Cryptography Reference
In-Depth Information
in different cities, want to decide who gets the car”).
48
In 1991, Simmons,
a cryptographer working at Sandia National Laboratories,—a R&D facility
specialized in nuclear security and nonproliferation—reported on a similar
issue: how could the Soviet Union and the United States collaborate and
agree on methods for verifying compliances with SALT treaties requiring
test bans and reduction in nuclear arsenals?
49
Implementing Reagan's famous quip, “trust but verify,” required placing
unmanned seismic sensors monitoring Russia's compliance with the test
ban. Though such sensors would return precisely delimited information
back to the United States, how could the Americans be sure that the Rus-
sians would not tamper with the information emitted by the censors?
Encryption would work, but how could the Russians then be assured that
no extra strategic information would be communicated by the sensors?
The issue required two mutually distrustful parties to engage in a collabora-
tive process yet achieve security goals to their mutual satisfaction.
In his wide-ranging investigation of these issues, Simmons discovered
that the authentication mechanisms used for such purposes could be sub-
verted to provide a hidden communication channel, which he called a
“subliminal channel.” He further demonstrated that various digital signa-
ture schemes could be used to communicate secret information through
such a high-capacity subliminal channel and that the very existence of the
channel could be proved only by breaking the digital signature scheme
itself.
50
He eventually concluded that “any time redundant information is
introduced into a communication to provide an overt function such as
digital signatures, error detection and/or correction, authentication, etc.,
it may be possible to subvert the purported function to create a covert
(subliminal) communications channel.”
51
Adam Young and Moti Yung further developed Simmons's discovery as
it applied to the covert operation of encryption systems, developing a
research agenda they humorously named “Kleptography.”
52
In a series of
papers, they demonstrated that “black-box” cryptosystems—that is, cryp-
tographic systems embedded in closed hardware devices—can be subverted
by their manufacturers so as to capture and “subliminally” transmit users'
private keys in the output of the system itself. Young and Yung showed
that important digital signatures algorithms such as RSA, El-Gamal, and
even the DSA federal standard could be subverted to effectively turn cryp-
tographic devices against their users.
