	Mandriva Linux Security Advisory : python-pycrypto (MDVSA-2013:120)	Nessus	Mandriva Local Security Checks	medium
61968	Mandriva Linux Security Advisory : python-pycrypto (MDVSA-2012:117)	Nessus	Mandriva Local Security Checks	medium
59783	Ubuntu 10.04 LTS / 11.04 / 11.10 / 12.04 LTS : python-crypto vulnerability (USN-1484-1)	Nessus	Ubuntu Local Security Checks	medium
59780	Debian DSA-2502-1 : python-crypto - programming error	Nessus	Debian Local Security Checks	medium
59700	FreeBSD : pycrypto -- vulnerable ElGamal key generation (f45c0049-be72-11e1-a284-0023ae8e59f0)	Nessus	FreeBSD Local Security Checks	medium
59676	GLSA-201206-23 : PyCrypto: Weak key generation	Nessus	Gentoo Local Security Checks	medium
59352	Fedora 15 : python-crypto-2.3-6.fc15 (2012-8490)	Nessus	Fedora Local Security Checks	medium
59350	Fedora 16 : python-crypto-2.3-6.fc16 (2012-8470)	Nessus	Fedora Local Security Checks	medium
59344	Fedora 17 : python-crypto-2.6-1.fc17 (2012-8392)	Nessus	Fedora Local Security Checks	medium

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