Bell Labs cryptologist sees digital signature flaw, fix

[InfoSec News <isn () C4I ORG>]

http://www.infoworld.com/articles/hn/xml/01/02/05/010205hndsa.xml?p=br&s=6

By James Evans
Monday, Feb. 5, 2001

A SCIENTIST AT Bell Labs, the research and development wing of Lucent
Technologies, has discovered a flaw in the Digital Signature Algorithm
(DSA) that could affect the integrity of secure transactions on the
Internet and adversely impact VPNs (virtual private networks), online
shopping, and online financial transactions.

Daniel Bleichenbacher, a member of Bell Labs' Information Sciences
Research Center, discovered a glitch in the random number generation
technique used with the DSA, according to the company in a statement.
He learned that the DSA's random number generator was biased and was
twice as likely to pick a set of numbers from one range than from
another.

The U.S. National Security Agency designed DSA and it is one of three
authentication algorithms approved for generating and verifying
digital signature under the Digital Signature Standard. Digital
signatures allow software at the end of an electronic transaction to
confirm the identity of the party initiating the transaction and to
verify the integrity of the information received.

The vulnerability does not pose any immediate threat as it takes
massive computing power to launch an attack on the flaw, according to
Bell Labs.

The Digital Signature Standard was developed by the U.S. National
Institute of Standards and Technology (NIST) and has been adopted by
the American National Standards Institute (ANSI) and the Institute of
Electrical and Electronics Engineers (IEEE).

The standards organizations could develop a simple fix for DSA, which
providers of applications and services could implement in software,
according to Bleichenbacher. NIST has agreed to fix the weakness in
the DSA and is now preparing a revision of the DSA specification,
which will be proposed in February, said Edward Roback, chief of the
computer security division in NIST's Information Technology
Laboratory, in a statement.

Bleichenbacher first disclosed the vulnerability last Nov. 15, during
a meeting of a IEEE working group that focused on standard
specifications for public-key cryptography. He found the flaw while
analyzing an appendix to the DSA and has since devised an alternation
to the DSA algorithm that would, for all practical purposes, eliminate
the bias in the random number generator, Bell Labs said.

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